{"gene":"SIK1","run_date":"2026-04-28T20:42:07","timeline":{"discoveries":[{"year":2007,"finding":"SIK1 functions as a class II HDAC kinase: it directly phosphorylates class II HDACs (e.g., HDAC5), causing their nuclear export and thereby activating MEF2 transcription factors in skeletal myocytes. SIK1 is transcriptionally induced by CREB in response to cAMP signals, establishing a CREB→SIK1→HDAC→MEF2 pathway essential for muscle gene expression and survival.","method":"Viral re-expression of SIK1 in M-ACREB transgenic mice, measurement of class II HDAC phosphorylation, MEF2 reporter assays, dystrophic phenotype rescue","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal in vivo and cellular methods; replicated in subsequent papers","pmids":["17468767"],"is_preprint":false},{"year":2008,"finding":"SIK1 (Thr182) is activated by LKB1-mediated phosphorylation; activated SIK1 then auto-phosphorylates Ser186 (a +4 position site). The Ser186 phospho-site is required for sustained SIK1 activity and is maintained by sequential phosphorylation involving GSK-3β. In C2C12 myoblasts treated with the AMPK agonist AICAR, SIK1 phosphorylates and causes nuclear export of HDAC5, leading to MEF2C activation and PGC-1α gene expression.","method":"In vitro kinase assay with GSK-3β purified from AICAR-treated cells, overexpression of SIK1, inhibitor studies, subcellular fractionation","journal":"Endocrine journal","confidence":"High","confidence_rationale":"Tier 1/2 — in vitro kinase assay plus cellular rescue experiments; consistent with multiple other studies","pmids":["18946175"],"is_preprint":false},{"year":2007,"finding":"SIK1 constitutively associates with the Na+,K+-ATPase (NK) regulatory complex and regulates active sodium transport. Elevated intracellular Na+ triggers Ca2+ influx via the Na+/Ca2+ exchanger, which activates SIK1 via CaM kinase-mediated phosphorylation at Thr-322. Activated SIK1 then phosphorylates PME-1 (phosphatase methylesterase-1), causing its dissociation from a PP2A/PME-1 complex on the NK α-subunit, leading to NK α-subunit dephosphorylation and increased catalytic activity.","method":"Co-immunoprecipitation, in vitro phosphorylation assays, calcium imaging, sodium loading experiments, siRNA knockdown","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP, in vitro kinase assay, multiple orthogonal methods in one study","pmids":["17939993"],"is_preprint":false},{"year":2009,"finding":"SIK1 mediates LKB1-dependent p53 activation during anoikis: SIK1 is required downstream of LKB1 for p53-dependent apoptosis triggered by cell detachment. Loss of SIK1 compromises p53 function and permits anchorage-independent growth and metastatic spread in vivo.","method":"Kinome-wide loss-of-function RNAi screen, in vitro anoikis assays, anchorage-independent growth, in vivo mouse metastasis model, epistasis analysis","journal":"Science signaling","confidence":"High","confidence_rationale":"Tier 2 — kinome-wide screen plus multiple orthogonal validation assays and in vivo epistasis","pmids":["19622832"],"is_preprint":false},{"year":2013,"finding":"In the circadian clock, light-induced CRTC1 coactivates CREB to drive Per1 and Sik1 transcription. SIK1 then creates a negative feedback loop by phosphorylating and inactivating CRTC1, suppressing further light-induced clock shifts. Knockdown of Sik1 in the SCN increases phase shifts and accelerates re-entrainment after jet lag.","method":"Transcriptome analysis of light-regulated SCN genes, in vivo Sik1 knockdown via SCN-targeted lentiviral shRNA, behavioral phase-shift assays, CRTC1 phosphorylation measurements","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 — in vivo loss-of-function with specific behavioral readout plus biochemical pathway placement; published in high-impact journal with multiple methods","pmids":["23993098"],"is_preprint":false},{"year":2019,"finding":"SIK1 and SIK3 mediate key tumor-suppressive effects of LKB1 in NSCLC: conditional genetic loss of Sik1 increases tumor growth in Kras-driven lung cancer mouse models. SIK1/3 loss upregulates AP1 and IL-6 signaling via the SIK substrate CRTC2, which is required for proliferation benefits from SIK loss, placing SIK1 downstream of LKB1 in suppressing CRTC2-driven transcription.","method":"CRISPR-based genetic deletion in NSCLC cell lines and conditional mouse models, gene expression analysis, epistasis with CRTC2","journal":"Cancer discovery","confidence":"High","confidence_rationale":"Tier 2 — CRISPR KO in mouse models plus gene-expression epistasis; replicated across cell lines and in vivo","pmids":["31350328"],"is_preprint":false},{"year":2012,"finding":"SIK1 protein stability during myogenesis is regulated by PKA-mediated phosphorylation at Thr475 within a PEST domain: PKA phosphorylation of Thr475 extends SIK1 half-life by protecting it from proteasomal degradation. In cell-free assays PKA directly phosphorylates Thr475. SIK1 depletion in primary muscle precursor cells impairs MEF2 protein accumulation and myogenic differentiation.","method":"Cycloheximide chase assays, cell-free PKA phosphorylation assay, mutagenesis of Thr475 and PEST domain, primary myoblast siRNA knockdown, differentiation assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1/2 — in vitro kinase assay plus mutagenesis plus primary cell loss-of-function; multiple orthogonal methods","pmids":["23256157"],"is_preprint":false},{"year":2016,"finding":"SIK1 phosphorylates SMRT at Thr1391, which promotes NCoR/SMRT association with TBL1/TBLR1 and disrupts β-catenin binding to the TBL1/TBLR1 complex, thereby inactivating Wnt/β-catenin transcriptional activity. SMRT-T1391A mutant reverses the tumor-suppressive effect of SIK1.","method":"In vitro kinase assay, immunoprecipitation, luciferase reporter, ChIP, SMRT phosphorylation-site mutagenesis, xenograft tumor models","journal":"Journal of hepatology","confidence":"High","confidence_rationale":"Tier 1/2 — in vitro kinase assay plus site-directed mutagenesis plus co-IP plus in vivo xenograft; multiple orthogonal methods","pmids":["26778753"],"is_preprint":false},{"year":2015,"finding":"SIK1 mutations causing developmental epilepsy occur outside the kinase domain; mutant SIK1 proteins retain autophosphorylation and kinase activity toward HDAC5 but show altered subcellular localization (nuclear vs. cytoplasmic distribution) compared to wild-type SIK1. Truncated mutants are resistant to proteasomal degradation.","method":"In vitro autophosphorylation and HDAC5 kinase assays, subcellular fractionation and immunofluorescence in patient-derived cells and transfected cells, cycloheximide chase","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 1/2 — in vitro kinase assay plus localization experiments plus protein stability measurements; multiple methods","pmids":["25839329"],"is_preprint":false},{"year":2015,"finding":"SIK1 forms a complex with SR-B1 via its cytoplasmic C-terminal domain and directly phosphorylates the SR-B1 C-terminal domain. In vitro kinase assays show SIK1-catalyzed phosphorylation of SR-B1 Ser496 is critical for stimulation of selective HDL cholesteryl ester uptake and steroidogenesis. Both SIK1 catalytic activity and its PKA-mediated phosphorylation are required for SR-B1 activation.","method":"Co-immunoprecipitation, in vitro kinase assay, site-directed mutagenesis of SR-B1 Ser496, HDL-BODIPY-CE uptake assay, SIK1 overexpression and knockdown","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay plus mutagenesis plus functional CE uptake assay; rigorous within one study","pmids":["26567857"],"is_preprint":false},{"year":2016,"finding":"SIK1 is recruited to sites of DNA replication via direct interaction with Sld5, a component of the GINS complex. SIK1 phosphorylates MCM2 at five conserved N-terminal residues, which is required for MCM helicase activation. SIK1 depletion causes defective DNA replication.","method":"Co-immunoprecipitation, in vitro kinase assay of MCM2 phosphorylation, siRNA knockdown, DNA replication assays, chromatin fractionation","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP and in vitro kinase assay; single lab with multiple methods","pmids":["27592030"],"is_preprint":false},{"year":2017,"finding":"RNF2 functions as an E3 ubiquitin ligase that directly binds SIK1 and targets it for ubiquitin-mediated proteasomal degradation in hepatocellular carcinoma cells, providing a mechanism for SIK1 downregulation.","method":"Co-immunoprecipitation, ubiquitination assay, RNF2 knockdown and overexpression, xenograft models","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 2/3 — co-IP plus ubiquitination assay; single lab, moderate evidence","pmids":["27911266"],"is_preprint":false},{"year":2018,"finding":"SIK1 suppresses gluconeogenic gene transcription by phosphorylating CRTC1 at S155, S167, S188, and S346, triggering K48-linked polyubiquitination via the RFWD2 ubiquitin ligase and proteasomal degradation of CRTC1. This mechanism is specific to SIK1 (not SIK2 or SIK3).","method":"In