{"gene":"PER2","run_date":"2026-06-10T05:19:53","timeline":{"discoveries":[{"year":2018,"finding":"CK1δ/ε (including the CK1δ2 splice variant) is itself the priming kinase for PER2, phosphorylating it at sites that are prerequisite for downstream stabilizing phosphorylations; the CK1 carboxyl-terminal tail modulates this priming activity and allows cellular signaling to influence circadian period.","method":"Comprehensive biochemical and biophysical analysis of mouse PER2 priming phosphorylation in cells; phosphoswitch mathematical modeling","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in-cell biochemical reconstitution with multiple phosphorylation-site analyses and computational modeling in a single focused study","pmids":["29784789"],"is_preprint":false},{"year":2020,"finding":"A conserved anion binding site in CK1 controls activation-loop conformation and determines which sites on PER2 are preferentially phosphorylated, thereby acting as a molecular switch that directly regulates PER2 stability; period-altering CK1 mutations in humans and Drosophila differentially modulate this switch.","method":"Integrated experimental (mutagenesis, in vitro kinase assays) and computational studies; cross-species period mutant analysis","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis plus in vitro assays plus computational modeling in one rigorous study","pmids":["32043967"],"is_preprint":false},{"year":2020,"finding":"CK1-mediated phosphorylation of PER2 at Ser478 creates a phosphodegron that recruits the E3 ligase β-TrCP for proteasomal degradation; PER2-Ser478Ala knock-in mice show longer circadian period and accumulation of PER2 protein (and associated PER1, CRY1, CRY2) in both nucleus and cytoplasm, with perturbed temperature compensation.","method":"PER2-Ser478Ala knock-in mouse generation; behavioral circadian analysis; western blotting; MEF bioluminescence (PER2::LUC) assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vivo knock-in mouse model with multiple orthogonal readouts (behavior, protein levels, bioluminescence)","pmids":["32354999"],"is_preprint":false},{"year":2006,"finding":"Protein phosphatase 1 (PP1) dephosphorylates CK1-phosphorylated PER2, stabilizing it against ubiquitin-proteasome degradation; PER2 co-immunoprecipitates with PP1c in mammalian cells, and dominant-negative PP1c or PP1 inhibitors accelerate PER2 degradation and shorten its half-life.","method":"Xenopus egg extract degradation assay; co-immunoprecipitation in HEK-293 cells; endogenous PP1 phosphatase assay from liver and brain; dominant-negative overexpression","journal":"The Biochemical Journal","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro dephosphorylation assay plus co-IP plus dominant-negative cell experiments in one study","pmids":["16813562"],"is_preprint":false},{"year":2008,"finding":"PER2 physically interacts with BMAL1 (at a distinct domain from CRY1/CRY2 binding sites) and with CLOCK, whereas CRY1 and CRY2 interact with BMAL1 but not with CLOCK; CRY proteins bind BMAL1 with higher affinity than PER2 and are stronger transcriptional repressors.","method":"Mammalian two-hybrid system; co-immunoprecipitation assays","journal":"BMC Molecular Biology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — two-hybrid and co-IP from a single lab, two complementary methods","pmids":["18430226"],"is_preprint":false},{"year":2010,"finding":"PER2 directly and specifically represses PPARγ transcriptional activity: PER2 blocks PPARγ recruitment to target promoters, thereby suppressing adipogenesis; PER2-deficient mice display drastically altered lipid metabolism and enhanced adipocyte differentiation. PER2 targets the S112 residue of PPARγ.","method":"Co-immunoprecipitation; chromatin immunoprecipitation; whole-genome microarray profiling; adipocyte differentiation assays in PER2-deficient fibroblasts; lipidomic profiling in white adipose tissue","journal":"Cell Metabolism","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (ChIP, Co-IP, microarray, lipidomics, in vivo KO) in one study with clear mechanistic conclusion","pmids":["21035761"],"is_preprint":false},{"year":2012,"finding":"PML (promyelocytic leukaemia) protein physically interacts with PER2 and is required for PER2 nuclear localization; in Pml−/− cells, PER2 is predominantly perinuclear/cytoplasmic. SIRT1 deacetylates PML at K487, and this deacetylation promotes PML-mediated nuclear localization of PER2.","method":"Co-immunoprecipitation; immunofluorescence localization in SCN neurons and MEFs; genetic KO (Pml−/−); SIRT1 deacetylation assay","journal":"The EMBO Journal","confidence":"High","confidence_rationale":"Tier 2 / Moderate — co-IP plus direct localization imaging plus genetic KO with functional consequence in a single rigorous study","pmids":["22274616"],"is_preprint":false},{"year":2017,"finding":"PER2 functions as a co-factor that facilitates recruitment of HIF-1α to hypoxia-response elements (HREs); PER2 physically interacts with HIF-1α via co-immunoprecipitation, and its enhancement of HIF-1 transcriptional activity requires the HIF-1α N803 asparagine to be unhydroxylated (hypoxic conditions).","method":"Co-immunoprecipitation; forced PER2 expression; HRE-reporter (VEGF promoter) assays; N803A point mutation; deferoxamine (N803-dioxygenase inhibitor) treatment","journal":"The FEBS Journal","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — co-IP plus reporter assay plus mutagenesis in single lab study","pmids":["28963769"],"is_preprint":false},{"year":2021,"finding":"PER2 acts as a co-factor of CREB to facilitate formation of a CREB/CRTC1/CBP transactivation complex on the CRE element of the Per1 gene in response to light or forskolin; absence of PER2 abolishes the CREB–CBP interaction and reduces histone H3 acetylation and RNA Pol II recruitment to the Per1 promoter.","method":"In vitro and in vivo CREB/PER2 interaction assays; chromatin immunoprecipitation; luciferase reporter assays; genetic KO; light-pulse experiments in mice","journal":"Scientific Reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP plus co-IP plus in vivo light induction in a single lab with multiple orthogonal methods","pmids":["34741086"],"is_preprint":false},{"year":2016,"finding":"SIRT1 and PER2 constitute a reciprocal negative regulatory loop in the liver: SIRT1 deficiency leads to enhanced H4K16 acetylation at the Per2 promoter, causing Per2 overexpression; in turn, PER2 suppresses Sirt1 transcription by binding to its promoter at the CLOCK/BMAL1 site.","method":"ChIP for H4K16 acetylation at Per2 promoter; Per2 promoter binding assay; Sirt1-deficient mouse liver analysis; human hepatocyte experiments","journal":"Scientific Reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP plus in vivo genetic KO plus human cell validation in single lab study","pmids":["27346580"],"is_preprint":false},{"year":2017,"finding":"SIK3 (salt-inducible kinase 3) facilitates phosphorylation-dependent destabilization of PER2 protein; SIK3 knockdown elevates PER2 protein levels while SIK3 overexpression decreases them, and PER2 accumulates in Sik3-deficient fibroblasts and liver.","method":"Sik3 knockout mouse; SIK3 knockdown/overexpression in cultured cells; bioluminescence rhythm monitoring; protein level assessment by western blotting","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo KO plus cellular knockdown/overexpression with protein-level and bioluminescence readouts in one study","pmids":["29227248"],"is_preprint":false},{"year":2019,"finding":"SIRT6 interacts with and deacetylates PER2, thereby preventing its proteasomal degradation; loss of Sirt6 jeopardizes circadian phase, and this is linked to PER2 acetylation status.","method":"Co-immunoprecipitation; deacetylation assay; Sirt6-knockdown circadian phenotype analysis","journal":"Biochemical and Biophysical Research Communications","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — co-IP plus deacetylation assay plus KD phenotype in single lab, moderate strength","pmids":["30782483"],"is_preprint":false},{"year":2004,"finding":"Per2(Brdm1) mutant mice (PAS domain deletion) display lowered expression of the glutamate transporter Eaat1 in astrocytes, leading to reduced glutamate uptake and elevated extracellular glutamate, which is mechanistically linked to increased alcohol intake; acamprosate normalizes glutamate levels and alcohol consumption in these mice.","method":"Per2 mutant mouse analysis; Eaat1 expression profiling; extracellular glutamate measurement; pharmacological rescue with acamprosate","journal":"Nature Medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo genetic model with molecular phenotype (transporter expression, glutamate levels) and pharmacological rescue","pmids":["15608650"],"is_preprint":false},{"year":2022,"finding":"CRY proteins are required for nuclear localization of PER2 in SCN neurons: in the absence of CRY, PER2 is predominantly cytoplasmic and more mobile (by FRAP); virally expressed CRY1 or CRY2 relocalize PER2 to the nucleus and initiate circadian rhythms; the CRY1 C-terminal tail is necessary for this nuclear relocalization.","method":"Confocal imaging of endogenous PER2::Venus in SCN of CRY-null mice; viral vector expression of CRY variants; FRAP; translational switching to control CRY1 abundance","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — live-cell imaging with FRAP, genetic null background, viral