{"gene":"RPS6KB1","run_date":"2026-04-28T20:42:06","timeline":{"discoveries":[{"year":1996,"finding":"T-389 is the principal regulatory phosphorylation site of p70(S6K); phosphorylation of T-389 together with hyperphosphorylation of autoinhibitory domain S/TP sites acutely regulates kinase activity, while T-229 in the activation loop is regulated by distinct, rapamycin-insensitive kinases. Mutation of T-389 to an acidic residue confers rapamycin and wortmannin resistance.","method":"Site-directed mutagenesis of phosphorylation sites combined with kinase activity assays, truncation mutant analysis, and inhibitor studies (rapamycin, wortmannin, SQ20006)","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — in vitro mutagenesis with multiple orthogonal functional readouts in a single study","pmids":["8887654"],"is_preprint":false},{"year":1998,"finding":"PDK1 directly phosphorylates p70S6K at T-229 (Thr229) in the activation loop, activating it in vitro and in vivo; PDK1-mediated p70S6K phosphorylation is dependent on prior phosphorylation of the carboxy-terminal tail (T-389/Thr412 in the p70 numbering used), establishing hierarchical phosphorylation as the activation mechanism.","method":"In vitro kinase assay with purified PDK1 and p70S6K, co-expression in cells, site-specific mutagenesis, phosphospecific antibody analysis","journal":"Science / Current biology","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with mutagenesis, independently reported in two concurrent papers","pmids":["9445476","9427642"],"is_preprint":false},{"year":1998,"finding":"Phosphorylation of the autoinhibitory domain S/TP sites acts cooperatively with T-389 phosphorylation to control T-229 (activation loop) phosphorylation through an intrasteric mechanism; T-389 acidic substitution plus S/TP acidic substitutions markedly increase basal T-229 phosphorylation and kinase activity, making the resulting mutant an excellent PDK1 substrate in vitro.","method":"Truncation and point mutants analyzed by kinase activity assay and in vitro PDK1 phosphorylation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with mutagenesis, rigorous epistatic analysis","pmids":["9614086"],"is_preprint":false},{"year":1998,"finding":"Homozygous disruption of the p70(S6K)/p85(S6K) gene in mice reduces body size (especially during embryogenesis) but does not abolish S6 phosphorylation in liver or fibroblasts; a novel homolog S6K2 is upregulated in knockout tissues and can compensate for S6K1 function, accounting for residual S6 phosphorylation.","method":"Gene knockout in mice, Western blot for S6 phosphorylation, polysome profiling, Northern/Western analysis of S6K2","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — clean knockout mouse with multiple orthogonal readouts; identified S6K2 as compensatory kinase","pmids":["9822608"],"is_preprint":false},{"year":1998,"finding":"Targeted disruption of p70(S6K) in murine embryonic stem cells abolishes ribosomal S6 phosphorylation, prevents serum-stimulated translational upregulation of ribosomal protein mRNAs (5'TOP mRNAs), and slows proliferation; rapamycin-sensitive inhibition of 4E-BP1 phosphorylation and general protein synthesis occurs independently of p70(S6K).","method":"Gene targeting in ES cells, 35S-methionine incorporation, sucrose gradient polysome analysis, immunoblotting","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — genetic loss-of-function with specific translational readouts","pmids":["9560223"],"is_preprint":false},{"year":1999,"finding":"p70(S6K) activity measured 6 h post-exercise in rat skeletal muscle correlates tightly (r = 0.998) with percent increase in muscle mass after 6 weeks of resistance training; polysome analysis suggests increased translation initiation after lengthening contractions, implicating p70(S6K) in load-induced muscle hypertrophy.","method":"Animal exercise model, immunoprecipitation kinase assay, polysome profiling, muscle mass measurement","journal":"The American journal of physiology","confidence":"Medium","confidence_rationale":"Tier 2 — correlative but used direct kinase activity assay and functional hypertrophy outcome in vivo","pmids":["9886927"],"is_preprint":false},{"year":1999,"finding":"Amino acid-dependent activation of p70(S6K) involves tRNA aminoacylation: amino acid alcohols that inhibit tRNA synthetases suppress p70(S6K) activity; cycloheximide or puromycin block suppression by amino acid withdrawal; a temperature-sensitive histidyl-tRNA synthetase mutant reduces p70(S6K) at non-permissive temperature. Deacylated tRNA may be a negative regulator of p70(S6K).","method":"Chemical inhibitors of tRNA aminoacylation, temperature-sensitive mutant cell line, rapamycin-resistant mTOR mutant, kinase activity assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal chemical and genetic approaches in a single study","pmids":["9873056"],"is_preprint":false},{"year":1999,"finding":"p70(S6K) activity in Xenopus oocytes is high at rest and decreases upon progesterone-induced maturation; rapamycin (which inhibits p70S6K) accelerates germinal vesicle breakdown and increases mos mRNA translation (a non-5'TOP mRNA), while 5'TOP-containing mRNAs are translated less efficiently under rapamycin. A constitutively active rapamycin-resistant p70(S6K) reverses rapamycin effects, defining p70(S6K) as the relevant effector.","method":"Xenopus oocyte system, rapamycin-resistant constitutively active S6K1 rescue, in vivo translation assays with 5'TOP and IRES reporters, S6 phosphorylation immunoblotting","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — reconstitution with rapamycin-resistant mutant rescues phenotype; orthogonal translation reporters","pmids":["10082514"],"is_preprint":false},{"year":1999,"finding":"Hydrogen peroxide activates p70(S6K) upstream of rapamycin-sensitive FRAP/mTOR and wortmannin-sensitive PI3K; Ca2+ chelation blocks H2O2-induced p70(S6K) activation, identifying Ca2+ as a mediator; PKC is not required. Growth factor-induced H2O2 generation contributes to p70(S6K) activation.","method":"Chemical inhibitors (rapamycin, wortmannin), Ca2+ chelation, PKC downregulation, glucose oxidase-generated H2O2, catalase pretreatment, kinase activity assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — multiple inhibitors and genetic tools defining pathway position","pmids":["10551813"],"is_preprint":false},{"year":2001,"finding":"The PIF-binding pocket in PDK1 is essential for T-loop phosphorylation and activation of S6K1 and SGK but not PKBα; prior phosphorylation of S6K1 at its hydrophobic motif (T-389) promotes docking into the PDK1 PIF-binding pocket, thereby enabling T-loop phosphorylation—establishing that hydrophobic motif phosphorylation converts S6K1 into a PDK1 substrate.","method":"PIF-binding pocket mutations in PDK1 expressed in cells, in vitro kinase assays, immunoprecipitation","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — structure-function mutagenesis combined with in vitro reconstitution","pmids":["11500365"],"is_preprint":false},{"year":2001,"finding":"Drosophila PDK1 (dPDK1) activates both dAkt and dS6K to control cell and organismal growth; genetic interactions show dPDK1 is required for dRSK but not dPKN function; dPDK1-dS6K constitutes an independent branch of insulin-mediated growth downstream of PI3K.","method":"Drosophila genetics, epistasis analysis, cell size measurements, kinase activity assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — in vivo genetic epistasis in Drosophila with multiple orthogonal readouts","pmids":["11752451"],"is_preprint":false},{"year":2001,"finding":"p70 S6K1 phosphorylates eEF2 kinase (eEF2K) at a conserved serine, inhibiting eEF2K activity and thereby promoting eEF2 activity and peptide elongation; this rapamycin-sensitive pathway requires PDK1 and links mTOR/S6K1 signaling to translational elongation control.","method":"In vitro kinase assay with purified S6K1 and eEF2K, PDK1 knockout cells, rapamycin treatment, Erk inhibitor studies","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay plus genetic knockout corroboration","pmids":["11500364"],"is_preprint":false},{"year":2001,"finding":"MEK/ERK signaling activates S6K2 (but not S6K1) in cardiomyocytes in response to phenylephrine in a PKB-independent manner; insulin activates S6K2 via both MEK/ERK and PKB-dependent pathways; both activation routes require mTOR (rapamycin-sensitive), establishing S6K2 as a point of convergence for MEK and mTOR signaling.","method":"Pharmacological MEK inhibitors, dominant-negative PKB expression, constitutively active MEK1 expression, immunoprecipitation kinase assays in adult rat ventricular cardiomyocytes","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple inhibitors and dominant-negative constructs with specific kinase activity readouts","pmids":["11431469"],"is_preprint":false},{"year":2003,"finding":"TSC1/2 acts as a GAP for the small GTPase Rheb; insulin-mediated Rheb activation is PI3K-dependent; Rheb overexpression induces S6K1 phosphorylation and inhibits PKB phosphorylation; a TSC2 disease-associated GAP-domain point mutation fails to stimulate Rheb GTPase activity or block Rheb activation of S6K1.","method":"GTPase activity assays, co-immunoprecipitation, overexpression of Rheb and TSC constructs, phosphospecific immunoblotting","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 — biochemical GAP assay combined with mutagenesis and cellular epistasis","pmids":["12820960"],"is_preprint":false},{"year":2003,"finding":"Drosophila Rheb functions downstream of TSC1-TSC2 and upstream of TOR/S6K to control cell growth; genetic loss-of-function of Rheb inhibits growth while overexpression promotes growth; S6K is identified as a major effector of Rheb function.","method":"Drosophila genetics (loss-of-function and overexpression), epistasis with TSC1/TSC2 and TOR, cell size measurements, biochemical S6K activity assays","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 — in vivo epistasis in Drosophila with biochemical validation","pmids":["12766775"],"is_preprint":false},{"year":2003,"finding":"In Drosophila, RNAi of dAkt also affects insulin-stimulated dS6K phosphorylation, indicating Akt influences dS6K phosphorylation; in contrast, 4E-BP phosphorylation is PI3K- and Akt-dependent while S6K phosphorylation has an additional PI3K/Akt-independent component through TOR.","method":"RNA interference of pathway components in Drosophila S2 cells, isoelectric focusing-SDS-PAGE for 4E-BP phosphorylation states, immunoblotting for dS6K","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 — systematic RNAi epistasis with orthogonal readouts","pmids":["14645523"],"is_preprint":false},{"year":2004,"finding":"Constitutive activation of the Rheb/mTOR/S6K cassette (by TSC1/TSC2 deletion or Rheb overexpression) induces IRS-1 and IRS-2 downregulation, creating insulin resistance and blocking IGF-I/insulin-stimulated Akt activation; S6K-mediated negative feedback on IRS proteins is sufficient to impair cell survival.","method":"TSC1/TSC2 genetic deletion, Rheb overexpression, immunoprecipitation, immunoblotting, cell survival/apoptosis assays","journal":"Current biology","confidence":"High","confidence_rationale":"Tier 2 — genetic deletion plus overexpression with multiple biochemical and phenotypic readouts","pmids":["15380067"],"is_preprint":false},{"year":2004,"finding":"S6K1 (p70S6K) is localized to the actin arc (a caveolin-enriched cytoskeletal structure at the leading edge of migrating cells), co-sediments with F-actin, and is required for EGF-induced actin arc formation and cell migration; rapamycin blocks actin arc formation; fibronectin-induced stress fibers suppress p70(S6K) activity.","method":"Subcellular fractionation, co-sedimentation with F-actin, immunocytochemistry, rapamycin treatment, cytochalasin D and Y-27632 pharmacology","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization experiments tied to functional cell migration assay","pmids":["15149849"],"is_preprint":false},{"year":2004,"finding":"Scylla and Charybdis (REDD1 homologs) act as negative regulators of growth in Drosophila by reducing S6K (but not PKB/Akt) activity; they function downstream of PKB and upstream of TSC, establishing a pathway position; REDD1/Scylla is induced by HIF-1 under hypoxia.","method":"Drosophila genetics (EP overexpression screen, double mutants), S6K and Akt kinase activity assays, epistasis analysis","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — in vivo Drosophila epistasis with kinase activity assays","pmids":["15545626"],"is_preprint":false},{"year":2005,"finding":"mTOR and S6K1 dynamically associate with the eIF3 translation preinitiation complex; inactive S6K1 is associated with eIF3 while mTOR/raptor is absent; cell stimulation recruits mTOR/raptor to eIF3 where it phosphorylates S6K1 at the hydrophobic motif, causing S6K1 dissociation and activation, followed by phosphorylation of eIF4B which is then recruited to the complex.","method":"Co-immunoprecipitation, mass spectrometry identification of eIF3 complex components, phosphospecific immunoblotting, rapamycin treatment, siRNA knockdown","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP with ordered phosphorylation analysis replicated with multiple tools","pmids":["16286006"],"is_preprint":false},{"year":2005,"finding":"Raptor binds p70S6K1 and 4E-BP1 through their TOS (TOR signaling) motifs; TOS motif mutation abolishes mTOR-catalyzed phosphorylation in vitro and eliminates rapamycin sensitivity and amino acid responsiveness in vivo, establishing raptor as the scaffold that recruits S6K1 to mTOR for phosphorylation.","method":"Co-immunoprecipitation, in vitro mTOR kinase assay, TOS motif mutagenesis, rapamycin and amino acid withdrawal experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase reconstitution with mutagenesis confirming substrate recruitment mechanism","pmids":["12604610"],"is_preprint":false},{"year":2005,"finding":"p70S6K phosphorylates mTOR at Ser-2448 in vitro and in cells; rapamycin blocks Ser-2448 phosphorylation in a manner not explained by Akt inhibition; rapamycin-resistant S6K1 restores Ser-2448 phosphorylation in rapamycin-treated cells; siRNA depletion of S6K1 reduces Ser-2448 phosphorylation, identifying S6K1 as a positive feedback kinase on mTOR.","method":"In vitro kinase assay with purified S6K1, rapamycin-resistant S6K1 rescue, siRNA knockdown, amino acid deprivation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay plus rapamycin-resistant rescue plus siRNA knockdown","pmids":["15899889"],"is_preprint":false},{"year":2006,"finding":"In response to mitogens, S6K1 phosphorylates PDCD4 at Ser67, targeting it for SCF(βTRCP)-mediated ubiquitin-proteasome degradation; stable PDCD4 that cannot bind βTRCP inhibits translation of mRNAs with structured 5'UTRs, reduces cell size, and slows cell cycle progression.","method":"In vitro S6K1 kinase assay, ubiquitination assays, stable PDCD4 mutant expression, translation reporter assays, cell size measurements","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay with mutagenesis and functional cellular readouts","pmids":["17053147"],"is_preprint":false},{"year":2007,"finding":"Mechanical stretch activates mTOR as the rapamycin-sensitive kinase responsible for T-389 phosphorylation in p70(S6K) through a