{"gene":"RMDN3","run_date":"2026-06-10T06:43:37","timeline":{"discoveries":[{"year":2011,"finding":"PTPIP51 (outer mitochondrial membrane protein) directly interacts with the ER-resident protein VAPB, and this interaction is required for normal mitochondrial Ca2+ uptake following release from ER stores. VAPB is a MAM (mitochondria-associated membrane) protein, and loss of either VAPB or PTPIP51 perturbs Ca2+ homeostasis. The ALS-linked VAPBP56S mutant shows altered binding to PTPIP51 and dysregulated Ca2+ uptake.","method":"Co-immunoprecipitation, siRNA knockdown, mitochondrial Ca2+ uptake assays, subcellular fractionation (MAM isolation)","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, siRNA loss-of-function with defined Ca2+ phenotype, replicated in multiple subsequent studies","pmids":["22131369"],"is_preprint":false},{"year":2014,"finding":"VAPB-PTPIP51 interaction tethers ER to mitochondria. TDP-43 (ALS/FTD-linked) disrupts this interaction and ER-mitochondria associations, perturbing Ca2+ homeostasis. TDP-43 overexpression activates GSK-3β, and GSK-3β regulates the VAPB-PTPIP51 interaction, placing GSK-3β as an upstream negative regulator of the tether.","method":"Co-immunoprecipitation, electron microscopy (ER-mitochondria contact quantification), Ca2+ imaging, GSK-3β kinase activity assays, siRNA","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (Co-IP, EM, Ca2+ assay, kinase assay), replicated in subsequent studies","pmids":["24893131"],"is_preprint":false},{"year":2016,"finding":"ALS/FTD-associated FUS disrupts the VAPB-PTPIP51 interaction and ER-mitochondria associations, leading to impaired mitochondrial Ca2+ uptake and reduced mitochondrial ATP production. FUS activates GSK-3β, which mediates these disruptions, consistent with a shared GSK-3β-dependent mechanism for ALS/FTD insults on the VAPB-PTPIP51 tether.","method":"Co-immunoprecipitation, electron microscopy, mitochondrial Ca2+ and ATP assays, GSK-3β inhibitor experiments","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods, consistent mechanistic pathway established across independent disease models","pmids":["27418313"],"is_preprint":false},{"year":2017,"finding":"The VAPB-PTPIP51 ER-mitochondria tethers regulate autophagy. Overexpression of VAPB or PTPIP51 (tightening contacts) impairs autophagosome formation, while siRNA-mediated knockdown (loosening contacts) stimulates it. An artificial ER-mitochondria linker rescues the effects of VAPB/PTPIP51 siRNA on autophagy, demonstrating that this is a direct consequence of tethering. The mechanism involves Ca2+ delivery from ER to mitochondria.","method":"siRNA knockdown, VAPB/PTPIP51 overexpression, synthetic ER-mitochondria linker rescue, autophagosome quantification (fluorescence microscopy), Ca2+ measurements","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis via synthetic linker rescue, multiple orthogonal methods, single lab with rigorous controls","pmids":["28132811"],"is_preprint":false},{"year":2017,"finding":"PTPIP51 regulates mitochondria-sarcoplasmic reticulum (SR) contact in cardiomyocytes. Overexpression of PTPIP51 increases mitochondria-SR contacts and elevates mitochondrial Ca2+ uptake via the mitochondrial Ca2+ uniporter (MCU). Cardiac-specific knockdown of PTPIP51 reduces myocardial infarct size and injury after ischemia/reperfusion. MCU inhibition/knockdown reverses PTPIP51-mediated mitochondrial Ca2+ increase and cardiomyocyte apoptosis.","method":"Adenovirus-mediated overexpression, cardiac-specific knockdown, electron microscopy (contact quantification), mitochondrial Ca2+ assays, MCU inhibitor/siRNA epistasis, infarct size measurement","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods, in vivo cardiac knockout with functional phenotype, MCU epistasis","pmids":["28345618"],"is_preprint":false},{"year":2019,"finding":"VAPB and PTPIP51 localize to neuronal synapses and form contacts there. Stimulating neuronal activity increases ER-mitochondria contacts and the VAPB-PTPIP51 interaction. siRNA loss of VAPB or PTPIP51 perturbs synaptic function and dendritic spine morphology, demonstrating a role for the tether in synaptic activity.","method":"Immunofluorescence co-localization, proximity ligation assay, live-cell Ca2+ imaging upon neuronal stimulation, siRNA knockdown with synaptic activity and spine morphology readouts","journal":"Acta neuropathologica communications","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods, siRNA with defined synaptic phenotype, neuronal activity-induced interaction changes","pmids":["30841933"],"is_preprint":false},{"year":2021,"finding":"Crystal structure of the TPR domain of PTPIP51 reveals an archetypal TPR fold with a lipid-like molecule in the binding pocket. PTPIP51 binds and transfers phospholipids, particularly phosphatidic acid (PA), in vitro. Depletion of PTPIP51 reduces mitochondrial cardiolipin levels. The PTPIP51-VAPB interaction is mediated by an FFAT-like motif in PTPIP51 and the MSP domain of VAPB.","method":"X-ray crystallography (TPR domain structure), in vitro phospholipid binding/transfer assays, siRNA knockdown with cardiolipin measurement, mutational analysis of FFAT-like motif and MSP domain","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure, in vitro reconstitution of lipid transfer, mutagenesis of interaction motifs, multiple orthogonal methods in one study","pmids":["33938112"],"is_preprint":false},{"year":2022,"finding":"The coiled-coil domain of PTPIP51 (not the FFAT motif alone) is essential for VAPB binding in the context of full-length proteins in cells, for formation of ER-mitochondria contacts, and for IP3 receptor-mediated delivery of Ca2+ from ER to mitochondria. Deletion of the FFAT motif had little effect on VAPB binding, while mutation/deletion of the coiled-coil domain markedly reduced binding and abrogated tethering and Ca2+ transfer functions.","method":"Immunoprecipitation from transfected cells with deletion/mutation constructs, electron microscopy (ER-mitochondria contact quantification), IP3R-mediated Ca2+ delivery assays","journal":"Frontiers in cell and developmental biology","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — mutagenesis with multiple orthogonal functional readouts (Co-IP, EM, Ca2+ assay), single lab","pmids":["36120587"],"is_preprint":false},{"year":2022,"finding":"The mitochondrial E3 ubiquitin ligase MITOL/MARCH5 interacts with and ubiquitinates RMDN3/PTPIP51 at lysine residue 89. Loss of MITOL or K89R substitution in RMDN3 significantly reduces its phosphatidic acid (PA)-binding activity, indicating that MITOL-mediated ubiquitination activates RMDN3 PA-transfer activity at the mitochondria-ER contact site.","method":"Proximity-dependent biotin labeling (APEX2), Co-IP, site-directed mutagenesis (K89R), in vitro PA-binding assay","journal":"Journal of biochemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — identification of ubiquitination site by mutagenesis, in vitro functional assay, multiple methods in single study","pmids":["34964862"],"is_preprint":false},{"year":2025,"finding":"Mitochondrial ROS increases MERC (mitochondria-ER contact) formation via RMDN3-VAPB tethering driven by RMDN3 phosphorylation. RMDN3 transfers lipid radicals from mitochondria to the ER via its TPR domain (demonstrated by in vitro liposome assay). Disruption of RMDN3-VAPB tethering causes lipid radical accumulation in mitochondria and cell death, defining a cell survival role for MERCs in lipid radical removal under mitochondrial damage.","method":"NanoBiT/MERBiT split-luciferase system for live-cell MERC measurement, in vitro liposome lipid radical transfer assay, RMDN3 phosphorylation analysis, siRNA/genetic disruption with lipid radical and cell death readouts","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — novel live-cell MERC assay, in vitro reconstitution of lipid radical transfer, multiple orthogonal methods, single study","pmids":["39929810"],"is_preprint":false},{"year":2006,"finding":"PTPIP51 