{"gene":"FAIM2","run_date":"2026-06-09T23:54:43","timeline":{"discoveries":[{"year":1999,"finding":"LFG (FAIM2) was identified by genetic screen as an anti-apoptotic protein that protects cells from Fas-mediated apoptosis but not TNF-alpha-mediated death. LFG binds to the Fas receptor but does not regulate Fas expression, does not interfere with agonist antibody binding to Fas, and does not inhibit FADD binding to Fas.","method":"Genetic screen, co-immunoprecipitation (LFG-Fas binding), cell-based apoptosis assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — original discovery paper using genetic screen plus direct binding assay, multiple mechanistic controls; foundational paper replicated by many subsequent studies","pmids":["10535980"],"is_preprint":false},{"year":1998,"finding":"NMP35 (FAIM2) protein is predominantly expressed in the adult nervous system with a neuronal expression pattern, and is strongly upregulated during postnatal development. The protein shares homology with rat glutamate-binding protein (GBP), Drosophila NMDARA1, and C. elegans genes, suggesting membership in a conserved gene family.","method":"RAP-PCR differential display, Northern blot, in situ hybridization, database comparisons","journal":"Molecular and cellular neurosciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct expression profiling with in situ hybridization and protein characterization, single lab but multiple methods","pmids":["9698393"],"is_preprint":false},{"year":2002,"finding":"NMP35/Lifeguard (FAIM2) protein localizes to dendrites and postsynaptic membranes in the adult CNS, colocalizing with the glutamate receptor GluR2 and adjacent to the presynaptic vesicle protein synaptophysin. Immunoelectron microscopy confirmed postsynaptic membrane and density localization.","method":"Immunofluorescence confocal microscopy, immunoelectron microscopy, subcellular fractionation with affinity-purified antibodies","journal":"Brain research. Molecular brain research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct subcellular localization by both immunofluorescence and immunoelectron microscopy, two orthogonal methods in one study","pmids":["12414123"],"is_preprint":false},{"year":2005,"finding":"LFG/NMP35 (FAIM2) expression in cerebellar granule neurons (CGNs) is regulated by the PI3-kinase/Akt/PKB signaling pathway. Inhibition of PI3-kinase or dominant-negative Akt reduced LFG reporter activity, while constitutively active Akt increased it. Knockdown of LFG by antisense oligonucleotides or siRNA sensitized CGNs to FasL-induced caspase-8 cleavage and cell death. LFG gene transfer into FasL-sensitive glioma cells conferred protection.","method":"siRNA/antisense knockdown, reporter assay, dominant-negative and constitutively active Akt constructs, pharmacological PI3-kinase inhibition, caspase-8 cleavage assay","journal":"The Journal of neuroscience : the official journal of the Society for Neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (siRNA, dominant-negative constructs, reporter assay, pharmacological inhibition) establishing PI3K/Akt regulation of FAIM2 and its functional role in FasL resistance","pmids":["16033886"],"is_preprint":false},{"year":2006,"finding":"Bioinformatic analysis predicts LFG (FAIM2) resides in cellular membranes including the ER and plasma membrane, with seven transmembrane spanners and a small cytoplasmic domain. The UPF0005 consensus motif is found in the C-terminus, and the structure resembles Bax Inhibitor-1 (BI-1). Bax was found to co-immunoprecipitate with LFG.","method":"Bioinformatic sequence analysis, co-immunoprecipitation (Bax-LFG interaction)","journal":"International journal of molecular medicine","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP for Bax interaction, structural predictions are computational; limited experimental validation","pmids":["16964429"],"is_preprint":false},{"year":2007,"finding":"Lifeguard (FAIM2) is an endogenous inhibitor of FasL-mediated neuronal death independent of FLICE inhibitory protein (FLIP). Overexpression of LFG protected cortical neurons from FasL-induced apoptosis and decreased caspase activation. siRNA knockdown sensitized cerebellar granular and cortical neurons to FasL-induced death and caspase-8 activation. LFG was detected in lipid raft microdomains where it may interact with Fas receptor.","method":"siRNA knockdown, overexpression, caspase activity assay, lipid raft fractionation","journal":"Journal of neurochemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal loss-of-function and gain-of-function experiments, caspase-8 assays, lipid raft localization, multiple neuronal cell types","pmids":["17635665"],"is_preprint":false},{"year":2011,"finding":"Faim2-deficient mice showed increased susceptibility to oxygen-glucose deprivation in primary neurons in vitro and increased caspase-associated cell death, stroke volume, and neurological impairment after cerebral ischemia in vivo. Lentiviral Faim2 gene transfer rescued these effects, demonstrating Faim2 is neuroprotective in cerebral ischemia.","method":"Faim2 knockout mouse, middle cerebral artery occlusion model, oxygen-glucose deprivation, caspase assay, lentiviral gene transfer rescue","journal":"The Journal of neuroscience : the official journal of the Society for Neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with rescue by lentiviral gene transfer, both in vitro and in vivo models, caspase mechanistic readout","pmids":["21209208"],"is_preprint":false},{"year":2011,"finding":"LFG (FAIM2) is required for survival and maintenance of Purkinje cells and granular cells in the cerebellum. Mice with reduced LFG expression (shRNA lentiviral transgenesis) or LFG null mice showed reduced cerebellar size, decreased internal granular layer thickness, and abnormal Purkinje cell morphology with increased active caspase-8 and caspase-3. Biochemical analysis showed LFG inhibits Fas-mediated cell death by interfering with caspase-8 activation.","method":"shRNA lentiviral transgenesis, LFG knockout mice, immunostaining for active caspase-8 and caspase-3, organotypic cerebellar culture","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic loss-of-function (shRNA transgenic + KO), specific cellular phenotype, mechanistic caspase-8 readout, in vivo and in vitro validation","pmids":["21957071"],"is_preprint":false},{"year":2012,"finding":"Faim2 expression in 661W photoreceptor-like cells is upregulated following Fas receptor activation and is regulated by ERK signaling. Pharmacological inhibition of ERK reduced Faim2 levels and increased susceptibility to Fas-induced caspase activation and apoptosis. siRNA knockdown of Faim2 resulted in earlier and more robust caspase activation and increased cell death after Fas antibody treatment.","method":"Pharmacological ERK pathway inhibition, siRNA knockdown, Fas-activating antibody treatment, caspase activity assay, Western blot","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown and pharmacological inhibition with caspase readouts, single lab, two orthogonal methods","pmids":["23029562"],"is_preprint":false},{"year":2015,"finding":"Lifeguard (FAIM2) localizes primarily to the endoplasmic reticulum and Golgi apparatus in murine cortical neurons (confirmed by subcellular fractionation). LFG interacts with Bcl-XL and Bcl-2 (but not Bax or Bak) by co-immunoprecipitation, likely at the ER. LFG protects only type II apoptotic cells from FasL-induced death in a Bcl-XL-dependent manner. LFG inhibits calcium release from the ER following FasL stimulation, which correlates with blockage of cytochrome c release and caspase activation.","method":"Subcellular fractionation, co-immunoprecipitation, calcium mobilization assay, cytochrome c release assay, caspase assay, overexpression and siRNA experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal methods: subcellular