{"gene":"CREB3L2","run_date":"2026-04-28T17:28:53","timeline":{"discoveries":[{"year":2006,"finding":"CREB3L2/BBF2H7 is an ER-resident transmembrane protein with a bZIP domain in the cytoplasmic portion; it is cleaved at the membrane in response to ER stress, and the cleaved N-terminal fragment translocates to the nucleus where it binds directly to CRE sites to activate transcription of target genes. The protein is not expressed under normal conditions but is markedly induced at the translational level during ER stress.","method":"Biochemical fractionation, reporter assays, Western blot, siRNA knockdown, overexpression in neuroblastoma cells","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal localization, cleavage assay, CRE binding, functional KD/OE with cellular phenotype; foundational paper","pmids":["17178827"],"is_preprint":false},{"year":2009,"finding":"BBF2H7/CREB3L2 directly binds a CRE-like sequence in the Sec23a promoter to activate its transcription, promoting COPII-mediated ER-to-Golgi transport of cartilage matrix proteins (type II collagen, COMP). Bbf2h7-knockout mice show severe chondrodysplasia with aggregated matrix proteins in the ER; reintroduction of Sec23a into Bbf2h7−/− chondrocytes fully restores secretion.","method":"Bbf2h7-knockout mouse, promoter binding assay (ChIP-like/reporter), rescue experiment with Sec23a transfection, immunofluorescence","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1–2 — in vivo KO with specific phenotype, direct promoter binding, genetic rescue; highly cited foundational study","pmids":["19767744"],"is_preprint":false},{"year":2007,"finding":"Full-length CREB3L2 and FUS/CREB3L2 proteins localize to reticular (ER) cytoplasmic structures, whereas truncated versions lacking the transmembrane domain reside in the nucleus. Transcriptional activation is achieved via box-B, ATF6, and CRE binding sites as well as the GRP78 promoter; the FUS/CREB3L2 chimera shows stronger transcriptional activation than wild-type CREB3L2.","method":"Transfection of NIH3T3 and HEK-293 cells with full-length and truncated constructs, reporter assays, subcellular localization imaging","journal":"Genes, chromosomes & cancer","confidence":"Medium","confidence_rationale":"Tier 2–3 — multiple constructs and reporter assays in two cell lines, single lab","pmids":["17117415"],"is_preprint":false},{"year":2008,"finding":"Native CREB3L2 is cleaved to a nuclear form by regulated intramembrane proteolysis (S1P and S2P proteases) in normal thyroid cells. Nuclear CREB3L2 stimulates transcription 8-fold from the EVX1 CRE in the absence of cAMP. The CREB3L2–PPARγ fusion protein inhibits transcription from EVX1 6-fold and suppresses thyroglobulin expression in TSH-treated primary thyroid cells.","method":"Reporter gene assay (EVX1-CRE), western blot of cleavage products, primary thyroid cell overexpression, co-immunoprecipitation-inferred proteolysis","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro reporter assay, RIP cleavage demonstration, primary cell functional assay with orthogonal methods","pmids":["18757431"],"is_preprint":false},{"year":2012,"finding":"BBF2H7/CREB3L2 directly activates transcription of Atf5 in chondrocytes; ATF5 in turn activates Mcl1 transcription to suppress ER stress-induced apoptosis. This BBF2H7–ATF5–MCL1 pathway is specifically required to prevent apoptosis in proliferating chondrocytes, as shown by increased TUNEL staining in Bbf2h7−/− cartilage.","method":"Bbf2h7-knockout mouse, TUNEL assay, promoter reporter assay, ChIP, siRNA knockdown","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — in vivo KO phenotype plus direct promoter activation assay; replicated pathway from independent group","pmids":["22936798"],"is_preprint":false},{"year":2013,"finding":"After ER stress-induced cleavage of BBF2H7/CREB3L2, the luminal C-terminal fragment is secreted into the extracellular space, where it directly binds both Indian hedgehog (Ihh) and its receptor Patched-1, activating Hedgehog signaling in neighboring chondrocytes to stimulate their proliferation.","method":"Co-immunoprecipitation, pull-down assay, conditioned medium transfer, Hedgehog reporter assay, chondrocyte proliferation assay","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1–2 — direct binding demonstrated by pulldown/Co-IP, functional signaling assay, paracrine cell-communication experiment","pmids":["24332809"],"is_preprint":false},{"year":2014,"finding":"Sox9, the master chondrogenesis transcription factor, directly binds the Sox DNA-binding motif in the Bbf2h7 promoter to activate its transcription, placing CREB3L2 downstream of Sox9 in the chondrogenic differentiation program.","method":"ChIP assay, promoter reporter assay with Sox9 binding site mutations, Sox9 knockdown in chondrocytes","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — ChIP plus mutagenesis of binding site plus KD functional readout","pmids":["24711445"],"is_preprint":false},{"year":2017,"finding":"CREB3L2 mediates isoform-specific upregulation of the COPII components Sec23A and Sec24D during hepatic stellate cell (HSC) activation. Knockdown of CREB3L2 or Sec23A/Sec24D abrogates HSC activation, demonstrating that CREB3L2-driven ER-to-Golgi trafficking is required for this fibrogenic process.","method":"siRNA knockdown, Western blot, immunofluorescence, HSC activation assays","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2–3 — siRNA KD with specific activation phenotype and downstream target identification, single lab","pmids":["28801610"],"is_preprint":false},{"year":2017,"finding":"In medaka fish, BBF2H7 regulates a complete set of COPII vesicle enlargement genes (Sec23/24/13/31, Tango1, Sedlin, KLHL12) essential for accommodating long-chain (type II) collagen for ER-export, providing cargo- and developmental stage-specific UPR transducer function.","method":"Genetic loss-of-function in medaka, reporter assays, gene expression analysis; ortholog study","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 — vertebrate ortholog in vivo with specific gene targets identified; single study","pmids":["28500182"],"is_preprint":false},{"year":2019,"finding":"S1P cleaves BBF2H7 just before its RXXL recognition motif, while S2P cleaves at multiple sites within the transmembrane domain (next to Leu380, Met381, Leu385), generating BBF2H7-derived small peptide (BSP) fragments that aggregate in an amyloid-like manner under ER stress.","method":"In vitro protease assay, mass spectrometry of cleavage products, mutagenesis of cleavage sites, cell-based ER stress induction","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 1 — precise cleavage site mapping by biochemical assay with mutagenesis and MS confirmation","pmids":["31914686"],"is_preprint":false},{"year":2019,"finding":"Creb3l2 directly binds ~75% of regulatory and effector genes for translation in pituitary secretory cells, acting as a scaling factor for translation capacity. Its expression is dependent on the pituitary differentiation factor Tpit, placing Creb3l2 downstream of Tpit in the secretory cell differentiation program.","method":"ChIP-seq, RNA-seq, Creb3l2 and Tpit knockout mice, ribosome profiling/translation assay","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1–2 — ChIP-seq genome-wide binding plus KO mouse with specific translational phenotype","pmids":["31481663"],"is_preprint":false},{"year":2010,"finding":"A