{"gene":"TIAM2","run_date":"2026-06-10T10:51:55","timeline":{"discoveries":[{"year":1999,"finding":"STEF/TIAM2 is a novel guanine nucleotide exchange factor (GEF) that specifically activates Rac1 but not RhoA or Cdc42. In vitro GDP dissociation assays demonstrated selective GDP release from Rac1. The protein contains two pleckstrin homology (PH) domains, a PDZ domain, and a Dbl homology (DH) domain. Expression of a truncated STEF in cultured cells induced membrane ruffling with altered actin localization, indicating in vivo Rac1 activation.","method":"In vitro GDP dissociation assay, domain structure analysis, cell-based ruffling assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro biochemical GEF assay plus cell-based functional validation, replicated across multiple subsequent studies","pmids":["10364228"],"is_preprint":false},{"year":1999,"finding":"TIAM2 (cloned independently as a TIAM1 homolog) encodes a protein with GDP-GTP exchange activity, confirmed by direct purification and exchange assay.","method":"Protein purification, GDP-GTP exchange assay","journal":"Genomics","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct in vitro biochemical assay with purified protein, consistent with independent cloning of STEF","pmids":["10512681"],"is_preprint":false},{"year":2001,"finding":"Domain dissection of STEF revealed that the N-terminal PH domain (PHnTSS) is required for membrane association, the DH domain carries enzymatic GEF activity, and the C-terminal PH domain (PHc) promotes catalytic activity. A dominant-negative PHnTSS fragment inhibited both STEF and Tiam1 function and blocked neurite outgrowth in N1E-115 neuroblastoma cells; this inhibition was rescued by exogenous STEF or Tiam1, demonstrating STEF acts through Rac1 to drive neurite formation.","method":"Deletion mutagenesis, dominant-negative expression, neurite outgrowth assay, rescue experiment","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple domain mutants with enzymatic and cellular readouts, rescue experiment in single lab","pmids":["11707441"],"is_preprint":false},{"year":2003,"finding":"In vivo gene transfer by in utero electroporation showed that STEF/Tiam1 (Rac1 activators) are required for radial migration of cortical neurons. Functional repression of STEF/Tiam1 or Rac1 inhibited neuronal migration and caused loss of the leading process; downstream JNK (activated by Rac1) regulates microtubule dynamics via MAP1B phosphorylation in migrating neurons.","method":"In utero electroporation (dominant-negative/shRNA), cortical migration assay, JNK inhibitor treatment, MAP1B phosphorylation assay","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo loss-of-function with defined morphological and molecular phenotypes, replicated across multiple constructs","pmids":["12912917"],"is_preprint":false},{"year":2003,"finding":"STEF and Tiam1 localize within growth cones of primary hippocampal neurons and are essential for formation of growth cone lamellipodia and neurite growth. STEF/Tiam1 mediate extracellular laminin signals and intracellular Cdc42 signals to activate Rac1 in the growth cone; RhoA inhibits the STEF/Tiam1-Rac1 pathway.","method":"Dominant-negative expression, immunolocalization in primary neurons, growth cone morphology assay, epistasis with Cdc42 and RhoA","journal":"Molecular and cellular neurosciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — dominant-negative epistasis plus localization, single lab","pmids":["14550769"],"is_preprint":false},{"year":2005,"finding":"PAR-3 directly interacts with STEF/Tiam1 (Rac-specific GEFs) and STEF forms a complex with PAR-3-aPKC-PAR-6-Cdc42-GTP. This complex mediates Cdc42-induced Rac activation and lamellipodia formation in neuroblastoma cells and cultured hippocampal neurons, establishing a Cdc42-PAR-6-PAR-3-STEF-Rac pathway required for neuronal polarity. Disruption of PAR-3-STEF binding inhibited Cdc42-induced lamellipodia but not filopodia. STEF accumulates at the tip of the growing axon co-localizing with PAR-3.","method":"Co-immunoprecipitation, direct binding assay, dominant-negative and overexpression in N1E-115 cells and hippocampal neurons, Rac1 activation assay","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, epistasis, localization, and cellular phenotype with multiple constructs across cell types","pmids":["15723051"],"is_preprint":false},{"year":2007,"finding":"Rho-kinase phosphorylates STEF at Thr1662 in vitro, reducing STEF-induced Rac1 activation in COS7 cells. LPA-induced phosphorylation of STEF in PC12D cells is suppressed by Y-27632 (Rho-kinase inhibitor). Phosphorylation diminishes STEF interaction with microtubule-associated protein 1B (MAP1B), and a phosphomimetic STEF mutant has weakened ability to enhance NGF-induced neurite outgrowth.","method":"In vitro kinase assay, site-directed mutagenesis, Rac1 activation assay, Co-immunoprecipitation, neurite outgrowth assay, pharmacological inhibitor","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro phosphorylation assay plus mutagenesis and functional cellular readouts, single lab","pmids":["17320046"],"is_preprint":false},{"year":2007,"finding":"STEF physically associates with activated Rap1 through its TSS region. Rap1-STEF interaction downstream of the cAMP/Epac/Rap1 cascade activates Rac1, which mediates non-amyloidogenic alpha-cleavage of APP (sAPPα secretion). A deleted TSS domain of STEF fails to activate Rac1 and dramatically decreases sAPPα secretion induced by Epac.","method":"Co-immunoprecipitation (Rap1-STEF), deletion mutagenesis (ΔTSS), Rac1 activation assay, sAPPα secretion assay","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus deletion mutant with functional readout, single lab","pmids":["18047838"],"is_preprint":false},{"year":2010,"finding":"STEF/TIAM2 is required for Rac activation during microtubule regrowth (following nocodazole washout), which drives focal adhesion (FA) disassembly. STEF knockdown reduces the rate of multiple FA targeting by microtubules, leading to enlarged FAs and reduced cell migration speed.","method":"siRNA knockdown, Rac1 activation assay (FRET/pulldown), live imaging of FA dynamics (fluorescence microscopy), nocodazole washout assay, migration speed measurement","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — siRNA with multiple orthogonal readouts (Rac activation, FA dynamics, migration), mechanistic link established","pmids":["20224579"],"is_preprint":false},{"year":2011,"finding":"The PDZ domains of Tiam1 and Tiam2 have overlapping but distinct ligand specificities determined by non-conserved residues in the S(0) and S(-2) pockets. Site-directed mutagenesis of four non-conserved residues in Tiam1's PDZ domain converted its specificity to that of Tiam2, as confirmed by combinatorial peptide library screening and binding assays with native protein-derived peptides.","method":"Combinatorial peptide library, peptide binding assays, site-directed mutagenesis, double mutant cycle analysis","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro biochemical reconstitution with mutagenesis and peptide library, rigorous specificity determination","pmids":["21192692"],"is_preprint":false},{"year":2011,"finding":"PKA phosphorylates STEF at three residues (Thr-749, Ser-782, Ser-1562); phosphorylation at Thr-749 is specifically critical for cAMP/dbcAMP-induced Rac1 activation and neurite outgrowth in PC12D cells. STEF depletion drastically reduces dbcAMP-induced neurite outgrowth. During dbcAMP stimulation, PKA activation at the plasma membrane becomes localized to neurite tips, coinciding with local Rac1 activation via STEF.","method":"FRET-based biosensors (Rac1, Cdc42, PIP3), STEF siRNA knockdown, site-directed mutagenesis (phosphorylation-site mutants), neurite outgrowth assay, PKA activity reporter","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis of specific phosphorylation sites, FRET biosensors, and KD with rescue in single lab with