rescue with domain-mutant controls; multiple orthogonal approaches in one rigorous study","pmids":["35046033"],"is_preprint":false},{"year":2007,"finding":"PER2 binds ERα and enhances ERα degradation; conversely, suppression of PER2 levels leads to ERα stabilization; PER2 expression is itself estrogen-inducible in breast cancer cells, suggesting a feedback mechanism to attenuate estrogen stimulation.","method":"Co-immunoprecipitation; PER2 overexpression and suppression in breast cancer cells; ERα protein stability assays; estrogen induction experiments","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — co-IP plus gain/loss-of-function protein stability assay in single lab","pmids":["17599055"],"is_preprint":false},{"year":2023,"finding":"PER2 binds HSP90 through its PAS1 domain and reduces the interaction of HSP90 with IKKs, promoting ubiquitination of IKKα/β and thereby suppressing IKK/NF-κB pathway activity and PD-L1 expression in oral squamous cell carcinoma cells.","method":"Co-immunoprecipitation; GST pull-down; cycloheximide chase assay; western blotting; overexpression/knockdown; in vivo xenograft humanized immune model","journal":"Journal for Immunotherapy of Cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — GST pull-down plus co-IP plus functional in vivo rescue in single lab study","pmids":["37914384"],"is_preprint":false},{"year":2025,"finding":"PER2 binds HSP70 through its C-terminal domain, reducing the HSP70–AKT interaction and promoting AKT ubiquitination and degradation, which upregulates cuproptosis-related proteins (DLAT, PDHB, SLC31A1) and promotes cuproptosis in OSCC cells. ATF3 is an upstream transcriptional activator of PER2, binding the PER2 promoter at −807 to −796 bp.","method":"Co-immunoprecipitation; GST pull-down; domain deletion mapping; ubiquitination assay; ATF3 ChIP/promoter analysis; in vivo xenograft","journal":"Cell Death & Disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP, GST pulldown, domain mapping, and ubiquitination assay in single lab study","pmids":["40113747"],"is_preprint":false},{"year":2021,"finding":"Per2 (together with Per1) is required for activation of Igf2 transcription during myoblast differentiation; Per proteins are recruited to the Igf2 promoter and enhancer, driving dynamic histone modifications and promoter-enhancer looping that create a circadian time window for myoblast differentiation initiation.","method":"Per1/Per2 depletion in myoblasts; in vivo muscle regeneration assay; RNA Pol II ChIP; histone modification ChIP; chromatin conformation capture (promoter-enhancer interaction); Per2 KO mice","journal":"The Journal of Cell Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP plus chromatin conformation capture plus in vivo KO rescue experiments; multiple orthogonal methods in single lab","pmids":["34009269"],"is_preprint":false},{"year":2008,"finding":"Estrogen (17β-estradiol) directly shortens the period of PER2::LUC circadian rhythms in uterine tissue explants but not in SCN explants; this effect is blocked by the ER antagonist raloxifene, indicating an estrogen-receptor-mediated direct modulation of the peripheral (uterine) molecular clock.","method":"Tissue explant bioluminescence assays from PER2::LUC knock-in mice; ovariectomy and estradiol/raloxifene treatment","journal":"American Journal of Physiology. Endocrinology and Metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct pharmacological and genetic manipulation in tissue explant with quantitative reporter readout in single study","pmids":["18728223"],"is_preprint":false},{"year":2014,"finding":"Sevoflurane anesthesia reduces CLOCK binding to the E'-box of the Per2 promoter and decreases histone H4 acetylation at the proximal Per2 promoter region, leading to suppressed Per2 expression in the SCN; this occurs independently of NAD+ concentration.","method":"Chromatin immunoprecipitation (anti-acetylated-histone H4 and anti-CLOCK); quantitative in situ hybridization; LC-MS measurement of NAD+","journal":"PloS One","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP for histone acetylation and CLOCK binding plus metabolite measurement in single lab study","pmids":["24498074"],"is_preprint":false},{"year":2016,"finding":"Per2 is activated predominantly in lymphoid-biased haematopoietic stem cells (HSCs) under DNA damage and ageing conditions, where it stimulates DNA damage signalling and p53-dependent apoptosis; Per2 deletion ameliorates replication stress, improves maintenance of Ly-biased HSCs, and extends lifespan without increasing DNA damage accumulation. Batf/p53-dependent HSC differentiation induction persists in Per2-deficient mice.","method":"In vivo RNAi screening; Per2 conditional KO mouse; HSC isolation and transplantation; DNA damage signalling analysis; lifespan measurement","journal":"Nature Cell Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo RNAi screen plus genetic KO with multiple cellular and physiological readouts in single lab study","pmids":["27088856"],"is_preprint":false},{"year":2008,"finding":"Per2 mutation causes Akt-dependent increase in endothelial cell senescence and impairs ischemia-induced EPC mobilization and revascularization; bone marrow transplantation or infusion of wild-type EPCs rescues blood flow recovery in Per2 mutant mice.","method":"Per2 mutant mouse; endothelial cell Akt signaling analysis; hind-limb ischemia model; bone marrow transplantation; matrigel neovascularization assay","journal":"Circulation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo genetic model with signaling pathway analysis and rescue experiments in single study","pmids":["18981300"],"is_preprint":false},{"year":2012,"finding":"PER2 regulates AKT activity; cells with downregulated PER2 show prolonged elevated AKT T308 phosphorylation after growth factor stimulation or DNA damage, and PER2 downregulation delays DNA-damage-induced Chk2 activation while overriding apoptosis and cell cycle arrest.","method":"PER2 knockdown and overexpression in cancer cells; western blotting for AKT T308 phosphorylation and Chk2 activation after growth factor and DNA damage stimuli","journal":"Biochemistry and Cell Biology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, KD/OE with protein phosphorylation readout; no in vitro reconstitution or epistasis","pmids":["22905719"],"is_preprint":false},{"year":2013,"finding":"TNF-α inhibits Per2 transcription in rheumatoid synovial cells through D-box 1 and D-box 2 motifs in the Per2 promoter, acting via the D-box binding transcriptional activators DBP, HLF, and TEF (which are downregulated by TNF-α) and the repressor E4BP4 (which is upregulated).","method":"Site-directed mutagenesis of Per2 D-box motifs; luciferase reporter assay; real-time PCR in primary human synovial cells treated with TNF-α","journal":"Scandinavian Journal of Rheumatology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — promoter mutagenesis combined with reporter assay and primary human cell model in single lab study","pmids":["23496259"],"is_preprint":false},{"year":2022,"finding":"IL-1β induces PER2 upregulation in primary human chondrocytes via NMDA receptor activation → CREB phosphorylation; CREB knockdown or inhibition prevents IL-1β-induced PER2 increase. IL-1β simultaneously reduces BMAL1 via NF-κB activation; NF-κB inhibition prevents BMAL1 reduction and partially mitigates PER2 increase.","method":"NMDAR antagonist (MK801); CREB knockdown; NF-κB inhibitor; phosphorylation assays (GluN1, CREB, p65) in primary human chondrocytes","journal":"Cellular Signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological and genetic (knockdown) dissection of signaling pathway with multiple targets in primary human cells","pmids":["34481895"],"is_preprint":false},{"year":2022,"finding":"EGR1 transcription factor binds the PER2 promoter and promotes IL-4-induced transcriptional activation of PER2 in human keratinocytes; this is required for normal circadian oscillation of PER2 under IL-4 exposure. IL-4 uses both MAPK and JAK signaling pathways to induce EGR1-mediated PER2 expression.","method":"Promoter-reporter assay; EMSA; DNA affinity precipitation; ChIP; Egr1−/− mouse atopic dermatitis model; real-time bioluminescence oscillation assay","journal":"The Journal of Investigative Dermatology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple complementary promoter-binding methods plus in vivo KO model plus bioluminescence assay in single lab","pmids":["35398375"],"is_preprint":false},{"year":2008,"finding":"Per2 mutation is associated with endothelial dysfunction involving decreased NO production and reduced vasodilatory prostaglandins, combined with increased cyclooxygenase-1-derived vasoconstrictors; COX-1 protein is upregulated in aortas of Per2 mutant mice without changes in eNOS or M3 receptor expression.","method":"Aortic ring organ-bath relaxation studies; indomethacin (COX inhibitor) pharmacology; COX-1/COX-2 and eNOS western blotting","journal":"Circulation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological dissection plus protein expression analysis in vascular explants from Per2 mutant mice","pmids":["17404161"],"is_preprint":false},{"year":2021,"finding":"Deletion of Per2 specifically in glial cells (but not neurons) reduces glutamate levels in the nucleus accumbens and increases GAT2/Slc6a13 and Drd3 mRNA, leading to reduced despair and anxiety behaviors; neuronal Per2 