vitro kinase assay, phosphorylation-site mutagenesis, ubiquitination assay, proteasome inhibitor experiments, PEPCK luciferase reporter, SIK1 knockdown and overexpression","journal":"Biochimica et biophysica acta. Gene regulatory mechanisms","confidence":"High","confidence_rationale":"Tier 1/2 — in vitro kinase assay plus site mutagenesis plus ubiquitination assay plus reporter; multiple orthogonal methods","pmids":["29408765"],"is_preprint":false},{"year":2023,"finding":"AKT directly binds SIK1 and phosphorylates it, relieving SIK1-mediated repression of STAT3 in a phosphorylation-dependent manner. AKT-phosphorylated SIK1 interacts with 14-3-3 and is translocated to the cytoplasm, where Pin1 isomerase facilitates SIK1 interaction with the E3 ligase ITCH, promoting SIK1 ubiquitination and degradation.","method":"Mass spectrometry-based interactomics, co-immunoprecipitation, in vitro kinase assay, subcellular fractionation, ubiquitination assay, mutagenesis, breast cancer cell phenotypic assays","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 1/2 — MS-based binding, in vitro kinase assay, co-IP, ubiquitination, and functional assays; multiple orthogonal methods","pmids":["36806887"],"is_preprint":false},{"year":2020,"finding":"SIK1 activates phosphodiesterase 4 (PDE4), increasing cAMP degradation and thereby suppressing the cAMP/PKA/CREB pathway to inhibit hepatic gluconeogenesis. This mechanism is distinct from direct CRTC2 phosphorylation and represents an additional route by which SIK1 dampens cAMP signaling.","method":"Primary hepatocyte gluconeogenesis assay, siRNA knockdown of SIK1, pan-SIK inhibitor HG-9-91-01, SIK1 overexpression, direct PDE4 activity measurement, ob/ob mouse model","journal":"Molecular metabolism","confidence":"Medium","confidence_rationale":"Tier 2 — multiple cellular methods plus in vivo validation; single lab","pmids":["32599076"],"is_preprint":false},{"year":2010,"finding":"Sik1 knockout in mouse embryonic stem cells impairs cardiomyogenesis by reducing expression of the cyclin-dependent kinase inhibitor p57Kip2, delaying cell cycle exit required for terminal cardiomyocyte differentiation.","method":"Gene-trap sik1 null ES cells, embryoid body differentiation assay, expression profiling, cell cycle analysis","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — genetic null model with defined cellular phenotype; single lab","pmids":["20140255"],"is_preprint":false},{"year":2011,"finding":"Cocaine activates SIK1 in rat striatum via phosphorylation at Thr-182, causing SIK1 nuclear import. Nuclear SIK1 then phosphorylates HDAC5, driving its nuclear-to-cytoplasmic shuttling and activating MEF2C transcription. SIK1 activation also causes nuclear export of TORC1/3 coactivators.","method":"In vivo cocaine treatment, phospho-Thr182 SIK1 immunoblot, subcellular fractionation for SIK1, HDAC5, and TORC1/3, MEF2C gene expression","journal":"Synapse (New York, N.Y.)","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo phosphorylation and fractionation; single lab, moderate evidence","pmids":["21954104"],"is_preprint":false},{"year":2015,"finding":"In steroidogenic cells, SIK1 represses StAR expression through inhibition of CRTC2-mediated transcription and splicing processing. SIK1 is rapidly induced by cAMP/PKA signaling and provides a negative feedback brake on StAR gene activation.","method":"Fluorescence in situ hybridization (FISH) for StAR RNA in single cells, SIK1 overexpression and siRNA knockdown in Y1 and MA10 cells, qPCR","journal":"Molecular and cellular endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 — single-cell FISH plus genetic manipulation; single lab","pmids":["25662274"],"is_preprint":false},{"year":2020,"finding":"PKA-mediated phosphorylation of SIK1 at its conserved site S577 negatively regulates sleep need: SIK1-S577A knock-in mice show increased NREM sleep time and higher NREM delta power, indicating that PKA phosphorylation of SIK1 suppresses sleep pressure.","method":"CRISPR knock-in mice (Sik1S577A), EEG/EMG sleep recording, sleep deprivation protocol, circadian behavior assays","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 — precise knock-in mutagenesis with defined electrophysiological phenotype; single lab","pmids":["32457359"],"is_preprint":false},{"year":2021,"finding":"SIK1 C-terminal truncation mutations associated with autism/epilepsy shift SIK1 subcellular distribution from exclusively nuclear to both nuclear and cytoplasmic. In SIK1-MT mice generated by CRISPR, this mislocalization is associated with increased excitatory synaptic transmission, disrupted E/I balance in cortical pyramidal neurons, and repetitive behavior.","method":"CRISPR/Cas9 knock-in mice, immunofluorescence localization, whole-cell electrophysiology, behavioral assays","journal":"Frontiers in molecular neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 — precise genetic model plus electrophysiology plus behavior; single lab","pmids":["34295222"],"is_preprint":false},{"year":2025,"finding":"SIK1 promotes ferroptosis resistance in pancreatic cancer via a HDAC5-STAT6-SLC7A11 axis: SIK1 phosphorylates HDAC5 at Ser498, promoting its interaction with 14-3-3 and protecting HDAC5 from TRIM28-mediated ubiquitination and degradation. Stabilized HDAC5 deacetylates STAT6, enhancing its transcriptional activation of SLC7A11, which confers resistance to ferroptosis.","method":"In vitro kinase assay (SIK1 phosphorylation of HDAC5 Ser498), co-immunoprecipitation, ubiquitination assay, site-directed mutagenesis, HDAC activity assay, organoid and PDX models","journal":"Cancer letters","confidence":"High","confidence_rationale":"Tier 1/2 — in vitro kinase assay plus mutagenesis plus co-IP plus ubiquitination plus PDX validation; multiple orthogonal methods","pmids":["40250791"],"is_preprint":false},{"year":2015,"finding":"Arterial blood pressure regulation by SIK1 involves TGF-β1 signaling: SIK1 knockout mice on high-salt diet exhibit upregulated TGF-β1 signaling, increased endothelin-1 expression, and enhanced vascular smooth muscle cell contractile marker expression. In vitro SIK1 knockdown in VSMCs increases contractile markers and endothelin-1, while knockdown in adventitial fibroblasts increases collagen deposition.","method":"SIK1 knockout mouse model, high-salt diet challenge, in vitro SIK1 siRNA knockdown in VSMCs and fibroblasts, blood pressure telemetry, Western blot, histology","journal":"Circulation research","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO mouse plus in vitro validation; single lab","pmids":["25556206"],"is_preprint":false},{"year":2023,"finding":"SIK1-selective inhibitors that engage two differentiating features of the SIK catalytic site reduce phosphorylation of the SIK substrate CRTC3 at Ser329, suppress pro-inflammatory cytokine production, and induce anti-inflammatory IL-10 in myeloid cells following LPS challenge, demonstrating SIK1/2 as key regulators of innate immune cytokine balance via the CRTC-CREB axis.","method":"Structure-based inhibitor design, in vitro kinase selectivity panel, phospho-CRTC3 antibody-based cellular assay, LPS-stimulated macrophage cytokine assays, murine colitis model","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1/2 — structure-based design plus biochemical substrate assay plus in vivo disease model; multiple methods","pmids":["38147543"],"is_preprint":false},{"year":2014,"finding":"Gastrin induces SIK1 expression in gastric adenocarcinoma cells via CCK2 receptor-Gq/G11 signaling, causing LKB1 Ser428 phosphorylation and SIK1 Thr182 phosphorylation. Activated SIK1 phosphorylates HDAC4 and promotes its nuclear export, enhancing CRE-, SRE-, AP1-, and NF-κB-driven transcription. SIK1 knockdown increases cell migration.","method":"SIK1 overexpression and siRNA knockdown, phosphorylation-specific immunoblot, luciferase reporter assays, subcellular fractionation of HDACs, transwell migration assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — multiple cellular assays with mechanistic follow-up; single lab","pmids":["25384047"],"is_preprint":false},{"year":2004,"finding":"SNF1LK (SIK1) kinase domain expression in CHO cells causes cell cycle arrest with re-replication to 8N and 16N DNA content without cell division, suggesting a role in G2/M regulation. The protein is expressed in early cardiac and skeletal muscle progenitor cells during mouse embryogenesis.","method":"Tetracycline-inducible SNF1LK kinase domain expression in CHO cells, flow cytometry DNA content analysis, in situ hybridization for developmental expression","journal":"Genomics","confidence":"Low","confidence_rationale":"Tier 3 — single overexpression experiment with phenotypic readout; no mechanistic target identified","pmids":["15177563"],"is_preprint":false}],"current_model":"SIK1 is a serine/threonine kinase of the AMPK family that is activated by LKB1-mediated phosphorylation at Thr182 (with sustained activity requiring auto-phosphorylation at Ser186 and GSK-3β input), and negatively regulated by PKA-mediated phosphorylation at Ser577/Thr475 (which promotes 14-3-3 binding, cytoplasmic translocation, and proteasomal degradation via ITCH); once active, SIK1 suppresses cAMP-CREB transcriptional output by phosphorylating and inactivating CRTC coactivators and by activating PDE4, phosphorylates and drives nuclear export of class IIa HDACs (HDAC4/5) to activate MEF2, phosphorylates SR-B1 to stimulate cholesterol uptake, phosphorylates SMRT to inactivate Wnt/β-catenin, phosphorylates HDAC5-Ser498 to stabilize it and activate STAT6-SLC7A11 ferroptosis resistance, and links LKB1 to p53-dependent anoikis suppression, collectively placing SIK1 as a central integrator of energy, sodium, cAMP, and stress signals that controls muscle differentiation, circadian entrainment, gluconeogenesis, vascular sodium handling, and tumor suppression."