is a mitochondrial protein requiring its N-terminal transmembrane (TM) domain for mitochondrial targeting. Overexpression induces apoptosis via decrease in mitochondrial membrane potential, cytochrome c release, caspase-3 activation, PARP cleavage, and phosphatidylserine externalization. Deletion of the TM domain prevents mitochondrial localization and abrogates apoptosis-inducing function.","method":"GFP-fusion subcellular localization, deletion mutant analysis, mitochondrial membrane potential assay (JC-1), cytochrome c release assay, caspase-3 and PARP cleavage, Annexin V staining","journal":"Apoptosis : an international journal on programmed cell death","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — deletion mutagenesis linking TM domain to localization and apoptosis, multiple downstream readouts, single lab","pmids":["16820967"],"is_preprint":false},{"year":2008,"finding":"PTPIP51 regulates cell morphology and motility via the Raf-MEK-ERK cascade. It interacts with Raf-1 through 14-3-3 scaffold proteins and activates ERK; this is blocked by MEK inhibitor or dominant-negative Raf-1 but not dominant-negative Ras. Two redundant 14-3-3-binding domains in PTPIP51 were identified by deletion/mutation analysis.","method":"Overexpression/siRNA knockdown with migration/adhesion assays, MEK inhibitor and dominant-negative Raf-1/Ras epistasis, Co-IP for Raf-1/14-3-3 interaction, deletion/mutation analysis of 14-3-3-binding domains","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis with dominant-negative constructs and pharmacological inhibitors, Co-IP, deletion mapping, single lab","pmids":["18771726"],"is_preprint":false},{"year":2012,"finding":"Tyrosine 176 phosphorylation of PTPIP51 by c-Src regulates its interaction with 14-3-3β and Raf-1. Increased phosphorylation at Y176 causes a sharp drop in PTPIP51-14-3-3β and 14-3-3β-Raf-1 interactions. Phosphorylation status also regulates PTPIP51 interactions with DAGKα and PKA.","method":"Pharmacological modulation of c-Src activity and PTP1B phosphatase inhibition in HaCaT keratinocytes, proximity ligation assay (Duolink) for protein interactions, confocal microscopy","journal":"Cell biochemistry and biophysics","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — proximity ligation assay for in situ interactions, phosphorylation manipulation, multiple interaction partners tested, single lab","pmids":["22544307"],"is_preprint":false},{"year":2012,"finding":"PTPIP51 interacts with CGI-99 and Nuf2 in vitro and in vivo, and the PTPIP51/CGI-99 and PTPIP51/Nuf-2 complexes localize to the equatorial region during mitosis. PTPIP51 associates with the microtubular cytoskeleton and spindle apparatus. Phosphorylated PTPIP51 accumulates at spindle poles. During M/G1 transition, PTPIP51 interacts strongly with PTP1B, restoring PTPIP51-Raf-1 interaction that is depleted in mitotic cells.","method":"Proximity ligation assay (Duolink), confocal microscopy, cell synchronization with nocodazole","journal":"Biomolecules","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — proximity ligation assay for in situ interactions, cell cycle synchronization, multiple interaction partners, single lab","pmids":["24970130"],"is_preprint":false},{"year":2011,"finding":"PTPIP51 is phosphorylated at tyrosine 176 by Lyn and c-Src kinases in AML cells. In AML blasts, PTP1B (the cognate phosphatase for PTPIP51) is absent, preventing dephosphorylation. PTPIP51 interacts with c-Kit in AML cells, identifying it as a component of c-Kit signaling. The hyperphosphorylation prevents PTPIP51-Raf-1 interaction, contributing to increased MAPK-driven proliferation.","method":"Immunohistochemistry with peptide-specific antibodies, proximity ligation assay, confocal co-localization, immunoblot","journal":"Leukemia research","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — proximity ligation assay for in situ interactions, multiple disease context validations, single lab","pmids":["21513978"],"is_preprint":false},{"year":2025,"finding":"RHOA (small GTPase) binds to the ER protein VAPB and regulates complex formation between VAPB and mitochondrial PTPIP51, thereby tuning MERCS levels. RHOA knockdown or increased degradation via CUL3 overexpression reduces MERCS; RHOA upregulation increases MERCS. Disease alleles of RHOA, CUL3, and VAPB perturb this regulatory mechanism.","method":"Genome-wide CRISPRi screen, Co-IP (RHOA-VAPB binding), MERCS quantification upon RHOA/CUL3 manipulation, disease allele analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genome-wide unbiased screen with validation, Co-IP of RHOA-VAPB interaction, functional MERCS quantification, multiple genetic perturbations","pmids":["41392169"],"is_preprint":false},{"year":2022,"finding":"VAPB protein levels are reduced and VAPB-PTPIP51 tethers are disrupted in post-mortem spinal cord motor neurons from ALS patients, as quantified by proximity ligation assay, confirming that disruption of the tether occurs in human ALS tissue.","method":"Proximity ligation assay in post-mortem human spinal cord sections, immunoblotting for VAPB levels","journal":"Frontiers in cell and developmental biology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — proximity ligation assay in human post-mortem tissue, confirms disruption in disease context, single lab","pmids":["36051435"],"is_preprint":false},{"year":2024,"finding":"Overexpression of VAPB or PTPIP51 corrects mutant TDP43-induced damage to IP3 receptor delivery of Ca2+ to mitochondria and to synaptic function. UDCA (FDA-approved drug) corrects TDP43-linked damage to the VAPB-PTPIP51 interaction by inhibiting TDP43-mediated GSK3β activation, identifying GSK3β inhibition as the mechanism of UDCA action on this tether.","method":"VAPB/PTPIP51 overexpression rescue experiments, Ca2+ imaging, synaptic activity assays, UDCA pharmacological treatment, GSK3β activity assays","journal":"Acta neuropathologica communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — overexpression rescue of defined molecular phenotype, pharmacological epistasis, multiple functional readouts, single lab","pmids":["38395965"],"is_preprint":false},{"year":2022,"finding":"PTPIP51 interacts with PTEN to form a PTPIP51-PTEN-CK2 complex, which induces phosphorylation of PTEN at Thr382/383. This leads to ubiquitylation and lysosomal degradation of EGFR, thereby suppressing PI3K/Akt, RAS/RAF/ERK, and JAK/STAT3 downstream signaling in NSCLC cells.","method":"Co-immunoprecipitation, PTPIP51 overexpression and knockdown, EGFR ubiquitylation assay, lysosomal inhibitor experiments, downstream signaling (immunoblot), in vivo xenograft","journal":"Life sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP of complex, ubiquitylation assay, in vivo and in vitro functional readouts, single lab","pmids":["35240162"],"is_preprint":false},{"year":2015,"finding":"PTPIP51 is required for the differentiation of photoreceptors. Silencing of PTPIP51 in postnatal retinal explants severely impairs final differentiation of photoreceptors (decreased rhodopsin-positive cells), while PTPIP51 misexpression does not alter RPC commitment, indicating a specific role in terminal photoreceptor maturation.","method":"Ex vivo electroporation for siRNA knockdown and misexpression in postnatal rat retinal explants, immunostaining for rhodopsin and lineage markers","journal":"Neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — ex vivo loss-of-function with defined differentiation phenotype, single lab, single method","pmids":["25999297"],"is_preprint":false},{"year":2015,"finding":"PTPIP51 forms a complex with RelA and IκBα. RelA bound to the PTPIP51 promoter represses its mRNA and protein expression. TNFα modulates this PTPIP51/RelA/IκBα complex. Direct PTPIP51-RelA and PTPIP51-IκBα interactions were confirmed in situ.","method":"Promoter binding assay, proximity ligation assay (Duolink) for direct protein-protein interactions, immunofluorescence