{"gene":"SPRR1B","run_date":"2026-04-28T20:42:08","timeline":{"discoveries":[{"year":2000,"finding":"PMA-induced SPRR1B transcription in tracheobronchial epithelial cells is regulated by a PKCδ/Ras/MEKK1/MKK1-dependent/AP-1 signaling pathway, with dominant negative forms of PKCδ, Ras, MEKK1, and MKK1 each suppressing promoter activity, while dominant negative c-Jun abolished PMA-stimulated expression; ERK1/2 are not required despite MEK1/2 involvement.","method":"Dominant negative and constitutively active mutant overexpression, pharmacological inhibitors (rottlerin, UO126, PD98095), reporter gene assays in tracheobronchial epithelial cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal genetic and pharmacological methods, rigorous dissection of pathway components","pmids":["10918063"],"is_preprint":false},{"year":2001,"finding":"Repression of SPRR1B in malignant bronchial epithelial cells correlates with loss of in vivo protein-DNA interactions at two TRE sites in the -152 bp promoter; differential AP-1 composition (Fra1 vs. Fra2) determines SPRR1B expression: Fra1 overexpression enhances promoter activity in malignant cells, while Fra2 overexpression reduces basal and PMA-inducible promoter activity in normal cells.","method":"Chromatin immunoprecipitation/in vivo footprinting, electrophoretic mobility shift assay (EMSA), AP-1 protein overexpression, reporter gene assays in normal vs. malignant bronchial epithelial cells","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (in vivo footprinting, EMSA, overexpression) in matched cell systems","pmids":["11313996"],"is_preprint":false},{"year":2002,"finding":"ERK5 (BMK1), activated via the MEK5 pathway, is required for PMA-inducible SPRR1B transcription in Clara-like H441 cells; dominant negative ERK5 suppresses both basal and PMA-inducible promoter activity, and c-Jun overexpression rescues this suppression, placing ERK5 upstream of AP-1-mediated SPRR1B transcription.","method":"Dominant negative and wild-type ERK5/MEK5 overexpression, reporter gene assays, kinase activation assays in H441 cells","journal":"American journal of respiratory cell and molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple genetic tools in single cell line; single lab","pmids":["12091247"],"is_preprint":false},{"year":2000,"finding":"The amino-terminal sequence of SPRR1 (specifically Gln clusters Gln4-Gln6 and Gln22-Gln25) is required for incorporation into cross-linked envelopes of human tracheobronchial epithelial cells, while the carboxyl-terminal sequence (including the last lysine residue) is required for high-level protein expression; the two termini thus have distinct roles in the SPRR1 protein life cycle.","method":"Deletion and site-directed mutagenesis of Flag-SPRR1 fusion protein, liposome-mediated transfection in human TBE cells, immunological detection of cross-linked envelope incorporation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstitution in primary human cells with site-directed mutagenesis identifying specific residues","pmids":["10681560"],"is_preprint":false},{"year":2003,"finding":"Inducible overexpression of SPRR1B in CHO cells for short periods accelerates entry into G0/G1 phase without affecting growth rate or ploidy, while prolonged stable overexpression induces tetraploidy, indicating SPRR1B is coupled to signals for withdrawal from the proliferative state.","method":"Stable and inducible (ecdysone system) SPRR1B overexpression in CHO, mouse, and human tumor cell lines; cell cycle analysis; ploidy measurement","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"Medium","confidence_rationale":"Tier 2 — inducible expression system with cell cycle readouts in multiple cell lines; single lab","pmids":["12832281"],"is_preprint":false},{"year":2008,"finding":"Inflammatory cytokines IL-1α, IL-1β, IL-6, IFN-γ, and TNF-α each induce SPRR1B expression in ocular surface epithelial cells in vitro; adoptive transfer of CD4+ T cells from aire-deficient mice to immunodeficient recipients caused ocular surface keratinization with elevated SPRR1B, establishing inflammation as a direct driver of SPRR1B-mediated squamous metaplasia.","method":"In vitro cytokine stimulation with RT-PCR/IHC readout; adoptive transfer experiment in mouse models; quantitative RT-PCR in human Sjögren's syndrome tissues","journal":"Investigative ophthalmology & visual science","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro and in vivo experiments with mechanistic cytokine identification; single lab but multiple models","pmids":["18172072"],"is_preprint":false},{"year":2021,"finding":"SPRR1B promotes proliferation in oral squamous cell carcinoma cells by inducing p38 MAPK phosphorylation, placing SPRR1B upstream of p38 signaling in this context.","method":"Cell-based assays with SPRR1B expression manipulation; western blot for p38 phosphorylation in OSCC cells","journal":"Journal of cancer research and clinical oncology","confidence":"Low","confidence_rationale":"Tier 3 — single lab, limited mechanistic follow-up beyond phosphorylation assay","pmids":["33620575"],"is_preprint":false},{"year":2021,"finding":"lncRNA DGUOK-AS1 acts as a ceRNA to sponge miR-499a-5p, thereby releasing SPRR1B from miR-499a-5p-mediated repression; luciferase assays validated direct DGUOK-AS1–miR-499a-5p and miR-499a-5p–SPRR1B interactions, and SPRR1B silencing