{"gene":"SIK2","run_date":"2026-06-10T07:46:32","timeline":{"discoveries":[{"year":2010,"finding":"SIK2 localizes at the centrosome and regulates centrosome linker protein C-Nap1 localization through phosphorylation of C-Nap1 at Ser2392. PKA (a known SIK2 inhibitor) induces SIK2-dependent centrosome splitting in interphase, while SIK2 depletion blocks centrosome separation in mitosis and reduces AKT phosphorylation.","method":"Immunofluorescence localization, phosphorylation mapping by mutagenesis, siRNA depletion with mitotic phenotype readout, xenograft studies","journal":"Cancer cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal functional experiments including localization, phosphorylation site identification, KD phenotype, and in vivo validation; replicated by subsequent studies","pmids":["20708153"],"is_preprint":false},{"year":2011,"finding":"SIK2 phosphorylates and suppresses TORC1 (CRTC1) nuclear translocation, thereby repressing CREB-mediated gene expression in neurons. During oxygen-glucose deprivation, CaMK I/IV phosphorylate SIK2 at Thr484, leading to SIK2 protein degradation and consequent TORC1 dephosphorylation and CREB activation, promoting neuronal survival.","method":"In vitro kinase assay (CaMK phosphorylation of SIK2), sik2−/− mouse neurons with OGD survival assay, transient focal ischemia model, immunoblotting for TORC1 phosphorylation","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with defined phenotype, identified upstream kinase, identified substrate phosphorylation site, replicated in vivo ischemia model","pmids":["21220102"],"is_preprint":false},{"year":2010,"finding":"SIK2 suppresses TORC1 nuclear translocation and CREB-mediated Mitf gene expression in melanocytes, thereby repressing eumelanogenesis. In vivo, Sik2−/− mice on an agouti (Ay/a) background showed brown hair, demonstrating that SIK2 represses eumelanogenesis.","method":"B16 melanoma cell overexpression/KO, UV-induced TORC1 nuclear translocation assay, Sik2−/− mouse genetics with Ay/a background, hair pigmentation analysis","journal":"Pigment cell & melanoma research","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with clear phenotype, mechanistic pathway through TORC1-CREB-Mitf confirmed in cells and in vivo","pmids":["20819186"],"is_preprint":false},{"year":2013,"finding":"LKB1 activates SIK2 (and SIK3), which then phosphorylates class IIa HDACs (HDAC4, -5, -7, -9) at conserved motifs to promote 14-3-3 binding and nuclear export. SIK2 activates MEF2-dependent transcription and relieves repression of myogenesis by the HDACs. This pathway is PKA-sensitive.","method":"In vitro kinase assay, 14-3-3 binding assay, subcellular fractionation, MEF2 reporter assay, myogenesis assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro kinase assay establishing direct phosphorylation, 14-3-3 binding, and functional MEF2/myogenesis readout; single lab but multiple orthogonal methods","pmids":["23393134"],"is_preprint":false},{"year":2013,"finding":"SIK2 kinase activity is regulated by reversible acetylation: p300/CBP-mediated acetylation at Lys-53 inhibits SIK2 kinase activity, whereas HDAC6-mediated deacetylation restores it. The acetylation-mimetic SIK2-K53Q mutant causes autophagosome accumulation, while SIK2 knockdown abrogates autophagosome-lysosome fusion and impairs TDP-43Δ inclusion body clearance.","method":"In vitro kinase assay, acetylation-mimetic and non-acetylatable mutagenesis, autophagosome accumulation assay, lysosome fusion assay, siRNA knockdown","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct in vitro kinase assay with mutagenesis identifying acetylation site, functional autophagy readouts; single lab but multiple orthogonal methods","pmids":["23322770"],"is_preprint":false},{"year":2013,"finding":"SIK2 physically interacts with p97/VCP (co-localized at ER membrane) and phosphorylates p97/VCP to stimulate its ATPase activity, thereby promoting degradation of ERAD substrates. Kinase-deficient SIK2 or knockdown impairs ERAD substrate degradation and disrupts ER homeostasis.","method":"Co-immunoprecipitation, co-localization by immunofluorescence, in vitro ATPase activity assay, ERAD substrate degradation assay, kinase-dead mutant analysis, siRNA knockdown","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — direct biochemical interaction, in vitro activity assay with functional readout, mutagenesis; single lab with multiple orthogonal methods","pmids":["24129571"],"is_preprint":false},{"year":2014,"finding":"SIK2 forms a complex with CDK5 activator p35 and E3 ligase PJA2 in pancreatic β-cells. Following glucose stimulation, SIK2 phosphorylates p35 at Ser91, triggering p35 ubiquitylation by PJA2 and promoting insulin secretion. β-cell-specific SIK2 knockout leads to p35 accumulation and impaired insulin secretion.","method":"Co-immunoprecipitation, in vitro kinase assay (SIK2 phosphorylation of p35 at Ser91), ubiquitylation assay, β-cell-specific KO mouse with insulin secretion phenotype, mass spectrometry for complex identification","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted complex with in vitro kinase assay identifying phosphorylation site, ubiquitylation assay, and genetic KO with functional secretion phenotype","pmids":["24561619"],"is_preprint":false},{"year":2014,"finding":"SIK2 KO mice exhibit increased CRTC2-CREB transcriptional activity in white adipocytes, elevated ATF3, reduced GLUT4 expression, reduced glucose uptake in muscle and adipocytes, hypertriglyceridemia due to increased lipolysis, and impaired glucose and insulin tolerance.","method":"SIK2 KO mouse metabolic phenotyping, glucose/insulin tolerance tests, lipolysis assays, CRTC2-CREB pathway analysis, 3T3-L1 adipocyte culture, CRTC2 KO comparison","journal":"Diabetes","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with multiple defined metabolic phenotypes and pathway attribution through CRTC2-CREB; replicated in vitro","pmids":["24898145"],"is_preprint":false},{"year":2012,"finding":"PKA phosphorylates SIK2 at Ser358 in adipocytes in response to cAMP elevation (e.g., forskolin, β-adrenergic agonist), promoting 14-3-3 binding and a phosphorylation-dependent relocalization of SIK2 from a particulate fraction to the cytosol. Ser358Ala mutation abolishes 14-3-3 binding and relocalization.","method":"Phosphopeptide mapping of SIK2, site-directed mutagenesis (Ser358Ala), 14-3-3 binding assay, adipocyte fractionation, immunocytochemistry","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — phosphopeptide mapping, mutagenesis confirming binding site, subcellular fractionation in primary adipocytes; single lab with multiple orthogonal methods","pmids":["22462548"],"is_preprint":false},{"year":2015,"finding":"In adipocytes, SIK2 directly phosphorylates CRTC2, CRTC3, and HDAC4. CRTC2, CRTC3, HDAC4, and PP2A all interact with SIK2. PKA-mediated phosphorylation of SIK2 at Ser358 reduces binding of CRTCs and PP2A to SIK2. SIK2 increases GLUT4 protein levels and glucose uptake in adipocytes through this pathway.","method":"Co-immunoprecipitation (SIK2 with CRTC2/3, HDAC4, PP2A), siRNA knockdown of SIK2/CRTC2/HDAC4, GLUT4 protein measurement, glucose uptake assay, SIK2 overexpression and pharmacological inhibition","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP identifying multiple substrates/partners, functional glucose uptake readout, validated in human adipocytes; single lab with multiple orthogonal methods","pmids":["25472719"],"is_preprint":false},{"year":2008,"finding":"SIK2 is activated in 3T3-L1 adipocytes by nutrient deprivation, ATP synthesis inhibition, and AICAR treatment. SIK2 overexpression represses lipogenic gene expression (FAS, ACC2, SCD1) by reducing SREBP-1 nuclear translocation, independent of AMPK; knockdown increases these genes.","method":"In vitro kinase activity assay (peptide substrate phosphorylation), adenovirus-mediated overexpression and siRNA knockdown, FAS promoter-luciferase reporter, SREBP-1 nuclear translocation by immunoblot","journal":"Obesity (Silver Spring, Md.)","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — direct kinase activity assay, promoter reporter, nuclear translocation, multiple functional readouts; single lab","pmids":["18239551"],"is_preprint":false},{"year":2016,"finding":"SIK2 restricts autophagic flux in triple-negative breast cancer cells. Genetic or pharmacological inhibition of SIK2 increases autophagic flux and selectively causes cell death in breast cancer cells (especially claudin-low subtype). Depletion of ATG5 rescues viability loss after SIK2 inhibition, placing SIK2 upstream of autophagosome formation.","method":"Loss-of-function screening, siRNA/pharmacological SIK2 inhibition, autophagic flux assay, ATG5 depletion rescue, in vivo tumor growth assay","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — epistasis via ATG5 rescue, in vivo validation, multiple cell lines; single lab with multiple orthogonal methods","pmids":["27697861"],"is_preprint":false},{"year":2016,"finding":"SIK2 and SIK3 contribute to macrophage polarization. Knock-in of catalytically inactive SIK2 and SIK3 in mice demonstrated that inhibition of SIK2 and SIK3 during macrophage differentiation greatly enhances IL-10 production and produces a stable anti-inflammatory macrophage phenotype even after kinase reactivation.","method":"Knock-in mice expressing catalytically inactive SIK1, SIK2, SIK3; primary macrophage cytokine production assays; pharmacological inhibition during differentiation","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — catalytically inactive knock-in mice with defined cytokine phenotype; isoform-specific genetic dissection with functional readout","pmids":["27920213"],"is_preprint":false},{"year":2016,"finding":"SIK2 phosphorylates p300 at Ser89, disrupting p300-PPARα interaction (which normally occurs via a conserved LXXLL motif on p300) and thereby decreasing PPARα-mediated ketogenic gene expression. The phosphorylation-defective p300 S89A mutant shows increased PPARα interaction and abolishes SIK2 suppression of ketogenesis.","method":"In