multiple orthogonal methods","pmids":["21460187"],"is_preprint":false},{"year":2011,"finding":"Expression of TIAM2S (short isoform) in HepG2 hepatocellular carcinoma cells promoted cell growth, invasiveness, and in vivo tumor formation in xenograft mice. TIAM2S expression upregulated N-cadherin and vimentin and caused redistribution of E-cadherin, indicating promotion of epithelial-to-mesenchymal transition (EMT).","method":"Stable overexpression, proliferation and invasion assays, xenograft mouse model, Western blot for EMT markers","journal":"International journal of cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — stable overexpression with in vitro and in vivo readouts, single lab","pmids":["21469146"],"is_preprint":false},{"year":2013,"finding":"TIAM2 knockdown by siRNA in NSCLC cells suppressed Rac1 activation (assessed by GST pulldown), reduced invasion and motility, upregulated E-cadherin, and downregulated MMP-3, Twist, and Snail, linking TIAM2-mediated Rac1 activation to EMT regulation in lung cancer cells.","method":"siRNA knockdown, GST-Rac1 pulldown activation assay, invasion/motility assay, Western blot for EMT markers","journal":"Asian Pacific journal of cancer prevention","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — siRNA with Rac1 activity assay and molecular readouts, single lab, single study","pmids":["24377522"],"is_preprint":false},{"year":2018,"finding":"STEF/TIAM2 localizes at the nuclear envelope, co-localizing with Nesprin-2G and Non-muscle myosin IIB (NMMIIB), where it regulates perinuclear Rac1 activity. STEF depletion reduces apical perinuclear actin cables (rescued by targeting active Rac1 to the nuclear envelope), increases nuclear height, impairs nuclear re-orientation, reduces perinuclear pMLC and myosin-generated tension at the nuclear envelope, decreases nuclear stiffness, and reduces TAZ-regulated gene expression.","method":"siRNA knockdown, fluorescence localization (co-localization with Nesprin-2G and NMMIIB), FRET-based perinuclear Rac1 biosensor, active-Rac1 nuclear envelope targeting rescue, FRAP, nuclear morphology assay, TAZ reporter","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — KD with rescue experiment, FRET biosensor for localized activity, multiple orthogonal phenotypic readouts in single study","pmids":["29844364"],"is_preprint":false},{"year":2019,"finding":"Two isoforms of TIAM2 act oppositely in regulating transmission ratio distortion (TRD) by the mouse t-haplotype: the short isoform (Tiam2s), whose expression is strongly increased from the t-allele, enhances t-haplotype transmission (sperm motility-linked), while the full-length isoform (Tiam2l) has the opposite effect. Both isoforms affect Rac1 signaling in sperm.","method":"Transgenic mouse approaches, transmission ratio distortion assay, isoform-specific expression analysis","journal":"PLoS genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — transgenic in vivo epistasis, two isoforms with opposing effects, single lab","pmids":["30817801"],"is_preprint":false},{"year":2021,"finding":"TIAM2 is identified as an essential Rac-GEF responsible for Rac1-mediated lung adenocarcinoma cell migration downstream of EGFR and c-Met receptor tyrosine kinases. TIAM2 controls distinctive aspects of ruffle dynamics in a non-redundant manner with FARP1 and ARHGEF39. The AXL-Gab1-PI3K axis confers pro-motility signaling in this context.","method":"siRNA knockdown (functional screen), Rac1 activity assay, ruffle dynamics live imaging, epistasis with EGFR/c-Met/AXL-Gab1-PI3K pathway","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA screen with mechanistic follow-up, pathway epistasis, single lab","pmids":["34731623"],"is_preprint":false},{"year":2023,"finding":"NSUN2-catalyzed m5C methylation of TIAM2 mRNA stabilizes the transcript in a YBX1-dependent manner. Loss of NSUN2 decreases m5C modification on TIAM2 mRNA, accelerates its decay, reduces TIAM2 expression, and suppresses pancreatic cancer EMT, growth, and metastasis. Rescue experiments confirmed TIAM2 acts downstream of NSUN2.","method":"m5C-seq, RNA-seq, lentiviral knockdown/overexpression, mRNA stability assay, YBX1 dependency assay, in vivo xenograft","journal":"Cell death discovery","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — m5C-seq plus mRNA decay assay with YBX1 dependency, single lab, in vitro and in vivo","pmids":["37393317"],"is_preprint":false},{"year":2023,"finding":"Dually lipidated CaMKIγ (prenylated and palmitoylated) functionally couples to STEF-Rac1 signaling at lipid rafts to drive neurite extension in PC12 cells. Palmitoylation is specifically required for CaMKIγ to activate the compartmentalized STEF-Rac1 pathway; prenylation alone is insufficient for this functional coupling.","method":"Lipid raft fractionation, palmitoylation/prenylation mutants, Rac1 activity assay, neurite outgrowth assay in PC12 cells lacking endogenous CaMKIγ","journal":"Frontiers in cellular neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — lipid modification mutants with Rac1 activity and morphogenesis readouts, single lab","pmids":["37601281"],"is_preprint":false}],"current_model":"STEF/TIAM2 is a Rac1-selective guanine nucleotide exchange factor (GEF) that activates Rac1 through its DH domain (catalytic) assisted by its C-terminal PH domain, with the N-terminal PH domain mediating membrane association; its activity is positively regulated by PKA phosphorylation at Thr-749 and negatively regulated by Rho-kinase phosphorylation at Thr-1662, and it operates in several spatially distinct signaling complexes—including the PAR-3/PAR-6/aPKC/Cdc42 polarity complex and the Epac/Rap1 complex—to drive Rac1-dependent cytoskeletal reorganization underlying neurite outgrowth, axon specification, cortical neuron migration, growth cone lamellipodium formation, microtubule-mediated focal adhesion disassembly during cell migration, and perinuclear actin cap maintenance at the nuclear envelope; its PDZ domain has distinct ligand specificity from Tiam1 and it is post-transcriptionally regulated by NSUN2-mediated m5C methylation of its mRNA."},"narrative":{"mechanistic_narrative":"STEF/TIAM2 is a Rac1-selective guanine nucleotide exchange factor that converts upstream receptor and small-GTPase signals into localized Rac1 activation driving actin cytoskeletal remodeling [PMID:10364228]. Its catalytic DH domain mediates selective GDP release from Rac1 (not RhoA or Cdc42), with the C-terminal PH domain promoting catalysis and the N-terminal PH/TSS region directing membrane association; loss of this membrane-targeting module blocks Rac1-dependent neurite outgrowth [PMID:10364228, PMID:11707441]. TIAM2 operates within defined spatial signaling assemblies: it binds PAR-3 to join the PAR-3/aPKC/PAR-6/Cdc42-GTP polarity complex that couples Cdc42 to Rac1 activation and lamellipodia formation during neuronal polarization [PMID:15723051], and it associates with activated Rap1 through its TSS region downstream of cAMP/Epac signaling [PMID:18047838]. Through these inputs TIAM2 supports radial migration of cortical neurons via a Rac1-JNK-MAP1B axis controlling microtubule dynamics [PMID:12912917], growth-cone lamellipodium formation [PMID:14550769], microtubule-induced focal adhesion disassembly during cell migration [PMID:20224579], and maintenance of the perinuclear actin cap at the nuclear envelope where it co-localizes with Nesprin-2G and non-muscle myosin IIB to regulate nuclear mechanics and TAZ-dependent transcription [PMID:29844364]. Its activity is bidirectionally tuned by phosphorylation: PKA phosphorylation at Thr-749 is required for cAMP-induced Rac1 activation and neurite outgrowth [PMID:21460187], whereas Rho-kinase phosphorylation at Thr-1662 suppresses Rac1 activation and weakens its interaction with MAP1B [PMID:17320046]. TIAM2 also drives Rac1-dependent invasion and epithelial-to-mesenchymal transition in carcinoma cells downstream of EGFR/c-Met receptor tyrosine