fractionation confirming ER/Golgi localization, reciprocal Co-IP for Bcl-XL/Bcl-2 interaction, functional calcium release assay, cytochrome c release, caspase activation all in one study","pmids":["26582200"],"is_preprint":false},{"year":2015,"finding":"Lifeguard (FAIM2) inhibits Fas-mediated apoptosis downstream of Fas trimerization by inhibiting caspase-8 activation in triple-negative breast cancer (MDA-MB-231) cells. Knockdown of Lifeguard via shRNA increased cisplatin efficacy, increased caspase-8 activity, and increased sensitivity to FasL-mediated cell death.","method":"shRNA knockdown, caspase-8 activity assay, cell viability assay, FasL treatment","journal":"Biomedicine & pharmacotherapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — shRNA knockdown with specific caspase-8 mechanistic readout, single lab, two orthogonal functional assays","pmids":["26796280"],"is_preprint":false},{"year":2015,"finding":"TRIM21 negatively modulates LFG (FAIM2) at the protein level in MDA-MB-231 breast cancer cells. TRIM21-LFG interaction was demonstrated by co-immunoprecipitation. Addition of TRIM21 decreased LFG protein levels and was associated with decreased Fas-induced apoptosis.","method":"Protein array screen, co-immunoprecipitation, Western blot, RT-PCR, flow cytometry apoptosis assay","journal":"International journal of oncology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single Co-IP, protein array finding confirmed by Western blot, apoptosis assay, single lab","pmids":["26398169"],"is_preprint":false},{"year":2010,"finding":"LFG (FAIM2) expression is regulated by the Akt/LEF-1 transcriptional pathway in breast cancer cells. GSK3β inhibition stabilizes β-catenin which associates with LEF-1 to drive LFG transcription. siRNA knockdown of LEF-1 reduced LFG mRNA levels in MDA-MB-231 cells.","method":"siRNA knockdown of LEF-1, Western blot, RT-PCR","journal":"Apoptosis : an international journal on programmed cell death","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with mRNA readout, Western blot, single lab, two methods","pmids":["20336373"],"is_preprint":false},{"year":2014,"finding":"MYCN directly represses LFG (FAIM2) expression at the transcriptional level in neuroblastoma. LFG repression in neuroblastoma cells reduced cell adhesion, increased sphere growth, and enhanced migration, conferring higher metastatic capacity, independent of its anti-apoptotic function.","method":"Expression analysis in human NBL datasets, ChIP (MYCN binding), siRNA knockdown, cell adhesion and migration assays, sphere formation assay","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP for direct transcriptional repression, functional assays with siRNA, single lab","pmids":["25188511"],"is_preprint":false},{"year":2016,"finding":"Faim2-deficient mice showed significantly increased loss of dopaminergic neurons and fibers in the MPTP model of Parkinson disease compared to controls. Faim2 expression in mouse midbrain was decreased after MPTP administration, suggesting Fas-induced apoptosis contributes to dopaminergic cell death.","method":"Faim2 knockout mouse, MPTP administration, stereological counting of dopaminergic neurons, dopaminergic fiber density measurement, qRT-PCR","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with in vivo stereological quantification, single lab, single method for pathway placement","pmids":["27638043"],"is_preprint":false},{"year":2018,"finding":"Faim2 upregulation contributes to the neuroprotective effects of low-dose erythropoietin (EPO) in transient brain ischemia. Low-dose EPO increased Faim2 expression and reduced stroke volume in wild-type mice, but failed to significantly reduce stroke volume in Faim2-deficient mice, placing Faim2 downstream of the EPO/PI3K/Akt signaling pathway in neuroprotection.","method":"Faim2 knockout mouse, middle cerebral artery occlusion, EPO administration, qRT-PCR, infarct volume measurement","journal":"Journal of neurochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis using KO mouse showing Faim2 is required for EPO neuroprotection, single lab","pmids":["29315561"],"is_preprint":false},{"year":2019,"finding":"FAIM2 (TMBIM-2) and GRINA (TMBIM-3) are both neuroprotective in transient brain ischemia and are regulated by EPO. Double-deficient mice (GRINA-/-FAIM2-/-) showed the largest infarct sizes and worst neurological deficits. FAIM2 deficiency led to upregulation of cleaved-caspase 3, pro-apoptotic BAX mRNA, and caspase-8 (not caspase-9). EPO upregulated FAIM2 and GRINA mRNA in wildtype mice.","method":"GRINA/FAIM2 single and double knockout mice, tMCAo model, OGD in primary neurons, overexpression by transfection, caspase and BAX mRNA analysis","journal":"Experimental neurology","confidence":"High","confidence_rationale":"Tier 2 / Strong — double-KO genetic epistasis, multiple caspase mechanistic readouts, in vivo and in vitro validation, EPO regulation confirmed","pmids":["31211943"],"is_preprint":false},{"year":2022,"finding":"FAIM2 is targeted for degradation by TRIM21, an E3 ubiquitin ligase that is itself a DUX4 target gene; DUX4 expression reduces cellular FAIM2 levels through TRIM21. Inhibition of miR-3202 (which targets FAIM2) upregulates FAIM2. FAIM2 is required for myoblast differentiation into myotubes; FAIM2 knockdown causes increased apoptosis and failure to differentiate. FAIM2 overexpression rescued DUX4-induced cell death and myogenic differentiation defects.","method":"miR inhibitor screen, siRNA knockdown of FAIM2, FAIM2 overexpression, DUX4 overexpression, TRIM21 knockdown, differentiation assay, apoptosis assay","journal":"Cell death & disease","confidence":"High","confidence_rationale":"Tier 2 / Strong — mechanistic screen followed by multiple orthogonal methods establishing TRIM21-mediated FAIM2 degradation, rescue experiments, myogenic differentiation phenotype with specific KD and OE","pmids":["35468884"],"is_preprint":false},{"year":2025,"finding":"TMBIM-2 (FAIM2 ortholog in C. elegans, XBX-6/TMBIM-2) mediates neuronal mitochondrial stress-triggered spatiotemporal Ca2+ oscillations through the Ca2+ efflux pump MCA-3, facilitating serotonin release from ADF neurons and activation of the neuronal-to-intestinal mitochondrial unfolded protein response (UPRmt). TMBIM-2 overexpression counteracted age-related decline in aversive learning and extended lifespan.","method":"C. elegans genetics, calcium imaging, serotonin release assay, UPRmt reporter, lifespan assay, TMBIM-2 overexpression","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — rigorous C. elegans ortholog study with calcium imaging and genetic epistasis, but C. elegans ortholog, not direct human/mammalian FAIM2","pmids":["40100072"],"is_preprint":false},{"year":2024,"finding":"αA-crystallin (HSPB4) interacts with FAIM2 in the retina following retinal detachment, as demonstrated by co-immunoprecipitation. Phosphorylation of αA-crystallin at T148 is important for this interaction and for their combined neuroprotective effect on photoreceptors. FAIM2 is induced following retinal detachment.","method":"Co-immunoprecipitation (FAIM2-αA-crystallin), phospho-mutant analysis, TUNEL staining, immunohistochemistry, immunoblotting","journal":"Neurology international","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP for interaction, phospho-mutant for mechanistic insight, single lab, multiple methods","pmids":["39311341"],"is_preprint":false},{"year":2014,"finding":"In bacterial meningitis model, Faim2 deficiency leads to increased caspase-associated hippocampal apoptotic cell death and increased ERK activation during acute infection. After antibiotic rescue, Faim2 deficiency paradoxically led to increased hippocampal neurogenesis and improved spatial learning and memory performance.","method":"Faim2 knockout mouse, Streptococcus pneumoniae subarachnoid infection, caspase immunostaining, ERK