genome-wide RNAi screen identified CREB3L2 as a transcriptional activator of ATF5 in malignant glioma, operating downstream of RAS-MAPK or PI3K signaling. CREB3L2 directly activates ATF5 expression, which in turn stimulates MCL1 transcription to promote cell survival.","method":"Genome-wide RNAi screen, reporter assay, ChIP, siRNA knockdown, glioma mouse model","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 1–2 — genome-wide screen plus direct ChIP confirmation, in vivo model; highly cited","pmids":["20495567"],"is_preprint":false},{"year":2012,"finding":"The BBF2H7-mediated Sec23A pathway is required for IGF-I-induced ER-to-Golgi transport of procollagen in dermal fibroblasts. Both MAPK and PI3K pathways downstream of IGF-I receptor are required for BBF2H7 induction; knockdown of BBF2H7 reduces type I and III collagen expression and causes COPII vehicle hypoplasia and Golgi dysmorphology.","method":"siRNA knockdown, immunofluorescence microscopy, Western blot, IGF-I stimulation assays","journal":"The Journal of investigative dermatology","confidence":"Medium","confidence_rationale":"Tier 2–3 — siRNA KD with specific organelle and secretion phenotype, pathway inhibitors used, single lab","pmids":["22495181"],"is_preprint":false},{"year":2021,"finding":"CREB3L2 is upregulated by NGF via MAPK and cAMP signaling pathways in PC12 cells; overexpression of CREB3L2 inhibits NGF-induced neurite outgrowth and increases Rab5 GTPase levels, while CREB3L2 depletion enhances morphological differentiation and reduces Rab5 levels, indicating CREB3L2 modulates neuronal differentiation through regulation of Rab5.","method":"Overexpression and siRNA knockdown in PC12 cells, immunofluorescence, pathway inhibitors (MAPK, cAMP)","journal":"Frontiers in molecular neuroscience","confidence":"Medium","confidence_rationale":"Tier 2–3 — KD/OE with specific phenotype and downstream effector (Rab5) identified, single lab","pmids":["34421533"],"is_preprint":false},{"year":2021,"finding":"Androgen receptor (AR) directly regulates CREB3L2 expression and collaborates with CREB3L2 to mediate ER-to-Golgi trafficking in prostate cancer cells, controlling androgen-dependent vesicular transport, cell growth, and survival.","method":"Single-cell transcriptome analysis, ChIP-seq, siRNA knockdown, ER-to-Golgi trafficking assay","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP-seq plus functional trafficking assay plus KD phenotype; single lab","pmids":["34611310"],"is_preprint":false},{"year":2022,"finding":"Simultaneous knockdown of CREB3L1 and CREB3L2 in decidualizing endometrial stromal cells impairs Golgi enlargement, causes ER dilation with collagen accumulation, and decreases protein secretion, demonstrating that both factors are required for Golgi remodeling and efficient protein secretion during decidualization.","method":"siRNA double knockdown, immunofluorescence, electron microscopy, secretion assay, transcriptomic time-course","journal":"Frontiers in cell and developmental biology","confidence":"Medium","confidence_rationale":"Tier 2–3 — double KD with multiple organelle and functional readouts, single lab","pmids":["36313580"],"is_preprint":false},{"year":2023,"finding":"Glucose activates CREB3L2 in pancreatic β-cells through two mechanisms: O-GlcNAcylation stabilizes full-length CREB3L2 by impairing its proteasomal degradation, and mTORC1 stimulation enhances its conversion to the transcriptionally active cleavage product (P60). CREB3L2 deletion impairs ER export of proinsulin, prevents formation of nascent insulin secretory granules, and impairs glucose-stimulated insulin secretion in vivo on high-fat diet.","method":"Conditional β-cell Creb3l2 KO mouse (Ins1-CreER), inhibitor studies (mTORC1, O-GlcNAc), immunoblot, live GFP-proinsulin trafficking assay, RNAseq, glucose tolerance test","journal":"Molecular metabolism","confidence":"High","confidence_rationale":"Tier 1–2 — conditional KO mouse with in vivo metabolic phenotype plus mechanistic dissection of post-translational stabilization by two orthogonal pathways","pmids":["38013154"],"is_preprint":false},{"year":2025,"finding":"CREB3L2 overexpression in triple-negative breast cancer leads to its cleavage and secretion of a C-terminal fragment that activates the Hedgehog pathway in neighboring CD8+ T cells, repressing their activation and cytotoxic function, thereby mediating immune evasion. Hedgehog pathway inhibition impedes CREB3L2-overexpressed tumor growth and sensitizes tumors to immune checkpoint blockade.","method":"Overexpression and knockdown in tumor cells, co-culture with CD8+ T cells, Hedgehog reporter assay, mouse tumor model, ICB treatment","journal":"Science advances","confidence":"Medium","confidence_rationale":"Tier 2 — direct secreted fragment/Hedgehog signaling mechanism demonstrated with in vivo model, single lab","pmids":["39792663"],"is_preprint":false},{"year":2025,"finding":"CREB3L2 upregulates SREBP1 protein expression and stability through increased acetylation mediated by histone acetyltransferase-1 (HAT1), driving fatty acid synthesis and contributing to lenvatinib resistance and hepatocellular carcinoma progression.","method":"Overexpression and knockdown in HCC cells and xenograft models, Co-IP, acetylation assay, Western blot","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2–3 — Co-IP plus in vivo xenograft with HAT1-mediated acetylation mechanism, single lab","pmids":["41285809"],"is_preprint":false},{"year":2025,"finding":"In neurons exposed to oligomeric Aβ42, CREB3L2 forms heterodimers with ATF4. Proteasome inhibition induced by Aβ42 increases nuclear levels of both CREB3L2 and CREB3L2–ATF4 heterodimers, causing transcriptional dysregulation (e.g., of SNX3). HRI kinase activation decreases CREB3L2 and heterodimer levels, suggesting CREB3L2 is normally kept low by rapid proteasomal degradation.","method":"Co-IP for heterodimer detection, proteasome inhibitor treatment, HRI activator treatment, reporter gene assay for target (SNX3), neuronal cell culture","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2–3 — Co-IP for heterodimer plus functional transcriptional readout and pharmacological rescue, single lab","pmids":["40164587"],"is_preprint":false},{"year":2026,"finding":"BBF2H7/CREB3L2 is activated by mild ER stress induced by abundant tyrosinase synthesis in melanocytes, whereupon it induces Sec23a expression to enhance COPII-mediated anterograde transport of tyrosinase from the ER to melanosomes; loss of BBF2H7 causes tyrosinase accumulation in the ER and reduced melanin production, which is rescued by restoration of BBF2H7 or Sec23a.","method":"Bbf2h7-knockout melanocytes, rescue by BBF2H7 or Sec23a re-expression, immunofluorescence, melanin quantification, Western blot","journal":"International journal of molecular sciences","confidence":"High","confidence_rationale":"Tier 1–2 — KO with specific cargo trafficking and metabolic phenotype plus dual genetic rescue (BBF2H7 and Sec23a)","pmids":["41516372"],"is_preprint":false}],"current_model":"CREB3L2/BBF2H7 is an ER-resident transmembrane bZIP transcription factor that, upon ER stress or physiological secretory demand, undergoes regulated intramembrane proteolysis by S1P (at the RXXL motif) and S2P (at multiple transmembrane sites): the released cytoplasmic N-terminal fragment translocates to the nucleus and directly activates CRE/ATF6-element-containing target genes—most prominently Sec23a—to expand COPII vesicle capacity and ER-to-Golgi trafficking, while the secreted luminal C-terminal fragment acts as a paracrine ligand that binds Indian hedgehog and Patched-1 to activate Hedgehog signaling in neighboring cells; nuclear CREB3L2 also drives ATF5–MCL1 anti-apoptotic signaling, scales translation capacity in secretory cells, and is itself regulated by Sox9 (in chondrocytes), androgen receptor (in prostate cancer), and glucose-dependent O-GlcNAcylation/mTORC1 signaling (in β-cells), with its stability controlled by proteasomal degradation under basal conditions."