kinases [PMID:21469146, PMID:24377522, PMID:34731623], and its mRNA is stabilized by NSUN2-catalyzed m5C methylation in a YBX1-dependent manner [PMID:37393317].","teleology":[{"year":1999,"claim":"Established that TIAM2 is a catalytically active GEF with selectivity for Rac1, defining its core biochemical identity and downstream effector.","evidence":"In vitro GDP dissociation/exchange assays with purified protein, domain analysis, and cell-based ruffling assay; independent cloning as STEF and as a TIAM1 homolog","pmids":["10364228","10512681"],"confidence":"High","gaps":["Did not resolve how Rac1 selectivity is structurally encoded","Upstream activators unknown at this stage"]},{"year":2001,"claim":"Mapped functional roles to individual domains, showing membrane targeting (N-terminal PH), catalysis (DH), and catalytic enhancement (C-terminal PH) are separable and that TIAM2 drives neurite outgrowth through Rac1.","evidence":"Deletion mutagenesis, dominant-negative expression with rescue, neurite outgrowth assay in N1E-115 neuroblastoma cells","pmids":["11707441"],"confidence":"High","gaps":["Dominant-negative PHnTSS fragment also inhibits Tiam1, leaving paralog-specific contributions unresolved","Membrane lipid/protein determinants of PH targeting not defined"]},{"year":2003,"claim":"Demonstrated an in vivo requirement for TIAM2/Tiam1-Rac1 signaling in cortical neuron migration and linked it to a Rac1-JNK-MAP1B microtubule-regulatory axis.","evidence":"In utero electroporation of dominant-negative/shRNA constructs, cortical migration assay, JNK inhibitor and MAP1B phosphorylation analysis","pmids":["12912917"],"confidence":"High","gaps":["Does not separate TIAM2 from Tiam1 contributions in vivo","Upstream receptor triggering migratory Rac1 activation not identified"]},{"year":2003,"claim":"Localized TIAM2 to growth cones and placed it at the convergence of laminin and Cdc42 inputs activating Rac1, with RhoA acting antagonistically.","evidence":"Dominant-negative expression, immunolocalization in primary hippocampal neurons, growth cone morphology assay, epistasis with Cdc42 and RhoA","pmids":["14550769"],"confidence":"Medium","gaps":["Epistasis relies on dominant-negative constructs without direct binding data for laminin receptor coupling","Mechanism of RhoA antagonism not defined here"]},{"year":2005,"claim":"Defined the molecular bridge by which Cdc42 activates Rac1, showing direct PAR-3 binding incorporates TIAM2 into the PAR polarity complex to drive lamellipodia and neuronal polarity.","evidence":"Reciprocal co-immunoprecipitation, direct binding assays, dominant-negative/overexpression and Rac1 activation assays in N1E-115 cells and hippocampal neurons","pmids":["15723051"],"confidence":"High","gaps":["Which TIAM2 domain mediates PAR-3 binding not pinpointed","How complex assembly is spatially restricted to the axon tip not fully resolved"]},{"year":2007,"claim":"Identified Rho-kinase phosphorylation at Thr-1662 as a negative regulatory input that dampens Rac1 activation and disrupts the TIAM2-MAP1B interaction.","evidence":"In vitro kinase assay, site-directed mutagenesis, Rac1 activation assay, Co-IP, neurite outgrowth assay, Y-27632 inhibitor in PC12D cells","pmids":["17320046"],"confidence":"High","gaps":["Structural basis for how Thr-1662 phosphorylation alters activity not determined","Physiological stimuli engaging this brake beyond LPA not mapped"]},{"year":2007,"claim":"Connected TIAM2 to the cAMP/Epac/Rap1 cascade via TSS-region binding to activated Rap1, linking it to Rac1-dependent non-amyloidogenic APP processing.","evidence":"Co-IP of Rap1-STEF, ΔTSS deletion mutant, Rac1 activation and sAPPα secretion assays","pmids":["18047838"],"confidence":"Medium","gaps":["Single-lab Co-IP without structural mapping of the Rap1-TSS interface","Whether Rap1 binding is direct or complex-mediated not established"]},{"year":2010,"claim":"Revealed a role in cell migration whereby TIAM2-driven Rac1 activation couples microtubule regrowth to focal adhesion disassembly.","evidence":"siRNA knockdown, Rac1 activation assay, live imaging of FA dynamics, nocodazole washout, migration speed measurement","pmids":["20224579"],"confidence":"High","gaps":["How microtubule contact triggers TIAM2 recruitment/activation not defined","Direct microtubule-TIAM2 association not demonstrated"]},{"year":2011,"claim":"Defined the distinct PDZ ligand specificity of TIAM2 relative to Tiam1 at the residue level, establishing non-redundant scaffolding interactions.","evidence":"Combinatorial peptide library, peptide binding assays, site-directed mutagenesis, double mutant cycle analysis","pmids":["21192692"],"confidence":"High","gaps":["Endogenous physiological PDZ ligands of TIAM2 not identified","Functional consequence of distinct specificity in cells untested"]},{"year":2011,"claim":"Identified PKA phosphorylation at Thr-749 as a positive regulatory input required for cAMP-induced, spatially localized Rac1 activation and neurite outgrowth.","evidence":"FRET biosensors, siRNA knockdown, phosphorylation-site mutants, neurite outgrowth and PKA activity reporters in PC12D cells","pmids":["21460187"],"confidence":"High","gaps":["Mechanism by which Thr-749 phosphorylation enhances GEF activity not structurally resolved","Interplay with Rho-kinase inhibitory phosphorylation not directly tested"]},{"year":2018,"claim":"Uncovered a nuclear-envelope function in which TIAM2 controls perinuclear Rac1 to maintain the actin cap, nuclear mechanics, and TAZ-dependent transcription.","evidence":"siRNA knockdown with active-Rac1 nuclear-envelope targeting rescue, perinuclear FRET biosensor, FRAP, nuclear morphology and TAZ reporter assays; co-localization with Nesprin-2G and NMMIIB","pmids":["29844364"],"confidence":"High","gaps":["How TIAM2 is recruited to the nuclear envelope not defined","Whether Nesprin-2G binding is direct not established"]},{"year":2011,"claim":"Implicated TIAM2 (and a short isoform) in carcinoma progression by promoting Rac1-dependent invasion and epithelial-to-mesenchymal transition.","evidence":"Stable overexpression/siRNA knockdown, proliferation/invasion assays, xenograft models, and EMT marker analysis in hepatocellular and lung cancer cells","pmids":["21469146","24377522"],"confidence":"Medium","gaps":["Causal upstream activators of TIAM2 in these tumors not fully defined here","Isoform-specific mechanisms not resolved in the carcinoma context"]},{"year":2019,"claim":"Showed isoform-specific and opposing TIAM2 functions in mouse t-haplotype transmission ratio distortion via Rac1 signaling in sperm.","evidence":"Transgenic mouse approaches, transmission ratio distortion assay, isoform-specific expression analysis","pmids":["30817801"],"confidence":"Medium","gaps":["Molecular basis for opposing short vs full-length isoform activity unresolved","Direct sperm Rac1 substrate/effector readouts limited"]},{"year":2021,"claim":"Positioned TIAM2 as a non-redundant Rac-GEF for lung adenocarcinoma cell migration downstream of EGFR/c-Met receptor tyrosine kinases controlling distinct ruffle dynamics.","evidence":"siRNA functional screen, Rac1 activity assay, ruffle dynamics imaging, epistasis with EGFR/c-Met/AXL-Gab1-PI3K","pmids":["34731623"],"confidence":"Medium","gaps":["Direct receptor-to-TIAM2 coupling mechanism not defined","Basis for non-redundancy with FARP1/ARHGEF39 unresolved"]},{"year":2023,"claim":"Identified post-transcriptional control of TIAM2 by NSUN2-mediated m5C mRNA methylation, stabilizing the transcript and supporting cancer EMT and metastasis.","evidence":"m5C-seq, RNA-seq, knockdown/overexpression, mRNA stability and YBX1 dependency assays, xenograft in pancreatic cancer","pmids":["37393317"],"confidence":"Medium","gaps":["Methylated residues on TIAM2 mRNA not pinpointed","Whether m5C control operates in non-cancer contexts unknown"]},{"year":2023,"claim":"Demonstrated that dually lipidated CaMKIγ couples to compartmentalized