},"narrative":{"teleology":[{"year":2004,"claim":"Early characterization showed that forced expression of the SIK1 kinase domain causes endoreduplication without division, hinting at a cell-cycle regulatory role, but the molecular target was unknown.","evidence":"Inducible kinase-domain expression in CHO cells with flow cytometry and in situ hybridization in mouse embryos","pmids":["15177563"],"confidence":"Low","gaps":["No substrate or downstream pathway identified","Overexpression artifact not ruled out","Endoreduplication phenotype not independently confirmed"]},{"year":2007,"claim":"Two studies established SIK1's first direct substrates and physiological roles: SIK1 phosphorylates class IIa HDACs to activate MEF2-dependent muscle gene expression, and SIK1 phosphorylates PME-1 at the Na+,K+-ATPase complex to regulate sodium transport, revealing SIK1 as a signal-responsive kinase with both transcriptional and metabolic outputs.","evidence":"Viral re-expression in dystrophic mice with MEF2 reporter and HDAC phosphorylation assays; co-IP, in vitro kinase assay, and sodium-loading experiments in renal epithelial cells","pmids":["17468767","17939993"],"confidence":"High","gaps":["Whether HDAC phosphorylation sites are identical to those used by other AMPK-family kinases was not resolved","The CaM kinase–Thr322 activation axis for SIK1 at the NK complex was not confirmed in vivo"]},{"year":2008,"claim":"The activation mechanism of SIK1 was dissected: LKB1 phosphorylates Thr182 to initiate activity, SIK1 auto-phosphorylates Ser186 for sustained signaling, and GSK-3β contributes to maintaining the Ser186 phosphosite, placing SIK1 at a convergence of LKB1 and Wnt/insulin pathways.","evidence":"In vitro kinase assay with purified kinases, mutagenesis, AICAR-treated C2C12 myoblasts with subcellular fractionation","pmids":["18946175"],"confidence":"High","gaps":["Structural basis for LKB1→SIK1→auto-phosphorylation cascade not determined","Contribution of GSK-3β in vivo remains indirect"]},{"year":2009,"claim":"A kinome-wide screen revealed that SIK1 is essential for LKB1-dependent p53 activation during anoikis, establishing SIK1 as a tumor suppressor that prevents anchorage-independent growth and metastasis.","evidence":"RNAi screen, in vitro anoikis assays, soft agar, and mouse metastasis model with epistasis analysis","pmids":["19622832"],"confidence":"High","gaps":["Direct SIK1 substrate linking to p53 stabilization not identified","Whether SIK1 tumor-suppressive function is kinase-activity-dependent was not tested"]},{"year":2010,"claim":"SIK1 knockout ES cells revealed a role in cardiomyocyte differentiation via p57Kip2-dependent cell-cycle exit, broadening SIK1's functions beyond skeletal muscle.","evidence":"Gene-trap null ES cells, embryoid body differentiation, expression profiling, cell-cycle analysis","pmids":["20140255"],"confidence":"Medium","gaps":["Mechanism by which SIK1 controls p57Kip2 expression is unknown","Not validated in whole-animal cardiac development"]},{"year":2012,"claim":"PKA phosphorylation of SIK1 at Thr475 was shown to stabilize SIK1 protein by protecting it from proteasomal degradation, revealing a feed-forward mechanism wherein cAMP signaling sustains SIK1 levels during myogenic differentiation.","evidence":"Cycloheximide chase, cell-free PKA kinase assay, PEST-domain and Thr475 mutagenesis, primary myoblast siRNA knockdown","pmids":["23256157"],"confidence":"High","gaps":["E3 ligase responsible for basal SIK1 turnover in myoblasts was not identified at this time"]},{"year":2013,"claim":"SIK1 was placed in the circadian clock as a light-induced negative-feedback kinase: SIK1 phosphorylates and inactivates CRTC1 in the SCN to limit CREB-driven Per1 transcription, gating the magnitude of photic phase shifts.","evidence":"Transcriptomics of light-treated SCN, in vivo lentiviral shRNA knockdown of Sik1, behavioral phase-shift assays, CRTC1 phosphorylation measurements","pmids":["23993098"],"confidence":"High","gaps":["Whether SIK2/SIK3 have redundant roles in circadian entrainment was not fully dissected","CRTC1 phosphorylation sites targeted by SIK1 in SCN not mapped"]},{"year":2015,"claim":"Multiple 2015 studies expanded SIK1's substrate repertoire and disease connections: SIK1 phosphorylates SR-B1 Ser496 to stimulate HDL cholesterol uptake; SIK1 represses StAR via CRTC2 in steroidogenic cells; SIK1 loss in vascular smooth muscle derepresses TGF-β1/endothelin-1 to elevate blood pressure on high-salt diet; and de novo SIK1 mutations cause developmental epilepsy through altered subcellular localization rather than loss of kinase activity.","evidence":"In vitro kinase assays, co-IP, mutagenesis, HDL-CE uptake assay, single-cell FISH, SIK1 KO mice on high-salt diet, patient-derived cell immunofluorescence and cycloheximide chase","pmids":["26567857","25662274","25556206","25839329"],"confidence":"High","gaps":["Whether SR-B1 phosphorylation occurs in vivo at the hepatic level is unknown","Epilepsy-causing mutations' effect on specific HDAC or CRTC substrates in neurons not fully resolved"]},{"year":2016,"claim":"SIK1 was shown to suppress Wnt/β-catenin signaling by phosphorylating SMRT-Thr1391, promoting NCoR/SMRT–TBL1 complex formation and displacing β-catenin, establishing a direct kinase-substrate mechanism for SIK1's tumor-suppressive role in hepatocellular carcinoma.","evidence":"In vitro kinase assay, co-IP, ChIP, SMRT-T1391A mutagenesis, xenograft tumor models","pmids":["26778753"],"confidence":"High","gaps":["Whether SMRT phosphorylation by SIK1 operates in non-hepatic Wnt-driven cancers is untested"]},{"year":2016,"claim":"SIK1 was found to interact with the GINS complex subunit Sld5 and phosphorylate MCM2 at N-terminal residues required for helicase activation, linking SIK1 to DNA replication initiation.","evidence":"Co-IP, in vitro kinase assay of MCM2, siRNA knockdown, DNA replication assays, chromatin fractionation","pmids":["27592030"],"confidence":"Medium","gaps":["Independent confirmation of SIK1–GINS interaction is lacking","Whether kinase-dead SIK1 phenocopies the replication defect is untested","In vivo relevance to replication licensing not established"]},{"year":2018,"claim":"The CRTC1 phosphorylation mechanism by SIK1 was mapped to four specific serine sites, and downstream K48-ubiquitination via RFWD2 was identified, explaining how SIK1 specifically targets CRTC1 for proteasomal degradation to suppress gluconeogenic gene expression.","evidence":"In vitro kinase assay, phosphosite mutagenesis, ubiquitination assay with proteasome inhibitor, PEPCK luciferase reporter","pmids":["29408765"],"confidence":"High","gaps":["Whether RFWD2-mediated CRTC1 degradation is regulated by feeding/fasting in vivo is unknown"]},{"year":2019,"claim":"Genetic studies in Kras-driven lung cancer models demonstrated that SIK1 (with SIK3) is the critical tumor-suppressive effector downstream of LKB1, acting through CRTC2 to restrain AP1 and IL-6 pro-tumorigenic transcription.","evidence":"CRISPR deletion of Sik1 in NSCLC cell lines and conditional mouse models, gene expression analysis, epistasis with CRTC2","pmids":["31350328"],"confidence":"High","gaps":["Individual contribution of SIK1 vs. SIK3 not fully separated","Whether pharmacological SIK activation could substitute for LKB1 loss in NSCLC is unexplored"]},{"year":2020,"claim":"Two studies revealed additional SIK1 regulatory outputs: SIK1 activates PDE4 to degrade cAMP independently of CRTC phosphorylation, providing an extra brake on hepatic gluconeogenesis; and PKA phosphorylation of SIK1 at Ser577 suppresses sleep need, as shown by increased NREM sleep in Sik1-S577A knock-in mice.","evidence":"Primary hepatocyte assays, PDE4 activity measurement, ob/ob mouse model; CRISPR Sik1-S577A knock-in mice with EEG/EMG sleep recording","pmids":["32599076","32457359"],"confidence":"Medium","gaps":["Direct SIK1 phosphorylation site on PDE4 is not identified","Sleep phenotype mechanism (which SIK1 substrate in neurons) is unknown"]},{"year":2021,"claim":"CRISPR knock-in mice bearing autism/epilepsy-associated SIK1 truncations showed that cytoplasmic mislocalization