{"gene":"RAP1B","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":2004,"finding":"Rap1B localizes to the tip of a single neurite in rat hippocampal neurons and is necessary and sufficient to specify axonal identity, acting upstream of Cdc42 and the Par complex (Par3/Par6/aPKC) in neuronal polarity establishment.","method":"GTPase dominant-active/dominant-negative mutants, RNA interference, live imaging of neuronal cultures","journal":"Nature neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal gain- and loss-of-function experiments with epistasis (Rap1B→Cdc42→Par complex) replicated across multiple approaches in the same study","pmids":["15286792"],"is_preprint":false},{"year":2005,"finding":"Rap1b is required downstream of GPCR-linked and GPCR-independent agonists for integrin αIIbβ3 inside-out activation and platelet aggregation; Rap1b-null mice have a bleeding defect and are protected from arterial thrombosis.","method":"Rap1b knockout mouse, platelet aggregation assays, integrin activation assays (fibrinogen binding), in vivo thrombosis model","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with multiple orthogonal phenotypic readouts (aggregation, integrin activation, in vivo hemostasis/thrombosis)","pmids":["15696195"],"is_preprint":false},{"year":2002,"finding":"Rap1B is activated in platelets via Gαi-family members (Gαz and Gαi2) and this activation is dependent on PI3Kγ-generated phosphoinositides downstream of Gi-coupled receptors (P2Y12 for ADP, α2A-adrenergic receptor for epinephrine).","method":"Platelets from Gαz-/-, Gαi2-/-, Gαq-/-, and PI3Kγ-/- mice; Rap1-GTP pull-down; selective receptor inhibitors","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple knockout mouse lines and pharmacological inhibitors converging on the same pathway","pmids":["11970953"],"is_preprint":false},{"year":2002,"finding":"Constitutively active Rap1b (V12) augments agonist-induced fibrinogen binding to integrin αIIbβ3 in megakaryocytes through an effect on integrin affinity that requires intact actin polymerization; dominant-negative Rap1b (N17) and RapGAP suppress this binding.","method":"Retroviral transduction of GFP-Rap1b chimeras into murine megakaryocytes, fibrinogen binding assay, cytochalasin D/latrunculin A treatment","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — gain- and loss-of-function in the same cell system with mechanistic link to actin and integrin affinity","pmids":["11994301"],"is_preprint":false},{"year":2008,"finding":"X-ray crystal structure of Epac2 in complex with a cAMP analogue and RAP1B reveals that cAMP binding causes the cyclic nucleotide-binding domain to swing away from a position blocking the Rap binding site toward a docking site at the Ras exchange motif domain, trapping RAP1B mid-exchange reaction.","method":"X-ray crystallography, single-particle electron microscopy","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — atomic-resolution crystal structure with EM validation, defining the cAMP-activated GEF mechanism","pmids":["18660803"],"is_preprint":false},{"year":2017,"finding":"Talin-F0 domain binds Rap1b like canonical Rap1 effectors despite little sequence homology; this interaction becomes strong upon attachment of activated Rap1b to vesicular membranes, providing a membrane-targeting mechanism for talin to activate integrin. Disruption of the Rap1b-talin interaction strongly impairs integrin activation, cell adhesion, and cell spreading.","method":"X-ray crystallography of Rap1b–talin-F0 complex, vesicle-binding assays, mutagenesis, cell adhesion and spreading assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus functional mutagenesis plus in-cell phenotype in one study","pmids":["29170462"],"is_preprint":false},{"year":1994,"finding":"Rap1A and Rap1B proteins localize to late endocytic compartments (late endosomes/lysosomes) in fibroblasts and to phagosomes with late-endosomal features in macrophages, as shown by confocal immunofluorescence and subcellular fractionation.","method":"Confocal immunofluorescence microscopy with specific antibodies, subcellular fractionation, vaccinia T7 overexpression system","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization by two orthogonal methods (immunofluorescence + fractionation), but no functional consequence established for Rap1B specifically at these compartments","pmids":["7962206"],"is_preprint":false},{"year":1996,"finding":"GTP-bound, post-translationally lipid-modified Rap1B directly activates B-Raf protein kinase from bovine brain (immunoprecipitated) in a cell-free assay, stimulating MEK phosphorylation to a level comparable to Ki-Ras.","method":"Cell-free B-Raf kinase assay with recombinant Rap1B (GTP vs GDP form, lipid-modified vs unmodified), MEK phosphorylation readout","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with multiple biochemical controls (nucleotide state, lipid modification); replicated in related study PMID:8663012","pmids":["8576107"],"is_preprint":false},{"year":1990,"finding":"Rap1B is phosphorylated by cAMP-dependent protein kinase (PKA) in intact human platelets; peptide sequencing of the purified phosphorylated protein confirms it is rap1b and not rap1a.","method":"32P labeling of platelets, immunoprecipitation with anti-H-ras antibody (M90), proteolytic cleavage and amino acid sequencing, comparison of PKA phosphorylation kinetics of synthetic C-terminal peptides","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct peptide sequencing of phosphorylated protein from intact cells, corroborated by synthetic peptide kinetics","pmids":["1696481"],"is_preprint":false},{"year":1990,"finding":"In resting platelets, Rap1B is membrane-associated; upon activation with thrombin or calcium ionophore A23187, Rap1B translocates quantitatively to the actin cytoskeleton fraction.","method":"Platelet fractionation (Triton X-100 lysis, differential centrifugation), Western blotting","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct fractionation experiment replicated with two different agonists; independently confirmed in later studies","pmids":["2123187"],"is_preprint":false},{"year":1993,"finding":"Ser179 in the C-terminal region of Rap1b is the PKA phosphorylation site; substitution with Lys (resembling Rap1a) shifts phosphorylation to Ser180.","method":"Site-directed mutagenesis, transient expression with epitope-tagged protein, cAMP stimulation and SDS-PAGE mobility shift analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis defining the exact phosphorylation site, single lab","pmids":["8463283"],"is_preprint":false},{"year":1992,"finding":"Rap1b is also phosphorylated by cGMP-dependent protein kinase (PKG) at the same Ser179 residue that is targeted by PKA.","method":"Cell-free phosphorylation assay with purified PKG and recombinant Rap1b; Km and Vmax determination","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay with defined Km/Vmax, single lab","pmids":["1551424"],"is_preprint":false},{"year":1991,"finding":"CaM kinase Gr (a neuron-specific Ca2+/calmodulin-dependent kinase) phosphorylates Rap1b on a serine near the C-terminus with ~1:1 stoichiometry; phosphorylation is reversed by an endogenous brain phosphatase. Other Ras-family GTPases (Rab3A, Rap2b, Ha-ras p21) are not substrates.","method":"In vitro kinase assay with purified CaM kinase Gr and Rap1b; stoichiometry determination; phosphatase reversal assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with stoichiometry measurement, substrate specificity panel, and phosphatase reversal","pmids":["1901412"],"is_preprint":false},{"year":1995,"finding":"cAMP-elevating agents (cholera toxin, IBMX, forskolin) activate Rap1b in intact cells, as measured by increased Rap1b-bound GTP/GDP ratio, demonstrating agonist-dependent Rap1b activation for the first time.","method":"Guanine nucleotide binding assay (GTP/GDP ratio) on immunoprecipitated Rap1b from 32P-labeled cells","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct biochemical measurement of GTP loading in intact cells, single lab, foundational finding","pmids":["7737967"],"is_preprint":false},{"year":2002,"finding":"cAMP inhibition of Akt activity in thyroid cells requires both PKA-mediated activation and phosphorylation of Rap1b; dominant-negative Rap1b blocks cAMP-induced Akt inhibition.","method":"Dominant-negative Rap1b expression, cAMP stimulation, Akt kinase activity assay in PCCL3 thyroid cells","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — dominant-negative epistasis and kinase activity measurement, single lab","pmids":["12089143"],"is_preprint":false},{"year":2002,"finding":"cAMP-dependent mitogenic G1/S entry in thyroid follicular cells requires both PKA-mediated phosphorylation and activation of Rap1b; blocking either phosphorylation or GTP binding of Rap1b is sufficient to abrogate the cAMP mitogenic response.","method":"Expression of phosphorylation-deficient and activation-deficient Rap1b mutants in PCCL3 cells, DNA synthesis assay (BrdU/thymidine incorporation)","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple Rap1b mutants with defined biochemical properties tested in physiologically relevant cell system, single lab","pmids":["11959997"],"is_preprint":false},{"year":2007,"finding":"Ubiquitin E3 ligase Smurf2 ubiquitinates inactive (GDP-bound) Rap1B and targets it for proteasomal degradation. This degradation restricts Rap1B to a single neurite tip, ensuring formation of a single axon. Smurf1 regulates Rho but not Rap1B.","method":"RNAi knockdown of Smurf1/Smurf2, ubiquitination assay, proteasome inhibitor rescue, imaging of Rap1B localization in hippocampal neurons","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct ubiquitination assay plus proteasome-inhibitor rescue plus RNAi with spatial imaging, establishing writer (Smurf2) and substrate (inactive Rap1B)","pmids":["17318188"],"is_preprint":false},{"year":2008,"finding":"PI3K and Rheb/mTOR pathway act upstream of Rap1B to control neuronal polarity; mTOR promotes Rap1B protein levels by counteracting Smurf2-mediated degradation. Inhibiting mTOR or expressing mTOR-insensitive 4E-BP1 reduces Rap1B and blocks axon formation.","method":"RNAi of Rheb, mTOR inhibitor (rapamycin), mTOR-insensitive 4E-BP1 mutants, Rap1B protein level quantification in hippocampal neurons","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with multiple RNAi and pharmacological tools, single lab","pmids":["18842593"],"is_preprint":false},{"year":2002,"finding":"A Gi-dependent pathway (via P2Y12 receptor, not P2Y1) is necessary and sufficient to activate Rap1B in platelets; Gq-mediated Ca2+ signaling alone is insufficient for Rap1B activation through P2Y12.","method":"Rap1B-GTP pull-down assay in human platelets; selective P2Y12 and P2Y1 antagonists; ADP scavengers; epinephrine and serotonin receptor agonists","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — pharmacological dissection with receptor-selective antagonists plus agonist specificity panel converging on Gi/P2Y12→Rap1B pathway","pmids":["11815620"],"is_preprint":false},{"year":2002,"finding":"Gi-dependent activation of Rap1B in platelets requires PI3K-generated PtdIns(3,4,5)P3 (but not PtdIns(3,4)P2), but is independent of adenylyl cyclase inhibition and cAMP changes. PI3Kγ is not the relevant isoform in mouse platelets.","method":"Wortmannin/LY294002 inhibition, PI3Kγ-/- mouse platelets, exogenous PtdIns(3,4,5)P3 and PtdIns(3,4)P2 rescue, dideoxyadenosine/SQ22536 control; Rap1B-GTP pull-down","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — knockout mice plus pharmacology plus lipid rescue experiment, multiple orthogonal methods","pmids":["12407113"],"is_preprint":false},{"year":2013,"finding":"Adenosine A2B receptor activation promotes PKA-mediated phosphorylation of Rap1B, which decreases its interaction with the chaperone SmgGDS-607, suppresses Rap1B prenylation, causes cytosolic/nuclear accumulation of non-prenylated Rap1B, and promotes cell scattering.","method":"A2B receptor agonist treatment, PKA inhibitors, co-immunoprecipitation of Rap1B-SmgGDS, prenylation assay, subcellular fractionation, cell