STEF-Rac1 signaling at lipid rafts to drive neurite extension, requiring palmitoylation.","evidence":"Lipid raft fractionation, palmitoylation/prenylation mutants, Rac1 activity and neurite outgrowth assays in PC12 cells","pmids":["37601281"],"confidence":"Medium","gaps":["Whether CaMKIγ directly modifies/binds TIAM2 not established","Lipid-raft recruitment determinants of TIAM2 undefined"]},{"year":null,"claim":"The structural basis for how phosphorylation (Thr-749 activation vs Thr-1662 inhibition) and partner binding (PAR-3, Rap1, Nesprin-2G) toggle TIAM2 catalytic activity, and how distinct spatial pools are coordinated, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of full-length TIAM2 or its regulatory interfaces in the corpus","Direct vs scaffold-mediated nature of several key partner interactions undetermined","Mechanism integrating opposing kinase inputs on a single molecule not defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,2,6,8,10]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,5,7]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[5,13]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,2,10]},{"term_id":"GO:0005635","term_label":"nuclear envelope","supporting_discovery_ids":[13]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[4,8,13]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,5,7,10]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[2,3,4,5]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[11,12,15,16]}],"complexes":["PAR-3/aPKC/PAR-6/Cdc42 polarity complex"],"partners":["RAC1","PARD3","RAP1","MAP1B","SYNE2","MYH10","CDC42"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8IVF5","full_name":"Rho guanine nucleotide exchange factor TIAM2","aliases":["SIF and TIAM1-like exchange factor","T-lymphoma invasion and metastasis-inducing protein 2","TIAM-2"],"length_aa":1701,"mass_kda":190.1,"function":"Modulates the activity of RHO-like proteins and connects extracellular signals to cytoskeletal activities. Acts as a GDP-dissociation stimulator protein that stimulates the GDP-GTP exchange activity of RHO-like GTPases and activates them. Mediates extracellular laminin signals to activate Rac1, contributing to neurite growth. Involved in lamellipodial formation and advancement of the growth cone of embryonic hippocampal neurons. Promotes migration of neurons in the cerebral cortex. When overexpressed, induces membrane ruffling accompanied by the accumulation of actin filaments along the altered plasma membrane (By similarity). Activates specifically RAC1, but not CDC42 and RHOA","subcellular_location":"Cytoplasm; Cell projection, lamellipodium; Cell projection, filopodium; Cell projection, growth cone; Cell projection, neuron projection; Perikaryon","url":"https://www.uniprot.org/uniprotkb/Q8IVF5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TIAM2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TIAM2","total_profiled":1310},"omim":[{"mim_id":"604709","title":"T-CELL LYMPHOMA INVASION AND METASTASIS 2; TIAM2","url":"https://www.omim.org/entry/604709"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Nucleoli fibrillar center","reliability":"Supported"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":11.9},{"tissue":"testis","ntpm":12.2}],"url":"https://www.proteinatlas.org/search/TIAM2"},"hgnc":{"alias_symbol":["STEF"],"prev_symbol":[]},"alphafold":{"accession":"Q8IVF5","domains":[{"cath_id":"2.30.29.30","chopping":"505-756","consensus_level":"medium","plddt":85.2823,"start":505,"end":756},{"cath_id":"3.10.20.90","chopping":"809-886","consensus_level":"medium","plddt":81.1192,"start":809,"end":886},{"cath_id":"2.30.42.10","chopping":"901-976","consensus_level":"medium","plddt":80.9916,"start":901,"end":976},{"cath_id":"1.20.900.10","chopping":"1096-1311","consensus_level":"medium","plddt":88.6225,"start":1096,"end":1311},{"cath_id":"2.30.29.30","chopping":"1313-1369_1388-1465","consensus_level":"medium","plddt":81.7915,"start":1313,"end":1465}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8IVF5","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8IVF5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8IVF5-F1-predicted_aligned_error_v6.png","plddt_mean":56.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TIAM2","jax_strain_url":"https://www.jax.org/strain/search?query=TIAM2"},"sequence":{"accession":"Q8IVF5","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8IVF5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8IVF5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8IVF5"}},"corpus_meta":[{"pmid":"15723051","id":"PMC_15723051","title":"PAR-6-PAR-3 mediates Cdc42-induced Rac activation through the Rac GEFs STEF/Tiam1.","date":"2005","source":"Nature cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/15723051","citation_count":313,"is_preprint":false},{"pmid":"12912917","id":"PMC_12912917","title":"The in vivo roles of STEF/Tiam1, Rac1 and JNK in cortical neuronal migration.","date":"2003","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/12912917","citation_count":258,"is_preprint":false},{"pmid":"10364228","id":"PMC_10364228","title":"Identification of the stef gene that encodes a novel guanine nucleotide exchange factor specific for Rac1.","date":"1999","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10364228","citation_count":96,"is_preprint":false},{"pmid":"20224579","id":"PMC_20224579","title":"The Rac activator STEF (Tiam2) regulates cell migration by microtubule-mediated focal adhesion disassembly.","date":"2010","source":"EMBO reports","url":"https://pubmed.ncbi.nlm.nih.gov/20224579","citation_count":77,"is_preprint":false},{"pmid":"11707441","id":"PMC_11707441","title":"Characterization of STEF, a guanine nucleotide exchange factor for Rac1, required for neurite growth.","date":"2001","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11707441","citation_count":76,"is_preprint":false},{"pmid":"37393317","id":"PMC_37393317","title":"NSUN2 stimulates tumor progression via enhancing TIAM2 mRNA stability in pancreatic cancer.","date":"2023","source":"Cell death discovery","url":"https://pubmed.ncbi.nlm.nih.gov/37393317","citation_count":48,"is_preprint":false},{"pmid":"29844364","id":"PMC_29844364","title":"STEF/TIAM2-mediated Rac1 activity at the nuclear envelope regulates the perinuclear actin cap.","date":"2018","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/29844364","citation_count":48,"is_preprint":false},{"pmid":"14550769","id":"PMC_14550769","title":"Roles of STEF/Tiam1, guanine nucleotide exchange factors for Rac1, in regulation of growth cone morphology.","date":"2003","source":"Molecular and cellular neurosciences","url":"https://pubmed.ncbi.nlm.nih.gov/14550769","citation_count":46,"is_preprint":false},{"pmid":"21469146","id":"PMC_21469146","title":"Expression of T-cell lymphoma invasion and metastasis 2 (TIAM2) promotes proliferation and invasion of liver cancer.","date":"2011","source":"International journal of cancer","url":"https://pubmed.ncbi.nlm.nih.gov/21469146","citation_count":44,"is_preprint":false},{"pmid":"10512681","id":"PMC_10512681","title":"Cloning and characterization of T-cell lymphoma invasion and metastasis 2 (TIAM2), a novel guanine nucleotide exchange factor related to TIAM1.","date":"1999","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/10512681","citation_count":42,"is_preprint":false},{"pmid":"18047838","id":"PMC_18047838","title":"Epac signaling pathway involves STEF, a guanine nucleotide exchange factor for Rac, to regulate APP processing.","date":"2007","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/18047838","citation_count":33,"is_preprint":false},{"pmid":"21192692","id":"PMC_21192692","title":"Distinct ligand specificity of the Tiam1 and Tiam2 PDZ domains.","date":"2011","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/21192692","citation_count":32,"is_preprint":false},{"pmid":"34731623","id":"PMC_34731623","title":"FARP1, ARHGEF39, and TIAM2 are essential