vitro kinase assay (SIK2 phosphorylation of p300), co-immunoprecipitation (p300-PPARα interaction), site-directed mutagenesis (p300 S89A), ketogenic gene expression assay in liver","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay with mutagenesis identifying phosphorylation site, functional gene expression readout, Co-IP confirming interaction disruption; single lab","pmids":["26983400"],"is_preprint":false},{"year":2018,"finding":"PTH(1-34) activates PKA, which inhibits SIK2 and SIK3 in osteoblasts, leading to nuclear translocation of CRTC2 and CRTC3 and upregulation of RANKL transcription. Knockdown of SIK2 and SIK3, and PP1/PP2A inhibition, demonstrated that SIK2/3 and protein phosphatases 1/2A are part of the PTH-CRTC2/3-RANKL regulatory pathway.","method":"siRNA knockdown of SIK2/3 and CRTCs in primary calvarial osteoblasts, PP1/PP2A inhibitor experiments, RANKL qPCR, CRTC nuclear localization by immunofluorescence","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — siRNA epistasis in primary osteoblasts, multiple pathway components tested, in vitro and in vivo RANKL validation; single lab with multiple orthogonal methods","pmids":["30377251"],"is_preprint":false},{"year":2019,"finding":"SIK2 promotes mitochondrial fission through phosphorylation of Drp1 at Ser616, thereby inhibiting mitochondrial oxidative phosphorylation. SIK2 also upregulates HIF-1α by activating the PI3K/AKT signaling pathway, which directly upregulates glycolytic gene transcription (Warburg effect) in ovarian cancer cells.","method":"SIK2 overexpression/knockdown, phospho-specific immunoblotting for Drp1-pSer616, PI3K/AKT pathway analysis, mitochondrial function assays, glycolysis assays","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — phosphorylation site identified with phospho-specific antibody, functional mitochondrial and glycolytic readouts; but direct in vitro kinase assay for Drp1 phosphorylation not clearly stated in abstract","pmids":["31639424"],"is_preprint":false},{"year":2020,"finding":"SIK2 promotes lipid synthesis in ovarian cancer by upregulating SREBP1c (and thus FASN) and SREBP2 (and thus HMGCR) through the PI3K/Akt signaling pathway, increasing both fatty acid and cholesterol synthesis.","method":"SIK2 knockdown/overexpression, SREBP1c/SREBP2 expression assays, PI3K/Akt pathway inhibition, in vitro and in vivo lipid synthesis assays","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — functional lipid synthesis assays with pathway inhibition; multiple in vitro and in vivo readouts; single lab","pmids":["31932581"],"is_preprint":false},{"year":2020,"finding":"SIK2 suppresses gastric cancer cell migration/invasion by phosphorylating and activating mTORC1, which inhibits autophagic degradation of protein phosphatases PHLPP2 and PP2A. The upregulated PHLPP2 and PP2A then dephosphorylate and inactivate AKT, thereby inhibiting AKT/GSK3β/β-catenin signaling and EMT.","method":"SIK2 overexpression/knockdown, mTORC1 phosphorylation assay, autophagy flux assay, PHLPP2/PP2A protein stability assay, AKT phosphorylation by immunoblot, migration/invasion assay","journal":"Molecular oncology","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — mechanistic pathway established via multiple molecular assays; single lab, no direct in vitro kinase reconstitution of full pathway","pmids":["33128264"],"is_preprint":false},{"year":2020,"finding":"Fbxw7 targets SIK2 for proteasomal degradation by binding the 'TPPPS' motif of SIK2. Endogenous Fbxw7 downregulates SIK2 protein level to control cell cycle progression, interfering with the SIK2/TORC2/AKT signaling pathway and modulating p21 expression.","method":"Co-immunoprecipitation (Fbxw7-SIK2 interaction), motif mutation analysis, ubiquitination assay, SIK2 half-life measurement, cell cycle analysis","journal":"Cell biology international","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — Co-IP, motif identification, ubiquitination assay; single lab with multiple methods but no mutagenesis of ubiquitination sites confirmed","pmids":["32437091"],"is_preprint":false},{"year":2021,"finding":"SIK2 is recruited to the Salmonella-containing vacuole (SCV) together with the Arp2/3 complex and formins during Salmonella infection. Under basal conditions, SIK2 associates with actin filaments. SIK2 depletion causes a severe actin nucleation and polymerization defect at the SCV, promotes bacterial escape from the SCV, and impairs xenophagy.","method":"Global host phosphoproteome analysis post-infection, SIK2 siRNA depletion, immunofluorescence localization to SCV and actin, bacterial survival/proliferation assay, xenophagy assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Moderate — phosphoproteomics to identify SIK2, localization studies, epistasis via depletion with defined bacterial and autophagy phenotypes; single lab, multiple orthogonal methods","pmids":["33947818"],"is_preprint":false},{"year":2021,"finding":"ARN-3236 (SIK2 inhibitor) produces antidepressant-like effects in mice via the hippocampal CRTC1-CREB-BDNF pathway. SIK2 inhibition prevents cytoplasmic sequestration of CRTC1 and restores BDNF expression; hippocampal CRTC1 mediates these effects as demonstrated by viral gene transfer.","method":"Chronic stress mouse models (CSDS, CUMS), stereotactic viral-mediated gene transfer of CRTC1, co-immunoprecipitation, immunofluorescence, western blotting","journal":"Frontiers in pharmacology","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — viral-mediated epistasis placing CRTC1 downstream of SIK2 in behavioral context; single lab with multiple behavioral and molecular methods","pmids":["33519490"],"is_preprint":false},{"year":2022,"finding":"SIK2 directly phosphorylates MYLK (myosin light chain kinase, smooth muscle) at Ser343, activating MYLK which then phosphorylates its downstream effector MYL2 (myosin light chain 2), thereby promoting ovarian cancer cell motility and metastasis. Adipocytes induce both SIK2 phosphorylation at Ser358 and MYLK phosphorylation at Ser343.","method":"In vitro kinase assay (SIK2 phosphorylating MYLK at Ser343), phospho-specific immunoblotting, Co-immunoprecipitation, siRNA knockdown, cell motility/migration assays, in vivo metastasis model","journal":"Molecular oncology","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro kinase assay identifying phosphorylation site, functional motility readout in vitro and in vivo; single lab with multiple orthogonal methods","pmids":["35278271"],"is_preprint":false},{"year":2022,"finding":"SIK2 inhibitors decrease phosphorylation of class-IIa HDACs (HDAC4/5/7) and abolish HDAC4/5/7-associated transcriptional activity of MEF2D, decreasing MEF2D binding to regulatory regions of FANCD2, EXO1, and XRCC4 genes, resulting in repression of DNA double-strand break repair. SIK2 inhibition also decreases PARP enzyme activity.","method":"SIK2 inhibitors (ARN3236, ARN3261) in cancer cells, HDAC4/5/7 phosphorylation immunoblotting, MEF2D chromatin accessibility (ATAC-seq), MEF2D ChIP at target gene loci, DNA DSB repair assays, PARP activity assay, xenograft studies","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods including HDAC phosphorylation, ChIP, ATAC-seq, DNA repair assays, and in vivo validation; single lab","pmids":["35642638"],"is_preprint":false},{"year":2022,"finding":"SIK2 inhibition by ARN-3236 prevents fibroblast differentiation and reduces extracellular matrix expression. Mechanistically, SIK2 inactivation results in dephosphorylation and nuclear translocation of CRTC2, which then binds CREB to promote CREB-dependent anti-fibrotic gene expression.","method":"Western blot of SIK2/pCRTC2 in fibroblasts, ARN-3236 treatment and siRNA knockdown, CRTC2 nuclear translocation by fractionation, bleomycin mouse model of pulmonary fibrosis, immunohistochemistry","journal":"BMC pulmonary medicine","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — CRTC2 localization and CREB binding established, in vivo fibrosis model; single lab","pmids":["35410283"],"is_preprint":false},{"year":2022,"finding":"SIK2 overexpression reduces ER stress-mediated tubular epithelial apoptosis by inhibiting the histone acetyltransferase activity of p300, thereby activating HSF1/Hsp70. This mechanism underlies SIK2 protection against diabetic kidney disease.","method":"SIK2 KO and overexpression in diabetic mice, transcriptome sequencing, p300 histone acetyltransferase activity assay, HSF1/Hsp70 pathway analysis, ER stress markers","journal":"Translational research : the journal of laboratory and clinical medicine","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — mechanistic pathway via p300 inhibition to HSF1/Hsp70 with functional apoptosis readout; in vivo validation; single lab","pmids":["36075517"],"is_preprint":false},{"year":2022,"finding":"SIK2 directly phosphorylates LRP6, leading to Wnt/β-catenin signaling pathway activation and induction of IDH1 expression in breast cancer stem cells. This phosphorylation is kinase activity-dependent. SIK2 itself is phosphorylated upstream by CK1α.","method":"In vitro kinase assay (SIK2 phosphorylation of LRP6), β-catenin accumulation assay, SIK2 kinase-dead mutant analysis, SIK2 inhibitors (ARN-3236, HG-9-91-01) blocking LRP6 phosphorylation, breast cancer stem cell proportion assays, IDH1 expression analysis","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro kinase assay with kinase-dead validation, pharmacological confirmation, functional stemness readout; single lab with multiple orthogonal methods","pmids":["35277657"],"is_preprint":false},{"year":2013,"finding":"In DLBCL, siRNA-mediated downregulation of SIK2 results in upregulation of the CREB target gene BIM, consistent with SIK2's role in phosphorylating and inhibiting its cofactor TORC2/CRTC2, thereby repressing CREB-mediated transcription.","method":"siRNA knockdown of SIK2, RT-PCR for BIM expression, Western blot, cAMP and dexamethasone treatment","journal":"Leukemia & lymphoma","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — siRNA knockdown with defined target gene readout; establishes