PI3K-independent mechanism; rapamycin-resistant mTOR mutants restore mechanically-induced T-389 phosphorylation in rapamycin-treated cells.","method":"Rapamycin-resistant mTOR mutant expression combined with mechanical stretch, phosphospecific immunoblotting","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 2 — rapamycin-resistant mutant rescue definitively identifies mTOR as the relevant kinase","pmids":["17825298"],"is_preprint":false},{"year":2007,"finding":"SF2/ASF splicing factor controls alternative splicing of S6K1 to generate an unusual isoform (isoform-2) that lacks the autoinhibitory domain and is constitutively active; this isoform recapitulates the transforming activity of SF2/ASF, and knockdown of either SF2/ASF or S6K1 isoform-2 reverses transformation in vitro and in vivo.","method":"Alternative splicing analysis, RT-PCR, siRNA knockdown, soft agar colony assay, nude mouse xenograft","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 2 — loss-of-function with specific isoform identification and in vivo tumor phenotype","pmids":["17310252"],"is_preprint":false},{"year":2008,"finding":"S6K1 directly phosphorylates IRS-1 at Ser-270, Ser-307, Ser-636, and Ser-1101 in response to TNF-α, with Ser-270 phosphorylation being a key docking site for S6K1 on IRS-1; TNF-α activates S6K1 via an IKK2-dependent pathway; RNAi knockdown of S6K1 prevents TNF-α-induced IRS-1 inhibition and impaired glucose uptake.","method":"In vitro kinase assay with purified IRS-1 and S6K1, point mutant IRS-1 (S270A), RNAi knockdown, dominant-negative S6K1, IKK2 knockout cells, glucose uptake assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay with multiple site-specific mutants plus genetic loss-of-function","pmids":["18952604"],"is_preprint":false},{"year":2009,"finding":"IFN-α and IFN-γ stimulate phosphorylation of eIF4B at Ser422 in a cell-type-specific manner via p70 S6K1; S6K1-mediated eIF4B phosphorylation enhances eIF4B interaction with eIF3A and increases associated ATPase activity; S6K1/S6K2 double-knockout MEFs show diminished IFN-inducible ISG15 and CXCL10 protein expression, establishing S6K as a mediator of IFN-dependent translation.","method":"S6K1/S6K2 double-knockout MEFs, siRNA knockdown of eIF4B/eIF3A, ATPase activity assays, co-immunoprecipitation, phosphospecific immunoblotting","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — double knockout MEFs plus siRNA knockdown with multiple functional readouts","pmids":["19289497"],"is_preprint":false},{"year":2010,"finding":"PP2A-B' (PPP2R5C in humans) specifically targets the PP2A holoenzyme to dephosphorylate S6K; PP2A-B' physically interacts with S6K; Drosophila PP2A-B' knockout elevates S6K phosphorylation and phenocopies elevated insulin signaling; human PPP2R5C counteracts S6K1 phosphorylation, indicating a conserved mechanism.","method":"Drosophila knockout genetics, co-immunoprecipitation (PP2A-B' with S6K), phosphospecific immunoblotting, mammalian PPP2R5C overexpression/knockdown","journal":"Cell metabolism","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP plus genetic knockout with conserved mammalian validation","pmids":["20444422"],"is_preprint":false},{"year":2010,"finding":"Leucine activates the cardiac mTOR/p70(S6K) pathway through a PDK1-dependent but PKB/Akt-independent mechanism; leucine also phosphorylates PRAS40, a key mTOR regulator; the PDK1 L155E mutation (preserving insulin/Akt-dependent mTOR signaling) abolishes leucine effects, demonstrating leucine uses a distinct PDK1 interaction interface.","method":"PDK1 knockout hearts, PDK1 L155E knock-in, leucine and insulin stimulation, p70S6K kinase assays, PRAS40 phosphospecific immunoblotting","journal":"American journal of physiology. Endocrinology and metabolism","confidence":"High","confidence_rationale":"Tier 2 — genetic PDK1 knockout plus separation-of-function PDK1 mutation with kinase activity readouts","pmids":["20051528"],"is_preprint":false},{"year":2010,"finding":"Constitutively active S6K1 in pancreatic β-cells impairs IRS/Akt signaling (negative feedback), decreases G1-S progression, increases apoptosis via elevated p16 and p27 and reduced Cdk2, and improves insulin secretion without expanding β-cell mass, demonstrating that S6K-mediated IRS downregulation induces β-cell insulin resistance in vivo.","method":"Transgenic mice with β-cell-specific constitutively active S6K1, cell cycle protein analysis, Akt phosphorylation, insulin secretion assays, TUNEL apoptosis","journal":"Diabetes","confidence":"High","confidence_rationale":"Tier 2 — in vivo transgenic model with mechanistic biochemical readouts","pmids":["20622167"],"is_preprint":false},{"year":2010,"finding":"mTOR-mediated activation of p70 S6K1 induces differentiation of human embryonic stem cells; constitutively active p70 S6K1 (but not wild-type) triggers differentiation; siRNA knockdown of TSC2 and Rictor elevates S6K1 activity and induces differentiation; hESCs preferentially express rapamycin-insensitive mTORC2 and high TSC1/TSC2 levels to restrain mTORC1/S6K1 activity.","method":"siRNA knockdown, constitutively active S6K1 expression, rapamycin treatment, pluripotency marker analysis (Oct4, Nanog), differentiation assays","journal":"Cellular reprogramming","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA and constitutively active mutant with specific differentiation phenotype","pmids":["20698768"],"is_preprint":false},{"year":2016,"finding":"S6K1 interacts with the signaling adaptor STING in a cGAS-dependent manner upon DNA virus infection; the kinase domain (but not kinase activity) of S6K1 is required for the S6K1-STING interaction; TBK1 promotes formation of a tripartite S6K1-STING-TBK1 complex required for IRF3 activation and early antiviral gene expression.","method":"Co-immunoprecipitation, kinase-dead S6K1 mutants, cGAS knockout cells, TBK1 inhibitor, antiviral response assays (IRF3 target gene expression, T cell responses)","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP with domain mutagenesis and genetic knockouts defining complex assembly and function","pmids":["27043414"],"is_preprint":false},{"year":2018,"finding":"The mTOR-S6K pathway phosphorylates RNF168 at Ser60 to inhibit its E3 ligase activity, accelerate its proteolysis, and impair DNA damage response (DDR); loss of LKB1 hyperactivates mTORC1-S6K, decreasing RNF168 expression; phospho-deficient RNF168-S60A rescues DDR defects and suppresses tumorigenesis caused by Lkb1 loss.","method":"In vitro S6K kinase assay on RNF168, phospho-deficient mutant rescue, ubiquitination assays, γH2AX DDR readouts, LKB1 knockout mouse model, tumor xenografts","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay with phospho-deficient rescue and in vivo tumor model","pmids":["29403037"],"is_preprint":false},{"year":2020,"finding":"During mitotic arrest, mTORC1/S6K activity is dramatically reduced due to mitotic phosphorylation of raptor; expression of a non-phosphorylatable raptor mutant reactivates mTORC1 and reduces Taxol cytotoxicity via S6K-mediated phosphorylation and degradation of the eIF4A inhibitor PDCD4, promoting translation; pharmacological eIF4A inhibition enhances Taxol effects and restores sensitivity in resistant cells.","method":"Non-phosphorylatable raptor mutant, mTORC1 activity immunoblotting, PDCD4 stability assays, pharmacological eIF4A inhibition, Taxol sensitivity assays","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 — separation-of-function raptor mutant with mechanistic pathway dissection and drug combination readouts","pmids":["33027666"],"is_preprint":false},{"year":2004,"finding":"Specific interaction between S6K1 and CoA synthase is detected by co-immunoprecipitation of native and overexpressed proteins and by BIAcore in vitro; the interaction maps to the C-terminal regions of both proteins; CoA synthase is not a substrate for S6K1 and the interaction does not affect enzymatic activities of either partner, suggesting a regulatory scaffolding role linking mTOR/S6K signaling to CoA biosynthesis and energy metabolism.","method":"Co-immunoprecipitation, BIAcore binding analysis, in vitro kinase assay, C-terminal deletion mapping","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 3 — Co-IP and BIAcore confirm binding but functional significance remains to be elucidated","pmids":["15589845"],"is_preprint":false},{"year":2015,"finding":"Hepatic amino acid/mTORC1/S6K signaling modulates systemic lipid metabolism via neuronal inter-tissue communication; hepatic active-S6K expression elevates serum triglycerides and downregulates adipose lipoprotein lipase (LPL); dominant-negative S6K expression blocks TG elevation; denervation, pharmacological deafferentation, and β-blockade suppress hypertriglyceridemia with adipose LPL upregulation, indicating signal transduction via afferent vagal and efferent sympathetic nerves.","method":"Adenoviral hepatic expression of active/dominant-negative S6K, SNAT2, Rheb; surgical/pharmacological denervation; metabolic measurements","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — genetic gain/loss-of-function with neuronal intervention experiments in vivo","pmids":["26268630"],"is_preprint":false},{"year":2016,"finding":"Loss of S6K in Drosophila fat body blocks rapamycin-mediated lifespan extension and causes accumulation of multilamellar lysosomes; Syntaxin 13 mediates TORC1-S6K effects on lysosome morphology and inflammaging (age-related NF-κB-like immune pathway hyperactivation); rapamycin also elevates Syntaxin 12/13 levels in mouse liver and prevents age-related non-canonical NF-κB signaling, indicating a conserved mechanism.","method":"Tissue-specific S6K activation in Drosophila fat body, lifespan assays, lysosome morphology analysis, Syntaxin 13 genetic interaction, mouse liver proteomic/biochemical analysis","journal":"Nature aging","confidence":"High","confidence_rationale":"Tier 2 — tissue-specific genetics with mechanistic pathway identification and mammalian validation","pmids":["38413780"],"is_preprint":false}],"current_model":"RPS6KB1 (S6K1/p70S6K) is a serine/threonine kinase that is activated downstream of mTORC1 (via raptor-TOS motif docking) through a hierarchical phosphorylation cascade in which mTOR phosphorylates T-389 in the hydrophobic motif, enabling PDK1 PIF-pocket docking and T-229 activation-loop phosphorylation; once active, S6K1 phosphorylates multiple substrates—including rpS6, eIF4B, eEF2K, PDCD4 (targeting it for βTRCP-dependent degradation), IRS-1 (creating a negative feedback loop that drives insulin resistance), RNF168 (linking growth signaling to DNA damage response), and mTOR itself (Ser-2448 positive feedback)—and also forms a non-catalytic complex with STING-TBK1 to promote IRF3-dependent antiviral immunity, while its activity is negatively regulated by PP2A-B' (PPP2R5C)-mediated dephosphorylation and is physiologically engaged by nutrients (amino acids via tRNA aminoacylation sensing), mechanical load, growth factors, and reactive oxygen species to control cell size, protein synthesis, autophagy, muscle hypertrophy, stem cell differentiation, and systemic lipid metabolism."},"narrative":{"teleology":[{"year":1996,"claim":"Mapping the activation mechanism: identification of T-389 as the principal rapamycin-sensitive regulatory phosphorylation site resolved how extracellular signals converge on S6K1 activity, with autoinhibitory-domain phosphorylation and T-229 activation-loop phosphorylation constituting additional, distinctly regulated layers.","evidence":"Site-directed mutagenesis with kinase activity assays, truncation mutants, and inhibitor panels in cultured cells","pmids":["8887654"],"confidence":"High","gaps":["Identity of the T-389 kinase was not established","Structural basis of autoinhibition was unknown"]},{"year":1998,"claim":"Establishing the hierarchical phosphorylation cascade: PDK1 was identified as the activation-loop kinase for S6K1, with prior T-389 phosphorylation creating a PIF-pocket docking site on PDK1 — explaining why hydrophobic-motif phosphorylation is prerequisite for full activation.","evidence":"In vitro kinase assays with purified PDK1 and S6K1, cooperative mutagenesis of autoinhibitory and hydrophobic-motif sites, reported independently in two concurrent papers","pmids":["9445476","9427642","9614086"],"confidence":"High","gaps":["Identity of the upstream T-389 kinase remained unresolved at this point","How PDK1 PIF-pocket selectivity distinguishes S6K1 from PKB was not yet dissected"]},{"year":1998,"claim":"Genetic loss-of-function in mice established that S6K1 controls organismal body size and 5’TOP mRNA translation, while revealing compensatory S6K2 upregulation that preserves residual S6 phosphorylation.","evidence":"Homozygous S6K1 knockout mice and targeted ES cells with polysome profiling, translational assays, and Northern/Western identification of S6K2","pmids":["9822608","9560223"],"confidence":"High","gaps":["S6K2 functional overlap precluded definitive assignment of all S6K1-specific functions","Whether reduced body size reflects cell size versus cell number was not resolved"]},{"year":1999,"claim":"Upstream input integration was expanded to include amino acid sensing via tRNA aminoacylation, mechanical load-correlated muscle hypertrophy, and reactive oxygen species signaling, establishing S6K1 as a multi-input growth integrator.","evidence":"Amino acid alcohol inhibitors and ts-histidyl-tRNA synthetase mutant for nutrient sensing; exercise-induced kinase activity correlation with muscle mass; H₂O₂ activation via Ca²⁺-dependent PI3K/mTOR pathway","pmids":["9873056","9886927","10551813"],"confidence":"Medium","gaps":["Molecular identity of the amino acid sensor upstream of mTOR/S6K was unknown","Muscle hypertrophy correlation was not causal","Ca²⁺-ROS link lacked molecular target identification"]},{"year":2001,"claim":"The PDK1 PIF-pocket was shown to be essential for S6K1 activation but dispensable for PKBα, resolving how PDK1 achieves substrate selectivity; concurrently, eEF2K was identified as a direct S6K1 substrate, extending S6K1 function from translational initiation to elongation control.","evidence":"PIF-pocket mutations in PDK1 in cells and in vitro; in vitro kinase assay of S6K1 on eEF2K combined with PDK1 knockout cells","pmids":["11500365","11500364"],"confidence":"High","gaps":["Structural basis of PIF-pocket selectivity was inferred, not crystallographically resolved at this point","Physiological importance of eEF2K phosphorylation by S6K1 versus ERK was not delineated"]},{"year":2003,"claim":"Placement of the TSC1/TSC2-Rheb module upstream of mTOR/S6K1 established the complete PI3K→Akt→TSC→Rheb→mTOR→S6K1 signaling axis, explaining how growth factor and nutrient signals converge on S6K1.","evidence":"Biochemical GAP assays for TSC2 on Rheb, Drosophila epistasis, disease-associated TSC2 mutations, S6K phosphorylation readouts","pmids":["12820960","12766775"],"confidence":"High","gaps":["Direct Rheb-mTOR activation mechanism was biochemically undefined","Whether Rheb activates mTORC1 at endomembranes was unknown"]},{"year":2005,"claim":"The raptor TOS-motif docking mechanism and the dynamic S6K1-eIF3 scaffold model resolved how mTORC1 recruits and activates S6K1 at the ribosome: inactive S6K1 resides on eIF3, mTOR/raptor is recruited upon stimulation, phosphorylates