receptor tyrosine kinase effectors for Rac1-dependent cell motility in human lung adenocarcinoma.","date":"2021","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/34731623","citation_count":30,"is_preprint":false},{"pmid":"36142328","id":"PMC_36142328","title":"TIAM2 Contributes to Osimertinib Resistance, Cell Motility, and Tumor-Associated Macrophage M2-like Polarization in Lung Adenocarcinoma.","date":"2022","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/36142328","citation_count":28,"is_preprint":false},{"pmid":"21460187","id":"PMC_21460187","title":"Phosphorylation of STEF/Tiam2 by protein kinase A is critical for Rac1 activation and neurite outgrowth in dibutyryl cAMP-treated PC12D cells.","date":"2011","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/21460187","citation_count":28,"is_preprint":false},{"pmid":"30817801","id":"PMC_30817801","title":"Two isoforms of the RAC-specific guanine nucleotide exchange factor TIAM2 act oppositely on transmission ratio distortion by the mouse t-haplotype.","date":"2019","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/30817801","citation_count":26,"is_preprint":false},{"pmid":"17320046","id":"PMC_17320046","title":"Rho-kinase modulates the function of STEF, a Rac GEF, through its phosphorylation.","date":"2007","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/17320046","citation_count":24,"is_preprint":false},{"pmid":"11900975","id":"PMC_11900975","title":"Expression of stef, an activator of Rac1, correlates with the stages of neuronal morphological development in the mouse brain.","date":"2002","source":"Mechanisms of development","url":"https://pubmed.ncbi.nlm.nih.gov/11900975","citation_count":22,"is_preprint":false},{"pmid":"24377522","id":"PMC_24377522","title":"TIAM2 enhances non-small cell lung cancer cell invasion and motility.","date":"2013","source":"Asian Pacific journal of cancer prevention : APJCP","url":"https://pubmed.ncbi.nlm.nih.gov/24377522","citation_count":20,"is_preprint":false},{"pmid":"31205545","id":"PMC_31205545","title":"The Fibroblast TIAM2 Promotes Lung Cancer Cell Invasion and Metastasis.","date":"2019","source":"Journal of Cancer","url":"https://pubmed.ncbi.nlm.nih.gov/31205545","citation_count":15,"is_preprint":false},{"pmid":"35078582","id":"PMC_35078582","title":"The invasive alien red-eared slider turtle, Trachemys scripta, as a carrier of STEF-disease pathogens.","date":"2021","source":"Fungal biology","url":"https://pubmed.ncbi.nlm.nih.gov/35078582","citation_count":11,"is_preprint":false},{"pmid":"37601281","id":"PMC_37601281","title":"Lipidation states orchestrate CLICK-III/CaMKIγ's stepwise association with Golgi and rafts-enriched membranes and specify its functional coupling to STEF-Rac1-dependent neurite extension.","date":"2023","source":"Frontiers in cellular neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/37601281","citation_count":4,"is_preprint":false},{"pmid":"39598318","id":"PMC_39598318","title":"Verbascum ponticum (Stef.) Extract Induces Lung Cancer Apoptosis via Mitochondrial-Dependent Apoptosis Pathway.","date":"2024","source":"Life (Basel, Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/39598318","citation_count":4,"is_preprint":false},{"pmid":"36419799","id":"PMC_36419799","title":"TIAM2 promotes proliferation and invasion of osteosarcoma cells by activating the JAK2/STAT3 signaling pathway.","date":"2022","source":"Journal of bone oncology","url":"https://pubmed.ncbi.nlm.nih.gov/36419799","citation_count":3,"is_preprint":false},{"pmid":"39093764","id":"PMC_39093764","title":"The analysis on Tiam2 for expression in esophageal carcinoma: A descriptive study.","date":"2024","source":"Medicine","url":"https://pubmed.ncbi.nlm.nih.gov/39093764","citation_count":0,"is_preprint":false},{"pmid":"42035529","id":"PMC_42035529","title":"TIAM2 and ADCY7 polymorphisms and their association with feed efficiency in Huaibei partridge chickens.","date":"2026","source":"Poultry science","url":"https://pubmed.ncbi.nlm.nih.gov/42035529","citation_count":0,"is_preprint":false},{"pmid":"42197197","id":"PMC_42197197","title":"Biologically Active Compounds and Antioxidant and DNA-Protective Potential of Rhodope Avens (Geum rhodopaeum Stoj.&Stef.) Dry Tinctures.","date":"2026","source":"Molecules (Basel, Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/42197197","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":14997,"output_tokens":4927,"usd":0.059448,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":13042,"output_tokens":5418,"usd":0.10033,"stage2_stop_reason":"end_turn"},"total_usd":0.159778,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1999,\n      \"finding\": \"STEF/TIAM2 is a novel guanine nucleotide exchange factor (GEF) that specifically activates Rac1 but not RhoA or Cdc42. In vitro GDP dissociation assays demonstrated selective GDP release from Rac1. The protein contains two pleckstrin homology (PH) domains, a PDZ domain, and a Dbl homology (DH) domain. Expression of a truncated STEF in cultured cells induced membrane ruffling with altered actin localization, indicating in vivo Rac1 activation.\",\n      \"method\": \"In vitro GDP dissociation assay, domain structure analysis, cell-based ruffling assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro biochemical GEF assay plus cell-based functional validation, replicated across multiple subsequent studies\",\n      \"pmids\": [\"10364228\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"TIAM2 (cloned independently as a TIAM1 homolog) encodes a protein with GDP-GTP exchange activity, confirmed by direct purification and exchange assay.\",\n      \"method\": \"Protein purification, GDP-GTP exchange assay\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct in vitro biochemical assay with purified protein, consistent with independent cloning of STEF\",\n      \"pmids\": [\"10512681\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Domain dissection of STEF revealed that the N-terminal PH domain (PHnTSS) is required for membrane association, the DH domain carries enzymatic GEF activity, and the C-terminal PH domain (PHc) promotes catalytic activity. A dominant-negative PHnTSS fragment inhibited both STEF and Tiam1 function and blocked neurite outgrowth in N1E-115 neuroblastoma cells; this inhibition was rescued by exogenous STEF or Tiam1, demonstrating STEF acts through Rac1 to drive neurite formation.\",\n      \"method\": \"Deletion mutagenesis, dominant-negative expression, neurite outgrowth assay, rescue experiment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple domain mutants with enzymatic and cellular readouts, rescue experiment in single lab\",\n      \"pmids\": [\"11707441\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"In vivo gene transfer by in utero electroporation showed that STEF/Tiam1 (Rac1 activators) are required for radial migration of cortical neurons. Functional repression of STEF/Tiam1 or Rac1 inhibited neuronal migration and caused loss of the leading process; downstream JNK (activated by Rac1) regulates microtubule dynamics via MAP1B phosphorylation in migrating neurons.\",\n      \"method\": \"In utero electroporation (dominant-negative/shRNA), cortical migration assay, JNK inhibitor treatment, MAP1B phosphorylation assay\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo loss-of-function with defined morphological and molecular phenotypes, replicated across multiple constructs\",\n      \"pmids\": [\"12912917\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"STEF and Tiam1 localize within growth cones of primary hippocampal neurons and are essential for formation of growth cone lamellipodia and neurite growth. STEF/Tiam1 mediate extracellular laminin signals and intracellular Cdc42 signals to activate Rac1 in the growth cone; RhoA inhibits the STEF/Tiam1-Rac1 pathway.