CRTC2-CREB pathway in lymphoma context; single lab","pmids":["20367563"],"is_preprint":false},{"year":2015,"finding":"B55gamma (PPP2R2C) interacts with and stabilizes SIK2 protein. The B55gamma-SIK2 complex is required for B55gamma-mediated suppression of S6K phosphorylation and promotion of glioma cell survival under glucose starvation.","method":"Co-immunoprecipitation (B55gamma-SIK2 interaction), siRNA knockdown of SIK2, S6K phosphorylation assay, cell viability under glucose deprivation","journal":"Cancer cell international","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP and epistasis via SIK2 knockdown; single lab, limited functional follow-up","pmids":["25792973"],"is_preprint":false},{"year":2014,"finding":"SIK2 is required for cardiac left ventricular hypertrophy (LVH) development in response to chronic high-salt diet. Sik2−/− mice do not develop LVH upon high-salt feeding, while wild-type mice do. In cardiac myocytes, α-adducin regulates SIK2 expression, and SIK2 mediates adducin's effects on hypertrophy marker gene activation.","method":"Sik2−/− mouse model on high-salt diet, echocardiography (LV wall thickness), gene expression of hypertrophy markers, cardiac myocyte culture with α-adducin manipulation","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic KO with defined cardiac phenotype, pathway dissection in cardiac myocytes; single lab with in vivo and in vitro validation","pmids":["24752134"],"is_preprint":false},{"year":2020,"finding":"PKA phosphorylation site Ser587 of SIK2 regulates sleep need. Sik2S587A knock-in mice showed increased NREM sleep delta density, indicating that the PKA-SIK2 signaling axis is involved in regulating sleep.","method":"Sik2S587A knock-in mice, EEG/EMG sleep recording (NREM sleep time, delta density), sleep deprivation recovery experiments","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — knock-in mice with defined PKA site mutation and EEG sleep phenotype; single lab","pmids":["32457359"],"is_preprint":false},{"year":2013,"finding":"In Müller glia, SIK2 activity increases in response to insulin stimulation and is associated with increased IRS1-SIK2 interaction. SIK2 negatively modulates insulin-dependent cell survival: overexpression reduces pAkt levels while knockdown increases pAkt and reduces apoptosis. Under hyperglycemia, increased SIK2 activity correlates with reduced Akt activation and enhanced apoptosis.","method":"In vitro kinase assay (SIK2 activity), co-immunoprecipitation (IRS1-SIK2), siRNA knockdown and overexpression, pAkt immunoblotting, TUNEL apoptosis assay, streptozotocin rat model","journal":"Investigative ophthalmology & visual science","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — kinase activity assay, Co-IP, functional overexpression/KD; single lab with multiple methods","pmids":["23599336"],"is_preprint":false},{"year":2018,"finding":"Insulin induces phosphorylation of SIK2 at Thr484 in primary adipocytes, which is associated with increased SIK2 protein stability but does not affect SIK2 catalytic activity or its activity towards HDAC4.","method":"Phospho-specific antibody for SIK2-Thr484, in vitro kinase assay (no change in activity), SIK2 protein level with MG132 proteasome inhibitor, primary human and rat adipocytes","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — phospho-specific antibody and in vitro kinase assay in primary cells; single lab with multiple methods","pmids":["30586628"],"is_preprint":false},{"year":2024,"finding":"SIK2 phosphorylates GABARAPL2 at Ser72, which is essential for autophagosome-lysosome fusion. The phosphorylation-mimetic GABARAPL2-S72E mutant replicates SIK2-mediated autophagic flux enhancement and reduces Aβ pathology in 5×FAD AD mice, while the non-phosphorylatable S72A mutant fails to show protective effects.","method":"Co-immunoprecipitation, GST pull-down, phosphoproteomics, site-directed mutagenesis (S72E, S72A), AAV-mediated hippocampal delivery, mRFP-GFP-LC3 tandem fluorescence autophagy assay, Morris water maze, LTP recording, electron microscopy","journal":"Translational neurodegeneration","confidence":"High","confidence_rationale":"Tier 1 / Moderate — phosphoproteomics identifying substrate, mutagenesis confirming functional site, multiple orthogonal methods including structural and behavioral readouts; single lab but rigorous","pmids":["41126299"],"is_preprint":false},{"year":2024,"finding":"SIK2 acts as a negative feedback regulator of FGF2/Ras/ERK1/2 signaling in retinal Müller glia. SIK2 phosphorylates Gab1 at Ser266, which weakens Gab1 interactions with Grb2 and Shp2, thereby downregulating ERK1/2 activation. SIK2 itself is activated downstream of ERK1/2 in an FGF2-dependent manner.","method":"In vitro kinase assay (SIK2 phosphorylating Gab1 at Ser266), site-directed mutagenesis, Co-immunoprecipitation (Gab1-Grb2/Shp2), SIK2 overexpression/knockdown with ERK1/2 activation assay","journal":"Advanced biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct in vitro kinase assay identifying phosphorylation site with mutagenesis, Co-IP confirming complex disruption, functional ERK1/2 readout; single lab with multiple orthogonal methods","pmids":["39267218"],"is_preprint":false},{"year":2021,"finding":"SIK2 is synthetic lethal with loss of FANCA. FANCA co-localizes with SIK2 at centrosomes and regulates SIK2 activity at centrosomes. SIK2 depletion in FANCA-deficient cells causes impaired G2-M transition, delayed mitotic progression, cytokinesis failure, and abrogates nocodazole-induced prometaphase arrest, suggesting a role for SIK2 in the spindle assembly checkpoint.","method":"Kinome-wide synthetic lethality screen in FANCA-/- fibroblasts, co-localization of FANCA and SIK2 at mitotic structures by immunofluorescence, SIK2 kinase activity assay at centrosomes, pharmacological SIK2 inhibition with cell cycle analysis","journal":"Molecular oncology","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — genetic screen plus localization and kinase activity studies; single lab with multiple methods","pmids":["34058059"],"is_preprint":false},{"year":2024,"finding":"SIC-19 promotes SIK2 ubiquitination and degradation via the CUL4B-DDB1 E3 ubiquitin ligase complex. Lysine 144 (K144) is the critical ubiquitination site on SIK2 mediating its degradation. CUL4B is functionally required for SIC-19-induced SIK2 degradation.","method":"Mass spectrometry identifying ubiquitin ligases binding SIK2, co-immunoprecipitation (SIK2-CUL4B-DDB1), Western blot for SIK2 half-life, site-directed mutagenesis (K144), ubiquitination assay, CUL4B knockdown","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — MS identification, Co-IP validation, mutagenesis confirming ubiquitination site, functional degradation assay; single lab with multiple orthogonal methods","pmids":["42213109"],"is_preprint":false},{"year":2024,"finding":"SIK2 knockdown in ovarian cancer cells reduces RAD50 phosphorylation at Ser635, prevents nuclear translocation of RAD50, disrupts nuclear filament assembly, and impairs homologous recombination DNA repair, inducing apoptosis.","method":"SIK2 siRNA knockdown and SIC-19 inhibitor, phospho-RAD50(Ser635) immunoblotting, RAD50 nuclear localization assay, HR repair functional assay, apoptosis assay","journal":"Drug resistance updates","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — functional HR repair assay with phospho-site identification; but direct kinase assay for SIK2 phosphorylating RAD50 not explicitly confirmed in abstract; single lab","pmids":["38518726"],"is_preprint":false},{"year":2000,"finding":"SIK2 (originally named Qik) is a serine-threonine kinase belonging to the AMPK/SNF1 family, capable of autophosphorylation as demonstrated by in vitro kinase assay.","method":"In vitro kinase assay (autophosphorylation), representational difference analysis for gene identification","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — direct in vitro kinase assay; single study, foundational characterization","pmids":["11027514"],"is_preprint":false}],"current_model":"SIK2 is an AMPK-family serine/threonine kinase activated by LKB1 and regulated by PKA (phosphorylation at Ser358/Ser587, promoting 14-3-3 binding and relocalization), CaMK I/IV (Thr484 phosphorylation leading to degradation), insulin (Thr484 stabilization), and acetylation (p300/CBP at Lys53 inhibits; HDAC6 restores activity); it phosphorylates multiple substrates including CRTC1/2/3 (suppressing CREB-mediated transcription), class IIa HDACs (promoting nuclear export), p35/CDK5R1 (regulating insulin secretion via PJA2 ubiquitylation), Drp1 (Ser616, mitochondrial fission), MYLK (Ser343, cell motility), LRP6 (Wnt/β-catenin activation), p300 (Ser89, disrupting PPARα-mediated ketogenesis), Gab1 (Ser266, negative feedback on FGF2/ERK signaling), p97/VCP (promoting ERAD), and GABARAPL2 (Ser72, autophagosome-lysosome fusion); it localizes to centrosomes, ER membranes, and actin filaments, and controls mitosis, glucose/lipid metabolism, melanogenesis, neuronal survival, macrophage polarization, β-cell insulin secretion, cardiac hypertrophy, and DNA damage repair."