of mutant SIK1 increases excitatory synaptic transmission and disrupts cortical E/I balance, providing a circuit-level mechanism for the neurodevelopmental phenotype.","evidence":"CRISPR/Cas9 knock-in mice, immunofluorescence, whole-cell electrophysiology, behavioral assays","pmids":["34295222"],"confidence":"Medium","gaps":["Whether mislocalized SIK1 gains cytoplasmic substrates or loses nuclear ones is unresolved","Specific synaptic SIK1 substrates not identified"]},{"year":2023,"claim":"The full degradation cascade for SIK1 in cancer was delineated: AKT phosphorylates SIK1, enabling 14-3-3 binding and cytoplasmic translocation, where Pin1 isomerase facilitates ITCH-mediated ubiquitination and proteasomal destruction, thereby relieving SIK1 repression of STAT3 and promoting tumor progression.","evidence":"MS-based interactomics, co-IP, in vitro kinase assay, ubiquitination assay, mutagenesis, breast cancer cell phenotypic assays","pmids":["36806887"],"confidence":"High","gaps":["Whether ITCH-mediated SIK1 degradation operates outside breast cancer contexts is untested","Relative contributions of AKT vs. PKA to SIK1 cytoplasmic translocation not compared"]},{"year":2023,"claim":"Structure-based SIK1/2-selective inhibitors validated the CRTC-CREB axis as the key anti-inflammatory output of SIK activity: inhibition dephosphorylates CRTC3 at Ser329, suppresses pro-inflammatory cytokines, and induces IL-10 in macrophages.","evidence":"Structure-based inhibitor design, in vitro kinase selectivity panel, phospho-CRTC3 cellular assay, LPS-stimulated macrophage assay, murine colitis model","pmids":["38147543"],"confidence":"High","gaps":["Whether SIK1 or SIK2 is the dominant isoform controlling innate immune cytokine balance is not resolved","Long-term immunological consequences of SIK inhibition unknown"]},{"year":2025,"claim":"A new SIK1–HDAC5 axis was uncovered in pancreatic cancer: SIK1 phosphorylates HDAC5 at Ser498, stabilizing it via 14-3-3 and protecting it from TRIM28-mediated degradation; stabilized HDAC5 deacetylates STAT6 to drive SLC7A11 expression and ferroptosis resistance.","evidence":"In vitro kinase assay, co-IP, ubiquitination assay, mutagenesis, organoid and PDX models","pmids":["40250791"],"confidence":"High","gaps":["Whether HDAC5-Ser498 phosphorylation is a general SIK1 output across tissues or context-specific is unknown","Relationship between ferroptosis-protective and tumor-suppressive functions of SIK1 is unresolved"]},{"year":null,"claim":"Key unresolved questions include the structural basis of SIK1's substrate selectivity versus SIK2/SIK3, the identity of neuronal substrates responsible for E/I imbalance in SIK1-associated epilepsy, and how context determines whether SIK1 acts as tumor suppressor (via CRTC/SMRT) or tumor promoter (via HDAC5-STAT6-ferroptosis resistance).","evidence":"","pmids":[],"confidence":"Low","gaps":["No crystal structure of full-length SIK1 available","Neuronal SIK1 substrates causing synaptic phenotype unidentified","Context-dependency of SIK1 pro- vs anti-tumor effects not mechanistically reconciled"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,2,7,8,9,10,12,20]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[4,5,14,17]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[8,16,19]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[8,13,19]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[2]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,4,7,13,14,22]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,4,5,12,17]},{"term_id":"R-HSA-9909396","term_label":"Circadian clock","supporting_discovery_ids":[4,18]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[0,6,15]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[3,20]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[5,7,20]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[22]}],"complexes":[],"partners":["HDAC5","HDAC4","CRTC1","CRTC2","LKB1","SR-B1","SMRT","14-3-3"],"other_free_text":[]},"mechanistic_narrative":"SIK1 is an LKB1-activated, AMPK-family serine/threonine kinase that functions as a central integrator of cAMP, energy, and stress signaling by phosphorylating transcriptional regulators to reshape gene expression programs in muscle, liver, brain, vasculature, and immune cells. Its principal substrates are CRTC coactivators (CRTC1–3), whose SIK1-mediated phosphorylation triggers 14-3-3 binding, nuclear export, and—in the case of CRTC1—RFWD2-dependent proteasomal degradation, thereby suppressing CREB-dependent transcription of gluconeogenic, circadian, and steroidogenic genes [PMID:23993098, PMID:29408765, PMID:25662274]; SIK1 also phosphorylates class IIa HDACs (HDAC4/5) to drive their cytoplasmic translocation and activate MEF2-dependent myogenic and neuronal gene programs, and phosphorylates HDAC5-Ser498 to stabilize HDAC5 and promote STAT6-SLC7A11-mediated ferroptosis resistance [PMID:17468767, PMID:40250791]. SIK1 activity is positively regulated by LKB1 phosphorylation at Thr182 and autophosphorylation at Ser186, and negatively regulated by AKT- and PKA-mediated phosphorylation that promotes 14-3-3 binding, cytoplasmic sequestration, and ITCH-dependent ubiquitin–proteasomal degradation [PMID:18946175, PMID:36806887]. De novo mutations in SIK1 cause a developmental epileptic encephalopathy, with disease-associated truncations shifting SIK1 from nuclear to cytoplasmic distribution without abolishing kinase activity, disrupting excitatory/inhibitory synaptic balance [PMID:25839329, PMID:34295222]."},"prefetch_data":{"uniprot":{"accession":"P57059","full_name":"Serine/threonine-protein kinase SIK1","aliases":["Salt-inducible kinase 1","SIK-1","Serine/threonine-protein kinase SNF1-like kinase 1","Serine/threonine-protein kinase SNF1LK"],"length_aa":783,"mass_kda":84.9,"function":"Serine/threonine-protein kinase involved in various processes such as cell cycle regulation, gluconeogenesis and lipogenesis regulation, muscle growth and differentiation and tumor suppression. Phosphorylates HDAC4, HDAC5, PPME1, SREBF1, CRTC1/TORC1. Inhibits CREB activity by phosphorylating and inhibiting activity of TORCs, the CREB-specific coactivators, like CRTC2/TORC2 and CRTC3/TORC3 in response to cAMP signaling (PubMed:29211348). Acts as a tumor suppressor and plays a key role in p53/TP53-dependent anoikis, a type of apoptosis triggered by cell detachment: required for phosphorylation of p53/TP53 in response to loss of adhesion and is able to suppress metastasis. Part of a sodium-sensing signaling network, probably by mediating phosphorylation of PPME1: following increases in intracellular sodium, SIK1 is activated by CaMK1 and phosphorylates PPME1 subunit of protein phosphatase 2A (PP2A), leading to dephosphorylation of sodium/potassium-transporting ATPase ATP1A1 and subsequent increase activity of ATP1A1. Acts as a regulator of muscle cells by phosphorylating and inhibiting class II histone deacetylases HDAC4 and HDAC5, leading to promote expression of MEF2 target genes in myocytes. Also required during cardiomyogenesis by regulating the exit of cardiomyoblasts from the cell cycle via down-regulation of CDKN1C/p57Kip2. Acts as a regulator of hepatic gluconeogenesis by phosphorylating and repressing the CREB-specific coactivators CRTC1/TORC1 and CRTC2/TORC2, leading to inhibit CREB activity. Also regulates hepatic lipogenesis by phosphorylating and inhibiting SREBF1. In concert with CRTC1/TORC1, regulates the light-induced entrainment of the circadian clock by attenuating PER1 induction; represses CREB-mediated transcription of PER1 by phosphorylating and deactivating CRTC1/TORC1 (By similarity)","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/P57059/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SIK1","classification":"Not Classified","n_dependent_lines":9,"n_total_lines":1208,"dependency_fraction":0.0074503311258278145},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SIK1","total_profiled":1310},"omim":[{"mim_id":"616341","title":"DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 30; DEE30","url":"https://www.omim.org/entry/616341"},{"mim_id":"614776","title":"SIK FAMILY KINASE 3; SIK3","url":"https://www.omim.org/entry/614776"},{"mim_id":"614545","title":"ENDOPLASMIC RETICULUM MEMBRANE PROTEIN COMPLEX, SUBUNIT 10; EMC10","url":"https://www.omim.org/entry/614545"},{"mim_id":"605705","title":"SALT-INDUCIBLE KINASE 1; SIK1","url":"https://www.omim.org/entry/605705"},{"mim_id":"312612","title":"RETINITIS PIGMENTOSA 6; RP6","url":"https://www.omim.org/entry/312612"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Vesicles","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SIK1"},"hgnc":{"alias_symbol":["msk"],"prev_symbol":["SNF1LK"]},"alphafold":{"accession":"P57059","domains":[{"cath_id":"3.30.200.20","chopping":"24-104","consensus_level":"medium","plddt":94.1394,"start":24,"end":104},{"cath_id":"1.10.510.10","chopping":"110-279","consensus_level":"high","plddt":93.9548,"start":110,"end":279},{"cath_id":"-","chopping":"307-353","consensus_level":"medium","plddt":90.7336,"start":307,"end":353}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P57059","model_url":"https://alphafold.ebi.ac.uk/files/AF-P57059-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P57059-F1-predicted_aligned_error_v6.png","plddt_mean":59.34},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SIK1","jax_strain_url":"https://www.jax.org/strain/search?query=SIK1"},"sequence":{"accession":"P57059","fasta_url":"https://rest.uniprot.org/uniprotkb/P57059.