\",\n      \"method\": \"Dominant-negative expression, immunolocalization in primary neurons, growth cone morphology assay, epistasis with Cdc42 and RhoA\",\n      \"journal\": \"Molecular and cellular neurosciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — dominant-negative epistasis plus localization, single lab\",\n      \"pmids\": [\"14550769\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PAR-3 directly interacts with STEF/Tiam1 (Rac-specific GEFs) and STEF forms a complex with PAR-3-aPKC-PAR-6-Cdc42-GTP. This complex mediates Cdc42-induced Rac activation and lamellipodia formation in neuroblastoma cells and cultured hippocampal neurons, establishing a Cdc42-PAR-6-PAR-3-STEF-Rac pathway required for neuronal polarity. Disruption of PAR-3-STEF binding inhibited Cdc42-induced lamellipodia but not filopodia. STEF accumulates at the tip of the growing axon co-localizing with PAR-3.\",\n      \"method\": \"Co-immunoprecipitation, direct binding assay, dominant-negative and overexpression in N1E-115 cells and hippocampal neurons, Rac1 activation assay\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, epistasis, localization, and cellular phenotype with multiple constructs across cell types\",\n      \"pmids\": [\"15723051\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Rho-kinase phosphorylates STEF at Thr1662 in vitro, reducing STEF-induced Rac1 activation in COS7 cells. LPA-induced phosphorylation of STEF in PC12D cells is suppressed by Y-27632 (Rho-kinase inhibitor). Phosphorylation diminishes STEF interaction with microtubule-associated protein 1B (MAP1B), and a phosphomimetic STEF mutant has weakened ability to enhance NGF-induced neurite outgrowth.\",\n      \"method\": \"In vitro kinase assay, site-directed mutagenesis, Rac1 activation assay, Co-immunoprecipitation, neurite outgrowth assay, pharmacological inhibitor\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro phosphorylation assay plus mutagenesis and functional cellular readouts, single lab\",\n      \"pmids\": [\"17320046\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"STEF physically associates with activated Rap1 through its TSS region. Rap1-STEF interaction downstream of the cAMP/Epac/Rap1 cascade activates Rac1, which mediates non-amyloidogenic alpha-cleavage of APP (sAPPα secretion). A deleted TSS domain of STEF fails to activate Rac1 and dramatically decreases sAPPα secretion induced by Epac.\",\n      \"method\": \"Co-immunoprecipitation (Rap1-STEF), deletion mutagenesis (ΔTSS), Rac1 activation assay, sAPPα secretion assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus deletion mutant with functional readout, single lab\",\n      \"pmids\": [\"18047838\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"STEF/TIAM2 is required for Rac activation during microtubule regrowth (following nocodazole washout), which drives focal adhesion (FA) disassembly. STEF knockdown reduces the rate of multiple FA targeting by microtubules, leading to enlarged FAs and reduced cell migration speed.\",\n      \"method\": \"siRNA knockdown, Rac1 activation assay (FRET/pulldown), live imaging of FA dynamics (fluorescence microscopy), nocodazole washout assay, migration speed measurement\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — siRNA with multiple orthogonal readouts (Rac activation, FA dynamics, migration), mechanistic link established\",\n      \"pmids\": [\"20224579\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The PDZ domains of Tiam1 and Tiam2 have overlapping but distinct ligand specificities determined by non-conserved residues in the S(0) and S(-2) pockets. Site-directed mutagenesis of four non-conserved residues in Tiam1's PDZ domain converted its specificity to that of Tiam2, as confirmed by combinatorial peptide library screening and binding assays with native protein-derived peptides.\",\n      \"method\": \"Combinatorial peptide library, peptide binding assays, site-directed mutagenesis, double mutant cycle analysis\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro biochemical reconstitution with mutagenesis and peptide library, rigorous specificity determination\",\n      \"pmids\": [\"21192692\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PKA phosphorylates STEF at three residues (Thr-749, Ser-782, Ser-1562); phosphorylation at Thr-749 is specifically critical for cAMP/dbcAMP-induced Rac1 activation and neurite outgrowth in PC12D cells. STEF depletion drastically reduces dbcAMP-induced neurite outgrowth. During dbcAMP stimulation, PKA activation at the plasma membrane becomes localized to neurite tips, coinciding with local Rac1 activation via STEF.\",\n      \"method\": \"FRET-based biosensors (Rac1, Cdc42, PIP3), STEF siRNA knockdown, site-directed mutagenesis (phosphorylation-site mutants), neurite outgrowth assay, PKA activity reporter\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis of specific phosphorylation sites, FRET biosensors, and KD with rescue in single lab with multiple orthogonal methods\",\n      \"pmids\": [\"21460187\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Expression of TIAM2S (short isoform) in HepG2 hepatocellular carcinoma cells promoted cell growth, invasiveness, and in vivo tumor formation in xenograft mice. TIAM2S expression upregulated N-cadherin and vimentin and caused redistribution of E-cadherin, indicating promotion of epithelial-to-mesenchymal transition (EMT).\",\n      \"method\": \"Stable overexpression, proliferation and invasion assays, xenograft mouse model, Western blot for EMT markers\",\n      \"journal\": \"International journal of cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — stable overexpression with in vitro and in vivo readouts, single lab\",\n      \"pmids\": [\"21469146\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"TIAM2 knockdown by siRNA in NSCLC cells suppressed Rac1 activation (assessed by GST pulldown), reduced invasion and motility, upregulated E-cadherin, and downregulated MMP-3, Twist, and Snail, linking TIAM2-mediated Rac1 activation to EMT regulation in lung cancer cells.\",\n      \"method\": \"siRNA knockdown, GST-Rac1 pulldown activation assay, invasion/motility assay, Western blot for EMT markers\",\n      \"journal\": \"Asian Pacific journal of cancer prevention\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — siRNA with Rac1 activity assay and molecular readouts, single lab, single study\",\n      \"pmids\": [\"24377522\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"STEF/TIAM2 localizes at the nuclear envelope, co-localizing with Nesprin-2G and Non-muscle myosin IIB (NMMIIB), where it regulates perinuclear Rac1 activity. STEF depletion reduces apical perinuclear actin cables (rescued by targeting active Rac1 to the nuclear envelope), increases nuclear height, impairs nuclear re-orientation, reduces perinuclear pMLC and myosin-generated tension at the nuclear envelope, decreases nuclear stiffness, and reduces TAZ-regulated gene expression.\",\n      \"method\": \"siRNA knockdown, fluorescence localization (co-localization with Nesprin-2G and NMMIIB), FRET-based perinuclear Rac1 biosensor, active-Rac1 nuclear envelope targeting rescue, FRAP, nuclear morphology assay, TAZ reporter\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — KD with rescue experiment, FRET biosensor for localized activity, multiple orthogonal phenotypic readouts in single study\",\n      \"pmids\": [\"29844364\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Two isoforms of TIAM2 act oppositely in regulating transmission ratio distortion (TRD) by the mouse t-haplotype: the short isoform (Tiam2s), whose expression is strongly increased from the t-allele, enhances t-haplotype transmission (sperm motility-linked), while the full-length isoform (Tiam2l) has the opposite effect. Both isoforms affect Rac1 signaling in sperm.