},"narrative":{"teleology":[{"year":2006,"claim":"The fundamental identity of CREB3L2 as an ER stress-induced, membrane-anchored transcription factor was established, resolving how an ER-resident protein could activate nuclear gene expression: regulated cleavage releases an N-terminal fragment that translocates to the nucleus and binds CRE elements.","evidence":"Biochemical fractionation, reporter assays, siRNA knockdown, and overexpression in neuroblastoma cells","pmids":["17178827"],"confidence":"High","gaps":["Identity of the specific proteases (S1P/S2P) performing the cleavage was not yet demonstrated","Physiological target genes downstream of nuclear CREB3L2 were unknown","In vivo relevance was untested"]},{"year":2007,"claim":"Demonstration that full-length CREB3L2 localizes to ER structures while transmembrane-deleted forms are nuclear, and that CREB3L2 activates box-B, ATF6, and CRE sites, clarified the dual-compartment logic of its activation mechanism.","evidence":"Transfection of tagged constructs in NIH3T3 and HEK-293 cells with reporter assays and imaging","pmids":["17117415"],"confidence":"Medium","gaps":["Endogenous cleavage was not directly shown in these cell types","FUS–CREB3L2 fusion context limits generalizability of transcriptional strength comparisons"]},{"year":2008,"claim":"Regulated intramembrane proteolysis by S1P and S2P was directly demonstrated for endogenous CREB3L2 in primary thyroid cells, establishing the specific proteolytic mechanism and showing that the nuclear fragment activates transcription independently of cAMP.","evidence":"Reporter assays with EVX1-CRE, Western blot of cleavage intermediates, and primary thyroid cell overexpression","pmids":["18757431"],"confidence":"High","gaps":["Precise cleavage sites within the transmembrane domain were unresolved","In vivo physiological role outside of thyroid was unknown"]},{"year":2009,"claim":"The critical in vivo function of CREB3L2 was revealed: it directly activates Sec23a transcription to expand COPII vesicle capacity for secretory cargo export, and its loss causes severe chondrodysplasia due to ER retention of cartilage matrix proteins.","evidence":"Bbf2h7-knockout mouse, promoter-binding and reporter assays, genetic rescue by Sec23a re-expression","pmids":["19767744"],"confidence":"High","gaps":["Whether CREB3L2 regulates additional COPII components beyond Sec23a was unclear","Mechanism of CREB3L2 induction in chondrocytes was not determined"]},{"year":2010,"claim":"An unbiased genome-wide screen identified the CREB3L2→ATF5→MCL1 anti-apoptotic axis, revealing a survival function beyond vesicular trafficking and connecting CREB3L2 to RAS-MAPK/PI3K oncogenic signaling in glioma.","evidence":"Genome-wide RNAi screen, ChIP, siRNA knockdown, and glioma mouse model","pmids":["20495567"],"confidence":"High","gaps":["Whether the ATF5–MCL1 axis operates in non-malignant secretory cells was untested","Direct versus indirect transcriptional activation of ATF5 needed further dissection"]},{"year":2012,"claim":"The anti-apoptotic role was confirmed in vivo: CREB3L2 directly activates Atf5 in chondrocytes, whose product drives Mcl1 transcription to prevent ER stress-induced apoptosis during cartilage proliferation; separately, the BBF2H7–Sec23a axis was shown to be required for IGF-I-stimulated procollagen export in dermal fibroblasts, broadening the cell-type scope.","evidence":"Bbf2h7-KO mouse TUNEL assays with ChIP; siRNA knockdown with IGF-I stimulation in fibroblasts","pmids":["22936798","22495181"],"confidence":"High","gaps":["How IGF-I signaling induces BBF2H7 at the molecular level was incompletely mapped","Relative contribution of survival vs. trafficking functions to the KO phenotype was unclear"]},{"year":2013,"claim":"A previously unrecognized paracrine signaling function was uncovered: after cleavage, the secreted C-terminal luminal fragment of CREB3L2 directly binds Indian hedgehog and Patched-1, activating Hedgehog signaling and proliferation in neighboring chondrocytes.","evidence":"Co-immunoprecipitation, pull-down, conditioned medium transfer, Hedgehog reporter assay","pmids":["24332809"],"confidence":"High","gaps":["Structural basis of C-terminal fragment interaction with Ihh/Ptch1 was unknown","Whether this paracrine mechanism operates in tissues other than cartilage was untested"]},{"year":2014,"claim":"The transcriptional regulation of CREB3L2 itself was resolved in chondrocytes: Sox9 directly binds the Bbf2h7 promoter, placing CREB3L2 within the master chondrogenic transcription factor hierarchy.","evidence":"ChIP, promoter-reporter assay with binding-site mutagenesis, Sox9 knockdown","pmids":["24711445"],"confidence":"High","gaps":["Whether other tissue-specific transcription factors regulate CREB3L2 in non-cartilage contexts was unknown"]},{"year":2017,"claim":"CREB3L2's target gene repertoire was expanded to include Sec24D and a full suite of COPII-enlargement genes (Sec13/31, Tango1, Sedlin, KLHL12), establishing it as a master regulator of large-cargo vesicle biogenesis across vertebrates and cell types including hepatic stellate cells.","evidence":"siRNA knockdown in HSCs with activation assays; medaka loss-of-function with gene expression analysis","pmids":["28801610","28500182"],"confidence":"Medium","gaps":["Direct ChIP evidence for all proposed COPII targets in mammalian cells was lacking","Medaka findings await confirmation of full conservation in mammals"]},{"year":2019,"claim":"Precise S1P/S2P cleavage sites were mapped, and CREB3L2's role as a genome-wide scaling factor for translation was discovered: in pituitary secretory cells, it directly binds ~75% of translation-regulatory gene promoters, downstream of the differentiation factor Tpit.","evidence":"Mass spectrometry and mutagenesis for cleavage-site mapping; ChIP-seq and RNA-seq with Creb3l2-KO pituitary","pmids":["31914686","31481663"],"confidence":"High","gaps":["Whether translation scaling is a universal function in all CREB3L2-expressing secretory cells was untested","Functional significance of amyloid-like BSP aggregates from S2P cleavage products was unclear"]},{"year":2021,"claim":"Cell-type-specific upstream regulators were identified: androgen receptor directly controls CREB3L2 expression and collaborates with it for ER-to-Golgi trafficking in prostate cancer, while NGF/MAPK/cAMP induces CREB3L2 in neurons where it modulates differentiation via Rab5.","evidence":"ChIP-seq and trafficking assays in prostate cancer cells; OE/KD with pathway inhibitors in PC12 neurons","pmids":["34611310","34421533"],"confidence":"Medium","gaps":["Direct transcriptional targets mediating Rab5 regulation were not identified","Whether AR–CREB3L2 cooperation is