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P57059/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P57059"}},"corpus_meta":[{"pmid":"25801821","id":"PMC_25801821","title":"Memorial 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SIK1-cAMP/CREB signaling to suppress hepatic gluconeogenesis.","date":"2022","source":"European journal of medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/35152093","citation_count":12,"is_preprint":false},{"pmid":"27573101","id":"PMC_27573101","title":"New non-renal congenital disorders associated with medullary sponge kidney (MSK) support the pathogenic role of GDNF and point to the diagnosis of MSK in recurrent stone formers.","date":"2016","source":"Urolithiasis","url":"https://pubmed.ncbi.nlm.nih.gov/27573101","citation_count":12,"is_preprint":false},{"pmid":"34504479","id":"PMC_34504479","title":"Virulent Drexlervirial Bacteriophage MSK, Morphological and Genome Resemblance With Rtp Bacteriophage Inhibits the Multidrug-Resistant Bacteria.","date":"2021","source":"Frontiers in microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/34504479","citation_count":12,"is_preprint":false},{"pmid":"32020874","id":"PMC_32020874","title":"Zhenqing recipe attenuates non-alcoholic 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SIK1 is transcriptionally induced by CREB in response to cAMP signals, establishing a CREB→SIK1→HDAC→MEF2 pathway essential for muscle gene expression and survival.\",\n      \"method\": \"Viral re-expression of SIK1 in M-ACREB transgenic mice, measurement of class II HDAC phosphorylation, MEF2 reporter assays, dystrophic phenotype rescue\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal in vivo and cellular methods; replicated in subsequent papers\",\n      \"pmids\": [\"17468767\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SIK1 (Thr182) is activated by LKB1-mediated phosphorylation; activated SIK1 then auto-phosphorylates Ser186 (a +4 position site). The Ser186 phospho-site is required for sustained SIK1 activity and is maintained by sequential phosphorylation involving GSK-3β. In C2C12 myoblasts treated with the AMPK agonist AICAR, SIK1 phosphorylates and causes nuclear export of HDAC5, leading to MEF2C activation and PGC-1α gene expression.\",\n      \"method\": \"In vitro kinase assay with GSK-3β purified from AICAR-treated cells, overexpression of SIK1, inhibitor studies, subcellular fractionation\",\n      \"journal\": \"Endocrine journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — in vitro kinase assay plus cellular rescue experiments; consistent with multiple other studies\",\n      \"pmids\": [\"18946175\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SIK1 constitutively associates with the Na+,K+-ATPase (NK) regulatory complex and regulates active sodium transport. Elevated intracellular Na+ triggers Ca2+ influx via the Na+/Ca2+ exchanger, which activates SIK1 via CaM kinase-mediated phosphorylation at Thr-322. Activated SIK1 then phosphorylates PME-1 (phosphatase methylesterase-1), causing its dissociation from a PP2A/PME-1 complex on the NK α-subunit, leading to NK α-subunit dephosphorylation and increased catalytic activity.\",\n      \"method\": \"Co-immunoprecipitation, in vitro phosphorylation assays, calcium imaging, sodium loading experiments, siRNA knockdown\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP, in vitro kinase assay, multiple orthogonal methods in one study\",\n      \"pmids\": [\"17939993\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"SIK1 mediates LKB1-dependent p53 activation during anoikis: SIK1 is required downstream of LKB1 for p53-dependent apoptosis triggered by cell detachment. Loss of SIK1 compromises p53 function and permits anchorage-independent growth and metastatic spread in vivo.\",\n      \"method\": \"Kinome-wide loss-of-function RNAi screen, in vitro anoikis assays, anchorage-independent growth, in vivo mouse metastasis model, epistasis analysis\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — kinome-wide screen plus multiple orthogonal validation assays and in vivo epistasis\",\n      \"pmids\": [\"19622832\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"In the circadian clock, light-induced CRTC1 coactivates CREB to drive Per1 and Sik1 transcription. SIK1 then creates a negative feedback loop by phosphorylating and inactivating CRTC1, suppressing further light-induced clock shifts. Knockdown of Sik1 in the SCN increases phase shifts and accelerates re-entrainment after jet lag.\",\n      \"method\": \"Transcriptome analysis of light-regulated SCN genes, in vivo Sik1 knockdown via SCN-targeted lentiviral shRNA, behavioral phase-shift assays, CRTC1 phosphorylation measurements\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo loss-of-function with specific behavioral readout plus biochemical pathway placement; published in high-impact journal with multiple methods\",\n      \"pmids\": [\"23993098\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SIK1 and SIK3 mediate key tumor-suppressive effects of LKB1 in NSCLC: conditional genetic loss of Sik1 increases tumor growth in Kras-driven lung cancer mouse models. SIK1/3 loss upregulates AP1 and IL-6 signaling via the SIK substrate CRTC2, which is required for proliferation benefits from SIK loss, placing SIK1 downstream of LKB1 in suppressing CRTC2-driven transcription.\",\n      \"method\": \"CRISPR-based genetic deletion in NSCLC cell lines and conditional mouse models, gene expression analysis, epistasis with CRTC2\",\n      \"journal\": \"Cancer discovery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — CRISPR KO in mouse models plus gene-expression epistasis; replicated across cell lines and in vivo\",\n      \"pmids\": [\"31350328\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"SIK1 protein stability during myogenesis is regulated by PKA-mediated phosphorylation at Thr475 within a PEST domain: PKA phosphorylation of Thr475 extends SIK1 half-life by protecting it from proteasomal degradation. In cell-free assays PKA directly phosphorylates Thr475. SIK1 depletion in primary muscle precursor cells impairs MEF2 protein accumulation and myogenic differentiation.\",\n      \"method\": \"Cycloheximide chase assays, cell-free PKA phosphorylation assay, mutagenesis of Thr475 and PEST domain, primary myoblast siRNA knockdown, differentiation assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — in vitro kinase assay plus mutagenesis plus primary cell loss-of-function; multiple orthogonal methods\",\n      \"pmids\": [\"23256157\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SIK1 phosphorylates SMRT at Thr1391, which promotes NCoR/SMRT association with TBL1/TBLR1 and disrupts β-catenin binding to the TBL1/TBLR1 complex, thereby inactivating Wnt/β-catenin transcriptional activity. SMRT-T1391A mutant reverses the tumor-suppressive effect of SIK1.\",\n      \"method\": \"In vitro kinase assay, immunoprecipitation, luciferase reporter, ChIP, SMRT phosphorylation-site mutagenesis, xenograft tumor models\",\n      \"journal\": \"Journal of hepatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — in vitro kinase assay plus site-directed mutagenesis plus co-IP plus in vivo xenograft; multiple orthogonal methods\",\n      \"pmids\": [\"26778753\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SIK1 mutations causing developmental epilepsy occur outside the kinase domain; mutant SIK1 proteins retain autophosphorylation and kinase activity toward HDAC5 but show altered subcellular localization (nuclear vs. cytoplasmic distribution) compared to wild-type SIK1. Truncated mutants are resistant to proteasomal degradation.\",\n      \"method\": \"In vitro autophosphorylation and HDAC5 kinase assays, subcellular fractionation and immunofluorescence in patient-derived cells and transfected cells, cycloheximide chase\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — in vitro kinase assay plus localization experiments plus protein stability measurements; multiple methods\",\n      \"pmids\": [\"25839329\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SIK1 forms a complex with SR-B1 via its cytoplasmic C-terminal domain and directly phosphorylates the SR-B1 C-terminal domain. In vitro kinase assays show SIK1-catalyzed phosphorylation of SR-B1 Ser496 is critical for stimulation of selective HDL cholesteryl ester uptake and steroidogenesis. Both SIK1 catalytic activity and its PKA-mediated phosphorylation are required for SR-B1 activation.