immunostaining, Morris water maze","journal":"Journal of neuropathology and experimental neurology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with specific caspase and ERK mechanistic readouts in disease model, single lab","pmids":["24335530"],"is_preprint":false},{"year":2021,"finding":"FAIM2 promotes NSCLC cell proliferation, migration, and invasion and inhibits apoptosis by activating the Wnt/β-catenin signaling pathway and facilitating EMT. FAIM2 knockdown in HARA-B4 cells reduced these activities and enhanced osteocyte adhesion. In vivo, FAIM2 participated in regulating NSCLC bone metastasis.","method":"FAIM2 overexpression and siRNA knockdown, proliferation/migration/invasion assays, Wnt/β-catenin pathway analysis, EMT marker analysis, in vivo bone metastasis model","journal":"Frontiers in oncology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — functional overexpression/knockdown assays with pathway analysis, but no direct mechanistic demonstration of how FAIM2 activates Wnt/β-catenin, single lab","pmids":["34568020"],"is_preprint":false},{"year":2015,"finding":"LFG KO T cells show increased cell death during the initial phase of anti-viral immune response (LCMV infection), resulting in decreased numbers of activated CD8 and CD4 T cells and LCMV-specific memory T cells. LFG KO and WT T cells were equally sensitive to Fas antibody Jo-2 ex vivo, and blocking extrinsic death pathways (FasL or caspase-8 inhibitors) did not rescue the LFG KO phenotype in vivo, suggesting LFG protects T cells via a Fas-independent mechanism during early immune response.","method":"LFG knockout bone marrow chimeras, LCMV infection, T cell proliferation assay, ex vivo FasL/caspase-8 inhibitor treatment, cell death assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO in immune model with specific mechanistic controls (FasL and caspase-8 inhibitors tested), single lab","pmids":["26565411"],"is_preprint":false},{"year":2024,"finding":"The rs7132908 obesity risk allele within the 3' UTR of FAIM2 has allele-specific cis-regulatory activity demonstrated by luciferase reporter assay. In isogenic hESC lines differentiated to hypothalamic neurons, the risk allele influenced FAIM2 expression, decreased the proportion of neurons produced, upregulated cell death gene sets, and downregulated neuron differentiation gene sets.","method":"Luciferase reporter assay, CRISPR-Cas9 homology-directed repair to generate isogenic hESC lines, RNA-seq during hypothalamic neuron differentiation, 3D genomic data","journal":"Cell genomics","confidence":"High","confidence_rationale":"Tier 1 / Strong — isogenic CRISPR lines plus luciferase reporter assay plus transcriptomics during differentiation, multiple orthogonal methods, published peer-reviewed","pmids":["38697123"],"is_preprint":false}],"current_model":"FAIM2 (Lifeguard/NMP35/LFG) is an evolutionarily conserved multi-pass transmembrane protein localizing primarily to the endoplasmic reticulum (and lipid rafts), where it inhibits Fas/CD95-mediated apoptosis by blocking caspase-8 activation and suppressing ER calcium release required for cytochrome c release and downstream caspase activation; it interacts directly with the Fas receptor, with Bcl-XL/Bcl-2 at the ER, and with αA-crystallin, and is regulated transcriptionally by the PI3K/Akt/LEF-1 pathway and post-translationally by TRIM21-mediated degradation, while playing essential roles in neuronal survival (cerebellum, ischemia, Parkinson models), T cell memory maintenance, myoblast differentiation, and hypothalamic neurodevelopment."},"narrative":{"mechanistic_narrative":"FAIM2 (Lifeguard/NMP35/LFG) is an evolutionarily conserved multi-pass membrane protein that acts as a selective endogenous inhibitor of Fas/CD95-mediated apoptosis and a determinant of neuronal survival [PMID:10535980, PMID:17635665, PMID:21957071]. Originally identified in a genetic screen as protecting cells from Fas- but not TNF-alpha-mediated death, it binds the Fas receptor without altering Fas expression, agonist binding, or FADD recruitment [PMID:10535980], and instead blocks apoptosis downstream of Fas trimerization by suppressing caspase-8 activation [PMID:21957071, PMID:26796280]. It localizes predominantly to the endoplasmic reticulum and Golgi and to lipid raft microdomains, where it interacts with the anti-apoptotic proteins Bcl-XL and Bcl-2 and protects type II apoptotic cells in a Bcl-XL-dependent manner by inhibiting ER calcium release, thereby blocking cytochrome c release and downstream caspase activation [PMID:17635665, PMID:26582200]. FAIM2 expression is controlled transcriptionally by the PI3K/Akt pathway acting through LEF-1/beta-catenin [PMID:16033886, PMID:20336373] and is regulated post-translationally by TRIM21-mediated degradation [PMID:26398169, PMID:35468884]. Functionally, FAIM2 is neuroprotective: its loss sensitizes neurons to caspase-driven death and worsens injury in cerebral ischemia, Parkinson-model dopaminergic loss, and cerebellar Purkinje/granule cell maintenance, where it acts downstream of erythropoietin/PI3K/Akt signaling alongside the related TMBIM protein GRINA [PMID:21209208, PMID:21957071, PMID:27638043, PMID:31211943]. Beyond neurons, FAIM2 supports T-cell survival during early anti-viral responses through a Fas-independent mechanism [PMID:26565411], is required for myoblast differentiation [PMID:35468884], and a 3'-UTR obesity risk variant alters its expression and biases hypothalamic neuron differentiation toward cell death [PMID:38697123].","teleology":[{"year":1998,"claim":"Established FAIM2 as a nervous-system-enriched membrane protein of a conserved gene family before its function was known, defining its expression domain.","evidence":"RAP-PCR differential display, Northern blot, and in situ hybridization in adult rodent nervous tissue","pmids":["9698393"],"confidence":"Medium","gaps":["No molecular function assigned at this stage","Homology to glutamate-binding proteins not functionally validated"]},{"year":1999,"claim":"Defined the core anti-apoptotic activity: FAIM2 protects selectively against Fas-mediated death and binds Fas without blocking the canonical DISC assembly steps, indicating a non-canonical inhibitory mechanism.","evidence":"Genetic screen plus co-immunoprecipitation and cell-based apoptosis assays with mechanistic controls (Fas expression, agonist binding, FADD recruitment)","pmids":["10535980"],"confidence":"High","gaps":["Mechanism of caspase-8 suppression not resolved","Subcellular site of action undefined"]},{"year":2002,"claim":"Localized FAIM2 to postsynaptic membranes and densities, linking the survival protein to synaptic neuronal compartments.","evidence":"Immunofluorescence and immunoelectron microscopy with subcellular fractionation in adult CNS","pmids":["12414123"],"confidence":"High","gaps":["Functional consequence of synaptic localization unknown","Relationship to apoptotic protection not addressed"]},{"year":2005,"claim":"Connected FAIM2 expression to PI3K/Akt survival signaling and demonstrated it is functionally required to resist FasL-induced caspase-8 cleavage in neurons.","evidence":"Reporter assays, dominant-negative/constitutively active Akt, PI3K inhibition, siRNA/antisense knockdown, and gene transfer in cerebellar granule neurons and glioma cells","pmids":["16033886"],"confidence":"High","gaps":["Direct transcription factor downstream of Akt not yet identified","Biochemical target of FAIM2 unresolved"]},{"year":2007,"claim":"Showed FAIM2 acts independently of FLIP and localizes to lipid rafts, establishing it as a distinct, FLIP-independent endogenous Fas inhibitor in neurons.","evidence":"Reciprocal overexpression/siRNA, caspase activity assays, and lipid raft fractionation in cortical and cerebellar neurons","pmids":["17635665"],"confidence":"High","gaps":["Direct partners in rafts not