direct at shared promoters was not resolved"]},{"year":2022,"claim":"Functional redundancy with CREB3L1 was demonstrated: both factors are required for Golgi enlargement and efficient protein secretion during endometrial decidualization, establishing CREB3L2 as part of a broader CREB3-family organelle-remodeling program.","evidence":"siRNA double knockdown with electron microscopy, secretion assay, and transcriptomic time-course in endometrial stromal cells","pmids":["36313580"],"confidence":"Medium","gaps":["Individual contributions of CREB3L1 vs. CREB3L2 to specific target genes were not separated","Whether other CREB3 family members compensate in single-KD conditions was untested"]},{"year":2023,"claim":"Post-translational control of CREB3L2 stability and activation was mechanistically dissected in β-cells: glucose-driven O-GlcNAcylation stabilizes full-length CREB3L2 by blocking proteasomal degradation, while mTORC1 promotes its activating cleavage, linking metabolic sensing to COPII-mediated proinsulin export and insulin granule biogenesis.","evidence":"Conditional β-cell Creb3l2-KO mouse, mTORC1/O-GlcNAc inhibitors, live GFP-proinsulin trafficking, glucose tolerance tests","pmids":["38013154"],"confidence":"High","gaps":["Specific O-GlcNAcylation sites on CREB3L2 were not mapped","Whether this dual post-translational regulation operates in non-β-cell secretory tissues was unknown"]},{"year":2025,"claim":"The paracrine Hedgehog function of CREB3L2's C-terminal fragment was extended to tumor immunology: in triple-negative breast cancer, the secreted fragment suppresses CD8+ T cell activation, enabling immune evasion that can be reversed by Hedgehog inhibition; separately, CREB3L2 was found to stabilize SREBP1 via HAT1-mediated acetylation to drive lipogenesis and drug resistance in HCC, and to heterodimerize with ATF4 under proteasome impairment in Aβ42-treated neurons.","evidence":"Tumor-immune co-culture and mouse models; Co-IP and xenograft in HCC; Co-IP and pharmacological manipulation in neurons","pmids":["39792663","41285809","40164587"],"confidence":"Medium","gaps":["Structural basis for C-terminal fragment immunosuppression is unresolved","HAT1 acetylation of SREBP1 downstream of CREB3L2 needs independent replication","Physiological relevance of CREB3L2–ATF4 heterodimers outside of Aβ pathology is unknown"]},{"year":2026,"claim":"The CREB3L2→Sec23a axis was validated in melanocytes, where mild ER stress from tyrosinase synthesis activates BBF2H7 to enhance COPII transport of tyrosinase to melanosomes; loss causes ER retention and hypopigmentation, rescued by either BBF2H7 or Sec23a.","evidence":"Bbf2h7-KO melanocytes with dual genetic rescue, melanin quantification, immunofluorescence","pmids":["41516372"],"confidence":"High","gaps":["Whether other melanogenic enzymes depend on the same pathway is untested","Contribution of the C-terminal paracrine fragment in skin biology is unexplored"]},{"year":null,"claim":"Key unresolved questions include the structural basis of CREB3L2 interactions with S1P/S2P and with Ihh/Ptch1, the identity of O-GlcNAcylation sites, whether amyloid-like BSP aggregates have signaling or pathological functions, and whether CREB3L2 mutations cause Mendelian skeletal or metabolic disease in humans.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model of CREB3L2 or its cleavage intermediates exists","Human genetic disease linkage from loss-of-function variants has not been reported","Functional significance of S2P-derived amyloid-like peptides is entirely unexplored"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,1,2,3,4,10,11]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[0,1,10]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[0,2,16]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,2,3,10]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[5,17]}],"pathway":[{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[1,7,8,12,14,16,20]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[0,3,9,16]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[1,7,8,14,15,20]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,1,4,10,11]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[4,11]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[5,17]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[1,6,8]}],"complexes":[],"partners":["SEC23A","ATF5","ATF4","IHH","PTCH1","SOX9","SREBF1","HAT1"],"other_free_text":[]},"mechanistic_narrative":"CREB3L2 (BBF2H7) is an ER-resident transmembrane bZIP transcription factor that couples secretory load sensing to transcriptional expansion of the vesicular transport machinery. Upon ER stress or physiological secretory demand, CREB3L2 undergoes regulated intramembrane proteolysis by S1P/S2P; the released N-terminal fragment translocates to the nucleus and directly activates CRE/ATF6-element target genes—most critically Sec23a (and Sec24D)—thereby enlarging COPII vesicle capacity for ER-to-Golgi transport of bulky cargoes such as procollagens, proinsulin, and tyrosinase [PMID:17178827, PMID:19767744, PMID:38013154, PMID:41516372]. The secreted luminal C-terminal fragment functions as a paracrine ligand that binds Indian hedgehog and Patched-1 to activate Hedgehog signaling in neighboring cells [PMID:24332809, PMID:39792663]. Beyond trafficking, nuclear CREB3L2 drives an ATF5–MCL1 anti-apoptotic pathway [PMID:20495567, PMID:22936798], scales translation capacity in secretory cells by binding regulatory genes genome-wide [PMID:31481663], and is itself regulated transcriptionally by Sox9 and androgen receptor, and post-translationally by O-GlcNAcylation, mTORC1-stimulated cleavage, and proteasomal degradation [PMID:24711445, PMID:38013154, PMID:40164587]."},"prefetch_data":{"uniprot":{"accession":"Q70SY1","full_name":"Cyclic AMP-responsive element-binding protein 3-like protein 2","aliases":["BBF2 human homolog on chromosome 7"],"length_aa":520,"mass_kda":57.4,"function":"Transcription factor involved in unfolded protein response (UPR). In the absence of endoplasmic reticulum (ER) stress, inserted into ER membranes, with N-terminal DNA-binding and transcription activation domains oriented toward the cytosolic face of the membrane. In response to ER stress, transported to the Golgi, where it is cleaved in a site-specific manner by resident proteases S1P/MBTPS1 and S2P/MBTPS2. The released N-terminal cytosolic domain is translocated to the nucleus to effect transcription of specific target genes. Plays a critical role in chondrogenesis by activating the transcription of SEC23A, which promotes the transport and secretion of cartilage matrix proteins, and possibly that of ER biogenesis-related genes (By similarity). In a neuroblastoma cell line, protects cells from ER stress-induced death (PubMed:17178827). In vitro activates transcription of target genes via direct binding to the CRE site (PubMed:17178827)","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q70SY1/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/CREB3L2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/CREB3L2","total_profiled":1310},"omim":[{"mim_id":"616215","title":"cAMP RESPONSE ELEMENT-BINDING PROTEIN 3-LIKE 1; CREB3L1","url":"https://www.omim.org/entry/616215"},{"mim_id":"608834","title":"cAMP RESPONSE ELEMENT-BINDING PROTEIN 3-LIKE 2; CREB3L2","url":"https://www.omim.org/entry/608834"},{"mim_id":"606398","title":"ACTIVATING TRANSCRIPTION FACTOR 5; ATF5","url":"https://www.omim.org/entry/606398"},{"mim_id":"603355","title":"MEMBRANE-BOUND TRANSCRIPTION FACTOR PROTEASE, SITE 1; MBTPS1","url":"https://www.omim.org/entry/603355"},{"mim_id":"137800","title":"GLIOMA SUSCEPTIBILITY 1; GLM1","url":"https://www.omim.org/entry/137800"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Endoplasmic reticulum","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in 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The protein is not expressed under normal conditions but is markedly induced at the translational level during ER stress.