reversed pro-tumorigenic effects in cervical squamous cell carcinoma cells.","method":"Luciferase reporter assays, miRNA inhibitor/overexpression, siRNA knockdown, cell viability/migration/apoptosis assays in SiHa and HeLa cells","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2-3 — luciferase validation of direct interactions plus functional rescue experiments; single lab","pmids":["34808501"],"is_preprint":false},{"year":2022,"finding":"lncRNA HAGLROS functions as a miR-330-5p sponge (ceRNA) to positively regulate SPRR1B expression; luciferase reporter assays confirmed direct HAGLROS–miR-330-5p and miR-330-5p–SPRR1B binding; SPRR1B silencing reversed the malignant phenotypes (proliferation, migration, invasion) promoted by miR-330-5p inhibition in bladder cancer cells.","method":"Luciferase reporter assays, FISH, subcellular fractionation, miRNA inhibitor/mimic experiments, siRNA knockdown, in vivo xenograft model","journal":"Frontiers in oncology","confidence":"Medium","confidence_rationale":"Tier 2 — luciferase validation, in vitro and in vivo confirmation; single lab","pmids":["35664787"],"is_preprint":false},{"year":2024,"finding":"SPRR1B+ keratinocytes are induced via STAT3 activation and promote oral mucosal wound healing; SPRR1B knockdown significantly inhibits mucosal keratinocyte migration in vitro, and SPRR1B+ keratinocytes are constitutively abundant in normal oral mucosa but absent in normal skin, correlating with the faster healing of mucosal wounds.","method":"Single-cell RNA sequencing, bulk-mRNA sequencing, SPRR1B knockdown with keratinocyte migration assays, murine wound healing model","journal":"Communications biology","confidence":"Medium","confidence_rationale":"Tier 2 — loss-of-function with specific migration phenotype, combined with scRNA-seq and animal model validation; single lab","pmids":["39300285"],"is_preprint":false},{"year":2024,"finding":"Silencing SPRR1B in IFN-γ-treated HaCaT keratinocytes significantly reduces IFN-γ-induced upregulation of IL-17, IL-22, KRT6, and KRT16, placing SPRR1B downstream of IFN-γ signaling and upstream of these inflammatory/differentiation effectors in psoriasis-relevant keratinocytes.","method":"siRNA-mediated SPRR1B knockdown in IFN-γ-treated HaCaT cells; RT-PCR for downstream targets","journal":"International journal of general medicine","confidence":"Low","confidence_rationale":"Tier 3 — single knockdown experiment in one cell line, limited mechanistic depth","pmids":["38333021"],"is_preprint":false},{"year":2023,"finding":"Sprr1a (mouse ortholog closely related to SPRR1B) suppresses senescence-like phenotype: reduced Sprr1a levels (including via miR-130b) promote upregulation of p16, p53, and p21 and increase β-galactosidase activity, while Sprr1a expression protects cells from senescence induced by radiation or doxorubicin.","method":"miR-130b and Sprr1a overexpression/knockdown; β-galactosidase assay; western blot for p16, p53, p21 in cell lines","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 — preprint, single lab, mouse ortholog (Sprr1a not Sprr1b), functional readouts without deep mechanistic dissection","pmids":["37961492"],"is_preprint":true}],"current_model":"SPRR1B is a squamous differentiation marker whose transcription is driven by a PKCδ/Ras/MEKK1/MKK1/ERK5–AP-1 (particularly Fra1/Fra2-dependent) signaling axis in epithelial cells; its protein incorporates into cross-linked cornified envelopes via amino-terminal Gln clusters, while its carboxyl terminus controls protein stability; upstream, inflammatory cytokines (IL-1β, IFN-γ) and lncRNA ceRNA networks (sponging miR-499a-5p or miR-330-5p) regulate its levels, and SPRR1B in turn promotes keratinocyte migration (via STAT3), p38 MAPK phosphorylation, and cell cycle G0 entry, collectively linking it to epithelial barrier formation, squamous metaplasia, and wound healing."},"narrative":{"teleology":[{"year":2000,"claim":"Identifying the structural requirements for SPRR1 incorporation into the cornified envelope resolved how this small protein participates in barrier assembly: amino-terminal Gln clusters are transglutaminase substrates for cross-linking, while the C-terminus controls protein stability.","evidence":"Site-directed and deletion mutagenesis of Flag-SPRR1 in primary human tracheobronchial epithelial cells with immunological detection of envelope incorporation","pmids":["10681560"],"confidence":"High","gaps":["The specific transglutaminase(s) catalyzing cross-linking of SPRR1B in vivo are not identified","How the C-terminal lysine controls protein stability (proteasomal degradation vs. other mechanism) is unknown"]},{"year":2000,"claim":"Mapping the signaling cascade upstream of SPRR1B transcription established that PKCδ, Ras, MEKK1, and MKK1 form a linear pathway converging on AP-1, with ERK1/2 dispensable despite MEK1/2 involvement, defining a non-canonical MAPK route to squamous differentiation gene expression.","evidence":"Dominant-negative and constitutively active kinase mutants combined with pharmacological inhibitors and reporter assays in tracheobronchial epithelial cells","pmids":["10918063"],"confidence":"High","gaps":["The direct phosphorylation substrate of MKK1 that activates AP-1 in this pathway was unresolved at this stage","Whether the same cascade operates in non-airway squamous epithelia was not