},"narrative":{"mechanistic_narrative":"SIK2 is a serine/threonine kinase of the AMPK/SNF1 family that integrates hormonal, metabolic, and stress cues to control transcription, organelle dynamics, autophagy, and the cell cycle [PMID:11027514, PMID:21220102]. Its best-defined output is repression of CREB-driven transcription: SIK2 phosphorylates the CRTC/TORC coactivators (CRTC1/2/3) to retain them in the cytoplasm and phosphorylates class IIa HDACs (HDAC4/5/7/9) to promote their 14-3-3 binding and nuclear export, thereby tuning CREB- and MEF2-dependent gene programs [PMID:21220102, PMID:23393134, PMID:25472719]. This kinase activity is gated by PKA, which phosphorylates SIK2 at Ser358 and Ser587 to drive 14-3-3 binding and relocalization and to release CRTC/PP2A from SIK2, and by additional inputs including CaMK I/IV-mediated Thr484 phosphorylation that triggers SIK2 degradation, insulin-induced Thr484 stabilization, and reversible acetylation at Lys53 (inhibitory p300/CBP acetylation reversed by HDAC6) [PMID:22462548, PMID:25472719, PMID:21220102, PMID:23322770, PMID:30586628]. Through these axes SIK2 governs metabolic homeostasis—glucose uptake and GLUT4 levels, lipogenic and ketogenic gene expression, and β-cell insulin secretion via the SIK2–p35–PJA2 module [PMID:24898145, PMID:25472719, PMID:24561619, PMID:26983400]. Beyond transcription, SIK2 localizes to centrosomes where it controls centrosome separation and mitotic progression, phosphorylates p97/VCP at the ER to drive ERAD, and acts in autophagy through GABARAPL2 Ser72 phosphorylation to enable autophagosome–lysosome fusion [PMID:20708153, PMID:24129571, PMID:41126299]. SIK2 additionally phosphorylates a broad substrate set linking it to motility (MYLK Ser343), mitochondrial fission (Drp1 Ser616), Wnt activation (LRP6), negative feedback on FGF/ERK signaling (Gab1 Ser266), and DNA double-strand break repair, and is itself targeted for degradation by Fbxw7 and the CUL4B–DDB1 complex [PMID:35278271, PMID:31639424, PMID:35277657, PMID:39267218, PMID:35642638, PMID:32437091, PMID:42213109].","teleology":[{"year":2000,"claim":"Established SIK2 as a catalytically active serine/threonine kinase of the AMPK/SNF1 family, defining the protein class before any substrate was known.","evidence":"In vitro autophosphorylation kinase assay following gene identification by representational difference analysis","pmids":["11027514"],"confidence":"Medium","gaps":["No physiological substrate identified","No upstream activating kinase defined","Foundational single study"]},{"year":2010,"claim":"Defined the core SIK2 transcriptional axis—suppression of CRTC/TORC nuclear translocation to repress CREB-target genes—and linked it to a physiological output (melanogenesis) and to centrosome biology in mitosis.","evidence":"Sik2-/- mice (agouti background pigmentation; centrosome phenotypes), C-Nap1 phosphosite mapping, siRNA mitotic readouts, xenografts","pmids":["20819186","20708153"],"confidence":"High","gaps":["Whether centrosomal and transcriptional roles share regulatory inputs unresolved","Direct in vivo CRTC phosphosite occupancy not mapped in melanocytes"]},{"year":2011,"claim":"Showed SIK2 abundance itself is a regulated node: CaMK I/IV phosphorylation at Thr484 drives SIK2 degradation, relieving CRTC1 repression to promote CREB-dependent neuronal survival.","evidence":"In vitro CaMK kinase assay, sik2-/- neurons under oxygen-glucose deprivation, transient focal ischemia model","pmids":["21220102"],"confidence":"High","gaps":["Identity of the degradation machinery acting after Thr484 phosphorylation not defined here","Generalizability beyond ischemic neurons untested"]},{"year":2013,"claim":"Expanded the SIK2 substrate repertoire beyond CRTCs to class IIa HDACs, p97/VCP, and p300, and revealed acetylation as a direct regulator of kinase activity—connecting SIK2 to MEF2 transcription, ERAD, and autophagy.","evidence":"In vitro kinase and 14-3-3 binding assays, ATPase assays, ERAD substrate degradation, acetylation-mimetic mutagenesis, autophagy flux assays","pmids":["23393134","24129571","23322770"],"confidence":"High","gaps":["Whether HDAC, VCP, and CRTC branches are co-regulated or context-segregated unclear","Acetylation dynamics in vivo not established"]},{"year":2014,"claim":"Connected SIK2 to whole-body metabolic control and β-cell function, defining the SIK2–p35–PJA2 ubiquitylation module for insulin secretion and CRTC2-CREB-dependent adipose/muscle glucose handling, plus a cardiac hypertrophy role.","evidence":"β-cell-specific and global Sik2-/- mice, in vitro p35 Ser91 kinase and ubiquitylation assays, metabolic phenotyping, high-salt cardiac model","pmids":["24561619","24898145","24752134"],"confidence":"High","gaps":["Tissue-specific upstream activators differ and are incompletely mapped","Relationship between secretory and transcriptional metabolic roles not unified"]},{"year":2012,"claim":"Mechanistically resolved PKA control of SIK2: Ser358 phosphorylation creates a 14-3-3 binding site driving cytosolic relocalization, providing the molecular basis for cAMP-dependent inhibition of SIK2 function.","evidence":"Phosphopeptide mapping, Ser358Ala mutagenesis, 14-3-3 binding and adipocyte fractionation","pmids":["22462548"],"confidence":"High","gaps":["How relocalization couples to substrate selection not defined","Role of additional PKA sites left open"]},{"year":2015,"claim":"Showed PKA Ser358 phosphorylation simultaneously releases CRTC and PP2A from SIK2, integrating multiple substrate/regulator interactions into one regulated complex controlling GLUT4 and glucose uptake; also identified B55gamma as a stabilizing partner.","evidence":"Reciprocal Co-IP (CRTC2/3, HDAC4, PP2A, B55gamma), siRNA, glucose uptake assays in human adipocytes and glioma","pmids":["25472719","25792973"],"confidence":"Medium","gaps":["Stoichiometry and assembly order of the SIK2-PP2A-CRTC complex unknown","B55gamma stabilization mechanism not structurally defined"]},{"year":2016,"claim":"Extended SIK2 substrate-level control to lipid/ketone metabolism (p300 Ser89 disrupting PPARα), autophagy restraint in breast cancer, and isoform-resolved macrophage polarization, broadening SIK2 from a transcriptional regulator to a hub over metabolism, cell death, and immunity.","evidence":"In vitro p300 kinase assay and S89A mutagenesis, ATG5-rescue epistasis, catalytically-inactive SIK2/SIK3 knock-in mice with IL-10 readouts","pmids":["26983400","27697861","27920213"],"confidence":"High","gaps":["Functional redundancy versus specificity between SIK2 and SIK3 incompletely parsed","How SIK2 both restricts and later promotes autophagy across contexts unresolved"]},{"year":2018,"claim":"Clarified divergent inputs to Thr484: insulin phosphorylation stabilizes SIK2 without altering catalytic activity, contrasting with the degradative CaMK signal, and PKA Ser587 was tied to sleep regulation.","evidence":"Thr484 phospho-specific antibody and kinase assays in primary adipocytes; Sik2S587A knock-in EEG sleep recordings; osteoblast PTH-CRTC-RANKL siRNA epistasis","pmids":["30586628","32457359","30377251"],"confidence":"Medium","gaps":["How identical Thr484 site yields opposite stability outcomes depending on signal unresolved","Direct substrate(s) underlying sleep phenotype not identified"]},{"year":2022,"claim":"Identified direct kinase-substrate relationships driving cancer phenotypes—MYLK Ser343 for motility/metastasis and LRP6 for Wnt/β-catenin and stemness—and linked SIK2-HDAC-MEF2D signaling to DNA double-strand break repair gene expression.","evidence":"In vitro kinase assays with phosphosite mutagenesis, kinase-dead/inhibitor validation, ChIP/ATAC-seq, DSB repair and metastasis assays","pmids":["35278271","35277657","35642638"],"confidence":"High","gaps":["Whether centrosomal and DNA-repair roles converge mechanistically unclear","In vivo therapeutic windows for SIK2 inhibition not defined here"]},{"year":2024,"claim":"Defined GABARAPL2 Ser72 as a direct SIK2 substrate enabling autophagosome-lysosome fusion with protective effects in Alzheimer's models, and Gab1 Ser266 phosphorylation as a negative-feedback brake on FGF2/ERK signaling, while CUL4B-DDB1 (via K144) was identified as a degradation route.","evidence":"Phosphoproteomics, S72E/S72A and S266 mutagenesis, AAV delivery and behavioral/LTP assays, in vitro Gab1 kinase assay, MS identification of CUL4B-DDB1 with K144 mutagenesis","pmids":["41126299","39267218","42213109"],"confidence":"High","gaps":["How SIK2 selects between autophagy-promoting and autophagy-restricting roles across tissues unresolved","Upstream signals controlling CUL4B-DDB1-mediated SIK2 turnover unknown"]},{"year":null,"claim":"It remains unresolved how a single kinase coordinates its many spatially distinct functions—centrosomal mitotic control, ER-associated ERAD, autophagosome fusion, and nuclear transcriptional repression—and what determines substrate selection under competing PKA, CaMK, insulin, and acetylation inputs.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model of how regulatory inputs route SIK2 to specific substrate pools","Structural basis of substrate discrimination unknown","Context-dependent pro- versus anti-autophagic roles unreconciled"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,3,5,6,13,21,25,32,33]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[37,6,21,25,33]},{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[37]}],"localization":[{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[0,34]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[5]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[19]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[8]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[1,3,9,13,26]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[7,10,13,16,6]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[4,11,32]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[0,18,34]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[25,33,8]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[5,6,35]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[12]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[22,36]}],"complexes":[],"partners":["CRTC2","HDAC4","PP2A","P35/CDK5R1","PJA2","P97/VCP","FBXW7","CUL4B"],"other_free_text":[]}},"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 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Yi xue ban = Journal of Zhejiang University. 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PKA (a known SIK2 inhibitor) induces SIK2-dependent centrosome splitting in interphase, while SIK2 depletion blocks centrosome separation in mitosis and reduces AKT phosphorylation.