\",\n      \"method\": \"Biochemical fractionation, reporter assays, Western blot, siRNA knockdown, overexpression in neuroblastoma cells\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal localization, cleavage assay, CRE binding, functional KD/OE with cellular phenotype; foundational paper\",\n      \"pmids\": [\"17178827\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"BBF2H7/CREB3L2 directly binds a CRE-like sequence in the Sec23a promoter to activate its transcription, promoting COPII-mediated ER-to-Golgi transport of cartilage matrix proteins (type II collagen, COMP). Bbf2h7-knockout mice show severe chondrodysplasia with aggregated matrix proteins in the ER; reintroduction of Sec23a into Bbf2h7−/− chondrocytes fully restores secretion.\",\n      \"method\": \"Bbf2h7-knockout mouse, promoter binding assay (ChIP-like/reporter), rescue experiment with Sec23a transfection, immunofluorescence\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vivo KO with specific phenotype, direct promoter binding, genetic rescue; highly cited foundational study\",\n      \"pmids\": [\"19767744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Full-length CREB3L2 and FUS/CREB3L2 proteins localize to reticular (ER) cytoplasmic structures, whereas truncated versions lacking the transmembrane domain reside in the nucleus. Transcriptional activation is achieved via box-B, ATF6, and CRE binding sites as well as the GRP78 promoter; the FUS/CREB3L2 chimera shows stronger transcriptional activation than wild-type CREB3L2.\",\n      \"method\": \"Transfection of NIH3T3 and HEK-293 cells with full-length and truncated constructs, reporter assays, subcellular localization imaging\",\n      \"journal\": \"Genes, chromosomes & cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — multiple constructs and reporter assays in two cell lines, single lab\",\n      \"pmids\": [\"17117415\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Native CREB3L2 is cleaved to a nuclear form by regulated intramembrane proteolysis (S1P and S2P proteases) in normal thyroid cells. Nuclear CREB3L2 stimulates transcription 8-fold from the EVX1 CRE in the absence of cAMP. The CREB3L2–PPARγ fusion protein inhibits transcription from EVX1 6-fold and suppresses thyroglobulin expression in TSH-treated primary thyroid cells.\",\n      \"method\": \"Reporter gene assay (EVX1-CRE), western blot of cleavage products, primary thyroid cell overexpression, co-immunoprecipitation-inferred proteolysis\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro reporter assay, RIP cleavage demonstration, primary cell functional assay with orthogonal methods\",\n      \"pmids\": [\"18757431\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"BBF2H7/CREB3L2 directly activates transcription of Atf5 in chondrocytes; ATF5 in turn activates Mcl1 transcription to suppress ER stress-induced apoptosis. This BBF2H7–ATF5–MCL1 pathway is specifically required to prevent apoptosis in proliferating chondrocytes, as shown by increased TUNEL staining in Bbf2h7−/− cartilage.\",\n      \"method\": \"Bbf2h7-knockout mouse, TUNEL assay, promoter reporter assay, ChIP, siRNA knockdown\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo KO phenotype plus direct promoter activation assay; replicated pathway from independent group\",\n      \"pmids\": [\"22936798\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"After ER stress-induced cleavage of BBF2H7/CREB3L2, the luminal C-terminal fragment is secreted into the extracellular space, where it directly binds both Indian hedgehog (Ihh) and its receptor Patched-1, activating Hedgehog signaling in neighboring chondrocytes to stimulate their proliferation.\",\n      \"method\": \"Co-immunoprecipitation, pull-down assay, conditioned medium transfer, Hedgehog reporter assay, chondrocyte proliferation assay\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct binding demonstrated by pulldown/Co-IP, functional signaling assay, paracrine cell-communication experiment\",\n      \"pmids\": [\"24332809\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Sox9, the master chondrogenesis transcription factor, directly binds the Sox DNA-binding motif in the Bbf2h7 promoter to activate its transcription, placing CREB3L2 downstream of Sox9 in the chondrogenic differentiation program.\",\n      \"method\": \"ChIP assay, promoter reporter assay with Sox9 binding site mutations, Sox9 knockdown in chondrocytes\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — ChIP plus mutagenesis of binding site plus KD functional readout\",\n      \"pmids\": [\"24711445\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CREB3L2 mediates isoform-specific upregulation of the COPII components Sec23A and Sec24D during hepatic stellate cell (HSC) activation. Knockdown of CREB3L2 or Sec23A/Sec24D abrogates HSC activation, demonstrating that CREB3L2-driven ER-to-Golgi trafficking is required for this fibrogenic process.\",\n      \"method\": \"siRNA knockdown, Western blot, immunofluorescence, HSC activation assays\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — siRNA KD with specific activation phenotype and downstream target identification, single lab\",\n      \"pmids\": [\"28801610\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In medaka fish, BBF2H7 regulates a complete set of COPII vesicle enlargement genes (Sec23/24/13/31, Tango1, Sedlin, KLHL12) essential for accommodating long-chain (type II) collagen for ER-export, providing cargo- and developmental stage-specific UPR transducer function.\",\n      \"method\": \"Genetic loss-of-function in medaka, reporter assays, gene expression analysis; ortholog study\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — vertebrate ortholog in vivo with specific gene targets identified; single study\",\n      \"pmids\": [\"28500182\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"S1P cleaves BBF2H7 just before its RXXL recognition motif, while S2P cleaves at multiple sites within the transmembrane domain (next to Leu380, Met381, Leu385), generating BBF2H7-derived small peptide (BSP) fragments that aggregate in an amyloid-like manner under ER stress.\",\n      \"method\": \"In vitro protease assay, mass spectrometry of cleavage products, mutagenesis of cleavage sites, cell-based ER stress induction\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — precise cleavage site mapping by biochemical assay with mutagenesis and MS confirmation\",\n      \"pmids\": [\"31914686\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Creb3l2 directly binds ~75% of regulatory and effector genes for translation in pituitary secretory cells, acting as a scaling factor for translation capacity. Its expression is dependent on the pituitary differentiation factor Tpit, placing Creb3l2 downstream of Tpit in the secretory cell differentiation program.