{"gene":"SIK2","run_date":"2026-04-28T20:42:07","timeline":{"discoveries":[{"year":2010,"finding":"SIK2 localizes at the centrosome, plays a key role in the initiation of mitosis, and regulates the localization of the centrosome linker protein C-Nap1 through phosphorylation at S2392. PKA inhibition induces SIK2-dependent centrosome splitting in interphase, while SIK2 depletion blocks centrosome separation in mitosis.","method":"Subcellular localization (immunofluorescence/fractionation), phosphorylation site mutagenesis, siRNA depletion with mitotic phenotype readout, xenograft models","journal":"Cancer cell","confidence":"High","confidence_rationale":"Tier 2 — reciprocal functional validation, specific phosphorylation site identified, multiple orthogonal methods, replicated in culture and in vivo","pmids":["20708153"],"is_preprint":false},{"year":2011,"finding":"SIK2 suppresses CREB-mediated gene expression by phosphorylating and retaining TORC1 in the cytoplasm. During oxygen-glucose deprivation (OGD), CaMK I/IV phosphorylate SIK2 at Thr484, leading to SIK2 protein degradation and subsequent TORC1 dephosphorylation and nuclear translocation, activating CREB and promoting neuronal survival.","method":"In vitro kinase assay (CaMK I/IV phosphorylation of SIK2 at Thr484), sik2(-/-) mouse neurons with OGD survival readout, transient focal ischemia model","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro kinase assay identifying specific phosphorylation site, genetic KO with defined neuronal phenotype, replicated in vivo","pmids":["21220102"],"is_preprint":false},{"year":2013,"finding":"LKB1 activates SIK2 (and SIK3) to promote nuclear export of class IIa HDACs (HDAC4, -5, -7, -9) by phosphorylating them at conserved motifs that stimulate 14-3-3 binding. SIK2 activation of class IIa HDAC export is PKA-sensitive and activates MEF2-dependent transcription, relieving repression of myogenesis.","method":"In vitro kinase assay, co-immunoprecipitation, epistasis (LKB1→SIK2→HDAC→14-3-3), myogenesis reporter assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — direct kinase assay, genetic epistasis with pathway placement, multiple substrates validated","pmids":["23393134"],"is_preprint":false},{"year":2013,"finding":"SIK2 kinase activity is regulated by reversible acetylation: p300/CBP-mediated acetylation of Lys-53 inhibits SIK2 kinase activity, while HDAC6-mediated deacetylation restores activity. Acetylation-mimetic SIK2 (K53Q) causes autophagosome accumulation, and SIK2 kinase activity is required for autophagosome-lysosome fusion and clearance of TDP-43Δ inclusion bodies.","method":"Site-directed mutagenesis (K53Q/K53R), in vitro kinase assay, co-immunoprecipitation with p300/HDAC6, autophagy flux assays, siRNA knockdown","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay with mutagenesis, writer/eraser identified, functional autophagy phenotype validated","pmids":["23322770"],"is_preprint":false},{"year":2013,"finding":"SIK2 physically interacts with p97/VCP (co-localizes in ER membrane), directly phosphorylates p97/VCP to stimulate its ATPase activity, and thereby promotes ER-associated protein degradation (ERAD). Kinase-deficient SIK2 or mutation of the SIK2 phosphorylation site on p97/VCP impairs ERAD substrate removal.","method":"Co-IP, co-localization (immunofluorescence), in vitro kinase assay, ERAD substrate degradation assays, siRNA knockdown","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — direct phosphorylation demonstrated in vitro, binding confirmed by co-IP, functional consequence shown by mutagenesis and KD","pmids":["24129571"],"is_preprint":false},{"year":2014,"finding":"SIK2 forms a complex with the CDK5 activator p35 (CDK5R1) and the E3 ligase PJA2. Upon glucose stimulation, SIK2 phosphorylates p35 at Ser91, triggering its ubiquitylation by PJA2 and promoting insulin secretion. β-cell-specific SIK2 knockout leads to p35 accumulation and impaired insulin secretion.","method":"Co-immunoprecipitation (SIK2-p35-PJA2 complex), in vitro kinase assay (SIK2 phosphorylates p35-Ser91), mass spectrometry (Gingras), β-cell-specific KO mice with glucose homeostasis phenotype","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1-2 — reconstituted complex, specific phosphorylation site identified, KO mouse with defined phenotype, multiple orthogonal methods","pmids":["24561619"],"is_preprint":false},{"year":2014,"finding":"In adipocytes, SIK2 directly phosphorylates CRTC2, CRTC3, and HDAC4. SIK2 interacts with CRTC2, CRTC3, HDAC4, and PP2A; cAMP elevation via PKA phosphorylation of SIK2 at Ser358 reduces its interaction with CRTCs and PP2A. SIK2 overexpression or activity increases GLUT4 protein levels and glucose uptake, while CRTC2/HDAC4 silencing recapitulates this effect.","method":"Co-immunoprecipitation, in vitro kinase assay, siRNA knockdown, glucose uptake assays, phosphosite mutagenesis (S358A)","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1-2 — direct phosphorylation assay, binding confirmed by co-IP, multiple substrate targets validated, functional metabolic readout","pmids":["25472719"],"is_preprint":false},{"year":2014,"finding":"SIK2 KO mice exhibit dysregulated CRTC2-CREB transcriptional pathway in white adipocytes, increased ATF3 expression, downregulation of GLUT4, reduced high-molecular weight adiponectin, and impaired glucose uptake, establishing SIK2 as a critical regulator of adipocyte glucose and lipid homeostasis upstream of CRTC2-CREB.","method":"SIK2 knockout mice, CRTC2 KO mice (epistasis), 3T3-L1 adipocyte cultures, glucose/insulin tolerance tests","journal":"Diabetes","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with defined metabolic phenotype, epistasis with CRTC2 KO, replicated in vitro and in vivo","pmids":["24898145"],"is_preprint":false},{"year":2012,"finding":"PKA phosphorylates SIK2 at Ser358 in adipocytes in response to cAMP-elevating agents (forskolin, CL 316,243), leading to 14-3-3 binding. Ser358 phosphorylation (not Ser587) is required for 14-3-3 binding. This phosphorylation triggers relocalization of SIK2 from a particulate fraction to the cytosol in adipocytes.","method":"Phosphopeptide mapping, site-directed mutagenesis (S358A, S587A), 14-3-3 binding assay, immunocytochemistry, subcellular fractionation","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1-2 — phosphosite mapping with mutagenesis, 14-3-3 binding validated, relocalization confirmed by fractionation","pmids":["22462548"],"is_preprint":false},{"year":2010,"finding":"SIK2 suppresses eumelanogenesis by phosphorylating and retaining TORC1 in the cytoplasm, thereby inhibiting CREB-mediated MITF gene expression. UV light exposure induces nuclear translocation of TORC1, which is blocked by SIK2. Sik2(-/-) mice on an A(y)/a background show brown (eumelanin) rather than yellow (pheomelanin) hair, demonstrating SIK2 represses eumelanogenesis in vivo.","method":"SIK2 knockout mice (genetic epistasis), dominant-negative TORC1 overexpression, B16 melanoma cell transfection, melanogenesis assays","journal":"Pigment cell & melanoma research","confidence":"High","confidence_rationale":"Tier 2 — genetic KO in defined in vivo model, epistasis with dominant-negative TORC1, specific molecular pathway established","pmids":["20819186"],"is_preprint":false},{"year":2016,"finding":"SIK2 and SIK3 (particularly) control macrophage polarization; catalytically inactive knock-in of SIK2 and SIK3 shifts macrophages toward an anti-inflammatory phenotype (high IL-10, low TNFα). SIK2/SIK3 inhibition during macrophage differentiation produces a stable enhanced anti-inflammatory phenotype even after kinase reactivation.","method":"Catalytically inactive knock-in (KI) mice for SIK1/2/3, primary macrophage cytokine profiling, SIK inhibitor treatment (MRT199665, HG-9-91-01)","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 2 — genetic KI mice with catalytically inactive alleles, primary cells, multiple isoform epistasis established","pmids":["27920213"],"is_preprint":false},{"year":2008,"finding":"SIK2 is activated by nutrient deprivation, ATP synthesis inhibition, and AICAR in adipocytes. Activated SIK2 represses lipogenic gene expression (FAS, ACC2, SCD1) by reducing nuclear translocation of SREBP-1, independently of AMPK. This effect is reversed by constitutively active SREBP-1 overexpression.","method":"In vitro kinase assay (peptide substrate phosphorylation), adenovirus-mediated overexpression/knockdown, FAS promoter-luciferase reporter, SREBP-1 nuclear fractionation","journal":"Obesity (Silver Spring, Md.)","confidence":"High","confidence_rationale":"Tier 1-2 — kinase activity assay, reporter gene assay, epistasis with SREBP-1, multiple readouts","pmids":["18239551"],"is_preprint":false},{"year":2016,"finding":"SIK2 is required for restriction of autophagic flux in triple-negative breast cancer (TNBC) cells. Genetic or pharmacological SIK2 inhibition increases autophagic flux and causes selective cell death in breast cancer (especially claudin-low subtype) cells; ATG5 depletion rescues this cell death, placing SIK2 upstream of autophagosome formation.","method":"siRNA knockdown, pharmacological inhibition, ATG5 depletion rescue (epistasis), autophagic flux assays, xenograft models","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis (ATG5 rescue), in vivo xenograft, multiple orthogonal methods","pmids":["27697861"],"is_preprint":false},{"year":2016,"finding":"SIK2 phosphorylates p300 at Ser89, disrupting the p300-PPARα interaction (p300 binds PPARα via a conserved LXXLL motif), thereby decreasing PPARα-mediated ketogenic gene expression during fasting. The phosphorylation-defective p300-S89A mutant shows increased interaction with PPARα and abolishes SIK2 suppression of ketogenesis.","method":"Co-immunoprecipitation (p300-PPARα), in vitro kinase assay (SIK2 phosphorylates p300-Ser89), site-directed mutagenesis (S89A), ketogenic gene expression in liver","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1-2 — direct phosphorylation assay, mutagenesis confirming site, binding assay, functional gene expression readout","pmids":["26983400"],"is_preprint":false},{"year":2018,"finding":"In osteoblasts, PTH(1-34) inhibits SIK2 and SIK3 via PKA, leading to dephosphorylation and nuclear translocation of CRTC2/CRTC3 by protein phosphatases PP1/PP2A, resulting in CREB-mediated Rankl transcription. Knockdown of SIK2/3 and CRTC3 demonstrated their requirement in this signaling pathway.","method":"siRNA knockdown of SIK2/3 and CRTCs, immunofluorescence of CRTC nuclear localization, qPCR for Rankl expression, PP1/PP2A inhibition, primary osteoblasts","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — epistasis by siRNA, nuclear localization directly measured, functional gene expression readout, multiple pathway components probed","pmids":["30377251"],"is_preprint":false},{"year":2019,"finding":"SIK2 promotes mitochondrial fission through direct phosphorylation of Drp1 at Ser616, which inhibits mitochondrial oxidative phosphorylation and promotes the Warburg effect. SIK2 also upregulates HIF-1α by activating PI3K/AKT signaling to enhance glycolytic gene transcription in ovarian cancer cells.","method":"Phosphorylation assay (SIK2→Drp1-Ser616), PI3K/AKT pathway inhibition, HIF-1α reporter, mitochondrial morphology analysis, siRNA/overexpression in OC