tested"]},{"year":2001,"claim":"Demonstrating differential AP-1 composition at the SPRR1B promoter in normal versus malignant bronchial cells explained how SPRR1B is silenced during malignant transformation: Fra1 activates and Fra2 represses the promoter via two TRE sites within −152 bp.","evidence":"In vivo footprinting, EMSA, and AP-1 overexpression with reporter assays in matched normal and malignant bronchial epithelial cells","pmids":["11313996"],"confidence":"High","gaps":["Whether Fra1/Fra2 switch is driven by epigenetic changes at their own loci or by upstream signaling alterations is unknown","No chromatin immunoprecipitation for histone marks at the SPRR1B locus was performed"]},{"year":2002,"claim":"Placing ERK5 (BMK1) upstream of AP-1-dependent SPRR1B transcription completed the kinase cascade and resolved the identity of the ERK1/2-independent MAP kinase branch required for inducible expression.","evidence":"Dominant-negative ERK5/MEK5 overexpression with reporter assays and c-Jun rescue in H441 Clara-like cells","pmids":["12091247"],"confidence":"Medium","gaps":["Direct ERK5-mediated phosphorylation of c-Jun or another AP-1 component was not demonstrated biochemically","Findings in a single cell line (H441)"]},{"year":2003,"claim":"Showing that inducible SPRR1B overexpression drives G0/G1 entry linked this structural envelope protein to cell cycle control, suggesting a dual role in differentiation-associated growth arrest.","evidence":"Ecdysone-inducible SPRR1B expression system in CHO and tumor cell lines with cell cycle analysis","pmids":["12832281"],"confidence":"Medium","gaps":["The molecular mechanism by which SPRR1B influences cell cycle machinery (CDK inhibitors, Rb pathway) is unknown","Tetraploidy from prolonged overexpression was not mechanistically explained"]},{"year":2008,"claim":"Demonstrating that multiple inflammatory cytokines (IL-1β, IFN-γ, TNF-α) directly induce SPRR1B in ocular surface epithelium, and that T-cell-driven inflammation causes SPRR1B-positive squamous metaplasia in vivo, established inflammation as a physiological driver of SPRR1B expression.","evidence":"In vitro cytokine stimulation with RT-PCR/IHC; adoptive transfer of CD4+ T cells from aire-deficient mice; validation in human Sjögren's syndrome tissue","pmids":["18172072"],"confidence":"Medium","gaps":["Which cytokine-activated transcription factors directly bind the SPRR1B promoter (NF-κB, STAT, or AP-1) was not resolved","Whether cytokine induction uses the same PKCδ/ERK5 axis or a parallel pathway is unknown"]},{"year":2021,"claim":"Identifying SPRR1B as a target of miR-499a-5p (sponged by lncRNA DGUOK-AS1) and showing that SPRR1B silencing reverses pro-tumorigenic phenotypes revealed a post-transcriptional regulatory layer controlling SPRR1B abundance in squamous carcinoma.","evidence":"Luciferase reporter assays validating direct miRNA–SPRR1B 3′-UTR interaction, siRNA knockdown and functional rescue in cervical cancer cell lines","pmids":["34808501"],"confidence":"Medium","gaps":["Whether miR-499a-5p regulation of SPRR1B operates in normal epithelial differentiation contexts is untested","Endogenous stoichiometry of ceRNA network components was not measured"]},{"year":2022,"claim":"A second ceRNA axis (lncRNA HAGLROS/miR-330-5p/SPRR1B) was validated with in vivo xenograft confirmation, reinforcing miRNA-mediated control of SPRR1B and extending it to bladder cancer.","evidence":"Luciferase reporter assays, miRNA mimic/inhibitor experiments, siRNA knockdown, and xenograft tumor model","pmids":["35664787"],"confidence":"Medium","gaps":["Whether miR-330-5p and miR-499a-5p cooperatively regulate SPRR1B or target distinct cell contexts is unknown","The contribution of SPRR1B versus other miR-330-5p targets to the in vivo phenotype was not isolated"]},{"year":2024,"claim":"Identifying SPRR1B as a STAT3-induced gene in oral mucosal keratinocytes that is required for efficient migration established a direct functional role in wound healing and explained the faster healing of oral mucosa compared to skin.","evidence":"Single-cell RNA-seq, SPRR1B knockdown migration assays, and murine wound healing model","pmids":["39300285"],"confidence":"Medium","gaps":["How SPRR1B mechanistically promotes migration (cytoskeletal remodeling, adhesion modulation) is unknown","Whether STAT3 directly binds the SPRR1B promoter or acts indirectly was not resolved"]},{"year":null,"claim":"The mechanism by which SPRR1B—a small, intrinsically disordered envelope protein—signals to intracellular pathways (p38 MAPK, cell cycle machinery, STAT3-dependent migration) remains unresolved; whether these activities require its structural cross-linking function or represent a moonlighting role is unknown.","evidence":"","pmids":[],"confidence":"Low","gaps":["No binding partners mediating SPRR1B's signaling functions have been identified","No structural or biophysical characterization of SPRR1B has been reported","Whether SPRR1B signaling functions operate in its soluble versus cross-linked form is untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[3]}],"localization":[{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[3]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,2,6]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[3,5,9]}],"complexes":[],"partners":["FRA1","FRA2","JUN"],"other_free_text":[]},"mechanistic_narrative":"SPRR1B