scattering assay; validated in breast/lung/pancreatic cancer lines","journal":"Science signaling","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (Co-IP, fractionation, prenylation assay, functional scattering) across multiple cell lines","pmids":["23716716"],"is_preprint":false},{"year":2015,"finding":"β-adrenergic receptor (βAR) activation via Gαs/PKA phosphorylates Rap1B, inhibits its prenylation and membrane localization, reduces cell-cell adhesion, and promotes breast cancer cell scattering; propranolol (βAR blocker) decreases cell migration.","method":"Cholera toxin and βAR agonist treatment, Western blot for Rap1B phosphorylation, prenylation assay, membrane fractionation, cell-cell adhesion and scattering assay","journal":"Cancer biology & therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple biochemical readouts in one lab, mechanistically extends the GPCR→PKA→Rap1B prenylation axis","pmids":["26209110"],"is_preprint":false},{"year":1992,"finding":"Epinephrine, acting through the α2-adrenergic receptor, specifically suppresses Rap1B.GAP-stimulated GTPase activity in platelet lysates (without affecting Ras.GAP or Rap2B.GAP activities), as shown by selective α2-adrenergic antagonist yohimbine blockade.","method":"[γ-32P]GTP hydrolysis assay on Rap1B immunoprecipitated from lysates of epinephrine-stimulated platelets; yohimbine antagonism; UK14304 agonist confirmation","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical specificity panel with pharmacological controls, single lab","pmids":["1313568"],"is_preprint":false},{"year":1992,"finding":"Rap1B co-immunoprecipitates with rasGAP upon thrombin stimulation of platelets, forming a signaling complex with rasGAP and phospholipase C-γ1.","method":"Immunoprecipitation of rasGAP followed by Western blot for Rap1B; co-precipitation in resting vs thrombin-stimulated platelets","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single Co-IP experiment; functional consequence of this complex not fully established","pmids":["1323853"],"is_preprint":false},{"year":1999,"finding":"von Willebrand factor (vWF) induces translocation of Rap1B (in a later phase than Rap2B) to the platelet cytoskeleton via glycoprotein Ib and FcγRII receptor-mediated tyrosine phosphorylation; translocation is blocked by cytochalasin D, anti-FcγRII antibody, and tyrosine kinase inhibitors.","method":"Platelet fractionation, Western blotting, neutralizing antibodies against GPIb and FcγRII, cytochalasin D, tyrosine kinase inhibitor genistein","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple receptor-blocking and inhibitor experiments defining the pathway, single lab","pmids":["10224142"],"is_preprint":false},{"year":2011,"finding":"Rap1b plays a role in both αIIbβ3 inside-out signaling/platelet secretion (granule ATP release, P-selectin expression) and αIIbβ3 outside-in signaling (platelet spreading on fibrinogen, clot retraction); outside-in Rap1b activation is Src-, PKC-, and Ca2+-dependent but independent of P2Y12 or TXA2 receptors.","method":"Rap1b-/- platelets, ATP secretion assay, P-selectin expression (FACS), spreading on fibrinogen, clot retraction, selective Src inhibitor PP2, PKC inhibitor, Ca2+ chelator, P2Y12/TXA2 KO platelets","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with multiple distinct functional readouts and pharmacological pathway dissection","pmids":["21940635"],"is_preprint":false},{"year":2005,"finding":"Integrin α2β1 outside-in signaling activates Rap1b via PLC-derived Ca2+ and PKC through the exchange factor CalDAG-GEFI; activated Rap1b then mediates inside-out activation of αIIbβ3 (fibrinogen binding). CalDAG-GEFI-deficient platelets fail to activate Rap1b downstream of α2β1.","method":"Platelet adhesion to α2β1 ligands, Rap1b-GTP pull-down, CalDAG-GEFI-/- mouse platelets, PLC inhibitor U73122, Ca2+ and PKC pathway dissection","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — knockout mouse plus pharmacological dissection establishing CalDAG-GEFI as the GEF linking α2β1 to Rap1b","pmids":["16357324"],"is_preprint":false},{"year":2009,"finding":"PKA phosphorylation at Ser179 induces allosteric conformational changes in Rap1b's switch I and switch II loops (distal from the phosphorylation site), as detected by amide hydrogen/deuterium exchange mass spectrometry; phosphomimetic S179D reproduces these changes.","method":"Hydrogen/deuterium exchange mass spectrometry (DXMS) on PKA-phosphorylated Rap1b vs S179D phosphomimetic mutant","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — structural mass spectrometry with phosphomimetic validation, single lab; establishes allosteric mechanism of phosphorylation","pmids":["19651783"],"is_preprint":false},{"year":2013,"finding":"PKA phosphorylates CalDAG-GEFI at S587 (major site) and S116/117 (minor sites), and this phosphorylation abolishes CalDAG-GEFI-mediated Rap1b activation; complete abrogation of PKA-mediated Rap1b inhibition requires mutation of all three sites.","method":"Radioactive phosphate incorporation, mass spectrometry, phospho-specific antibody, phosphomimetic and alanine mutants in HEK293 and platelets, Rap1-GTP pull-down assay","journal":"Journal of thrombosis and haemostasis","confidence":"High","confidence_rationale":"Tier 1 / Strong — site identification by MS plus mutagenesis plus functional Rap1b activation readout in two cell systems","pmids":["23611601"],"is_preprint":false},{"year":2013,"finding":"PKA phosphorylates CalDAG-GEFI at Ser116 and Ser586, inhibiting its ability to activate Rap1b in response to Ca2+ ionophore; phospho-mimetic S586D CalDAG-GEFI abolishes agonist-induced Rap1b activation and platelet aggregation.","method":"In vitro PKA phosphorylation of recombinant CalDAG-GEFI, alanine/aspartate mutants, Rap1b-GTP pull-down in HEK293 cells and platelets","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro phosphorylation plus mutagenesis plus functional Rap1b activation assay, corroborates PMID:23611601","pmids":["23600630"],"is_preprint":false},{"year":2016,"finding":"VASP forms a complex with the adaptor Crkl via VASP's SH3-binding proline-rich region; PKA-mediated phosphorylation of VASP at Ser157 abrogates VASP-Crkl binding. VASP-null platelets show reduced agonist-induced Rap1b activation, placing the C3G/Crkl/VASP complex upstream of Rap1b.","method":"Co-immunoprecipitation, confocal microscopy of spreading platelets, GST pull-down with Crkl SH3 domains, VASP-null mouse platelets, Rap1b-GTP pull-down","journal":"Cell communication and signaling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP plus GST pull-down plus KO platelets, single lab","pmids":["27620165"],"is_preprint":false},{"year":2008,"finding":"Rap1b is the dominant isoform in NK cells; its absence impairs LFA1 polarization, spreading, MTOC formation, and cytokine/chemokine production. Upon activation, Rap1b co-localizes with IQGAP1 and facilitates sequential phosphorylation of B-Raf, C-Raf, and ERK1/2, forming a large signalosome in the perinuclear region.","method":"Rap1a/Rap1b KO mice, LFA1 polarization assay, MTOC staining, cytokine assays, co-immunoprecipitation of Rap1b-IQGAP1, B-Raf/C-Raf/ERK phosphorylation Western blot","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with multiple orthogonal readouts plus co-IP identifying signalosome components","pmids":["20733035"],"is_preprint":false},{"year":2008,"finding":"Rap1b deficiency impairs B cell adhesion to stromal cells, reduces chemotaxis to SDF-1 and CXCL13, and decreases in vivo B cell homing to lymph nodes; Rap1b-deficient B cells show impaired SDF-1-mediated Pyk2 activation but normal ERK, p38, and Akt activation via BCR or LPS.","method":"Rap1b KO mouse, adhesion assay, chemotaxis assay, in vivo homing assay, Pyk2 phosphorylation Western blot","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with multiple functional assays and specific signaling pathway readout distinguishing Rap1b-dependent (Pyk2) from independent (ERK/Akt) pathways","pmids":["18319399"],"is_preprint":false},{"year":2014,"finding":"Rap1b deficiency in neutrophils promotes transcellular (rather than paracellular) diapedesis through endothelial cells via enhanced PI3K-Akt activation and invadopodia-like protrusions; in vivo, this leads to enhanced neutrophil lung recruitment and susceptibility to endotoxin shock. The inhibitory effect of Rap1b on PI3K signaling may be mediated by activation of phosphatase SHP-1.","method":"Rap1b-/- mice, neutrophil transmigration assays, Akt inhibitor rescue in vivo, SHP-1 activity assay, invadopodia imaging","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with in vitro mechanistic dissection and in vivo rescue, multiple readouts","pmids":["25092872"],"is_preprint":false},{"year":2014,"finding":"Rap1b in both smooth muscle cells and endothelium is required for normal vascular tone and blood pressure; its loss leads to increased smooth muscle contractility (with increased inhibitory phosphorylation of myosin phosphatase), decreased cAMP/Epac-dependent relaxation, and reduced endothelial NO-dependent vasodilation.","method":"Rap1b-/- mice, blood pressure monitoring, aortic ring contraction/relaxation assays, myosin phosphatase phosphorylation (Western blot), nitric oxide vasodilation assay","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with mechanistic ex vivo vascular assays and losartan rescue linking hypertension to vascular tone","pmids":["24790136"],"is_preprint":false},{"year":2018,"finding":"Rap1b deficiency abolishes VEGF-induced endothelial barrier dissolution and AJ remodeling in vitro, while Rap1A deficiency (not Rap1b) increases basal vascular permeability; both isoforms are required for de novo AJ formation and recovery from LPS-induced barrier disruption.","method":"EC-specific Rap1A and Rap1B KO mice, electrical impedance sensing, VE-cadherin immunostaining, in vivo VEGF permeability assay, STZ-induced diabetes model","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — isoform-specific conditional KO mice with multiple orthogonal in vitro and in vivo barrier readouts","pmids":["29222111"],"is_preprint":false},{"year":2015,"finding":"EPAC (exchange protein directly activated by cAMP) activates Rap1b to specify and elongate the axon in hippocampal neurons; EPAC1 KO neurons have axon elongation and polarization defects; pharmacological EPAC activation (8-pCPT) induces supernumerary axons via Rap1b.","method":"EPAC1 KO mice neurons, shRNA knockdown, EPAC pharmacological activator (8-pCPT), axon markers (ankyrinG, synaptophysin), dominant-negative/active Rap1b","journal":"The Journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mice plus pharmacology plus genetic Rap1b manipulation, single lab, identifying EPAC as the GEF upstream of Rap1b in neurons","pmids":["26269639"],"is_preprint":false},{"year":2013,"finding":"Rap1B activity is specifically elevated at the tip of the future axon (longest neurite) as shown by FRET imaging; effector mutant analysis identifies RalA and Nore1A as downstream targets of one pathway and PI3K as a target of another, both contributing to supernumerary axon formation.","method":"FRET imaging in hippocampal neurons, Rap1B effector-loop mutants (G12V/E37G and G12V/Y40C), dominant-negative RalA, Nore1A RNAi","journal":"Genes to cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — FRET-based spatial activity mapping plus effector mutant epistasis, single lab","pmids":["24165023"],"is_preprint":false},{"year":2002,"finding":"High glucose activates and up-regulates Rap1b in renal mesangial cells via a PKC-dependent mechanism; activated Rap1b then drives fibronectin synthesis through B-Raf (not Raf-1). Rap1b dominant-negative mutants (S17N or T61R) block high-glucose-induced fibronectin synthesis.","method":"Rap1b overexpression and dominant-negative mutant transfection in mesangial cells, PKC inhibitors, B-Raf/Raf-1 Western blot, fibronectin mRNA/protein quantification","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain- and loss-of-function with defined mutants and pathway component analysis, single lab","pmids":["12196513"],"is_preprint":false},{"year":2008,"finding":"Rap1b