defined","Stoichiometry with Fas unknown"]},{"year":2010,"claim":"Identified the Akt/GSK3beta/beta-catenin/LEF-1 axis as the transcriptional route driving FAIM2 expression, mechanistically linking survival signaling to FAIM2 levels.","evidence":"LEF-1 siRNA knockdown with mRNA and Western readouts in MDA-MB-231 cells","pmids":["20336373"],"confidence":"Medium","gaps":["Direct LEF-1 binding site on FAIM2 promoter not mapped","Single cell line"]},{"year":2011,"claim":"Provided in vivo genetic proof that FAIM2 is neuroprotective, with knockout worsening ischemic injury and cerebellar neuron loss, both rescuable and tied to caspase-8 activation.","evidence":"Faim2 knockout and shRNA-transgenic mice, MCAO and oxygen-glucose deprivation, lentiviral rescue, active caspase-8/3 immunostaining","pmids":["21209208","21957071"],"confidence":"High","gaps":["Precise biochemical step blocking caspase-8 unresolved","Cell-type-specific requirements not dissected"]},{"year":2014,"claim":"Extended FAIM2 regulation and function beyond neuronal survival, showing ERK-dependent induction in photoreceptors, MYCN-mediated repression in neuroblastoma, and an apoptosis-independent role in cell adhesion/migration.","evidence":"ERK inhibition and siRNA in 661W cells; ChIP, siRNA, adhesion/migration/sphere assays in neuroblastoma; KO meningitis model with caspase/ERK readouts","pmids":["23029562","25188511","24335530"],"confidence":"Medium","gaps":["Mechanism of adhesion/migration control independent of apoptosis unknown","Paradoxical neurogenesis benefit of FAIM2 loss unexplained"]},{"year":2015,"claim":"Resolved the subcellular mechanism: FAIM2 at the ER/Golgi interacts with Bcl-XL/Bcl-2 and inhibits FasL-triggered ER calcium release to block cytochrome c release, defining a type II, Bcl-XL-dependent mode of protection.","evidence":"Subcellular fractionation, reciprocal Co-IP, calcium mobilization, cytochrome c release and caspase assays in cortical neurons; shRNA in breast cancer cells; T-cell KO chimeras with Fas/caspase-8 inhibitor controls","pmids":["26582200","26796280","26565411"],"confidence":"High","gaps":["Molecular mechanism of calcium-channel regulation unknown","Fas-independent T-cell survival mechanism unidentified"]},{"year":2015,"claim":"Identified TRIM21 as a post-translational regulator that lowers FAIM2 protein and reduces Fas-induced apoptosis, adding a degradation layer to FAIM2 control.","evidence":"Protein array screen, Co-IP, Western blot, and apoptosis assays in breast cancer cells","pmids":["26398169"],"confidence":"Medium","gaps":["Direct ubiquitination of FAIM2 by TRIM21 not demonstrated","Single Co-IP without reciprocal validation"]},{"year":2018,"claim":"Placed FAIM2 genetically downstream of erythropoietin/PI3K/Akt neuroprotection and, with GRINA, in a shared TMBIM neuroprotective module against ischemia.","evidence":"EPO administration in Faim2 KO and GRINA/FAIM2 single/double KO mice, tMCAo, OGD, caspase-8/BAX readouts","pmids":["29315561","31211943"],"confidence":"High","gaps":["How EPO signaling induces FAIM2 transcription mechanistically unclear","Functional redundancy with GRINA at the molecular level undefined"]},{"year":2022,"claim":"Demonstrated a DUX4/TRIM21/miR-3202 regulatory circuit controlling FAIM2 and established FAIM2 as required for myoblast differentiation, broadening its role to muscle.","evidence":"miR inhibitor screen, siRNA/overexpression, DUX4 and TRIM21 manipulation, differentiation and apoptosis assays with rescue","pmids":["35468884"],"confidence":"High","gaps":["Whether differentiation role is separable from anti-apoptotic role unclear","Direct TRIM21 ubiquitination of FAIM2 still not shown biochemically"]},{"year":2024,"claim":"Identified new contexts and partners: alphaA-crystallin interacts with FAIM2 in retina with a phospho-dependent neuroprotective effect, and an obesity-risk 3'-UTR variant alters FAIM2 expression to bias hypothalamic neurogenesis toward cell death.","evidence":"Co-IP and phospho-mutant analysis in retinal detachment; luciferase reporter, CRISPR isogenic hESC lines, and RNA-seq during hypothalamic differentiation","pmids":["39311341","38697123"],"confidence":"High","gaps":["Functional consequence of alphaA-crystallin interaction at molecular level unclear","How FAIM2 dosage controls neuron differentiation gene programs unknown"]},{"year":2025,"claim":"Used the C. elegans ortholog to reveal an ancient role in mitochondrial-stress-triggered calcium oscillations driving serotonergic signaling and the mitochondrial UPR, linking FAIM2/TMBIM-2 calcium control to lifespan and learning.","evidence":"C. elegans genetics, calcium imaging, serotonin release and UPRmt reporters, lifespan and overexpression assays","pmids":["40100072"],"confidence":"Medium","gaps":["C. elegans ortholog, not directly demonstrated for mammalian FAIM2","Mechanistic link from calcium oscillation to apoptosis suppression in mammals not established"]},{"year":null,"claim":"The precise biochemical mechanism by which FAIM2 suppresses caspase-8 activation and regulates ER calcium fluxes—and how its anti-apoptotic and apoptosis-independent (adhesion, differentiation, calcium-signaling) functions are molecularly distinguished—remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of FAIM2 in complex with Fas or Bcl-XL","No direct biochemical demonstration of FAIM2 calcium-channel modulation","Substrate/effector basis of the Fas-independent survival functions undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,5,7,9,10]},{"term_id":"GO:0140313","term_label":"molecular sequestering activity","supporting_discovery_ids":[9]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[4,9]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[9]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[4,5]}],"pathway":[{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[0,5,7,9,10]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[3,12,15]}],"complexes":[],"partners":["FAS","BCL2L1","BCL2","BAX","TRIM21","CRYAA","GRINA"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9BWQ8","full_name":"Protein lifeguard 2","aliases":["Fas apoptotic inhibitory molecule 2","Neural membrane protein 35","Transmembrane BAX inhibitor motif-containing protein 2"],"length_aa":316,"mass_kda":35.1,"function":"Antiapoptotic protein which protects cells uniquely from Fas-induced apoptosis. Regulates Fas-mediated apoptosis in neurons by interfering with caspase-8 activation. May play a role in cerebellar development by affecting cerebellar size, internal granular layer (IGL) thickness, and Purkinje cell (PC) development","subcellular_location":"Cell membrane; Membrane raft; Postsynaptic cell membrane","url":"https://www.uniprot.org/uniprotkb/Q9BWQ8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/FAIM2","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/FAIM2","total_profiled":1310},"omim":[{"mim_id":"604306","title":"FAS APOPTOTIC INHIBITORY MOLECULE 2; FAIM2","url":"https://www.omim.org/entry/604306"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Uncertain","locations":[{"location":"Intermediate filaments","reliability":"Uncertain"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":309.1},{"tissue":"parathyroid gland","ntpm":91.9}],"url":"https://www.proteinatlas.org/search/FAIM2"},"hgnc":{"alias_symbol":["KIAA0950","LFG","NMP35","LIFEGUARD","TMBIM2","LFG2"],"prev_symbol":[]},"alphafold":{"accession":"Q9BWQ8","domains":[{"cath_id":"-","chopping":"97-310","consensus_level":"medium","plddt":91.9826,"start":97,"end":310}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BWQ8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BWQ8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BWQ8-F1-predicted_aligned_error_v6.png","plddt_mean":77.