T-389, and released active S6K1 then phosphorylates eIF4B and mTOR Ser-2448 (positive feedback).","evidence":"TOS motif mutagenesis with in vitro mTOR kinase assay; mass spectrometry identification of eIF3 complex interactions; rapamycin-resistant S6K1 rescue for Ser-2448 feedback","pmids":["12604610","16286006","15899889"],"confidence":"High","gaps":["Whether eIF3-scaffold model operates in all cell types was untested","Stoichiometry of S6K1 on eIF3 was not determined"]},{"year":2006,"claim":"PDCD4 was identified as a direct S6K1 substrate whose phosphorylation at Ser67 triggers βTRCP-dependent degradation, relieving inhibition of eIF4A helicase activity and promoting translation of structured mRNAs — linking S6K1 to cap-dependent translation beyond rpS6.","evidence":"In vitro S6K1 kinase assay, βTRCP interaction mapping, PDCD4 non-degradable mutant with cell size and translation readouts","pmids":["17053147"],"confidence":"High","gaps":["Full spectrum of mRNAs regulated via the S6K1-PDCD4-eIF4A axis was not defined","Whether S6K2 also phosphorylates PDCD4 was not tested"]},{"year":2008,"claim":"The negative feedback loop was molecularly detailed: S6K1 directly phosphorylates IRS-1 at Ser-270, -307, -636, and -1101, with Ser-270 serving as a docking site; TNFα activates this loop through IKK2, explaining how chronic mTORC1/S6K1 activation produces insulin resistance.","evidence":"In vitro kinase assay with purified proteins, site-specific IRS-1 mutants, S6K1 RNAi, IKK2 knockout cells, glucose uptake assays","pmids":["18952604"],"confidence":"High","gaps":["Relative contribution of individual IRS-1 phosphorylation sites in vivo was not resolved","Whether S6K1 phosphorylates IRS-2 at analogous sites was not tested"]},{"year":2010,"claim":"PP2A-B’ (PPP2R5C) was identified as a conserved negative regulator that directly dephosphorylates S6K, with Drosophila knockout phenocopying hyperactive insulin signaling; concurrently, constitutively active S6K1 in pancreatic β-cells was shown to induce insulin resistance and apoptosis through IRS/Akt impairment.","evidence":"Drosophila PP2A-B’ knockout with mammalian PPP2R5C validation via Co-IP; transgenic β-cell-specific active S6K1 mice with cell cycle and apoptosis analysis","pmids":["20444422","20622167"],"confidence":"High","gaps":["Phosphatase specificity for T-389 versus T-229 was not resolved","Whether PP2A-B’ regulation is nutrient-sensitive was not tested"]},{"year":2015,"claim":"Hepatic S6K1 was found to control systemic lipid metabolism through a neural circuit involving vagal afferent and sympathetic efferent signaling to adipose tissue, establishing S6K1 as a node for inter-organ metabolic communication.","evidence":"Adenoviral hepatic expression of active/dominant-negative S6K, surgical and pharmacological denervation, serum triglyceride and adipose LPL measurements","pmids":["26268630"],"confidence":"High","gaps":["Molecular identity of the hepatic afferent signal was not identified","Whether this neural relay is conserved in humans was untested"]},{"year":2016,"claim":"A non-catalytic immune function was uncovered: S6K1 kinase domain (but not activity) scaffolds a STING-TBK1 complex upon DNA virus sensing by cGAS, enabling IRF3 activation and antiviral gene expression — the first kinase-independent function of S6K1.","evidence":"Reciprocal Co-IP with kinase-dead S6K1, cGAS knockout cells, TBK1 inhibitor, antiviral gene expression readouts","pmids":["27043414"],"confidence":"High","gaps":["Structural basis of the non-catalytic STING interaction was not resolved","Whether mTORC1-driven S6K1 phosphorylation modulates the immune scaffolding function was not tested"]},{"year":2018,"claim":"S6K1 was shown to phosphorylate the E3 ligase RNF168 at Ser60, accelerating its proteolysis and impairing the DNA damage response; this linked hyperactive mTORC1/S6K signaling (e.g., from LKB1 loss) to genomic instability and tumorigenesis.","evidence":"In vitro S6K kinase assay on RNF168, phospho-deficient S60A rescue of DDR, LKB1 knockout mouse model, tumor xenografts","pmids":["29403037"],"confidence":"High","gaps":["Whether S6K1 targets other DDR factors was not explored","Contribution of S6K2 to RNF168 regulation was not assessed"]},{"year":2020,"claim":"Mitotic suppression of mTORC1/S6K1 via raptor phosphorylation was shown to be functionally important for Taxol cytotoxicity through PDCD4 stabilization; reactivation of S6K1 during mitotic arrest degraded PDCD4 and conferred Taxol resistance.","evidence":"Non-phosphorylatable raptor mutant, PDCD4 stability assays, pharmacological eIF4A inhibition restoring Taxol sensitivity","pmids":["33027666"],"confidence":"High","gaps":["Whether other S6K1 substrates contribute to mitotic drug resistance was not tested","Clinical relevance of eIF4A inhibitor combination was not validated in patient-derived models"]},{"year":null,"claim":"Key unresolved questions include: the full substrate repertoire of S6K1 versus S6K2, the structural basis for S6K1's non-catalytic immune scaffolding function, the molecular identity of the hepatic afferent signal mediating S6K1-driven lipid metabolism, and whether the S6K1-RNF168-DDR axis contributes to therapy resistance in human cancers.","evidence":"","pmids":[],"confidence":"Low","gaps":["Comprehensive substrate identification (e.g., phosphoproteomics in S6K1/2 double knockouts) is lacking","No high-resolution structure of S6K1 in complex with STING or eIF3","In vivo physiological relevance of many substrates has not been confirmed in conditional tissue-specific knockouts"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,11,22,25,32]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,1,11,21,22,25,32]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[31]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[19]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[17]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,9,13,16,20,27]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[11,19,22,26,33]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[31]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[32]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[35]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[33]}],"complexes":["S6K1-STING-TBK1","eIF3 preinitiation complex (dynamic)"],"partners":["MTOR","RPTOR","PDPK1","PPP2R5C","TMEM173","TBK1","IRS1","RNF168"],"other_free_text":[]},"mechanistic_narrative":"RPS6KB1 (p70S6K/S6K1) is a serine/threonine kinase that functions as the principal effector of mTORC1 signaling to control cell growth, protein synthesis, and metabolic homeostasis. It is activated through a hierarchical phosphorylation cascade in which raptor-mediated TOS-motif docking recruits S6K1 to mTOR for T-389 hydrophobic-motif phosphorylation, which in turn creates a docking site for the PDK1 PIF-pocket to enable activation-loop (T-229) phosphorylation; this activity is reversed by PP2A-B’ (PPP2R5C)-mediated dephosphorylation [PMID:8887654, PMID:9445476, PMID:11500365, PMID:12604610, PMID:20444422]. Once active, S6K1 phosphorylates substrates including rpS6, eIF4B, eEF2K, and PDCD4 to promote translation initiation and elongation, phosphorylates IRS-1 at multiple serines to create a negative feedback loop that drives insulin resistance, and phosphorylates RNF168 to attenuate the DNA damage response [PMID:11500364, PMID:17053147, PMID:18952604, PMID:29403037]. Beyond its catalytic roles, S6K1 forms a kinase-activity-independent complex with STING and TBK1 to promote IRF3-dependent antiviral innate immunity, and regulates systemic lipid metabolism through hepatic amino-acid sensing that signals via vagal afferent and sympathetic efferent nerves [PMID:27043414, PMID:26268630]."},"prefetch_data":{"uniprot":{"accession":"P23443","full_name":"Ribosomal protein S6 kinase beta-1","aliases":["70 kDa ribosomal protein S6 kinase 1","P70S6K1","p70-S6K 1","Ribosomal protein S6 kinase I","Serine/threonine-protein kinase 14A","p70 ribosomal S6 kinase alpha","p70 S6 kinase alpha","p70 S6K-alpha","p70 S6KA"],"length_aa":525,"mass_kda":59.1,"function":"Serine/threonine-protein kinase that acts downstream of mTOR signaling in response to growth factors and nutrients to promote cell proliferation, cell growth and cell cycle progression (PubMed:11500364, PubMed:12801526, PubMed:14673156, PubMed:15071500, PubMed:15341740, PubMed:16286006, PubMed:17052453, PubMed:17053147, PubMed:17936702, PubMed:18952604, PubMed:19085255, PubMed:19720745, PubMed:19935711, PubMed:19995915, PubMed:22017876, PubMed:23429703, PubMed:28178239). Regulates protein synthesis through phosphorylation of EIF4B, RPS6 and EEF2K, and contributes to cell survival by repressing the pro-apoptotic function of BAD (PubMed:11500364, PubMed:12801526, PubMed:14673156, PubMed:15071500, PubMed:15341740, PubMed:16286006, PubMed:17052453, PubMed:17053147, PubMed:17936702, PubMed:18952604, PubMed:19085255, PubMed:19720745, PubMed:19935711, PubMed:19995915, PubMed:22017876, PubMed:23429703, PubMed:28178239). Under conditions of nutrient depletion, the inactive form associates with the EIF3 translation initiation complex (PubMed:16286006). Upon mitogenic stimulation, phosphorylation by the mechanistic target of rapamycin complex 1 (mTORC1) leads to dissociation from the EIF3 complex and activation (PubMed:16286006). The active form then phosphorylates and activates several substrates in the pre-initiation complex, including the EIF2B complex and the cap-binding complex component EIF4B (PubMed:16286006). Also controls translation initiation by phosphorylating a negative regulator of EIF4A, PDCD4, targeting it for ubiquitination and subsequent proteolysis (PubMed:17053147). Promotes initiation of the pioneer round of protein synthesis by phosphorylating POLDIP3/SKAR (PubMed:15341740). In response to IGF1, activates translation elongation by phosphorylating EEF2 kinase (EEF2K), which leads to its inhibition and thus activation of EEF2 (PubMed:11500364). Also plays a role in feedback regulation of mTORC2 by mTORC1 by phosphorylating MAPKAP1/SIN1, MTOR and RICTOR, resulting in the inhibition of mTORC2 and AKT1 signaling (PubMed:15899889, PubMed:19720745, PubMed:19935711, PubMed:19995915). Also involved in feedback regulation of mTORC1 and mTORC2 by phosphorylating DEPTOR (PubMed:22017876). Mediates cell survival by phosphorylating the pro-apoptotic protein BAD and suppressing its pro-apoptotic function (By similarity). Phosphorylates mitochondrial URI1 leading to dissociation of a URI1-PPP1CC complex (PubMed:17936702). The free mitochondrial PPP1CC can then dephosphorylate RPS6KB1 at Thr-412, which is proposed to be a negative feedback mechanism for the RPS6KB1 anti-apoptotic function (PubMed:17936702). Mediates TNF-induced insulin resistance by phosphorylating IRS1 at multiple serine residues, resulting in accelerated degradation of IRS1 (PubMed:18952604). In cells lacking functional TSC1-2 complex, constitutively phosphorylates and inhibits GSK3B (PubMed:17052453). May be involved in cytoskeletal rearrangement through binding to neurabin (By similarity). Phosphorylates and activates the pyrimidine biosynthesis enzyme CAD, downstream of MTOR (PubMed:23429703). Following activation by mTORC1, phosphorylates EPRS and thereby plays a key role in fatty acid uptake by adipocytes and also most probably in interferon-gamma-induced translation inhibition (PubMed:28178239)","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/P23443/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/RPS6KB1","classification":"Not Classified","n_dependent_lines":36,"n_total_lines":1208,"dependency_fraction":0.029801324503311258},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000108443","cell_line_id":"CID001266","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"nucleoplasm","grade":3}],"interactors":[{"gene":"TUBB4A","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001266","total_profiled":1310},"omim":[{"mim_id":"621460","title":"NEURODEVELOPMENTAL DISORDER WITH SPASTICITY, THIN CORPUS CALLOSUM, AND DECREASED BRAIN WHITE MATTER; NEDSCW","url":"https://www.omim.org/entry/621460"},{"mim_id":"619331","title":"MTOR-ASSOCIATED PROTEIN, EAK7 HOMOLOG; MEAK7","url":"https://www.omim.org/entry/619331"},{"mim_id":"619294","title":"NIBAN APOPTOSIS REGULATOR 1; NIBAN1","url":"https://www.omim.org/entry/619294"},{"mim_id":"618990","title":"EVA1 HOMOLOG A, REGULATOR OF PROGRAMMED CELL DEATH; EVA1A","url":"https://www.omim.org/entry/618990"},{"mim_id":"617517","title":"RIBOSOMAL PROTEIN S6 KINASE C1; RPS6KC1","url":"https://www.omim.org/entry/617517"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/RPS6KB1"},"hgnc":{"alias_symbol":["S6K1","p70(S6K)-alpha","PS6K","S6K"],"prev_symbol":["STK14A"]},"alphafold":{"accession":"P23443","domains":[{"cath_id":"3.30.200.20","chopping":"86-176_378-426","consensus_level":"medium","plddt":87.4411,"start":86,"end":426},{"cath_id":"1.10.510.10","chopping":"179-372","consensus_level":"medium","plddt":93.3455,"start":179,"end":372}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P23443","model_url":"https://alphafold.ebi.ac.uk/files/AF-P23443-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P23443-F1-predicted_aligned_error_v6.png","plddt_mean":72.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RPS6KB1","jax_strain_url":"https://www.jax.org/strain/search?query=RPS6KB1"},"sequence":{"accession":"P23443","fasta_url":"https://rest.uniprot.org/uniprotkb/P23443.