deletion reduces despair but not anxiety; glial Bmal1 deletion has no effect on either behavior.","method":"Conditional Cre-lox genetic deletion of Per2 in glia or neurons; AAV-mediated deletion in NAc glia; neurotransmitter measurement; qRT-PCR for transporter/receptor expression; behavioral tests","journal":"Scientific Reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-type-specific conditional KO with molecular and behavioral readouts and specificity controls in single lab study","pmids":["34112905"],"is_preprint":false},{"year":2004,"finding":"In Xenopus photoreceptors, xPer2 is directly responsive to both light and dopamine (via quinpirole, a D2 agonist), with light-induced xPer2 upregulation not blocked by cAMP analogue but dopamine-induced upregulation blocked by pCPT-cAMP; both signals act specifically in photoreceptors.","method":"In situ hybridization; pharmacological manipulation (quinpirole, pCPT-cAMP); cellular localization in retinal sections","journal":"The European Journal of Neuroscience","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — pharmacological dissection with in situ localization in Xenopus retina, single lab","pmids":["15245489"],"is_preprint":false},{"year":2008,"finding":"Per2 null mice show enhanced UCP2 expression in the liver, leading to decreased intracellular ATP and increased production of toxic CCl4 derivatives; the absence of Per2 causes elevated CLOCK expression, which drives Ucp2 through a Clock-controlled PPARα signal transduction pathway.","method":"Per2-null mouse hepatotoxicity model; Ucp2 mRNA quantification; ATP measurement; Clock and PPARα expression analysis in Per2-null liver","journal":"The American Journal of Pathology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo KO model with pathway-level molecular mechanism (Clock–PPARα–Ucp2) and metabolite readouts in single lab study","pmids":["19056852"],"is_preprint":false}],"current_model":"PER2 is a core negative-arm component of the mammalian TTFL circadian clock whose abundance is controlled by a CK1δ/ε-driven phosphoswitch: CK1δ/ε first primes PER2, then phosphorylates a FASP/Ser478 phosphodegron that recruits β-TrCP/ubiquitin-E3 ligase for proteasomal degradation, while PP1 and SIRT6/SIRT1-mediated dephosphorylation/deacetylation counteract this to stabilize PER2; nuclear localization of PER2 requires CRY proteins (particularly via CRY1's C-terminal tail), and PML promotes this nuclear entry through a SIRT1-regulated mechanism. Beyond timekeeping, PER2 directly represses PPARγ transcriptional activity to control lipid metabolism, acts as a co-factor for CREB/CRTC1/CBP to mediate light-induced Per1 transcription, facilitates HIF-1α recruitment to hypoxia-response elements, and binds HSP90 via its PAS1 domain to suppress IKK/NF-κB and PD-L1 expression, as well as binding HSP70 via its C-terminus to promote AKT degradation and cuproptosis."},"narrative":{"mechanistic_narrative":"PER2 is a core negative-arm component of the mammalian transcription-translation feedback loop, where it physically associates with the positive-arm factors BMAL1 and CLOCK through a domain distinct from its CRY-binding interface [PMID:18430226]. PER2 abundance is set by a CK1δ/ε-driven phosphoswitch: CK1δ/ε first primes PER2 at sites prerequisite for downstream stabilizing phosphorylations, with the CK1 C-terminal tail and a conserved anion-binding site governing activation-loop conformation and thus which sites are modified [PMID:29784789, PMID:32043967]. CK1 phosphorylation of Ser478 creates a β-TrCP phosphodegron that drives proteasomal degradation, and abolishing this site (Ser478Ala knock-in) lengthens period and accumulates PER2 along with PER1, CRY1 and CRY2 [PMID:32354999]. This degradative axis is opposed by PP1, which dephosphorylates CK1-modified PER2 to extend its half-life, and by SIRT6-mediated deacetylation that prevents PER2 proteasomal turnover; SIK3 acts in the destabilizing direction [PMID:16813562, PMID:30782483, PMID:29227248]. Nuclear entry of PER2 depends on CRY proteins—particularly the CRY1 C-terminal tail—and on PML, whose PER2-promoting activity is licensed by SIRT1 deacetylation of PML at K487 [PMID:35046033, PMID:22274616]. Beyond timekeeping, PER2 directly represses PPARγ recruitment to target promoters to restrain adipogenesis and lipid metabolism [PMID:21035761], serves as a CREB co-factor that assembles a CREB/CRTC1/CBP complex driving light-induced Per1 transcription [PMID:34741086], facilitates HIF-1α recruitment to hypoxia-response elements under hypoxic conditions [PMID:28963769], and participates in a reciprocal regulatory loop with SIRT1 through promoter occupancy at each other's genes [PMID:27346580]. PER2 also functions in chaperone-coupled signaling control, binding HSP90 via its PAS1 domain to suppress IKK/NF-κB and PD-L1 expression [PMID:37914384] and HSP70 via its C-terminus to promote AKT degradation and cuproptosis [PMID:40113747].","teleology":[{"year":2006,"claim":"Established that PER2 stability is set by an opposing kinase-phosphatase balance, identifying PP1 as the dephosphorylating activity that protects CK1-phosphorylated PER2 from degradation.","evidence":"Xenopus egg extract degradation assays, co-IP with PP1c in HEK-293, and dominant-negative PP1 in cells","pmids":["16813562"],"confidence":"High","gaps":["Did not define the specific PER2 residues dephosphorylated","PP1 regulatory subunit targeting PER2 unidentified"]},{"year":2008,"claim":"Mapped the architecture of PER2 within the clock complex, showing PER2 contacts BMAL1 and CLOCK at sites distinct from CRY-binding interfaces while CRY proteins are the stronger repressors.","evidence":"Mammalian two-hybrid and co-immunoprecipitation","pmids":["18430226"],"confidence":"Medium","gaps":["Two-hybrid/co-IP without structural resolution of the complex","Functional consequence of PER2-BMAL1/CLOCK binding for repression not separated from CRY"]},{"year":2010,"claim":"Extended PER2 beyond timekeeping by showing it directly represses PPARγ transcriptional output to control adipogenesis and lipid metabolism.","evidence":"Co-IP, ChIP, microarray, adipocyte differentiation in PER2-deficient fibroblasts, and lipidomics in PER2-deficient mice","pmids":["21035761"],"confidence":"High","gaps":["Mechanism by which PER2 blocks PPARγ promoter recruitment not resolved at residue level","Relationship between this metabolic role and clock phase unclear"]},{"year":2012,"claim":"Resolved how PER2 reaches the nucleus, identifying PML as a binding partner required for PER2 nuclear localization under SIRT1-dependent control.","evidence":"Co-IP, immunofluorescence in SCN neurons and MEFs, Pml-/- KO, and SIRT1 deacetylation assay","pmids":["22274616"],"confidence":"High","gaps":["How PML physically escorts PER2 across the nuclear envelope undefined","Interplay between PML and CRY-driven nuclear entry not reconciled"]},{"year":2016,"claim":"Defined a reciprocal PER2-SIRT1 regulatory loop linking the clock to chromatin acetylation state in liver.","evidence":"ChIP for H4K16ac at Per2 promoter, Per2 binding at Sirt1 promoter, and Sirt1-deficient mouse liver / human hepatocytes","pmids":["27346580"],"confidence":"Medium","gaps":["Whether PER2 represses Sirt1 directly or via CLOCK/BMAL1 displacement not separated","Tissue specificity of the loop untested beyond liver"]},{"year":2017,"claim":"Showed PER2 couples the clock to hypoxia signaling by acting as a co-factor that facilitates HIF-1α recruitment to HREs only when N803 is unhydroxylated.","evidence":"Co-IP, HRE-reporter assays, N803A mutation, and deferoxamine treatment","pmids":["28963769"],"confidence":"Medium","gaps":["Single-lab co-IP/reporter evidence without in vivo hypoxia validation","Whether PER2 alters HIF-1α stability or only recruitment unresolved"]},{"year":2018,"claim":"Identified CK1δ/ε itself as the priming kinase for PER2, establishing the molecular entry point of the phosphoswitch that times PER2 turnover.","evidence":"In-cell biochemical and biophysical analysis of mouse PER2 priming phosphorylation plus phosphoswitch mathematical modeling","pmids":["29784789"],"confidence":"High","gaps":["Upstream signals that tune CK1 priming via its C-terminal tail not enumerated","Stoichiometry of priming vs degron phosphorylation in vivo not quantified"]},{"year":2020,"claim":"Mechanistically connected the phosphoswitch to PER2 degradation, defining Ser478 as a CK1-created β-TrCP phosphodegron and showing an anion-binding site in CK1 selects between stabilizing and destabilizing PER2 sites.","evidence":"PER2-Ser478Ala knock-in mice with behavior/protein/bioluminescence readouts; CK1 mutagenesis, in vitro kinase assays, and cross-species period-mutant analysis","pmids":["32354999","32043967"],"confidence":"High","gaps":["How cellular signals shift CK1 between the two site preferences in vivo not defined","Contribution of additional degrons beyond Ser478 to period control unmeasured"]},{"year":2019,"claim":"Added an acetylation arm to PER2 stability control, showing SIRT6 deacetylates PER2 to prevent its proteasomal degradation and maintain circadian phase.","evidence":"Co-IP, deacetylation assay, and Sirt6-knockdown phenotype","pmids":["30782483"],"confidence":"Medium","gaps":["Acetylated lysines on PER2 not mapped","Interplay of acetylation with the CK1 phosphodegron not dissected"]},{"year":2021,"claim":"Defined PER2 as a transcriptional co-factor