activates B-Raf and promotes Bcl-2 interaction (via the BH4 domain) in renal tubular cells, partially preventing high-glucose-induced mitochondrial dysfunction and apoptosis; Rap1b GTPase activity is decreased in diabetic kidneys.","method":"Rap1b overexpression in HK-2 cells, Western blot for Bcl-2/Bax, co-immunoprecipitation of Bcl-2-Rap1b, BH4 domain deletion mutant, GTPase activity assay, mitochondrial morphology (EM)","journal":"Journal of the American Society of Nephrology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — overexpression with domain deletion plus Co-IP plus functional mitochondrial readouts, single lab","pmids":["18753253"],"is_preprint":false},{"year":2003,"finding":"GTP-bound active Rap1B translocates to the nucleus in squamous cell carcinoma cells (not the GDP-bound form), as shown by GFP-tagged constitutively active vs inactive Rap1b mutants; nuclear translocation is also induced by growth factors.","method":"GFP-Rap1b transfection (constitutively active V12 vs dominant-negative N17), confocal microscopy, subcellular fractionation","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct imaging with nucleotide-state mutants establishing GTP dependence of nuclear localization, single lab","pmids":["13679863"],"is_preprint":false},{"year":2009,"finding":"In glioma cells, the cAMP/Epac/Rap1B pathway mediates isoproterenol-induced suppression of LPA-stimulated cell migration by inhibiting Rac1; this inhibitory action requires expression of PTEN, suggesting that PTEN-mediated reduction of PI3K activity is involved in Rap1B-dependent Rac1 inhibition.","method":"siRNA knockdown of Rap1B, dominant-negative Rap1B, Epac activator, Rac1 activation assay, PTEN expression analysis, migration assay","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNAi and dominant-negative epistasis with Rac1 activation readout and PTEN dependency, single lab","pmids":["19864456"],"is_preprint":false},{"year":2017,"finding":"RAP1B interacts with DVL2 (a Wnt pathway component) and activates β-catenin/TCF signaling in esophageal squamous cell carcinoma cells.","method":"Co-immunoprecipitation of RAP1B-DVL2, TCF reporter assay, gain- and loss-of-function experiments in ESCC cells","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single Co-IP plus reporter assay; functional consequence established but mechanism not deeply resolved","pmids":["28119087"],"is_preprint":false},{"year":2017,"finding":"Rap1b acts downstream of Axin2 and BMP signaling to promote chondrogenic fate while inhibiting MAPK (FGF) signaling and osteoblast differentiation; genetic deletion of Rap1b in mice causes defects in craniofacial and body skeletons due to impaired chondrocyte and enhanced osteoblast differentiation.","method":"Rap1b KO mouse, conditional Axin2 ablation, genetic epistasis analysis, MAPK signaling Western blot, chondrogenic/osteogenic differentiation assays","journal":"Journal of bone and mineral research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis in mouse model with differentiation assays, single lab","pmids":["28520221"],"is_preprint":false},{"year":2018,"finding":"Deletion of Rap1b (but not Rap1a or Epac1) in the setting of thyroid-specific Prkar1a knockout significantly decreases thyroid size and follicular cancer incidence, identifying Rap1b as the downstream effector of PKA in thyroid carcinogenesis.","method":"Tissue-specific compound KO mice (Prkar1a; Rap1a or Rap1b or Epac1 deletion), thyroid histology and tumor quantification","journal":"Thyroid","confidence":"High","confidence_rationale":"Tier 2 / Strong — isoform-specific in vivo genetic epistasis in a defined oncogenic context; definitive in vivo evidence","pmids":["29882482"],"is_preprint":false},{"year":2019,"finding":"In zebrafish, Rap1b stimulates integrin β1 to enhance PLPM cell adhesion to fibronectin at the somite boundary, facilitating physical contact with Notch-ligand-expressing somitic cells and thereby promoting Notch-mediated hemogenic endothelium specification and HSC development.","method":"Zebrafish rap1b knockdown/knockout, integrin β1 activation assay, cell adhesion to fibronectin, Notch reporter assay, live imaging of PLPM migration","journal":"Developmental cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo zebrafish genetics with defined cellular and signaling readouts, single lab","pmids":["31006651"],"is_preprint":false},{"year":2016,"finding":"Unlike Rap1B, phosphorylation in the polybasic region (PBR) of Rap1A does not inhibit its prenylation or binding to SmgGDS-607; GPCR-mediated suppression of Rap1A prenylation can occur independently of Rap1A phosphorylation and does not reduce Rap1A membrane localization.","method":"SmgGDS-607 binding assays with phosphorylated PBR peptides of Rap1A vs Rap1B, homology modelling, prenylation assay, membrane fractionation","journal":"Journal of molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — comparative biochemical analysis of two isoforms, single lab; establishes mechanistic difference in prenylation regulation","pmids":["27760305"],"is_preprint":false},{"year":2015,"finding":"Crystal structures of Rap1B and mutants reveal that Rap1B crystallizes in an intermediate (not fully activated) state when bound to a non-hydrolyzable GTP analogue, and that conservative mutations distant from the nucleotide-binding site control the propensity to adopt the fully activated conformation.","method":"X-ray crystallography of Rap1B and site-directed mutants","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — crystal structures with mutational analysis, single lab; functional validation limited to structural inference","pmids":["25935485"],"is_preprint":false},{"year":2011,"finding":"Rap1A (not Rap1B) is the predominant isoform for endothelial junction formation; Rap1A knockdown increases monolayer gaps and reduces the junctional pool of AF-6 co-immunoprecipitated, while Rap1B knockdown does not. GFP-Rap1A localizes more prominently at junctions than GFP-Rap1B.","method":"microRNA-based RNAi knockdown, electrical impedance sensing, VE-cadherin immunostaining, co-immunoprecipitation of AF-6 with GFP-Rap1A vs GFP-Rap1B, confocal microscopy","journal":"Small GTPases","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — isoform-specific knockdown plus localization plus Co-IP, establishes negative finding for Rap1B in junction maintenance vs positive role in VEGF permeability (consistent with PMID:29222111)","pmids":["21776404"],"is_preprint":false},{"year":2004,"finding":"Contribution of PAR-1, PAR-4, and GPIb-IX-V to thrombin-induced Rap1B activation was established: PAR-1 and PAR-4 both signal Rap1B via ADP-dependent P2Y12 pathway; GPIb-IX-V contributes to ADP-independent Rap1B activation only when both PAR-1 and PAR-4 are co-stimulated.","method":"PAR-1/PAR-4 activating peptides, PAR desensitization, GPIb cleavage by mocarhagin, P2Y12 antagonist, P2Y12-deficient human platelets, Rap1B-GTP pull-down","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological and genetic receptor dissection with multiple controls, single lab","pmids":["15078882"],"is_preprint":false},{"year":1993,"finding":"Phosphorylation of Rap1B by cAMP-dependent PKA does not inhibit its association with the cytoskeleton in thrombin-activated platelets.","method":"Platelet fractionation, Western blot, cAMP-induced phosphorylation of Rap1b prior to thrombin activation","journal":"Advances in experimental medicine and biology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single fractionation experiment, conference proceedings, negative finding","pmids":["8209787"],"is_preprint":false},{"year":1993,"finding":"Pre-phosphorylation of Rap1B by cAMP/iloprost does not inhibit platelet aggregation, ATP secretion, or responses to multiple agonists (collagen, phorbol ester, vasopressin, ADP, epinephrine), indicating that PKA-mediated Rap1B phosphorylation alone is not responsible for platelet inhibition by cyclic AMP.","method":"Iloprost pre-treatment, Western blot verification of Rap1B phosphorylation, platelet aggregation and ATP secretion with multiple agonists","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — negative mechanistic finding rigorously established with multiple agonists; single lab","pmids":["7684600"],"is_preprint":false},{"year":2008,"finding":"Rap1a siRNA knockdown in human microvascular endothelial cells reduces ERK, p38, and Rac activation in response to FGF2, and impairs cell adhesion, migration, and tubular structure formation; rap1b siRNA produces similar but not identical defects in adhesion and migration.","method":"siRNA knockdown of rap1a and rap1b in HMVECs, ERK/p38/Rac activation assays, adhesion/migration assays, Matrigel tube formation","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — parallel knockdown of both isoforms with multiple functional readouts, single lab","pmids":["18625726"],"is_preprint":false}],"current_model":"RAP1B is a small Ras-family GTPase that is activated by GTP loading (stimulated by cAMP/EPAC-mediated or Ca2+/CalDAG-GEFI-mediated exchange) and inactivated by GAP-stimulated GTP hydrolysis; it is post-translationally prenylated for membrane attachment, phosphorylated at Ser179 by PKA and PKG (which allosterically perturbs its switch regions and suppresses prenylation/membrane localization via reduced SmgGDS-607 interaction), and ubiquitinated on its inactive form by Smurf2 for proteasomal degradation; in platelets Rap1B functions as the central signaling switch downstream of Gi/P2Y12/PtdIns(3,4,5)P3 and CalDAG-GEFI to drive integrin αIIbβ3 inside-out and outside-in activation (including secretion and clot retraction), while structurally it binds talin-F0 at the membrane to recruit talin and activate integrins, and forms signaling complexes with IQGAP1, B-Raf, and Crkl/C3G; in neurons its spatially restricted activation at the future axon tip—controlled by the mTOR/Smurf2 axis and EPAC1—specifies axonal identity upstream of Cdc42 and the Par complex, and in endothelium it specifically mediates VEGF-induced barrier dissolution while maintaining vascular tone through nitric oxide release and smooth muscle myosin phosphatase regulation."},"narrative":{"mechanistic_narrative":"RAP1B is a Ras-family small GTPase that cycles between an inactive GDP-bound and active GTP-bound state to function as a spatially regulated signaling switch controlling integrin-dependent adhesion across platelets, leukocytes, endothelium, and neurons [PMID:15696195, PMID:21940635, PMID:20733035]. In platelets it is the central node for integrin αIIbβ3 inside-out and outside-in activation, secretion, and clot retraction, and its loss causes a bleeding defect with protection from arterial thrombosis [PMID:15696195, PMID:21940635]. Activation is achieved by distinct guanine-nucleotide exchange factors reading different second messengers: a Gi/P2Y12-PI3K-PtdIns(3,4,5)P3 axis and Ca2+/PKC signaling through CalDAG-GEFI in platelets [PMID:11970953, PMID:11815620, PMID:12407113, PMID:16357324], cAMP through EPAC, whose mid-exchange complex with RAP1B has been resolved structurally [PMID:18660803, PMID:26269639]. Once GTP-loaded, RAP1B binds the talin-F0 domain at the membrane to recruit talin and drive integrin activation, adhesion, and spreading [PMID:29170462], and engages downstream effectors including B-Raf to stimulate MEK/ERK signaling [PMID:8576107, PMID:20733035]. RAP1B activity is gated negatively by GAP-stimulated hydrolysis [PMID:1313568] and by PKA/PKG phosphorylation at Ser179, which allosterically perturbs the switch I/II regions and, by reducing SmgGDS-607 binding, suppresses prenylation and membrane localization [PMID:1696481, PMID:8463283, PMID:1551424, PMID:19651783, PMID:23716716]; PKA additionally inhibits RAP1B indirectly by phosphorylating CalDAG-GEFI [PMID:23611601, PMID:23600630]. Inactive GDP-bound RAP1B is ubiquitinated by Smurf2 for proteasomal degradation, and this turnover, balanced by mTOR, spatially restricts RAP1B to a single neurite tip to specify axonal identity upstream of Cdc42 and the Par complex [PMID:17318188, PMID:18842593, PMID:15286792]. In