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P23443/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P23443"}},"corpus_meta":[{"pmid":"12820960","id":"PMC_12820960","title":"Insulin activation of Rheb, a mediator of mTOR/S6K/4E-BP signaling, is inhibited by TSC1 and 2.","date":"2003","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/12820960","citation_count":853,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"22168436","id":"PMC_22168436","title":"Regulation and function of ribosomal protein S6 kinase (S6K) within mTOR signalling networks.","date":"2012","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/22168436","citation_count":809,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"15380067","id":"PMC_15380067","title":"Inappropriate activation of the TSC/Rheb/mTOR/S6K cassette induces IRS1/2 depletion, insulin resistance, and cell survival deficiencies.","date":"2004","source":"Current biology : CB","url":"https://pubmed.ncbi.nlm.nih.gov/15380067","citation_count":669,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"9886927","id":"PMC_9886927","title":"Phosphorylation of p70(S6k) correlates with increased skeletal muscle mass following resistance exercise.","date":"1999","source":"The American journal of physiology","url":"https://pubmed.ncbi.nlm.nih.gov/9886927","citation_count":557,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"9822608","id":"PMC_9822608","title":"Disruption of the p70(s6k)/p85(s6k) gene reveals a small mouse phenotype and a new functional S6 kinase.","date":"1998","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/9822608","citation_count":553,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"12766775","id":"PMC_12766775","title":"Rheb is an essential regulator of S6K in controlling cell growth in Drosophila.","date":"2003","source":"Nature cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/12766775","citation_count":433,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"15533996","id":"PMC_15533996","title":"Balancing Akt with S6K: implications for both metabolic diseases and tumorigenesis.","date":"2004","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/15533996","citation_count":408,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"27663511","id":"PMC_27663511","title":"Comparison of cancer cells in 2D vs 3D culture reveals differences in AKT-mTOR-S6K signaling and drug responses.","date":"2016","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/27663511","citation_count":349,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"11500365","id":"PMC_11500365","title":"The PIF-binding pocket in PDK1 is essential for activation of S6K and SGK, but not PKB.","date":"2001","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/11500365","citation_count":319,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"20471268","id":"PMC_20471268","title":"Sex peptide receptor and neuronal TOR/S6K signaling modulate nutrient balancing in Drosophila.","date":"2010","source":"Current biology : CB","url":"https://pubmed.ncbi.nlm.nih.gov/20471268","citation_count":253,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"15545626","id":"PMC_15545626","title":"The hypoxia-induced paralogs Scylla and Charybdis inhibit growth by down-regulating S6K activity upstream of TSC in Drosophila.","date":"2004","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/15545626","citation_count":248,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"18952604","id":"PMC_18952604","title":"S6K directly phosphorylates IRS-1 on Ser-270 to promote insulin resistance in response to TNF-(alpha) signaling through IKK2.","date":"2008","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/18952604","citation_count":243,"is_preprint":false,"source_track":"pubmed_title"},{"pmid":"11782951","id":"PMC_11782951","title":"Regulation of cell size in growth, development and human disease: PI3K, PKB and 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across labs (Garami et al. and Stocker et al. same year)\",\n      \"pmids\": [\"12820960\", \"12766775\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PDK1 phosphorylates S6K1 at its T-loop (Thr229/T229) via a 'PIF-binding pocket' in PDK1's kinase domain; prior phosphorylation of S6K1 at its hydrophobic motif (Thr389) promotes interaction with this pocket and enables T-loop phosphorylation; the PIF-binding pocket is not required for PKBα phosphorylation by PDK1.\",\n      \"method\": \"In vitro kinase assay, site-directed mutagenesis of PDK1 PIF-binding pocket, co-immunoprecipitation, phospho-specific readouts\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with mutagenesis, mechanistic dissection of substrate recognition\",\n      \"pmids\": [\"11500365\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Thr389 (in the hydrophobic/linker region) is the principal rapamycin-sensitive regulatory phosphorylation site of p70(S6K); Thr229 (activation loop) is a second rapamycin-sensitive site differentially regulated; acidic substitution at Thr389 confers resistance to wortmannin and SQ20006, indicating it is the common downstream target of these inhibitors; phosphorylation of S/TP autoinhibitory domain sites cooperates with Thr389 phosphorylation to enable Thr229 phosphorylation.\",\n      \"method\": \"Truncation and point mutants of p70(S6K), in vitro kinase assays, site-directed mutagenesis, metabolic labeling/phosphopeptide mapping\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis combined with in vitro kinase assays, foundational mechanistic study\",\n      \"pmids\": [\"8887654\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Phosphorylation of the four autoinhibitory domain S/TP sites cooperates with Thr389 phosphorylation through an intrasteric mechanism to control Thr229 activation-loop phosphorylation by PDK1; acidic substitution at both S/TP sites and Thr389 renders p70(S6K) an excellent PDK1 substrate in vitro.\",\n      \"method\": \"Point mutagenesis, in vitro PDK1 kinase assay, truncation mutants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro kinase assay with mutagenesis, mechanistic dissection\",\n      \"pmids\": [\"9614086\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Homozygous disruption of p70(S6K)/p85(S6K) (RPS6KB1) in mice reduces animal growth (especially during embryogenesis) but does not abolish S6 phosphorylation or 5'TOP mRNA translational upregulation, revealing a compensating S6K2; a novel S6K2 gene is upregulated in S6K1-deficient mouse tissues.\",\n      \"method\": \"Gene knockout in mice, polysome profiling, S6 phosphorylation Western blot, rapamycin sensitivity assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic knockout with defined phenotypic readouts, multiple assays\",\n      \"pmids\": [\"9822608\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"p70(S6K) knockout in murine ES cells abolishes ribosomal S6 phosphorylation and prevents serum-induced translational upregulation of ribosomal protein mRNAs, localizing p70(S6K) function specifically to ribosomal biogenesis via translational control of 5'TOP mRNAs; rapamycin still inhibits 4E-BP1 phosphorylation and general translation independently of p70(S6K).\",\n      \"method\": \"Gene disruption in ES cells, S6 phosphorylation assays, [35S]-methionine incorporation, polysome profiling\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean loss-of-function with specific mechanistic readouts\",\n      \"pmids\": [\"9560223\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Constitutive activation of the Rheb/mTOR/S6K cassette (via TSC1/TSC2 deletion or Rheb overexpression) induces insulin resistance by downregulating IRS1 and IRS2 protein levels, creating a negative feedback loop that attenuates PI3K/Akt signaling.\",\n      \"method\": \"Genetic deletion of TSC1/TSC2, Rheb overexpression, Western blot, insulin stimulation assays, Akt activity measurements\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic models with defined mechanistic pathway placement\",\n      \"pmids\": [\"15380067\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"S6K1 directly phosphorylates IRS-1 at Ser270 (human; Ser265 in rodents) as well as Ser307, Ser636, and Ser1101 to inhibit insulin signaling; S6K1 is activated at Thr389 downstream of TNF-α via an IKK2-dependent (not IKK1-dependent) pathway; Ser270 phosphorylation promotes IRS-1 association with S6K1 and facilitates phosphorylation at other sites.\",\n      \"method\": \"In vitro kinase assay with purified proteins, RNAi knockdown, point mutants of IRS-1 (S270A), IKK-null cells, glucose uptake assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro kinase assay with purified S6K1 and IRS-1, mutagenesis, multiple cell-based validations\",\n      \"pmids\": [\"18952604\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PP2A-B' (PPP2R5C in humans) is a phosphatase regulatory subunit that targets the PP2A holoenzyme to dephosphorylate S6K1; PP2A-B' physically interacts with S6K; loss of PP2A-B' elevates S6K phosphorylation in both Drosophila and mammalian cells, indicating a conserved mechanism.\",\n      \"method\": \"PP2A-B' knockout in Drosophila, co-immunoprecipitation, phospho-S6K Western blot, human PPP2R5C overexpression/knockdown\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP, genetic knockout, cross-species validation\",\n      \"pmids\": [\"20444422\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"mTORC1-S6K phosphorylates RNF168 at Ser60, inhibiting its E3 ubiquitin ligase activity and accelerating its proteolysis, thereby impairing the DNA damage response and causing genome instability; LKB1 loss hyperactivates mTORC1-S6K and decreases RNF168 expression; phospho-deficient RNF168-S60A rescues DNA damage repair defects.\",\n      \"method\": \"In vitro kinase assay, phospho-site mutagenesis (S60A), ubiquitin ligase activity assay, Western blot, tumor growth assays\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay with mutagenesis plus multiple cellular phenotypic readouts\",\n      \"pmids\": [\"29403037\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"S6K1 interacts with STING in a cGAS-dependent manner following DNA virus infection; the kinase domain (but not kinase activity) of S6K1 is required for the S6K1-STING interaction; TBK1 promotes formation of a tripartite S6K1-STING-TBK1 complex necessary for IRF3 activation; disruption impairs early antiviral gene expression and mucosal immunity.\",\n      \"method\": \"Co-immunoprecipitation, kinase-dead and domain mutants, RNAi knockdown, IRF3 reporter assays, viral infection models\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, domain mutagenesis, functional antiviral readouts\",\n      \"pmids\": [\"27043414\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"In Drosophila, dPDK1 controls cell and organism growth by activating both dAkt and S6 kinase (dS6K); genetic interaction studies show dPDK1 is required for dRSK but not dPKN activation, establishing two main growth-regulatory branches downstream of dPDK1.\",\n      \"method\": \"Drosophila genetics, genetic epistasis, loss-of-function and overexpression, growth phenotype analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis in Drosophila ortholog system with defined phenotypic readouts\",\n      \"pmids\": [\"11752451\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"p70(S6K) phosphorylation at 6 h post-exercise in rat skeletal muscle correlates tightly (r=0.998) with percent change in muscle mass after 6 weeks of resistance training; polysome profiles indicate increased translation initiation after high-resistance contractions, linking S6K1 activity to load-induced skeletal muscle hypertrophy.\",\n      \"method\": \"Rat resistance exercise model, p70(S6K) kinase activity immunoprecipitation assay, polysome profiling, muscle mass measurement\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct kinase activity assay with physiological phenotype, but correlative (no genetic manipulation)\",\n      \"pmids\": [\"9886927\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"mTOR is the rapamycin-sensitive kinase responsible for mechanically-induced phosphorylation of S6K1 at the hydrophobic motif Thr389; this activation occurs via a PI3K-independent mechanism, demonstrated using rapamycin-resistant mTOR mutants.\",\n      \"method\": \"Rapamycin-resistant mTOR mutants, mechanical stretch of muscle cells, phospho-Thr389 Western blot, PI3K inhibitor treatments\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — rapamycin-resistant rescue mutant experiment directly identifies mTOR as the kinase\",\n      \"pmids\": [\"17825298\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"p70(S6K) associates with the F-actin cytoskeleton (co-sedimentation assay), localizes to the actin arc at the leading edge of migrating cells together with Akt1, PDK1, and PI3K, and regulates cell migration; EGF-induced actin arc formation and cell migration are blocked by rapamycin; stress fibers inactivate p70(S6K), while their disruption activates it.\",\n      \"method\": \"F-actin co-sedimentation, subcellular fractionation, immunocytochemistry, rapamycin treatment, cytochalasin D and Y-27632 pharmacology\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — direct localization by fractionation and immunocytochemistry with functional migration readout, single lab\",\n      \"pmids\": [\"15149849\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Amino acid availability controls p70(S6K) activity through tRNA aminoacylation status; amino acid alcohols (inhibitors of tRNA aminoacylation), cycloheximide/puromycin (which block deacylated tRNA accumulation), and a temperature-sensitive histidyl-tRNA synthetase mutant all modulate p70(S6K) activity, suggesting deacylated tRNA is a negative regulator upstream of mTOR/S6K.\",\n      \"method\": \"Pharmacological inhibitors of aminoacylation, cycloheximide/puromycin, temperature-sensitive tRNA synthetase mutant cells, rapamycin comparison, kinase activity assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple chemical and genetic perturbations in a single lab, mechanistic pathway identification\",\n      \"pmids\": [\"9873056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"S6K1 phosphorylates eIF4B at Ser422 during interferon signaling, enhancing eIF4B interaction with eIF3A and its ATPase activity; IFN-inducible gene expression and growth-inhibitory effects on leukemic progenitors depend on S6K1/S6K2 activity and the S6K/eIF4B pathway; S6k1/S6k2 double-knockout MEFs show impaired IFN-stimulated ISG15 and CXCL-10 protein expression.\",\n      \"method\": \"S6K1/2 double-knockout MEFs, kinase assay, co-immunoprecipitation (eIF4B-eIF3A), ATPase activity assay, siRNA knockdown, colony-forming assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — knockout cells combined with biochemical interaction and activity assays\",\n      \"pmids\": [\"19289497\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Phosphatidic acid (PA), the product of PLD2 activity, binds to and signals through ribosomal S6 kinases (S6K); S6K1 specifically interacts with CoA synthase via C-terminal regions of both proteins (demonstrated by co-IP and BIAcore in vitro), linking mTOR/S6K signaling to CoA biosynthesis and energy metabolism.\",\n      \"method\": \"Co-immunoprecipitation of native and overexpressed proteins, BIAcore in vitro binding, enzymatic activity assays\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP confirmed by in vitro BIAcore, single lab, physiological significance unclear\",\n      \"pmids\": [\"15589845\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"p70(S6K) is activated by H2O2 (ROS) through a pathway requiring PI3K (wortmannin-sensitive) and mTOR/FRAP (rapamycin-sensitive), and dependent on Ca2+; TPA-responsive PKC is not required; PDGF and EGF stimulate endogenous H2O2 production that contributes to p70(S6K) activation, and catalase blocks this growth factor-induced S6K activation.\",\n      \"method\": \"Pharmacological inhibitors (rapamycin, wortmannin, PKC inhibitor Ro-31-8220), Ca2+ chelation, catalase treatment, kinase activity assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple inhibitors defining pathway position, single lab\",\n      \"pmids\": [\"10551813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"In cardiomyocytes, MEK/ERK signaling (but not PKB) is required for phenylephrine-induced activation of S6K2; insulin activates S6K2 via both PKB-dependent and MEK-dependent mechanisms; rapamycin completely blocks S6K2 activation by both agonists, placing S6K2 downstream of mTOR in this context.\",\n      \"method\": \"MEK inhibitors (three different), constitutively active MEK1 expression, dominant-negative PKB, rapamycin treatment, S6K2 immunoprecipitation kinase assay in cardiomyocytes\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple pharmacological and genetic tools in a single study, single lab\",\n      \"pmids\": [\"11431469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"p70(S6K) is activated in Xenopus oocytes during maturation and embryogenesis; rapamycin (inhibiting p70(S6K)) accelerates germinal vesicle breakdown and increases sensitivity to progesterone; constitutively active rapamycin-resistant p70(S6K) reverses rapamycin effects; p70(S6K) selectively promotes translation of 5'TOP mRNAs while suppressing non-5'TOP mRNAs (mos, Cdc25A) during oocyte maturation.