co-localization, PDTC/TNFα pharmacological manipulation","journal":"Biomolecules","confidence":"Low","confidence_rationale":"Tier 3 / Weak — proximity ligation assay for interactions, pharmacological modulation, single lab, single method per interaction","pmids":["25893721"],"is_preprint":false},{"year":2025,"finding":"Phosphorylation of α-synuclein at serine 129 increases VAPB-PTPIP51 interactions. α-syn interacts directly with PTPIP51, and this interaction is modulated by the phosphorylation state of α-syn at S129 (confirmed by Co-IP and molecular dynamics simulation).","method":"Co-immunoprecipitation, mass spectrometry, molecular dynamics simulation, Co-IP in Thy1-SNCA transgenic mouse brain","journal":"Acta neuropathologica communications","confidence":"Low","confidence_rationale":"Tier 3 / Weak — Co-IP with computational support, single study, no in vitro reconstitution of direct binding","pmids":["39994794"],"is_preprint":false}],"current_model":"RMDN3/PTPIP51 is an outer mitochondrial membrane protein that, together with the ER protein VAPB, forms a tethering complex at mitochondria-associated ER membranes (MAMs/MERCs); the interaction is mediated by a coiled-coil domain in PTPIP51 and the MSP domain of VAPB, and it facilitates IP3 receptor-mediated Ca2+ transfer from ER to mitochondria, phosphatidic acid and lipid radical transfer via its TPR domain, regulation of autophagy, synaptic activity, and mitochondrial ATP production. The tether is regulated by phosphorylation (RMDN3 phosphorylation enhances tethering under mitochondrial ROS), ubiquitination by MITOL/MARCH5 at K89 (activating its PA-binding activity), GSK-3β (which disrupts the interaction downstream of ALS/FTD insults such as TDP-43 and FUS), and RHOA (which binds VAPB to tune complex formation). PTPIP51 also acts as a scaffold in the MAPK pathway by interacting with Raf-1 through 14-3-3 proteins in a manner regulated by c-Src phosphorylation at Y176 and dephosphorylation by PTP1B, and it can interact with PTEN to promote EGFR lysosomal degradation."},"narrative":{"mechanistic_narrative":"RMDN3 (PTPIP51) is an outer mitochondrial membrane protein that physically tethers mitochondria to the endoplasmic reticulum by binding the ER protein VAPB, establishing mitochondria-associated ER membranes (MERCs/MAMs) that govern interorganelle Ca2+ and lipid exchange [PMID:22131369, PMID:33938112]. Mitochondrial targeting requires its N-terminal transmembrane domain [PMID:16820967], while the VAPB interaction is mediated principally by a coiled-coil domain in PTPIP51 acting together with an FFAT-like motif that engages the MSP domain of VAPB [PMID:33938112, PMID:36120587]. Through this tether, RMDN3 supports IP3 receptor-mediated transfer of Ca2+ from ER to mitochondria, and its loss or disruption perturbs mitochondrial Ca2+ uptake [PMID:22131369, PMID:36120587]. A crystallized TPR domain confers lipid binding and transfer activity: RMDN3 binds and transfers phosphatidic acid, contributes to mitochondrial cardiolipin content [PMID:33938112], and under mitochondrial ROS transfers lipid radicals from mitochondria to the ER, defining a survival function in removing damaging oxidized lipids [PMID:39929810]. The strength of tethering is set by post-translational regulation — RMDN3 phosphorylation enhances contact formation under oxidative stress [PMID:39929810], MITOL/MARCH5-mediated ubiquitination at K89 activates its PA-binding activity [PMID:34964862], and RHOA binding to VAPB tunes complex assembly [PMID:41392169]. Functionally, the tether constrains autophagosome formation [PMID:28132811], shapes mitochondria-SR contacts and Ca2+-dependent apoptosis in cardiomyocytes [PMID:28345618], and supports synaptic activity and dendritic spine morphology in neurons [PMID:30841933]. The tether is a convergence point for ALS/FTD pathology: TDP-43 and FUS disrupt the VAPB-PTPIP51 interaction through GSK-3β activation, and tether disruption is observed in ALS patient motor neurons [PMID:24893131, PMID:27418313, PMID:36051435]. Independently of its tethering role, PTPIP51 acts as a 14-3-3-dependent scaffold for Raf-1 in the MAPK cascade, regulated by c-Src phosphorylation at Y176 [PMID:18771726, PMID:22544307].","teleology":[{"year":2006,"claim":"Established that PTPIP51 is a mitochondrial protein whose localization depends on its N-terminal transmembrane domain and which can drive intrinsic apoptosis, anchoring its membrane topology before its tethering role was known.","evidence":"GFP-fusion localization and TM deletion mutants with mitochondrial membrane potential, cytochrome c, caspase-3 and Annexin V readouts","pmids":["16820967"],"confidence":"Medium","gaps":["Did not connect mitochondrial localization to ER contact sites","Apoptosis driven by overexpression; physiological relevance untested"]},{"year":2011,"claim":"Identified the direct PTPIP51-VAPB interaction and showed it is required for ER-to-mitochondria Ca2+ transfer, defining PTPIP51 as a MAM tethering partner.","evidence":"Reciprocal Co-IP, siRNA knockdown, mitochondrial Ca2+ uptake assays and MAM fractionation","pmids":["22131369"],"confidence":"High","gaps":["Interaction interface on PTPIP51 not yet mapped","Did not establish whether tethering is structural cause or correlate of Ca2+ defect"]},{"year":2011,"claim":"Showed PTPIP51 is tyrosine-176 phosphorylated by Lyn and c-Src and interacts with c-Kit in AML, defining a kinase-regulated signaling role distinct from tethering.","evidence":"IHC, proximity ligation assay and immunoblot in AML blasts lacking the cognate phosphatase PTP1B","pmids":["21513978"],"confidence":"Medium","gaps":["In situ interaction assays without biochemical reconstitution","Causal contribution to leukemic proliferation not directly tested"]},{"year":2008,"claim":"Defined PTPIP51 as a 14-3-3-dependent scaffold linking to Raf-1 and activating ERK to control cell morphology and motility, separate from its mitochondrial functions.","evidence":"Migration/adhesion assays, dominant-negative Raf-1/Ras and MEK inhibitor epistasis, Co-IP and deletion mapping of 14-3-3 sites","pmids":["18771726"],"confidence":"Medium","gaps":["Relationship between scaffold and tether pools of PTPIP51 unclear","Endogenous physiological setting not defined"]},{"year":2012,"claim":"Established that c-Src phosphorylation at Y176 and PTP1B dephosphorylation toggle PTPIP51's association with 14-3-3β and Raf-1, providing a switch controlling the MAPK scaffold.","evidence":"Pharmacological c-Src/PTP1B modulation with proximity ligation assays in keratinocytes","pmids":["22544307"],"confidence":"Medium","gaps":["No direct phosphosite mutagenesis in functional MAPK output","Interactions inferred from in situ proximity, not reconstituted"]},{"year":2014,"claim":"Showed the VAPB-PTPIP51 interaction physically tethers ER to mitochondria and that TDP-43 disrupts it via GSK-3β, placing the tether downstream of an ALS/FTD insult and identifying GSK-3β as an upstream negative regulator.","evidence":"Co-IP, EM contact quantification, Ca2+ imaging and GSK-3β kinase assays","pmids":["24893131"],"confidence":"High","gaps":["GSK-3β substrate site on the tether not identified","Whether GSK-3β acts on PTPIP51 or VAPB unresolved"]},{"year":2016,"claim":"Extended the GSK-3β-dependent tether-disruption mechanism to FUS, showing convergent ALS/FTD pathology on VAPB-PTPIP51 with impaired Ca2+ uptake and ATP production.","evidence":"Co-IP, EM, mitochondrial Ca2+/ATP assays and GSK-3β inhibitor experiments","pmids":["27418313"],"confidence":"High","gaps":["Direct molecular target of GSK-3β still unmapped","In vivo relevance in FUS models not addressed"]},{"year":2017,"claim":"Demonstrated the tether regulates autophagy through Ca2+ delivery, using a synthetic ER-mitochondria linker to prove causality of contact tightness on autophagosome formation.","evidence":"siRNA, overexpression, synthetic linker rescue and autophagosome quantification with Ca2+ measurements","pmids":["28132811"],"confidence":"High","gaps":["Downstream autophagy machinery linkage not detailed","Ca2+ target effectors not identified"]},{"year":2017,"claim":"Established a tissue-specific role in cardiomyocytes where PTPIP51 sets mitochondria-SR contact and MCU-dependent Ca2+ uptake, with cardiac knockdown protective against ischemia/reperfusion injury.","evidence":"Adenoviral overexpression, cardiac-specific knockdown, EM, MCU epistasis and infarct size measurement in vivo","pmids":["28345618"],"confidence":"High","gaps":["Whether VAPB is the relevant ER partner in cardiomyocytes untested","Upstream regulation in the heart unknown"]},{"year":2019,"claim":"Showed the tether operates at neuronal synapses and is activity-dependent, with loss perturbing synaptic function and spine morphology, linking interorganelle contacts to neuronal physiology.","evidence":"Immunofluorescence, proximity ligation assay, activity-evoked Ca2+ imaging and siRNA with synaptic readouts","pmids":["30841933"],"confidence":"High","gaps":["Molecular link between activity and increased contact undefined","In vivo synaptic phenotype not established"]},{"year":2021,"claim":"Provided the structural basis for lipid handling by crystallizing the TPR domain and demonstrating PTPIP51 binds and transfers phosphatidic acid, contributing to mitochondrial cardiolipin, and mapped VAPB binding to an FFAT-like motif engaging the MSP domain.","evidence":"X-ray crystallography, in vitro phospholipid transfer assays, cardiolipin measurement and motif mutagenesis","pmids":["33938112"],"confidence":"High","gaps":["In-cell directionality and flux of PA transfer not quantified","Relationship between lipid transfer and Ca2+ functions unresolved"]},{"year":2022,"claim":"Refined the interaction interface by showing the coiled-coil domain, not the FFAT motif alone, is essential for VAPB binding and tethering in full-length proteins, revising the binding model in cells.","evidence":"Co-IP with deletion/mutation constructs, EM contact quantification and IP3R-mediated Ca2+ assays","pmids":["36120587"],"confidence":"High","gaps":["Apparent discordance with FFAT-based in vitro model not fully reconciled","Structure of the coiled-coil/VAPB interface unknown"]},{"year":2022,"claim":"Identified MITOL/MARCH5 ubiquitination of RMDN3 at K89 as an activating modification for its PA-binding activity, adding post-translational control over lipid-transfer function.","evidence":"APEX2 proximity labeling, Co-IP, K89R mutagenesis and in vitro PA-binding assay","pmids":["34964862"],"confidence":"High","gaps":["Whether ubiquitination affects tethering or only lipid binding unclear","In-cell consequences for cardiolipin/PA flux not measured"]},{"year":2022,"claim":"Confirmed disease relevance by showing reduced VAPB levels and disrupted tethers in human ALS spinal cord motor neurons, translating cell-model findings to patient tissue.","evidence":"Proximity ligation assay in post-mortem human spinal cord and VAPB immunoblotting","pmids":["36051435"],"confidence":"Medium","gaps":["Correlative tissue analysis, not causal","Whether tether loss precedes or follows neurodegeneration unknown"]},{"year":2022,"claim":"Described a tether-independent PTPIP51-PTEN-CK2 complex that drives EGFR lysosomal degradation and suppresses growth signaling in NSCLC, broadening PTPIP51's signaling repertoire.","evidence":"Co-IP, EGFR ubiquitylation and lysosomal inhibitor assays, downstream signaling immunoblots and xenograft","pmids":["35240162"],"confidence":"Medium","gaps":["How a mitochondrial protein accesses PTEN/EGFR machinery unclear","Single lab; mechanism of CK2 recruitment undefined"]},{"year":2024,"claim":"Demonstrated therapeutic tractability by rescuing TDP-43-induced tether and synaptic defects with VAPB/PTPIP51 overexpression and with UDCA acting through GSK-3β inhibition.","evidence":"Overexpression rescue, Ca2+ and synaptic assays, UDCA treatment and GSK-3β activity assays","pmids":["38395965"],"confidence":"Medium","gaps":["In vivo efficacy not established","GSK-3β substrate on the tether still unidentified"]},{"year":2025,"claim":"Defined a cell-survival function of the tether in oxidative stress: RMDN3 phosphorylation increases MERCs and the TPR domain transfers lipid radicals from mitochondria to ER, preventing toxic accumulation.","evidence":"NanoBiT/MERBiT live-cell MERC assay, in vitro liposome lipid radical transfer, phosphorylation analysis and disruption with cell death readouts","pmids":["39929810"],"confidence":"High","gaps":["Phosphosite(s) and responsible kinase not fully defined","Fate of transferred lipid radicals in the ER not traced"]},{"year":2025,"claim":"Identified RHOA as an upstream tuner of the tether through binding VAPB and CUL3-regulated turnover, integrating a small-GTPase axis into MERC control.","evidence":"Genome-wide CRISPRi screen, RHOA-VAPB Co-IP, MERCS quantification and disease allele analysis","pmids":["41392169"],"confidence":"High","gaps":["Whether RHOA binds PTPIP51 directly not shown (binds VAPB)","Downstream effector linking RHOA to contact formation undefined"]},{"year":null,"claim":"How the multiple regulatory inputs (phosphorylation, K89 ubiquitination, RHOA tuning, GSK-3β disruption) are integrated to set tether strength, and how the lipid-transfer versus Ca2+-transfer functions are coordinated, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model coupling lipid and Ca2+ transfer","GSK-3β phosphorylation site on the tether unidentified","Structure of the full PTPIP51-VAPB tethering interface unsolved"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[6,8,9]},{"term_id":"GO:0140104","term_label":"molecular carrier activity","supporting_discovery_ids":[6,9]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,7,11]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,4,10]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[0,3]}],"pathway":[{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[3]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[6,9]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[11,18]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[4,10]}],"complexes":["VAPB-PTPIP51 ER-mitochondria tether","PTPIP51-Raf-1-14-3-3 scaffold","PTPIP51-PTEN-CK2 complex"],"partners":["VAPB","RHOA","MARCH5","RAF1","PTEN","PTPN1","SNCA","CGI-99"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q96TC7","full_name":"Regulator of microtubule dynamics protein 3","aliases":["Cerebral protein 10","Protein FAM82A2","Protein FAM82C","Protein tyrosine phosphatase-interacting protein 51","TCPTP-interacting protein 51"],"length_aa":470,"mass_kda":52.1,"function":"Involved in cellular calcium homeostasis regulation. May participate in differentiation and apoptosis of keratinocytes. Overexpression induces apoptosis","subcellular_location":"Mitochondrion outer membrane; Cytoplasm; Nucleus; Cytoplasm, cytoskeleton, spindle; Cytoplasm, cytoskeleton, spindle pole","url":"https://www.uniprot.org/uniprotkb/Q96TC7/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/RMDN3","classification":"Not Classified","n_dependent_lines":7,"n_total_lines":1208,"dependency_fraction":0.005794701986754967},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"LMAN1","stoichiometry":0.2},{"gene":"VAPA","stoichiometry":0.2},{"gene":"VAPB","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/RMDN3","total_profiled":1310},"omim":[{"mim_id":"611873","title":"REGULATOR OF MICROTUBULE DYNAMICS 3; RMDN3","url":"https://www.omim.org/entry/611873"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Mitochondria","reliability":"Enhanced"},{"location":"Cytokinetic bridge","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in 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ER-resident protein VAPB, and this interaction is required for normal mitochondrial Ca2+ uptake following release from ER stores. VAPB is a MAM (mitochondria-associated membrane) protein, and loss of either VAPB or PTPIP51 perturbs Ca2+ homeostasis. The ALS-linked VAPBP56S mutant shows altered binding to PTPIP51 and dysregulated Ca2+ uptake.