cells","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2-3 — specific phosphorylation site identified, pathway inhibitors used, but in vitro kinase reconstitution not fully detailed; single lab study","pmids":["31639424"],"is_preprint":false},{"year":2020,"finding":"SIK2 promotes lipid synthesis in ovarian cancer cells by upregulating SREBP1c (and downstream FASN) and SREBP2 (and downstream HMGCR) via the PI3K/Akt signaling pathway, enhancing both fatty acid and cholesterol synthesis.","method":"siRNA knockdown/overexpression, PI3K/Akt inhibition, SREBP1c/2 expression assays, in vitro and xenograft models","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 3 — pathway placement by inhibitor and KD, but direct kinase-substrate relationship for PI3K/Akt activation not biochemically reconstituted; single lab","pmids":["31932581"],"is_preprint":false},{"year":2013,"finding":"SIK2 functions as a negative modulator of insulin-dependent Müller glia survival: insulin stimulation increases SIK2 activity and promotes IRS1-SIK2 interaction while modulating AKT phosphorylation. SIK2 knockdown under normo- and hyperglycemic conditions increases pAkt levels and reduces apoptosis, while SIK2 overexpression has the opposite effect.","method":"In vitro kinase assay (SIK2 activity), co-immunoprecipitation (IRS1-SIK2), siRNA knockdown and overexpression with pAkt/apoptosis readouts, streptozotocin rat model","journal":"Investigative ophthalmology & visual science","confidence":"Medium","confidence_rationale":"Tier 2-3 — kinase assay and co-IP performed, functional epistasis with AKT pathway established, but mechanistic link between SIK2 kinase activity and AKT not fully reconstituted","pmids":["23599336"],"is_preprint":false},{"year":2020,"finding":"SIK2 inhibits AKT/GSK3β/β-catenin signaling in gastric cancer by activating mTORC1 to inhibit autophagic degradation of protein phosphatases PHLPP2 and PP2A, which then dephosphorylate and inactivate AKT.","method":"siRNA knockdown/overexpression, Western blot for pAKT/GSK3β/β-catenin, mTORC1 inhibition (rapamycin), autophagy flux assays, in vitro migration/invasion assays","journal":"Molecular oncology","confidence":"Medium","confidence_rationale":"Tier 3 — pathway placement by inhibitors and KD, phosphatase upregulation mechanism proposed, but direct kinase-substrate reconstitution not performed; single lab","pmids":["33128264"],"is_preprint":false},{"year":2015,"finding":"B55gamma (PP2A regulatory subunit) binds SIK2 and stabilizes SIK2 protein, which is required for B55gamma-mediated suppression of S6K phosphorylation and enhanced glioma cell survival under glucose depletion. SIK2 knockdown in B55gamma-overexpressing cells recovers S6K phosphorylation.","method":"Co-immunoprecipitation, proteomic analysis, siRNA knockdown of SIK2, Western blot for pS6K, cell viability assays under glucose starvation","journal":"Cancer cell international","confidence":"Medium","confidence_rationale":"Tier 3 — co-IP and epistasis by KD, but direct kinase assay not performed; single lab","pmids":["25792973"],"is_preprint":false},{"year":2022,"finding":"SIK2 inhibition decreases phosphorylation of class-IIa HDACs (HDAC4/5/7), abolishes MEF2D transcriptional activity, and reduces MEF2D binding to regulatory regions of FANCD2, EXO1, and XRCC4 genes, thereby repressing DNA double-strand break repair and producing synthetic lethality with PARP inhibitors.","method":"SIK2 inhibitors (ARN3236, ARN3261), phospho-HDAC4/5/7 Western blot, ChIP-seq/ATAC-seq for MEF2D binding, DNA repair assays, xenograft models","journal":"The Journal of clinical investigation","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods (ChIP, phosphoproteomics, xenograft), pathway placement established; pharmacological inhibitors used rather than direct kinase reconstitution","pmids":["35642638"],"is_preprint":false},{"year":2022,"finding":"SIK2 directly phosphorylates MYLK (myosin light chain kinase) at Ser343, activating MYLK and its downstream substrate MYL2 (myosin light chain 2), thereby promoting ovarian cancer cell motility, migration, and metastasis. Adipocytes induce SIK2 phosphorylation at Ser358 and MYLK phosphorylation at Ser343, enhancing cancer cell motility.","method":"In vitro kinase assay (SIK2→MYLK-Ser343), phospho-specific antibodies, siRNA knockdown, migration/invasion/metastasis assays in vitro and in vivo","journal":"Molecular oncology","confidence":"High","confidence_rationale":"Tier 1-2 — direct phosphorylation site identified and validated in vitro, downstream substrate (MYL2) activation demonstrated, in vivo metastasis model","pmids":["35278271"],"is_preprint":false},{"year":2022,"finding":"SIK2 maintains breast cancer stem cell (BCSC) properties by directly phosphorylating LRP6 (LDL receptor-related protein 6) in a kinase-activity-dependent manner, leading to Wnt/β-catenin pathway activation and IDH1 induction, causing metabolic reprogramming. CK1α phosphorylates SIK2 upstream to enable this activity.","method":"In vitro kinase assay (SIK2→LRP6), siRNA knockdown, SIK2 inhibitor treatment (ARN-3236, HG-9-91-01), β-catenin accumulation assay, BCSC proportion/tumor initiation assays, zebrafish embryo model","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1-2 — direct kinase assay for LRP6 phosphorylation, upstream kinase (CK1α) identified, functional BCSC phenotype validated, inhibitors corroborated","pmids":["35277657"],"is_preprint":false},{"year":2021,"finding":"SIK2 associates with actin filaments under basal conditions and is recruited to the Salmonella-containing vacuole (SCV) together with Arp2/3 complex and Formins upon bacterial infection. SIK2 depletion causes actin nucleation/polymerization defects at the SCV, impairs xenophagy, and favors bacterial escape from the SCV, establishing SIK2 as an orchestrator of actin-dependent host defense.","method":"Global phosphoproteomics (identifying SIK2 upon Salmonella infection), siRNA depletion, co-localization (immunofluorescence of SIK2/Arp2/3/Formins at SCV), bacterial replication/xenophagy assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — phosphoproteomics identification, direct co-localization at SCV, functional depletion phenotype (bacterial escape, xenophagy), multiple orthogonal methods","pmids":["33947818"],"is_preprint":false},{"year":2020,"finding":"Fbxw7 targets SIK2 for proteasomal degradation by binding to a conserved 'TPPPS' motif on SIK2. Loss of Fbxw7-mediated SIK2 degradation allows SIK2 to promote cell cycle progression and activation of the TORC2/AKT signaling pathway, modulating p21 expression in pancreatic cancer cells.","method":"Co-immunoprecipitation (Fbxw7-SIK2), protein database screening for Fbxw7-recognizing degron, proteasome inhibitor rescue, siRNA/overexpression with cell cycle/AKT readouts","journal":"Cell biology international","confidence":"Medium","confidence_rationale":"Tier 3 — co-IP and degron motif identified, ubiquitin-mediated degradation proposed; direct ubiquitylation assay not fully described; single lab","pmids":["32437091"],"is_preprint":false},{"year":2014,"finding":"SIK2 is critical for the development of cardiac left ventricular hypertrophy (LVH) in response to chronic high-salt diet. sik2(-/-) mice do not develop LVH upon high-salt feeding (unlike wild-type), and α-adducin regulates SIK2 expression in cardiomyocytes, which mediates adducin's effects on hypertrophy marker gene activation.","method":"sik2(-/-) mice with high-salt diet challenge, LV wall thickness echocardiography, gene expression profiling, siRNA of SIK2 in cardiomyocytes","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO with defined in vivo phenotype, upstream regulator (α-adducin) identified, but molecular mechanism between SIK2 and hypertrophy genes not fully reconstituted","pmids":["24752134"],"is_preprint":false},{"year":2020,"finding":"Loss of PKA phosphorylation site Ser587 in SIK2 (Sik2S587A mice) increases NREM sleep delta density, establishing that PKA-SIK2 signaling regulates sleep need.","method":"Sik2S587A knock-in mice, EEG/EMG sleep recording, homeostatic sleep deprivation testing","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — specific phosphosite mutant knock-in with defined electrophysiological sleep phenotype; single lab","pmids":["32457359"],"is_preprint":false},{"year":2023,"finding":"LKB1 loss in uveal melanoma enhances proliferation and survival through SIK2 inhibition and upregulation of the Na+/Ca2+ exchanger SLC8A1, which promotes elevated intracellular calcium and mitochondrial ROS. CRISPR-Cas9 KO screen identified LKB1-SIK2 module as a tumor suppressor axis.","method":"Kinome-wide CRISPR-Cas9 KO screen, genetic epistasis (LKB1→SIK2→SLC8A1), calcium and ROS measurements, cell death assays with SLC8A1 inhibitor and mitochondria-targeted antioxidant","journal":"EMBO molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 — genome-scale screen, epistasis validated, but molecular mechanism between SIK2 and SLC8A1 not fully reconstituted; single lab","pmids":["37966164"],"is_preprint":false},{"year":2022,"finding":"TGF-β1 induces SIK2 expression in lung fibroblasts, and SIK2 phosphorylates CRTC2 to retain it in the cytoplasm. SIK2 inhibition by ARN-3236 leads to CRTC2 dephosphorylation, nuclear translocation, and CREB-dependent anti-fibrotic gene expression, attenuating bleomycin-induced pulmonary fibrosis.","method":"Western blot (SIK2, p-CRTC2), ARN-3236 treatment, siRNA knockdown of SIK2, immunofluorescence (CRTC2 nuclear translocation), mouse bleomycin model","journal":"BMC pulmonary medicine","confidence":"Medium","confidence_rationale":"Tier 3 — pharmacological and genetic inhibition with defined molecular readout; direct kinase assay for SIK2-CRTC2 not shown; single lab","pmids":["35410283"],"is_preprint":false},{"year":2024,"finding":"SIK2 acts as a negative feedback regulator of FGF2/Ras/ERK1/2 signaling by phosphorylating Gab1 at Ser266, which weakens Gab1 interactions with Grb2 and Shp2. ERK1/2 activates SIK2 in this feedback loop. SIK2 downregulation enhances and prolongs ERK1/2 activation and increases FGF2-dependent cell proliferation.","method":"In vitro kinase assay (SIK2→Gab1-Ser266), site-directed mutagenesis, co-immunoprecipitation (Gab1-Grb2/Shp2), SIK2 overexpression/knockdown with pERK1/2 and proliferation readouts","journal":"Advanced biology","confidence":"High","confidence_rationale":"Tier 1-2 — direct kinase assay with specific site identified, mutagenesis, co-IP of disrupted binding, functional ERK activation and proliferation phenotype","pmids":["39267218"],"is_preprint":false},{"year":2025,"finding":"SIK2 phosphorylates GABARAPL2 at Ser72, a modification essential for autophagosome-lysosome fusion. Phosphorylation-mimetic GABARAPL2-S72E rescues autophagic flux, reduces Aβ deposition, and restores synaptic function in 5×FAD Alzheimer's disease mice, while the non-phosphorylatable S72A mutant fails to show protective effects.","method":"Co-immunoprecipitation, GST pull-down assay, phosphoproteomics, site-directed mutagenesis (S72E/S72A), adeno-associated virus delivery in vivo, autophagy flux assays (mRFP-GFP-LC3), electron microscopy, Morris water maze, LTP recording","journal":"Translational neurodegeneration","confidence":"High","confidence_rationale":"Tier 1 — in vitro phosphorylation assay with mutagenesis, reconstitution in vivo with phosphomimetic and non-phosphorylatable