for CREB, required to assemble the CREB/CRTC1/CBP complex that drives light-induced Per1 transcription.","evidence":"CREB/PER2 interaction assays, ChIP, luciferase reporters, KO, and light-pulse experiments in mice","pmids":["34741086"],"confidence":"Medium","gaps":["Whether PER2 acts catalytically or stoichiometrically in complex assembly unclear","Generality beyond the Per1 CRE not established"]},{"year":2022,"claim":"Demonstrated CRY proteins, via the CRY1 C-terminal tail, drive PER2 nuclear relocalization and rhythm initiation in SCN neurons.","evidence":"Confocal imaging of endogenous PER2::Venus in CRY-null SCN, viral CRY-variant rescue, FRAP, and translational switching","pmids":["35046033"],"confidence":"High","gaps":["How CRY-driven and PML-driven nuclear import integrate not resolved","Structural basis of CRY1 tail action on PER2 mobility undefined"]},{"year":2023,"claim":"Revealed a chaperone-coupled signaling role, with PER2 binding HSP90 through its PAS1 domain to displace IKKs, suppressing NF-κB activity and PD-L1 expression.","evidence":"Co-IP, GST pull-down, cycloheximide chase, and humanized-immune xenograft in OSCC","pmids":["37914384"],"confidence":"Medium","gaps":["Single-lab/single-cancer-context evidence","Whether this is clock-dependent not addressed"]},{"year":2025,"claim":"Extended PER2 chaperone control to HSP70, showing C-terminal binding reduces HSP70-AKT interaction to promote AKT degradation and cuproptosis, with ATF3 identified as an upstream activator of PER2 transcription.","evidence":"Co-IP, GST pull-down, domain mapping, ubiquitination assay, ATF3 ChIP, and xenograft in OSCC","pmids":["40113747"],"confidence":"Medium","gaps":["Single-context evidence in OSCC","Direct vs indirect effect of PER2 on AKT ubiquitination machinery not isolated"]},{"year":null,"claim":"How the multiple PER2 stability inputs (CK1 priming/degron, PP1, SIRT1/SIRT6, SIK3) and the two distinct nuclear-import routes (CRY1 tail vs PML/SIRT1) are quantitatively integrated to set period in vivo remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified kinetic model linking phosphorylation, acetylation, and import","Structural picture of PER2 in the repressive complex absent","Tissue-specific weighting of metabolic vs timekeeping functions unclear"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[5,8,9]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[5,7,15,16]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[8,7]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[6,13,2]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[6,13]}],"pathway":[{"term_id":"R-HSA-9909396","term_label":"Circadian clock","supporting_discovery_ids":[0,1,2,13]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[5,8,9]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[2,3,15,16]}],"complexes":["CLOCK/BMAL1 clock complex","CREB/CRTC1/CBP transactivation complex"],"partners":["CSNK1D","PPP1CA","BMAL1","CLOCK","PML","CRY1","HIF1A","HSP90"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O15055","full_name":"Period circadian protein homolog 2","aliases":["Circadian clock protein PERIOD 2"],"length_aa":1255,"mass_kda":136.6,"function":"Transcriptional repressor which forms a core component of the circadian clock. The circadian clock, an internal time-keeping system, regulates various physiological processes through the generation of approximately 24 hour circadian rhythms in gene expression, which are translated into rhythms in metabolism and behavior. It is derived from the Latin roots 'circa' (about) and 'diem' (day) and acts as an important regulator of a wide array of physiological functions including metabolism, sleep, body temperature, blood pressure, endocrine, immune, cardiovascular, and renal function. Consists of two major components: the central clock, residing in the suprachiasmatic nucleus (SCN) of the brain, and the peripheral clocks that are present in nearly every tissue and organ system. Both the central and peripheral clocks can be reset by environmental cues, also known as Zeitgebers (German for 'timegivers'). The predominant Zeitgeber for the central clock is light, which is sensed by retina and signals directly to the SCN. The central clock entrains the peripheral clocks through neuronal and hormonal signals, body temperature and feeding-related cues, aligning all clocks with the external light/dark cycle. Circadian rhythms allow an organism to achieve temporal homeostasis with its environment at the molecular level by regulating gene expression to create a peak of protein expression once every 24 hours to control when a particular physiological process is most active with respect to the solar day. Transcription and translation of core clock components (CLOCK, NPAS2, BMAL1, BMAL2, PER1, PER2, PER3, CRY1 and CRY2) plays a critical role in rhythm generation, whereas delays imposed by post-translational modifications (PTMs) are important for determining the period (tau) of the rhythms (tau refers to the period of a rhythm and is the length, in time, of one complete cycle). A diurnal rhythm is synchronized with the day/night cycle, while the ultradian and infradian rhythms have a period shorter and longer than 24 hours, respectively. Disruptions in the circadian rhythms contribute to the pathology of cardiovascular diseases, cancer, metabolic syndrome and aging. A transcription/translation feedback loop (TTFL) forms the core of the molecular circadian clock mechanism. Transcription factors, CLOCK or NPAS2 and BMAL1 or BMAL2, form the positive limb of the feedback loop, act in the form of a heterodimer and activate the transcription of core clock genes and clock-controlled genes (involved in key metabolic processes), harboring E-box elements (5'-CACGTG-3') within their promoters. The core clock genes: PER1/2/3 and CRY1/2 which are transcriptional repressors form the negative limb of the feedback loop and interact with the CLOCK|NPAS2-BMAL1|BMAL2 heterodimer inhibiting its activity and thereby negatively regulating their own expression. This heterodimer also activates nuclear receptors NR1D1/2 and RORA/B/G, which form a second feedback loop and which activate and repress BMAL1 transcription, respectively. PER1 and PER2 proteins transport CRY1 and CRY2 into the nucleus with appropriate circadian timing, but also contribute directly to repression of clock-controlled target genes through interaction with several classes of RNA-binding proteins, helicases and others transcriptional repressors. PER appears to regulate circadian control of transcription by at least three different modes. First, interacts directly with the CLOCK-BMAL1 at the tail end of the nascent transcript peak to recruit complexes containing the SIN3-HDAC that remodel chromatin to repress transcription. Second, brings H3K9 methyltransferases such as SUV39H1 and SUV39H2 to the E-box elements of the circadian target genes, like PER2 itself or PER1. The recruitment of each repressive modifier to the DNA seems to be very precisely temporally orchestrated by the large PER complex, the deacetylases acting before than the methyltransferases. Additionally, large PER complexes are also recruited to the target genes 3' termination site through interactions with RNA-binding proteins and helicases that may play a role in transcription termination to regulate transcription independently of CLOCK-BMAL1 interactions. Recruitment of large PER complexes to the elongating polymerase at PER and CRY termination sites inhibited SETX action, impeding RNA polymerase II release and thereby repressing transcriptional reinitiation. May propagate clock information to metabolic pathways via the interaction with nuclear receptors. Coactivator of PPARA and corepressor of NR1D1, binds rhythmically at the promoter of nuclear receptors target genes like BMAL1 or G6PC1. Directly and specifically represses PPARG proadipogenic activity by blocking PPARG recruitment to target promoters and thereby inhibiting transcriptional activation. Required for fatty acid and lipid metabolism, is involved as well in the regulation of circulating insulin levels. Plays an important role in the maintenance of cardiovascular functions through the regulation of NO and vasodilatatory prostaglandins production in aortas. Controls circadian glutamate uptake in synaptic vesicles through the regulation of VGLUT1 expression. May also be involved in the regulation of inflammatory processes. Represses the CLOCK-BMAL1 induced transcription of BHLHE40/DEC1 and ATF4. Negatively regulates the formation of the TIMELESS-CRY1 complex by competing with TIMELESS for binding to CRY1","subcellular_location":"Nucleus, nucleolus","url":"https://www.uniprot.org/uniprotkb/O15055/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PER2","classification":"Not Classified","n_dependent_lines":24,"n_total_lines":1208,"dependency_fraction":0.019867549668874173},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PER2","total_profiled":1310},"omim":[{"mim_id":"619771","title":"VRK SERINE/THREONINE KINASE 3; VRK3","url":"https://www.omim.org/entry/619771"},{"mim_id":"616882","title":"ADVANCED SLEEP PHASE SYNDROME, FAMILIAL, 3; FASPS3","url":"https://www.omim.org/entry/616882"},{"mim_id":"614776","title":"SIK FAMILY KINASE 3; SIK3","url":"https://www.omim.org/entry/614776"},{"mim_id":"614517","title":"BRAIN AND MUSCLE ARNT-LIKE PROTEIN 2; BMAL2","url":"https://www.omim.org/entry/614517"},{"mim_id":"610016","title":"MICRO RNA 132; MIR132","url":"https://www.omim.org/entry/610016"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PER2"},"hgnc":{"alias_symbol":["KIAA0347"],"prev_symbol":[]},"alphafold":{"accession":"O15055","domains":[{"cath_id":"3.30.450.20","chopping":"149-155_170-317","consensus_level":"medium","plddt":81.071,"start":149,"end":317},{"cath_id":"3.30.450.20","chopping":"319-449_457-473","consensus_level":"medium","plddt":91.527,"start":319,"end":473}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O15055","model_url":"https://alphafold.ebi.ac.uk/files/AF-O15055-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O15055-F1-predicted_aligned_error_v6.png","plddt_mean":52.