endothelium RAP1B specifically mediates VEGF-induced barrier dissolution and supports vascular tone via NO release and myosin phosphatase regulation [PMID:24790136, PMID:29222111]. RAP1B has not been linked to a Mendelian disease within this corpus.","teleology":[{"year":1990,"claim":"Established that RAP1B is a direct, physiological substrate of cAMP-dependent kinase signaling, distinguishing it from Rap1A and providing the first regulatory handle on the protein.","evidence":"32P labeling and peptide sequencing of phosphorylated protein from intact human platelets; cytoskeletal fractionation with thrombin/A23187","pmids":["1696481","2123187"],"confidence":"High","gaps":["Functional consequence of phosphorylation not yet defined","Exact phosphoacceptor residue not yet mapped"]},{"year":1993,"claim":"Pinpointed Ser179 as the PKA/PKG phosphorylation site and showed RAP1B is also a CaM kinase Gr substrate, defining the precise modified residue and broadening the kinase set.","evidence":"Site-directed mutagenesis with mobility-shift, in vitro PKG kinase assay, and CaM kinase Gr substrate specificity panel","pmids":["8463283","1551424","1901412"],"confidence":"High","gaps":["Downstream effect of Ser179 phosphorylation on GTPase activity not established","Physiological role of CaM kinase Gr phosphorylation in neurons unresolved"]},{"year":1992,"claim":"Showed that agonists tune RAP1B nucleotide state and that it physically partners with rasGAP, linking RAP1B to receptor signaling and a candidate inactivating GAP.","evidence":"GTP hydrolysis assay with α2-adrenergic pharmacology; rasGAP co-immunoprecipitation in thrombin-stimulated platelets","pmids":["1313568","1323853"],"confidence":"Medium","gaps":["rasGAP Co-IP is single, without reciprocal validation","Functional consequence of the rasGAP/PLC-γ1 complex unresolved"]},{"year":1995,"claim":"Demonstrated agonist-dependent GTP loading of RAP1B in intact cells, formally establishing it as a signal-activated GTPase.","evidence":"Guanine nucleotide binding (GTP/GDP ratio) on immunoprecipitated RAP1B from cAMP-stimulated cells","pmids":["7737967"],"confidence":"Medium","gaps":["GEF responsible for cAMP-driven activation not identified here","Downstream effectors not defined"]},{"year":1996,"claim":"Identified B-Raf as a direct RAP1B effector, connecting RAP1B to the MEK/ERK cascade in a nucleotide- and lipid-modification-dependent manner.","evidence":"Cell-free B-Raf kinase assay with GTP/GDP and lipid-modified/unmodified recombinant RAP1B, MEK phosphorylation readout","pmids":["8576107"],"confidence":"High","gaps":["In-cell relevance of RAP1B→B-Raf not established here","Whether RAP1B activates or antagonizes ERK in different cell types unresolved"]},{"year":2002,"claim":"Dissected the platelet activation pathway, placing RAP1B downstream of Gi/P2Y12 and PI3K-generated PtdIns(3,4,5)P3 and showing it controls integrin αIIbβ3 affinity.","evidence":"Multiple Gα and PI3K knockout mouse platelets, receptor-selective antagonists, lipid rescue, and Rap1-GTP pull-down; megakaryocyte fibrinogen-binding with active/dominant-negative mutants and actin inhibitors","pmids":["11970953","11815620","12407113","11994301"],"confidence":"High","gaps":["Identity of the relevant Gi-coupled GEF not established","How PtdIns(3,4,5)P3 connects to RAP1B exchange unresolved"]},{"year":2005,"claim":"Provided genetic proof that RAP1B is required for integrin inside-out activation and hemostasis, and identified CalDAG-GEFI as the GEF coupling Ca2+/PKC and collagen-integrin signaling to RAP1B.","evidence":"Rap1b knockout mouse with aggregation, integrin activation, and in vivo thrombosis assays; CalDAG-GEFI-deficient platelets in α2β1 outside-in signaling","pmids":["15696195","16357324"],"confidence":"High","gaps":["Precise effector linking RAP1B to integrin affinity not yet defined here","Distinction between inside-out and outside-in RAP1B pools unresolved"]},{"year":2008,"claim":"Resolved the cAMP-activated EPAC2–RAP1B exchange mechanism at atomic resolution, explaining how cyclic nucleotide binding triggers nucleotide exchange.","evidence":"X-ray crystallography and single-particle EM of Epac2–cAMP–RAP1B","pmids":["18660803"],"confidence":"High","gaps":["EPAC1 (the neuronal GEF) not structurally captured","In-cell kinetics of the trapped intermediate not addressed"]},{"year":2008,"claim":"Extended RAP1B function to immune cell adhesion and trafficking, defining isoform-specific roles in NK cell signalosome assembly and B/neutrophil migration.","evidence":"Rap1b knockout mouse leukocytes; LFA1 polarization, MTOC, IQGAP1/B-Raf/ERK co-IP and Western; chemotaxis, homing, and transmigration assays","pmids":["20733035","18319399","25092872"],"confidence":"High","gaps":["Mechanism of IQGAP1 signalosome assembly not fully resolved","How RAP1B negatively gates PI3K/Akt via SHP-1 unconfirmed structurally"]},{"year":2009,"claim":"Defined the allosteric structural basis by which Ser179 phosphorylation perturbs the catalytic switch regions, mechanistically linking PKA/PKG to RAP1B regulation.","evidence":"Hydrogen/deuterium exchange mass spectrometry of phosphorylated RAP1B and S179D phosphomimetic","pmids":["19651783"],"confidence":"High","gaps":["Functional consequence of switch perturbation on effector binding not directly measured","Reversal by phosphatase in vivo not addressed"]},{"year":2007,"claim":"Established the Smurf2/mTOR turnover axis that spatially restricts RAP1B to a single neurite tip, explaining how RAP1B specifies a single axon upstream of Cdc42/Par.","evidence":"RNAi, ubiquitination and proteasome-rescue assays, mTOR pharmacology, and spatial imaging in hippocampal neurons; EPAC1 KO and FRET activity mapping","pmids":["17318188","18842593","15286792","26269639","24165023"],"confidence":"High","gaps":["GEF/GAP machinery localizing RAP1B activity to the tip incompletely defined","How EPAC1 and Smurf2 are coordinated spatially unresolved"]},{"year":2013,"claim":"Resolved a dual mechanism by which PKA inhibits RAP1B: direct Ser179 phosphorylation that suppresses prenylation via reduced SmgGDS-607 binding, and phosphorylation of the upstream GEF CalDAG-GEFI.","evidence":"A2B/βAR agonist treatment, SmgGDS co-IP, prenylation and fractionation assays; MS site-mapping and phosphomimetic mutagenesis of CalDAG-GEFI in HEK293 and platelets","pmids":["23716716","28119087","23611601","23600630"],"confidence":"High","gaps":["Relative in vivo contributions of direct vs GEF-level inhibition unresolved","Note: idx 42 (DVL2) is a distinct interaction; consolidation here is editorial"]},{"year":2017,"claim":"Defined the structural basis of RAP1B-driven integrin activation by capturing the membrane-dependent talin-F0 interaction.","evidence":"X-ray crystallography of RAP1B–talin-F0, vesicle-binding assays, mutagenesis, and adhesion/spreading phenotypes","pmids":["29170462"],"confidence":"High","gaps":["Whether other talin domains contribute to RAP1B-dependent activation not addressed","Cell-type generality of the talin-F0 route unresolved"]},{"year":2018,"claim":"Demonstrated isoform-specialized endothelial functions, with RAP1B mediating VEGF-induced barrier dissolution and vascular tone while RAP1A maintains basal junctions.","evidence":"Endothelial-specific Rap1A/Rap1B knockout mice, impedance sensing, VE-cadherin imaging, in vivo permeability; vascular tone, NO, and myosin phosphatase assays","pmids":["29222111","24790136","21776404"],"confidence":"High","gaps":["Effectors mediating VEGF-specific barrier dissolution not identified","Mechanism distinguishing RAP1A vs RAP1B junctional pools unresolved"]},{"year":2018,"claim":"Provided in vivo genetic evidence that RAP1B is a downstream effector of PKA in tumorigenesis and a developmental regulator of skeletal and hematopoietic fate.","evidence":"Isoform-specific compound KO mice in thyroid carcinogenesis; Rap1b KO skeletal phenotyping with Axin2/BMP epistasis; zebrafish rap1b loss in HSC specification","pmids":["29882482","28520221","31006651"],"confidence":"High","gaps":["Molecular effectors of RAP1B in chondrogenesis vs osteogenesis incompletely defined","How RAP1B integrates with Notch/integrin β1 in HSC niche unresolved"]},{"year":null,"claim":"How distinct GEFs, GAPs, phosphorylation, and Smurf2-mediated degradation are spatiotemporally coordinated to generate cell-type-specific RAP1B activity pools, and which effectors dominate in each context, remains incompletely defined.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model of context-specific effector selection","GAPs acting on RAP1B in non-platelet cells largely unidentified","Quantitative interplay of phosphorylation and ubiquitination not resolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003924","term_label":"GTPase activity","supporting_discovery_ids":[22,47]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[1,25,2]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[5,7,31]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[9,5,20]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[9,24]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[40,20]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[6]}],"pathway":[{"term_id":"R-HSA-109582","term_label":"Hemostasis","supporting_discovery_ids":[1,25,26]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,4,18]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[31,32,33]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[0,43,45]},{"term_id":"R-HSA-1474244","term_label":"Extracellular matrix organization","supporting_discovery_ids":[5,35]}],"complexes":[],"partners":["TLN1","BRAF","IQGAP1","RASA1","SMGGDS","CRKL","DVL2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P61224","full_name":"Ras-related protein Rap-1b","aliases":["GTP-binding protein smg p21B"],"length_aa":184,"mass_kda":20.8,"function":"GTP-binding protein that possesses intrinsic GTPase activity. Contributes to the polarizing activity of KRIT1 and CDH5 in the establishment and maintenance of correct endothelial cell polarity and vascular lumen. Required for the localization of phosphorylated PRKCZ, PARD3 and TIAM1 to the cell junction. Plays a role in the establishment of basal endothelial barrier function","subcellular_location":"Cell membrane; Cytoplasm, cytosol; Cell junction","url":"https://www.uniprot.org/uniprotkb/P61224/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/RAP1B","classification":"Common Essential","n_dependent_lines":458,"n_total_lines":1208,"dependency_fraction":0.3791390728476821},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/RAP1B","total_profiled":1310},"omim":[{"mim_id":"620654","title":"THROMBOCYTOPENIA 11 WITH MULTIPLE CONGENITAL ANOMALIES AND DYSMORPHIC FACIES; THC11","url":"https://www.omim.org/entry/620654"},{"mim_id":"612664","title":"RAS-LIKE AND ESTROGEN-REGULATED GROWTH INHIBITOR; RERG","url":"https://www.omim.org/entry/612664"},{"mim_id":"611418","title":"SMALL G PROTEIN SIGNALING MODULATOR 2; SGSM2","url":"https://www.omim.org/entry/611418"},{"mim_id":"611417","title":"SMALL G PROTEIN SIGNALING MODULATOR 1; SGSM1","url":"https://www.omim.org/entry/611417"},{"mim_id":"610440","title":"SMALL G PROTEIN SIGNALING MODULATOR 3; SGSM3","url":"https://www.omim.org/entry/610440"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/RAP1B"},"hgnc":{"alias_symbol":["K-REV","RAL1B","DKFZp586H0723"],"prev_symbol":[]},"alphafold":{"accession":"P61224","domains":[{"cath_id":"3.40.50.300","chopping":"1-167","consensus_level":"high","plddt":95.1635,"start":1,"end":167}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P61224","model_url":"https://alphafold.ebi.ac.uk/files/AF-P61224-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P61224-F1-predicted_aligned_error_v6.png","plddt_mean":92.25},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RAP1B","jax_strain_url":"https://www.jax.org/strain/search?query=RAP1B"},"sequence":{"accession":"P61224","fasta_url":"https://rest.uniprot.org/uniprotkb/P61224.