\",\n      \"method\": \"ChIP-seq, RNA-seq, Creb3l2 and Tpit knockout mice, ribosome profiling/translation assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — ChIP-seq genome-wide binding plus KO mouse with specific translational phenotype\",\n      \"pmids\": [\"31481663\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"A genome-wide RNAi screen identified CREB3L2 as a transcriptional activator of ATF5 in malignant glioma, operating downstream of RAS-MAPK or PI3K signaling. CREB3L2 directly activates ATF5 expression, which in turn stimulates MCL1 transcription to promote cell survival.\",\n      \"method\": \"Genome-wide RNAi screen, reporter assay, ChIP, siRNA knockdown, glioma mouse model\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — genome-wide screen plus direct ChIP confirmation, in vivo model; highly cited\",\n      \"pmids\": [\"20495567\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The BBF2H7-mediated Sec23A pathway is required for IGF-I-induced ER-to-Golgi transport of procollagen in dermal fibroblasts. Both MAPK and PI3K pathways downstream of IGF-I receptor are required for BBF2H7 induction; knockdown of BBF2H7 reduces type I and III collagen expression and causes COPII vehicle hypoplasia and Golgi dysmorphology.\",\n      \"method\": \"siRNA knockdown, immunofluorescence microscopy, Western blot, IGF-I stimulation assays\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — siRNA KD with specific organelle and secretion phenotype, pathway inhibitors used, single lab\",\n      \"pmids\": [\"22495181\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CREB3L2 is upregulated by NGF via MAPK and cAMP signaling pathways in PC12 cells; overexpression of CREB3L2 inhibits NGF-induced neurite outgrowth and increases Rab5 GTPase levels, while CREB3L2 depletion enhances morphological differentiation and reduces Rab5 levels, indicating CREB3L2 modulates neuronal differentiation through regulation of Rab5.\",\n      \"method\": \"Overexpression and siRNA knockdown in PC12 cells, immunofluorescence, pathway inhibitors (MAPK, cAMP)\",\n      \"journal\": \"Frontiers in molecular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — KD/OE with specific phenotype and downstream effector (Rab5) identified, single lab\",\n      \"pmids\": [\"34421533\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Androgen receptor (AR) directly regulates CREB3L2 expression and collaborates with CREB3L2 to mediate ER-to-Golgi trafficking in prostate cancer cells, controlling androgen-dependent vesicular transport, cell growth, and survival.\",\n      \"method\": \"Single-cell transcriptome analysis, ChIP-seq, siRNA knockdown, ER-to-Golgi trafficking assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP-seq plus functional trafficking assay plus KD phenotype; single lab\",\n      \"pmids\": [\"34611310\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Simultaneous knockdown of CREB3L1 and CREB3L2 in decidualizing endometrial stromal cells impairs Golgi enlargement, causes ER dilation with collagen accumulation, and decreases protein secretion, demonstrating that both factors are required for Golgi remodeling and efficient protein secretion during decidualization.\",\n      \"method\": \"siRNA double knockdown, immunofluorescence, electron microscopy, secretion assay, transcriptomic time-course\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — double KD with multiple organelle and functional readouts, single lab\",\n      \"pmids\": [\"36313580\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Glucose activates CREB3L2 in pancreatic β-cells through two mechanisms: O-GlcNAcylation stabilizes full-length CREB3L2 by impairing its proteasomal degradation, and mTORC1 stimulation enhances its conversion to the transcriptionally active cleavage product (P60). CREB3L2 deletion impairs ER export of proinsulin, prevents formation of nascent insulin secretory granules, and impairs glucose-stimulated insulin secretion in vivo on high-fat diet.\",\n      \"method\": \"Conditional β-cell Creb3l2 KO mouse (Ins1-CreER), inhibitor studies (mTORC1, O-GlcNAc), immunoblot, live GFP-proinsulin trafficking assay, RNAseq, glucose tolerance test\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — conditional KO mouse with in vivo metabolic phenotype plus mechanistic dissection of post-translational stabilization by two orthogonal pathways\",\n      \"pmids\": [\"38013154\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CREB3L2 overexpression in triple-negative breast cancer leads to its cleavage and secretion of a C-terminal fragment that activates the Hedgehog pathway in neighboring CD8+ T cells, repressing their activation and cytotoxic function, thereby mediating immune evasion. Hedgehog pathway inhibition impedes CREB3L2-overexpressed tumor growth and sensitizes tumors to immune checkpoint blockade.\",\n      \"method\": \"Overexpression and knockdown in tumor cells, co-culture with CD8+ T cells, Hedgehog reporter assay, mouse tumor model, ICB treatment\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct secreted fragment/Hedgehog signaling mechanism demonstrated with in vivo model, single lab\",\n      \"pmids\": [\"39792663\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CREB3L2 upregulates SREBP1 protein expression and stability through increased acetylation mediated by histone acetyltransferase-1 (HAT1), driving fatty acid synthesis and contributing to lenvatinib resistance and hepatocellular carcinoma progression.\",\n      \"method\": \"Overexpression and knockdown in HCC cells and xenograft models, Co-IP, acetylation assay, Western blot\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — Co-IP plus in vivo xenograft with HAT1-mediated acetylation mechanism, single lab\",\n      \"pmids\": [\"41285809\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In neurons exposed to oligomeric Aβ42, CREB3L2 forms heterodimers with ATF4. Proteasome inhibition induced by Aβ42 increases nuclear levels of both CREB3L2 and CREB3L2–ATF4 heterodimers, causing transcriptional dysregulation (e.g., of SNX3). HRI kinase activation decreases CREB3L2 and heterodimer levels, suggesting CREB3L2 is normally kept low by rapid proteasomal degradation.\",\n      \"method\": \"Co-IP for heterodimer detection, proteasome inhibitor treatment, HRI activator treatment, reporter gene assay for target (SNX3), neuronal cell culture\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — Co-IP for heterodimer plus functional transcriptional readout and pharmacological rescue, single lab\",\n      \"pmids\": [\"40164587\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"BBF2H7/CREB3L2 is activated by mild ER stress induced by abundant tyrosinase synthesis in melanocytes, whereupon it induces Sec23a expression to enhance COPII-mediated anterograde transport of tyrosinase from the ER to melanosomes; loss of BBF2H7 causes tyrosinase accumulation in the ER and reduced melanin production, which is rescued by restoration of BBF2H7 or Sec23a.