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PER2","jax_strain_url":"https://www.jax.org/strain/search?query=PER2"},"sequence":{"accession":"O15055","fasta_url":"https://rest.uniprot.org/uniprotkb/O15055.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O15055/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O15055"}},"corpus_meta":[{"pmid":"15608650","id":"PMC_15608650","title":"The clock gene Per2 influences the glutamatergic system and modulates alcohol consumption.","date":"2004","source":"Nature medicine","url":"https://pubmed.ncbi.nlm.nih.gov/15608650","citation_count":463,"is_preprint":false},{"pmid":"21035761","id":"PMC_21035761","title":"PER2 controls lipid metabolism by direct regulation of PPARγ.","date":"2010","source":"Cell metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/21035761","citation_count":394,"is_preprint":false},{"pmid":"15790588","id":"PMC_15790588","title":"Deregulated expression of the PER1, PER2 and PER3 genes in breast cancers.","date":"2005","source":"Carcinogenesis","url":"https://pubmed.ncbi.nlm.nih.gov/15790588","citation_count":313,"is_preprint":false},{"pmid":"17404161","id":"PMC_17404161","title":"Mutation of the circadian clock gene Per2 alters vascular endothelial function.","date":"2007","source":"Circulation","url":"https://pubmed.ncbi.nlm.nih.gov/17404161","citation_count":193,"is_preprint":false},{"pmid":"17599055","id":"PMC_17599055","title":"The clock gene Per2 links the circadian system to the estrogen receptor.","date":"2007","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/17599055","citation_count":165,"is_preprint":false},{"pmid":"23003921","id":"PMC_23003921","title":"CLOCK, PER2 and BMAL1 DNA methylation: association with obesity and metabolic syndrome characteristics and monounsaturated fat intake.","date":"2012","source":"Chronobiology international","url":"https://pubmed.ncbi.nlm.nih.gov/23003921","citation_count":138,"is_preprint":false},{"pmid":"17971899","id":"PMC_17971899","title":"Expression of the circadian clock genes Per1 and Per2 in sporadic and familial breast tumors.","date":"2007","source":"Neoplasia (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/17971899","citation_count":132,"is_preprint":false},{"pmid":"29784789","id":"PMC_29784789","title":"CK1δ/ε protein kinase primes the PER2 circadian phosphoswitch.","date":"2018","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/29784789","citation_count":128,"is_preprint":false},{"pmid":"11982626","id":"PMC_11982626","title":"Gradients in the circadian expression of Per1 and Per2 genes in the rat suprachiasmatic nucleus.","date":"2002","source":"The European journal of neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/11982626","citation_count":127,"is_preprint":false},{"pmid":"18430226","id":"PMC_18430226","title":"Interaction of circadian clock proteins PER2 and CRY with BMAL1 and CLOCK.","date":"2008","source":"BMC molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/18430226","citation_count":115,"is_preprint":false},{"pmid":"18728223","id":"PMC_18728223","title":"Estrogen directly modulates circadian rhythms of PER2 expression in the uterus.","date":"2008","source":"American journal of physiology. 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dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/35398375","citation_count":12,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":47669,"output_tokens":7480,"usd":0.127604,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":16910,"output_tokens":4475,"usd":0.098212,"stage2_stop_reason":"end_turn"},"total_usd":0.225816,"stage1_batch_id":"msgbatch_013a8chtv3AWyTqv4z4sEF4C","stage2_batch_id":"msgbatch_01AHsuW63vinsvuTgzmQ3n62","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2018,\n      \"finding\": \"CK1δ/ε (including the CK1δ2 splice variant) is itself the priming kinase for PER2, phosphorylating it at sites that are prerequisite for downstream stabilizing phosphorylations; the CK1 carboxyl-terminal tail modulates this priming activity and allows cellular signaling to influence circadian period.\",\n      \"method\": \"Comprehensive biochemical and biophysical analysis of mouse PER2 priming phosphorylation in cells; phosphoswitch mathematical modeling\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in-cell biochemical reconstitution with multiple phosphorylation-site analyses and computational modeling in a single focused study\",\n      \"pmids\": [\"29784789\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"A conserved anion binding site in CK1 controls activation-loop conformation and determines which sites on PER2 are preferentially phosphorylated, thereby acting as a molecular switch that directly regulates PER2 stability; period-altering CK1 mutations in humans and Drosophila differentially modulate this switch.\",\n      \"method\": \"Integrated experimental (mutagenesis, in vitro kinase assays) and computational studies; cross-species period mutant analysis\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis plus in vitro assays plus computational modeling in one rigorous study\",\n      \"pmids\": [\"32043967\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"CK1-mediated phosphorylation of PER2 at Ser478 creates a phosphodegron that recruits the E3 ligase β-TrCP for proteasomal degradation; PER2-Ser478Ala knock-in mice show longer circadian period and accumulation of PER2 protein (and associated PER1, CRY1, CRY2) in both nucleus and cytoplasm, with perturbed temperature compensation.\",\n      \"method\": \"PER2-Ser478Ala knock-in mouse generation; behavioral circadian analysis; western blotting; MEF bioluminescence (PER2::LUC) assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vivo knock-in mouse model with multiple orthogonal readouts (behavior, protein levels, bioluminescence)\",\n      \"pmids\": [\"32354999\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Protein phosphatase 1 (PP1) dephosphorylates CK1-phosphorylated PER2, stabilizing it against ubiquitin-proteasome degradation; PER2 co-immunoprecipitates with PP1c in mammalian cells, and dominant-negative PP1c or PP1 inhibitors accelerate PER2 degradation and shorten its half-life.\",\n      \"method\": \"Xenopus egg extract degradation assay; co-immunoprecipitation in HEK-293 cells; endogenous PP1 phosphatase assay from liver and brain; dominant-negative overexpression\",\n      \"journal\": \"The Biochemical Journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro dephosphorylation assay plus co-IP plus dominant-negative cell experiments in one study\",\n      \"pmids\": [\"16813562\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PER2 physically interacts with BMAL1 (at a distinct domain from CRY1/CRY2 binding sites) and with CLOCK, whereas CRY1 and CRY2 interact with BMAL1 but not with CLOCK; CRY proteins bind BMAL1 with higher affinity than PER2 and are stronger transcriptional repressors.\",\n      \"method\": \"Mammalian two-hybrid system; co-immunoprecipitation assays\",\n      \"journal\": \"BMC Molecular Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — two-hybrid and co-IP from a single lab, two complementary methods\",\n      \"pmids\": [\"18430226\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PER2 directly and specifically represses PPARγ transcriptional activity: PER2 blocks PPARγ recruitment to target promoters, thereby suppressing adipogenesis; PER2-deficient mice display drastically altered lipid metabolism and enhanced adipocyte differentiation. PER2 targets the S112 residue of PPARγ.\",\n      \"method\": \"Co-immunoprecipitation; chromatin immunoprecipitation; whole-genome microarray profiling; adipocyte differentiation assays in PER2-deficient fibroblasts; lipidomic profiling in white adipose tissue\",\n      \"journal\": \"Cell Metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (ChIP, Co-IP, microarray, lipidomics, in vivo KO) in one study with clear mechanistic conclusion\",\n      \"pmids\": [\"21035761\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"PML (promyelocytic leukaemia) protein physically interacts with PER2 and is required for PER2 nuclear localization; in Pml−/− cells, PER2 is predominantly perinuclear/cytoplasmic. SIRT1 deacetylates PML at K487, and this deacetylation promotes PML-mediated nuclear localization of PER2.\",\n      \"method\": \"Co-immunoprecipitation; immunofluorescence localization in SCN neurons and MEFs; genetic KO (Pml−/−); SIRT1 deacetylation assay\",\n      \"journal\": \"The EMBO Journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP plus direct localization imaging plus genetic KO with functional consequence in a single rigorous study\",\n      \"pmids\": [\"22274616\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PER2 functions as a co-factor that facilitates recruitment of HIF-1α to hypoxia-response elements (HREs); PER2 physically interacts with HIF-1α via co-immunoprecipitation, and its enhancement of HIF-1 transcriptional activity requires the HIF-1α N803 asparagine to be unhydroxylated (hypoxic conditions).