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=FAIM2","jax_strain_url":"https://www.jax.org/strain/search?query=FAIM2"},"sequence":{"accession":"Q9BWQ8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9BWQ8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9BWQ8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BWQ8"}},"corpus_meta":[{"pmid":"26122615","id":"PMC_26122615","title":"p53 in survival, death and metabolic health: a lifeguard with a licence to kill.","date":"2015","source":"Nature reviews. 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LFG binds to the Fas receptor but does not regulate Fas expression, does not interfere with agonist antibody binding to Fas, and does not inhibit FADD binding to Fas.\",\n      \"method\": \"Genetic screen, co-immunoprecipitation (LFG-Fas binding), cell-based apoptosis assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — original discovery paper using genetic screen plus direct binding assay, multiple mechanistic controls; foundational paper replicated by many subsequent studies\",\n      \"pmids\": [\"10535980\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"NMP35 (FAIM2) protein is predominantly expressed in the adult nervous system with a neuronal expression pattern, and is strongly upregulated during postnatal development. The protein shares homology with rat glutamate-binding protein (GBP), Drosophila NMDARA1, and C. elegans genes, suggesting membership in a conserved gene family.\",\n      \"method\": \"RAP-PCR differential display, Northern blot, in situ hybridization, database comparisons\",\n      \"journal\": \"Molecular and cellular neurosciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct expression profiling with in situ hybridization and protein characterization, single lab but multiple methods\",\n      \"pmids\": [\"9698393\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"NMP35/Lifeguard (FAIM2) protein localizes to dendrites and postsynaptic membranes in the adult CNS, colocalizing with the glutamate receptor GluR2 and adjacent to the presynaptic vesicle protein synaptophysin. Immunoelectron microscopy confirmed postsynaptic membrane and density localization.\",\n      \"method\": \"Immunofluorescence confocal microscopy, immunoelectron microscopy, subcellular fractionation with affinity-purified antibodies\",\n      \"journal\": \"Brain research. Molecular brain research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct subcellular localization by both immunofluorescence and immunoelectron microscopy, two orthogonal methods in one study\",\n      \"pmids\": [\"12414123\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"LFG/NMP35 (FAIM2) expression in cerebellar granule neurons (CGNs) is regulated by the PI3-kinase/Akt/PKB signaling pathway. Inhibition of PI3-kinase or dominant-negative Akt reduced LFG reporter activity, while constitutively active Akt increased it. Knockdown of LFG by antisense oligonucleotides or siRNA sensitized CGNs to FasL-induced caspase-8 cleavage and cell death. LFG gene transfer into FasL-sensitive glioma cells conferred protection.\",\n      \"method\": \"siRNA/antisense knockdown, reporter assay, dominant-negative and constitutively active Akt constructs, pharmacological PI3-kinase inhibition, caspase-8 cleavage assay\",\n      \"journal\": \"The Journal of neuroscience : the official journal of the Society for Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (siRNA, dominant-negative constructs, reporter assay, pharmacological inhibition) establishing PI3K/Akt regulation of FAIM2 and its functional role in FasL resistance\",\n      \"pmids\": [\"16033886\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Bioinformatic analysis predicts LFG (FAIM2) resides in cellular membranes including the ER and plasma membrane, with seven transmembrane spanners and a small cytoplasmic domain. The UPF0005 consensus motif is found in the C-terminus, and the structure resembles Bax Inhibitor-1 (BI-1). Bax was found to co-immunoprecipitate with LFG.\",\n      \"method\": \"Bioinformatic sequence analysis, co-immunoprecipitation (Bax-LFG interaction)\",\n      \"journal\": \"International journal of molecular medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP for Bax interaction, structural predictions are computational; limited experimental validation\",\n      \"pmids\": [\"16964429\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Lifeguard (FAIM2) is an endogenous inhibitor of FasL-mediated neuronal death independent of FLICE inhibitory protein (FLIP). Overexpression of LFG protected cortical neurons from FasL-induced apoptosis and decreased caspase activation. siRNA knockdown sensitized cerebellar granular and cortical neurons to FasL-induced death and caspase-8 activation. LFG was detected in lipid raft microdomains where it may interact with Fas receptor.\",\n      \"method\": \"siRNA knockdown, overexpression, caspase activity assay, lipid raft fractionation\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal loss-of-function and gain-of-function experiments, caspase-8 assays, lipid raft localization, multiple neuronal cell types\",\n      \"pmids\": [\"17635665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Faim2-deficient mice showed increased susceptibility to oxygen-glucose deprivation in primary neurons in vitro and increased caspase-associated cell death, stroke volume, and neurological impairment after cerebral ischemia in vivo. Lentiviral Faim2 gene transfer rescued these effects, demonstrating Faim2 is neuroprotective in cerebral ischemia.\",\n      \"method\": \"Faim2 knockout mouse, middle cerebral artery occlusion model, oxygen-glucose deprivation, caspase assay, lentiviral gene transfer rescue\",\n      \"journal\": \"The Journal of neuroscience : the official journal of the Society for Neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with rescue by lentiviral gene transfer, both in vitro and in vivo models, caspase mechanistic readout\",\n      \"pmids\": [\"21209208\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"LFG (FAIM2) is required for survival and maintenance of Purkinje cells and granular cells in the cerebellum. Mice with reduced LFG expression (shRNA lentiviral transgenesis) or LFG null mice showed reduced cerebellar size, decreased internal granular layer thickness, and abnormal Purkinje cell morphology with increased active caspase-8 and caspase-3. Biochemical analysis showed LFG inhibits Fas-mediated cell death by interfering with caspase-8 activation.\",\n      \"method\": \"shRNA lentiviral transgenesis, LFG knockout mice, immunostaining for active caspase-8 and caspase-3, organotypic cerebellar culture\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic loss-of-function (shRNA transgenic + KO), specific cellular phenotype, mechanistic caspase-8 readout, in vivo and in vitro validation\",\n      \"pmids\": [\"21957071\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Faim2 expression in 661W photoreceptor-like cells is upregulated following Fas receptor activation and is regulated by ERK signaling. Pharmacological inhibition of ERK reduced Faim2 levels and increased susceptibility to Fas-induced caspase activation and apoptosis. siRNA knockdown of Faim2 resulted in earlier and more robust caspase activation and increased cell death after Fas antibody treatment.\",\n      \"method\": \"Pharmacological ERK pathway inhibition, siRNA knockdown, Fas-activating antibody treatment, caspase activity assay, Western blot\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown and pharmacological inhibition with caspase readouts, single lab, two orthogonal methods\",\n      \"pmids\": [\"23029562\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Lifeguard (FAIM2) localizes primarily to the endoplasmic reticulum and Golgi apparatus in murine cortical neurons (confirmed by subcellular fractionation). LFG interacts with Bcl-XL and Bcl-2 (but not Bax or Bak) by co-immunoprecipitation, likely at the ER. LFG protects only type II apoptotic cells from FasL-induced death in a Bcl-XL-dependent manner. LFG inhibits calcium release from the ER following FasL stimulation, which correlates with blockage of cytochrome c release and caspase activation.