\",\n      \"method\": \"Immunofluorescence localization, phosphorylation mapping by mutagenesis, siRNA depletion with mitotic phenotype readout, xenograft studies\",\n      \"journal\": \"Cancer cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal functional experiments including localization, phosphorylation site identification, KD phenotype, and in vivo validation; replicated by subsequent studies\",\n      \"pmids\": [\"20708153\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SIK2 phosphorylates and suppresses TORC1 (CRTC1) nuclear translocation, thereby repressing CREB-mediated gene expression in neurons. During oxygen-glucose deprivation, CaMK I/IV phosphorylate SIK2 at Thr484, leading to SIK2 protein degradation and consequent TORC1 dephosphorylation and CREB activation, promoting neuronal survival.\",\n      \"method\": \"In vitro kinase assay (CaMK phosphorylation of SIK2), sik2−/− mouse neurons with OGD survival assay, transient focal ischemia model, immunoblotting for TORC1 phosphorylation\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with defined phenotype, identified upstream kinase, identified substrate phosphorylation site, replicated in vivo ischemia model\",\n      \"pmids\": [\"21220102\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SIK2 suppresses TORC1 nuclear translocation and CREB-mediated Mitf gene expression in melanocytes, thereby repressing eumelanogenesis. In vivo, Sik2−/− mice on an agouti (Ay/a) background showed brown hair, demonstrating that SIK2 represses eumelanogenesis.\",\n      \"method\": \"B16 melanoma cell overexpression/KO, UV-induced TORC1 nuclear translocation assay, Sik2−/− mouse genetics with Ay/a background, hair pigmentation analysis\",\n      \"journal\": \"Pigment cell & melanoma research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with clear phenotype, mechanistic pathway through TORC1-CREB-Mitf confirmed in cells and in vivo\",\n      \"pmids\": [\"20819186\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"LKB1 activates SIK2 (and SIK3), which then phosphorylates class IIa HDACs (HDAC4, -5, -7, -9) at conserved motifs to promote 14-3-3 binding and nuclear export. SIK2 activates MEF2-dependent transcription and relieves repression of myogenesis by the HDACs. This pathway is PKA-sensitive.\",\n      \"method\": \"In vitro kinase assay, 14-3-3 binding assay, subcellular fractionation, MEF2 reporter assay, myogenesis assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro kinase assay establishing direct phosphorylation, 14-3-3 binding, and functional MEF2/myogenesis readout; single lab but multiple orthogonal methods\",\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 at Lys-53 inhibits SIK2 kinase activity, whereas HDAC6-mediated deacetylation restores it. The acetylation-mimetic SIK2-K53Q mutant causes autophagosome accumulation, while SIK2 knockdown abrogates autophagosome-lysosome fusion and impairs TDP-43Δ inclusion body clearance.\",\n      \"method\": \"In vitro kinase assay, acetylation-mimetic and non-acetylatable mutagenesis, autophagosome accumulation assay, lysosome fusion assay, siRNA knockdown\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct in vitro kinase assay with mutagenesis identifying acetylation site, functional autophagy readouts; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"23322770\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SIK2 physically interacts with p97/VCP (co-localized at ER membrane) and phosphorylates p97/VCP to stimulate its ATPase activity, thereby promoting degradation of ERAD substrates. Kinase-deficient SIK2 or knockdown impairs ERAD substrate degradation and disrupts ER homeostasis.\",\n      \"method\": \"Co-immunoprecipitation, co-localization by immunofluorescence, in vitro ATPase activity assay, ERAD substrate degradation assay, kinase-dead mutant analysis, siRNA knockdown\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — direct biochemical interaction, in vitro activity assay with functional readout, mutagenesis; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"24129571\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SIK2 forms a complex with CDK5 activator p35 and E3 ligase PJA2 in pancreatic β-cells. Following glucose stimulation, SIK2 phosphorylates p35 at Ser91, triggering p35 ubiquitylation by PJA2 and promoting insulin secretion. β-cell-specific SIK2 knockout leads to p35 accumulation and impaired insulin secretion.\",\n      \"method\": \"Co-immunoprecipitation, in vitro kinase assay (SIK2 phosphorylation of p35 at Ser91), ubiquitylation assay, β-cell-specific KO mouse with insulin secretion phenotype, mass spectrometry for complex identification\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted complex with in vitro kinase assay identifying phosphorylation site, ubiquitylation assay, and genetic KO with functional secretion phenotype\",\n      \"pmids\": [\"24561619\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SIK2 KO mice exhibit increased CRTC2-CREB transcriptional activity in white adipocytes, elevated ATF3, reduced GLUT4 expression, reduced glucose uptake in muscle and adipocytes, hypertriglyceridemia due to increased lipolysis, and impaired glucose and insulin tolerance.\",\n      \"method\": \"SIK2 KO mouse metabolic phenotyping, glucose/insulin tolerance tests, lipolysis assays, CRTC2-CREB pathway analysis, 3T3-L1 adipocyte culture, CRTC2 KO comparison\",\n      \"journal\": \"Diabetes\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with multiple defined metabolic phenotypes and pathway attribution through CRTC2-CREB; replicated in vitro\",\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 elevation (e.g., forskolin, β-adrenergic agonist), promoting 14-3-3 binding and a phosphorylation-dependent relocalization of SIK2 from a particulate fraction to the cytosol. Ser358Ala mutation abolishes 14-3-3 binding and relocalization.\",\n      \"method\": \"Phosphopeptide mapping of SIK2, site-directed mutagenesis (Ser358Ala), 14-3-3 binding assay, adipocyte fractionation, immunocytochemistry\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — phosphopeptide mapping, mutagenesis confirming binding site, subcellular fractionation in primary adipocytes; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"22462548\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"In adipocytes, SIK2 directly phosphorylates CRTC2, CRTC3, and HDAC4. CRTC2, CRTC3, HDAC4, and PP2A all interact with SIK2. PKA-mediated phosphorylation of SIK2 at Ser358 reduces binding of CRTCs and PP2A to SIK2. SIK2 increases GLUT4 protein levels and glucose uptake in adipocytes through this pathway.\",\n      \"method\": \"Co-immunoprecipitation (SIK2 with CRTC2/3, HDAC4, PP2A), siRNA knockdown of SIK2/CRTC2/HDAC4, GLUT4 protein measurement, glucose uptake assay, SIK2 overexpression and pharmacological inhibition\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP identifying multiple substrates/partners, functional glucose uptake readout, validated in human adipocytes; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"25472719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SIK2 is activated in 3T3-L1 adipocytes by nutrient deprivation, ATP synthesis inhibition, and AICAR treatment. SIK2 overexpression represses lipogenic gene expression (FAS, ACC2, SCD1) by reducing SREBP-1 nuclear translocation, independent of AMPK; knockdown increases these genes.\",\n      \"method\": \"In vitro kinase activity assay (peptide substrate phosphorylation), adenovirus-mediated overexpression and siRNA knockdown, FAS promoter-luciferase reporter, SREBP-1 nuclear translocation by immunoblot\",\n      \"journal\": \"Obesity (Silver Spring, Md.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — direct kinase activity assay, promoter reporter, nuclear translocation, multiple functional readouts; single lab\",\n      \"pmids\": [\"18239551\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SIK2 restricts autophagic flux in triple-negative breast cancer cells. Genetic or pharmacological inhibition of SIK2 increases autophagic flux and selectively causes cell death in breast cancer cells (especially claudin-low subtype). Depletion of ATG5 rescues viability loss after SIK2 inhibition, placing SIK2 upstream of autophagosome formation.\",\n      \"method\": \"Loss-of-function screening, siRNA/pharmacological SIK2 inhibition, autophagic flux assay, ATG5 depletion rescue, in vivo tumor growth assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis via ATG5 rescue, in vivo validation, multiple cell lines; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"27697861\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SIK2 and SIK3 contribute to macrophage polarization. Knock-in of catalytically inactive SIK2 and SIK3 in mice demonstrated that inhibition of SIK2 and SIK3 during macrophage differentiation greatly enhances IL-10 production and produces a stable anti-inflammatory macrophage phenotype even after kinase reactivation.\",\n      \"method\": \"Knock-in mice expressing catalytically inactive SIK1, SIK2, SIK3; primary macrophage cytokine production assays; pharmacological inhibition during differentiation\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — catalytically inactive knock-in mice with defined cytokine phenotype; isoform-specific genetic dissection with functional readout\",\n      \"pmids\": [\"27920213\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SIK2 phosphorylates p300 at Ser89, disrupting p300-PPARα interaction (which normally occurs via a conserved LXXLL motif on p300) and thereby decreasing PPARα-mediated ketogenic gene expression. The phosphorylation-defective p300 S89A mutant shows increased PPARα interaction and abolishes SIK2 suppression of ketogenesis.\",\n      \"method\": \"In vitro kinase assay (SIK2 phosphorylation of p300), co-immunoprecipitation (p300-PPARα interaction), site-directed mutagenesis (p300 S89A), ketogenic gene expression assay in liver\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay with mutagenesis identifying phosphorylation site, functional gene expression readout, Co-IP confirming interaction disruption; single lab\",\n      \"pmids\": [\"26983400\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PTH(1-34) activates PKA, which inhibits SIK2 and SIK3 in osteoblasts, leading to nuclear translocation of CRTC2 and CRTC3 and upregulation of RANKL transcription. Knockdown of SIK2 and SIK3, and PP1/PP2A inhibition, demonstrated that SIK2/3 and protein phosphatases 1/2A are part of the PTH-CRTC2/3-RANKL regulatory pathway.