is a small proline-rich protein that functions as a structural component of the cornified envelope in stratified and metaplastic epithelia, contributing to epithelial barrier formation, squamous differentiation, and wound healing. Its amino-terminal glutamine clusters (Gln4–Gln6, Gln22–Gln25) serve as transglutaminase acceptor sites required for covalent cross-linking into cornified envelopes, while its carboxyl terminus governs protein stability [PMID:10681560]. Transcription of SPRR1B is driven by a PKCδ/Ras/MEKK1/MKK1/ERK5 cascade converging on AP-1 (Fra1/Fra2–c-Jun) elements within the proximal promoter, and is further induced by inflammatory cytokines (IL-1β, IFN-γ, TNF-α) and regulated post-transcriptionally by miR-499a-5p and miR-330-5p [PMID:10918063, PMID:11313996, PMID:12091247, PMID:18172072, PMID:34808501]. Functionally, SPRR1B promotes keratinocyte migration via STAT3 activation, accelerates G0/G1 entry, and acts upstream of p38 MAPK phosphorylation, linking it to wound healing, cell cycle withdrawal, and inflammatory epithelial remodeling [PMID:39300285, PMID:12832281, PMID:33620575]."},"prefetch_data":{"uniprot":{"accession":"P22528","full_name":"Cornifin-B","aliases":["14.9 kDa pancornulin","Small proline-rich protein IB","SPR-IB"],"length_aa":89,"mass_kda":9.9,"function":"Cross-linked envelope protein of keratinocytes. It is a keratinocyte protein that first appears in the cell cytosol, but ultimately becomes cross-linked to membrane proteins by transglutaminase. All that results in the formation of an insoluble envelope beneath the plasma membrane. Can function as both amine donor and acceptor in transglutaminase-mediated cross-linkage","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/P22528/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SPRR1B","classification":"Not Classified","n_dependent_lines":165,"n_total_lines":381,"dependency_fraction":0.4330708661417323},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SPRR1B","total_profiled":1310},"omim":[{"mim_id":"610378","title":"GLIS FAMILY ZINC FINGER PROTEIN 1; GLIS1","url":"https://www.omim.org/entry/610378"},{"mim_id":"182266","title":"SMALL PROLINE-RICH PROTEIN 1B; SPRR1B","url":"https://www.omim.org/entry/182266"},{"mim_id":"182265","title":"SMALL PROLINE-RICH PROTEIN 1A; SPRR1A","url":"https://www.omim.org/entry/182265"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"cervix","ntpm":1541.1},{"tissue":"esophagus","ntpm":2176.6},{"tissue":"vagina","ntpm":1767.0}],"url":"https://www.proteinatlas.org/search/SPRR1B"},"hgnc":{"alias_symbol":["GADD33"],"prev_symbol":["SPRR1"]},"alphafold":{"accession":"P22528","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P22528","model_url":"https://alphafold.ebi.ac.uk/files/AF-P22528-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P22528-F1-predicted_aligned_error_v6.png","plddt_mean":70.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SPRR1B","jax_strain_url":"https://www.jax.org/strain/search?query=SPRR1B"},"sequence":{"accession":"P22528","fasta_url":"https://rest.uniprot.org/uniprotkb/P22528.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P22528/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P22528"}},"corpus_meta":[{"pmid":"18172072","id":"PMC_18172072","title":"Small proline-rich protein 1B (SPRR1B) is a biomarker for squamous metaplasia in dry eye disease.","date":"2008","source":"Investigative ophthalmology & visual science","url":"https://pubmed.ncbi.nlm.nih.gov/18172072","citation_count":67,"is_preprint":false},{"pmid":"10918063","id":"PMC_10918063","title":"Phorbol ester-induced expression of airway squamous cell differentiation marker, SPRR1B, is regulated by protein kinase Cdelta /Ras/MEKK1/MKK1-dependent/AP-1 signal transduction pathway.","date":"2000","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10918063","citation_count":41,"is_preprint":false},{"pmid":"8624253","id":"PMC_8624253","title":"A small proline-rich protein, SPRR1, is upregulated early during tobacco smoke-induced squamous metaplasia in rat nasal epithelia.","date":"1996","source":"American journal of respiratory cell and molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/8624253","citation_count":38,"is_preprint":false},{"pmid":"11313996","id":"PMC_11313996","title":"Mechanism of repression of squamous differentiation marker, SPRR1B, in malignant bronchial epithelial cells: role of critical TRE-sites and its transacting factors.","date":"2001","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/11313996","citation_count":31,"is_preprint":false},{"pmid":"8617999","id":"PMC_8617999","title":"Localization and expression of cornifin-alpha/SPRR1 in mouse epidermis, anagen hair follicles, and skin neoplasms.","date":"1996","source":"The Journal of investigative dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/8617999","citation_count":23,"is_preprint":false},{"pmid":"10771479","id":"PMC_10771479","title":"SPRR1 gene induction and barrier formation occur as coordinated moving fronts in terminally differentiating epithelia.","date":"2000","source":"The Journal of investigative dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/10771479","citation_count":18,"is_preprint":false},{"pmid":"12832281","id":"PMC_12832281","title":"SPRR1B overexpression enhances entry of cells into the G0 phase of the cell cycle.","date":"2003","source":"American