\",\n      \"method\": \"Bbf2h7-knockout melanocytes, rescue by BBF2H7 or Sec23a re-expression, immunofluorescence, melanin quantification, Western blot\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — KO with specific cargo trafficking and metabolic phenotype plus dual genetic rescue (BBF2H7 and Sec23a)\",\n      \"pmids\": [\"41516372\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CREB3L2/BBF2H7 is an ER-resident transmembrane bZIP transcription factor that, upon ER stress or physiological secretory demand, undergoes regulated intramembrane proteolysis by S1P (at the RXXL motif) and S2P (at multiple transmembrane sites): the released cytoplasmic N-terminal fragment translocates to the nucleus and directly activates CRE/ATF6-element-containing target genes—most prominently Sec23a—to expand COPII vesicle capacity and ER-to-Golgi trafficking, while the secreted luminal C-terminal fragment acts as a paracrine ligand that binds Indian hedgehog and Patched-1 to activate Hedgehog signaling in neighboring cells; nuclear CREB3L2 also drives ATF5–MCL1 anti-apoptotic signaling, scales translation capacity in secretory cells, and is itself regulated by Sox9 (in chondrocytes), androgen receptor (in prostate cancer), and glucose-dependent O-GlcNAcylation/mTORC1 signaling (in β-cells), with its stability controlled by proteasomal degradation under basal conditions.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CREB3L2 (BBF2H7) is an ER-resident transmembrane bZIP transcription factor that couples secretory load sensing to transcriptional expansion of the vesicular transport machinery. Upon ER stress or physiological secretory demand, CREB3L2 undergoes regulated intramembrane proteolysis by S1P/S2P; the released N-terminal fragment translocates to the nucleus and directly activates CRE/ATF6-element target genes—most critically Sec23a (and Sec24D)—thereby enlarging COPII vesicle capacity for ER-to-Golgi transport of bulky cargoes such as procollagens, proinsulin, and tyrosinase [PMID:17178827, PMID:19767744, PMID:38013154, PMID:41516372]. The secreted luminal C-terminal fragment functions as a paracrine ligand that binds Indian hedgehog and Patched-1 to activate Hedgehog signaling in neighboring cells [PMID:24332809, PMID:39792663]. Beyond trafficking, nuclear CREB3L2 drives an ATF5–MCL1 anti-apoptotic pathway [PMID:20495567, PMID:22936798], scales translation capacity in secretory cells by binding regulatory genes genome-wide [PMID:31481663], and is itself regulated transcriptionally by Sox9 and androgen receptor, and post-translationally by O-GlcNAcylation, mTORC1-stimulated cleavage, and proteasomal degradation [PMID:24711445, PMID:38013154, PMID:40164587].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"The fundamental identity of CREB3L2 as an ER stress-induced, membrane-anchored transcription factor was established, resolving how an ER-resident protein could activate nuclear gene expression: regulated cleavage releases an N-terminal fragment that translocates to the nucleus and binds CRE elements.\",\n      \"evidence\": \"Biochemical fractionation, reporter assays, siRNA knockdown, and overexpression in neuroblastoma cells\",\n      \"pmids\": [\"17178827\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the specific proteases (S1P/S2P) performing the cleavage was not yet demonstrated\", \"Physiological target genes downstream of nuclear CREB3L2 were unknown\", \"In vivo relevance was untested\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Demonstration that full-length CREB3L2 localizes to ER structures while transmembrane-deleted forms are nuclear, and that CREB3L2 activates box-B, ATF6, and CRE sites, clarified the dual-compartment logic of its activation mechanism.\",\n      \"evidence\": \"Transfection of tagged constructs in NIH3T3 and HEK-293 cells with reporter assays and imaging\",\n      \"pmids\": [\"17117415\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Endogenous cleavage was not directly shown in these cell types\", \"FUS–CREB3L2 fusion context limits generalizability of transcriptional strength comparisons\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Regulated intramembrane proteolysis by S1P and S2P was directly demonstrated for endogenous CREB3L2 in primary thyroid cells, establishing the specific proteolytic mechanism and showing that the nuclear fragment activates transcription independently of cAMP.\",\n      \"evidence\": \"Reporter assays with EVX1-CRE, Western blot of cleavage intermediates, and primary thyroid cell overexpression\",\n      \"pmids\": [\"18757431\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise cleavage sites within the transmembrane domain were unresolved\", \"In vivo physiological role outside of thyroid was unknown\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"The critical in vivo function of CREB3L2 was revealed: it directly activates Sec23a transcription to expand COPII vesicle capacity for secretory cargo export, and its loss causes severe chondrodysplasia due to ER retention of cartilage matrix proteins.\",\n      \"evidence\": \"Bbf2h7-knockout mouse, promoter-binding and reporter assays, genetic rescue by Sec23a re-expression\",\n      \"pmids\": [\"19767744\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CREB3L2 regulates additional COPII components beyond Sec23a was unclear\", \"Mechanism of CREB3L2 induction in chondrocytes was not determined\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"An unbiased genome-wide screen identified the CREB3L2→ATF5→MCL1 anti-apoptotic axis, revealing a survival function beyond vesicular trafficking and connecting CREB3L2 to RAS-MAPK/PI3K oncogenic signaling in glioma.\",\n      \"evidence\": \"Genome-wide RNAi screen, ChIP, siRNA knockdown, and glioma mouse model\",\n      \"pmids\": [\"20495567\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the ATF5–MCL1 axis operates in non-malignant secretory cells was untested\", \"Direct versus indirect transcriptional activation of ATF5 needed further dissection\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"The anti-apoptotic role was confirmed in vivo: CREB3L2 directly activates Atf5 in chondrocytes, whose product drives Mcl1 transcription to prevent ER stress-induced apoptosis during cartilage proliferation; separately, the BBF2H7–Sec23a axis was shown to be required for IGF-I-stimulated procollagen export in dermal fibroblasts, broadening the cell-type scope.\",\n      \"evidence\": \"Bbf2h7-KO mouse TUNEL assays with ChIP; siRNA knockdown with IGF-I stimulation in fibroblasts\",\n      \"pmids\": [\"22936798\", \"22495181\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How IGF-I signaling induces BBF2H7 at the molecular level was incompletely mapped\", \"Relative contribution of survival vs. trafficking functions to the KO phenotype was unclear\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"A previously unrecognized paracrine signaling function was uncovered: after cleavage, the secreted C-terminal luminal fragment of CREB3L2 directly binds Indian hedgehog and Patched-1, activating Hedgehog signaling and proliferation in neighboring chondrocytes.\",\n      \"evidence\": \"Co-immunoprecipitation, pull-down, conditioned medium transfer, Hedgehog reporter assay\",\n      \"pmids\": [\"24332809\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of C-terminal fragment interaction with Ihh/Ptch1 was unknown\", \"Whether this paracrine mechanism operates in tissues other than cartilage was untested\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"The transcriptional regulation of CREB3L2 itself was resolved in chondrocytes: Sox9 directly binds the Bbf2h7 promoter, placing CREB3L2 within the master chondrogenic transcription factor hierarchy.