\",\n      \"method\": \"siRNA knockdown of SIK2/3 and CRTCs in primary calvarial osteoblasts, PP1/PP2A inhibitor experiments, RANKL qPCR, CRTC nuclear localization by immunofluorescence\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA epistasis in primary osteoblasts, multiple pathway components tested, in vitro and in vivo RANKL validation; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"30377251\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SIK2 promotes mitochondrial fission through phosphorylation of Drp1 at Ser616, thereby inhibiting mitochondrial oxidative phosphorylation. SIK2 also upregulates HIF-1α by activating the PI3K/AKT signaling pathway, which directly upregulates glycolytic gene transcription (Warburg effect) in ovarian cancer cells.\",\n      \"method\": \"SIK2 overexpression/knockdown, phospho-specific immunoblotting for Drp1-pSer616, PI3K/AKT pathway analysis, mitochondrial function assays, glycolysis assays\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — phosphorylation site identified with phospho-specific antibody, functional mitochondrial and glycolytic readouts; but direct in vitro kinase assay for Drp1 phosphorylation not clearly stated in abstract\",\n      \"pmids\": [\"31639424\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SIK2 promotes lipid synthesis in ovarian cancer by upregulating SREBP1c (and thus FASN) and SREBP2 (and thus HMGCR) through the PI3K/Akt signaling pathway, increasing both fatty acid and cholesterol synthesis.\",\n      \"method\": \"SIK2 knockdown/overexpression, SREBP1c/SREBP2 expression assays, PI3K/Akt pathway inhibition, in vitro and in vivo lipid synthesis assays\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — functional lipid synthesis assays with pathway inhibition; multiple in vitro and in vivo readouts; single lab\",\n      \"pmids\": [\"31932581\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SIK2 suppresses gastric cancer cell migration/invasion by phosphorylating and activating mTORC1, which inhibits autophagic degradation of protein phosphatases PHLPP2 and PP2A. The upregulated PHLPP2 and PP2A then dephosphorylate and inactivate AKT, thereby inhibiting AKT/GSK3β/β-catenin signaling and EMT.\",\n      \"method\": \"SIK2 overexpression/knockdown, mTORC1 phosphorylation assay, autophagy flux assay, PHLPP2/PP2A protein stability assay, AKT phosphorylation by immunoblot, migration/invasion assay\",\n      \"journal\": \"Molecular oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — mechanistic pathway established via multiple molecular assays; single lab, no direct in vitro kinase reconstitution of full pathway\",\n      \"pmids\": [\"33128264\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Fbxw7 targets SIK2 for proteasomal degradation by binding the 'TPPPS' motif of SIK2. Endogenous Fbxw7 downregulates SIK2 protein level to control cell cycle progression, interfering with the SIK2/TORC2/AKT signaling pathway and modulating p21 expression.\",\n      \"method\": \"Co-immunoprecipitation (Fbxw7-SIK2 interaction), motif mutation analysis, ubiquitination assay, SIK2 half-life measurement, cell cycle analysis\",\n      \"journal\": \"Cell biology international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — Co-IP, motif identification, ubiquitination assay; single lab with multiple methods but no mutagenesis of ubiquitination sites confirmed\",\n      \"pmids\": [\"32437091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SIK2 is recruited to the Salmonella-containing vacuole (SCV) together with the Arp2/3 complex and formins during Salmonella infection. Under basal conditions, SIK2 associates with actin filaments. SIK2 depletion causes a severe actin nucleation and polymerization defect at the SCV, promotes bacterial escape from the SCV, and impairs xenophagy.\",\n      \"method\": \"Global host phosphoproteome analysis post-infection, SIK2 siRNA depletion, immunofluorescence localization to SCV and actin, bacterial survival/proliferation assay, xenophagy assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — phosphoproteomics to identify SIK2, localization studies, epistasis via depletion with defined bacterial and autophagy phenotypes; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"33947818\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ARN-3236 (SIK2 inhibitor) produces antidepressant-like effects in mice via the hippocampal CRTC1-CREB-BDNF pathway. SIK2 inhibition prevents cytoplasmic sequestration of CRTC1 and restores BDNF expression; hippocampal CRTC1 mediates these effects as demonstrated by viral gene transfer.\",\n      \"method\": \"Chronic stress mouse models (CSDS, CUMS), stereotactic viral-mediated gene transfer of CRTC1, co-immunoprecipitation, immunofluorescence, western blotting\",\n      \"journal\": \"Frontiers in pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — viral-mediated epistasis placing CRTC1 downstream of SIK2 in behavioral context; single lab with multiple behavioral and molecular methods\",\n      \"pmids\": [\"33519490\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SIK2 directly phosphorylates MYLK (myosin light chain kinase, smooth muscle) at Ser343, activating MYLK which then phosphorylates its downstream effector MYL2 (myosin light chain 2), thereby promoting ovarian cancer cell motility and metastasis. Adipocytes induce both SIK2 phosphorylation at Ser358 and MYLK phosphorylation at Ser343.\",\n      \"method\": \"In vitro kinase assay (SIK2 phosphorylating MYLK at Ser343), phospho-specific immunoblotting, Co-immunoprecipitation, siRNA knockdown, cell motility/migration assays, in vivo metastasis model\",\n      \"journal\": \"Molecular oncology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro kinase assay identifying phosphorylation site, functional motility readout in vitro and in vivo; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"35278271\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SIK2 inhibitors decrease phosphorylation of class-IIa HDACs (HDAC4/5/7) and abolish HDAC4/5/7-associated transcriptional activity of MEF2D, decreasing MEF2D binding to regulatory regions of FANCD2, EXO1, and XRCC4 genes, resulting in repression of DNA double-strand break repair. SIK2 inhibition also decreases PARP enzyme activity.\",\n      \"method\": \"SIK2 inhibitors (ARN3236, ARN3261) in cancer cells, HDAC4/5/7 phosphorylation immunoblotting, MEF2D chromatin accessibility (ATAC-seq), MEF2D ChIP at target gene loci, DNA DSB repair assays, PARP activity assay, xenograft studies\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods including HDAC phosphorylation, ChIP, ATAC-seq, DNA repair assays, and in vivo validation; single lab\",\n      \"pmids\": [\"35642638\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SIK2 inhibition by ARN-3236 prevents fibroblast differentiation and reduces extracellular matrix expression. Mechanistically, SIK2 inactivation results in dephosphorylation and nuclear translocation of CRTC2, which then binds CREB to promote CREB-dependent anti-fibrotic gene expression.\",\n      \"method\": \"Western blot of SIK2/pCRTC2 in fibroblasts, ARN-3236 treatment and siRNA knockdown, CRTC2 nuclear translocation by fractionation, bleomycin mouse model of pulmonary fibrosis, immunohistochemistry\",\n      \"journal\": \"BMC pulmonary medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — CRTC2 localization and CREB binding established, in vivo fibrosis model; single lab\",\n      \"pmids\": [\"35410283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SIK2 overexpression reduces ER stress-mediated tubular epithelial apoptosis by inhibiting the histone acetyltransferase activity of p300, thereby activating HSF1/Hsp70. This mechanism underlies SIK2 protection against diabetic kidney disease.\",\n      \"method\": \"SIK2 KO and overexpression in diabetic mice, transcriptome sequencing, p300 histone acetyltransferase activity assay, HSF1/Hsp70 pathway analysis, ER stress markers\",\n      \"journal\": \"Translational research : the journal of laboratory and clinical medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — mechanistic pathway via p300 inhibition to HSF1/Hsp70 with functional apoptosis readout; in vivo validation; single lab\",\n      \"pmids\": [\"36075517\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SIK2 directly phosphorylates LRP6, leading to Wnt/β-catenin signaling pathway activation and induction of IDH1 expression in breast cancer stem cells. This phosphorylation is kinase activity-dependent. SIK2 itself is phosphorylated upstream by CK1α.\",\n      \"method\": \"In vitro kinase assay (SIK2 phosphorylation of LRP6), β-catenin accumulation assay, SIK2 kinase-dead mutant analysis, SIK2 inhibitors (ARN-3236, HG-9-91-01) blocking LRP6 phosphorylation, breast cancer stem cell proportion assays, IDH1 expression analysis\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro kinase assay with kinase-dead validation, pharmacological confirmation, functional stemness readout; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"35277657\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"In DLBCL, siRNA-mediated downregulation of SIK2 results in upregulation of the CREB target gene BIM, consistent with SIK2's role in phosphorylating and inhibiting its cofactor TORC2/CRTC2, thereby repressing CREB-mediated transcription.\",\n      \"method\": \"siRNA knockdown of SIK2, RT-PCR for BIM expression, Western blot, cAMP and dexamethasone treatment\",\n      \"journal\": \"Leukemia & lymphoma\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — siRNA knockdown with defined target gene readout; establishes CRTC2-CREB pathway in lymphoma context; single lab\",\n      \"pmids\": [\"20367563\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"B55gamma (PPP2R2C) interacts with and stabilizes SIK2 protein. The B55gamma-SIK2 complex is required for B55gamma-mediated suppression of S6K phosphorylation and promotion of glioma cell survival under glucose starvation.