journal of physiology. Lung cellular and molecular physiology","url":"https://pubmed.ncbi.nlm.nih.gov/12832281","citation_count":14,"is_preprint":false},{"pmid":"12091247","id":"PMC_12091247","title":"BMK1 (ERK5) regulates squamous differentiation marker SPRR1B transcription in Clara-like H441 cells.","date":"2002","source":"American journal of respiratory cell and molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/12091247","citation_count":13,"is_preprint":false},{"pmid":"33620575","id":"PMC_33620575","title":"Identification of oral squamous cell carcinoma markers MUC2 and SPRR1B downstream of TANGO.","date":"2021","source":"Journal of cancer research and clinical oncology","url":"https://pubmed.ncbi.nlm.nih.gov/33620575","citation_count":11,"is_preprint":false},{"pmid":"34808501","id":"PMC_34808501","title":"DGUOK-AS1 promotes cervical squamous cell carcinoma progression by suppressing miR-499a-5p that targets SPRR1B in vitro.","date":"2021","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/34808501","citation_count":11,"is_preprint":false},{"pmid":"34737950","id":"PMC_34737950","title":"Integration Analysis of m6A Related Genes in Skin Cutaneous Melanoma and the Biological Function Research of the SPRR1B.","date":"2021","source":"Frontiers in oncology","url":"https://pubmed.ncbi.nlm.nih.gov/34737950","citation_count":9,"is_preprint":false},{"pmid":"35664787","id":"PMC_35664787","title":"Long Noncoding RNA HAGLROS Promotes the Malignant Progression of Bladder Cancer by Regulating the miR-330-5p/SPRR1B Axis.","date":"2022","source":"Frontiers in oncology","url":"https://pubmed.ncbi.nlm.nih.gov/35664787","citation_count":7,"is_preprint":false},{"pmid":"39300285","id":"PMC_39300285","title":"SPRR1B+ keratinocytes prime oral mucosa for rapid wound healing via STAT3 activation.","date":"2024","source":"Communications biology","url":"https://pubmed.ncbi.nlm.nih.gov/39300285","citation_count":7,"is_preprint":false},{"pmid":"10681560","id":"PMC_10681560","title":"Distinct roles for amino- and carboxyl-terminal sequences of SPRR1 protein in the formation of cross-linked envelopes of conducting airway epithelial cells.","date":"2000","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10681560","citation_count":6,"is_preprint":false},{"pmid":"38333021","id":"PMC_38333021","title":"SPRR1B is Related to the Immune Microenvironment and Can Be Used as a Biomarker for the Diagnosis of Psoriasis.","date":"2024","source":"International journal of general medicine","url":"https://pubmed.ncbi.nlm.nih.gov/38333021","citation_count":4,"is_preprint":false},{"pmid":"37961492","id":"PMC_37961492","title":"Sprr1 and miR-130b contribute to the senescence-like phenotype in aging.","date":"2023","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/37961492","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10483,"output_tokens":3159,"usd":0.039417},"stage2":{"model":"claude-opus-4-6","input_tokens":6577,"output_tokens":2698,"usd":0.150503},"total_usd":0.18992,"stage1_batch_id":"msgbatch_011rkcQdVV1RaFq9XhcG6df6","stage2_batch_id":"msgbatch_01RzgrJafdF4EWHhj5mNi6dh","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2000,\n      \"finding\": \"PMA-induced SPRR1B transcription in tracheobronchial epithelial cells is regulated by a PKCδ/Ras/MEKK1/MKK1-dependent/AP-1 signaling pathway, with dominant negative forms of PKCδ, Ras, MEKK1, and MKK1 each suppressing promoter activity, while dominant negative c-Jun abolished PMA-stimulated expression; ERK1/2 are not required despite MEK1/2 involvement.\",\n      \"method\": \"Dominant negative and constitutively active mutant overexpression, pharmacological inhibitors (rottlerin, UO126, PD98095), reporter gene assays in tracheobronchial epithelial cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal genetic and pharmacological methods, rigorous dissection of pathway components\",\n      \"pmids\": [\"10918063\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Repression of SPRR1B in malignant bronchial epithelial cells correlates with loss of in vivo protein-DNA interactions at two TRE sites in the -152 bp promoter; differential AP-1 composition (Fra1 vs. Fra2) determines SPRR1B expression: Fra1 overexpression enhances promoter activity in malignant cells, while Fra2 overexpression reduces basal and PMA-inducible promoter activity in normal cells.\",\n      \"method\": \"Chromatin immunoprecipitation/in vivo footprinting, electrophoretic mobility shift assay (EMSA), AP-1 protein overexpression, reporter gene assays in normal vs. malignant bronchial epithelial cells\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (in vivo footprinting, EMSA, overexpression) in matched cell systems\",\n      \"pmids\": [\"11313996\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"ERK5 (BMK1), activated via the MEK5 pathway, is required for PMA-inducible SPRR1B transcription in Clara-like H441 cells; dominant negative ERK5 suppresses both basal and PMA-inducible promoter activity, and c-Jun overexpression rescues this suppression, placing ERK5 upstream of AP-1-mediated SPRR1B transcription.