\",\n      \"method\": \"Co-immunoprecipitation; forced PER2 expression; HRE-reporter (VEGF promoter) assays; N803A point mutation; deferoxamine (N803-dioxygenase inhibitor) treatment\",\n      \"journal\": \"The FEBS Journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — co-IP plus reporter assay plus mutagenesis in single lab study\",\n      \"pmids\": [\"28963769\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PER2 acts as a co-factor of CREB to facilitate formation of a CREB/CRTC1/CBP transactivation complex on the CRE element of the Per1 gene in response to light or forskolin; absence of PER2 abolishes the CREB–CBP interaction and reduces histone H3 acetylation and RNA Pol II recruitment to the Per1 promoter.\",\n      \"method\": \"In vitro and in vivo CREB/PER2 interaction assays; chromatin immunoprecipitation; luciferase reporter assays; genetic KO; light-pulse experiments in mice\",\n      \"journal\": \"Scientific Reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP plus co-IP plus in vivo light induction in a single lab with multiple orthogonal methods\",\n      \"pmids\": [\"34741086\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SIRT1 and PER2 constitute a reciprocal negative regulatory loop in the liver: SIRT1 deficiency leads to enhanced H4K16 acetylation at the Per2 promoter, causing Per2 overexpression; in turn, PER2 suppresses Sirt1 transcription by binding to its promoter at the CLOCK/BMAL1 site.\",\n      \"method\": \"ChIP for H4K16 acetylation at Per2 promoter; Per2 promoter binding assay; Sirt1-deficient mouse liver analysis; human hepatocyte experiments\",\n      \"journal\": \"Scientific Reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP plus in vivo genetic KO plus human cell validation in single lab study\",\n      \"pmids\": [\"27346580\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SIK3 (salt-inducible kinase 3) facilitates phosphorylation-dependent destabilization of PER2 protein; SIK3 knockdown elevates PER2 protein levels while SIK3 overexpression decreases them, and PER2 accumulates in Sik3-deficient fibroblasts and liver.\",\n      \"method\": \"Sik3 knockout mouse; SIK3 knockdown/overexpression in cultured cells; bioluminescence rhythm monitoring; protein level assessment by western blotting\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo KO plus cellular knockdown/overexpression with protein-level and bioluminescence readouts in one study\",\n      \"pmids\": [\"29227248\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SIRT6 interacts with and deacetylates PER2, thereby preventing its proteasomal degradation; loss of Sirt6 jeopardizes circadian phase, and this is linked to PER2 acetylation status.\",\n      \"method\": \"Co-immunoprecipitation; deacetylation assay; Sirt6-knockdown circadian phenotype analysis\",\n      \"journal\": \"Biochemical and Biophysical Research Communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — co-IP plus deacetylation assay plus KD phenotype in single lab, moderate strength\",\n      \"pmids\": [\"30782483\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Per2(Brdm1) mutant mice (PAS domain deletion) display lowered expression of the glutamate transporter Eaat1 in astrocytes, leading to reduced glutamate uptake and elevated extracellular glutamate, which is mechanistically linked to increased alcohol intake; acamprosate normalizes glutamate levels and alcohol consumption in these mice.\",\n      \"method\": \"Per2 mutant mouse analysis; Eaat1 expression profiling; extracellular glutamate measurement; pharmacological rescue with acamprosate\",\n      \"journal\": \"Nature Medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo genetic model with molecular phenotype (transporter expression, glutamate levels) and pharmacological rescue\",\n      \"pmids\": [\"15608650\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CRY proteins are required for nuclear localization of PER2 in SCN neurons: in the absence of CRY, PER2 is predominantly cytoplasmic and more mobile (by FRAP); virally expressed CRY1 or CRY2 relocalize PER2 to the nucleus and initiate circadian rhythms; the CRY1 C-terminal tail is necessary for this nuclear relocalization.\",\n      \"method\": \"Confocal imaging of endogenous PER2::Venus in SCN of CRY-null mice; viral vector expression of CRY variants; FRAP; translational switching to control CRY1 abundance\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — live-cell imaging with FRAP, genetic null background, viral rescue with domain-mutant controls; multiple orthogonal approaches in one rigorous study\",\n      \"pmids\": [\"35046033\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PER2 binds ERα and enhances ERα degradation; conversely, suppression of PER2 levels leads to ERα stabilization; PER2 expression is itself estrogen-inducible in breast cancer cells, suggesting a feedback mechanism to attenuate estrogen stimulation.\",\n      \"method\": \"Co-immunoprecipitation; PER2 overexpression and suppression in breast cancer cells; ERα protein stability assays; estrogen induction experiments\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — co-IP plus gain/loss-of-function protein stability assay in single lab\",\n      \"pmids\": [\"17599055\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PER2 binds HSP90 through its PAS1 domain and reduces the interaction of HSP90 with IKKs, promoting ubiquitination of IKKα/β and thereby suppressing IKK/NF-κB pathway activity and PD-L1 expression in oral squamous cell carcinoma cells.\",\n      \"method\": \"Co-immunoprecipitation; GST pull-down; cycloheximide chase assay; western blotting; overexpression/knockdown; in vivo xenograft humanized immune model\",\n      \"journal\": \"Journal for Immunotherapy of Cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — GST pull-down plus co-IP plus functional in vivo rescue in single lab study\",\n      \"pmids\": [\"37914384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PER2 binds HSP70 through its C-terminal domain, reducing the HSP70–AKT interaction and promoting AKT ubiquitination and degradation, which upregulates cuproptosis-related proteins (DLAT, PDHB, SLC31A1) and promotes cuproptosis in OSCC cells. ATF3 is an upstream transcriptional activator of PER2, binding the PER2 promoter at −807 to −796 bp.\",\n      \"method\": \"Co-immunoprecipitation; GST pull-down; domain deletion mapping; ubiquitination assay; ATF3 ChIP/promoter analysis; in vivo xenograft\",\n      \"journal\": \"Cell Death & Disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP, GST pulldown, domain mapping, and ubiquitination assay in single lab study\",\n      \"pmids\": [\"40113747\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Per2 (together with Per1) is required for activation of Igf2 transcription during myoblast differentiation; Per proteins are recruited to the Igf2 promoter and enhancer, driving dynamic histone modifications and promoter-enhancer looping that create a circadian time window for myoblast differentiation initiation.\",\n      \"method\": \"Per1/Per2 depletion in myoblasts; in vivo muscle regeneration assay; RNA Pol II ChIP; histone modification ChIP; chromatin conformation capture (promoter-enhancer interaction); Per2 KO mice\",\n      \"journal\": \"The Journal of Cell Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP plus chromatin conformation capture plus in vivo KO rescue experiments; multiple orthogonal methods in single lab\",\n      \"pmids\": [\"34009269\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Estrogen (17β-estradiol) directly shortens the period of PER2::LUC circadian rhythms in uterine tissue explants but not in SCN explants; this effect is blocked by the ER antagonist raloxifene, indicating an estrogen-receptor-mediated direct modulation of the peripheral (uterine) molecular clock.\",\n      \"method\": \"Tissue explant bioluminescence assays from PER2::LUC knock-in mice; ovariectomy and estradiol/raloxifene treatment\",\n      \"journal\": \"American Journal of Physiology. Endocrinology and Metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct pharmacological and genetic manipulation in tissue explant with quantitative reporter readout in single study\",\n      \"pmids\": [\"18728223\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Sevoflurane anesthesia reduces CLOCK binding to the E'-box of the Per2 promoter and decreases histone H4 acetylation at the proximal Per2 promoter region, leading to suppressed Per2 expression in the SCN; this occurs independently of NAD+ concentration.\",\n      \"method\": \"Chromatin immunoprecipitation (anti-acetylated-histone H4 and anti-CLOCK); quantitative in situ hybridization; LC-MS measurement of NAD+\",\n      \"journal\": \"PloS One\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP for histone acetylation and CLOCK binding plus metabolite measurement in single lab study\",\n      \"pmids\": [\"24498074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Per2 is activated predominantly in lymphoid-biased haematopoietic stem cells (HSCs) under DNA damage and ageing conditions, where it stimulates DNA damage signalling and p53-dependent apoptosis; Per2 deletion ameliorates replication stress, improves maintenance of Ly-biased HSCs, and extends lifespan without increasing DNA damage accumulation. Batf/p53-dependent HSC differentiation induction persists in Per2-deficient mice.