\",\n      \"method\": \"Xenopus oocyte injection of rapamycin-resistant S6K mutant, rapamycin treatment, in vivo translation assays with 5'TOP reporter constructs, S6 phosphorylation assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — rapamycin-resistant rescue mutant in Xenopus with direct translational readouts, ortholog functional study\",\n      \"pmids\": [\"10082514\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"p70(S6K) activity (but not Akt or MAP kinase) is stimulated by insulin but not by contraction in rat skeletal muscle, whereas contraction potently activates MAP kinase independently of IRS1/IRS2 tyrosine phosphorylation; these discordant responses establish S6K1 as selectively insulin-responsive in skeletal muscle.\",\n      \"method\": \"Rat sciatic nerve electrical stimulation, immunoprecipitation kinase assays, Shc/Grb2 co-immunoprecipitation, IRS1/2 phosphorylation\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct kinase activity assays comparing two physiological stimuli with mechanistic readouts, single lab\",\n      \"pmids\": [\"10329981\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"p70(S6K) plays a positive role in cell cycle progression from G1 to S phase; a rapamycin-resistant p70(S6K) mutant expressed in T lymphocytes restores rapamycin-suppressed E2F transcriptional activity, establishing p70(S6K) as the rapamycin-sensitive mediator of IL-2/PI3K-induced E2F regulation.\",\n      \"method\": \"Rapamycin-resistant p70(S6K) mutant overexpression in primary T cells, E2F reporter assay, cell cycle analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — rapamycin-resistant rescue mutant directly implicating S6K1 in E2F regulation, defined cellular phenotype\",\n      \"pmids\": [\"10373522\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Constitutively active S6K overexpression in pancreatic β-cells in vivo improves insulin secretion but impairs IRS/Akt signaling (negative feedback), decreases G1-S cell cycle progression (via increased p16, p27, decreased Cdk2), and increases apoptosis, resulting in no net β-cell mass expansion.\",\n      \"method\": \"Transgenic mice with rat insulin promoter-driven constitutively active S6K, Western blot for cell cycle proteins, β-cell mass morphometry, glucose tolerance tests\",\n      \"journal\": \"Diabetes\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo transgenic model with multiple mechanistic readouts (cell cycle, apoptosis, insulin signaling)\",\n      \"pmids\": [\"20622167\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"mTOR-mediated activation of p70 S6K drives differentiation of human embryonic stem cells (hESCs); constitutively active (but not wild-type) p70 S6K induces hESC differentiation; siRNA knockdown of TSC2 and Rictor elevates S6K activity and induces differentiation; hESCs preferentially express mTORC2 and maintain high TSC1/TSC2 to suppress mTORC1/S6K.\",\n      \"method\": \"Constitutively active S6K overexpression, siRNA knockdown of TSC2 and Rictor, pluripotency marker immunostaining, rapamycin treatment\",\n      \"journal\": \"Cellular reprogramming\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — gain-of-function and loss-of-function with defined differentiation phenotype, single lab\",\n      \"pmids\": [\"20698768\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Leucine-induced activation of mTOR/p70(S6K) in the heart requires PDK1 acting through a mechanism distinct from insulin/PKB signaling; leucine activates PRAS40 phosphorylation in a PDK1-dependent manner; PDK1 with L155E mutation (preserving PKB-dependent mTOR signaling) abolishes leucine effects, placing PDK1 upstream of mTOR/S6K in the leucine pathway.\",\n      \"method\": \"PDK1 knockout hearts, PDK1 L155E knock-in mice, S6K and PRAS40 phosphorylation Western blot, leucine/insulin comparison\",\n      \"journal\": \"American journal of physiology. Endocrinology and metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout and knock-in models with mechanistic readouts, clear epistasis\",\n      \"pmids\": [\"20051528\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"mTORC1/S6K phosphorylates PDCD4, promoting its degradation and thereby de-repressing eIF4A to facilitate translation; this mTORC1/S6K/PDCD4/eIF4A axis determines cell fate (death vs. slippage) during mitotic arrest; non-phosphorylatable raptor mutant reactivates mTORC1 during mitosis and reduces Taxol-induced cytotoxicity via PDCD4 degradation.\",\n      \"method\": \"Non-phosphorylatable raptor mutant expression, rapamycin treatment, PDCD4 Western blot, eIF4A inhibitor, Taxol resistance assays\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — phospho-mutant rescue experiment with defined mechanistic pathway and functional phenotype\",\n      \"pmids\": [\"33027666\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Hepatic amino acid sensing via mTORC1/S6K signaling modulates systemic lipid metabolism (serum TG elevation, adipose LPL downregulation) through neuronal inter-tissue communication; hepatic Rheb or active-S6K expression phenocopy the effect; dominant-negative S6K in liver blocks hypertriglyceridemia; denervation and β-blockers suppress obesity-related hypertriglyceridemia.\",\n      \"method\": \"Hepatic viral expression of SNAT2/Rheb/active-S6K/DN-S6K, denervation, pharmacological deafferentation, triglyceride/LPL measurements\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic tools (active and dominant-negative S6K) with defined systemic metabolic phenotypes and mechanistic pathway\",\n      \"pmids\": [\"26268630\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"p70(S6K) is activated by the PS6K gene product (RPS6KB1) localized to chromosome 17q23; amplification in breast cancer leads to corresponding increases in mRNA and protein, suggesting oncogenic activity of this kinase.\",\n      \"method\": \"Fluorescence in situ hybridization (FISH), Northern blot, Western blot, comparative genomic hybridization\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — chromosomal localization and expression; mechanistic content limited\",\n      \"pmids\": [\"10197603\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RPS6KB1 (S6K1/p70S6K) is a serine/threonine kinase activated downstream of the mTORC1 pathway: mTOR phosphorylates S6K1 at Thr389 (hydrophobic motif), which enables PDK1 to phosphorylate the activation-loop Thr229 via the PIF-binding pocket, resulting in full kinase activation; active S6K1 phosphorylates ribosomal protein S6, eIF4B, IRS-1 (negative feedback at multiple serine residues to attenuate insulin signaling), RNF168 (suppressing DNA damage response), and PDCD4 (regulating translation by relieving eIF4A repression), while also interacting with STING to scaffold IRF3 activation during antiviral responses; upstream, the TSC1/2 complex restrains S6K1 by acting as a GAP for Rheb, and PP2A-B' (PPP2R5C) dephosphorylates S6K1; collectively, S6K1 integrates nutrient, growth factor, and mechanical signals to control translation, cell growth/size, cell cycle progression, metabolism, and genome stability.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1996,\n      \"finding\": \"T-389 is the principal regulatory phosphorylation site of p70(S6K); phosphorylation of T-389 together with hyperphosphorylation of autoinhibitory domain S/TP sites acutely regulates kinase activity, while T-229 in the activation loop is regulated by distinct, rapamycin-insensitive kinases. Mutation of T-389 to an acidic residue confers rapamycin and wortmannin resistance.\",\n      \"method\": \"Site-directed mutagenesis of phosphorylation sites combined with kinase activity assays, truncation mutant analysis, and inhibitor studies (rapamycin, wortmannin, SQ20006)\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro mutagenesis with multiple orthogonal functional readouts in a single study\",\n      \"pmids\": [\"8887654\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"PDK1 directly phosphorylates p70S6K at T-229 (Thr229) in the activation loop, activating it in vitro and in vivo; PDK1-mediated p70S6K phosphorylation is dependent on prior phosphorylation of the carboxy-terminal tail (T-389/Thr412 in the p70 numbering used), establishing hierarchical phosphorylation as the activation mechanism.\",\n      \"method\": \"In vitro kinase assay with purified PDK1 and p70S6K, co-expression in cells, site-specific mutagenesis, phosphospecific antibody analysis\",\n      \"journal\": \"Science / Current biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with mutagenesis, independently reported in two concurrent papers\",\n      \"pmids\": [\"9445476\", \"9427642\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Phosphorylation of the autoinhibitory domain S/TP sites acts cooperatively with T-389 phosphorylation to control T-229 (activation loop) phosphorylation through an intrasteric mechanism; T-389 acidic substitution plus S/TP acidic substitutions markedly increase basal T-229 phosphorylation and kinase activity, making the resulting mutant an excellent PDK1 substrate in vitro.\",\n      \"method\": \"Truncation and point mutants analyzed by kinase activity assay and in vitro PDK1 phosphorylation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with mutagenesis, rigorous epistatic analysis\",\n      \"pmids\": [\"9614086\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Homozygous disruption of the p70(S6K)/p85(S6K) gene in mice reduces body size (especially during embryogenesis) but does not abolish S6 phosphorylation in liver or fibroblasts; a novel homolog S6K2 is upregulated in knockout tissues and can compensate for S6K1 function, accounting for residual S6 phosphorylation.\",\n      \"method\": \"Gene knockout in mice, Western blot for S6 phosphorylation, polysome profiling, Northern/Western analysis of S6K2\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean knockout mouse with multiple orthogonal readouts; identified S6K2 as compensatory kinase\",\n      \"pmids\": [\"9822608\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Targeted disruption of p70(S6K) in murine embryonic stem cells abolishes ribosomal S6 phosphorylation, prevents serum-stimulated translational upregulation of ribosomal protein mRNAs (5'TOP mRNAs), and slows proliferation; rapamycin-sensitive inhibition of 4E-BP1 phosphorylation and general protein synthesis occurs independently of p70(S6K).\",\n      \"method\": \"Gene targeting in ES cells, 35S-methionine incorporation, sucrose gradient polysome analysis, immunoblotting\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic loss-of-function with specific translational readouts\",\n      \"pmids\": [\"9560223\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"p70(S6K) activity measured 6 h post-exercise in rat skeletal muscle correlates tightly (r = 0.998) with percent increase in muscle mass after 6 weeks of resistance training; polysome analysis suggests increased translation initiation after lengthening contractions, implicating p70(S6K) in load-induced muscle hypertrophy.\",\n      \"method\": \"Animal exercise model, immunoprecipitation kinase assay, polysome profiling, muscle mass measurement\",\n      \"journal\": \"The American journal of physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — correlative but used direct kinase activity assay and functional hypertrophy outcome in vivo\",\n      \"pmids\": [\"9886927\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Amino acid-dependent activation of p70(S6K) involves tRNA aminoacylation: amino acid alcohols that inhibit tRNA synthetases suppress p70(S6K) activity; cycloheximide or puromycin block suppression by amino acid withdrawal; a temperature-sensitive histidyl-tRNA synthetase mutant reduces p70(S6K) at non-permissive temperature. Deacylated tRNA may be a negative regulator of p70(S6K).\",\n      \"method\": \"Chemical inhibitors of tRNA aminoacylation, temperature-sensitive mutant cell line, rapamycin-resistant mTOR mutant, kinase activity assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal chemical and genetic approaches in a single study\",\n      \"pmids\": [\"9873056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"p70(S6K) activity in Xenopus oocytes is high at rest and decreases upon progesterone-induced maturation; rapamycin (which inhibits p70S6K) accelerates germinal vesicle breakdown and increases mos mRNA translation (a non-5'TOP mRNA), while 5'TOP-containing mRNAs are translated less efficiently under rapamycin. A constitutively active rapamycin-resistant p70(S6K) reverses rapamycin effects, defining p70(S6K) as the relevant effector.\",\n      \"method\": \"Xenopus oocyte system, rapamycin-resistant constitutively active S6K1 rescue, in vivo translation assays with 5'TOP and IRES reporters, S6 phosphorylation immunoblotting\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with rapamycin-resistant mutant rescues phenotype; orthogonal translation reporters\",\n      \"pmids\": [\"10082514\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Hydrogen peroxide activates p70(S6K) upstream of rapamycin-sensitive FRAP/mTOR and wortmannin-sensitive PI3K; Ca2+ chelation blocks H2O2-induced p70(S6K) activation, identifying Ca2+ as a mediator; PKC is not required. Growth factor-induced H2O2 generation contributes to p70(S6K) activation.\",\n      \"method\": \"Chemical inhibitors (rapamycin, wortmannin), Ca2+ chelation, PKC downregulation, glucose oxidase-generated H2O2, catalase pretreatment, kinase activity assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple inhibitors and genetic tools defining pathway position\",\n      \"pmids\": [\"10551813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The PIF-binding pocket in PDK1 is essential for T-loop phosphorylation and activation of S6K1 and SGK but not PKBα; prior phosphorylation of S6K1 at its hydrophobic motif (T-389) promotes docking into the PDK1 PIF-binding pocket, thereby enabling T-loop phosphorylation—establishing that hydrophobic motif phosphorylation converts S6K1 into a PDK1 substrate.\",\n      \"method\": \"PIF-binding pocket mutations in PDK1 expressed in cells, in vitro kinase assays, immunoprecipitation\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structure-function mutagenesis combined with in vitro reconstitution\",\n      \"pmids\": [\"11500365\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Drosophila PDK1 (dPDK1) activates both dAkt and dS6K to control cell and organismal growth; genetic interactions show dPDK1 is required for dRSK but not dPKN function; dPDK1-dS6K constitutes an independent branch of insulin-mediated growth downstream of PI3K.\",\n      \"method\": \"Drosophila genetics, epistasis analysis, cell size measurements, kinase activity assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo genetic epistasis in Drosophila with multiple orthogonal readouts\",\n      \"pmids\": [\"11752451\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"p70 S6K1 phosphorylates eEF2 kinase (eEF2K) at a conserved serine, inhibiting eEF2K activity and thereby promoting eEF2 activity and peptide elongation; this rapamycin-sensitive pathway requires PDK1 and links mTOR/S6K1 signaling to translational elongation control.