\",\n      \"method\": \"Dominant negative and wild-type ERK5/MEK5 overexpression, reporter gene assays, kinase activation assays in H441 cells\",\n      \"journal\": \"American journal of respiratory cell and molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple genetic tools in single cell line; single lab\",\n      \"pmids\": [\"12091247\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The amino-terminal sequence of SPRR1 (specifically Gln clusters Gln4-Gln6 and Gln22-Gln25) is required for incorporation into cross-linked envelopes of human tracheobronchial epithelial cells, while the carboxyl-terminal sequence (including the last lysine residue) is required for high-level protein expression; the two termini thus have distinct roles in the SPRR1 protein life cycle.\",\n      \"method\": \"Deletion and site-directed mutagenesis of Flag-SPRR1 fusion protein, liposome-mediated transfection in human TBE cells, immunological detection of cross-linked envelope incorporation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution in primary human cells with site-directed mutagenesis identifying specific residues\",\n      \"pmids\": [\"10681560\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Inducible overexpression of SPRR1B in CHO cells for short periods accelerates entry into G0/G1 phase without affecting growth rate or ploidy, while prolonged stable overexpression induces tetraploidy, indicating SPRR1B is coupled to signals for withdrawal from the proliferative state.\",\n      \"method\": \"Stable and inducible (ecdysone system) SPRR1B overexpression in CHO, mouse, and human tumor cell lines; cell cycle analysis; ploidy measurement\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — inducible expression system with cell cycle readouts in multiple cell lines; single lab\",\n      \"pmids\": [\"12832281\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Inflammatory cytokines IL-1α, IL-1β, IL-6, IFN-γ, and TNF-α each induce SPRR1B expression in ocular surface epithelial cells in vitro; adoptive transfer of CD4+ T cells from aire-deficient mice to immunodeficient recipients caused ocular surface keratinization with elevated SPRR1B, establishing inflammation as a direct driver of SPRR1B-mediated squamous metaplasia.\",\n      \"method\": \"In vitro cytokine stimulation with RT-PCR/IHC readout; adoptive transfer experiment in mouse models; quantitative RT-PCR in human Sjögren's syndrome tissues\",\n      \"journal\": \"Investigative ophthalmology & visual science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro and in vivo experiments with mechanistic cytokine identification; single lab but multiple models\",\n      \"pmids\": [\"18172072\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SPRR1B promotes proliferation in oral squamous cell carcinoma cells by inducing p38 MAPK phosphorylation, placing SPRR1B upstream of p38 signaling in this context.\",\n      \"method\": \"Cell-based assays with SPRR1B expression manipulation; western blot for p38 phosphorylation in OSCC cells\",\n      \"journal\": \"Journal of cancer research and clinical oncology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, limited mechanistic follow-up beyond phosphorylation assay\",\n      \"pmids\": [\"33620575\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"lncRNA DGUOK-AS1 acts as a ceRNA to sponge miR-499a-5p, thereby releasing SPRR1B from miR-499a-5p-mediated repression; luciferase assays validated direct DGUOK-AS1–miR-499a-5p and miR-499a-5p–SPRR1B interactions, and SPRR1B silencing reversed pro-tumorigenic effects in cervical squamous cell carcinoma cells.\",\n      \"method\": \"Luciferase reporter assays, miRNA inhibitor/overexpression, siRNA knockdown, cell viability/migration/apoptosis assays in SiHa and HeLa cells\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — luciferase validation of direct interactions plus functional rescue experiments; single lab\",\n      \"pmids\": [\"34808501\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"lncRNA HAGLROS functions as a miR-330-5p sponge (ceRNA) to positively regulate SPRR1B expression; luciferase reporter assays confirmed direct HAGLROS–miR-330-5p and miR-330-5p–SPRR1B binding; SPRR1B silencing reversed the malignant phenotypes (proliferation, migration, invasion) promoted by miR-330-5p inhibition in bladder cancer cells.\",\n      \"method\": \"Luciferase reporter assays, FISH, subcellular fractionation, miRNA inhibitor/mimic experiments, siRNA knockdown, in vivo xenograft model\",\n      \"journal\": \"Frontiers in oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — luciferase validation, in vitro and in vivo confirmation; single lab\",\n      \"pmids\": [\"35664787\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SPRR1B+ keratinocytes are induced via STAT3 activation and promote oral mucosal wound healing; SPRR1B knockdown significantly inhibits mucosal keratinocyte migration in vitro, and SPRR1B+ keratinocytes are constitutively abundant in normal oral mucosa but absent in normal skin, correlating with the faster healing of mucosal wounds.\",\n      \"method\": \"Single-cell RNA sequencing, bulk-mRNA sequencing, SPRR1B knockdown with keratinocyte migration assays, murine wound healing model\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with specific migration phenotype, combined with scRNA-seq and animal model validation; single lab\",\n      \"pmids\": [\"39300285\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Silencing SPRR1B in IFN-γ-treated HaCaT keratinocytes significantly reduces IFN-γ-induced upregulation of IL-17, IL-22, KRT6, and KRT16, placing SPRR1B downstream of IFN-γ signaling and upstream of these inflammatory/differentiation effectors in psoriasis-relevant keratinocytes.