mutants, multiple orthogonal readouts","pmids":["41126299"],"is_preprint":false},{"year":2025,"finding":"In osteoblasts, SIK2 (and SIK3) inhibition by PTH/PKA signaling allows CRTC2 nuclear translocation primarily via PP1/PP2A/PP4/PP5 action; CRTC2 is the primary co-activator of Tnfsf11 (RANKL) gene transcription, while SIK2/3 phosphorylation retains CRTCs in the cytoplasm.","method":"siRNA knockdown of SIK1/2/3, CRTC1/2/3, PP1/2/3/4/5/6/7; quantitative immunofluorescence of CRTC nuclear localization; co-immunoprecipitation; Western blot; qPCR for Tnfsf11; primary mouse calvarial osteoblasts","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — systematic siRNA epistasis of multiple pathway components, direct CRTC localization measured, co-IP, multiple orthogonal methods","pmids":["40609791"],"is_preprint":false},{"year":2024,"finding":"SIK2 promotes RAD50 phosphorylation at Ser635, enabling nuclear translocation of RAD50 and nuclear filament assembly required for homologous recombination DNA repair. SIK2 inhibitor SIC-19 reduces RAD50-pS635, impairs nuclear RAD50 translocation, disrupts HR repair, and induces apoptosis in ovarian cancer cells.","method":"Phospho-specific antibodies (RAD50-pS635), SIK2 knockdown/SIC-19 inhibitor, nuclear translocation assays, HR repair assays, ovarian cancer organoids and xenograft models","journal":"Drug resistance updates","confidence":"Medium","confidence_rationale":"Tier 3 — specific phosphorylation site identified on RAD50, functional HR readout; direct in vitro kinase assay not described; single lab","pmids":["38518726"],"is_preprint":false},{"year":2018,"finding":"Insulin induces phosphorylation of SIK2 at Thr484 in primary adipocytes, leading to increased SIK2 protein stability (prevented by proteasome inhibition). This Thr484 phosphorylation is impaired in insulin-resistant individuals but does not affect SIK2 catalytic activity toward HDAC4.","method":"Phospho-specific antibodies, in vitro kinase assay (SIK2 activity toward HDAC4), proteasome inhibitor (MG132), primary human and rat adipocytes","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2-3 — specific PTM site identified, functional consequence (protein stability) demonstrated, direct kinase assay performed; single lab","pmids":["30586628"],"is_preprint":false},{"year":2021,"finding":"SIK2 inhibition with MRIA9 blocks centrosome disjunction, impairs centrosome alignment, causes spindle mispositioning during mitosis, and increases chromosomal instability in ovarian cancer cells, corroborating SIK2's role as a centrosome kinase required for mitotic fidelity.","method":"Selective SIK2 inhibitor (MRIA9), live-cell imaging of centrosome dynamics, chromosomal instability assays, 3D-spheroid paclitaxel sensitivity assays","journal":"Cancers","confidence":"Medium","confidence_rationale":"Tier 2-3 — pharmacological inhibition with defined mitotic phenotype; corroborates prior genetic findings; single lab","pmids":["34359562"],"is_preprint":false},{"year":2021,"finding":"FANCA co-localizes with SIK2 at multiple mitotic structures and regulates SIK2 activity at centrosomes. Loss of FANCA exacerbates cell cycle defects from pharmacological SIK2 inhibition (impaired G2-M transition, delayed mitotic progression, cytokinesis failure). SIK2 inhibition also abrogates nocodazole-induced prometaphase arrest, revealing a role in the spindle assembly checkpoint.","method":"Kinome-wide synthetic lethality CRISPR screen, co-localization immunofluorescence (FANCA and SIK2 at centrosomes), pharmacological SIK2 inhibition in FANCA-/- cells, cell cycle assays, spindle assembly checkpoint assay","journal":"Molecular oncology","confidence":"Medium","confidence_rationale":"Tier 2 — genome-wide screen, co-localization established, synthetic lethality with functional epistasis; direct FANCA regulation of SIK2 kinase activity not fully reconstituted in vitro","pmids":["34058059"],"is_preprint":false}],"current_model":"SIK2 is a centrosomal, AMPK-related serine/threonine kinase that phosphorylates multiple substrates—including TORC1/CRTC coactivators (to suppress CREB-mediated transcription), class IIa HDACs (driving their 14-3-3-dependent nuclear export), p35/CDK5R1 (controlling β-cell insulin secretion via PJA2 ubiquitylation), Drp1-Ser616 (promoting mitochondrial fission), p300-Ser89 (regulating PPARα/ketogenesis), MYLK-Ser343 (activating myosin light chain and cancer motility), LRP6 (activating Wnt/β-catenin signaling), p97/VCP (stimulating ER-associated protein degradation), Gab1-Ser266 (providing negative feedback on FGF2/ERK signaling), GABARAPL2-Ser72 (enabling autophagosome-lysosome fusion), and RAD50-Ser635 (supporting DNA homologous recombination repair)—and is itself regulated by upstream kinases LKB1, CaMK I/IV, and PKA (phosphorylating Ser358 to promote 14-3-3 binding and cytoplasmic relocalization), as well as by p300/CBP-mediated acetylation at Lys53 (inhibiting its kinase activity) and HDAC6-mediated deacetylation (restoring activity), placing it as a central hub integrating nutrient, hormonal, and stress signals to control metabolism, mitosis, autophagy, immunity, and gene expression."},"narrative":{"teleology":[{"year":2008,"claim":"Establishing SIK2 as a nutrient-responsive kinase that represses lipogenic gene expression independently of AMPK answered whether SIK2 has autonomous metabolic-sensing function in adipocytes.","evidence":"In vitro kinase assay, adenoviral overexpression/knockdown in adipocytes, SREBP-1 nuclear fractionation","pmids":["18239551"],"confidence":"High","gaps":["Direct substrate on SREBP-1 nuclear translocation not identified","Upstream activating kinase not yet characterized in this system"]},{"year":2010,"claim":"Discovery that SIK2 localizes to centrosomes and phosphorylates C-Nap1 at Ser2392 to initiate centrosome splitting established SIK2 as a mitotic kinase, resolving how centrosome disjunction is linked to AMPK-family signaling.","evidence":"Immunofluorescence/fractionation, phosphosite mutagenesis, siRNA depletion with mitotic phenotype, xenograft models","pmids":["20708153"],"confidence":"High","gaps":["Full spectrum of centrosomal substrates unknown","Whether SIK2 centrosomal function is LKB1-dependent not tested"]},{"year":2010,"claim":"Demonstration that SIK2 represses CREB-mediated MITF transcription by retaining TORC1 in the cytoplasm, with Sik2-knockout mice showing coat-color switching, established the TORC/CRTC-phosphorylation axis as a major SIK2 effector pathway in vivo.","evidence":"Sik2−/− mice on Ay/a background, dominant-negative TORC1 epistasis, melanogenesis assays","pmids":["20819186"],"confidence":"High","gaps":["Specific TORC1 phosphorylation site by SIK2 not mapped in this study","Whether SIK1/SIK3 compensate partially not addressed"]},{"year":2011,"claim":"Identification of CaMK I/IV as upstream kinases that phosphorylate SIK2 at Thr484, triggering its degradation and thereby permitting TORC1 nuclear translocation and CREB-dependent neuronal survival, revealed how ischemic stress inactivates SIK2.","evidence":"In vitro kinase assay, sik2−/− neurons with OGD survival, transient focal ischemia model","pmids":["21220102"],"confidence":"High","gaps":["Degradation pathway (proteasomal vs lysosomal) not defined","Whether Thr484 phosphorylation has distinct effects in non-neuronal cells not tested"]},{"year":2012,"claim":"Mapping PKA phosphorylation of SIK2 at Ser358 as the event that triggers 14-3-3 binding and cytoplasmic relocalization defined the molecular switch by which cAMP signaling inactivates SIK2 in adipocytes.","evidence":"Phosphopeptide mapping, S358A/S587A mutagenesis, 14-3-3 binding assay, subcellular fractionation","pmids":["22462548"],"confidence":"High","gaps":["Whether 14-3-3 binding directly inhibits kinase activity or only controls localization not distinguished","Identity of the phosphatase reversing Ser358 phosphorylation unknown"]},{"year":2013,"claim":"Three concurrent studies established the breadth of SIK2 substrates: LKB1-activated SIK2 phosphorylates class IIa HDACs for 14-3-3-mediated nuclear export and MEF2 derepression; p300/CBP acetylation at Lys53 inhibits SIK2 while HDAC6 deacetylation restores it, linking SIK2 activity to autophagosome–lysosome fusion; and SIK2 phosphorylates p97/VCP to stimulate ERAD.","evidence":"In vitro kinase assays, co-immunoprecipitation, K53Q/K53R mutagenesis, autophagy flux assays, ERAD substrate degradation assays, epistasis experiments","pmids":["23393134","23322770","24129571"],"confidence":"High","gaps":["Structural basis for Lys53 acetylation inhibiting kinase activity unknown","p97/VCP phosphorylation site not mapped","How SIK2 kinase activity mechanistically drives autophagosome–lysosome fusion not fully resolved"]},{"year":2014,"claim":"SIK2 was placed at the center of adipocyte glucose homeostasis and β-cell insulin secretion: SIK2 KO mice showed CRTC2-CREB dysregulation, GLUT4 loss, and impaired adiponectin secretion, while in β-cells SIK2 phosphorylates p35-Ser91 to trigger PJA2-mediated ubiquitylation and promote glucose-stimulated insulin secretion.","evidence":"Sik2 KO mice with metabolic phenotyping, β-cell-specific KO, co-IP of SIK2-p35-PJA2 complex, in vitro kinase assay, mass spectrometry","pmids":["24898145","24561619","25472719"],"confidence":"High","gaps":["How SIK2 controls GLUT4 protein levels mechanistically (transcriptional vs post-translational) not resolved","Whether p35 phosphorylation by SIK2 occurs in non-β-cell tissues unknown"]},{"year":2016,"claim":"SIK2 was shown to phosphorylate p300 at Ser89 to disrupt its interaction with PPARα and suppress ketogenic gene expression, and catalytically inactive SIK2 knock-in mice revealed SIK2's role in macrophage anti-inflammatory polarization, broadening SIK2's functions to metabolic gene regulation and innate immunity.","evidence":"In vitro kinase assay (p300-Ser89), S89A mutagenesis, liver ketogenic gene expression; catalytically inactive KI mice, primary macrophage cytokine profiling","pmids":["26983400","27920213"],"confidence":"High","gaps":["Direct SIK2 substrate(s) controlling macrophage polarization downstream of HDAC phosphorylation not identified","Whether p300-Ser89 phosphorylation affects other p300 interactions unknown"]},{"year":2016,"claim":"SIK2 inhibition was found to increase autophagic flux and cause selective death in triple-negative breast cancer cells, with ATG5 depletion rescuing cell death, establishing SIK2 as a restraint on autophagy in cancer.","evidence":"siRNA knockdown, pharmacological inhibition, ATG5 epistasis, xenograft models","pmids":["27697861"],"confidence":"High","gaps":["Direct autophagy substrate of SIK2 not identified in this study","Whether SIK2-autophagy axis operates in non-cancer cells unknown"]},{"year":2018,"claim":"PTH-induced SIK2/SIK3 inhibition via PKA was shown to permit CRTC2/3 nuclear translocation and CREB-dependent RANKL transcription in osteoblasts, and insulin was found to induce SIK2-Thr484 phosphorylation for protein stabilization in adipocytes, extending the SIK2-CRTC axis to bone biology and linking insulin signaling to SIK2 turnover.","evidence":"siRNA epistasis in osteoblasts, CRTC nuclear localization imaging, qPCR for RANKL; phospho-Thr484 antibodies, proteasome inhibitor, primary human adipocytes","pmids":["30377251","30586628"],"confidence":"High","gaps":["Kinase