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P61224/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P61224"}},"corpus_meta":[{"pmid":"15286792","id":"PMC_15286792","title":"The sequential 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and is necessary and sufficient to specify axonal identity, acting upstream of Cdc42 and the Par complex (Par3/Par6/aPKC) in neuronal polarity establishment.\",\n      \"method\": \"GTPase dominant-active/dominant-negative mutants, RNA interference, live imaging of neuronal cultures\",\n      \"journal\": \"Nature neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal gain- and loss-of-function experiments with epistasis (Rap1B→Cdc42→Par complex) replicated across multiple approaches in the same study\",\n      \"pmids\": [\"15286792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Rap1b is required downstream of GPCR-linked and GPCR-independent agonists for integrin αIIbβ3 inside-out activation and platelet aggregation; Rap1b-null mice have a bleeding defect and are protected from arterial thrombosis.\",\n      \"method\": \"Rap1b knockout mouse, platelet aggregation assays, integrin activation assays (fibrinogen binding), in vivo thrombosis model\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with multiple orthogonal phenotypic readouts (aggregation, integrin activation, in vivo hemostasis/thrombosis)\",\n      \"pmids\": [\"15696195\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Rap1B is activated in platelets via Gαi-family members (Gαz and Gαi2) and this activation is dependent on PI3Kγ-generated phosphoinositides downstream of Gi-coupled receptors (P2Y12 for ADP, α2A-adrenergic receptor for epinephrine).\",\n      \"method\": \"Platelets from Gαz-/-, Gαi2-/-, Gαq-/-, and PI3Kγ-/- mice; Rap1-GTP pull-down; selective receptor inhibitors\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple knockout mouse lines and pharmacological inhibitors converging on the same pathway\",\n      \"pmids\": [\"11970953\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Constitutively active Rap1b (V12) augments agonist-induced fibrinogen binding to integrin αIIbβ3 in megakaryocytes through an effect on integrin affinity that requires intact actin polymerization; dominant-negative Rap1b (N17) and RapGAP suppress this binding.\",\n      \"method\": \"Retroviral transduction of GFP-Rap1b chimeras into murine megakaryocytes, fibrinogen binding assay, cytochalasin D/latrunculin A treatment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — gain- and loss-of-function in the same cell system with mechanistic link to actin and integrin affinity\",\n      \"pmids\": [\"11994301\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"X-ray crystal structure of Epac2 in complex with a cAMP analogue and RAP1B reveals that cAMP binding causes the cyclic nucleotide-binding domain to swing away from a position blocking the Rap binding site toward a docking site at the Ras exchange motif domain, trapping RAP1B mid-exchange reaction.\",\n      \"method\": \"X-ray crystallography, single-particle electron microscopy\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — atomic-resolution crystal structure with EM validation, defining the cAMP-activated GEF mechanism\",\n      \"pmids\": [\"18660803\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Talin-F0 domain binds Rap1b like canonical Rap1 effectors despite little sequence homology; this interaction becomes strong upon attachment of activated Rap1b to vesicular membranes, providing a membrane-targeting mechanism for talin to activate integrin. Disruption of the Rap1b-talin interaction strongly impairs integrin activation, cell adhesion, and cell spreading.\",\n      \"method\": \"X-ray crystallography of Rap1b–talin-F0 complex, vesicle-binding assays, mutagenesis, cell adhesion and spreading assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus functional mutagenesis plus in-cell phenotype in one study\",\n      \"pmids\": [\"29170462\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Rap1A and Rap1B proteins localize to late endocytic compartments (late endosomes/lysosomes) in fibroblasts and to phagosomes with late-endosomal features in macrophages, as shown by confocal immunofluorescence and subcellular fractionation.\",\n      \"method\": \"Confocal immunofluorescence microscopy with specific antibodies, subcellular fractionation, vaccinia T7 overexpression system\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization by two orthogonal methods (immunofluorescence + fractionation), but no functional consequence established for Rap1B specifically at these compartments\",\n      \"pmids\": [\"7962206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"GTP-bound, post-translationally lipid-modified Rap1B directly activates B-Raf protein kinase from bovine brain (immunoprecipitated) in a cell-free assay, stimulating MEK phosphorylation to a level comparable to Ki-Ras.\",\n      \"method\": \"Cell-free B-Raf kinase assay with recombinant Rap1B (GTP vs GDP form, lipid-modified vs unmodified), MEK phosphorylation readout\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with multiple biochemical controls (nucleotide state, lipid modification); replicated in related study PMID:8663012\",\n      \"pmids\": [\"8576107\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"Rap1B is phosphorylated by cAMP-dependent protein kinase (PKA) in intact human platelets; peptide sequencing of the purified phosphorylated protein confirms it is rap1b and not rap1a.\",\n      \"method\": \"32P labeling of platelets, immunoprecipitation with anti-H-ras antibody (M90), proteolytic cleavage and amino acid sequencing, comparison of PKA phosphorylation kinetics of synthetic C-terminal peptides\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct peptide sequencing of phosphorylated protein from intact cells, corroborated by synthetic peptide kinetics\",\n      \"pmids\": [\"1696481\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"In resting platelets, Rap1B is membrane-associated; upon activation with thrombin or calcium ionophore A23187, Rap1B translocates quantitatively to the actin cytoskeleton fraction.\",\n      \"method\": \"Platelet fractionation (Triton X-100 lysis, differential centrifugation), Western blotting\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct fractionation experiment replicated with two different agonists; independently confirmed in later studies\",\n      \"pmids\": [\"2123187\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Ser179 in the C-terminal region of Rap1b is the PKA phosphorylation site; substitution with Lys (resembling Rap1a) shifts phosphorylation to Ser180.\",\n      \"method\": \"Site-directed mutagenesis, transient expression with epitope-tagged protein, cAMP stimulation and SDS-PAGE mobility shift analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis defining the exact phosphorylation site, single lab\",\n      \"pmids\": [\"8463283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"Rap1b is also phosphorylated by cGMP-dependent protein kinase (PKG) at the same Ser179 residue that is targeted by PKA.\",\n      \"method\": \"Cell-free phosphorylation assay with purified PKG and recombinant Rap1b; Km and Vmax determination\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay with defined Km/Vmax, single lab\",\n      \"pmids\": [\"1551424\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"CaM kinase Gr (a neuron-specific Ca2+/calmodulin-dependent kinase) phosphorylates Rap1b on a serine near the C-terminus with ~1:1 stoichiometry; phosphorylation is reversed by an endogenous brain phosphatase. Other Ras-family GTPases (Rab3A, Rap2b, Ha-ras p21) are not substrates.\",\n      \"method\": \"In vitro kinase assay with purified CaM kinase Gr and Rap1b; stoichiometry determination; phosphatase reversal assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with stoichiometry measurement, substrate specificity panel, and phosphatase reversal\",\n      \"pmids\": [\"1901412\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"cAMP-elevating agents (cholera toxin, IBMX, forskolin) activate Rap1b in intact cells, as measured by increased Rap1b-bound GTP/GDP ratio, demonstrating agonist-dependent Rap1b activation for the first time.\",\n      \"method\": \"Guanine nucleotide binding assay (GTP/GDP ratio) on immunoprecipitated Rap1b from 32P-labeled cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct biochemical measurement of GTP loading in intact cells, single lab, foundational finding\",\n      \"pmids\": [\"7737967\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"cAMP inhibition of Akt activity in thyroid cells requires both PKA-mediated activation and phosphorylation of Rap1b; dominant-negative Rap1b blocks cAMP-induced Akt inhibition.\",\n      \"method\": \"Dominant-negative Rap1b expression, cAMP stimulation, Akt kinase activity assay in PCCL3 thyroid cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — dominant-negative epistasis and kinase activity measurement, single lab\",\n      \"pmids\": [\"12089143\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"cAMP-dependent mitogenic G1/S entry in thyroid follicular cells requires both PKA-mediated phosphorylation and activation of Rap1b; blocking either phosphorylation or GTP binding of Rap1b is sufficient to abrogate the cAMP mitogenic response.\",\n      \"method\": \"Expression of phosphorylation-deficient and activation-deficient Rap1b mutants in PCCL3 cells, DNA synthesis assay (BrdU/thymidine incorporation)\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple Rap1b mutants with defined biochemical properties tested in physiologically relevant cell system, single lab\",\n      \"pmids\": [\"11959997\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Ubiquitin E3 ligase Smurf2 ubiquitinates inactive (GDP-bound) Rap1B and targets it for proteasomal degradation. This degradation restricts Rap1B to a single neurite tip, ensuring formation of a single axon. Smurf1 regulates Rho but not Rap1B.\",\n      \"method\": \"RNAi knockdown of Smurf1/Smurf2, ubiquitination assay, proteasome inhibitor rescue, imaging of Rap1B localization in hippocampal neurons\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct ubiquitination assay plus proteasome-inhibitor rescue plus RNAi with spatial imaging, establishing writer (Smurf2) and substrate (inactive Rap1B)\",\n      \"pmids\": [\"17318188\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PI3K and Rheb/mTOR pathway act upstream of Rap1B to control neuronal polarity; mTOR promotes Rap1B protein levels by counteracting Smurf2-mediated degradation. Inhibiting mTOR or expressing mTOR-insensitive 4E-BP1 reduces Rap1B and blocks axon formation.\",\n      \"method\": \"RNAi of Rheb, mTOR inhibitor (rapamycin), mTOR-insensitive 4E-BP1 mutants, Rap1B protein level quantification in hippocampal neurons\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with multiple RNAi and pharmacological tools, single lab\",\n      \"pmids\": [\"18842593\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"A Gi-dependent pathway (via P2Y12 receptor, not P2Y1) is necessary and sufficient to activate Rap1B in platelets; Gq-mediated Ca2+ signaling alone is insufficient for Rap1B activation through P2Y12.\",\n      \"method\": \"Rap1B-GTP pull-down assay in human platelets; selective P2Y12 and P2Y1 antagonists; ADP scavengers; epinephrine and serotonin receptor agonists\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — pharmacological dissection with receptor-selective antagonists plus agonist specificity panel converging on Gi/P2Y12→Rap1B pathway\",\n      \"pmids\": [\"11815620\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Gi-dependent activation of Rap1B in platelets requires PI3K-generated PtdIns(3,4,5)P3 (but not PtdIns(3,4)P2), but is independent of adenylyl cyclase inhibition and cAMP changes. PI3Kγ is not the relevant isoform in mouse platelets.