\",\n      \"method\": \"siRNA-mediated SPRR1B knockdown in IFN-γ-treated HaCaT cells; RT-PCR for downstream targets\",\n      \"journal\": \"International journal of general medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single knockdown experiment in one cell line, limited mechanistic depth\",\n      \"pmids\": [\"38333021\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Sprr1a (mouse ortholog closely related to SPRR1B) suppresses senescence-like phenotype: reduced Sprr1a levels (including via miR-130b) promote upregulation of p16, p53, and p21 and increase β-galactosidase activity, while Sprr1a expression protects cells from senescence induced by radiation or doxorubicin.\",\n      \"method\": \"miR-130b and Sprr1a overexpression/knockdown; β-galactosidase assay; western blot for p16, p53, p21 in cell lines\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — preprint, single lab, mouse ortholog (Sprr1a not Sprr1b), functional readouts without deep mechanistic dissection\",\n      \"pmids\": [\"37961492\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"SPRR1B is a squamous differentiation marker whose transcription is driven by a PKCδ/Ras/MEKK1/MKK1/ERK5–AP-1 (particularly Fra1/Fra2-dependent) signaling axis in epithelial cells; its protein incorporates into cross-linked cornified envelopes via amino-terminal Gln clusters, while its carboxyl terminus controls protein stability; upstream, inflammatory cytokines (IL-1β, IFN-γ) and lncRNA ceRNA networks (sponging miR-499a-5p or miR-330-5p) regulate its levels, and SPRR1B in turn promotes keratinocyte migration (via STAT3), p38 MAPK phosphorylation, and cell cycle G0 entry, collectively linking it to epithelial barrier formation, squamous metaplasia, and wound healing.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SPRR1B is a small proline-rich protein that functions as a structural component of the cornified envelope in stratified and metaplastic epithelia, contributing to epithelial barrier formation, squamous differentiation, and wound healing. Its amino-terminal glutamine clusters (Gln4–Gln6, Gln22–Gln25) serve as transglutaminase acceptor sites required for covalent cross-linking into cornified envelopes, while its carboxyl terminus governs protein stability [PMID:10681560]. Transcription of SPRR1B is driven by a PKCδ/Ras/MEKK1/MKK1/ERK5 cascade converging on AP-1 (Fra1/Fra2–c-Jun) elements within the proximal promoter, and is further induced by inflammatory cytokines (IL-1β, IFN-γ, TNF-α) and regulated post-transcriptionally by miR-499a-5p and miR-330-5p [PMID:10918063, PMID:11313996, PMID:12091247, PMID:18172072, PMID:34808501]. Functionally, SPRR1B promotes keratinocyte migration via STAT3 activation, accelerates G0/G1 entry, and acts upstream of p38 MAPK phosphorylation, linking it to wound healing, cell cycle withdrawal, and inflammatory epithelial remodeling [PMID:39300285, PMID:12832281, PMID:33620575].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Identifying the structural requirements for SPRR1 incorporation into the cornified envelope resolved how this small protein participates in barrier assembly: amino-terminal Gln clusters are transglutaminase substrates for cross-linking, while the C-terminus controls protein stability.\",\n      \"evidence\": \"Site-directed and deletion mutagenesis of Flag-SPRR1 in primary human tracheobronchial epithelial cells with immunological detection of envelope incorporation\",\n      \"pmids\": [\"10681560\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"The specific transglutaminase(s) catalyzing cross-linking of SPRR1B in vivo are not identified\",\n        \"How the C-terminal lysine controls protein stability (proteasomal degradation vs. other mechanism) is unknown\"\n      ]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Mapping the signaling cascade upstream of SPRR1B transcription established that PKCδ, Ras, MEKK1, and MKK1 form a linear pathway converging on AP-1, with ERK1/2 dispensable despite MEK1/2 involvement, defining a non-canonical MAPK route to squamous differentiation gene expression.\",\n      \"evidence\": \"Dominant-negative and constitutively active kinase mutants combined with pharmacological inhibitors and reporter assays in tracheobronchial epithelial cells\",\n      \"pmids\": [\"10918063\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"The direct phosphorylation substrate of MKK1 that activates AP-1 in this pathway was unresolved at this stage\",\n        \"Whether the same cascade operates in non-airway squamous epithelia was not tested\"\n      ]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Demonstrating differential AP-1 composition at the SPRR1B promoter in normal versus malignant bronchial cells explained how SPRR1B is silenced during malignant transformation: Fra1 activates and Fra2 represses the promoter via two TRE sites within −152 bp.