\",\n      \"method\": \"Co-immunoprecipitation (B55gamma-SIK2 interaction), siRNA knockdown of SIK2, S6K phosphorylation assay, cell viability under glucose deprivation\",\n      \"journal\": \"Cancer cell international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP and epistasis via SIK2 knockdown; single lab, limited functional follow-up\",\n      \"pmids\": [\"25792973\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SIK2 is required for cardiac left ventricular hypertrophy (LVH) development in response to chronic high-salt diet. Sik2−/− mice do not develop LVH upon high-salt feeding, while wild-type mice do. In cardiac myocytes, α-adducin regulates SIK2 expression, and SIK2 mediates adducin's effects on hypertrophy marker gene activation.\",\n      \"method\": \"Sik2−/− mouse model on high-salt diet, echocardiography (LV wall thickness), gene expression of hypertrophy markers, cardiac myocyte culture with α-adducin manipulation\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with defined cardiac phenotype, pathway dissection in cardiac myocytes; single lab with in vivo and in vitro validation\",\n      \"pmids\": [\"24752134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PKA phosphorylation site Ser587 of SIK2 regulates sleep need. Sik2S587A knock-in mice showed increased NREM sleep delta density, indicating that the PKA-SIK2 signaling axis is involved in regulating sleep.\",\n      \"method\": \"Sik2S587A knock-in mice, EEG/EMG sleep recording (NREM sleep time, delta density), sleep deprivation recovery experiments\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — knock-in mice with defined PKA site mutation and EEG sleep phenotype; single lab\",\n      \"pmids\": [\"32457359\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"In Müller glia, SIK2 activity increases in response to insulin stimulation and is associated with increased IRS1-SIK2 interaction. SIK2 negatively modulates insulin-dependent cell survival: overexpression reduces pAkt levels while knockdown increases pAkt and reduces apoptosis. Under hyperglycemia, increased SIK2 activity correlates with reduced Akt activation and enhanced apoptosis.\",\n      \"method\": \"In vitro kinase assay (SIK2 activity), co-immunoprecipitation (IRS1-SIK2), siRNA knockdown and overexpression, pAkt immunoblotting, TUNEL apoptosis assay, streptozotocin rat model\",\n      \"journal\": \"Investigative ophthalmology & visual science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — kinase activity assay, Co-IP, functional overexpression/KD; single lab with multiple methods\",\n      \"pmids\": [\"23599336\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Insulin induces phosphorylation of SIK2 at Thr484 in primary adipocytes, which is associated with increased SIK2 protein stability but does not affect SIK2 catalytic activity or its activity towards HDAC4.\",\n      \"method\": \"Phospho-specific antibody for SIK2-Thr484, in vitro kinase assay (no change in activity), SIK2 protein level with MG132 proteasome inhibitor, primary human and rat adipocytes\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — phospho-specific antibody and in vitro kinase assay in primary cells; single lab with multiple methods\",\n      \"pmids\": [\"30586628\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SIK2 phosphorylates GABARAPL2 at Ser72, which is essential for autophagosome-lysosome fusion. The phosphorylation-mimetic GABARAPL2-S72E mutant replicates SIK2-mediated autophagic flux enhancement and reduces Aβ pathology in 5×FAD AD mice, while the non-phosphorylatable S72A mutant fails to show protective effects.\",\n      \"method\": \"Co-immunoprecipitation, GST pull-down, phosphoproteomics, site-directed mutagenesis (S72E, S72A), AAV-mediated hippocampal delivery, mRFP-GFP-LC3 tandem fluorescence autophagy assay, Morris water maze, LTP recording, electron microscopy\",\n      \"journal\": \"Translational neurodegeneration\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — phosphoproteomics identifying substrate, mutagenesis confirming functional site, multiple orthogonal methods including structural and behavioral readouts; single lab but rigorous\",\n      \"pmids\": [\"41126299\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SIK2 acts as a negative feedback regulator of FGF2/Ras/ERK1/2 signaling in retinal Müller glia. SIK2 phosphorylates Gab1 at Ser266, which weakens Gab1 interactions with Grb2 and Shp2, thereby downregulating ERK1/2 activation. SIK2 itself is activated downstream of ERK1/2 in an FGF2-dependent manner.\",\n      \"method\": \"In vitro kinase assay (SIK2 phosphorylating Gab1 at Ser266), site-directed mutagenesis, Co-immunoprecipitation (Gab1-Grb2/Shp2), SIK2 overexpression/knockdown with ERK1/2 activation assay\",\n      \"journal\": \"Advanced biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct in vitro kinase assay identifying phosphorylation site with mutagenesis, Co-IP confirming complex disruption, functional ERK1/2 readout; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"39267218\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SIK2 is synthetic lethal with loss of FANCA. FANCA co-localizes with SIK2 at centrosomes and regulates SIK2 activity at centrosomes. SIK2 depletion in FANCA-deficient cells causes impaired G2-M transition, delayed mitotic progression, cytokinesis failure, and abrogates nocodazole-induced prometaphase arrest, suggesting a role for SIK2 in the spindle assembly checkpoint.\",\n      \"method\": \"Kinome-wide synthetic lethality screen in FANCA-/- fibroblasts, co-localization of FANCA and SIK2 at mitotic structures by immunofluorescence, SIK2 kinase activity assay at centrosomes, pharmacological SIK2 inhibition with cell cycle analysis\",\n      \"journal\": \"Molecular oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — genetic screen plus localization and kinase activity studies; single lab with multiple methods\",\n      \"pmids\": [\"34058059\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SIC-19 promotes SIK2 ubiquitination and degradation via the CUL4B-DDB1 E3 ubiquitin ligase complex. Lysine 144 (K144) is the critical ubiquitination site on SIK2 mediating its degradation. CUL4B is functionally required for SIC-19-induced SIK2 degradation.\",\n      \"method\": \"Mass spectrometry identifying ubiquitin ligases binding SIK2, co-immunoprecipitation (SIK2-CUL4B-DDB1), Western blot for SIK2 half-life, site-directed mutagenesis (K144), ubiquitination assay, CUL4B knockdown\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — MS identification, Co-IP validation, mutagenesis confirming ubiquitination site, functional degradation assay; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"42213109\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SIK2 knockdown in ovarian cancer cells reduces RAD50 phosphorylation at Ser635, prevents nuclear translocation of RAD50, disrupts nuclear filament assembly, and impairs homologous recombination DNA repair, inducing apoptosis.\",\n      \"method\": \"SIK2 siRNA knockdown and SIC-19 inhibitor, phospho-RAD50(Ser635) immunoblotting, RAD50 nuclear localization assay, HR repair functional assay, apoptosis assay\",\n      \"journal\": \"Drug resistance updates\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — functional HR repair assay with phospho-site identification; but direct kinase assay for SIK2 phosphorylating RAD50 not explicitly confirmed in abstract; single lab\",\n      \"pmids\": [\"38518726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"SIK2 (originally named Qik) is a serine-threonine kinase belonging to the AMPK/SNF1 family, capable of autophosphorylation as demonstrated by in vitro kinase assay.\",\n      \"method\": \"In vitro kinase assay (autophosphorylation), representational difference analysis for gene identification\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — direct in vitro kinase assay; single study, foundational characterization\",\n      \"pmids\": [\"11027514\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SIK2 is an AMPK-family serine/threonine kinase activated by LKB1 and regulated by PKA (phosphorylation at Ser358/Ser587, promoting 14-3-3 binding and relocalization), CaMK I/IV (Thr484 phosphorylation leading to degradation), insulin (Thr484 stabilization), and acetylation (p300/CBP at Lys53 inhibits; HDAC6 restores activity); it phosphorylates multiple substrates including CRTC1/2/3 (suppressing CREB-mediated transcription), class IIa HDACs (promoting nuclear export), p35/CDK5R1 (regulating insulin secretion via PJA2 ubiquitylation), Drp1 (Ser616, mitochondrial fission), MYLK (Ser343, cell motility), LRP6 (Wnt/β-catenin activation), p300 (Ser89, disrupting PPARα-mediated ketogenesis), Gab1 (Ser266, negative feedback on FGF2/ERK signaling), p97/VCP (promoting ERAD), and GABARAPL2 (Ser72, autophagosome-lysosome fusion); it localizes to centrosomes, ER membranes, and actin filaments, and controls mitosis, glucose/lipid metabolism, melanogenesis, neuronal survival, macrophage polarization, β-cell insulin secretion, cardiac hypertrophy, and DNA damage repair.