{"gene":"HIP1R","run_date":"2026-06-10T01:55:22","timeline":{"discoveries":[{"year":2001,"finding":"Hip1R binds to clathrin via its putative central coiled-coil domain; it localizes to clathrin-coated pits in vivo; it promotes clathrin cage assembly in vitro; it is a rod-shaped apparent dimer with globular heads at either end and can assemble clathrin-coated vesicles and F-actin into higher order structures.","method":"Co-immunoprecipitation, live-cell fluorescence imaging (Hip1R-YFP / DsRed-clathrin LC), immunogold EM of unroofed cells, in vitro clathrin assembly assay, electron microscopy of protein architecture","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple orthogonal methods (live imaging, EM, in vitro assembly assay, overexpression) in a single rigorous study; foundational paper replicated by subsequent work","pmids":["11564758"],"is_preprint":false},{"year":2004,"finding":"Hip1R depletion by RNAi causes clathrin-coated structures to become stably associated with dynamin, actin, Arp2/3, and cortactin (rather than transiently), and this stabilization depends on cortactin; demonstrating that Hip1R makes the actin–endocytic machinery interaction transient and functional. FRAP showed dynamic actin filament assembly can occur at CCSs.","method":"RNAi knockdown, fluorescence microscopy, FRAP, double RNAi depletion epistasis, EM of unroofed cells","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean RNAi with defined phenotypic readout, epistasis (double depletion), and live-cell FRAP; replicated conceptually by multiple subsequent studies","pmids":["14742709"],"is_preprint":false},{"year":2002,"finding":"HIP12 (HIP1R) co-sediments with F-actin in vitro (unlike HIP1, which shows no actin interaction). Both HIP1 and HIP1R stimulate clathrin assembly through their central helical domain, and this domain binds directly to clathrin light chain. HIP1R does not bind to AP2 nor to the terminal domain of clathrin heavy chain with high affinity (unlike HIP1).","method":"F-actin co-sedimentation assay, in vitro clathrin assembly assay, direct binding assays for clathrin heavy chain terminal domain and AP2 alpha ear","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution assays with multiple binding partners; single lab but multiple orthogonal biochemical methods","pmids":["11889126"],"is_preprint":false},{"year":2004,"finding":"HIP1R binds clathrin light chains via the conserved 22-amino acid sequence of the light chain N-terminus; HIP1R prefers light chains associated with clathrin heavy chain; mutations in the conserved light-chain sequence that abolish HIP1R binding block HIP1R-stimulated clathrin assembly in vitro; overexpression of the HIP1R-binding light-chain fragment disrupts cellular actin distribution.","method":"In vitro binding assays, site-directed mutagenesis of clathrin light chain, in vitro clathrin assembly assay, overexpression in cells with actin imaging","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis combined with in vitro assembly assay and cell imaging; single lab with multiple orthogonal approaches","pmids":["15533940"],"is_preprint":false},{"year":2007,"finding":"The C-terminal proline-rich domain of Hip1R binds the SH3 domain of cortactin; this Hip1R–cortactin complex inhibits actin assembly by blocking actin filament barbed-end elongation. Hip1R deleted for the cortactin-binding site cannot fully rescue the abnormal actin structures at endocytic sites caused by Hip1R siRNA. In vivo, maximum recruitment of Hip1R, clathrin, and cortactin to endocytic sites is coincident and all disappear together upon vesicle formation.","method":"In vitro binding assay (proline-rich domain / SH3 interaction), actin assembly assay (barbed-end elongation), siRNA rescue with deletion mutant, live-cell fluorescence imaging","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro barbed-end elongation assay plus siRNA rescue with domain-deletion mutant plus live imaging; single lab but multiple orthogonal methods","pmids":["17318189"],"is_preprint":false},{"year":2006,"finding":"The 1.9-Å crystal structure of the HIP1R THATCH domain reveals a unique five-helix bundle; a large sequence-conserved surface patch formed primarily by helices 3 and 4 mediates F-actin binding, as shown by point mutations at seven contiguous patch residues that significantly reduce F-actin binding. The THATCH domain also has a conserved C-terminal latch capable of oligomerizing the core, modulating F-actin engagement.","method":"X-ray crystallography (1.9 Å), site-directed mutagenesis of surface-patch residues, F-actin binding assay","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution crystal structure validated by mutagenesis and functional F-actin binding assay; rigorous single study","pmids":["16415883"],"is_preprint":false},{"year":2008,"finding":"Hip1 and Hip1R coiled-coil domains form stable homodimers in vitro with no propensity to heterodimerize; homodimers are also predominant in vivo. Clathrin light chain binding induces a compact conformation of Hip1R and significantly reduces actin binding by the THATCH domain, establishing clathrin as a negative regulator of Hip1R–actin interactions.","method":"Biophysical analysis of recombinant coiled-coil domains (sedimentation, gel filtration), in vivo co-immunoprecipitation for oligomerization, actin binding assay in the presence/absence of clathrin light chain","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro reconstitution with biophysics plus in vivo validation; single lab with multiple orthogonal methods","pmids":["18790740"],"is_preprint":false},{"year":2004,"finding":"Hip1R (Hip12) binds F-actin through its I/LWEQ module, but actin binding is regulated by intrasteric occlusion — a conserved structural element within the module inhibits the primary actin-binding