\",\n      \"method\": \"Wortmannin/LY294002 inhibition, PI3Kγ-/- mouse platelets, exogenous PtdIns(3,4,5)P3 and PtdIns(3,4)P2 rescue, dideoxyadenosine/SQ22536 control; Rap1B-GTP pull-down\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — knockout mice plus pharmacology plus lipid rescue experiment, multiple orthogonal methods\",\n      \"pmids\": [\"12407113\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Adenosine A2B receptor activation promotes PKA-mediated phosphorylation of Rap1B, which decreases its interaction with the chaperone SmgGDS-607, suppresses Rap1B prenylation, causes cytosolic/nuclear accumulation of non-prenylated Rap1B, and promotes cell scattering.\",\n      \"method\": \"A2B receptor agonist treatment, PKA inhibitors, co-immunoprecipitation of Rap1B-SmgGDS, prenylation assay, subcellular fractionation, cell scattering assay; validated in breast/lung/pancreatic cancer lines\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (Co-IP, fractionation, prenylation assay, functional scattering) across multiple cell lines\",\n      \"pmids\": [\"23716716\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"β-adrenergic receptor (βAR) activation via Gαs/PKA phosphorylates Rap1B, inhibits its prenylation and membrane localization, reduces cell-cell adhesion, and promotes breast cancer cell scattering; propranolol (βAR blocker) decreases cell migration.\",\n      \"method\": \"Cholera toxin and βAR agonist treatment, Western blot for Rap1B phosphorylation, prenylation assay, membrane fractionation, cell-cell adhesion and scattering assay\",\n      \"journal\": \"Cancer biology & therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple biochemical readouts in one lab, mechanistically extends the GPCR→PKA→Rap1B prenylation axis\",\n      \"pmids\": [\"26209110\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"Epinephrine, acting through the α2-adrenergic receptor, specifically suppresses Rap1B.GAP-stimulated GTPase activity in platelet lysates (without affecting Ras.GAP or Rap2B.GAP activities), as shown by selective α2-adrenergic antagonist yohimbine blockade.\",\n      \"method\": \"[γ-32P]GTP hydrolysis assay on Rap1B immunoprecipitated from lysates of epinephrine-stimulated platelets; yohimbine antagonism; UK14304 agonist confirmation\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical specificity panel with pharmacological controls, single lab\",\n      \"pmids\": [\"1313568\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"Rap1B co-immunoprecipitates with rasGAP upon thrombin stimulation of platelets, forming a signaling complex with rasGAP and phospholipase C-γ1.\",\n      \"method\": \"Immunoprecipitation of rasGAP followed by Western blot for Rap1B; co-precipitation in resting vs thrombin-stimulated platelets\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single Co-IP experiment; functional consequence of this complex not fully established\",\n      \"pmids\": [\"1323853\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"von Willebrand factor (vWF) induces translocation of Rap1B (in a later phase than Rap2B) to the platelet cytoskeleton via glycoprotein Ib and FcγRII receptor-mediated tyrosine phosphorylation; translocation is blocked by cytochalasin D, anti-FcγRII antibody, and tyrosine kinase inhibitors.\",\n      \"method\": \"Platelet fractionation, Western blotting, neutralizing antibodies against GPIb and FcγRII, cytochalasin D, tyrosine kinase inhibitor genistein\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple receptor-blocking and inhibitor experiments defining the pathway, single lab\",\n      \"pmids\": [\"10224142\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Rap1b plays a role in both αIIbβ3 inside-out signaling/platelet secretion (granule ATP release, P-selectin expression) and αIIbβ3 outside-in signaling (platelet spreading on fibrinogen, clot retraction); outside-in Rap1b activation is Src-, PKC-, and Ca2+-dependent but independent of P2Y12 or TXA2 receptors.\",\n      \"method\": \"Rap1b-/- platelets, ATP secretion assay, P-selectin expression (FACS), spreading on fibrinogen, clot retraction, selective Src inhibitor PP2, PKC inhibitor, Ca2+ chelator, P2Y12/TXA2 KO platelets\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with multiple distinct functional readouts and pharmacological pathway dissection\",\n      \"pmids\": [\"21940635\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Integrin α2β1 outside-in signaling activates Rap1b via PLC-derived Ca2+ and PKC through the exchange factor CalDAG-GEFI; activated Rap1b then mediates inside-out activation of αIIbβ3 (fibrinogen binding). CalDAG-GEFI-deficient platelets fail to activate Rap1b downstream of α2β1.\",\n      \"method\": \"Platelet adhesion to α2β1 ligands, Rap1b-GTP pull-down, CalDAG-GEFI-/- mouse platelets, PLC inhibitor U73122, Ca2+ and PKC pathway dissection\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — knockout mouse plus pharmacological dissection establishing CalDAG-GEFI as the GEF linking α2β1 to Rap1b\",\n      \"pmids\": [\"16357324\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"PKA phosphorylation at Ser179 induces allosteric conformational changes in Rap1b's switch I and switch II loops (distal from the phosphorylation site), as detected by amide hydrogen/deuterium exchange mass spectrometry; phosphomimetic S179D reproduces these changes.\",\n      \"method\": \"Hydrogen/deuterium exchange mass spectrometry (DXMS) on PKA-phosphorylated Rap1b vs S179D phosphomimetic mutant\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — structural mass spectrometry with phosphomimetic validation, single lab; establishes allosteric mechanism of phosphorylation\",\n      \"pmids\": [\"19651783\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PKA phosphorylates CalDAG-GEFI at S587 (major site) and S116/117 (minor sites), and this phosphorylation abolishes CalDAG-GEFI-mediated Rap1b activation; complete abrogation of PKA-mediated Rap1b inhibition requires mutation of all three sites.\",\n      \"method\": \"Radioactive phosphate incorporation, mass spectrometry, phospho-specific antibody, phosphomimetic and alanine mutants in HEK293 and platelets, Rap1-GTP pull-down assay\",\n      \"journal\": \"Journal of thrombosis and haemostasis\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — site identification by MS plus mutagenesis plus functional Rap1b activation readout in two cell systems\",\n      \"pmids\": [\"23611601\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PKA phosphorylates CalDAG-GEFI at Ser116 and Ser586, inhibiting its ability to activate Rap1b in response to Ca2+ ionophore; phospho-mimetic S586D CalDAG-GEFI abolishes agonist-induced Rap1b activation and platelet aggregation.\",\n      \"method\": \"In vitro PKA phosphorylation of recombinant CalDAG-GEFI, alanine/aspartate mutants, Rap1b-GTP pull-down in HEK293 cells and platelets\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro phosphorylation plus mutagenesis plus functional Rap1b activation assay, corroborates PMID:23611601\",\n      \"pmids\": [\"23600630\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"VASP forms a complex with the adaptor Crkl via VASP's SH3-binding proline-rich region; PKA-mediated phosphorylation of VASP at Ser157 abrogates VASP-Crkl binding. VASP-null platelets show reduced agonist-induced Rap1b activation, placing the C3G/Crkl/VASP complex upstream of Rap1b.\",\n      \"method\": \"Co-immunoprecipitation, confocal microscopy of spreading platelets, GST pull-down with Crkl SH3 domains, VASP-null mouse platelets, Rap1b-GTP pull-down\",\n      \"journal\": \"Cell communication and signaling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP plus GST pull-down plus KO platelets, single lab\",\n      \"pmids\": [\"27620165\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Rap1b is the dominant isoform in NK cells; its absence impairs LFA1 polarization, spreading, MTOC formation, and cytokine/chemokine production. Upon activation, Rap1b co-localizes with IQGAP1 and facilitates sequential phosphorylation of B-Raf, C-Raf, and ERK1/2, forming a large signalosome in the perinuclear region.\",\n      \"method\": \"Rap1a/Rap1b KO mice, LFA1 polarization assay, MTOC staining, cytokine assays, co-immunoprecipitation of Rap1b-IQGAP1, B-Raf/C-Raf/ERK phosphorylation Western blot\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with multiple orthogonal readouts plus co-IP identifying signalosome components\",\n      \"pmids\": [\"20733035\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Rap1b deficiency impairs B cell adhesion to stromal cells, reduces chemotaxis to SDF-1 and CXCL13, and decreases in vivo B cell homing to lymph nodes; Rap1b-deficient B cells show impaired SDF-1-mediated Pyk2 activation but normal ERK, p38, and Akt activation via BCR or LPS.\",\n      \"method\": \"Rap1b KO mouse, adhesion assay, chemotaxis assay, in vivo homing assay, Pyk2 phosphorylation Western blot\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with multiple functional assays and specific signaling pathway readout distinguishing Rap1b-dependent (Pyk2) from independent (ERK/Akt) pathways\",\n      \"pmids\": [\"18319399\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Rap1b deficiency in neutrophils promotes transcellular (rather than paracellular) diapedesis through endothelial cells via enhanced PI3K-Akt activation and invadopodia-like protrusions; in vivo, this leads to enhanced neutrophil lung recruitment and susceptibility to endotoxin shock. The inhibitory effect of Rap1b on PI3K signaling may be mediated by activation of phosphatase SHP-1.\",\n      \"method\": \"Rap1b-/- mice, neutrophil transmigration assays, Akt inhibitor rescue in vivo, SHP-1 activity assay, invadopodia imaging\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with in vitro mechanistic dissection and in vivo rescue, multiple readouts\",\n      \"pmids\": [\"25092872\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Rap1b in both smooth muscle cells and endothelium is required for normal vascular tone and blood pressure; its loss leads to increased smooth muscle contractility (with increased inhibitory phosphorylation of myosin phosphatase), decreased cAMP/Epac-dependent relaxation, and reduced endothelial NO-dependent vasodilation.\",\n      \"method\": \"Rap1b-/- mice, blood pressure monitoring, aortic ring contraction/relaxation assays, myosin phosphatase phosphorylation (Western blot), nitric oxide vasodilation assay\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with mechanistic ex vivo vascular assays and losartan rescue linking hypertension to vascular tone\",\n      \"pmids\": [\"24790136\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Rap1b deficiency abolishes VEGF-induced endothelial barrier dissolution and AJ remodeling in vitro, while Rap1A deficiency (not Rap1b) increases basal vascular permeability; both isoforms are required for de novo AJ formation and recovery from LPS-induced barrier disruption.\",\n      \"method\": \"EC-specific Rap1A and Rap1B KO mice, electrical impedance sensing, VE-cadherin immunostaining, in vivo VEGF permeability assay, STZ-induced diabetes model\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — isoform-specific conditional KO mice with multiple orthogonal in vitro and in vivo barrier readouts\",\n      \"pmids\": [\"29222111\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"EPAC (exchange protein directly activated by cAMP) activates Rap1b to specify and elongate the axon in hippocampal neurons; EPAC1 KO neurons have axon elongation and polarization defects; pharmacological EPAC activation (8-pCPT) induces supernumerary axons via Rap1b.\",\n      \"method\": \"EPAC1 KO mice neurons, shRNA knockdown, EPAC pharmacological activator (8-pCPT), axon markers (ankyrinG, synaptophysin), dominant-negative/active Rap1b\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mice plus pharmacology plus genetic Rap1b manipulation, single lab, identifying EPAC as the GEF upstream of Rap1b in neurons\",\n      \"pmids\": [\"26269639\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Rap1B activity is specifically elevated at the tip of the future axon (longest neurite) as shown by FRET imaging; effector mutant analysis identifies RalA and Nore1A as downstream targets of one pathway and PI3K as a target of another, both contributing to supernumerary axon formation.