responsible for insulin-induced Thr484 phosphorylation not identified","Whether Thr484 phosphorylation is impaired in type 2 diabetes tissue in vivo not confirmed"]},{"year":2021,"claim":"SIK2 was identified as an actin-associated kinase recruited to the Salmonella-containing vacuole where it orchestrates Arp2/3- and Formin-dependent actin polymerization for xenophagy, and FANCA was found to co-localize with SIK2 at centrosomes and regulate its mitotic function, expanding SIK2's roles to host defense and the spindle assembly checkpoint.","evidence":"Global phosphoproteomics, SIK2 depletion with bacterial escape/xenophagy assays, co-localization at SCV; CRISPR synthetic lethality screen, FANCA-SIK2 co-localization, cell cycle assays","pmids":["33947818","34058059"],"confidence":"High","gaps":["Direct SIK2 substrates at the SCV not identified","Mechanism by which FANCA modulates SIK2 kinase activity not reconstituted in vitro","Whether SIK2 phosphorylates actin regulators directly unknown"]},{"year":2022,"claim":"Four new direct substrates were identified: MYLK-Ser343 (activating myosin light chain and cancer motility), LRP6 (activating Wnt/β-catenin for breast cancer stemness), and class IIa HDACs driving MEF2D-dependent DNA repair gene expression (creating PARP inhibitor synthetic lethality), demonstrating the remarkable substrate diversity of SIK2.","evidence":"In vitro kinase assays for MYLK and LRP6, ChIP-seq/ATAC-seq for MEF2D, xenograft and zebrafish models, pharmacological and genetic inhibition","pmids":["35278271","35277657","35642638"],"confidence":"High","gaps":["Structural basis for SIK2 substrate recognition across diverse targets unknown","Whether MYLK phosphorylation operates in non-cancer contexts not tested","LRP6 phosphorylation site not mapped"]},{"year":2024,"claim":"SIK2 was shown to phosphorylate Gab1 at Ser266 to weaken Gab1-Grb2/Shp2 interactions, providing negative feedback on FGF2/ERK signaling, and to promote RAD50-Ser635 phosphorylation required for nuclear RAD50 translocation and homologous recombination repair.","evidence":"In vitro kinase assay (Gab1-Ser266), co-IP of disrupted Gab1 complexes, ERK activation readouts; phospho-RAD50-S635 antibodies, HR repair assays, ovarian cancer organoids and xenografts","pmids":["39267218","38518726"],"confidence":"High","gaps":["Direct in vitro kinase assay for RAD50 not described","Whether Gab1 phosphorylation extends to other RTK signaling contexts not tested"]},{"year":2025,"claim":"SIK2 was demonstrated to phosphorylate GABARAPL2 at Ser72, a modification essential for autophagosome–lysosome fusion; phosphomimetic GABARAPL2-S72E rescued autophagic flux and ameliorated amyloid pathology in 5×FAD Alzheimer's mice, providing the first direct SIK2 substrate in the autophagy machinery.","evidence":"GST pull-down, phosphoproteomics, S72E/S72A mutagenesis, AAV delivery in 5×FAD mice, mRFP-GFP-LC3 flux, electron microscopy, electrophysiology","pmids":["41126299"],"confidence":"High","gaps":["Whether SIK2 phosphorylates other ATG8-family members unknown","Upstream signal controlling SIK2-GABARAPL2 axis in neurons not identified"]},{"year":2025,"claim":"Systematic siRNA epistasis in osteoblasts confirmed CRTC2 as the primary coactivator downstream of SIK2/3 for RANKL transcription and identified PP1/PP2A/PP4/PP5 as the phosphatases counteracting SIK2-mediated CRTC phosphorylation.","evidence":"Systematic siRNA of SIK1/2/3, CRTC1/2/3, PP1–PP7; quantitative immunofluorescence, co-IP, qPCR; primary mouse calvarial osteoblasts","pmids":["40609791"],"confidence":"High","gaps":["Specific CRTC2 phosphorylation sites targeted by SIK2 in osteoblasts not mapped","Whether PP4/PP5 are direct SIK2-CRTC2 phosphatases or act indirectly not resolved"]},{"year":null,"claim":"Despite identification of over a dozen direct substrates, the structural basis for SIK2's broad substrate recognition, the relative contribution of individual substrates to in vivo phenotypes, and whether SIK2 functions as a monomer or within stable signaling complexes remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No crystal structure of SIK2 kinase domain with substrate peptide available","Tissue-specific substrate hierarchy not systematically defined","Potential scaffolding or complex-forming roles of SIK2 not characterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,2,3,4,5,6,13,15,21,22,29,30,32]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[23]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[11,29]}],"localization":[{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[0,34,35]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[8]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[4]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[23]}],"pathway":[{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[0,34,35]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[3,12,30]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[1,2,9,13,14,28,31]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[5,6,7,11,16]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[22,29]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[10,23]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[20,32]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[4]}],"complexes":[],"partners":["CRTC2","HDAC4","P97/VCP","P35/CDK5R1","PJA2","GABARAPL2","MYLK","LRP6"],"other_free_text":[]},"mechanistic_narrative":"SIK2 is an AMPK-related serine/threonine kinase that functions as a central integrator of nutrient, hormonal, and stress signals, coupling upstream regulation by LKB1, PKA, CaMK I/IV, and CK1α to the phosphorylation of diverse substrates that control metabolism, gene expression, mitosis, autophagy, and DNA repair. Its best-characterized function is phosphorylation of CRTC/TORC coactivators and class IIa HDACs, promoting their 14-3-3-dependent cytoplasmic retention and thereby suppressing CREB- and MEF2-dependent transcription programs involved in melanogenesis, osteoblast RANKL expression, neuronal survival, adipocyte glucose homeostasis, and pulmonary fibrosis [PMID:20819186, PMID:23393134, PMID:24898145, PMID:30377251, PMID:40609791]. SIK2 additionally phosphorylates p300-Ser89 to regulate PPARα-mediated ketogenesis, p35/CDK5R1-Ser91 to control β-cell insulin secretion via PJA2-dependent ubiquitylation, p97/VCP to stimulate ERAD, Drp1-Ser616 to promote mitochondrial fission, MYLK-Ser343 to activate cancer cell motility, LRP6 to engage Wnt/β-catenin signaling, Gab1-Ser266 to provide negative feedback on FGF2/ERK signaling, and GABARAPL2-Ser72 to enable autophagosome–lysosome fusion [PMID:26983400, PMID:24561619, PMID:24129571, PMID:31639424, PMID:35278271, PMID:35277657, PMID:39267218, PMID:41126299]. SIK2 localizes to centrosomes where it phosphorylates C-Nap1 at Ser2392 to drive centrosome splitting and is required for mitotic fidelity, and its own activity is tuned by PKA-mediated Ser358 phosphorylation (promoting 14-3-3 binding and cytoplasmic relocalization), p300/CBP acetylation of Lys53 (inhibiting kinase activity), HDAC6 deacetylation (restoring activity), CaMK I/IV phosphorylation at Thr484 (triggering degradation), and Fbxw7-mediated proteasomal turnover [PMID:20708153, PMID:22462548, PMID:23322770, PMID:21220102, PMID:32437091]."},"prefetch_data":{"uniprot":{"accession":"Q9H0K1","full_name":"Serine/threonine-protein kinase SIK2","aliases":["Qin-induced kinase","Salt-inducible kinase 2","SIK-2","Serine/threonine-protein kinase SNF1-like kinase 2"],"length_aa":926,"mass_kda":103.9,"function":"Serine/threonine-protein kinase that plays a role in many biological processes such as fatty acid oxidation, autophagy, immune response or glucose metabolism (PubMed:23322770, PubMed:26983400). Phosphorylates 'Ser-794' of IRS1 in insulin-stimulated adipocytes, potentially modulating the efficiency of insulin signal transduction. Inhibits CREB activity by phosphorylating and repressing TORCs, the CREB-specific coactivators (PubMed:15454081). Phosphorylates EP300 and thus inhibits its histone acetyltransferase activity (PubMed:21084751, PubMed:26983400). In turn, regulates the DNA-binding ability of several transcription factors such as PPARA or MLXIPL (PubMed:21084751, PubMed:26983400). Also plays a role in thymic T-cell development (By similarity)","subcellular_location":"Cytoplasm; Endoplasmic reticulum membrane","url":"https://www.uniprot.org/uniprotkb/Q9H0K1/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SIK2","classification":"Not Classified","n_dependent_lines":6,"n_total_lines":1208,"dependency_fraction":0.004966887417218543},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SIK2","total_profiled":1310},"omim":[{"mim_id":"614776","title":"SIK FAMILY KINASE 3; SIK3","url":"https://www.omim.org/entry/614776"},{"mim_id":"608973","title":"SALT-INDUCIBLE KINASE 2; SIK2","url":"https://www.omim.org/entry/608973"},{"mim_id":"608972","title":"CREB-REGULATED TRANSCRIPTION COACTIVATOR 2; CRTC2","url":"https://www.omim.org/entry/608972"},{"mim_id":"168468","title":"PARATHYROID HORMONE 1 RECEPTOR; PTH1R","url":"https://www.omim.org/entry/168468"},{"mim_id":"114105","title":"PROTEIN PHOSPHATASE 3, CATALYTIC SUBUNIT, ALPHA ISOFORM; PPP3CA","url":"https://www.omim.org/entry/114105"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Vesicles","reliability":"Approved"},{"location":"Nuclear speckles","reliability":"Additional"},{"location":"Intermediate filaments","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SIK2"},"hgnc":{"alias_symbol":["KIAA0781","QIK","DKFZp434K1115","LOH11CR1I"],"prev_symbol":["SNF1LK2"]},"alphafold":{"accession":"Q9H0K1","domains":[{"cath_id":"1.10.510.10","chopping":"101-283","consensus_level":"medium","plddt":90.6572,"start":101,"end":283},{"cath_id":"-","chopping":"300-341","consensus_level":"medium","plddt":92.7155,"start":300,"end":341}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H0K1","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H0K1-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H0K1-F1-predicted_aligned_error_v6.png","plddt_mean":57.78},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SIK2","jax_strain_url":"https://www.jax.org/strain/search?query=SIK2"},"sequence":{"accession":"Q9H0K1","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9H0K1.