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SIK2 is a serine/threonine kinase of the AMPK/SNF1 family that integrates hormonal, metabolic, and stress cues to control transcription, organelle dynamics, autophagy, and the cell cycle [#37, #1]. Its best-defined output is repression of CREB-driven transcription: SIK2 phosphorylates the CRTC/TORC coactivators (CRTC1/2/3) to retain them in the cytoplasm and phosphorylates class IIa HDACs (HDAC4/5/7/9) to promote their 14-3-3 binding and nuclear export, thereby tuning CREB- and MEF2-dependent gene programs [#1, #3, #9]. This kinase activity is gated by PKA, which phosphorylates SIK2 at Ser358 and Ser587 to drive 14-3-3 binding and relocalization and to release CRTC/PP2A from SIK2, and by additional inputs including CaMK I/IV-mediated Thr484 phosphorylation that triggers SIK2 degradation, insulin-induced Thr484 stabilization, and reversible acetylation at Lys53 (inhibitory p300/CBP acetylation reversed by HDAC6) [#8, #9, #1, #4, #31]. Through these axes SIK2 governs metabolic homeostasis—glucose uptake and GLUT4 levels, lipogenic and ketogenic gene expression, and β-cell insulin secretion via the SIK2–p35–PJA2 module [#7, #9, #6, #13]. Beyond transcription, SIK2 localizes to centrosomes where it controls centrosome separation and mitotic progression, phosphorylates p97/VCP at the ER to drive ERAD, and acts in autophagy through GABARAPL2 Ser72 phosphorylation to enable autophagosome–lysosome fusion [#0, #5, #32]. SIK2 additionally phosphorylates a broad substrate set linking it to motility (MYLK Ser343), mitochondrial fission (Drp1 Ser616), Wnt activation (LRP6), negative feedback on FGF/ERK signaling (Gab1 Ser266), and DNA double-strand break repair, and is itself targeted for degradation by Fbxw7 and the CUL4B–DDB1 complex [#21, #15, #25, #33, #22, #18, #35].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established SIK2 as a catalytically active serine/threonine kinase of the AMPK/SNF1 family, defining the protein class before any substrate was known.\",\n      \"evidence\": \"In vitro autophosphorylation kinase assay following gene identification by representational difference analysis\",\n      \"pmids\": [\"11027514\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No physiological substrate identified\", \"No upstream activating kinase defined\", \"Foundational single study\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined the core SIK2 transcriptional axis—suppression of CRTC/TORC nuclear translocation to repress CREB-target genes—and linked it to a physiological output (melanogenesis) and to centrosome biology in mitosis.\",\n      \"evidence\": \"Sik2-/- mice (agouti background pigmentation; centrosome phenotypes), C-Nap1 phosphosite mapping, siRNA mitotic readouts, xenografts\",\n      \"pmids\": [\"20819186\", \"20708153\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether centrosomal and transcriptional roles share regulatory inputs unresolved\", \"Direct in vivo CRTC phosphosite occupancy not mapped in melanocytes\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Showed SIK2 abundance itself is a regulated node: CaMK I/IV phosphorylation at Thr484 drives SIK2 degradation, relieving CRTC1 repression to promote CREB-dependent neuronal survival.\",\n      \"evidence\": \"In vitro CaMK kinase assay, sik2-/- neurons under oxygen-glucose deprivation, transient focal ischemia model\",\n      \"pmids\": [\"21220102\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the degradation machinery acting after Thr484 phosphorylation not defined here\", \"Generalizability beyond ischemic neurons untested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Expanded the SIK2 substrate repertoire beyond CRTCs to class IIa HDACs, p97/VCP, and p300, and revealed acetylation as a direct regulator of kinase activity—connecting SIK2 to MEF2 transcription, ERAD, and autophagy.\",\n      \"evidence\": \"In vitro kinase and 14-3-3 binding assays, ATPase assays, ERAD substrate degradation, acetylation-mimetic mutagenesis, autophagy flux assays\",\n      \"pmids\": [\"23393134\", \"24129571\", \"23322770\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether HDAC, VCP, and CRTC branches are co-regulated or context-segregated unclear\", \"Acetylation dynamics in vivo not established\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Connected SIK2 to whole-body metabolic control and β-cell function, defining the SIK2–p35–PJA2 ubiquitylation module for insulin secretion and CRTC2-CREB-dependent adipose/muscle glucose handling, plus a cardiac hypertrophy role.\",\n      \"evidence\": \"β-cell-specific and global Sik2-/- mice, in vitro p35 Ser91 kinase and ubiquitylation assays, metabolic phenotyping, high-salt cardiac model\",\n      \"pmids\": [\"24561619\", \"24898145\", \"24752134\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tissue-specific upstream activators differ and are incompletely mapped\", \"Relationship between secretory and transcriptional metabolic roles not unified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Mechanistically resolved PKA control of SIK2: Ser358 phosphorylation creates a 14-3-3 binding site driving cytosolic relocalization, providing the molecular basis for cAMP-dependent inhibition of SIK2 function.\",\n      \"evidence\": \"Phosphopeptide mapping, Ser358Ala mutagenesis, 14-3-3 binding and adipocyte fractionation\",\n      \"pmids\": [\"22462548\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How relocalization couples to substrate selection not defined\", \"Role of additional PKA sites left open\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Showed PKA Ser358 phosphorylation simultaneously releases CRTC and PP2A from SIK2, integrating multiple substrate/regulator interactions into one regulated complex controlling GLUT4 and glucose uptake; also identified B55gamma as a stabilizing partner.\",\n      \"evidence\": \"Reciprocal Co-IP (CRTC2/3, HDAC4, PP2A, B55gamma), siRNA, glucose uptake assays in human adipocytes and glioma\",\n      \"pmids\": [\"25472719\", \"25792973\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Stoichiometry and assembly order of the SIK2-PP2A-CRTC complex unknown\", \"B55gamma stabilization mechanism not structurally defined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Extended SIK2 substrate-level control to lipid/ketone metabolism (p300 Ser89 disrupting PPARα), autophagy restraint in breast cancer, and isoform-resolved macrophage polarization, broadening SIK2 from a transcriptional regulator to a hub over metabolism, cell death, and immunity.\",\n      \"evidence\": \"In vitro p300 kinase assay and S89A mutagenesis, ATG5-rescue epistasis, catalytically-inactive SIK2/SIK3 knock-in mice with IL-10 readouts\",\n      \"pmids\": [\"26983400\", \"27697861\", \"27920213\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional redundancy versus specificity between SIK2 and SIK3 incompletely parsed\", \"How SIK2 both restricts and later promotes autophagy across contexts unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Clarified divergent inputs to Thr484: insulin phosphorylation stabilizes SIK2 without altering catalytic activity, contrasting with the degradative CaMK signal, and PKA Ser587 was tied to sleep regulation.\",\n      \"evidence\": \"Thr484 phospho-specific antibody and kinase assays in primary adipocytes; Sik2S587A knock-in EEG sleep recordings; osteoblast PTH-CRTC-RANKL siRNA epistasis\",\n      \"pmids\": [\"30586628\", \"32457359\", \"30377251\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How identical Thr484 site yields opposite stability outcomes depending on signal unresolved\", \"Direct substrate(s) underlying sleep phenotype not identified\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified direct kinase-substrate relationships driving cancer phenotypes—MYLK Ser343 for motility/metastasis and LRP6 for Wnt/β-catenin and stemness—and linked SIK2-HDAC-MEF2D signaling to DNA double-strand break repair gene expression.\",\n      \"evidence\": \"In vitro kinase assays with phosphosite mutagenesis, kinase-dead/inhibitor validation, ChIP/ATAC-seq, DSB repair and metastasis assays\",\n      \"pmids\": [\"35278271\", \"35277657\", \"35642638\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether centrosomal and DNA-repair roles converge mechanistically unclear\", \"In vivo therapeutic windows for SIK2 inhibition not defined here\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined GABARAPL2 Ser72 as a direct SIK2 substrate enabling autophagosome-lysosome fusion with protective effects in Alzheimer's models, and Gab1 Ser266 phosphorylation as a negative-feedback brake on FGF2/ERK signaling, while CUL4B-DDB1 (via K144) was identified as a degradation route.\",\n      \"evidence\": \"Phosphoproteomics, S72E/S72A and S266 mutagenesis, AAV delivery and behavioral/LTP assays, in vitro Gab1 kinase assay, MS identification of CUL4B-DDB1 with K144 mutagenesis\",\n      \"pmids\": [\"41126299\", \"39267218\", \"42213109\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How SIK2 selects between autophagy-promoting and autophagy-restricting roles across tissues unresolved\", \"Upstream signals controlling CUL4B-DDB1-mediated SIK2 turnover unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unresolved how a single kinase coordinates its many spatially distinct functions—centrosomal mitotic control, ER-associated ERAD, autophagosome fusion, and nuclear transcriptional repression—and what determines substrate selection under competing PKA, CaMK, insulin, and acetylation inputs.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model of how regulatory inputs route SIK2 to specific substrate pools\", \"Structural basis of substrate discrimination unknown\", \"Context-dependent pro- versus anti-autophagic roles unreconciled\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 3, 5, 6, 13, 21, 25, 32, 33]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [37, 6, 21, 25, 33]},\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [37]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [0, 34]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [19]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [1, 3, 9, 13, 26]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [7, 10, 13, 16, 6]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [4, 11, 32]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [0, 18, 34]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [25, 33, 8]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [5, 6, 35]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [12]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [22, 36]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"CRTC2\", \"HDAC4\", \"PP2A\", \"p35/CDK5R1\", \"PJA2\", \"p97/VCP\", \"Fbxw7\", \"CUL4B\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}