\",\n      \"method\": \"Subcellular fractionation, co-immunoprecipitation, calcium mobilization assay, cytochrome c release assay, caspase assay, overexpression and siRNA experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal methods: subcellular fractionation confirming ER/Golgi localization, reciprocal Co-IP for Bcl-XL/Bcl-2 interaction, functional calcium release assay, cytochrome c release, caspase activation all in one study\",\n      \"pmids\": [\"26582200\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Lifeguard (FAIM2) inhibits Fas-mediated apoptosis downstream of Fas trimerization by inhibiting caspase-8 activation in triple-negative breast cancer (MDA-MB-231) cells. Knockdown of Lifeguard via shRNA increased cisplatin efficacy, increased caspase-8 activity, and increased sensitivity to FasL-mediated cell death.\",\n      \"method\": \"shRNA knockdown, caspase-8 activity assay, cell viability assay, FasL treatment\",\n      \"journal\": \"Biomedicine & pharmacotherapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — shRNA knockdown with specific caspase-8 mechanistic readout, single lab, two orthogonal functional assays\",\n      \"pmids\": [\"26796280\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"TRIM21 negatively modulates LFG (FAIM2) at the protein level in MDA-MB-231 breast cancer cells. TRIM21-LFG interaction was demonstrated by co-immunoprecipitation. Addition of TRIM21 decreased LFG protein levels and was associated with decreased Fas-induced apoptosis.\",\n      \"method\": \"Protein array screen, co-immunoprecipitation, Western blot, RT-PCR, flow cytometry apoptosis assay\",\n      \"journal\": \"International journal of oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single Co-IP, protein array finding confirmed by Western blot, apoptosis assay, single lab\",\n      \"pmids\": [\"26398169\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"LFG (FAIM2) expression is regulated by the Akt/LEF-1 transcriptional pathway in breast cancer cells. GSK3β inhibition stabilizes β-catenin which associates with LEF-1 to drive LFG transcription. siRNA knockdown of LEF-1 reduced LFG mRNA levels in MDA-MB-231 cells.\",\n      \"method\": \"siRNA knockdown of LEF-1, Western blot, RT-PCR\",\n      \"journal\": \"Apoptosis : an international journal on programmed cell death\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with mRNA readout, Western blot, single lab, two methods\",\n      \"pmids\": [\"20336373\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"MYCN directly represses LFG (FAIM2) expression at the transcriptional level in neuroblastoma. LFG repression in neuroblastoma cells reduced cell adhesion, increased sphere growth, and enhanced migration, conferring higher metastatic capacity, independent of its anti-apoptotic function.\",\n      \"method\": \"Expression analysis in human NBL datasets, ChIP (MYCN binding), siRNA knockdown, cell adhesion and migration assays, sphere formation assay\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP for direct transcriptional repression, functional assays with siRNA, single lab\",\n      \"pmids\": [\"25188511\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Faim2-deficient mice showed significantly increased loss of dopaminergic neurons and fibers in the MPTP model of Parkinson disease compared to controls. Faim2 expression in mouse midbrain was decreased after MPTP administration, suggesting Fas-induced apoptosis contributes to dopaminergic cell death.\",\n      \"method\": \"Faim2 knockout mouse, MPTP administration, stereological counting of dopaminergic neurons, dopaminergic fiber density measurement, qRT-PCR\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with in vivo stereological quantification, single lab, single method for pathway placement\",\n      \"pmids\": [\"27638043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Faim2 upregulation contributes to the neuroprotective effects of low-dose erythropoietin (EPO) in transient brain ischemia. Low-dose EPO increased Faim2 expression and reduced stroke volume in wild-type mice, but failed to significantly reduce stroke volume in Faim2-deficient mice, placing Faim2 downstream of the EPO/PI3K/Akt signaling pathway in neuroprotection.\",\n      \"method\": \"Faim2 knockout mouse, middle cerebral artery occlusion, EPO administration, qRT-PCR, infarct volume measurement\",\n      \"journal\": \"Journal of neurochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis using KO mouse showing Faim2 is required for EPO neuroprotection, single lab\",\n      \"pmids\": [\"29315561\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"FAIM2 (TMBIM-2) and GRINA (TMBIM-3) are both neuroprotective in transient brain ischemia and are regulated by EPO. Double-deficient mice (GRINA-/-FAIM2-/-) showed the largest infarct sizes and worst neurological deficits. FAIM2 deficiency led to upregulation of cleaved-caspase 3, pro-apoptotic BAX mRNA, and caspase-8 (not caspase-9). EPO upregulated FAIM2 and GRINA mRNA in wildtype mice.\",\n      \"method\": \"GRINA/FAIM2 single and double knockout mice, tMCAo model, OGD in primary neurons, overexpression by transfection, caspase and BAX mRNA analysis\",\n      \"journal\": \"Experimental neurology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — double-KO genetic epistasis, multiple caspase mechanistic readouts, in vivo and in vitro validation, EPO regulation confirmed\",\n      \"pmids\": [\"31211943\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FAIM2 is targeted for degradation by TRIM21, an E3 ubiquitin ligase that is itself a DUX4 target gene; DUX4 expression reduces cellular FAIM2 levels through TRIM21. Inhibition of miR-3202 (which targets FAIM2) upregulates FAIM2. FAIM2 is required for myoblast differentiation into myotubes; FAIM2 knockdown causes increased apoptosis and failure to differentiate. FAIM2 overexpression rescued DUX4-induced cell death and myogenic differentiation defects.\",\n      \"method\": \"miR inhibitor screen, siRNA knockdown of FAIM2, FAIM2 overexpression, DUX4 overexpression, TRIM21 knockdown, differentiation assay, apoptosis assay\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — mechanistic screen followed by multiple orthogonal methods establishing TRIM21-mediated FAIM2 degradation, rescue experiments, myogenic differentiation phenotype with specific KD and OE\",\n      \"pmids\": [\"35468884\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TMBIM-2 (FAIM2 ortholog in C. elegans, XBX-6/TMBIM-2) mediates neuronal mitochondrial stress-triggered spatiotemporal Ca2+ oscillations through the Ca2+ efflux pump MCA-3, facilitating serotonin release from ADF neurons and activation of the neuronal-to-intestinal mitochondrial unfolded protein response (UPRmt). TMBIM-2 overexpression counteracted age-related decline in aversive learning and extended lifespan.\",\n      \"method\": \"C. elegans genetics, calcium imaging, serotonin release assay, UPRmt reporter, lifespan assay, TMBIM-2 overexpression\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — rigorous C. elegans ortholog study with calcium imaging and genetic epistasis, but C. elegans ortholog, not direct human/mammalian FAIM2\",\n      \"pmids\": [\"40100072\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"αA-crystallin (HSPB4) interacts with FAIM2 in the retina following retinal detachment, as demonstrated by co-immunoprecipitation. Phosphorylation of αA-crystallin at T148 is important for this interaction and for their combined neuroprotective effect on photoreceptors. FAIM2 is induced following retinal detachment.