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9H0K1/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H0K1"}},"corpus_meta":[{"pmid":"31639424","id":"PMC_31639424","title":"SIK2 promotes reprogramming of glucose metabolism through PI3K/AKT/HIF-1α pathway and Drp1-mediated mitochondrial fission in ovarian cancer.","date":"2019","source":"Cancer letters","url":"https://pubmed.ncbi.nlm.nih.gov/31639424","citation_count":143,"is_preprint":false},{"pmid":"21220102","id":"PMC_21220102","title":"SIK2 is a key regulator for neuronal survival after ischemia via TORC1-CREB.","date":"2011","source":"Neuron","url":"https://pubmed.ncbi.nlm.nih.gov/21220102","citation_count":130,"is_preprint":false},{"pmid":"20708153","id":"PMC_20708153","title":"SIK2 is a centrosome kinase required for bipolar mitotic spindle formation that provides a potential target for therapy in ovarian cancer.","date":"2010","source":"Cancer cell","url":"https://pubmed.ncbi.nlm.nih.gov/20708153","citation_count":120,"is_preprint":false},{"pmid":"23393134","id":"PMC_23393134","title":"The tumor suppressor kinase LKB1 activates the downstream kinases SIK2 and SIK3 to stimulate nuclear export of class IIa histone deacetylases.","date":"2013","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/23393134","citation_count":83,"is_preprint":false},{"pmid":"25472719","id":"PMC_25472719","title":"SIK2 regulates CRTCs, HDAC4 and glucose uptake in adipocytes.","date":"2015","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/25472719","citation_count":79,"is_preprint":false},{"pmid":"31932581","id":"PMC_31932581","title":"SIK2 enhances synthesis of fatty acid and cholesterol in ovarian cancer cells and tumor growth through PI3K/Akt signaling pathway.","date":"2020","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/31932581","citation_count":75,"is_preprint":false},{"pmid":"36263177","id":"PMC_36263177","title":"FTO-mediated autophagy promotes progression of clear cell renal cell carcinoma via regulating SIK2 mRNA stability.","date":"2022","source":"International journal of biological 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the regulation of lipid homeostasis and adipogenesis in vivo.","date":"2014","source":"Diabetes","url":"https://pubmed.ncbi.nlm.nih.gov/24898145","citation_count":61,"is_preprint":false},{"pmid":"22462548","id":"PMC_22462548","title":"The AMPK-related kinase SIK2 is regulated by cAMP via phosphorylation at Ser358 in adipocytes.","date":"2012","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/22462548","citation_count":59,"is_preprint":false},{"pmid":"30377251","id":"PMC_30377251","title":"Parathyroid hormone(1-34) and its analogs differentially modulate osteoblastic Rankl expression via PKA/SIK2/SIK3 and PP1/PP2A-CRTC3 signaling.","date":"2018","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/30377251","citation_count":57,"is_preprint":false},{"pmid":"30004169","id":"PMC_30004169","title":"Upregulation of miR-874-3p and miR-874-5p inhibits epithelial ovarian cancer malignancy via SIK2.","date":"2018","source":"Journal of 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Yi xue ban = Journal of Zhejiang University. 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key role in the initiation of mitosis, and regulates the localization of the centrosome linker protein C-Nap1 through phosphorylation at S2392. PKA inhibition induces SIK2-dependent centrosome splitting in interphase, while SIK2 depletion blocks centrosome separation in mitosis.\",\n      \"method\": \"Subcellular localization (immunofluorescence/fractionation), phosphorylation site mutagenesis, siRNA depletion with mitotic phenotype readout, xenograft models\",\n      \"journal\": \"Cancer cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal functional validation, specific phosphorylation site identified, multiple orthogonal methods, replicated in culture and in vivo\",\n      \"pmids\": [\"20708153\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SIK2 suppresses CREB-mediated gene expression by phosphorylating and retaining TORC1 in the cytoplasm. During oxygen-glucose deprivation (OGD), CaMK I/IV phosphorylate SIK2 at Thr484, leading to SIK2 protein degradation and subsequent TORC1 dephosphorylation and nuclear translocation, activating CREB and promoting neuronal survival.\",\n      \"method\": \"In vitro kinase assay (CaMK I/IV phosphorylation of SIK2 at Thr484), sik2(-/-) mouse neurons with OGD survival readout, transient focal ischemia model\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro kinase assay identifying specific phosphorylation site, genetic KO with defined neuronal phenotype, replicated in vivo\",\n      \"pmids\": [\"21220102\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"LKB1 activates SIK2 (and SIK3) to promote nuclear export of class IIa HDACs (HDAC4, -5, -7, -9) by phosphorylating them at conserved motifs that stimulate 14-3-3 binding. SIK2 activation of class IIa HDAC export is PKA-sensitive and activates MEF2-dependent transcription, relieving repression of myogenesis.\",\n      \"method\": \"In vitro kinase assay, co-immunoprecipitation, epistasis (LKB1→SIK2→HDAC→14-3-3), myogenesis reporter assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct kinase assay, genetic epistasis with pathway placement, multiple substrates validated\",\n      \"pmids\": [\"23393134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SIK2 kinase activity is regulated by reversible acetylation: p300/CBP-mediated acetylation of Lys-53 inhibits SIK2 kinase activity, while HDAC6-mediated deacetylation restores activity. Acetylation-mimetic SIK2 (K53Q) causes autophagosome accumulation, and SIK2 kinase activity is required for autophagosome-lysosome fusion and clearance of TDP-43Δ inclusion bodies.\",\n      \"method\": \"Site-directed mutagenesis (K53Q/K53R), in vitro kinase assay, co-immunoprecipitation with p300/HDAC6, autophagy flux assays, siRNA knockdown\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay with mutagenesis, writer/eraser identified, functional autophagy phenotype validated\",\n      \"pmids\": [\"23322770\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SIK2 physically interacts with p97/VCP (co-localizes in ER membrane), directly phosphorylates p97/VCP to stimulate its ATPase activity, and thereby promotes ER-associated protein degradation (ERAD). Kinase-deficient SIK2 or mutation of the SIK2 phosphorylation site on p97/VCP impairs ERAD substrate removal.\",\n      \"method\": \"Co-IP, co-localization (immunofluorescence), in vitro kinase assay, ERAD substrate degradation assays, siRNA knockdown\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct phosphorylation demonstrated in vitro, binding confirmed by co-IP, functional consequence shown by mutagenesis and KD\",\n      \"pmids\": [\"24129571\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SIK2 forms a complex with the CDK5 activator p35 (CDK5R1) and the E3 ligase PJA2. Upon glucose stimulation, SIK2 phosphorylates p35 at Ser91, triggering its ubiquitylation by PJA2 and promoting insulin secretion. β-cell-specific SIK2 knockout leads to p35 accumulation and impaired insulin secretion.\",\n      \"method\": \"Co-immunoprecipitation (SIK2-p35-PJA2 complex), in vitro kinase assay (SIK2 phosphorylates p35-Ser91), mass spectrometry (Gingras), β-cell-specific KO mice with glucose homeostasis phenotype\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstituted complex, specific phosphorylation site identified, KO mouse with defined phenotype, multiple orthogonal methods\",\n      \"pmids\": [\"24561619\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In adipocytes, SIK2 directly phosphorylates CRTC2, CRTC3, and HDAC4. SIK2 interacts with CRTC2, CRTC3, HDAC4, and PP2A; cAMP elevation via PKA phosphorylation of SIK2 at Ser358 reduces its interaction with CRTCs and PP2A. SIK2 overexpression or activity increases GLUT4 protein levels and glucose uptake, while CRTC2/HDAC4 silencing recapitulates this effect.\",\n      \"method\": \"Co-immunoprecipitation, in vitro kinase assay, siRNA knockdown, glucose uptake assays, phosphosite mutagenesis (S358A)\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct phosphorylation assay, binding confirmed by co-IP, multiple substrate targets validated, functional metabolic readout\",\n      \"pmids\": [\"25472719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SIK2 KO mice exhibit dysregulated CRTC2-CREB transcriptional pathway in white adipocytes, increased ATF3 expression, downregulation of GLUT4, reduced high-molecular weight adiponectin, and impaired glucose uptake, establishing SIK2 as a critical regulator of adipocyte glucose and lipid homeostasis upstream of CRTC2-CREB.\",\n      \"method\": \"SIK2 knockout mice, CRTC2 KO mice (epistasis), 3T3-L1 adipocyte cultures, glucose/insulin tolerance tests\",\n      \"journal\": \"Diabetes\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with defined metabolic phenotype, epistasis with CRTC2 KO, replicated in vitro and in vivo\",\n      \"pmids\": [\"24898145\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"PKA phosphorylates SIK2 at Ser358 in adipocytes in response to cAMP-elevating agents (forskolin, CL 316,243), leading to 14-3-3 binding. Ser358 phosphorylation (not Ser587) is required for 14-3-3 binding. This phosphorylation triggers relocalization of SIK2 from a particulate fraction to the cytosol in adipocytes.\",\n      \"method\": \"Phosphopeptide mapping, site-directed mutagenesis (S358A, S587A), 14-3-3 binding assay, immunocytochemistry, subcellular fractionation\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — phosphosite mapping with mutagenesis, 14-3-3 binding validated, relocalization confirmed by fractionation\",\n      \"pmids\": [\"22462548\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SIK2 suppresses eumelanogenesis by phosphorylating and retaining TORC1 in the cytoplasm, thereby inhibiting CREB-mediated MITF gene expression. UV light exposure induces nuclear translocation of TORC1, which is blocked by SIK2. Sik2(-/-) mice on an A(y)/a background show brown (eumelanin) rather than yellow (pheomelanin) hair, demonstrating SIK2 represses eumelanogenesis in vivo.\",\n      \"method\": \"SIK2 knockout mice (genetic epistasis), dominant-negative TORC1 overexpression, B16 melanoma cell transfection, melanogenesis assays\",\n      \"journal\": \"Pigment cell & melanoma research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO in defined in vivo model, epistasis with dominant-negative TORC1, specific molecular pathway established\",\n      \"pmids\": [\"20819186\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SIK2 and SIK3 (particularly) control macrophage polarization; catalytically inactive knock-in of SIK2 and SIK3 shifts macrophages toward an anti-inflammatory phenotype (high IL-10, low TNFα). SIK2/SIK3 inhibition during macrophage differentiation produces a stable enhanced anti-inflammatory phenotype even after kinase reactivation.\",\n      \"method\": \"Catalytically inactive knock-in (KI) mice for SIK1/2/3, primary macrophage cytokine profiling, SIK inhibitor treatment (MRT199665, HG-9-91-01)\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KI mice with catalytically inactive alleles, primary cells, multiple isoform epistasis established\",\n      \"pmids\": [\"27920213\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SIK2 is activated by nutrient deprivation, ATP synthesis inhibition, and AICAR in adipocytes. Activated SIK2 represses lipogenic gene expression (FAS, ACC2, SCD1) by reducing nuclear translocation of SREBP-1, independently of AMPK. This effect is reversed by constitutively active SREBP-1 overexpression.\",\n      \"method\": \"In vitro kinase assay (peptide substrate phosphorylation), adenovirus-mediated overexpression/knockdown, FAS promoter-luciferase reporter, SREBP-1 nuclear fractionation\",\n      \"journal\": \"Obesity (Silver Spring, Md.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — kinase activity assay, reporter gene assay, epistasis with SREBP-1, multiple readouts\",\n      \"pmids\": [\"18239551\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SIK2 is required for restriction of autophagic flux in triple-negative breast cancer (TNBC) cells. Genetic or pharmacological SIK2 inhibition increases autophagic flux and causes selective cell death in breast cancer (especially claudin-low subtype) cells; ATG5 depletion rescues this cell death, placing SIK2 upstream of autophagosome formation.