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, mitochondrial Ca2+ uptake assays, subcellular fractionation (MAM isolation)\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, siRNA loss-of-function with defined Ca2+ phenotype, replicated in multiple subsequent studies\",\n      \"pmids\": [\"22131369\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"VAPB-PTPIP51 interaction tethers ER to mitochondria. TDP-43 (ALS/FTD-linked) disrupts this interaction and ER-mitochondria associations, perturbing Ca2+ homeostasis. TDP-43 overexpression activates GSK-3β, and GSK-3β regulates the VAPB-PTPIP51 interaction, placing GSK-3β as an upstream negative regulator of the tether.\",\n      \"method\": \"Co-immunoprecipitation, electron microscopy (ER-mitochondria contact quantification), Ca2+ imaging, GSK-3β kinase activity assays, siRNA\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (Co-IP, EM, Ca2+ assay, kinase assay), replicated in subsequent studies\",\n      \"pmids\": [\"24893131\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"ALS/FTD-associated FUS disrupts the VAPB-PTPIP51 interaction and ER-mitochondria associations, leading to impaired mitochondrial Ca2+ uptake and reduced mitochondrial ATP production. FUS activates GSK-3β, which mediates these disruptions, consistent with a shared GSK-3β-dependent mechanism for ALS/FTD insults on the VAPB-PTPIP51 tether.\",\n      \"method\": \"Co-immunoprecipitation, electron microscopy, mitochondrial Ca2+ and ATP assays, GSK-3β inhibitor experiments\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods, consistent mechanistic pathway established across independent disease models\",\n      \"pmids\": [\"27418313\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The VAPB-PTPIP51 ER-mitochondria tethers regulate autophagy. Overexpression of VAPB or PTPIP51 (tightening contacts) impairs autophagosome formation, while siRNA-mediated knockdown (loosening contacts) stimulates it. An artificial ER-mitochondria linker rescues the effects of VAPB/PTPIP51 siRNA on autophagy, demonstrating that this is a direct consequence of tethering. The mechanism involves Ca2+ delivery from ER to mitochondria.\",\n      \"method\": \"siRNA knockdown, VAPB/PTPIP51 overexpression, synthetic ER-mitochondria linker rescue, autophagosome quantification (fluorescence microscopy), Ca2+ measurements\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis via synthetic linker rescue, multiple orthogonal methods, single lab with rigorous controls\",\n      \"pmids\": [\"28132811\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PTPIP51 regulates mitochondria-sarcoplasmic reticulum (SR) contact in cardiomyocytes. Overexpression of PTPIP51 increases mitochondria-SR contacts and elevates mitochondrial Ca2+ uptake via the mitochondrial Ca2+ uniporter (MCU). Cardiac-specific knockdown of PTPIP51 reduces myocardial infarct size and injury after ischemia/reperfusion. MCU inhibition/knockdown reverses PTPIP51-mediated mitochondrial Ca2+ increase and cardiomyocyte apoptosis.\",\n      \"method\": \"Adenovirus-mediated overexpression, cardiac-specific knockdown, electron microscopy (contact quantification), mitochondrial Ca2+ assays, MCU inhibitor/siRNA epistasis, infarct size measurement\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods, in vivo cardiac knockout with functional phenotype, MCU epistasis\",\n      \"pmids\": [\"28345618\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"VAPB and PTPIP51 localize to neuronal synapses and form contacts there. Stimulating neuronal activity increases ER-mitochondria contacts and the VAPB-PTPIP51 interaction. siRNA loss of VAPB or PTPIP51 perturbs synaptic function and dendritic spine morphology, demonstrating a role for the tether in synaptic activity.\",\n      \"method\": \"Immunofluorescence co-localization, proximity ligation assay, live-cell Ca2+ imaging upon neuronal stimulation, siRNA knockdown with synaptic activity and spine morphology readouts\",\n      \"journal\": \"Acta neuropathologica communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods, siRNA with defined synaptic phenotype, neuronal activity-induced interaction changes\",\n      \"pmids\": [\"30841933\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Crystal structure of the TPR domain of PTPIP51 reveals an archetypal TPR fold with a lipid-like molecule in the binding pocket. PTPIP51 binds and transfers phospholipids, particularly phosphatidic acid (PA), in vitro. Depletion of PTPIP51 reduces mitochondrial cardiolipin levels. The PTPIP51-VAPB interaction is mediated by an FFAT-like motif in PTPIP51 and the MSP domain of VAPB.\",\n      \"method\": \"X-ray crystallography (TPR domain structure), in vitro phospholipid binding/transfer assays, siRNA knockdown with cardiolipin measurement, mutational analysis of FFAT-like motif and MSP domain\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure, in vitro reconstitution of lipid transfer, mutagenesis of interaction motifs, multiple orthogonal methods in one study\",\n      \"pmids\": [\"33938112\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The coiled-coil domain of PTPIP51 (not the FFAT motif alone) is essential for VAPB binding in the context of full-length proteins in cells, for formation of ER-mitochondria contacts, and for IP3 receptor-mediated delivery of Ca2+ from ER to mitochondria. Deletion of the FFAT motif had little effect on VAPB binding, while mutation/deletion of the coiled-coil domain markedly reduced binding and abrogated tethering and Ca2+ transfer functions.\",\n      \"method\": \"Immunoprecipitation from transfected cells with deletion/mutation constructs, electron microscopy (ER-mitochondria contact quantification), IP3R-mediated Ca2+ delivery assays\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — mutagenesis with multiple orthogonal functional readouts (Co-IP, EM, Ca2+ assay), single lab\",\n      \"pmids\": [\"36120587\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The mitochondrial E3 ubiquitin ligase MITOL/MARCH5 interacts with and ubiquitinates RMDN3/PTPIP51 at lysine residue 89. Loss of MITOL or K89R substitution in RMDN3 significantly reduces its phosphatidic acid (PA)-binding activity, indicating that MITOL-mediated ubiquitination activates RMDN3 PA-transfer activity at the mitochondria-ER contact site.\",\n      \"method\": \"Proximity-dependent biotin labeling (APEX2), Co-IP, site-directed mutagenesis (K89R), in vitro PA-binding assay\",\n      \"journal\": \"Journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — identification of ubiquitination site by mutagenesis, in vitro functional assay, multiple methods in single study\",\n      \"pmids\": [\"34964862\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Mitochondrial ROS increases MERC (mitochondria-ER contact) formation via RMDN3-VAPB tethering driven by RMDN3 phosphorylation. RMDN3 transfers lipid radicals from mitochondria to the ER via its TPR domain (demonstrated by in vitro liposome assay). Disruption of RMDN3-VAPB tethering causes lipid radical accumulation in mitochondria and cell death, defining a cell survival role for MERCs in lipid radical removal under mitochondrial damage.\",\n      \"method\": \"NanoBiT/MERBiT split-luciferase system for live-cell MERC measurement, in vitro liposome lipid radical transfer assay, RMDN3 phosphorylation analysis, siRNA/genetic disruption with lipid radical and cell death readouts\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — novel live-cell MERC assay, in vitro reconstitution of lipid radical transfer, multiple orthogonal methods, single study\",\n      \"pmids\": [\"39929810\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"PTPIP51 is a mitochondrial protein requiring its N-terminal transmembrane (TM) domain for mitochondrial targeting. Overexpression induces apoptosis via decrease in mitochondrial membrane potential, cytochrome c release, caspase-3 activation, PARP cleavage, and phosphatidylserine externalization. Deletion of the TM domain prevents mitochondrial localization and abrogates apoptosis-inducing function.