\",\n      \"evidence\": \"In vivo footprinting, EMSA, and AP-1 overexpression with reporter assays in matched normal and malignant bronchial epithelial cells\",\n      \"pmids\": [\"11313996\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether Fra1/Fra2 switch is driven by epigenetic changes at their own loci or by upstream signaling alterations is unknown\",\n        \"No chromatin immunoprecipitation for histone marks at the SPRR1B locus was performed\"\n      ]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Placing ERK5 (BMK1) upstream of AP-1-dependent SPRR1B transcription completed the kinase cascade and resolved the identity of the ERK1/2-independent MAP kinase branch required for inducible expression.\",\n      \"evidence\": \"Dominant-negative ERK5/MEK5 overexpression with reporter assays and c-Jun rescue in H441 Clara-like cells\",\n      \"pmids\": [\"12091247\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct ERK5-mediated phosphorylation of c-Jun or another AP-1 component was not demonstrated biochemically\",\n        \"Findings in a single cell line (H441)\"\n      ]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Showing that inducible SPRR1B overexpression drives G0/G1 entry linked this structural envelope protein to cell cycle control, suggesting a dual role in differentiation-associated growth arrest.\",\n      \"evidence\": \"Ecdysone-inducible SPRR1B expression system in CHO and tumor cell lines with cell cycle analysis\",\n      \"pmids\": [\"12832281\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The molecular mechanism by which SPRR1B influences cell cycle machinery (CDK inhibitors, Rb pathway) is unknown\",\n        \"Tetraploidy from prolonged overexpression was not mechanistically explained\"\n      ]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Demonstrating that multiple inflammatory cytokines (IL-1β, IFN-γ, TNF-α) directly induce SPRR1B in ocular surface epithelium, and that T-cell-driven inflammation causes SPRR1B-positive squamous metaplasia in vivo, established inflammation as a physiological driver of SPRR1B expression.\",\n      \"evidence\": \"In vitro cytokine stimulation with RT-PCR/IHC; adoptive transfer of CD4+ T cells from aire-deficient mice; validation in human Sjögren's syndrome tissue\",\n      \"pmids\": [\"18172072\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Which cytokine-activated transcription factors directly bind the SPRR1B promoter (NF-κB, STAT, or AP-1) was not resolved\",\n        \"Whether cytokine induction uses the same PKCδ/ERK5 axis or a parallel pathway is unknown\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identifying SPRR1B as a target of miR-499a-5p (sponged by lncRNA DGUOK-AS1) and showing that SPRR1B silencing reverses pro-tumorigenic phenotypes revealed a post-transcriptional regulatory layer controlling SPRR1B abundance in squamous carcinoma.\",\n      \"evidence\": \"Luciferase reporter assays validating direct miRNA–SPRR1B 3′-UTR interaction, siRNA knockdown and functional rescue in cervical cancer cell lines\",\n      \"pmids\": [\"34808501\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether miR-499a-5p regulation of SPRR1B operates in normal epithelial differentiation contexts is untested\",\n        \"Endogenous stoichiometry of ceRNA network components was not measured\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"A second ceRNA axis (lncRNA HAGLROS/miR-330-5p/SPRR1B) was validated with in vivo xenograft confirmation, reinforcing miRNA-mediated control of SPRR1B and extending it to bladder cancer.\",\n      \"evidence\": \"Luciferase reporter assays, miRNA mimic/inhibitor experiments, siRNA knockdown, and xenograft tumor model\",\n      \"pmids\": [\"35664787\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether miR-330-5p and miR-499a-5p cooperatively regulate SPRR1B or target distinct cell contexts is unknown\",\n        \"The contribution of SPRR1B versus other miR-330-5p targets to the in vivo phenotype was not isolated\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identifying SPRR1B as a STAT3-induced gene in oral mucosal keratinocytes that is required for efficient migration established a direct functional role in wound healing and explained the faster healing of oral mucosa compared to skin.\",\n      \"evidence\": \"Single-cell RNA-seq, SPRR1B knockdown migration assays, and murine wound healing model\",\n      \"pmids\": [\"39300285\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"How SPRR1B mechanistically promotes migration (cytoskeletal remodeling, adhesion modulation) is unknown\",\n        \"Whether STAT3 directly binds the SPRR1B promoter or acts indirectly was not resolved\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The mechanism by which SPRR1B—a small, intrinsically disordered envelope protein—signals to intracellular pathways (p38 MAPK, cell cycle machinery, STAT3-dependent migration) remains unresolved; whether these activities require its structural cross-linking function or represent a moonlighting role is unknown.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No binding partners mediating SPRR1B's signaling functions have been identified\",\n        \"No structural or biophysical characterization of SPRR1B has been reported\",\n        \"Whether SPRR1B signaling functions operate in its soluble versus cross-linked form is untested\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 2, 6]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [3, 5, 9]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"FRA1\",\n      \"FRA2\",\n      \"JUN\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}