\",\n      \"method\": \"Co-immunoprecipitation, in vitro kinase assay, site-directed mutagenesis of SR-B1 Ser496, HDL-BODIPY-CE uptake assay, SIK1 overexpression and knockdown\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay plus mutagenesis plus functional CE uptake assay; rigorous within one study\",\n      \"pmids\": [\"26567857\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SIK1 is recruited to sites of DNA replication via direct interaction with Sld5, a component of the GINS complex. SIK1 phosphorylates MCM2 at five conserved N-terminal residues, which is required for MCM helicase activation. SIK1 depletion causes defective DNA replication.\",\n      \"method\": \"Co-immunoprecipitation, in vitro kinase assay of MCM2 phosphorylation, siRNA knockdown, DNA replication assays, chromatin fractionation\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP and in vitro kinase assay; single lab with multiple methods\",\n      \"pmids\": [\"27592030\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"RNF2 functions as an E3 ubiquitin ligase that directly binds SIK1 and targets it for ubiquitin-mediated proteasomal degradation in hepatocellular carcinoma cells, providing a mechanism for SIK1 downregulation.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, RNF2 knockdown and overexpression, xenograft models\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2/3 — co-IP plus ubiquitination assay; single lab, moderate evidence\",\n      \"pmids\": [\"27911266\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SIK1 suppresses gluconeogenic gene transcription by phosphorylating CRTC1 at S155, S167, S188, and S346, triggering K48-linked polyubiquitination via the RFWD2 ubiquitin ligase and proteasomal degradation of CRTC1. This mechanism is specific to SIK1 (not SIK2 or SIK3).\",\n      \"method\": \"In vitro kinase assay, phosphorylation-site mutagenesis, ubiquitination assay, proteasome inhibitor experiments, PEPCK luciferase reporter, SIK1 knockdown and overexpression\",\n      \"journal\": \"Biochimica et biophysica acta. Gene regulatory mechanisms\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — in vitro kinase assay plus site mutagenesis plus ubiquitination assay plus reporter; multiple orthogonal methods\",\n      \"pmids\": [\"29408765\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"AKT directly binds SIK1 and phosphorylates it, relieving SIK1-mediated repression of STAT3 in a phosphorylation-dependent manner. AKT-phosphorylated SIK1 interacts with 14-3-3 and is translocated to the cytoplasm, where Pin1 isomerase facilitates SIK1 interaction with the E3 ligase ITCH, promoting SIK1 ubiquitination and degradation.\",\n      \"method\": \"Mass spectrometry-based interactomics, co-immunoprecipitation, in vitro kinase assay, subcellular fractionation, ubiquitination assay, mutagenesis, breast cancer cell phenotypic assays\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — MS-based binding, in vitro kinase assay, co-IP, ubiquitination, and functional assays; multiple orthogonal methods\",\n      \"pmids\": [\"36806887\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SIK1 activates phosphodiesterase 4 (PDE4), increasing cAMP degradation and thereby suppressing the cAMP/PKA/CREB pathway to inhibit hepatic gluconeogenesis. This mechanism is distinct from direct CRTC2 phosphorylation and represents an additional route by which SIK1 dampens cAMP signaling.\",\n      \"method\": \"Primary hepatocyte gluconeogenesis assay, siRNA knockdown of SIK1, pan-SIK inhibitor HG-9-91-01, SIK1 overexpression, direct PDE4 activity measurement, ob/ob mouse model\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple cellular methods plus in vivo validation; single lab\",\n      \"pmids\": [\"32599076\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Sik1 knockout in mouse embryonic stem cells impairs cardiomyogenesis by reducing expression of the cyclin-dependent kinase inhibitor p57Kip2, delaying cell cycle exit required for terminal cardiomyocyte differentiation.\",\n      \"method\": \"Gene-trap sik1 null ES cells, embryoid body differentiation assay, expression profiling, cell cycle analysis\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic null model with defined cellular phenotype; single lab\",\n      \"pmids\": [\"20140255\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Cocaine activates SIK1 in rat striatum via phosphorylation at Thr-182, causing SIK1 nuclear import. Nuclear SIK1 then phosphorylates HDAC5, driving its nuclear-to-cytoplasmic shuttling and activating MEF2C transcription. SIK1 activation also causes nuclear export of TORC1/3 coactivators.\",\n      \"method\": \"In vivo cocaine treatment, phospho-Thr182 SIK1 immunoblot, subcellular fractionation for SIK1, HDAC5, and TORC1/3, MEF2C gene expression\",\n      \"journal\": \"Synapse (New York, N.Y.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo phosphorylation and fractionation; single lab, moderate evidence\",\n      \"pmids\": [\"21954104\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"In steroidogenic cells, SIK1 represses StAR expression through inhibition of CRTC2-mediated transcription and splicing processing. SIK1 is rapidly induced by cAMP/PKA signaling and provides a negative feedback brake on StAR gene activation.\",\n      \"method\": \"Fluorescence in situ hybridization (FISH) for StAR RNA in single cells, SIK1 overexpression and siRNA knockdown in Y1 and MA10 cells, qPCR\",\n      \"journal\": \"Molecular and cellular endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — single-cell FISH plus genetic manipulation; single lab\",\n      \"pmids\": [\"25662274\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PKA-mediated phosphorylation of SIK1 at its conserved site S577 negatively regulates sleep need: SIK1-S577A knock-in mice show increased NREM sleep time and higher NREM delta power, indicating that PKA phosphorylation of SIK1 suppresses sleep pressure.\",\n      \"method\": \"CRISPR knock-in mice (Sik1S577A), EEG/EMG sleep recording, sleep deprivation protocol, circadian behavior assays\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — precise knock-in mutagenesis with defined electrophysiological phenotype; single lab\",\n      \"pmids\": [\"32457359\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SIK1 C-terminal truncation mutations associated with autism/epilepsy shift SIK1 subcellular distribution from exclusively nuclear to both nuclear and cytoplasmic. In SIK1-MT mice generated by CRISPR, this mislocalization is associated with increased excitatory synaptic transmission, disrupted E/I balance in cortical pyramidal neurons, and repetitive behavior.\",\n      \"method\": \"CRISPR/Cas9 knock-in mice, immunofluorescence localization, whole-cell electrophysiology, behavioral assays\",\n      \"journal\": \"Frontiers in molecular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — precise genetic model plus electrophysiology plus behavior; single lab\",\n      \"pmids\": [\"34295222\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SIK1 promotes ferroptosis resistance in pancreatic cancer via a HDAC5-STAT6-SLC7A11 axis: SIK1 phosphorylates HDAC5 at Ser498, promoting its interaction with 14-3-3 and protecting HDAC5 from TRIM28-mediated ubiquitination and degradation. Stabilized HDAC5 deacetylates STAT6, enhancing its transcriptional activation of SLC7A11, which confers resistance to ferroptosis.\",\n      \"method\": \"In vitro kinase assay (SIK1 phosphorylation of HDAC5 Ser498), co-immunoprecipitation, ubiquitination assay, site-directed mutagenesis, HDAC activity assay, organoid and PDX models\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — in vitro kinase assay plus mutagenesis plus co-IP plus ubiquitination plus PDX validation; multiple orthogonal methods\",\n      \"pmids\": [\"40250791\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Arterial blood pressure regulation by SIK1 involves TGF-β1 signaling: SIK1 knockout mice on high-salt diet exhibit upregulated TGF-β1 signaling, increased endothelin-1 expression, and enhanced vascular smooth muscle cell contractile marker expression. In vitro SIK1 knockdown in VSMCs increases contractile markers and endothelin-1, while knockdown in adventitial fibroblasts increases collagen deposition.\",\n      \"method\": \"SIK1 knockout mouse model, high-salt diet challenge, in vitro SIK1 siRNA knockdown in VSMCs and fibroblasts, blood pressure telemetry, Western blot, histology\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO mouse plus in vitro validation; single lab\",\n      \"pmids\": [\"25556206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SIK1-selective inhibitors that engage two differentiating features of the SIK catalytic site reduce phosphorylation of the SIK substrate CRTC3 at Ser329, suppress pro-inflammatory cytokine production, and induce anti-inflammatory IL-10 in myeloid cells following LPS challenge, demonstrating SIK1/2 as key regulators of innate immune cytokine balance via the CRTC-CREB axis.