\",\n      \"method\": \"In vivo RNAi screening; Per2 conditional KO mouse; HSC isolation and transplantation; DNA damage signalling analysis; lifespan measurement\",\n      \"journal\": \"Nature Cell Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo RNAi screen plus genetic KO with multiple cellular and physiological readouts in single lab study\",\n      \"pmids\": [\"27088856\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Per2 mutation causes Akt-dependent increase in endothelial cell senescence and impairs ischemia-induced EPC mobilization and revascularization; bone marrow transplantation or infusion of wild-type EPCs rescues blood flow recovery in Per2 mutant mice.\",\n      \"method\": \"Per2 mutant mouse; endothelial cell Akt signaling analysis; hind-limb ischemia model; bone marrow transplantation; matrigel neovascularization assay\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo genetic model with signaling pathway analysis and rescue experiments in single study\",\n      \"pmids\": [\"18981300\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"PER2 regulates AKT activity; cells with downregulated PER2 show prolonged elevated AKT T308 phosphorylation after growth factor stimulation or DNA damage, and PER2 downregulation delays DNA-damage-induced Chk2 activation while overriding apoptosis and cell cycle arrest.\",\n      \"method\": \"PER2 knockdown and overexpression in cancer cells; western blotting for AKT T308 phosphorylation and Chk2 activation after growth factor and DNA damage stimuli\",\n      \"journal\": \"Biochemistry and Cell Biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, KD/OE with protein phosphorylation readout; no in vitro reconstitution or epistasis\",\n      \"pmids\": [\"22905719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"TNF-α inhibits Per2 transcription in rheumatoid synovial cells through D-box 1 and D-box 2 motifs in the Per2 promoter, acting via the D-box binding transcriptional activators DBP, HLF, and TEF (which are downregulated by TNF-α) and the repressor E4BP4 (which is upregulated).\",\n      \"method\": \"Site-directed mutagenesis of Per2 D-box motifs; luciferase reporter assay; real-time PCR in primary human synovial cells treated with TNF-α\",\n      \"journal\": \"Scandinavian Journal of Rheumatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — promoter mutagenesis combined with reporter assay and primary human cell model in single lab study\",\n      \"pmids\": [\"23496259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"IL-1β induces PER2 upregulation in primary human chondrocytes via NMDA receptor activation → CREB phosphorylation; CREB knockdown or inhibition prevents IL-1β-induced PER2 increase. IL-1β simultaneously reduces BMAL1 via NF-κB activation; NF-κB inhibition prevents BMAL1 reduction and partially mitigates PER2 increase.\",\n      \"method\": \"NMDAR antagonist (MK801); CREB knockdown; NF-κB inhibitor; phosphorylation assays (GluN1, CREB, p65) in primary human chondrocytes\",\n      \"journal\": \"Cellular Signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological and genetic (knockdown) dissection of signaling pathway with multiple targets in primary human cells\",\n      \"pmids\": [\"34481895\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"EGR1 transcription factor binds the PER2 promoter and promotes IL-4-induced transcriptional activation of PER2 in human keratinocytes; this is required for normal circadian oscillation of PER2 under IL-4 exposure. IL-4 uses both MAPK and JAK signaling pathways to induce EGR1-mediated PER2 expression.\",\n      \"method\": \"Promoter-reporter assay; EMSA; DNA affinity precipitation; ChIP; Egr1−/− mouse atopic dermatitis model; real-time bioluminescence oscillation assay\",\n      \"journal\": \"The Journal of Investigative Dermatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple complementary promoter-binding methods plus in vivo KO model plus bioluminescence assay in single lab\",\n      \"pmids\": [\"35398375\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Per2 mutation is associated with endothelial dysfunction involving decreased NO production and reduced vasodilatory prostaglandins, combined with increased cyclooxygenase-1-derived vasoconstrictors; COX-1 protein is upregulated in aortas of Per2 mutant mice without changes in eNOS or M3 receptor expression.\",\n      \"method\": \"Aortic ring organ-bath relaxation studies; indomethacin (COX inhibitor) pharmacology; COX-1/COX-2 and eNOS western blotting\",\n      \"journal\": \"Circulation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological dissection plus protein expression analysis in vascular explants from Per2 mutant mice\",\n      \"pmids\": [\"17404161\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Deletion of Per2 specifically in glial cells (but not neurons) reduces glutamate levels in the nucleus accumbens and increases GAT2/Slc6a13 and Drd3 mRNA, leading to reduced despair and anxiety behaviors; neuronal Per2 deletion reduces despair but not anxiety; glial Bmal1 deletion has no effect on either behavior.\",\n      \"method\": \"Conditional Cre-lox genetic deletion of Per2 in glia or neurons; AAV-mediated deletion in NAc glia; neurotransmitter measurement; qRT-PCR for transporter/receptor expression; behavioral tests\",\n      \"journal\": \"Scientific Reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-type-specific conditional KO with molecular and behavioral readouts and specificity controls in single lab study\",\n      \"pmids\": [\"34112905\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"In Xenopus photoreceptors, xPer2 is directly responsive to both light and dopamine (via quinpirole, a D2 agonist), with light-induced xPer2 upregulation not blocked by cAMP analogue but dopamine-induced upregulation blocked by pCPT-cAMP; both signals act specifically in photoreceptors.\",\n      \"method\": \"In situ hybridization; pharmacological manipulation (quinpirole, pCPT-cAMP); cellular localization in retinal sections\",\n      \"journal\": \"The European Journal of Neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — pharmacological dissection with in situ localization in Xenopus retina, single lab\",\n      \"pmids\": [\"15245489\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Per2 null mice show enhanced UCP2 expression in the liver, leading to decreased intracellular ATP and increased production of toxic CCl4 derivatives; the absence of Per2 causes elevated CLOCK expression, which drives Ucp2 through a Clock-controlled PPARα signal transduction pathway.\",\n      \"method\": \"Per2-null mouse hepatotoxicity model; Ucp2 mRNA quantification; ATP measurement; Clock and PPARα expression analysis in Per2-null liver\",\n      \"journal\": \"The American Journal of Pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo KO model with pathway-level molecular mechanism (Clock–PPARα–Ucp2) and metabolite readouts in single lab study\",\n      \"pmids\": [\"19056852\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PER2 is a core negative-arm component of the mammalian TTFL circadian clock whose abundance is controlled by a CK1δ/ε-driven phosphoswitch: CK1δ/ε first primes PER2, then phosphorylates a FASP/Ser478 phosphodegron that recruits β-TrCP/ubiquitin-E3 ligase for proteasomal degradation, while PP1 and SIRT6/SIRT1-mediated dephosphorylation/deacetylation counteract this to stabilize PER2; nuclear localization of PER2 requires CRY proteins (particularly via CRY1's C-terminal tail), and PML promotes this nuclear entry through a SIRT1-regulated mechanism. Beyond timekeeping, PER2 directly represses PPARγ transcriptional activity to control lipid metabolism, acts as a co-factor for CREB/CRTC1/CBP to mediate light-induced Per1 transcription, facilitates HIF-1α recruitment to hypoxia-response elements, and binds HSP90 via its PAS1 domain to suppress IKK/NF-κB and PD-L1 expression, as well as binding HSP70 via its C-terminus to promote AKT degradation and cuproptosis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PER2 is a core negative-arm component of the mammalian transcription-translation feedback loop, where it physically associates with the positive-arm factors BMAL1 and CLOCK through a domain distinct from its CRY-binding interface [#4]. PER2 abundance is set by a CK1δ/ε-driven phosphoswitch: CK1δ/ε first primes PER2 at sites prerequisite for downstream stabilizing phosphorylations, with the CK1 C-terminal tail and a conserved anion-binding site governing activation-loop conformation and thus which sites are modified [#0, #1]. CK1 phosphorylation of Ser478 creates a β-TrCP phosphodegron that drives proteasomal degradation, and abolishing this site (Ser478Ala knock-in) lengthens period and accumulates PER2 along with PER1, CRY1 and CRY2 [#2]. This degradative axis is opposed by PP1, which dephosphorylates CK1-modified PER2 to extend its half-life, and by SIRT6-mediated deacetylation that prevents PER2 proteasomal turnover; SIK3 acts in the destabilizing direction [#3, #11, #10]. Nuclear entry of PER2 depends on CRY proteins—particularly the CRY1 C-terminal tail—and on PML, whose PER2-promoting activity is licensed by SIRT1 deacetylation of PML at K487 [#13, #6]. Beyond timekeeping, PER2 directly represses PPARγ recruitment to target promoters to restrain adipogenesis and lipid metabolism [#5], serves as a CREB co-factor that assembles a CREB/CRTC1/CBP complex driving light-induced Per1 transcription [#8], facilitates HIF-1α recruitment to hypoxia-response elements under hypoxic conditions [#7], and participates in a reciprocal regulatory loop with SIRT1 through promoter occupancy at each other's genes [#9]. PER2 also functions in chaperone-coupled signaling control, binding HSP90 via its PAS1 domain to suppress IKK/NF-κB and PD-L1 expression [#15] and HSP70 via its C-terminus to promote AKT degradation and cuproptosis [#16].