\",\n      \"method\": \"In vitro kinase assay with purified S6K1 and eEF2K, PDK1 knockout cells, rapamycin treatment, Erk inhibitor studies\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay plus genetic knockout corroboration\",\n      \"pmids\": [\"11500364\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"MEK/ERK signaling activates S6K2 (but not S6K1) in cardiomyocytes in response to phenylephrine in a PKB-independent manner; insulin activates S6K2 via both MEK/ERK and PKB-dependent pathways; both activation routes require mTOR (rapamycin-sensitive), establishing S6K2 as a point of convergence for MEK and mTOR signaling.\",\n      \"method\": \"Pharmacological MEK inhibitors, dominant-negative PKB expression, constitutively active MEK1 expression, immunoprecipitation kinase assays in adult rat ventricular cardiomyocytes\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple inhibitors and dominant-negative constructs with specific kinase activity readouts\",\n      \"pmids\": [\"11431469\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"TSC1/2 acts as a GAP for the small GTPase Rheb; insulin-mediated Rheb activation is PI3K-dependent; Rheb overexpression induces S6K1 phosphorylation and inhibits PKB phosphorylation; a TSC2 disease-associated GAP-domain point mutation fails to stimulate Rheb GTPase activity or block Rheb activation of S6K1.\",\n      \"method\": \"GTPase activity assays, co-immunoprecipitation, overexpression of Rheb and TSC constructs, phosphospecific immunoblotting\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical GAP assay combined with mutagenesis and cellular epistasis\",\n      \"pmids\": [\"12820960\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Drosophila Rheb functions downstream of TSC1-TSC2 and upstream of TOR/S6K to control cell growth; genetic loss-of-function of Rheb inhibits growth while overexpression promotes growth; S6K is identified as a major effector of Rheb function.\",\n      \"method\": \"Drosophila genetics (loss-of-function and overexpression), epistasis with TSC1/TSC2 and TOR, cell size measurements, biochemical S6K activity assays\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo epistasis in Drosophila with biochemical validation\",\n      \"pmids\": [\"12766775\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"In Drosophila, RNAi of dAkt also affects insulin-stimulated dS6K phosphorylation, indicating Akt influences dS6K phosphorylation; in contrast, 4E-BP phosphorylation is PI3K- and Akt-dependent while S6K phosphorylation has an additional PI3K/Akt-independent component through TOR.\",\n      \"method\": \"RNA interference of pathway components in Drosophila S2 cells, isoelectric focusing-SDS-PAGE for 4E-BP phosphorylation states, immunoblotting for dS6K\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic RNAi epistasis with orthogonal readouts\",\n      \"pmids\": [\"14645523\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Constitutive activation of the Rheb/mTOR/S6K cassette (by TSC1/TSC2 deletion or Rheb overexpression) induces IRS-1 and IRS-2 downregulation, creating insulin resistance and blocking IGF-I/insulin-stimulated Akt activation; S6K-mediated negative feedback on IRS proteins is sufficient to impair cell survival.\",\n      \"method\": \"TSC1/TSC2 genetic deletion, Rheb overexpression, immunoprecipitation, immunoblotting, cell survival/apoptosis assays\",\n      \"journal\": \"Current biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic deletion plus overexpression with multiple biochemical and phenotypic readouts\",\n      \"pmids\": [\"15380067\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"S6K1 (p70S6K) is localized to the actin arc (a caveolin-enriched cytoskeletal structure at the leading edge of migrating cells), co-sediments with F-actin, and is required for EGF-induced actin arc formation and cell migration; rapamycin blocks actin arc formation; fibronectin-induced stress fibers suppress p70(S6K) activity.\",\n      \"method\": \"Subcellular fractionation, co-sedimentation with F-actin, immunocytochemistry, rapamycin treatment, cytochalasin D and Y-27632 pharmacology\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization experiments tied to functional cell migration assay\",\n      \"pmids\": [\"15149849\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Scylla and Charybdis (REDD1 homologs) act as negative regulators of growth in Drosophila by reducing S6K (but not PKB/Akt) activity; they function downstream of PKB and upstream of TSC, establishing a pathway position; REDD1/Scylla is induced by HIF-1 under hypoxia.\",\n      \"method\": \"Drosophila genetics (EP overexpression screen, double mutants), S6K and Akt kinase activity assays, epistasis analysis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo Drosophila epistasis with kinase activity assays\",\n      \"pmids\": [\"15545626\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"mTOR and S6K1 dynamically associate with the eIF3 translation preinitiation complex; inactive S6K1 is associated with eIF3 while mTOR/raptor is absent; cell stimulation recruits mTOR/raptor to eIF3 where it phosphorylates S6K1 at the hydrophobic motif, causing S6K1 dissociation and activation, followed by phosphorylation of eIF4B which is then recruited to the complex.\",\n      \"method\": \"Co-immunoprecipitation, mass spectrometry identification of eIF3 complex components, phosphospecific immunoblotting, rapamycin treatment, siRNA knockdown\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP with ordered phosphorylation analysis replicated with multiple tools\",\n      \"pmids\": [\"16286006\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Raptor binds p70S6K1 and 4E-BP1 through their TOS (TOR signaling) motifs; TOS motif mutation abolishes mTOR-catalyzed phosphorylation in vitro and eliminates rapamycin sensitivity and amino acid responsiveness in vivo, establishing raptor as the scaffold that recruits S6K1 to mTOR for phosphorylation.\",\n      \"method\": \"Co-immunoprecipitation, in vitro mTOR kinase assay, TOS motif mutagenesis, rapamycin and amino acid withdrawal experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase reconstitution with mutagenesis confirming substrate recruitment mechanism\",\n      \"pmids\": [\"12604610\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"p70S6K phosphorylates mTOR at Ser-2448 in vitro and in cells; rapamycin blocks Ser-2448 phosphorylation in a manner not explained by Akt inhibition; rapamycin-resistant S6K1 restores Ser-2448 phosphorylation in rapamycin-treated cells; siRNA depletion of S6K1 reduces Ser-2448 phosphorylation, identifying S6K1 as a positive feedback kinase on mTOR.\",\n      \"method\": \"In vitro kinase assay with purified S6K1, rapamycin-resistant S6K1 rescue, siRNA knockdown, amino acid deprivation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay plus rapamycin-resistant rescue plus siRNA knockdown\",\n      \"pmids\": [\"15899889\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"In response to mitogens, S6K1 phosphorylates PDCD4 at Ser67, targeting it for SCF(βTRCP)-mediated ubiquitin-proteasome degradation; stable PDCD4 that cannot bind βTRCP inhibits translation of mRNAs with structured 5'UTRs, reduces cell size, and slows cell cycle progression.\",\n      \"method\": \"In vitro S6K1 kinase assay, ubiquitination assays, stable PDCD4 mutant expression, translation reporter assays, cell size measurements\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay with mutagenesis and functional cellular readouts\",\n      \"pmids\": [\"17053147\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Mechanical stretch activates mTOR as the rapamycin-sensitive kinase responsible for T-389 phosphorylation in p70(S6K) through a PI3K-independent mechanism; rapamycin-resistant mTOR mutants restore mechanically-induced T-389 phosphorylation in rapamycin-treated cells.\",\n      \"method\": \"Rapamycin-resistant mTOR mutant expression combined with mechanical stretch, phosphospecific immunoblotting\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — rapamycin-resistant mutant rescue definitively identifies mTOR as the relevant kinase\",\n      \"pmids\": [\"17825298\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SF2/ASF splicing factor controls alternative splicing of S6K1 to generate an unusual isoform (isoform-2) that lacks the autoinhibitory domain and is constitutively active; this isoform recapitulates the transforming activity of SF2/ASF, and knockdown of either SF2/ASF or S6K1 isoform-2 reverses transformation in vitro and in vivo.\",\n      \"method\": \"Alternative splicing analysis, RT-PCR, siRNA knockdown, soft agar colony assay, nude mouse xenograft\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with specific isoform identification and in vivo tumor phenotype\",\n      \"pmids\": [\"17310252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"S6K1 directly phosphorylates IRS-1 at Ser-270, Ser-307, Ser-636, and Ser-1101 in response to TNF-α, with Ser-270 phosphorylation being a key docking site for S6K1 on IRS-1; TNF-α activates S6K1 via an IKK2-dependent pathway; RNAi knockdown of S6K1 prevents TNF-α-induced IRS-1 inhibition and impaired glucose uptake.\",\n      \"method\": \"In vitro kinase assay with purified IRS-1 and S6K1, point mutant IRS-1 (S270A), RNAi knockdown, dominant-negative S6K1, IKK2 knockout cells, glucose uptake assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay with multiple site-specific mutants plus genetic loss-of-function\",\n      \"pmids\": [\"18952604\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"IFN-α and IFN-γ stimulate phosphorylation of eIF4B at Ser422 in a cell-type-specific manner via p70 S6K1; S6K1-mediated eIF4B phosphorylation enhances eIF4B interaction with eIF3A and increases associated ATPase activity; S6K1/S6K2 double-knockout MEFs show diminished IFN-inducible ISG15 and CXCL10 protein expression, establishing S6K as a mediator of IFN-dependent translation.\",\n      \"method\": \"S6K1/S6K2 double-knockout MEFs, siRNA knockdown of eIF4B/eIF3A, ATPase activity assays, co-immunoprecipitation, phosphospecific immunoblotting\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — double knockout MEFs plus siRNA knockdown with multiple functional readouts\",\n      \"pmids\": [\"19289497\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PP2A-B' (PPP2R5C in humans) specifically targets the PP2A holoenzyme to dephosphorylate S6K; PP2A-B' physically interacts with S6K; Drosophila PP2A-B' knockout elevates S6K phosphorylation and phenocopies elevated insulin signaling; human PPP2R5C counteracts S6K1 phosphorylation, indicating a conserved mechanism.\",\n      \"method\": \"Drosophila knockout genetics, co-immunoprecipitation (PP2A-B' with S6K), phosphospecific immunoblotting, mammalian PPP2R5C overexpression/knockdown\",\n      \"journal\": \"Cell metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus genetic knockout with conserved mammalian validation\",\n      \"pmids\": [\"20444422\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Leucine activates the cardiac mTOR/p70(S6K) pathway through a PDK1-dependent but PKB/Akt-independent mechanism; leucine also phosphorylates PRAS40, a key mTOR regulator; the PDK1 L155E mutation (preserving insulin/Akt-dependent mTOR signaling) abolishes leucine effects, demonstrating leucine uses a distinct PDK1 interaction interface.\",\n      \"method\": \"PDK1 knockout hearts, PDK1 L155E knock-in, leucine and insulin stimulation, p70S6K kinase assays, PRAS40 phosphospecific immunoblotting\",\n      \"journal\": \"American journal of physiology. Endocrinology and metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic PDK1 knockout plus separation-of-function PDK1 mutation with kinase activity readouts\",\n      \"pmids\": [\"20051528\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Constitutively active S6K1 in pancreatic β-cells impairs IRS/Akt signaling (negative feedback), decreases G1-S progression, increases apoptosis via elevated p16 and p27 and reduced Cdk2, and improves insulin secretion without expanding β-cell mass, demonstrating that S6K-mediated IRS downregulation induces β-cell insulin resistance in vivo.\",\n      \"method\": \"Transgenic mice with β-cell-specific constitutively active S6K1, cell cycle protein analysis, Akt phosphorylation, insulin secretion assays, TUNEL apoptosis\",\n      \"journal\": \"Diabetes\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo transgenic model with mechanistic biochemical readouts\",\n      \"pmids\": [\"20622167\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"mTOR-mediated activation of p70 S6K1 induces differentiation of human embryonic stem cells; constitutively active p70 S6K1 (but not wild-type) triggers differentiation; siRNA knockdown of TSC2 and Rictor elevates S6K1 activity and induces differentiation; hESCs preferentially express rapamycin-insensitive mTORC2 and high TSC1/TSC2 levels to restrain mTORC1/S6K1 activity.\",\n      \"method\": \"siRNA knockdown, constitutively active S6K1 expression, rapamycin treatment, pluripotency marker analysis (Oct4, Nanog), differentiation assays\",\n      \"journal\": \"Cellular reprogramming\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA and constitutively active mutant with specific differentiation phenotype\",\n      \"pmids\": [\"20698768\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"S6K1 interacts with the signaling adaptor STING in a cGAS-dependent manner upon DNA virus infection; the kinase domain (but not kinase activity) of S6K1 is required for the S6K1-STING interaction; TBK1 promotes formation of a tripartite S6K1-STING-TBK1 complex required for IRF3 activation and early antiviral gene expression.\",\n      \"method\": \"Co-immunoprecipitation, kinase-dead S6K1 mutants, cGAS knockout cells, TBK1 inhibitor, antiviral response assays (IRF3 target gene expression, T cell responses)\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP with domain mutagenesis and genetic knockouts defining complex assembly and function\",\n      \"pmids\": [\"27043414\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The mTOR-S6K pathway phosphorylates RNF168 at Ser60 to inhibit its E3 ligase activity, accelerate its proteolysis, and impair DNA damage response (DDR); loss of LKB1 hyperactivates mTORC1-S6K, decreasing RNF168 expression; phospho-deficient RNF168-S60A rescues DDR defects and suppresses tumorigenesis caused by Lkb1 loss.\",\n      \"method\": \"In vitro S6K kinase assay on RNF168, phospho-deficient mutant rescue, ubiquitination assays, γH2AX DDR readouts, LKB1 knockout mouse model, tumor xenografts\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay with phospho-deficient rescue and in vivo tumor model\",\n      \"pmids\": [\"29403037\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"During mitotic arrest, mTORC1/S6K activity is dramatically reduced due to mitotic phosphorylation of raptor; expression of a non-phosphorylatable raptor mutant reactivates mTORC1 and reduces Taxol cytotoxicity via S6K-mediated phosphorylation and degradation of the eIF4A inhibitor PDCD4, promoting translation; pharmacological eIF4A inhibition enhances Taxol effects and restores sensitivity in resistant cells.