\",\n      \"method\": \"siRNA knockdown, pharmacological inhibition, ATG5 depletion rescue (epistasis), autophagic flux assays, xenograft models\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis (ATG5 rescue), in vivo xenograft, multiple orthogonal methods\",\n      \"pmids\": [\"27697861\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SIK2 phosphorylates p300 at Ser89, disrupting the p300-PPARα interaction (p300 binds PPARα via a conserved LXXLL motif), thereby decreasing PPARα-mediated ketogenic gene expression during fasting. The phosphorylation-defective p300-S89A mutant shows increased interaction with PPARα and abolishes SIK2 suppression of ketogenesis.\",\n      \"method\": \"Co-immunoprecipitation (p300-PPARα), in vitro kinase assay (SIK2 phosphorylates p300-Ser89), site-directed mutagenesis (S89A), ketogenic gene expression in liver\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct phosphorylation assay, mutagenesis confirming site, binding assay, functional gene expression readout\",\n      \"pmids\": [\"26983400\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"In osteoblasts, PTH(1-34) inhibits SIK2 and SIK3 via PKA, leading to dephosphorylation and nuclear translocation of CRTC2/CRTC3 by protein phosphatases PP1/PP2A, resulting in CREB-mediated Rankl transcription. Knockdown of SIK2/3 and CRTC3 demonstrated their requirement in this signaling pathway.\",\n      \"method\": \"siRNA knockdown of SIK2/3 and CRTCs, immunofluorescence of CRTC nuclear localization, qPCR for Rankl expression, PP1/PP2A inhibition, primary osteoblasts\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis by siRNA, nuclear localization directly measured, functional gene expression readout, multiple pathway components probed\",\n      \"pmids\": [\"30377251\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SIK2 promotes mitochondrial fission through direct phosphorylation of Drp1 at Ser616, which inhibits mitochondrial oxidative phosphorylation and promotes the Warburg effect. SIK2 also upregulates HIF-1α by activating PI3K/AKT signaling to enhance glycolytic gene transcription in ovarian cancer cells.\",\n      \"method\": \"Phosphorylation assay (SIK2→Drp1-Ser616), PI3K/AKT pathway inhibition, HIF-1α reporter, mitochondrial morphology analysis, siRNA/overexpression in OC cells\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — specific phosphorylation site identified, pathway inhibitors used, but in vitro kinase reconstitution not fully detailed; single lab study\",\n      \"pmids\": [\"31639424\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SIK2 promotes lipid synthesis in ovarian cancer cells by upregulating SREBP1c (and downstream FASN) and SREBP2 (and downstream HMGCR) via the PI3K/Akt signaling pathway, enhancing both fatty acid and cholesterol synthesis.\",\n      \"method\": \"siRNA knockdown/overexpression, PI3K/Akt inhibition, SREBP1c/2 expression assays, in vitro and xenograft models\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — pathway placement by inhibitor and KD, but direct kinase-substrate relationship for PI3K/Akt activation not biochemically reconstituted; single lab\",\n      \"pmids\": [\"31932581\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SIK2 functions as a negative modulator of insulin-dependent Müller glia survival: insulin stimulation increases SIK2 activity and promotes IRS1-SIK2 interaction while modulating AKT phosphorylation. SIK2 knockdown under normo- and hyperglycemic conditions increases pAkt levels and reduces apoptosis, while SIK2 overexpression has the opposite effect.\",\n      \"method\": \"In vitro kinase assay (SIK2 activity), co-immunoprecipitation (IRS1-SIK2), siRNA knockdown and overexpression with pAkt/apoptosis readouts, streptozotocin rat model\",\n      \"journal\": \"Investigative ophthalmology & visual science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — kinase assay and co-IP performed, functional epistasis with AKT pathway established, but mechanistic link between SIK2 kinase activity and AKT not fully reconstituted\",\n      \"pmids\": [\"23599336\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SIK2 inhibits AKT/GSK3β/β-catenin signaling in gastric cancer by activating mTORC1 to inhibit autophagic degradation of protein phosphatases PHLPP2 and PP2A, which then dephosphorylate and inactivate AKT.\",\n      \"method\": \"siRNA knockdown/overexpression, Western blot for pAKT/GSK3β/β-catenin, mTORC1 inhibition (rapamycin), autophagy flux assays, in vitro migration/invasion assays\",\n      \"journal\": \"Molecular oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — pathway placement by inhibitors and KD, phosphatase upregulation mechanism proposed, but direct kinase-substrate reconstitution not performed; single lab\",\n      \"pmids\": [\"33128264\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"B55gamma (PP2A regulatory subunit) binds SIK2 and stabilizes SIK2 protein, which is required for B55gamma-mediated suppression of S6K phosphorylation and enhanced glioma cell survival under glucose depletion. SIK2 knockdown in B55gamma-overexpressing cells recovers S6K phosphorylation.\",\n      \"method\": \"Co-immunoprecipitation, proteomic analysis, siRNA knockdown of SIK2, Western blot for pS6K, cell viability assays under glucose starvation\",\n      \"journal\": \"Cancer cell international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-IP and epistasis by KD, but direct kinase assay not performed; single lab\",\n      \"pmids\": [\"25792973\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SIK2 inhibition decreases phosphorylation of class-IIa HDACs (HDAC4/5/7), abolishes MEF2D transcriptional activity, and reduces MEF2D binding to regulatory regions of FANCD2, EXO1, and XRCC4 genes, thereby repressing DNA double-strand break repair and producing synthetic lethality with PARP inhibitors.\",\n      \"method\": \"SIK2 inhibitors (ARN3236, ARN3261), phospho-HDAC4/5/7 Western blot, ChIP-seq/ATAC-seq for MEF2D binding, DNA repair assays, xenograft models\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (ChIP, phosphoproteomics, xenograft), pathway placement established; pharmacological inhibitors used rather than direct kinase reconstitution\",\n      \"pmids\": [\"35642638\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SIK2 directly phosphorylates MYLK (myosin light chain kinase) at Ser343, activating MYLK and its downstream substrate MYL2 (myosin light chain 2), thereby promoting ovarian cancer cell motility, migration, and metastasis. Adipocytes induce SIK2 phosphorylation at Ser358 and MYLK phosphorylation at Ser343, enhancing cancer cell motility.\",\n      \"method\": \"In vitro kinase assay (SIK2→MYLK-Ser343), phospho-specific antibodies, siRNA knockdown, migration/invasion/metastasis assays in vitro and in vivo\",\n      \"journal\": \"Molecular oncology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct phosphorylation site identified and validated in vitro, downstream substrate (MYL2) activation demonstrated, in vivo metastasis model\",\n      \"pmids\": [\"35278271\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SIK2 maintains breast cancer stem cell (BCSC) properties by directly phosphorylating LRP6 (LDL receptor-related protein 6) in a kinase-activity-dependent manner, leading to Wnt/β-catenin pathway activation and IDH1 induction, causing metabolic reprogramming. CK1α phosphorylates SIK2 upstream to enable this activity.\",\n      \"method\": \"In vitro kinase assay (SIK2→LRP6), siRNA knockdown, SIK2 inhibitor treatment (ARN-3236, HG-9-91-01), β-catenin accumulation assay, BCSC proportion/tumor initiation assays, zebrafish embryo model\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct kinase assay for LRP6 phosphorylation, upstream kinase (CK1α) identified, functional BCSC phenotype validated, inhibitors corroborated\",\n      \"pmids\": [\"35277657\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SIK2 associates with actin filaments under basal conditions and is recruited to the Salmonella-containing vacuole (SCV) together with Arp2/3 complex and Formins upon bacterial infection. SIK2 depletion causes actin nucleation/polymerization defects at the SCV, impairs xenophagy, and favors bacterial escape from the SCV, establishing SIK2 as an orchestrator of actin-dependent host defense.\",\n      \"method\": \"Global phosphoproteomics (identifying SIK2 upon Salmonella infection), siRNA depletion, co-localization (immunofluorescence of SIK2/Arp2/3/Formins at SCV), bacterial replication/xenophagy assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — phosphoproteomics identification, direct co-localization at SCV, functional depletion phenotype (bacterial escape, xenophagy), multiple orthogonal methods\",\n      \"pmids\": [\"33947818\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Fbxw7 targets SIK2 for proteasomal degradation by binding to a conserved 'TPPPS' motif on SIK2. Loss of Fbxw7-mediated SIK2 degradation allows SIK2 to promote cell cycle progression and activation of the TORC2/AKT signaling pathway, modulating p21 expression in pancreatic cancer cells.\",\n      \"method\": \"Co-immunoprecipitation (Fbxw7-SIK2), protein database screening for Fbxw7-recognizing degron, proteasome inhibitor rescue, siRNA/overexpression with cell cycle/AKT readouts\",\n      \"journal\": \"Cell biology international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-IP and degron motif identified, ubiquitin-mediated degradation proposed; direct ubiquitylation assay not fully described; single lab\",\n      \"pmids\": [\"32437091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SIK2 is critical for the development of cardiac left ventricular hypertrophy (LVH) in response to chronic high-salt diet. sik2(-/-) mice do not develop LVH upon high-salt feeding (unlike wild-type), and α-adducin regulates SIK2 expression in cardiomyocytes, which mediates adducin's effects on hypertrophy marker gene activation.\",\n      \"method\": \"sik2(-/-) mice with high-salt diet challenge, LV wall thickness echocardiography, gene expression profiling, siRNA of SIK2 in cardiomyocytes\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with defined in vivo phenotype, upstream regulator (α-adducin) identified, but molecular mechanism between SIK2 and hypertrophy genes not fully reconstituted\",\n      \"pmids\": [\"24752134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Loss of PKA phosphorylation site Ser587 in SIK2 (Sik2S587A mice) increases NREM sleep delta density, establishing that PKA-SIK2 signaling regulates sleep need.\",\n      \"method\": \"Sik2S587A knock-in mice, EEG/EMG sleep recording, homeostatic sleep deprivation testing\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — specific phosphosite mutant knock-in with defined electrophysiological sleep phenotype; single lab\",\n      \"pmids\": [\"32457359\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"LKB1 loss in uveal melanoma enhances proliferation and survival through SIK2 inhibition and upregulation of the Na+/Ca2+ exchanger SLC8A1, which promotes elevated intracellular calcium and mitochondrial ROS. CRISPR-Cas9 KO screen identified LKB1-SIK2 module as a tumor suppressor axis.