\",\n      \"method\": \"GFP-fusion subcellular localization, deletion mutant analysis, mitochondrial membrane potential assay (JC-1), cytochrome c release assay, caspase-3 and PARP cleavage, Annexin V staining\",\n      \"journal\": \"Apoptosis : an international journal on programmed cell death\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — deletion mutagenesis linking TM domain to localization and apoptosis, multiple downstream readouts, single lab\",\n      \"pmids\": [\"16820967\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PTPIP51 regulates cell morphology and motility via the Raf-MEK-ERK cascade. It interacts with Raf-1 through 14-3-3 scaffold proteins and activates ERK; this is blocked by MEK inhibitor or dominant-negative Raf-1 but not dominant-negative Ras. Two redundant 14-3-3-binding domains in PTPIP51 were identified by deletion/mutation analysis.\",\n      \"method\": \"Overexpression/siRNA knockdown with migration/adhesion assays, MEK inhibitor and dominant-negative Raf-1/Ras epistasis, Co-IP for Raf-1/14-3-3 interaction, deletion/mutation analysis of 14-3-3-binding domains\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis with dominant-negative constructs and pharmacological inhibitors, Co-IP, deletion mapping, single lab\",\n      \"pmids\": [\"18771726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Tyrosine 176 phosphorylation of PTPIP51 by c-Src regulates its interaction with 14-3-3β and Raf-1. Increased phosphorylation at Y176 causes a sharp drop in PTPIP51-14-3-3β and 14-3-3β-Raf-1 interactions. Phosphorylation status also regulates PTPIP51 interactions with DAGKα and PKA.\",\n      \"method\": \"Pharmacological modulation of c-Src activity and PTP1B phosphatase inhibition in HaCaT keratinocytes, proximity ligation assay (Duolink) for protein interactions, confocal microscopy\",\n      \"journal\": \"Cell biochemistry and biophysics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — proximity ligation assay for in situ interactions, phosphorylation manipulation, multiple interaction partners tested, single lab\",\n      \"pmids\": [\"22544307\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"PTPIP51 interacts with CGI-99 and Nuf2 in vitro and in vivo, and the PTPIP51/CGI-99 and PTPIP51/Nuf-2 complexes localize to the equatorial region during mitosis. PTPIP51 associates with the microtubular cytoskeleton and spindle apparatus. Phosphorylated PTPIP51 accumulates at spindle poles. During M/G1 transition, PTPIP51 interacts strongly with PTP1B, restoring PTPIP51-Raf-1 interaction that is depleted in mitotic cells.\",\n      \"method\": \"Proximity ligation assay (Duolink), confocal microscopy, cell synchronization with nocodazole\",\n      \"journal\": \"Biomolecules\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — proximity ligation assay for in situ interactions, cell cycle synchronization, multiple interaction partners, single lab\",\n      \"pmids\": [\"24970130\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"PTPIP51 is phosphorylated at tyrosine 176 by Lyn and c-Src kinases in AML cells. In AML blasts, PTP1B (the cognate phosphatase for PTPIP51) is absent, preventing dephosphorylation. PTPIP51 interacts with c-Kit in AML cells, identifying it as a component of c-Kit signaling. The hyperphosphorylation prevents PTPIP51-Raf-1 interaction, contributing to increased MAPK-driven proliferation.\",\n      \"method\": \"Immunohistochemistry with peptide-specific antibodies, proximity ligation assay, confocal co-localization, immunoblot\",\n      \"journal\": \"Leukemia research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — proximity ligation assay for in situ interactions, multiple disease context validations, single lab\",\n      \"pmids\": [\"21513978\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"RHOA (small GTPase) binds to the ER protein VAPB and regulates complex formation between VAPB and mitochondrial PTPIP51, thereby tuning MERCS levels. RHOA knockdown or increased degradation via CUL3 overexpression reduces MERCS; RHOA upregulation increases MERCS. Disease alleles of RHOA, CUL3, and VAPB perturb this regulatory mechanism.\",\n      \"method\": \"Genome-wide CRISPRi screen, Co-IP (RHOA-VAPB binding), MERCS quantification upon RHOA/CUL3 manipulation, disease allele analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genome-wide unbiased screen with validation, Co-IP of RHOA-VAPB interaction, functional MERCS quantification, multiple genetic perturbations\",\n      \"pmids\": [\"41392169\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"VAPB protein levels are reduced and VAPB-PTPIP51 tethers are disrupted in post-mortem spinal cord motor neurons from ALS patients, as quantified by proximity ligation assay, confirming that disruption of the tether occurs in human ALS tissue.\",\n      \"method\": \"Proximity ligation assay in post-mortem human spinal cord sections, immunoblotting for VAPB levels\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — proximity ligation assay in human post-mortem tissue, confirms disruption in disease context, single lab\",\n      \"pmids\": [\"36051435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Overexpression of VAPB or PTPIP51 corrects mutant TDP43-induced damage to IP3 receptor delivery of Ca2+ to mitochondria and to synaptic function. UDCA (FDA-approved drug) corrects TDP43-linked damage to the VAPB-PTPIP51 interaction by inhibiting TDP43-mediated GSK3β activation, identifying GSK3β inhibition as the mechanism of UDCA action on this tether.\",\n      \"method\": \"VAPB/PTPIP51 overexpression rescue experiments, Ca2+ imaging, synaptic activity assays, UDCA pharmacological treatment, GSK3β activity assays\",\n      \"journal\": \"Acta neuropathologica communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — overexpression rescue of defined molecular phenotype, pharmacological epistasis, multiple functional readouts, single lab\",\n      \"pmids\": [\"38395965\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PTPIP51 interacts with PTEN to form a PTPIP51-PTEN-CK2 complex, which induces phosphorylation of PTEN at Thr382/383. This leads to ubiquitylation and lysosomal degradation of EGFR, thereby suppressing PI3K/Akt, RAS/RAF/ERK, and JAK/STAT3 downstream signaling in NSCLC cells.\",\n      \"method\": \"Co-immunoprecipitation, PTPIP51 overexpression and knockdown, EGFR ubiquitylation assay, lysosomal inhibitor experiments, downstream signaling (immunoblot), in vivo xenograft\",\n      \"journal\": \"Life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP of complex, ubiquitylation assay, in vivo and in vitro functional readouts, single lab\",\n      \"pmids\": [\"35240162\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PTPIP51 is required for the differentiation of photoreceptors. Silencing of PTPIP51 in postnatal retinal explants severely impairs final differentiation of photoreceptors (decreased rhodopsin-positive cells), while PTPIP51 misexpression does not alter RPC commitment, indicating a specific role in terminal photoreceptor maturation.\",\n      \"method\": \"Ex vivo electroporation for siRNA knockdown and misexpression in postnatal rat retinal explants, immunostaining for rhodopsin and lineage markers\",\n      \"journal\": \"Neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — ex vivo loss-of-function with defined differentiation phenotype, single lab, single method\",\n      \"pmids\": [\"25999297\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PTPIP51 forms a complex with RelA and IκBα. RelA bound to the PTPIP51 promoter represses its mRNA and protein expression. TNFα modulates this PTPIP51/RelA/IκBα complex. Direct PTPIP51-RelA and PTPIP51-IκBα interactions were confirmed in situ.