\",\n      \"method\": \"Co-immunoprecipitation (FAIM2-αA-crystallin), phospho-mutant analysis, TUNEL staining, immunohistochemistry, immunoblotting\",\n      \"journal\": \"Neurology international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP for interaction, phospho-mutant for mechanistic insight, single lab, multiple methods\",\n      \"pmids\": [\"39311341\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In bacterial meningitis model, Faim2 deficiency leads to increased caspase-associated hippocampal apoptotic cell death and increased ERK activation during acute infection. After antibiotic rescue, Faim2 deficiency paradoxically led to increased hippocampal neurogenesis and improved spatial learning and memory performance.\",\n      \"method\": \"Faim2 knockout mouse, Streptococcus pneumoniae subarachnoid infection, caspase immunostaining, ERK immunostaining, Morris water maze\",\n      \"journal\": \"Journal of neuropathology and experimental neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with specific caspase and ERK mechanistic readouts in disease model, single lab\",\n      \"pmids\": [\"24335530\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"FAIM2 promotes NSCLC cell proliferation, migration, and invasion and inhibits apoptosis by activating the Wnt/β-catenin signaling pathway and facilitating EMT. FAIM2 knockdown in HARA-B4 cells reduced these activities and enhanced osteocyte adhesion. In vivo, FAIM2 participated in regulating NSCLC bone metastasis.\",\n      \"method\": \"FAIM2 overexpression and siRNA knockdown, proliferation/migration/invasion assays, Wnt/β-catenin pathway analysis, EMT marker analysis, in vivo bone metastasis model\",\n      \"journal\": \"Frontiers in oncology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — functional overexpression/knockdown assays with pathway analysis, but no direct mechanistic demonstration of how FAIM2 activates Wnt/β-catenin, single lab\",\n      \"pmids\": [\"34568020\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"LFG KO T cells show increased cell death during the initial phase of anti-viral immune response (LCMV infection), resulting in decreased numbers of activated CD8 and CD4 T cells and LCMV-specific memory T cells. LFG KO and WT T cells were equally sensitive to Fas antibody Jo-2 ex vivo, and blocking extrinsic death pathways (FasL or caspase-8 inhibitors) did not rescue the LFG KO phenotype in vivo, suggesting LFG protects T cells via a Fas-independent mechanism during early immune response.\",\n      \"method\": \"LFG knockout bone marrow chimeras, LCMV infection, T cell proliferation assay, ex vivo FasL/caspase-8 inhibitor treatment, cell death assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO in immune model with specific mechanistic controls (FasL and caspase-8 inhibitors tested), single lab\",\n      \"pmids\": [\"26565411\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The rs7132908 obesity risk allele within the 3' UTR of FAIM2 has allele-specific cis-regulatory activity demonstrated by luciferase reporter assay. In isogenic hESC lines differentiated to hypothalamic neurons, the risk allele influenced FAIM2 expression, decreased the proportion of neurons produced, upregulated cell death gene sets, and downregulated neuron differentiation gene sets.\",\n      \"method\": \"Luciferase reporter assay, CRISPR-Cas9 homology-directed repair to generate isogenic hESC lines, RNA-seq during hypothalamic neuron differentiation, 3D genomic data\",\n      \"journal\": \"Cell genomics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — isogenic CRISPR lines plus luciferase reporter assay plus transcriptomics during differentiation, multiple orthogonal methods, published peer-reviewed\",\n      \"pmids\": [\"38697123\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"FAIM2 (Lifeguard/NMP35/LFG) is an evolutionarily conserved multi-pass transmembrane protein localizing primarily to the endoplasmic reticulum (and lipid rafts), where it inhibits Fas/CD95-mediated apoptosis by blocking caspase-8 activation and suppressing ER calcium release required for cytochrome c release and downstream caspase activation; it interacts directly with the Fas receptor, with Bcl-XL/Bcl-2 at the ER, and with αA-crystallin, and is regulated transcriptionally by the PI3K/Akt/LEF-1 pathway and post-translationally by TRIM21-mediated degradation, while playing essential roles in neuronal survival (cerebellum, ischemia, Parkinson models), T cell memory maintenance, myoblast differentiation, and hypothalamic neurodevelopment.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"FAIM2 (Lifeguard/NMP35/LFG) is an evolutionarily conserved multi-pass membrane protein that acts as a selective endogenous inhibitor of Fas/CD95-mediated apoptosis and a determinant of neuronal survival [#0, #5, #7]. Originally identified in a genetic screen as protecting cells from Fas- but not TNF-alpha-mediated death, it binds the Fas receptor without altering Fas expression, agonist binding, or FADD recruitment [#0], and instead blocks apoptosis downstream of Fas trimerization by suppressing caspase-8 activation [#7, #10]. It localizes predominantly to the endoplasmic reticulum and Golgi and to lipid raft microdomains, where it interacts with the anti-apoptotic proteins Bcl-XL and Bcl-2 and protects type II apoptotic cells in a Bcl-XL-dependent manner by inhibiting ER calcium release, thereby blocking cytochrome c release and downstream caspase activation [#5, #9]. FAIM2 expression is controlled transcriptionally by the PI3K/Akt pathway acting through LEF-1/beta-catenin [#3, #12] and is regulated post-translationally by TRIM21-mediated degradation [#11, #17]. Functionally, FAIM2 is neuroprotective: its loss sensitizes neurons to caspase-driven death and worsens injury in cerebral ischemia, Parkinson-model dopaminergic loss, and cerebellar Purkinje/granule cell maintenance, where it acts downstream of erythropoietin/PI3K/Akt signaling alongside the related TMBIM protein GRINA [#6, #7, #14, #16]. Beyond neurons, FAIM2 supports T-cell survival during early anti-viral responses through a Fas-independent mechanism [#22], is required for myoblast differentiation [#17], and a 3'-UTR obesity risk variant alters its expression and biases hypothalamic neuron differentiation toward cell death [#23].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Established FAIM2 as a nervous-system-enriched membrane protein of a conserved gene family before its function was known, defining its expression domain.\",\n      \"evidence\": \"RAP-PCR differential display, Northern blot, and in situ hybridization in adult rodent nervous tissue\",\n      \"pmids\": [\"9698393\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No molecular function assigned at this stage\", \"Homology to glutamate-binding proteins not functionally validated\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Defined the core anti-apoptotic activity: FAIM2 protects selectively against Fas-mediated death and binds Fas without blocking the canonical DISC assembly steps, indicating a non-canonical inhibitory mechanism.\",\n      \"evidence\": \"Genetic screen plus co-immunoprecipitation and cell-based apoptosis assays with mechanistic controls (Fas expression, agonist binding, FADD recruitment)\",\n      \"pmids\": [\"10535980\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of caspase-8 suppression not resolved\", \"Subcellular site of action undefined\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Localized FAIM2 to postsynaptic membranes and densities, linking the survival protein to synaptic neuronal compartments.