\",\n      \"method\": \"Non-phosphorylatable raptor mutant, mTORC1 activity immunoblotting, PDCD4 stability assays, pharmacological eIF4A inhibition, Taxol sensitivity assays\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — separation-of-function raptor mutant with mechanistic pathway dissection and drug combination readouts\",\n      \"pmids\": [\"33027666\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Specific interaction between S6K1 and CoA synthase is detected by co-immunoprecipitation of native and overexpressed proteins and by BIAcore in vitro; the interaction maps to the C-terminal regions of both proteins; CoA synthase is not a substrate for S6K1 and the interaction does not affect enzymatic activities of either partner, suggesting a regulatory scaffolding role linking mTOR/S6K signaling to CoA biosynthesis and energy metabolism.\",\n      \"method\": \"Co-immunoprecipitation, BIAcore binding analysis, in vitro kinase assay, C-terminal deletion mapping\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP and BIAcore confirm binding but functional significance remains to be elucidated\",\n      \"pmids\": [\"15589845\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Hepatic amino acid/mTORC1/S6K signaling modulates systemic lipid metabolism via neuronal inter-tissue communication; hepatic active-S6K expression elevates serum triglycerides and downregulates adipose lipoprotein lipase (LPL); dominant-negative S6K expression blocks TG elevation; denervation, pharmacological deafferentation, and β-blockade suppress hypertriglyceridemia with adipose LPL upregulation, indicating signal transduction via afferent vagal and efferent sympathetic nerves.\",\n      \"method\": \"Adenoviral hepatic expression of active/dominant-negative S6K, SNAT2, Rheb; surgical/pharmacological denervation; metabolic measurements\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic gain/loss-of-function with neuronal intervention experiments in vivo\",\n      \"pmids\": [\"26268630\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Loss of S6K in Drosophila fat body blocks rapamycin-mediated lifespan extension and causes accumulation of multilamellar lysosomes; Syntaxin 13 mediates TORC1-S6K effects on lysosome morphology and inflammaging (age-related NF-κB-like immune pathway hyperactivation); rapamycin also elevates Syntaxin 12/13 levels in mouse liver and prevents age-related non-canonical NF-κB signaling, indicating a conserved mechanism.\",\n      \"method\": \"Tissue-specific S6K activation in Drosophila fat body, lifespan assays, lysosome morphology analysis, Syntaxin 13 genetic interaction, mouse liver proteomic/biochemical analysis\",\n      \"journal\": \"Nature aging\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — tissue-specific genetics with mechanistic pathway identification and mammalian validation\",\n      \"pmids\": [\"38413780\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RPS6KB1 (S6K1/p70S6K) is a serine/threonine kinase that is activated downstream of mTORC1 (via raptor-TOS motif docking) through a hierarchical phosphorylation cascade in which mTOR phosphorylates T-389 in the hydrophobic motif, enabling PDK1 PIF-pocket docking and T-229 activation-loop phosphorylation; once active, S6K1 phosphorylates multiple substrates—including rpS6, eIF4B, eEF2K, PDCD4 (targeting it for βTRCP-dependent degradation), IRS-1 (creating a negative feedback loop that drives insulin resistance), RNF168 (linking growth signaling to DNA damage response), and mTOR itself (Ser-2448 positive feedback)—and also forms a non-catalytic complex with STING-TBK1 to promote IRF3-dependent antiviral immunity, while its activity is negatively regulated by PP2A-B' (PPP2R5C)-mediated dephosphorylation and is physiologically engaged by nutrients (amino acids via tRNA aminoacylation sensing), mechanical load, growth factors, and reactive oxygen species to control cell size, protein synthesis, autophagy, muscle hypertrophy, stem cell differentiation, and systemic lipid metabolism.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"RPS6KB1 (p70S6K/S6K1) is a serine/threonine kinase that serves as a central effector of the mTORC1 signaling pathway, integrating nutrient, growth factor, and mechanical signals to control translation, cell growth, cell cycle progression, and metabolism. Full activation requires sequential phosphorylation: mTOR phosphorylates the hydrophobic motif at Thr389 in a rapamycin-sensitive manner, which creates a docking site on PDK1's PIF-binding pocket to enable activation-loop phosphorylation at Thr229, with autoinhibitory S/TP domain phosphorylation cooperating in this process [PMID:8887654, PMID:11500365, PMID:9614086]. Active S6K1 phosphorylates ribosomal protein S6 to promote 5′TOP mRNA translation and ribosomal biogenesis, eIF4B at Ser422 to enhance translation initiation, PDCD4 to de-repress eIF4A, IRS-1 at multiple serines (Ser270, Ser307, Ser636, Ser1101) to mediate negative feedback on insulin signaling, and RNF168 at Ser60 to suppress the DNA damage response [PMID:9560223, PMID:19289497, PMID:33027666, PMID:18952604, PMID:29403037]. Beyond its kinase-dependent substrates, S6K1 scaffolds a STING–TBK1 complex through its kinase domain (independent of catalytic activity) to activate IRF3 during antiviral innate immune responses, and it regulates systemic lipid metabolism through hepatic amino acid sensing and inter-tissue neuronal communication [PMID:27043414, PMID:26268630].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Identification of Thr389 and Thr229 as principal rapamycin-sensitive regulatory sites established the hierarchical, multi-step phosphorylation model for S6K1 activation, resolving how distinct upstream signals converge on kinase activation.\",\n      \"evidence\": \"Truncation/point mutants of p70S6K combined with in vitro kinase assays and phosphopeptide mapping\",\n      \"pmids\": [\"8887654\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the Thr389 kinase was not established in this study\", \"In vivo stoichiometry of multi-site phosphorylation unknown\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Reconstitution of PDK1-mediated Thr229 phosphorylation demonstrated that prior Thr389 and S/TP site phosphorylation relieves an intrasteric autoinhibitory mechanism, explaining the ordered activation sequence.\",\n      \"evidence\": \"In vitro PDK1 kinase assay with combinatorial S6K1 point mutants and truncations\",\n      \"pmids\": [\"9614086\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of autoinhibition not resolved\", \"Whether additional kinases contribute to S/TP phosphorylation in vivo not determined\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Gene knockout of S6K1 in mice and ES cells demonstrated that S6K1 is essential for S6 phosphorylation and 5′TOP mRNA translational control, defining its primary physiological output as ribosomal biogenesis, while also revealing compensatory S6K2 upregulation.\",\n      \"evidence\": \"S6K1 knockout mice and ES cells with polysome profiling, S6 phosphorylation, and metabolic labeling\",\n      \"pmids\": [\"9822608\", \"9560223\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of S6K1 vs S6K2 to whole-organism physiology unresolved until double knockouts\", \"Mechanism of S6K2 compensatory upregulation unknown\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Multiple studies established upstream input diversity: amino acid sensing through tRNA aminoacylation status, ROS/H2O2 via PI3K/mTOR/Ca2+, and selective insulin responsiveness in skeletal muscle were all shown to converge on S6K1 activation, broadening the signal-integration model beyond growth factors alone.\",\n      \"evidence\": \"Pharmacological inhibitors of aminoacylation, temperature-sensitive tRNA synthetase mutants, catalase treatment, and rat skeletal muscle kinase assays\",\n      \"pmids\": [\"9873056\", \"10551813\", \"9886927\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular sensor linking deacylated tRNA to mTOR not identified\", \"Direct mechanism of ROS-to-mTOR signaling not resolved\", \"Correlation between S6K activity and muscle hypertrophy lacked genetic confirmation\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"A rapamycin-resistant S6K1 mutant rescued E2F transcriptional activity in rapamycin-treated T cells and 5′TOP mRNA translation in Xenopus oocytes, directly implicating S6K1 as the rapamycin-sensitive mediator of G1/S progression and selective mRNA translation.\",\n      \"evidence\": \"Rapamycin-resistant S6K1 mutant expression in primary T lymphocytes (E2F reporter) and Xenopus oocytes (5′TOP reporter, cell cycle timing)\",\n      \"pmids\": [\"10373522\", \"10082514\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct phosphorylation targets linking S6K1 to E2F activation not identified\", \"Contribution of S6K2 in these contexts not tested\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Mechanistic dissection of PDK1's PIF-binding pocket showed it is specifically required for S6K1 T-loop phosphorylation but dispensable for PKBα, establishing substrate-selective recognition as a principle of PDK1 signaling.\",\n      \"evidence\": \"In vitro kinase assay with PDK1 PIF-pocket mutants and co-immunoprecipitation\",\n      \"pmids\": [\"11500365\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Crystal structure of PDK1–S6K1 complex not available\", \"Whether PIF-pocket mutations affect S6K2 identically not tested\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identification of Rheb as a GTPase directly activated by insulin (PI3K-dependent) and negatively regulated by TSC1/2 GAP activity placed the missing link between PI3K and mTOR/S6K1, completing the core linear pathway architecture.\",\n      \"evidence\": \"In vivo GTPase assays, Rheb overexpression inducing S6K1 phosphorylation, TSC2 GAP-domain disease mutant analysis\",\n      \"pmids\": [\"12820960\", \"12766775\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct Rheb–mTOR binding mechanism not resolved in this work\", \"How other inputs (amino acids) intersect with Rheb regulation unclear\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Discovery of S6K1-mediated negative feedback on IRS1/2 protein levels via the Rheb/mTOR/S6K cassette explained the paradox of insulin resistance in TSC-null and mTOR-hyperactive states, establishing S6K1 as a node for metabolic feedback.\",\n      \"evidence\": \"TSC1/TSC2 genetic deletion and Rheb overexpression with IRS protein quantification and Akt activity measurement\",\n      \"pmids\": [\"15380067\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific S6K1 phosphorylation sites on IRS1 not identified in this study\", \"Relative contribution of S6K1 vs S6K2 to IRS degradation not resolved\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Using rapamycin-resistant mTOR mutants, mTOR was identified as the kinase responsible for mechanically induced S6K1 Thr389 phosphorylation through a PI3K-independent route, separating mechanical from hormonal activation of S6K1.\",\n      \"evidence\": \"Rapamycin-resistant mTOR mutant rescue in mechanically stretched muscle cells with PI3K inhibitor controls\",\n      \"pmids\": [\"17825298\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanosensor upstream of mTOR not identified\", \"Whether PA/PLD contributes to mechanical activation not tested here\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Direct identification of IRS-1 phosphorylation sites (Ser270, Ser307, Ser636, Ser1101) by purified S6K1 resolved the molecular mechanism of the negative feedback loop and revealed TNFα-IKK2 as an alternative S6K1 activator linking inflammation to insulin resistance.\",\n      \"evidence\": \"In vitro kinase assay with purified S6K1 and IRS-1, S270A mutagenesis, IKK-null cells, glucose uptake assays\",\n      \"pmids\": [\"18952604\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative importance of individual IRS-1 phospho-sites in vivo not established\", \"Whether IKK2-S6K1 activation is mTOR-dependent or independent not fully resolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"S6K1 was shown to phosphorylate eIF4B at Ser422, enhancing its interaction with eIF3A and promoting translation of interferon-stimulated genes, extending S6K1's translational control beyond 5′TOP mRNAs to innate immune gene expression.\",\n      \"evidence\": \"S6K1/S6K2 double-knockout MEFs, in vitro kinase assay, eIF4B–eIF3A co-immunoprecipitation, ATPase activity assay\",\n      \"pmids\": [\"19289497\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether eIF4B Ser422 phosphorylation is S6K1- or S6K2-specific not resolved\", \"Structural basis of eIF4B–eIF3A enhanced interaction unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"PP2A-B′ (PPP2R5C) was identified as the phosphatase that dephosphorylates S6K1, establishing the first dedicated negative regulator of S6K1 phosphorylation status, conserved from Drosophila to mammals.\",\n      \"evidence\": \"PP2A-B′ knockout in Drosophila, reciprocal co-immunoprecipitation, PPP2R5C knockdown/overexpression in mammalian cells\",\n      \"pmids\": [\"20444422\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific S6K1 phospho-sites targeted by PP2A-B′ not mapped\", \"Regulation of PP2A-B′ itself in response to growth signals not addressed\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Hepatic S6K1 activation was found to modulate systemic triglyceride metabolism through neuronal inter-tissue communication, revealing a non-cell-autonomous metabolic function for S6K1 beyond translational control.\",\n      \"evidence\": \"Hepatic viral expression of active/dominant-negative S6K, denervation, β-blocker treatment, triglyceride and LPL measurement\",\n      \"pmids\": [\"26268630\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the neural afferent signal from liver to adipose not determined\", \"Whether this pathway operates in humans unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"S6K1 was shown to scaffold a STING–TBK1 complex for IRF3 activation via its kinase domain (independent of catalytic activity), establishing a kinase-independent scaffolding function in innate antiviral immunity.\",\n      \"evidence\": \"Co-immunoprecipitation with kinase-dead and domain mutants, RNAi, IRF3 reporter assays, viral infection models\",\n      \"pmids\": [\"27043414\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of kinase-domain–STING interaction not resolved\", \"Whether mTORC1-dependent phosphorylation of S6K1 regulates the scaffolding function unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"S6K1 was shown to phosphorylate RNF168 at Ser60, inhibiting its E3 ligase activity and accelerating its degradation, thereby impairing the DNA damage response — linking mTORC1/S6K1 hyperactivation to genome instability.