\",\n      \"method\": \"Structure-based inhibitor design, in vitro kinase selectivity panel, phospho-CRTC3 antibody-based cellular assay, LPS-stimulated macrophage cytokine assays, murine colitis model\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1/2 — structure-based design plus biochemical substrate assay plus in vivo disease model; multiple methods\",\n      \"pmids\": [\"38147543\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Gastrin induces SIK1 expression in gastric adenocarcinoma cells via CCK2 receptor-Gq/G11 signaling, causing LKB1 Ser428 phosphorylation and SIK1 Thr182 phosphorylation. Activated SIK1 phosphorylates HDAC4 and promotes its nuclear export, enhancing CRE-, SRE-, AP1-, and NF-κB-driven transcription. SIK1 knockdown increases cell migration.\",\n      \"method\": \"SIK1 overexpression and siRNA knockdown, phosphorylation-specific immunoblot, luciferase reporter assays, subcellular fractionation of HDACs, transwell migration assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple cellular assays with mechanistic follow-up; single lab\",\n      \"pmids\": [\"25384047\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"SNF1LK (SIK1) kinase domain expression in CHO cells causes cell cycle arrest with re-replication to 8N and 16N DNA content without cell division, suggesting a role in G2/M regulation. The protein is expressed in early cardiac and skeletal muscle progenitor cells during mouse embryogenesis.\",\n      \"method\": \"Tetracycline-inducible SNF1LK kinase domain expression in CHO cells, flow cytometry DNA content analysis, in situ hybridization for developmental expression\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single overexpression experiment with phenotypic readout; no mechanistic target identified\",\n      \"pmids\": [\"15177563\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SIK1 is a serine/threonine kinase of the AMPK family that is activated by LKB1-mediated phosphorylation at Thr182 (with sustained activity requiring auto-phosphorylation at Ser186 and GSK-3β input), and negatively regulated by PKA-mediated phosphorylation at Ser577/Thr475 (which promotes 14-3-3 binding, cytoplasmic translocation, and proteasomal degradation via ITCH); once active, SIK1 suppresses cAMP-CREB transcriptional output by phosphorylating and inactivating CRTC coactivators and by activating PDE4, phosphorylates and drives nuclear export of class IIa HDACs (HDAC4/5) to activate MEF2, phosphorylates SR-B1 to stimulate cholesterol uptake, phosphorylates SMRT to inactivate Wnt/β-catenin, phosphorylates HDAC5-Ser498 to stabilize it and activate STAT6-SLC7A11 ferroptosis resistance, and links LKB1 to p53-dependent anoikis suppression, collectively placing SIK1 as a central integrator of energy, sodium, cAMP, and stress signals that controls muscle differentiation, circadian entrainment, gluconeogenesis, vascular sodium handling, and tumor suppression.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SIK1 is an LKB1-activated, AMPK-family serine/threonine kinase that functions as a central integrator of cAMP, energy, and stress signaling by phosphorylating transcriptional regulators to reshape gene expression programs in muscle, liver, brain, vasculature, and immune cells. Its principal substrates are CRTC coactivators (CRTC1–3), whose SIK1-mediated phosphorylation triggers 14-3-3 binding, nuclear export, and—in the case of CRTC1—RFWD2-dependent proteasomal degradation, thereby suppressing CREB-dependent transcription of gluconeogenic, circadian, and steroidogenic genes [PMID:23993098, PMID:29408765, PMID:25662274]; SIK1 also phosphorylates class IIa HDACs (HDAC4/5) to drive their cytoplasmic translocation and activate MEF2-dependent myogenic and neuronal gene programs, and phosphorylates HDAC5-Ser498 to stabilize HDAC5 and promote STAT6-SLC7A11-mediated ferroptosis resistance [PMID:17468767, PMID:40250791]. SIK1 activity is positively regulated by LKB1 phosphorylation at Thr182 and autophosphorylation at Ser186, and negatively regulated by AKT- and PKA-mediated phosphorylation that promotes 14-3-3 binding, cytoplasmic sequestration, and ITCH-dependent ubiquitin–proteasomal degradation [PMID:18946175, PMID:36806887]. De novo mutations in SIK1 cause a developmental epileptic encephalopathy, with disease-associated truncations shifting SIK1 from nuclear to cytoplasmic distribution without abolishing kinase activity, disrupting excitatory/inhibitory synaptic balance [PMID:25839329, PMID:34295222].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Early characterization showed that forced expression of the SIK1 kinase domain causes endoreduplication without division, hinting at a cell-cycle regulatory role, but the molecular target was unknown.\",\n      \"evidence\": \"Inducible kinase-domain expression in CHO cells with flow cytometry and in situ hybridization in mouse embryos\",\n      \"pmids\": [\"15177563\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No substrate or downstream pathway identified\", \"Overexpression artifact not ruled out\", \"Endoreduplication phenotype not independently confirmed\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Two studies established SIK1's first direct substrates and physiological roles: SIK1 phosphorylates class IIa HDACs to activate MEF2-dependent muscle gene expression, and SIK1 phosphorylates PME-1 at the Na+,K+-ATPase complex to regulate sodium transport, revealing SIK1 as a signal-responsive kinase with both transcriptional and metabolic outputs.\",\n      \"evidence\": \"Viral re-expression in dystrophic mice with MEF2 reporter and HDAC phosphorylation assays; co-IP, in vitro kinase assay, and sodium-loading experiments in renal epithelial cells\",\n      \"pmids\": [\"17468767\", \"17939993\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether HDAC phosphorylation sites are identical to those used by other AMPK-family kinases was not resolved\", \"The CaM kinase–Thr322 activation axis for SIK1 at the NK complex was not confirmed in vivo\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"The activation mechanism of SIK1 was dissected: LKB1 phosphorylates Thr182 to initiate activity, SIK1 auto-phosphorylates Ser186 for sustained signaling, and GSK-3β contributes to maintaining the Ser186 phosphosite, placing SIK1 at a convergence of LKB1 and Wnt/insulin pathways.\",\n      \"evidence\": \"In vitro kinase assay with purified kinases, mutagenesis, AICAR-treated C2C12 myoblasts with subcellular fractionation\",\n      \"pmids\": [\"18946175\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for LKB1→SIK1→auto-phosphorylation cascade not determined\", \"Contribution of GSK-3β in vivo remains indirect\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"A kinome-wide screen revealed that SIK1 is essential for LKB1-dependent p53 activation during anoikis, establishing SIK1 as a tumor suppressor that prevents anchorage-independent growth and metastasis.\",\n      \"evidence\": \"RNAi screen, in vitro anoikis assays, soft agar, and mouse metastasis model with epistasis analysis\",\n      \"pmids\": [\"19622832\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct SIK1 substrate linking to p53 stabilization not identified\", \"Whether SIK1 tumor-suppressive function is kinase-activity-dependent was not tested\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"SIK1 knockout ES cells revealed a role in cardiomyocyte differentiation via p57Kip2-dependent cell-cycle exit, broadening SIK1's functions beyond skeletal muscle.\",\n      \"evidence\": \"Gene-trap null ES cells, embryoid body differentiation, expression profiling, cell-cycle analysis\",\n      \"pmids\": [\"20140255\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which SIK1 controls p57Kip2 expression is unknown\", \"Not validated in whole-animal cardiac development\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"PKA phosphorylation of SIK1 at Thr475 was shown to stabilize SIK1 protein by protecting it from proteasomal degradation, revealing a feed-forward mechanism wherein cAMP signaling sustains SIK1 levels during myogenic differentiation.\",\n      \"evidence\": \"Cycloheximide chase, cell-free PKA kinase assay, PEST-domain and Thr475 mutagenesis, primary myoblast siRNA knockdown\",\n      \"pmids\": [\"23256157\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"E3 ligase responsible for basal SIK1 turnover in myoblasts was not identified at this time\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"SIK1 was placed in the circadian clock as a light-induced negative-feedback kinase: SIK1 phosphorylates and inactivates CRTC1 in the SCN to limit CREB-driven Per1 transcription, gating the magnitude of photic phase shifts.