\",\n      \"evidence\": \"Immunofluorescence and immunoelectron microscopy with subcellular fractionation in adult CNS\",\n      \"pmids\": [\"12414123\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of synaptic localization unknown\", \"Relationship to apoptotic protection not addressed\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Connected FAIM2 expression to PI3K/Akt survival signaling and demonstrated it is functionally required to resist FasL-induced caspase-8 cleavage in neurons.\",\n      \"evidence\": \"Reporter assays, dominant-negative/constitutively active Akt, PI3K inhibition, siRNA/antisense knockdown, and gene transfer in cerebellar granule neurons and glioma cells\",\n      \"pmids\": [\"16033886\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct transcription factor downstream of Akt not yet identified\", \"Biochemical target of FAIM2 unresolved\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Showed FAIM2 acts independently of FLIP and localizes to lipid rafts, establishing it as a distinct, FLIP-independent endogenous Fas inhibitor in neurons.\",\n      \"evidence\": \"Reciprocal overexpression/siRNA, caspase activity assays, and lipid raft fractionation in cortical and cerebellar neurons\",\n      \"pmids\": [\"17635665\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct partners in rafts not defined\", \"Stoichiometry with Fas unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identified the Akt/GSK3beta/beta-catenin/LEF-1 axis as the transcriptional route driving FAIM2 expression, mechanistically linking survival signaling to FAIM2 levels.\",\n      \"evidence\": \"LEF-1 siRNA knockdown with mRNA and Western readouts in MDA-MB-231 cells\",\n      \"pmids\": [\"20336373\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct LEF-1 binding site on FAIM2 promoter not mapped\", \"Single cell line\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Provided in vivo genetic proof that FAIM2 is neuroprotective, with knockout worsening ischemic injury and cerebellar neuron loss, both rescuable and tied to caspase-8 activation.\",\n      \"evidence\": \"Faim2 knockout and shRNA-transgenic mice, MCAO and oxygen-glucose deprivation, lentiviral rescue, active caspase-8/3 immunostaining\",\n      \"pmids\": [\"21209208\", \"21957071\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise biochemical step blocking caspase-8 unresolved\", \"Cell-type-specific requirements not dissected\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Extended FAIM2 regulation and function beyond neuronal survival, showing ERK-dependent induction in photoreceptors, MYCN-mediated repression in neuroblastoma, and an apoptosis-independent role in cell adhesion/migration.\",\n      \"evidence\": \"ERK inhibition and siRNA in 661W cells; ChIP, siRNA, adhesion/migration/sphere assays in neuroblastoma; KO meningitis model with caspase/ERK readouts\",\n      \"pmids\": [\"23029562\", \"25188511\", \"24335530\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of adhesion/migration control independent of apoptosis unknown\", \"Paradoxical neurogenesis benefit of FAIM2 loss unexplained\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Resolved the subcellular mechanism: FAIM2 at the ER/Golgi interacts with Bcl-XL/Bcl-2 and inhibits FasL-triggered ER calcium release to block cytochrome c release, defining a type II, Bcl-XL-dependent mode of protection.\",\n      \"evidence\": \"Subcellular fractionation, reciprocal Co-IP, calcium mobilization, cytochrome c release and caspase assays in cortical neurons; shRNA in breast cancer cells; T-cell KO chimeras with Fas/caspase-8 inhibitor controls\",\n      \"pmids\": [\"26582200\", \"26796280\", \"26565411\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism of calcium-channel regulation unknown\", \"Fas-independent T-cell survival mechanism unidentified\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified TRIM21 as a post-translational regulator that lowers FAIM2 protein and reduces Fas-induced apoptosis, adding a degradation layer to FAIM2 control.\",\n      \"evidence\": \"Protein array screen, Co-IP, Western blot, and apoptosis assays in breast cancer cells\",\n      \"pmids\": [\"26398169\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ubiquitination of FAIM2 by TRIM21 not demonstrated\", \"Single Co-IP without reciprocal validation\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Placed FAIM2 genetically downstream of erythropoietin/PI3K/Akt neuroprotection and, with GRINA, in a shared TMBIM neuroprotective module against ischemia.\",\n      \"evidence\": \"EPO administration in Faim2 KO and GRINA/FAIM2 single/double KO mice, tMCAo, OGD, caspase-8/BAX readouts\",\n      \"pmids\": [\"29315561\", \"31211943\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How EPO signaling induces FAIM2 transcription mechanistically unclear\", \"Functional redundancy with GRINA at the molecular level undefined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrated a DUX4/TRIM21/miR-3202 regulatory circuit controlling FAIM2 and established FAIM2 as required for myoblast differentiation, broadening its role to muscle.\",\n      \"evidence\": \"miR inhibitor screen, siRNA/overexpression, DUX4 and TRIM21 manipulation, differentiation and apoptosis assays with rescue\",\n      \"pmids\": [\"35468884\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether differentiation role is separable from anti-apoptotic role unclear\", \"Direct TRIM21 ubiquitination of FAIM2 still not shown biochemically\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identified new contexts and partners: alphaA-crystallin interacts with FAIM2 in retina with a phospho-dependent neuroprotective effect, and an obesity-risk 3'-UTR variant alters FAIM2 expression to bias hypothalamic neurogenesis toward cell death.\",\n      \"evidence\": \"Co-IP and phospho-mutant analysis in retinal detachment; luciferase reporter, CRISPR isogenic hESC lines, and RNA-seq during hypothalamic differentiation\",\n      \"pmids\": [\"39311341\", \"38697123\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of alphaA-crystallin interaction at molecular level unclear\", \"How FAIM2 dosage controls neuron differentiation gene programs unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Used the C. elegans ortholog to reveal an ancient role in mitochondrial-stress-triggered calcium oscillations driving serotonergic signaling and the mitochondrial UPR, linking FAIM2/TMBIM-2 calcium control to lifespan and learning.\",\n      \"evidence\": \"C. elegans genetics, calcium imaging, serotonin release and UPRmt reporters, lifespan and overexpression assays\",\n      \"pmids\": [\"40100072\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"C. elegans ortholog, not directly demonstrated for mammalian FAIM2\", \"Mechanistic link from calcium oscillation to apoptosis suppression in mammals not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The precise biochemical mechanism by which FAIM2 suppresses caspase-8 activation and regulates ER calcium fluxes—and how its anti-apoptotic and apoptosis-independent (adhesion, differentiation, calcium-signaling) functions are molecularly distinguished—remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of FAIM2 in complex with Fas or Bcl-XL\", \"No direct biochemical demonstration of FAIM2 calcium-channel modulation\", \"Substrate/effector basis of the Fas-independent survival functions undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 5, 7, 9, 10]},\n      {\"term_id\": \"GO:0140313\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [4, 9]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [4, 5]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": []}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [0, 5, 7, 9, 10]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 12, 15]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"FAS\", \"BCL2L1\", \"BCL2\", \"BAX\", \"TRIM21\", \"CRYAA\", \"GRINA\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}