\",\n      \"method\": \"Transgenic mouse approaches, transmission ratio distortion assay, isoform-specific expression analysis\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — transgenic in vivo epistasis, two isoforms with opposing effects, single lab\",\n      \"pmids\": [\"30817801\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"TIAM2 is identified as an essential Rac-GEF responsible for Rac1-mediated lung adenocarcinoma cell migration downstream of EGFR and c-Met receptor tyrosine kinases. TIAM2 controls distinctive aspects of ruffle dynamics in a non-redundant manner with FARP1 and ARHGEF39. The AXL-Gab1-PI3K axis confers pro-motility signaling in this context.\",\n      \"method\": \"siRNA knockdown (functional screen), Rac1 activity assay, ruffle dynamics live imaging, epistasis with EGFR/c-Met/AXL-Gab1-PI3K pathway\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA screen with mechanistic follow-up, pathway epistasis, single lab\",\n      \"pmids\": [\"34731623\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"NSUN2-catalyzed m5C methylation of TIAM2 mRNA stabilizes the transcript in a YBX1-dependent manner. Loss of NSUN2 decreases m5C modification on TIAM2 mRNA, accelerates its decay, reduces TIAM2 expression, and suppresses pancreatic cancer EMT, growth, and metastasis. Rescue experiments confirmed TIAM2 acts downstream of NSUN2.\",\n      \"method\": \"m5C-seq, RNA-seq, lentiviral knockdown/overexpression, mRNA stability assay, YBX1 dependency assay, in vivo xenograft\",\n      \"journal\": \"Cell death discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — m5C-seq plus mRNA decay assay with YBX1 dependency, single lab, in vitro and in vivo\",\n      \"pmids\": [\"37393317\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Dually lipidated CaMKIγ (prenylated and palmitoylated) functionally couples to STEF-Rac1 signaling at lipid rafts to drive neurite extension in PC12 cells. Palmitoylation is specifically required for CaMKIγ to activate the compartmentalized STEF-Rac1 pathway; prenylation alone is insufficient for this functional coupling.\",\n      \"method\": \"Lipid raft fractionation, palmitoylation/prenylation mutants, Rac1 activity assay, neurite outgrowth assay in PC12 cells lacking endogenous CaMKIγ\",\n      \"journal\": \"Frontiers in cellular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — lipid modification mutants with Rac1 activity and morphogenesis readouts, single lab\",\n      \"pmids\": [\"37601281\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"STEF/TIAM2 is a Rac1-selective guanine nucleotide exchange factor (GEF) that activates Rac1 through its DH domain (catalytic) assisted by its C-terminal PH domain, with the N-terminal PH domain mediating membrane association; its activity is positively regulated by PKA phosphorylation at Thr-749 and negatively regulated by Rho-kinase phosphorylation at Thr-1662, and it operates in several spatially distinct signaling complexes—including the PAR-3/PAR-6/aPKC/Cdc42 polarity complex and the Epac/Rap1 complex—to drive Rac1-dependent cytoskeletal reorganization underlying neurite outgrowth, axon specification, cortical neuron migration, growth cone lamellipodium formation, microtubule-mediated focal adhesion disassembly during cell migration, and perinuclear actin cap maintenance at the nuclear envelope; its PDZ domain has distinct ligand specificity from Tiam1 and it is post-transcriptionally regulated by NSUN2-mediated m5C methylation of its mRNA.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"STEF/TIAM2 is a Rac1-selective guanine nucleotide exchange factor that converts upstream receptor and small-GTPase signals into localized Rac1 activation driving actin cytoskeletal remodeling [#0]. Its catalytic DH domain mediates selective GDP release from Rac1 (not RhoA or Cdc42), with the C-terminal PH domain promoting catalysis and the N-terminal PH/TSS region directing membrane association; loss of this membrane-targeting module blocks Rac1-dependent neurite outgrowth [#0, #2]. TIAM2 operates within defined spatial signaling assemblies: it binds PAR-3 to join the PAR-3/aPKC/PAR-6/Cdc42-GTP polarity complex that couples Cdc42 to Rac1 activation and lamellipodia formation during neuronal polarization [#5], and it associates with activated Rap1 through its TSS region downstream of cAMP/Epac signaling [#7]. Through these inputs TIAM2 supports radial migration of cortical neurons via a Rac1-JNK-MAP1B axis controlling microtubule dynamics [#3], growth-cone lamellipodium formation [#4], microtubule-induced focal adhesion disassembly during cell migration [#8], and maintenance of the perinuclear actin cap at the nuclear envelope where it co-localizes with Nesprin-2G and non-muscle myosin IIB to regulate nuclear mechanics and TAZ-dependent transcription [#13]. Its activity is bidirectionally tuned by phosphorylation: PKA phosphorylation at Thr-749 is required for cAMP-induced Rac1 activation and neurite outgrowth [#10], whereas Rho-kinase phosphorylation at Thr-1662 suppresses Rac1 activation and weakens its interaction with MAP1B [#6]. TIAM2 also drives Rac1-dependent invasion and epithelial-to-mesenchymal transition in carcinoma cells downstream of EGFR/c-Met receptor tyrosine kinases [#11, #12, #15], and its mRNA is stabilized by NSUN2-catalyzed m5C methylation in a YBX1-dependent manner [#16].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Established that TIAM2 is a catalytically active GEF with selectivity for Rac1, defining its core biochemical identity and downstream effector.\",\n      \"evidence\": \"In vitro GDP dissociation/exchange assays with purified protein, domain analysis, and cell-based ruffling assay; independent cloning as STEF and as a TIAM1 homolog\",\n      \"pmids\": [\"10364228\", \"10512681\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve how Rac1 selectivity is structurally encoded\", \"Upstream activators unknown at this stage\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Mapped functional roles to individual domains, showing membrane targeting (N-terminal PH), catalysis (DH), and catalytic enhancement (C-terminal PH) are separable and that TIAM2 drives neurite outgrowth through Rac1.\",\n      \"evidence\": \"Deletion mutagenesis, dominant-negative expression with rescue, neurite outgrowth assay in N1E-115 neuroblastoma cells\",\n      \"pmids\": [\"11707441\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Dominant-negative PHnTSS fragment also inhibits Tiam1, leaving paralog-specific contributions unresolved\", \"Membrane lipid/protein determinants of PH targeting not defined\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstrated an in vivo requirement for TIAM2/Tiam1-Rac1 signaling in cortical neuron migration and linked it to a Rac1-JNK-MAP1B microtubule-regulatory axis.\",\n      \"evidence\": \"In utero electroporation of dominant-negative/shRNA constructs, cortical migration assay, JNK inhibitor and MAP1B phosphorylation analysis\",\n      \"pmids\": [\"12912917\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not separate TIAM2 from Tiam1 contributions in vivo\", \"Upstream receptor triggering migratory Rac1 activation not identified\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Localized TIAM2 to growth cones and placed it at the convergence of laminin and Cdc42 inputs activating Rac1, with RhoA acting antagonistically.\",\n      \"evidence\": \"Dominant-negative expression, immunolocalization in primary hippocampal neurons, growth cone morphology assay, epistasis with Cdc42 and RhoA\",\n      \"pmids\": [\"14550769\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Epistasis relies on dominant-negative constructs without direct binding data for laminin receptor coupling\", \"Mechanism of RhoA antagonism not defined here\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Defined the molecular bridge by which Cdc42 activates Rac1, showing direct PAR-3 binding incorporates TIAM2 into the PAR polarity complex to drive lamellipodia and neuronal polarity.