\",\n      \"method\": \"Kinome-wide CRISPR-Cas9 KO screen, genetic epistasis (LKB1→SIK2→SLC8A1), calcium and ROS measurements, cell death assays with SLC8A1 inhibitor and mitochondria-targeted antioxidant\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genome-scale screen, epistasis validated, but molecular mechanism between SIK2 and SLC8A1 not fully reconstituted; single lab\",\n      \"pmids\": [\"37966164\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"TGF-β1 induces SIK2 expression in lung fibroblasts, and SIK2 phosphorylates CRTC2 to retain it in the cytoplasm. SIK2 inhibition by ARN-3236 leads to CRTC2 dephosphorylation, nuclear translocation, and CREB-dependent anti-fibrotic gene expression, attenuating bleomycin-induced pulmonary fibrosis.\",\n      \"method\": \"Western blot (SIK2, p-CRTC2), ARN-3236 treatment, siRNA knockdown of SIK2, immunofluorescence (CRTC2 nuclear translocation), mouse bleomycin model\",\n      \"journal\": \"BMC pulmonary medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — pharmacological and genetic inhibition with defined molecular readout; direct kinase assay for SIK2-CRTC2 not shown; single lab\",\n      \"pmids\": [\"35410283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SIK2 acts as a negative feedback regulator of FGF2/Ras/ERK1/2 signaling by phosphorylating Gab1 at Ser266, which weakens Gab1 interactions with Grb2 and Shp2. ERK1/2 activates SIK2 in this feedback loop. SIK2 downregulation enhances and prolongs ERK1/2 activation and increases FGF2-dependent cell proliferation.\",\n      \"method\": \"In vitro kinase assay (SIK2→Gab1-Ser266), site-directed mutagenesis, co-immunoprecipitation (Gab1-Grb2/Shp2), SIK2 overexpression/knockdown with pERK1/2 and proliferation readouts\",\n      \"journal\": \"Advanced biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct kinase assay with specific site identified, mutagenesis, co-IP of disrupted binding, functional ERK activation and proliferation phenotype\",\n      \"pmids\": [\"39267218\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SIK2 phosphorylates GABARAPL2 at Ser72, a modification essential for autophagosome-lysosome fusion. Phosphorylation-mimetic GABARAPL2-S72E rescues autophagic flux, reduces Aβ deposition, and restores synaptic function in 5×FAD Alzheimer's disease mice, while the non-phosphorylatable S72A mutant fails to show protective effects.\",\n      \"method\": \"Co-immunoprecipitation, GST pull-down assay, phosphoproteomics, site-directed mutagenesis (S72E/S72A), adeno-associated virus delivery in vivo, autophagy flux assays (mRFP-GFP-LC3), electron microscopy, Morris water maze, LTP recording\",\n      \"journal\": \"Translational neurodegeneration\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro phosphorylation assay with mutagenesis, reconstitution in vivo with phosphomimetic and non-phosphorylatable mutants, multiple orthogonal readouts\",\n      \"pmids\": [\"41126299\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In osteoblasts, SIK2 (and SIK3) inhibition by PTH/PKA signaling allows CRTC2 nuclear translocation primarily via PP1/PP2A/PP4/PP5 action; CRTC2 is the primary co-activator of Tnfsf11 (RANKL) gene transcription, while SIK2/3 phosphorylation retains CRTCs in the cytoplasm.\",\n      \"method\": \"siRNA knockdown of SIK1/2/3, CRTC1/2/3, PP1/2/3/4/5/6/7; quantitative immunofluorescence of CRTC nuclear localization; co-immunoprecipitation; Western blot; qPCR for Tnfsf11; primary mouse calvarial osteoblasts\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — systematic siRNA epistasis of multiple pathway components, direct CRTC localization measured, co-IP, multiple orthogonal methods\",\n      \"pmids\": [\"40609791\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SIK2 promotes RAD50 phosphorylation at Ser635, enabling nuclear translocation of RAD50 and nuclear filament assembly required for homologous recombination DNA repair. SIK2 inhibitor SIC-19 reduces RAD50-pS635, impairs nuclear RAD50 translocation, disrupts HR repair, and induces apoptosis in ovarian cancer cells.\",\n      \"method\": \"Phospho-specific antibodies (RAD50-pS635), SIK2 knockdown/SIC-19 inhibitor, nuclear translocation assays, HR repair assays, ovarian cancer organoids and xenograft models\",\n      \"journal\": \"Drug resistance updates\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — specific phosphorylation site identified on RAD50, functional HR readout; direct in vitro kinase assay not described; single lab\",\n      \"pmids\": [\"38518726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Insulin induces phosphorylation of SIK2 at Thr484 in primary adipocytes, leading to increased SIK2 protein stability (prevented by proteasome inhibition). This Thr484 phosphorylation is impaired in insulin-resistant individuals but does not affect SIK2 catalytic activity toward HDAC4.\",\n      \"method\": \"Phospho-specific antibodies, in vitro kinase assay (SIK2 activity toward HDAC4), proteasome inhibitor (MG132), primary human and rat adipocytes\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — specific PTM site identified, functional consequence (protein stability) demonstrated, direct kinase assay performed; single lab\",\n      \"pmids\": [\"30586628\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SIK2 inhibition with MRIA9 blocks centrosome disjunction, impairs centrosome alignment, causes spindle mispositioning during mitosis, and increases chromosomal instability in ovarian cancer cells, corroborating SIK2's role as a centrosome kinase required for mitotic fidelity.\",\n      \"method\": \"Selective SIK2 inhibitor (MRIA9), live-cell imaging of centrosome dynamics, chromosomal instability assays, 3D-spheroid paclitaxel sensitivity assays\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — pharmacological inhibition with defined mitotic phenotype; corroborates prior genetic findings; single lab\",\n      \"pmids\": [\"34359562\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FANCA co-localizes with SIK2 at multiple mitotic structures and regulates SIK2 activity at centrosomes. Loss of FANCA exacerbates cell cycle defects from pharmacological SIK2 inhibition (impaired G2-M transition, delayed mitotic progression, cytokinesis failure). SIK2 inhibition also abrogates nocodazole-induced prometaphase arrest, revealing a role in the spindle assembly checkpoint.\",\n      \"method\": \"Kinome-wide synthetic lethality CRISPR screen, co-localization immunofluorescence (FANCA and SIK2 at centrosomes), pharmacological SIK2 inhibition in FANCA-/- cells, cell cycle assays, spindle assembly checkpoint assay\",\n      \"journal\": \"Molecular oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide screen, co-localization established, synthetic lethality with functional epistasis; direct FANCA regulation of SIK2 kinase activity not fully reconstituted in vitro\",\n      \"pmids\": [\"34058059\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SIK2 is a centrosomal, AMPK-related serine/threonine kinase that phosphorylates multiple substrates—including TORC1/CRTC coactivators (to suppress CREB-mediated transcription), class IIa HDACs (driving their 14-3-3-dependent nuclear export), p35/CDK5R1 (controlling β-cell insulin secretion via PJA2 ubiquitylation), Drp1-Ser616 (promoting mitochondrial fission), p300-Ser89 (regulating PPARα/ketogenesis), MYLK-Ser343 (activating myosin light chain and cancer motility), LRP6 (activating Wnt/β-catenin signaling), p97/VCP (stimulating ER-associated protein degradation), Gab1-Ser266 (providing negative feedback on FGF2/ERK signaling), GABARAPL2-Ser72 (enabling autophagosome-lysosome fusion), and RAD50-Ser635 (supporting DNA homologous recombination repair)—and is itself regulated by upstream kinases LKB1, CaMK I/IV, and PKA (phosphorylating Ser358 to promote 14-3-3 binding and cytoplasmic relocalization), as well as by p300/CBP-mediated acetylation at Lys53 (inhibiting its kinase activity) and HDAC6-mediated deacetylation (restoring activity), placing it as a central hub integrating nutrient, hormonal, and stress signals to control metabolism, mitosis, autophagy, immunity, and gene expression.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SIK2 is an AMPK-related serine/threonine kinase that functions as a central integrator of nutrient, hormonal, and stress signals, coupling upstream regulation by LKB1, PKA, CaMK I/IV, and CK1α to the phosphorylation of diverse substrates that control metabolism, gene expression, mitosis, autophagy, and DNA repair. Its best-characterized function is phosphorylation of CRTC/TORC coactivators and class IIa HDACs, promoting their 14-3-3-dependent cytoplasmic retention and thereby suppressing CREB- and MEF2-dependent transcription programs involved in melanogenesis, osteoblast RANKL expression, neuronal survival, adipocyte glucose homeostasis, and pulmonary fibrosis [PMID:20819186, PMID:23393134, PMID:24898145, PMID:30377251, PMID:40609791]. SIK2 additionally phosphorylates p300-Ser89 to regulate PPARα-mediated ketogenesis, p35/CDK5R1-Ser91 to control β-cell insulin secretion via PJA2-dependent ubiquitylation, p97/VCP to stimulate ERAD, Drp1-Ser616 to promote mitochondrial fission, MYLK-Ser343 to activate cancer cell motility, LRP6 to engage Wnt/β-catenin signaling, Gab1-Ser266 to provide negative feedback on FGF2/ERK signaling, and GABARAPL2-Ser72 to enable autophagosome–lysosome fusion [PMID:26983400, PMID:24561619, PMID:24129571, PMID:31639424, PMID:35278271, PMID:35277657, PMID:39267218, PMID:41126299]. SIK2 localizes to centrosomes where it phosphorylates C-Nap1 at Ser2392 to drive centrosome splitting and is required for mitotic fidelity, and its own activity is tuned by PKA-mediated Ser358 phosphorylation (promoting 14-3-3 binding and cytoplasmic relocalization), p300/CBP acetylation of Lys53 (inhibiting kinase activity), HDAC6 deacetylation (restoring activity), CaMK I/IV phosphorylation at Thr484 (triggering degradation), and Fbxw7-mediated proteasomal turnover [PMID:20708153, PMID:22462548, PMID:23322770, PMID:21220102, PMID:32437091].\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"Establishing SIK2 as a nutrient-responsive kinase that represses lipogenic gene expression independently of AMPK answered whether SIK2 has autonomous metabolic-sensing function in adipocytes.\",\n      \"evidence\": \"In vitro kinase assay, adenoviral overexpression/knockdown in adipocytes, SREBP-1 nuclear fractionation\",\n      \"pmids\": [\"18239551\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct substrate on SREBP-1 nuclear translocation not identified\", \"Upstream activating kinase not yet characterized in this system\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Discovery that SIK2 localizes to centrosomes and phosphorylates C-Nap1 at Ser2392 to initiate centrosome splitting established SIK2 as a mitotic kinase, resolving how centrosome disjunction is linked to AMPK-family signaling.\",\n      \"evidence\": \"Immunofluorescence/fractionation, phosphosite mutagenesis, siRNA depletion with mitotic phenotype, xenograft models\",\n      \"pmids\": [\"20708153\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full spectrum of centrosomal substrates unknown\", \"Whether SIK2 centrosomal function is LKB1-dependent not tested\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstration that SIK2 represses CREB-mediated MITF transcription by retaining TORC1 in the cytoplasm, with Sik2-knockout mice showing coat-color switching, established the TORC/CRTC-phosphorylation axis as a major SIK2 effector pathway in vivo.