\",\n      \"method\": \"Promoter binding assay, proximity ligation assay (Duolink) for direct protein-protein interactions, immunofluorescence co-localization, PDTC/TNFα pharmacological manipulation\",\n      \"journal\": \"Biomolecules\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — proximity ligation assay for interactions, pharmacological modulation, single lab, single method per interaction\",\n      \"pmids\": [\"25893721\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Phosphorylation of α-synuclein at serine 129 increases VAPB-PTPIP51 interactions. α-syn interacts directly with PTPIP51, and this interaction is modulated by the phosphorylation state of α-syn at S129 (confirmed by Co-IP and molecular dynamics simulation).\",\n      \"method\": \"Co-immunoprecipitation, mass spectrometry, molecular dynamics simulation, Co-IP in Thy1-SNCA transgenic mouse brain\",\n      \"journal\": \"Acta neuropathologica communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — Co-IP with computational support, single study, no in vitro reconstitution of direct binding\",\n      \"pmids\": [\"39994794\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RMDN3/PTPIP51 is an outer mitochondrial membrane protein that, together with the ER protein VAPB, forms a tethering complex at mitochondria-associated ER membranes (MAMs/MERCs); the interaction is mediated by a coiled-coil domain in PTPIP51 and the MSP domain of VAPB, and it facilitates IP3 receptor-mediated Ca2+ transfer from ER to mitochondria, phosphatidic acid and lipid radical transfer via its TPR domain, regulation of autophagy, synaptic activity, and mitochondrial ATP production. The tether is regulated by phosphorylation (RMDN3 phosphorylation enhances tethering under mitochondrial ROS), ubiquitination by MITOL/MARCH5 at K89 (activating its PA-binding activity), GSK-3β (which disrupts the interaction downstream of ALS/FTD insults such as TDP-43 and FUS), and RHOA (which binds VAPB to tune complex formation). PTPIP51 also acts as a scaffold in the MAPK pathway by interacting with Raf-1 through 14-3-3 proteins in a manner regulated by c-Src phosphorylation at Y176 and dephosphorylation by PTP1B, and it can interact with PTEN to promote EGFR lysosomal degradation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"RMDN3 (PTPIP51) is an outer mitochondrial membrane protein that physically tethers mitochondria to the endoplasmic reticulum by binding the ER protein VAPB, establishing mitochondria-associated ER membranes (MERCs/MAMs) that govern interorganelle Ca2+ and lipid exchange [#0, #6]. Mitochondrial targeting requires its N-terminal transmembrane domain [#10], while the VAPB interaction is mediated principally by a coiled-coil domain in PTPIP51 acting together with an FFAT-like motif that engages the MSP domain of VAPB [#6, #7]. Through this tether, RMDN3 supports IP3 receptor-mediated transfer of Ca2+ from ER to mitochondria, and its loss or disruption perturbs mitochondrial Ca2+ uptake [#0, #7]. A crystallized TPR domain confers lipid binding and transfer activity: RMDN3 binds and transfers phosphatidic acid, contributes to mitochondrial cardiolipin content [#6], and under mitochondrial ROS transfers lipid radicals from mitochondria to the ER, defining a survival function in removing damaging oxidized lipids [#9]. The strength of tethering is set by post-translational regulation — RMDN3 phosphorylation enhances contact formation under oxidative stress [#9], MITOL/MARCH5-mediated ubiquitination at K89 activates its PA-binding activity [#8], and RHOA binding to VAPB tunes complex assembly [#15]. Functionally, the tether constrains autophagosome formation [#3], shapes mitochondria-SR contacts and Ca2+-dependent apoptosis in cardiomyocytes [#4], and supports synaptic activity and dendritic spine morphology in neurons [#5]. The tether is a convergence point for ALS/FTD pathology: TDP-43 and FUS disrupt the VAPB-PTPIP51 interaction through GSK-3\\u03b2 activation, and tether disruption is observed in ALS patient motor neurons [#1, #2, #16]. Independently of its tethering role, PTPIP51 acts as a 14-3-3-dependent scaffold for Raf-1 in the MAPK cascade, regulated by c-Src phosphorylation at Y176 [#11, #12].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Established that PTPIP51 is a mitochondrial protein whose localization depends on its N-terminal transmembrane domain and which can drive intrinsic apoptosis, anchoring its membrane topology before its tethering role was known.\",\n      \"evidence\": \"GFP-fusion localization and TM deletion mutants with mitochondrial membrane potential, cytochrome c, caspase-3 and Annexin V readouts\",\n      \"pmids\": [\"16820967\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not connect mitochondrial localization to ER contact sites\", \"Apoptosis driven by overexpression; physiological relevance untested\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identified the direct PTPIP51-VAPB interaction and showed it is required for ER-to-mitochondria Ca2+ transfer, defining PTPIP51 as a MAM tethering partner.\",\n      \"evidence\": \"Reciprocal Co-IP, siRNA knockdown, mitochondrial Ca2+ uptake assays and MAM fractionation\",\n      \"pmids\": [\"22131369\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Interaction interface on PTPIP51 not yet mapped\", \"Did not establish whether tethering is structural cause or correlate of Ca2+ defect\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Showed PTPIP51 is tyrosine-176 phosphorylated by Lyn and c-Src and interacts with c-Kit in AML, defining a kinase-regulated signaling role distinct from tethering.\",\n      \"evidence\": \"IHC, proximity ligation assay and immunoblot in AML blasts lacking the cognate phosphatase PTP1B\",\n      \"pmids\": [\"21513978\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In situ interaction assays without biochemical reconstitution\", \"Causal contribution to leukemic proliferation not directly tested\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Defined PTPIP51 as a 14-3-3-dependent scaffold linking to Raf-1 and activating ERK to control cell morphology and motility, separate from its mitochondrial functions.\",\n      \"evidence\": \"Migration/adhesion assays, dominant-negative Raf-1/Ras and MEK inhibitor epistasis, Co-IP and deletion mapping of 14-3-3 sites\",\n      \"pmids\": [\"18771726\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relationship between scaffold and tether pools of PTPIP51 unclear\", \"Endogenous physiological setting not defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Established that c-Src phosphorylation at Y176 and PTP1B dephosphorylation toggle PTPIP51's association with 14-3-3\\u03b2 and Raf-1, providing a switch controlling the MAPK scaffold.\",\n      \"evidence\": \"Pharmacological c-Src/PTP1B modulation with proximity ligation assays in keratinocytes\",\n      \"pmids\": [\"22544307\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No direct phosphosite mutagenesis in functional MAPK output\", \"Interactions inferred from in situ proximity, not reconstituted\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Showed the VAPB-PTPIP51 interaction physically tethers ER to mitochondria and that TDP-43 disrupts it via GSK-3\\u03b2, placing the tether downstream of an ALS/FTD insult and identifying GSK-3\\u03b2 as an upstream negative regulator.\",\n      \"evidence\": \"Co-IP, EM contact quantification, Ca2+ imaging and GSK-3\\u03b2 kinase assays\",\n      \"pmids\": [\"24893131\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"GSK-3\\u03b2 substrate site on the tether not identified\", \"Whether GSK-3\\u03b2 acts on PTPIP51 or VAPB unresolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Extended the GSK-3\\u03b2-dependent tether-disruption mechanism to FUS, showing convergent ALS/FTD pathology on VAPB-PTPIP51 with impaired Ca2+ uptake and ATP production.