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation, direct binding assays, dominant-negative/overexpression and Rac1 activation assays in N1E-115 cells and hippocampal neurons\",\n      \"pmids\": [\"15723051\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which TIAM2 domain mediates PAR-3 binding not pinpointed\", \"How complex assembly is spatially restricted to the axon tip not fully resolved\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identified Rho-kinase phosphorylation at Thr-1662 as a negative regulatory input that dampens Rac1 activation and disrupts the TIAM2-MAP1B interaction.\",\n      \"evidence\": \"In vitro kinase assay, site-directed mutagenesis, Rac1 activation assay, Co-IP, neurite outgrowth assay, Y-27632 inhibitor in PC12D cells\",\n      \"pmids\": [\"17320046\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for how Thr-1662 phosphorylation alters activity not determined\", \"Physiological stimuli engaging this brake beyond LPA not mapped\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Connected TIAM2 to the cAMP/Epac/Rap1 cascade via TSS-region binding to activated Rap1, linking it to Rac1-dependent non-amyloidogenic APP processing.\",\n      \"evidence\": \"Co-IP of Rap1-STEF, \\u0394TSS deletion mutant, Rac1 activation and sAPP\\u03b1 secretion assays\",\n      \"pmids\": [\"18047838\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab Co-IP without structural mapping of the Rap1-TSS interface\", \"Whether Rap1 binding is direct or complex-mediated not established\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Revealed a role in cell migration whereby TIAM2-driven Rac1 activation couples microtubule regrowth to focal adhesion disassembly.\",\n      \"evidence\": \"siRNA knockdown, Rac1 activation assay, live imaging of FA dynamics, nocodazole washout, migration speed measurement\",\n      \"pmids\": [\"20224579\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How microtubule contact triggers TIAM2 recruitment/activation not defined\", \"Direct microtubule-TIAM2 association not demonstrated\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Defined the distinct PDZ ligand specificity of TIAM2 relative to Tiam1 at the residue level, establishing non-redundant scaffolding interactions.\",\n      \"evidence\": \"Combinatorial peptide library, peptide binding assays, site-directed mutagenesis, double mutant cycle analysis\",\n      \"pmids\": [\"21192692\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endogenous physiological PDZ ligands of TIAM2 not identified\", \"Functional consequence of distinct specificity in cells untested\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identified PKA phosphorylation at Thr-749 as a positive regulatory input required for cAMP-induced, spatially localized Rac1 activation and neurite outgrowth.\",\n      \"evidence\": \"FRET biosensors, siRNA knockdown, phosphorylation-site mutants, neurite outgrowth and PKA activity reporters in PC12D cells\",\n      \"pmids\": [\"21460187\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which Thr-749 phosphorylation enhances GEF activity not structurally resolved\", \"Interplay with Rho-kinase inhibitory phosphorylation not directly tested\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Uncovered a nuclear-envelope function in which TIAM2 controls perinuclear Rac1 to maintain the actin cap, nuclear mechanics, and TAZ-dependent transcription.\",\n      \"evidence\": \"siRNA knockdown with active-Rac1 nuclear-envelope targeting rescue, perinuclear FRET biosensor, FRAP, nuclear morphology and TAZ reporter assays; co-localization with Nesprin-2G and NMMIIB\",\n      \"pmids\": [\"29844364\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How TIAM2 is recruited to the nuclear envelope not defined\", \"Whether Nesprin-2G binding is direct not established\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Implicated TIAM2 (and a short isoform) in carcinoma progression by promoting Rac1-dependent invasion and epithelial-to-mesenchymal transition.\",\n      \"evidence\": \"Stable overexpression/siRNA knockdown, proliferation/invasion assays, xenograft models, and EMT marker analysis in hepatocellular and lung cancer cells\",\n      \"pmids\": [\"21469146\", \"24377522\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal upstream activators of TIAM2 in these tumors not fully defined here\", \"Isoform-specific mechanisms not resolved in the carcinoma context\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Showed isoform-specific and opposing TIAM2 functions in mouse t-haplotype transmission ratio distortion via Rac1 signaling in sperm.\",\n      \"evidence\": \"Transgenic mouse approaches, transmission ratio distortion assay, isoform-specific expression analysis\",\n      \"pmids\": [\"30817801\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis for opposing short vs full-length isoform activity unresolved\", \"Direct sperm Rac1 substrate/effector readouts limited\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Positioned TIAM2 as a non-redundant Rac-GEF for lung adenocarcinoma cell migration downstream of EGFR/c-Met receptor tyrosine kinases controlling distinct ruffle dynamics.\",\n      \"evidence\": \"siRNA functional screen, Rac1 activity assay, ruffle dynamics imaging, epistasis with EGFR/c-Met/AXL-Gab1-PI3K\",\n      \"pmids\": [\"34731623\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct receptor-to-TIAM2 coupling mechanism not defined\", \"Basis for non-redundancy with FARP1/ARHGEF39 unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Identified post-transcriptional control of TIAM2 by NSUN2-mediated m5C mRNA methylation, stabilizing the transcript and supporting cancer EMT and metastasis.\",\n      \"evidence\": \"m5C-seq, RNA-seq, knockdown/overexpression, mRNA stability and YBX1 dependency assays, xenograft in pancreatic cancer\",\n      \"pmids\": [\"37393317\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Methylated residues on TIAM2 mRNA not pinpointed\", \"Whether m5C control operates in non-cancer contexts unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Demonstrated that dually lipidated CaMKI\\u03b3 couples to compartmentalized STEF-Rac1 signaling at lipid rafts to drive neurite extension, requiring palmitoylation.\",\n      \"evidence\": \"Lipid raft fractionation, palmitoylation/prenylation mutants, Rac1 activity and neurite outgrowth assays in PC12 cells\",\n      \"pmids\": [\"37601281\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether CaMKI\\u03b3 directly modifies/binds TIAM2 not established\", \"Lipid-raft recruitment determinants of TIAM2 undefined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural basis for how phosphorylation (Thr-749 activation vs Thr-1662 inhibition) and partner binding (PAR-3, Rap1, Nesprin-2G) toggle TIAM2 catalytic activity, and how distinct spatial pools are coordinated, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of full-length TIAM2 or its regulatory interfaces in the corpus\", \"Direct vs scaffold-mediated nature of several key partner interactions undetermined\", \"Mechanism integrating opposing kinase inputs on a single molecule not defined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 2, 6, 8, 10]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 5, 7]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [5, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 2, 10]},\n      {\"term_id\": \"GO:0005635\", \"supporting_discovery_ids\": [13]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [4, 8, 13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 5, 7, 10]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [2, 3, 4, 5]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [11, 12, 15, 16]}\n    ],\n    \"complexes\": [\n      \"PAR-3/aPKC/PAR-6/Cdc42 polarity complex\"\n    ],\n    \"partners\": [\n      \"RAC1\",\n      \"PARD3\",\n      \"RAP1\",\n      \"MAP1B\",\n      \"SYNE2\",\n      \"MYH10\",\n      \"CDC42\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}