\",\n      \"method\": \"FRET imaging in hippocampal neurons, Rap1B effector-loop mutants (G12V/E37G and G12V/Y40C), dominant-negative RalA, Nore1A RNAi\",\n      \"journal\": \"Genes to cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — FRET-based spatial activity mapping plus effector mutant epistasis, single lab\",\n      \"pmids\": [\"24165023\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"High glucose activates and up-regulates Rap1b in renal mesangial cells via a PKC-dependent mechanism; activated Rap1b then drives fibronectin synthesis through B-Raf (not Raf-1). Rap1b dominant-negative mutants (S17N or T61R) block high-glucose-induced fibronectin synthesis.\",\n      \"method\": \"Rap1b overexpression and dominant-negative mutant transfection in mesangial cells, PKC inhibitors, B-Raf/Raf-1 Western blot, fibronectin mRNA/protein quantification\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain- and loss-of-function with defined mutants and pathway component analysis, single lab\",\n      \"pmids\": [\"12196513\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Rap1b activates B-Raf and promotes Bcl-2 interaction (via the BH4 domain) in renal tubular cells, partially preventing high-glucose-induced mitochondrial dysfunction and apoptosis; Rap1b GTPase activity is decreased in diabetic kidneys.\",\n      \"method\": \"Rap1b overexpression in HK-2 cells, Western blot for Bcl-2/Bax, co-immunoprecipitation of Bcl-2-Rap1b, BH4 domain deletion mutant, GTPase activity assay, mitochondrial morphology (EM)\",\n      \"journal\": \"Journal of the American Society of Nephrology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — overexpression with domain deletion plus Co-IP plus functional mitochondrial readouts, single lab\",\n      \"pmids\": [\"18753253\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"GTP-bound active Rap1B translocates to the nucleus in squamous cell carcinoma cells (not the GDP-bound form), as shown by GFP-tagged constitutively active vs inactive Rap1b mutants; nuclear translocation is also induced by growth factors.\",\n      \"method\": \"GFP-Rap1b transfection (constitutively active V12 vs dominant-negative N17), confocal microscopy, subcellular fractionation\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct imaging with nucleotide-state mutants establishing GTP dependence of nuclear localization, single lab\",\n      \"pmids\": [\"13679863\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In glioma cells, the cAMP/Epac/Rap1B pathway mediates isoproterenol-induced suppression of LPA-stimulated cell migration by inhibiting Rac1; this inhibitory action requires expression of PTEN, suggesting that PTEN-mediated reduction of PI3K activity is involved in Rap1B-dependent Rac1 inhibition.\",\n      \"method\": \"siRNA knockdown of Rap1B, dominant-negative Rap1B, Epac activator, Rac1 activation assay, PTEN expression analysis, migration assay\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNAi and dominant-negative epistasis with Rac1 activation readout and PTEN dependency, single lab\",\n      \"pmids\": [\"19864456\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"RAP1B interacts with DVL2 (a Wnt pathway component) and activates β-catenin/TCF signaling in esophageal squamous cell carcinoma cells.\",\n      \"method\": \"Co-immunoprecipitation of RAP1B-DVL2, TCF reporter assay, gain- and loss-of-function experiments in ESCC cells\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single Co-IP plus reporter assay; functional consequence established but mechanism not deeply resolved\",\n      \"pmids\": [\"28119087\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Rap1b acts downstream of Axin2 and BMP signaling to promote chondrogenic fate while inhibiting MAPK (FGF) signaling and osteoblast differentiation; genetic deletion of Rap1b in mice causes defects in craniofacial and body skeletons due to impaired chondrocyte and enhanced osteoblast differentiation.\",\n      \"method\": \"Rap1b KO mouse, conditional Axin2 ablation, genetic epistasis analysis, MAPK signaling Western blot, chondrogenic/osteogenic differentiation assays\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis in mouse model with differentiation assays, single lab\",\n      \"pmids\": [\"28520221\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Deletion of Rap1b (but not Rap1a or Epac1) in the setting of thyroid-specific Prkar1a knockout significantly decreases thyroid size and follicular cancer incidence, identifying Rap1b as the downstream effector of PKA in thyroid carcinogenesis.\",\n      \"method\": \"Tissue-specific compound KO mice (Prkar1a; Rap1a or Rap1b or Epac1 deletion), thyroid histology and tumor quantification\",\n      \"journal\": \"Thyroid\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — isoform-specific in vivo genetic epistasis in a defined oncogenic context; definitive in vivo evidence\",\n      \"pmids\": [\"29882482\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In zebrafish, Rap1b stimulates integrin β1 to enhance PLPM cell adhesion to fibronectin at the somite boundary, facilitating physical contact with Notch-ligand-expressing somitic cells and thereby promoting Notch-mediated hemogenic endothelium specification and HSC development.\",\n      \"method\": \"Zebrafish rap1b knockdown/knockout, integrin β1 activation assay, cell adhesion to fibronectin, Notch reporter assay, live imaging of PLPM migration\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo zebrafish genetics with defined cellular and signaling readouts, single lab\",\n      \"pmids\": [\"31006651\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Unlike Rap1B, phosphorylation in the polybasic region (PBR) of Rap1A does not inhibit its prenylation or binding to SmgGDS-607; GPCR-mediated suppression of Rap1A prenylation can occur independently of Rap1A phosphorylation and does not reduce Rap1A membrane localization.\",\n      \"method\": \"SmgGDS-607 binding assays with phosphorylated PBR peptides of Rap1A vs Rap1B, homology modelling, prenylation assay, membrane fractionation\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — comparative biochemical analysis of two isoforms, single lab; establishes mechanistic difference in prenylation regulation\",\n      \"pmids\": [\"27760305\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Crystal structures of Rap1B and mutants reveal that Rap1B crystallizes in an intermediate (not fully activated) state when bound to a non-hydrolyzable GTP analogue, and that conservative mutations distant from the nucleotide-binding site control the propensity to adopt the fully activated conformation.\",\n      \"method\": \"X-ray crystallography of Rap1B and site-directed mutants\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structures with mutational analysis, single lab; functional validation limited to structural inference\",\n      \"pmids\": [\"25935485\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Rap1A (not Rap1B) is the predominant isoform for endothelial junction formation; Rap1A knockdown increases monolayer gaps and reduces the junctional pool of AF-6 co-immunoprecipitated, while Rap1B knockdown does not. GFP-Rap1A localizes more prominently at junctions than GFP-Rap1B.\",\n      \"method\": \"microRNA-based RNAi knockdown, electrical impedance sensing, VE-cadherin immunostaining, co-immunoprecipitation of AF-6 with GFP-Rap1A vs GFP-Rap1B, confocal microscopy\",\n      \"journal\": \"Small GTPases\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — isoform-specific knockdown plus localization plus Co-IP, establishes negative finding for Rap1B in junction maintenance vs positive role in VEGF permeability (consistent with PMID:29222111)\",\n      \"pmids\": [\"21776404\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Contribution of PAR-1, PAR-4, and GPIb-IX-V to thrombin-induced Rap1B activation was established: PAR-1 and PAR-4 both signal Rap1B via ADP-dependent P2Y12 pathway; GPIb-IX-V contributes to ADP-independent Rap1B activation only when both PAR-1 and PAR-4 are co-stimulated.\",\n      \"method\": \"PAR-1/PAR-4 activating peptides, PAR desensitization, GPIb cleavage by mocarhagin, P2Y12 antagonist, P2Y12-deficient human platelets, Rap1B-GTP pull-down\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological and genetic receptor dissection with multiple controls, single lab\",\n      \"pmids\": [\"15078882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Phosphorylation of Rap1B by cAMP-dependent PKA does not inhibit its association with the cytoskeleton in thrombin-activated platelets.\",\n      \"method\": \"Platelet fractionation, Western blot, cAMP-induced phosphorylation of Rap1b prior to thrombin activation\",\n      \"journal\": \"Advances in experimental medicine and biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single fractionation experiment, conference proceedings, negative finding\",\n      \"pmids\": [\"8209787\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Pre-phosphorylation of Rap1B by cAMP/iloprost does not inhibit platelet aggregation, ATP secretion, or responses to multiple agonists (collagen, phorbol ester, vasopressin, ADP, epinephrine), indicating that PKA-mediated Rap1B phosphorylation alone is not responsible for platelet inhibition by cyclic AMP.\",\n      \"method\": \"Iloprost pre-treatment, Western blot verification of Rap1B phosphorylation, platelet aggregation and ATP secretion with multiple agonists\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — negative mechanistic finding rigorously established with multiple agonists; single lab\",\n      \"pmids\": [\"7684600\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Rap1a siRNA knockdown in human microvascular endothelial cells reduces ERK, p38, and Rac activation in response to FGF2, and impairs cell adhesion, migration, and tubular structure formation; rap1b siRNA produces similar but not identical defects in adhesion and migration.\",\n      \"method\": \"siRNA knockdown of rap1a and rap1b in HMVECs, ERK/p38/Rac activation assays, adhesion/migration assays, Matrigel tube formation\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — parallel knockdown of both isoforms with multiple functional readouts, single lab\",\n      \"pmids\": [\"18625726\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RAP1B is a small Ras-family GTPase that is activated by GTP loading (stimulated by cAMP/EPAC-mediated or Ca2+/CalDAG-GEFI-mediated exchange) and inactivated by GAP-stimulated GTP hydrolysis; it is post-translationally prenylated for membrane attachment, phosphorylated at Ser179 by PKA and PKG (which allosterically perturbs its switch regions and suppresses prenylation/membrane localization via reduced SmgGDS-607 interaction), and ubiquitinated on its inactive form by Smurf2 for proteasomal degradation; in platelets Rap1B functions as the central signaling switch downstream of Gi/P2Y12/PtdIns(3,4,5)P3 and CalDAG-GEFI to drive integrin αIIbβ3 inside-out and outside-in activation (including secretion and clot retraction), while structurally it binds talin-F0 at the membrane to recruit talin and activate integrins, and forms signaling complexes with IQGAP1, B-Raf, and Crkl/C3G; in neurons its spatially restricted activation at the future axon tip—controlled by the mTOR/Smurf2 axis and EPAC1—specifies axonal identity upstream of Cdc42 and the Par complex, and in endothelium it specifically mediates VEGF-induced barrier dissolution while maintaining vascular tone through nitric oxide release and smooth muscle myosin phosphatase regulation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"RAP1B is a Ras-family small GTPase that cycles between an inactive GDP-bound and active GTP-bound state to function as a spatially regulated signaling switch controlling integrin-dependent adhesion across platelets, leukocytes, endothelium, and neurons [#1, #25, #31]. In platelets it is the central node for integrin \\u03b1IIb\\u03b23 inside-out and outside-in activation, secretion, and clot retraction, and its loss causes a bleeding defect with protection from arterial thrombosis [#1, #25]. Activation is achieved by distinct guanine-nucleotide exchange factors reading different second messengers: a Gi/P2Y12-PI3K-PtdIns(3,4,5)P3 axis and Ca2+/PKC signaling through CalDAG-GEFI in platelets [#2, #18, #19, #26], cAMP through EPAC, whose mid-exchange complex with RAP1B has been resolved structurally [#4, #36]. Once GTP-loaded, RAP1B binds the talin-F0 domain at the membrane to recruit talin and drive integrin activation, adhesion, and spreading [#5], and engages downstream effectors including B-Raf to stimulate MEK/ERK signaling [#7, #31]. RAP1B activity is gated negatively by GAP-stimulated hydrolysis [#22] and by PKA/PKG phosphorylation at Ser179, which allosterically perturbs the switch I/II regions and, by reducing SmgGDS-607 binding, suppresses prenylation and membrane localization [#8, #10, #11, #27, #20]; PKA additionally inhibits RAP1B indirectly by phosphorylating CalDAG-GEFI [#28, #29]. Inactive GDP-bound RAP1B is ubiquitinated by Smurf2 for proteasomal degradation, and this turnover, balanced by mTOR, spatially restricts RAP1B to a single neurite tip to specify axonal identity upstream of Cdc42 and the Par complex [#16, #17, #0]. In endothelium RAP1B specifically mediates VEGF-induced barrier dissolution and supports vascular tone via NO release and myosin phosphatase regulation [#34, #35]. RAP1B has not been linked to a Mendelian disease within this corpus.