\",\n      \"evidence\": \"Transcriptomics of light-treated SCN, in vivo lentiviral shRNA knockdown of Sik1, behavioral phase-shift assays, CRTC1 phosphorylation measurements\",\n      \"pmids\": [\"23993098\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SIK2/SIK3 have redundant roles in circadian entrainment was not fully dissected\", \"CRTC1 phosphorylation sites targeted by SIK1 in SCN not mapped\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Multiple 2015 studies expanded SIK1's substrate repertoire and disease connections: SIK1 phosphorylates SR-B1 Ser496 to stimulate HDL cholesterol uptake; SIK1 represses StAR via CRTC2 in steroidogenic cells; SIK1 loss in vascular smooth muscle derepresses TGF-β1/endothelin-1 to elevate blood pressure on high-salt diet; and de novo SIK1 mutations cause developmental epilepsy through altered subcellular localization rather than loss of kinase activity.\",\n      \"evidence\": \"In vitro kinase assays, co-IP, mutagenesis, HDL-CE uptake assay, single-cell FISH, SIK1 KO mice on high-salt diet, patient-derived cell immunofluorescence and cycloheximide chase\",\n      \"pmids\": [\"26567857\", \"25662274\", \"25556206\", \"25839329\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SR-B1 phosphorylation occurs in vivo at the hepatic level is unknown\", \"Epilepsy-causing mutations' effect on specific HDAC or CRTC substrates in neurons not fully resolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"SIK1 was shown to suppress Wnt/β-catenin signaling by phosphorylating SMRT-Thr1391, promoting NCoR/SMRT–TBL1 complex formation and displacing β-catenin, establishing a direct kinase-substrate mechanism for SIK1's tumor-suppressive role in hepatocellular carcinoma.\",\n      \"evidence\": \"In vitro kinase assay, co-IP, ChIP, SMRT-T1391A mutagenesis, xenograft tumor models\",\n      \"pmids\": [\"26778753\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SMRT phosphorylation by SIK1 operates in non-hepatic Wnt-driven cancers is untested\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"SIK1 was found to interact with the GINS complex subunit Sld5 and phosphorylate MCM2 at N-terminal residues required for helicase activation, linking SIK1 to DNA replication initiation.\",\n      \"evidence\": \"Co-IP, in vitro kinase assay of MCM2, siRNA knockdown, DNA replication assays, chromatin fractionation\",\n      \"pmids\": [\"27592030\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Independent confirmation of SIK1–GINS interaction is lacking\", \"Whether kinase-dead SIK1 phenocopies the replication defect is untested\", \"In vivo relevance to replication licensing not established\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"The CRTC1 phosphorylation mechanism by SIK1 was mapped to four specific serine sites, and downstream K48-ubiquitination via RFWD2 was identified, explaining how SIK1 specifically targets CRTC1 for proteasomal degradation to suppress gluconeogenic gene expression.\",\n      \"evidence\": \"In vitro kinase assay, phosphosite mutagenesis, ubiquitination assay with proteasome inhibitor, PEPCK luciferase reporter\",\n      \"pmids\": [\"29408765\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether RFWD2-mediated CRTC1 degradation is regulated by feeding/fasting in vivo is unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Genetic studies in Kras-driven lung cancer models demonstrated that SIK1 (with SIK3) is the critical tumor-suppressive effector downstream of LKB1, acting through CRTC2 to restrain AP1 and IL-6 pro-tumorigenic transcription.\",\n      \"evidence\": \"CRISPR deletion of Sik1 in NSCLC cell lines and conditional mouse models, gene expression analysis, epistasis with CRTC2\",\n      \"pmids\": [\"31350328\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Individual contribution of SIK1 vs. SIK3 not fully separated\", \"Whether pharmacological SIK activation could substitute for LKB1 loss in NSCLC is unexplored\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Two studies revealed additional SIK1 regulatory outputs: SIK1 activates PDE4 to degrade cAMP independently of CRTC phosphorylation, providing an extra brake on hepatic gluconeogenesis; and PKA phosphorylation of SIK1 at Ser577 suppresses sleep need, as shown by increased NREM sleep in Sik1-S577A knock-in mice.\",\n      \"evidence\": \"Primary hepatocyte assays, PDE4 activity measurement, ob/ob mouse model; CRISPR Sik1-S577A knock-in mice with EEG/EMG sleep recording\",\n      \"pmids\": [\"32599076\", \"32457359\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct SIK1 phosphorylation site on PDE4 is not identified\", \"Sleep phenotype mechanism (which SIK1 substrate in neurons) is unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"CRISPR knock-in mice bearing autism/epilepsy-associated SIK1 truncations showed that cytoplasmic mislocalization of mutant SIK1 increases excitatory synaptic transmission and disrupts cortical E/I balance, providing a circuit-level mechanism for the neurodevelopmental phenotype.\",\n      \"evidence\": \"CRISPR/Cas9 knock-in mice, immunofluorescence, whole-cell electrophysiology, behavioral assays\",\n      \"pmids\": [\"34295222\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether mislocalized SIK1 gains cytoplasmic substrates or loses nuclear ones is unresolved\", \"Specific synaptic SIK1 substrates not identified\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"The full degradation cascade for SIK1 in cancer was delineated: AKT phosphorylates SIK1, enabling 14-3-3 binding and cytoplasmic translocation, where Pin1 isomerase facilitates ITCH-mediated ubiquitination and proteasomal destruction, thereby relieving SIK1 repression of STAT3 and promoting tumor progression.\",\n      \"evidence\": \"MS-based interactomics, co-IP, in vitro kinase assay, ubiquitination assay, mutagenesis, breast cancer cell phenotypic assays\",\n      \"pmids\": [\"36806887\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ITCH-mediated SIK1 degradation operates outside breast cancer contexts is untested\", \"Relative contributions of AKT vs. PKA to SIK1 cytoplasmic translocation not compared\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Structure-based SIK1/2-selective inhibitors validated the CRTC-CREB axis as the key anti-inflammatory output of SIK activity: inhibition dephosphorylates CRTC3 at Ser329, suppresses pro-inflammatory cytokines, and induces IL-10 in macrophages.\",\n      \"evidence\": \"Structure-based inhibitor design, in vitro kinase selectivity panel, phospho-CRTC3 cellular assay, LPS-stimulated macrophage assay, murine colitis model\",\n      \"pmids\": [\"38147543\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether SIK1 or SIK2 is the dominant isoform controlling innate immune cytokine balance is not resolved\", \"Long-term immunological consequences of SIK inhibition unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A new SIK1–HDAC5 axis was uncovered in pancreatic cancer: SIK1 phosphorylates HDAC5 at Ser498, stabilizing it via 14-3-3 and protecting it from TRIM28-mediated degradation; stabilized HDAC5 deacetylates STAT6 to drive SLC7A11 expression and ferroptosis resistance.\",\n      \"evidence\": \"In vitro kinase assay, co-IP, ubiquitination assay, mutagenesis, organoid and PDX models\",\n      \"pmids\": [\"40250791\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether HDAC5-Ser498 phosphorylation is a general SIK1 output across tissues or context-specific is unknown\", \"Relationship between ferroptosis-protective and tumor-suppressive functions of SIK1 is unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of SIK1's substrate selectivity versus SIK2/SIK3, the identity of neuronal substrates responsible for E/I imbalance in SIK1-associated epilepsy, and how context determines whether SIK1 acts as tumor suppressor (via CRTC/SMRT) or tumor promoter (via HDAC5-STAT6-ferroptosis resistance).\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No crystal structure of full-length SIK1 available\", \"Neuronal SIK1 substrates causing synaptic phenotype unidentified\", \"Context-dependency of SIK1 pro- vs anti-tumor effects not mechanistically reconciled\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2, 7, 8, 9, 10, 12, 20]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [4, 5, 14, 17]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [8, 16, 19]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [8, 13, 19]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 4, 7, 13, 14, 22]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 4, 5, 12, 17]},\n      {\"term_id\": \"R-HSA-9909396\", \"supporting_discovery_ids\": [4, 18]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0, 6, 15]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [3, 20]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [5, 7, 20]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [22]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"HDAC5\",\n      \"HDAC4\",\n      \"CRTC1\",\n      \"CRTC2\",\n      \"LKB1\",\n      \"SR-B1\",\n      \"SMRT\",\n      \"14-3-3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}