\",\n      \"evidence\": \"ChIP, promoter-reporter assay with binding-site mutagenesis, Sox9 knockdown\",\n      \"pmids\": [\"24711445\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other tissue-specific transcription factors regulate CREB3L2 in non-cartilage contexts was unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"CREB3L2's target gene repertoire was expanded to include Sec24D and a full suite of COPII-enlargement genes (Sec13/31, Tango1, Sedlin, KLHL12), establishing it as a master regulator of large-cargo vesicle biogenesis across vertebrates and cell types including hepatic stellate cells.\",\n      \"evidence\": \"siRNA knockdown in HSCs with activation assays; medaka loss-of-function with gene expression analysis\",\n      \"pmids\": [\"28801610\", \"28500182\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ChIP evidence for all proposed COPII targets in mammalian cells was lacking\", \"Medaka findings await confirmation of full conservation in mammals\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Precise S1P/S2P cleavage sites were mapped, and CREB3L2's role as a genome-wide scaling factor for translation was discovered: in pituitary secretory cells, it directly binds ~75% of translation-regulatory gene promoters, downstream of the differentiation factor Tpit.\",\n      \"evidence\": \"Mass spectrometry and mutagenesis for cleavage-site mapping; ChIP-seq and RNA-seq with Creb3l2-KO pituitary\",\n      \"pmids\": [\"31914686\", \"31481663\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether translation scaling is a universal function in all CREB3L2-expressing secretory cells was untested\", \"Functional significance of amyloid-like BSP aggregates from S2P cleavage products was unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Cell-type-specific upstream regulators were identified: androgen receptor directly controls CREB3L2 expression and collaborates with it for ER-to-Golgi trafficking in prostate cancer, while NGF/MAPK/cAMP induces CREB3L2 in neurons where it modulates differentiation via Rab5.\",\n      \"evidence\": \"ChIP-seq and trafficking assays in prostate cancer cells; OE/KD with pathway inhibitors in PC12 neurons\",\n      \"pmids\": [\"34611310\", \"34421533\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct transcriptional targets mediating Rab5 regulation were not identified\", \"Whether AR–CREB3L2 cooperation is direct at shared promoters was not resolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Functional redundancy with CREB3L1 was demonstrated: both factors are required for Golgi enlargement and efficient protein secretion during endometrial decidualization, establishing CREB3L2 as part of a broader CREB3-family organelle-remodeling program.\",\n      \"evidence\": \"siRNA double knockdown with electron microscopy, secretion assay, and transcriptomic time-course in endometrial stromal cells\",\n      \"pmids\": [\"36313580\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Individual contributions of CREB3L1 vs. CREB3L2 to specific target genes were not separated\", \"Whether other CREB3 family members compensate in single-KD conditions was untested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Post-translational control of CREB3L2 stability and activation was mechanistically dissected in β-cells: glucose-driven O-GlcNAcylation stabilizes full-length CREB3L2 by blocking proteasomal degradation, while mTORC1 promotes its activating cleavage, linking metabolic sensing to COPII-mediated proinsulin export and insulin granule biogenesis.\",\n      \"evidence\": \"Conditional β-cell Creb3l2-KO mouse, mTORC1/O-GlcNAc inhibitors, live GFP-proinsulin trafficking, glucose tolerance tests\",\n      \"pmids\": [\"38013154\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific O-GlcNAcylation sites on CREB3L2 were not mapped\", \"Whether this dual post-translational regulation operates in non-β-cell secretory tissues was unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"The paracrine Hedgehog function of CREB3L2's C-terminal fragment was extended to tumor immunology: in triple-negative breast cancer, the secreted fragment suppresses CD8+ T cell activation, enabling immune evasion that can be reversed by Hedgehog inhibition; separately, CREB3L2 was found to stabilize SREBP1 via HAT1-mediated acetylation to drive lipogenesis and drug resistance in HCC, and to heterodimerize with ATF4 under proteasome impairment in Aβ42-treated neurons.\",\n      \"evidence\": \"Tumor-immune co-culture and mouse models; Co-IP and xenograft in HCC; Co-IP and pharmacological manipulation in neurons\",\n      \"pmids\": [\"39792663\", \"41285809\", \"40164587\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis for C-terminal fragment immunosuppression is unresolved\", \"HAT1 acetylation of SREBP1 downstream of CREB3L2 needs independent replication\", \"Physiological relevance of CREB3L2–ATF4 heterodimers outside of Aβ pathology is unknown\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"The CREB3L2→Sec23a axis was validated in melanocytes, where mild ER stress from tyrosinase synthesis activates BBF2H7 to enhance COPII transport of tyrosinase to melanosomes; loss causes ER retention and hypopigmentation, rescued by either BBF2H7 or Sec23a.\",\n      \"evidence\": \"Bbf2h7-KO melanocytes with dual genetic rescue, melanin quantification, immunofluorescence\",\n      \"pmids\": [\"41516372\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other melanogenic enzymes depend on the same pathway is untested\", \"Contribution of the C-terminal paracrine fragment in skin biology is unexplored\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis of CREB3L2 interactions with S1P/S2P and with Ihh/Ptch1, the identity of O-GlcNAcylation sites, whether amyloid-like BSP aggregates have signaling or pathological functions, and whether CREB3L2 mutations cause Mendelian skeletal or metabolic disease in humans.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural model of CREB3L2 or its cleavage intermediates exists\", \"Human genetic disease linkage from loss-of-function variants has not been reported\", \"Functional significance of S2P-derived amyloid-like peptides is entirely unexplored\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4, 10, 11]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [0, 1, 10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [0, 2, 16]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 2, 3, 10]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [5, 17]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [1, 7, 8, 12, 14, 16, 20]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [0, 3, 9, 16]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [1, 7, 8, 14, 15, 20]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 1, 4, 10, 11]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [4, 11]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5, 17]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [1, 6, 8]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"SEC23A\",\n      \"ATF5\",\n      \"ATF4\",\n      \"IHH\",\n      \"PTCH1\",\n      \"SOX9\",\n      \"SREBF1\",\n      \"HAT1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}