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Established that PER2 stability is set by an opposing kinase-phosphatase balance, identifying PP1 as the dephosphorylating activity that protects CK1-phosphorylated PER2 from degradation.\",\n      \"evidence\": \"Xenopus egg extract degradation assays, co-IP with PP1c in HEK-293, and dominant-negative PP1 in cells\",\n      \"pmids\": [\"16813562\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the specific PER2 residues dephosphorylated\", \"PP1 regulatory subunit targeting PER2 unidentified\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Mapped the architecture of PER2 within the clock complex, showing PER2 contacts BMAL1 and CLOCK at sites distinct from CRY-binding interfaces while CRY proteins are the stronger repressors.\",\n      \"evidence\": \"Mammalian two-hybrid and co-immunoprecipitation\",\n      \"pmids\": [\"18430226\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Two-hybrid/co-IP without structural resolution of the complex\", \"Functional consequence of PER2-BMAL1/CLOCK binding for repression not separated from CRY\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Extended PER2 beyond timekeeping by showing it directly represses PPARγ transcriptional output to control adipogenesis and lipid metabolism.\",\n      \"evidence\": \"Co-IP, ChIP, microarray, adipocyte differentiation in PER2-deficient fibroblasts, and lipidomics in PER2-deficient mice\",\n      \"pmids\": [\"21035761\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which PER2 blocks PPARγ promoter recruitment not resolved at residue level\", \"Relationship between this metabolic role and clock phase unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Resolved how PER2 reaches the nucleus, identifying PML as a binding partner required for PER2 nuclear localization under SIRT1-dependent control.\",\n      \"evidence\": \"Co-IP, immunofluorescence in SCN neurons and MEFs, Pml-/- KO, and SIRT1 deacetylation assay\",\n      \"pmids\": [\"22274616\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How PML physically escorts PER2 across the nuclear envelope undefined\", \"Interplay between PML and CRY-driven nuclear entry not reconciled\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Defined a reciprocal PER2-SIRT1 regulatory loop linking the clock to chromatin acetylation state in liver.\",\n      \"evidence\": \"ChIP for H4K16ac at Per2 promoter, Per2 binding at Sirt1 promoter, and Sirt1-deficient mouse liver / human hepatocytes\",\n      \"pmids\": [\"27346580\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether PER2 represses Sirt1 directly or via CLOCK/BMAL1 displacement not separated\", \"Tissue specificity of the loop untested beyond liver\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Showed PER2 couples the clock to hypoxia signaling by acting as a co-factor that facilitates HIF-1α recruitment to HREs only when N803 is unhydroxylated.\",\n      \"evidence\": \"Co-IP, HRE-reporter assays, N803A mutation, and deferoxamine treatment\",\n      \"pmids\": [\"28963769\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab co-IP/reporter evidence without in vivo hypoxia validation\", \"Whether PER2 alters HIF-1α stability or only recruitment unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified CK1δ/ε itself as the priming kinase for PER2, establishing the molecular entry point of the phosphoswitch that times PER2 turnover.\",\n      \"evidence\": \"In-cell biochemical and biophysical analysis of mouse PER2 priming phosphorylation plus phosphoswitch mathematical modeling\",\n      \"pmids\": [\"29784789\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream signals that tune CK1 priming via its C-terminal tail not enumerated\", \"Stoichiometry of priming vs degron phosphorylation in vivo not quantified\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Mechanistically connected the phosphoswitch to PER2 degradation, defining Ser478 as a CK1-created β-TrCP phosphodegron and showing an anion-binding site in CK1 selects between stabilizing and destabilizing PER2 sites.\",\n      \"evidence\": \"PER2-Ser478Ala knock-in mice with behavior/protein/bioluminescence readouts; CK1 mutagenesis, in vitro kinase assays, and cross-species period-mutant analysis\",\n      \"pmids\": [\"32354999\", \"32043967\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How cellular signals shift CK1 between the two site preferences in vivo not defined\", \"Contribution of additional degrons beyond Ser478 to period control unmeasured\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Added an acetylation arm to PER2 stability control, showing SIRT6 deacetylates PER2 to prevent its proteasomal degradation and maintain circadian phase.\",\n      \"evidence\": \"Co-IP, deacetylation assay, and Sirt6-knockdown phenotype\",\n      \"pmids\": [\"30782483\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Acetylated lysines on PER2 not mapped\", \"Interplay of acetylation with the CK1 phosphodegron not dissected\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined PER2 as a transcriptional co-factor for CREB, required to assemble the CREB/CRTC1/CBP complex that drives light-induced Per1 transcription.\",\n      \"evidence\": \"CREB/PER2 interaction assays, ChIP, luciferase reporters, KO, and light-pulse experiments in mice\",\n      \"pmids\": [\"34741086\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether PER2 acts catalytically or stoichiometrically in complex assembly unclear\", \"Generality beyond the Per1 CRE not established\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrated CRY proteins, via the CRY1 C-terminal tail, drive PER2 nuclear relocalization and rhythm initiation in SCN neurons.\",\n      \"evidence\": \"Confocal imaging of endogenous PER2::Venus in CRY-null SCN, viral CRY-variant rescue, FRAP, and translational switching\",\n      \"pmids\": [\"35046033\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How CRY-driven and PML-driven nuclear import integrate not resolved\", \"Structural basis of CRY1 tail action on PER2 mobility undefined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Revealed a chaperone-coupled signaling role, with PER2 binding HSP90 through its PAS1 domain to displace IKKs, suppressing NF-κB activity and PD-L1 expression.\",\n      \"evidence\": \"Co-IP, GST pull-down, cycloheximide chase, and humanized-immune xenograft in OSCC\",\n      \"pmids\": [\"37914384\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab/single-cancer-context evidence\", \"Whether this is clock-dependent not addressed\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Extended PER2 chaperone control to HSP70, showing C-terminal binding reduces HSP70-AKT interaction to promote AKT degradation and cuproptosis, with ATF3 identified as an upstream activator of PER2 transcription.\",\n      \"evidence\": \"Co-IP, GST pull-down, domain mapping, ubiquitination assay, ATF3 ChIP, and xenograft in OSCC\",\n      \"pmids\": [\"40113747\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-context evidence in OSCC\", \"Direct vs indirect effect of PER2 on AKT ubiquitination machinery not isolated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the multiple PER2 stability inputs (CK1 priming/degron, PP1, SIRT1/SIRT6, SIK3) and the two distinct nuclear-import routes (CRY1 tail vs PML/SIRT1) are quantitatively integrated to set period in vivo remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified kinetic model linking phosphorylation, acetylation, and import\", \"Structural picture of PER2 in the repressive complex absent\", \"Tissue-specific weighting of metabolic vs timekeeping functions unclear\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [5, 8, 9]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [5, 7, 15, 16]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [8, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [6, 13, 2]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [6, 13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9909396\", \"supporting_discovery_ids\": [0, 1, 2, 13]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [5, 8, 9]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [2, 3, 15, 16]}\n    ],\n    \"complexes\": [\"CLOCK/BMAL1 clock complex\", \"CREB/CRTC1/CBP transactivation complex\"],\n    \"partners\": [\"CSNK1D\", \"PPP1CA\", \"BMAL1\", \"CLOCK\", \"PML\", \"CRY1\", \"HIF1A\", \"HSP90\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}