\",\n      \"evidence\": \"In vitro kinase assay, S60A phospho-deficient mutant rescue of DNA repair, ubiquitin ligase activity assays, tumor models\",\n      \"pmids\": [\"29403037\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether S6K2 also phosphorylates RNF168 not tested\", \"Relevance to specific cancer types with mTORC1 hyperactivation not established clinically\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Phosphorylation and degradation of PDCD4 by mTORC1/S6K was shown to de-repress eIF4A during mitotic arrest, determining whether cells undergo death or mitotic slippage — revealing a translational checkpoint function for S6K1 in mitosis.\",\n      \"evidence\": \"Non-phosphorylatable raptor mutant, rapamycin treatment, PDCD4 degradation assays, eIF4A inhibitor, Taxol cytotoxicity assays\",\n      \"pmids\": [\"33027666\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct S6K1 phosphorylation sites on PDCD4 not mapped in this study\", \"Whether this mechanism operates in solid tumors treated with taxanes not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A comprehensive structural model of full-length S6K1 showing how autoinhibitory domain, hydrophobic motif, and activation loop cooperate during sequential phosphorylation remains unavailable, and the relative physiological contributions of S6K1 vs S6K2 to most downstream processes are not delineated.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No full-length S6K1 crystal or cryo-EM structure\", \"S6K1 vs S6K2 substrate specificity determinants not systematically mapped\", \"Complete in vivo phosphoproteome of S6K1-specific substrates not available\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [2, 3, 7, 9, 16, 26]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [7, 16]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [14]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 6, 8, 13, 25]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [2, 3, 5, 16, 20]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [22, 23]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [10, 16]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [6, 7, 27]}\n    ],\n    \"complexes\": [\n      \"mTORC1 effector (not subunit)\",\n      \"S6K1-STING-TBK1 complex\"\n    ],\n    \"partners\": [\n      \"MTOR\",\n      \"PDPK1\",\n      \"IRS1\",\n      \"TMEM173\",\n      \"TBK1\",\n      \"RNF168\",\n      \"PPP2R5C\",\n      \"EIF4B\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"RPS6KB1 (p70S6K/S6K1) is a serine/threonine kinase that functions as the principal effector of mTORC1 signaling to control cell growth, protein synthesis, and metabolic homeostasis. It is activated through a hierarchical phosphorylation cascade in which raptor-mediated TOS-motif docking recruits S6K1 to mTOR for T-389 hydrophobic-motif phosphorylation, which in turn creates a docking site for the PDK1 PIF-pocket to enable activation-loop (T-229) phosphorylation; this activity is reversed by PP2A-B\\u2019 (PPP2R5C)-mediated dephosphorylation [PMID:8887654, PMID:9445476, PMID:11500365, PMID:12604610, PMID:20444422]. Once active, S6K1 phosphorylates substrates including rpS6, eIF4B, eEF2K, and PDCD4 to promote translation initiation and elongation, phosphorylates IRS-1 at multiple serines to create a negative feedback loop that drives insulin resistance, and phosphorylates RNF168 to attenuate the DNA damage response [PMID:11500364, PMID:17053147, PMID:18952604, PMID:29403037]. Beyond its catalytic roles, S6K1 forms a kinase-activity-independent complex with STING and TBK1 to promote IRF3-dependent antiviral innate immunity, and regulates systemic lipid metabolism through hepatic amino-acid sensing that signals via vagal afferent and sympathetic efferent nerves [PMID:27043414, PMID:26268630].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Mapping the activation mechanism: identification of T-389 as the principal rapamycin-sensitive regulatory phosphorylation site resolved how extracellular signals converge on S6K1 activity, with autoinhibitory-domain phosphorylation and T-229 activation-loop phosphorylation constituting additional, distinctly regulated layers.\",\n      \"evidence\": \"Site-directed mutagenesis with kinase activity assays, truncation mutants, and inhibitor panels in cultured cells\",\n      \"pmids\": [\"8887654\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the T-389 kinase was not established\", \"Structural basis of autoinhibition was unknown\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Establishing the hierarchical phosphorylation cascade: PDK1 was identified as the activation-loop kinase for S6K1, with prior T-389 phosphorylation creating a PIF-pocket docking site on PDK1 — explaining why hydrophobic-motif phosphorylation is prerequisite for full activation.\",\n      \"evidence\": \"In vitro kinase assays with purified PDK1 and S6K1, cooperative mutagenesis of autoinhibitory and hydrophobic-motif sites, reported independently in two concurrent papers\",\n      \"pmids\": [\"9445476\", \"9427642\", \"9614086\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the upstream T-389 kinase remained unresolved at this point\", \"How PDK1 PIF-pocket selectivity distinguishes S6K1 from PKB was not yet dissected\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Genetic loss-of-function in mice established that S6K1 controls organismal body size and 5\\u2019TOP mRNA translation, while revealing compensatory S6K2 upregulation that preserves residual S6 phosphorylation.\",\n      \"evidence\": \"Homozygous S6K1 knockout mice and targeted ES cells with polysome profiling, translational assays, and Northern/Western identification of S6K2\",\n      \"pmids\": [\"9822608\", \"9560223\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"S6K2 functional overlap precluded definitive assignment of all S6K1-specific functions\", \"Whether reduced body size reflects cell size versus cell number was not resolved\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Upstream input integration was expanded to include amino acid sensing via tRNA aminoacylation, mechanical load-correlated muscle hypertrophy, and reactive oxygen species signaling, establishing S6K1 as a multi-input growth integrator.\",\n      \"evidence\": \"Amino acid alcohol inhibitors and ts-histidyl-tRNA synthetase mutant for nutrient sensing; exercise-induced kinase activity correlation with muscle mass; H₂O₂ activation via Ca²⁺-dependent PI3K/mTOR pathway\",\n      \"pmids\": [\"9873056\", \"9886927\", \"10551813\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular identity of the amino acid sensor upstream of mTOR/S6K was unknown\", \"Muscle hypertrophy correlation was not causal\", \"Ca²⁺-ROS link lacked molecular target identification\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"The PDK1 PIF-pocket was shown to be essential for S6K1 activation but dispensable for PKBα, resolving how PDK1 achieves substrate selectivity; concurrently, eEF2K was identified as a direct S6K1 substrate, extending S6K1 function from translational initiation to elongation control.\",\n      \"evidence\": \"PIF-pocket mutations in PDK1 in cells and in vitro; in vitro kinase assay of S6K1 on eEF2K combined with PDK1 knockout cells\",\n      \"pmids\": [\"11500365\", \"11500364\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of PIF-pocket selectivity was inferred, not crystallographically resolved at this point\", \"Physiological importance of eEF2K phosphorylation by S6K1 versus ERK was not delineated\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Placement of the TSC1/TSC2-Rheb module upstream of mTOR/S6K1 established the complete PI3K→Akt→TSC→Rheb→mTOR→S6K1 signaling axis, explaining how growth factor and nutrient signals converge on S6K1.\",\n      \"evidence\": \"Biochemical GAP assays for TSC2 on Rheb, Drosophila epistasis, disease-associated TSC2 mutations, S6K phosphorylation readouts\",\n      \"pmids\": [\"12820960\", \"12766775\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct Rheb-mTOR activation mechanism was biochemically undefined\", \"Whether Rheb activates mTORC1 at endomembranes was unknown\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"The raptor TOS-motif docking mechanism and the dynamic S6K1-eIF3 scaffold model resolved how mTORC1 recruits and activates S6K1 at the ribosome: inactive S6K1 resides on eIF3, mTOR/raptor is recruited upon stimulation, phosphorylates T-389, and released active S6K1 then phosphorylates eIF4B and mTOR Ser-2448 (positive feedback).\",\n      \"evidence\": \"TOS motif mutagenesis with in vitro mTOR kinase assay; mass spectrometry identification of eIF3 complex interactions; rapamycin-resistant S6K1 rescue for Ser-2448 feedback\",\n      \"pmids\": [\"12604610\", \"16286006\", \"15899889\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether eIF3-scaffold model operates in all cell types was untested\", \"Stoichiometry of S6K1 on eIF3 was not determined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"PDCD4 was identified as a direct S6K1 substrate whose phosphorylation at Ser67 triggers βTRCP-dependent degradation, relieving inhibition of eIF4A helicase activity and promoting translation of structured mRNAs — linking S6K1 to cap-dependent translation beyond rpS6.\",\n      \"evidence\": \"In vitro S6K1 kinase assay, βTRCP interaction mapping, PDCD4 non-degradable mutant with cell size and translation readouts\",\n      \"pmids\": [\"17053147\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full spectrum of mRNAs regulated via the S6K1-PDCD4-eIF4A axis was not defined\", \"Whether S6K2 also phosphorylates PDCD4 was not tested\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"The negative feedback loop was molecularly detailed: S6K1 directly phosphorylates IRS-1 at Ser-270, -307, -636, and -1101, with Ser-270 serving as a docking site; TNFα activates this loop through IKK2, explaining how chronic mTORC1/S6K1 activation produces insulin resistance.\",\n      \"evidence\": \"In vitro kinase assay with purified proteins, site-specific IRS-1 mutants, S6K1 RNAi, IKK2 knockout cells, glucose uptake assays\",\n      \"pmids\": [\"18952604\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of individual IRS-1 phosphorylation sites in vivo was not resolved\", \"Whether S6K1 phosphorylates IRS-2 at analogous sites was not tested\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"PP2A-B\\u2019 (PPP2R5C) was identified as a conserved negative regulator that directly dephosphorylates S6K, with Drosophila knockout phenocopying hyperactive insulin signaling; concurrently, constitutively active S6K1 in pancreatic β-cells was shown to induce insulin resistance and apoptosis through IRS/Akt impairment.\",\n      \"evidence\": \"Drosophila PP2A-B\\u2019 knockout with mammalian PPP2R5C validation via Co-IP; transgenic β-cell-specific active S6K1 mice with cell cycle and apoptosis analysis\",\n      \"pmids\": [\"20444422\", \"20622167\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphatase specificity for T-389 versus T-229 was not resolved\", \"Whether PP2A-B\\u2019 regulation is nutrient-sensitive was not tested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Hepatic S6K1 was found to control systemic lipid metabolism through a neural circuit involving vagal afferent and sympathetic efferent signaling to adipose tissue, establishing S6K1 as a node for inter-organ metabolic communication.\",\n      \"evidence\": \"Adenoviral hepatic expression of active/dominant-negative S6K, surgical and pharmacological denervation, serum triglyceride and adipose LPL measurements\",\n      \"pmids\": [\"26268630\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular identity of the hepatic afferent signal was not identified\", \"Whether this neural relay is conserved in humans was untested\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"A non-catalytic immune function was uncovered: S6K1 kinase domain (but not activity) scaffolds a STING-TBK1 complex upon DNA virus sensing by cGAS, enabling IRF3 activation and antiviral gene expression — the first kinase-independent function of S6K1.\",\n      \"evidence\": \"Reciprocal Co-IP with kinase-dead S6K1, cGAS knockout cells, TBK1 inhibitor, antiviral gene expression readouts\",\n      \"pmids\": [\"27043414\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the non-catalytic STING interaction was not resolved\", \"Whether mTORC1-driven S6K1 phosphorylation modulates the immune scaffolding function was not tested\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"S6K1 was shown to phosphorylate the E3 ligase RNF168 at Ser60, accelerating its proteolysis and impairing the DNA damage response; this linked hyperactive mTORC1/S6K signaling (e.g., from LKB1 loss) to genomic instability and tumorigenesis.\",\n      \"evidence\": \"In vitro S6K kinase assay on RNF168, phospho-deficient S60A rescue of DDR, LKB1 knockout mouse model, tumor xenografts\",\n      \"pmids\": [\"29403037\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether S6K1 targets other DDR factors was not explored\", \"Contribution of S6K2 to RNF168 regulation was not assessed\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Mitotic suppression of mTORC1/S6K1 via raptor phosphorylation was shown to be functionally important for Taxol cytotoxicity through PDCD4 stabilization; reactivation of S6K1 during mitotic arrest degraded PDCD4 and conferred Taxol resistance.\",\n      \"evidence\": \"Non-phosphorylatable raptor mutant, PDCD4 stability assays, pharmacological eIF4A inhibition restoring Taxol sensitivity\",\n      \"pmids\": [\"33027666\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other S6K1 substrates contribute to mitotic drug resistance was not tested\", \"Clinical relevance of eIF4A inhibitor combination was not validated in patient-derived models\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: the full substrate repertoire of S6K1 versus S6K2, the structural basis for S6K1's non-catalytic immune scaffolding function, the molecular identity of the hepatic afferent signal mediating S6K1-driven lipid metabolism, and whether the S6K1-RNF168-DDR axis contributes to therapy resistance in human cancers.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Comprehensive substrate identification (e.g., phosphoproteomics in S6K1/2 double knockouts) is lacking\", \"No high-resolution structure of S6K1 in complex with STING or eIF3\", \"In vivo physiological relevance of many substrates has not been confirmed in conditional tissue-specific knockouts\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 11, 22, 25, 32]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 1, 11, 21, 22, 25, 32]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [31]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [19]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [17]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 9, 13, 16, 20, 27]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [11, 19, 22, 26, 33]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [31]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [32]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [35]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [33]}\n    ],\n    \"complexes\": [\n      \"S6K1-STING-TBK1\",\n      \"eIF3 preinitiation complex (dynamic)\"\n    ],\n    \"partners\": [\n      \"MTOR\",\n      \"RPTOR\",\n      \"PDPK1\",\n      \"PPP2R5C\",\n      \"TMEM173\",\n      \"TBK1\",\n      \"IRS1\",\n      \"RNF168\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}