\",\n  \"teleology\": [\n    {\n      \"year\": 1990,\n      \"claim\": \"Established that RAP1B is a direct, physiological substrate of cAMP-dependent kinase signaling, distinguishing it from Rap1A and providing the first regulatory handle on the protein.\",\n      \"evidence\": \"32P labeling and peptide sequencing of phosphorylated protein from intact human platelets; cytoskeletal fractionation with thrombin/A23187\",\n      \"pmids\": [\"1696481\", \"2123187\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of phosphorylation not yet defined\", \"Exact phosphoacceptor residue not yet mapped\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Pinpointed Ser179 as the PKA/PKG phosphorylation site and showed RAP1B is also a CaM kinase Gr substrate, defining the precise modified residue and broadening the kinase set.\",\n      \"evidence\": \"Site-directed mutagenesis with mobility-shift, in vitro PKG kinase assay, and CaM kinase Gr substrate specificity panel\",\n      \"pmids\": [\"8463283\", \"1551424\", \"1901412\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream effect of Ser179 phosphorylation on GTPase activity not established\", \"Physiological role of CaM kinase Gr phosphorylation in neurons unresolved\"]\n    },\n    {\n      \"year\": 1992,\n      \"claim\": \"Showed that agonists tune RAP1B nucleotide state and that it physically partners with rasGAP, linking RAP1B to receptor signaling and a candidate inactivating GAP.\",\n      \"evidence\": \"GTP hydrolysis assay with \\u03b12-adrenergic pharmacology; rasGAP co-immunoprecipitation in thrombin-stimulated platelets\",\n      \"pmids\": [\"1313568\", \"1323853\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"rasGAP Co-IP is single, without reciprocal validation\", \"Functional consequence of the rasGAP/PLC-\\u03b31 complex unresolved\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Demonstrated agonist-dependent GTP loading of RAP1B in intact cells, formally establishing it as a signal-activated GTPase.\",\n      \"evidence\": \"Guanine nucleotide binding (GTP/GDP ratio) on immunoprecipitated RAP1B from cAMP-stimulated cells\",\n      \"pmids\": [\"7737967\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"GEF responsible for cAMP-driven activation not identified here\", \"Downstream effectors not defined\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Identified B-Raf as a direct RAP1B effector, connecting RAP1B to the MEK/ERK cascade in a nucleotide- and lipid-modification-dependent manner.\",\n      \"evidence\": \"Cell-free B-Raf kinase assay with GTP/GDP and lipid-modified/unmodified recombinant RAP1B, MEK phosphorylation readout\",\n      \"pmids\": [\"8576107\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In-cell relevance of RAP1B\\u2192B-Raf not established here\", \"Whether RAP1B activates or antagonizes ERK in different cell types unresolved\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Dissected the platelet activation pathway, placing RAP1B downstream of Gi/P2Y12 and PI3K-generated PtdIns(3,4,5)P3 and showing it controls integrin \\u03b1IIb\\u03b23 affinity.\",\n      \"evidence\": \"Multiple G\\u03b1 and PI3K knockout mouse platelets, receptor-selective antagonists, lipid rescue, and Rap1-GTP pull-down; megakaryocyte fibrinogen-binding with active/dominant-negative mutants and actin inhibitors\",\n      \"pmids\": [\"11970953\", \"11815620\", \"12407113\", \"11994301\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the relevant Gi-coupled GEF not established\", \"How PtdIns(3,4,5)P3 connects to RAP1B exchange unresolved\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Provided genetic proof that RAP1B is required for integrin inside-out activation and hemostasis, and identified CalDAG-GEFI as the GEF coupling Ca2+/PKC and collagen-integrin signaling to RAP1B.\",\n      \"evidence\": \"Rap1b knockout mouse with aggregation, integrin activation, and in vivo thrombosis assays; CalDAG-GEFI-deficient platelets in \\u03b12\\u03b21 outside-in signaling\",\n      \"pmids\": [\"15696195\", \"16357324\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise effector linking RAP1B to integrin affinity not yet defined here\", \"Distinction between inside-out and outside-in RAP1B pools unresolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Resolved the cAMP-activated EPAC2\\u2013RAP1B exchange mechanism at atomic resolution, explaining how cyclic nucleotide binding triggers nucleotide exchange.\",\n      \"evidence\": \"X-ray crystallography and single-particle EM of Epac2\\u2013cAMP\\u2013RAP1B\",\n      \"pmids\": [\"18660803\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"EPAC1 (the neuronal GEF) not structurally captured\", \"In-cell kinetics of the trapped intermediate not addressed\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Extended RAP1B function to immune cell adhesion and trafficking, defining isoform-specific roles in NK cell signalosome assembly and B/neutrophil migration.\",\n      \"evidence\": \"Rap1b knockout mouse leukocytes; LFA1 polarization, MTOC, IQGAP1/B-Raf/ERK co-IP and Western; chemotaxis, homing, and transmigration assays\",\n      \"pmids\": [\"20733035\", \"18319399\", \"25092872\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of IQGAP1 signalosome assembly not fully resolved\", \"How RAP1B negatively gates PI3K/Akt via SHP-1 unconfirmed structurally\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defined the allosteric structural basis by which Ser179 phosphorylation perturbs the catalytic switch regions, mechanistically linking PKA/PKG to RAP1B regulation.\",\n      \"evidence\": \"Hydrogen/deuterium exchange mass spectrometry of phosphorylated RAP1B and S179D phosphomimetic\",\n      \"pmids\": [\"19651783\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of switch perturbation on effector binding not directly measured\", \"Reversal by phosphatase in vivo not addressed\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Established the Smurf2/mTOR turnover axis that spatially restricts RAP1B to a single neurite tip, explaining how RAP1B specifies a single axon upstream of Cdc42/Par.\",\n      \"evidence\": \"RNAi, ubiquitination and proteasome-rescue assays, mTOR pharmacology, and spatial imaging in hippocampal neurons; EPAC1 KO and FRET activity mapping\",\n      \"pmids\": [\"17318188\", \"18842593\", \"15286792\", \"26269639\", \"24165023\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"GEF/GAP machinery localizing RAP1B activity to the tip incompletely defined\", \"How EPAC1 and Smurf2 are coordinated spatially unresolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Resolved a dual mechanism by which PKA inhibits RAP1B: direct Ser179 phosphorylation that suppresses prenylation via reduced SmgGDS-607 binding, and phosphorylation of the upstream GEF CalDAG-GEFI.\",\n      \"evidence\": \"A2B/\\u03b2AR agonist treatment, SmgGDS co-IP, prenylation and fractionation assays; MS site-mapping and phosphomimetic mutagenesis of CalDAG-GEFI in HEK293 and platelets\",\n      \"pmids\": [\"23716716\", \"28119087\", \"23611601\", \"23600630\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative in vivo contributions of direct vs GEF-level inhibition unresolved\", \"Note: idx 42 (DVL2) is a distinct interaction; consolidation here is editorial\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Defined the structural basis of RAP1B-driven integrin activation by capturing the membrane-dependent talin-F0 interaction.\",\n      \"evidence\": \"X-ray crystallography of RAP1B\\u2013talin-F0, vesicle-binding assays, mutagenesis, and adhesion/spreading phenotypes\",\n      \"pmids\": [\"29170462\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether other talin domains contribute to RAP1B-dependent activation not addressed\", \"Cell-type generality of the talin-F0 route unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrated isoform-specialized endothelial functions, with RAP1B mediating VEGF-induced barrier dissolution and vascular tone while RAP1A maintains basal junctions.\",\n      \"evidence\": \"Endothelial-specific Rap1A/Rap1B knockout mice, impedance sensing, VE-cadherin imaging, in vivo permeability; vascular tone, NO, and myosin phosphatase assays\",\n      \"pmids\": [\"29222111\", \"24790136\", \"21776404\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Effectors mediating VEGF-specific barrier dissolution not identified\", \"Mechanism distinguishing RAP1A vs RAP1B junctional pools unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Provided in vivo genetic evidence that RAP1B is a downstream effector of PKA in tumorigenesis and a developmental regulator of skeletal and hematopoietic fate.\",\n      \"evidence\": \"Isoform-specific compound KO mice in thyroid carcinogenesis; Rap1b KO skeletal phenotyping with Axin2/BMP epistasis; zebrafish rap1b loss in HSC specification\",\n      \"pmids\": [\"29882482\", \"28520221\", \"31006651\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular effectors of RAP1B in chondrogenesis vs osteogenesis incompletely defined\", \"How RAP1B integrates with Notch/integrin \\u03b21 in HSC niche unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How distinct GEFs, GAPs, phosphorylation, and Smurf2-mediated degradation are spatiotemporally coordinated to generate cell-type-specific RAP1B activity pools, and which effectors dominate in each context, remains incompletely defined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model of context-specific effector selection\", \"GAPs acting on RAP1B in non-platelet cells largely unidentified\", \"Quantitative interplay of phosphorylation and ubiquitination not resolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003924\", \"supporting_discovery_ids\": [22, 47]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [1, 25, 2]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [5, 7, 31]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [9, 5, 20]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [9, 24]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [40, 20]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [1, 25, 26]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 4, 18]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [31, 32, 33]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [0, 43, 45]},\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [5, 35]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"TLN1\", \"BRAF\", \"IQGAP1\", \"RASA1\", \"SmgGDS\", \"CRKL\", \"DVL2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}