\",\n      \"evidence\": \"Co-IP, EM, mitochondrial Ca2+/ATP assays and GSK-3\\u03b2 inhibitor experiments\",\n      \"pmids\": [\"27418313\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct molecular target of GSK-3\\u03b2 still unmapped\", \"In vivo relevance in FUS models not addressed\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrated the tether regulates autophagy through Ca2+ delivery, using a synthetic ER-mitochondria linker to prove causality of contact tightness on autophagosome formation.\",\n      \"evidence\": \"siRNA, overexpression, synthetic linker rescue and autophagosome quantification with Ca2+ measurements\",\n      \"pmids\": [\"28132811\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream autophagy machinery linkage not detailed\", \"Ca2+ target effectors not identified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Established a tissue-specific role in cardiomyocytes where PTPIP51 sets mitochondria-SR contact and MCU-dependent Ca2+ uptake, with cardiac knockdown protective against ischemia/reperfusion injury.\",\n      \"evidence\": \"Adenoviral overexpression, cardiac-specific knockdown, EM, MCU epistasis and infarct size measurement in vivo\",\n      \"pmids\": [\"28345618\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether VAPB is the relevant ER partner in cardiomyocytes untested\", \"Upstream regulation in the heart unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Showed the tether operates at neuronal synapses and is activity-dependent, with loss perturbing synaptic function and spine morphology, linking interorganelle contacts to neuronal physiology.\",\n      \"evidence\": \"Immunofluorescence, proximity ligation assay, activity-evoked Ca2+ imaging and siRNA with synaptic readouts\",\n      \"pmids\": [\"30841933\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular link between activity and increased contact undefined\", \"In vivo synaptic phenotype not established\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Provided the structural basis for lipid handling by crystallizing the TPR domain and demonstrating PTPIP51 binds and transfers phosphatidic acid, contributing to mitochondrial cardiolipin, and mapped VAPB binding to an FFAT-like motif engaging the MSP domain.\",\n      \"evidence\": \"X-ray crystallography, in vitro phospholipid transfer assays, cardiolipin measurement and motif mutagenesis\",\n      \"pmids\": [\"33938112\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In-cell directionality and flux of PA transfer not quantified\", \"Relationship between lipid transfer and Ca2+ functions unresolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Refined the interaction interface by showing the coiled-coil domain, not the FFAT motif alone, is essential for VAPB binding and tethering in full-length proteins, revising the binding model in cells.\",\n      \"evidence\": \"Co-IP with deletion/mutation constructs, EM contact quantification and IP3R-mediated Ca2+ assays\",\n      \"pmids\": [\"36120587\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Apparent discordance with FFAT-based in vitro model not fully reconciled\", \"Structure of the coiled-coil/VAPB interface unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified MITOL/MARCH5 ubiquitination of RMDN3 at K89 as an activating modification for its PA-binding activity, adding post-translational control over lipid-transfer function.\",\n      \"evidence\": \"APEX2 proximity labeling, Co-IP, K89R mutagenesis and in vitro PA-binding assay\",\n      \"pmids\": [\"34964862\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ubiquitination affects tethering or only lipid binding unclear\", \"In-cell consequences for cardiolipin/PA flux not measured\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Confirmed disease relevance by showing reduced VAPB levels and disrupted tethers in human ALS spinal cord motor neurons, translating cell-model findings to patient tissue.\",\n      \"evidence\": \"Proximity ligation assay in post-mortem human spinal cord and VAPB immunoblotting\",\n      \"pmids\": [\"36051435\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Correlative tissue analysis, not causal\", \"Whether tether loss precedes or follows neurodegeneration unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Described a tether-independent PTPIP51-PTEN-CK2 complex that drives EGFR lysosomal degradation and suppresses growth signaling in NSCLC, broadening PTPIP51's signaling repertoire.\",\n      \"evidence\": \"Co-IP, EGFR ubiquitylation and lysosomal inhibitor assays, downstream signaling immunoblots and xenograft\",\n      \"pmids\": [\"35240162\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How a mitochondrial protein accesses PTEN/EGFR machinery unclear\", \"Single lab; mechanism of CK2 recruitment undefined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrated therapeutic tractability by rescuing TDP-43-induced tether and synaptic defects with VAPB/PTPIP51 overexpression and with UDCA acting through GSK-3\\u03b2 inhibition.\",\n      \"evidence\": \"Overexpression rescue, Ca2+ and synaptic assays, UDCA treatment and GSK-3\\u03b2 activity assays\",\n      \"pmids\": [\"38395965\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo efficacy not established\", \"GSK-3\\u03b2 substrate on the tether still unidentified\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined a cell-survival function of the tether in oxidative stress: RMDN3 phosphorylation increases MERCs and the TPR domain transfers lipid radicals from mitochondria to ER, preventing toxic accumulation.\",\n      \"evidence\": \"NanoBiT/MERBiT live-cell MERC assay, in vitro liposome lipid radical transfer, phosphorylation analysis and disruption with cell death readouts\",\n      \"pmids\": [\"39929810\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphosite(s) and responsible kinase not fully defined\", \"Fate of transferred lipid radicals in the ER not traced\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified RHOA as an upstream tuner of the tether through binding VAPB and CUL3-regulated turnover, integrating a small-GTPase axis into MERC control.\",\n      \"evidence\": \"Genome-wide CRISPRi screen, RHOA-VAPB Co-IP, MERCS quantification and disease allele analysis\",\n      \"pmids\": [\"41392169\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether RHOA binds PTPIP51 directly not shown (binds VAPB)\", \"Downstream effector linking RHOA to contact formation undefined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the multiple regulatory inputs (phosphorylation, K89 ubiquitination, RHOA tuning, GSK-3\\u03b2 disruption) are integrated to set tether strength, and how the lipid-transfer versus Ca2+-transfer functions are coordinated, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model coupling lipid and Ca2+ transfer\", \"GSK-3\\u03b2 phosphorylation site on the tether unidentified\", \"Structure of the full PTPIP51-VAPB tethering interface unsolved\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [6, 8, 9]},\n      {\"term_id\": \"GO:0140104\", \"supporting_discovery_ids\": [6, 9]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 7, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005741\", \"supporting_discovery_ids\": [0, 10]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 4, 10]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [0, 3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [6, 9]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [11, 18]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [4, 10]}\n    ],\n    \"complexes\": [\n      \"VAPB-PTPIP51 ER-mitochondria tether\",\n      \"PTPIP51-Raf-1-14-3-3 scaffold\",\n      \"PTPIP51-PTEN-CK2 complex\"\n    ],\n    \"partners\": [\n      \"VAPB\",\n      \"RHOA\",\n      \"MARCH5\",\n      \"RAF1\",\n      \"PTEN\",\n      \"PTPN1\",\n      \"SNCA\",\n      \"CGI-99\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}