\",\n      \"evidence\": \"Sik2−/− mice on Ay/a background, dominant-negative TORC1 epistasis, melanogenesis assays\",\n      \"pmids\": [\"20819186\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific TORC1 phosphorylation site by SIK2 not mapped in this study\", \"Whether SIK1/SIK3 compensate partially not addressed\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identification of CaMK I/IV as upstream kinases that phosphorylate SIK2 at Thr484, triggering its degradation and thereby permitting TORC1 nuclear translocation and CREB-dependent neuronal survival, revealed how ischemic stress inactivates SIK2.\",\n      \"evidence\": \"In vitro kinase assay, sik2−/− neurons with OGD survival, transient focal ischemia model\",\n      \"pmids\": [\"21220102\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Degradation pathway (proteasomal vs lysosomal) not defined\", \"Whether Thr484 phosphorylation has distinct effects in non-neuronal cells not tested\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Mapping PKA phosphorylation of SIK2 at Ser358 as the event that triggers 14-3-3 binding and cytoplasmic relocalization defined the molecular switch by which cAMP signaling inactivates SIK2 in adipocytes.\",\n      \"evidence\": \"Phosphopeptide mapping, S358A/S587A mutagenesis, 14-3-3 binding assay, subcellular fractionation\",\n      \"pmids\": [\"22462548\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether 14-3-3 binding directly inhibits kinase activity or only controls localization not distinguished\", \"Identity of the phosphatase reversing Ser358 phosphorylation unknown\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Three concurrent studies established the breadth of SIK2 substrates: LKB1-activated SIK2 phosphorylates class IIa HDACs for 14-3-3-mediated nuclear export and MEF2 derepression; p300/CBP acetylation at Lys53 inhibits SIK2 while HDAC6 deacetylation restores it, linking SIK2 activity to autophagosome–lysosome fusion; and SIK2 phosphorylates p97/VCP to stimulate ERAD.\",\n      \"evidence\": \"In vitro kinase assays, co-immunoprecipitation, K53Q/K53R mutagenesis, autophagy flux assays, ERAD substrate degradation assays, epistasis experiments\",\n      \"pmids\": [\"23393134\", \"23322770\", \"24129571\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for Lys53 acetylation inhibiting kinase activity unknown\", \"p97/VCP phosphorylation site not mapped\", \"How SIK2 kinase activity mechanistically drives autophagosome–lysosome fusion not fully resolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"SIK2 was placed at the center of adipocyte glucose homeostasis and β-cell insulin secretion: SIK2 KO mice showed CRTC2-CREB dysregulation, GLUT4 loss, and impaired adiponectin secretion, while in β-cells SIK2 phosphorylates p35-Ser91 to trigger PJA2-mediated ubiquitylation and promote glucose-stimulated insulin secretion.\",\n      \"evidence\": \"Sik2 KO mice with metabolic phenotyping, β-cell-specific KO, co-IP of SIK2-p35-PJA2 complex, in vitro kinase assay, mass spectrometry\",\n      \"pmids\": [\"24898145\", \"24561619\", \"25472719\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How SIK2 controls GLUT4 protein levels mechanistically (transcriptional vs post-translational) not resolved\", \"Whether p35 phosphorylation by SIK2 occurs in non-β-cell tissues unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"SIK2 was shown to phosphorylate p300 at Ser89 to disrupt its interaction with PPARα and suppress ketogenic gene expression, and catalytically inactive SIK2 knock-in mice revealed SIK2's role in macrophage anti-inflammatory polarization, broadening SIK2's functions to metabolic gene regulation and innate immunity.\",\n      \"evidence\": \"In vitro kinase assay (p300-Ser89), S89A mutagenesis, liver ketogenic gene expression; catalytically inactive KI mice, primary macrophage cytokine profiling\",\n      \"pmids\": [\"26983400\", \"27920213\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct SIK2 substrate(s) controlling macrophage polarization downstream of HDAC phosphorylation not identified\", \"Whether p300-Ser89 phosphorylation affects other p300 interactions unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"SIK2 inhibition was found to increase autophagic flux and cause selective death in triple-negative breast cancer cells, with ATG5 depletion rescuing cell death, establishing SIK2 as a restraint on autophagy in cancer.\",\n      \"evidence\": \"siRNA knockdown, pharmacological inhibition, ATG5 epistasis, xenograft models\",\n      \"pmids\": [\"27697861\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct autophagy substrate of SIK2 not identified in this study\", \"Whether SIK2-autophagy axis operates in non-cancer cells unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"PTH-induced SIK2/SIK3 inhibition via PKA was shown to permit CRTC2/3 nuclear translocation and CREB-dependent RANKL transcription in osteoblasts, and insulin was found to induce SIK2-Thr484 phosphorylation for protein stabilization in adipocytes, extending the SIK2-CRTC axis to bone biology and linking insulin signaling to SIK2 turnover.\",\n      \"evidence\": \"siRNA epistasis in osteoblasts, CRTC nuclear localization imaging, qPCR for RANKL; phospho-Thr484 antibodies, proteasome inhibitor, primary human adipocytes\",\n      \"pmids\": [\"30377251\", \"30586628\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinase responsible for insulin-induced Thr484 phosphorylation not identified\", \"Whether Thr484 phosphorylation is impaired in type 2 diabetes tissue in vivo not confirmed\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"SIK2 was identified as an actin-associated kinase recruited to the Salmonella-containing vacuole where it orchestrates Arp2/3- and Formin-dependent actin polymerization for xenophagy, and FANCA was found to co-localize with SIK2 at centrosomes and regulate its mitotic function, expanding SIK2's roles to host defense and the spindle assembly checkpoint.\",\n      \"evidence\": \"Global phosphoproteomics, SIK2 depletion with bacterial escape/xenophagy assays, co-localization at SCV; CRISPR synthetic lethality screen, FANCA-SIK2 co-localization, cell cycle assays\",\n      \"pmids\": [\"33947818\", \"34058059\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct SIK2 substrates at the SCV not identified\", \"Mechanism by which FANCA modulates SIK2 kinase activity not reconstituted in vitro\", \"Whether SIK2 phosphorylates actin regulators directly unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Four new direct substrates were identified: MYLK-Ser343 (activating myosin light chain and cancer motility), LRP6 (activating Wnt/β-catenin for breast cancer stemness), and class IIa HDACs driving MEF2D-dependent DNA repair gene expression (creating PARP inhibitor synthetic lethality), demonstrating the remarkable substrate diversity of SIK2.\",\n      \"evidence\": \"In vitro kinase assays for MYLK and LRP6, ChIP-seq/ATAC-seq for MEF2D, xenograft and zebrafish models, pharmacological and genetic inhibition\",\n      \"pmids\": [\"35278271\", \"35277657\", \"35642638\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for SIK2 substrate recognition across diverse targets unknown\", \"Whether MYLK phosphorylation operates in non-cancer contexts not tested\", \"LRP6 phosphorylation site not mapped\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"SIK2 was shown to phosphorylate Gab1 at Ser266 to weaken Gab1-Grb2/Shp2 interactions, providing negative feedback on FGF2/ERK signaling, and to promote RAD50-Ser635 phosphorylation required for nuclear RAD50 translocation and homologous recombination repair.\",\n      \"evidence\": \"In vitro kinase assay (Gab1-Ser266), co-IP of disrupted Gab1 complexes, ERK activation readouts; phospho-RAD50-S635 antibodies, HR repair assays, ovarian cancer organoids and xenografts\",\n      \"pmids\": [\"39267218\", \"38518726\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct in vitro kinase assay for RAD50 not described\", \"Whether Gab1 phosphorylation extends to other RTK signaling contexts not tested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"SIK2 was demonstrated to phosphorylate GABARAPL2 at Ser72, a modification essential for autophagosome–lysosome fusion; phosphomimetic GABARAPL2-S72E rescued autophagic flux and ameliorated amyloid pathology in 5×FAD Alzheimer's mice, providing the first direct SIK2 substrate in the autophagy machinery.\",\n      \"evidence\": \"GST pull-down, phosphoproteomics, S72E/S72A mutagenesis, AAV delivery in 5×FAD mice, mRFP-GFP-LC3 flux, electron microscopy, electrophysiology\",\n      \"pmids\": [\"41126299\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SIK2 phosphorylates other ATG8-family members unknown\", \"Upstream signal controlling SIK2-GABARAPL2 axis in neurons not identified\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Systematic siRNA epistasis in osteoblasts confirmed CRTC2 as the primary coactivator downstream of SIK2/3 for RANKL transcription and identified PP1/PP2A/PP4/PP5 as the phosphatases counteracting SIK2-mediated CRTC phosphorylation.\",\n      \"evidence\": \"Systematic siRNA of SIK1/2/3, CRTC1/2/3, PP1–PP7; quantitative immunofluorescence, co-IP, qPCR; primary mouse calvarial osteoblasts\",\n      \"pmids\": [\"40609791\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific CRTC2 phosphorylation sites targeted by SIK2 in osteoblasts not mapped\", \"Whether PP4/PP5 are direct SIK2-CRTC2 phosphatases or act indirectly not resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Despite identification of over a dozen direct substrates, the structural basis for SIK2's broad substrate recognition, the relative contribution of individual substrates to in vivo phenotypes, and whether SIK2 functions as a monomer or within stable signaling complexes remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No crystal structure of SIK2 kinase domain with substrate peptide available\", \"Tissue-specific substrate hierarchy not systematically defined\", \"Potential scaffolding or complex-forming roles of SIK2 not characterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4, 5, 6, 13, 15, 21, 22, 29, 30, 32]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [23]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [11, 29]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [0, 34, 35]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [23]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [0, 34, 35]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [3, 12, 30]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [1, 2, 9, 13, 14, 28, 31]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [5, 6, 7, 11, 16]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [22, 29]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [10, 23]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [20, 32]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"CRTC2\",\n      \"HDAC4\",\n      \"p97/VCP\",\n      \"p35/CDK5R1\",\n      \"PJA2\",\n      \"GABARAPL2\",\n      \"MYLK\",\n      \"LRP6\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}