determinants in the native protein. The I/LWEQ module also contains a dimerization motif and stabilizes actin filaments against depolymerization.","method":"F-actin co-sedimentation assay with full-length and truncated proteins, actin depolymerization assay","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro biochemical reconstitution; single lab, single method type","pmids":["15581353"],"is_preprint":false},{"year":2004,"finding":"HIP1R ENTH domain binds 3-phosphoinositides (preferentially phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 3,5-bisphosphate); deletion of the ENTH domain abolishes lipid binding and induces apoptosis. Full-length HIP1R prolongs the half-life of growth factor receptors after ligand-induced endocytosis.","method":"Lipid-binding assay (ENTH domain deletion mutant), receptor half-life measurement by pulse-chase/Western blotting","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct lipid-binding assay with domain-deletion mutant plus receptor stability experiment; single lab, two orthogonal approaches","pmids":["14732715"],"is_preprint":false},{"year":2001,"finding":"Expression of the Hub fragment of clathrin heavy chain (dominant-negative) dissociates Hip1R from coated pits, and disrupts the linear alignment of clathrin-coated pits with the actin cytoskeleton; cytochalasin D (actin disassembly) and BDM (myosin inhibition) also disrupt coated-pit alignment, indicating that proper clathrin function and Hip1R–clathrin interaction are required for cytoskeletal organization of coated pits.","method":"Inducible expression of clathrin Hub dominant-negative, immunofluorescence microscopy, pharmacological actin disruption","journal":"Traffic (Copenhagen, Denmark)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — dominant-negative approach combined with pharmacological treatments and imaging; single lab, multiple perturbations","pmids":["11733052"],"is_preprint":false},{"year":2008,"finding":"Hip1r is expressed in gastric parietal cells, localizing predominantly with F-actin to canalicular membranes. Hip1r-deficient mice show loss of tubulovesicles and abnormal apical canalicular membranes in parietal cells, altered acid secretory dynamics, and increased parietal cell apoptosis; normalization of proliferation and gland height in double gastrin/Hip1r knockout mice indicates that elevated gastrin drives glandular hypertrophy secondary to Hip1r loss.","method":"Hip1r knockout mouse model, electron microscopy, immunofluorescence/localization, acid secretion assay in isolated gastric glands, double knockout epistasis","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean knockout mouse with multiple orthogonal readouts (EM, secretion assay, double-KO epistasis); rigorous in vivo study","pmids":["18535670"],"is_preprint":false},{"year":2006,"finding":"Yeast Hip1R homologue Sla2p directly inhibits Pan1p (yeast Eps15-related Arp2/3 activator) Arp2/3 complex activation activity in vitro; the coiled-coil region of Sla2p is required for Pan1p inhibition; a pan1 partial loss-of-function mutation suppresses temperature sensitivity, endocytic defects, and actin phenotypes of sla2 coiled-coil deletion mutants, placing Sla2p upstream of Pan1p in negative regulation of actin polymerization during endocytosis.","method":"Tandem affinity purification–mass spectrometry (Pan1p interactors), in vitro Arp2/3 activation assay, domain-deletion mapping, genetic epistasis (double mutants)","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro reconstitution of inhibition plus genetic epistasis; single lab but orthogonal biochemical and genetic approaches","pmids":["17151356"],"is_preprint":false},{"year":2011,"finding":"In yeast, clathrin light chain (CLC) N-terminus binding to Sla2 (Hip1R orthologue) inhibits Sla2 interaction with F-actin in actin sedimentation assays; CLC N-terminus deletion suppresses endocytic defects of rvs and vrp1 mutants in a manner requiring the Sla2 THATCH actin-binding domain, suggesting that CLC regulates endocytic progression by controlling Sla2–actin attachments.","method":"Synthetic genetic array analysis, F-actin sedimentation assay with CLC and Sla2, genetic epistasis with THATCH domain requirement","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro actin sedimentation plus systematic genetic epistasis in yeast; replicates and extends mammalian findings","pmids":["21849475"],"is_preprint":false},{"year":2018,"finding":"HIP1R physically interacts with PD-L1 and delivers PD-L1 to the lysosome via a lysosomal targeting signal; depletion of HIP1R in tumor cells causes PD-L1 accumulation and suppresses T cell-mediated cytotoxicity; a chimeric peptide (PD-LYSO) incorporating HIP1R's lysosomal-sorting signal and PD-L1-binding sequence depletes PD-L1.","method":"Co-immunoprecipitation (HIP1R–PD-L1), RNAi knockdown with flow cytometry for PD-L1 levels, T cell cytotoxicity co-culture assay, chimeric peptide functional study","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP, RNAi with functional readout (T cell killing), and peptide rescue experiment; single lab with multiple orthogonal methods","pmids":["30397328"],"is_preprint":false},{"year":2010,"finding":"In Dictyostelium, epsin is required for membrane recruitment and phosphorylation of Hip1r; epsin-null cells phenocopy Hip1r-null cells for actin/clathrin dynamics defects; the ENTH domain of epsin is sufficient to restore Hip1r phosphorylation and restricted plasma-membrane localization, establishing epsin as an upstream regulator of Hip1r localization and phosphorylation.","method":"Dictyostelium null mutant analysis, fluorescence imaging of Hip1r localization, phosphorylation detection by mobility shift, ENTH domain rescue experiment, epistasis of double-null cells","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis plus domain-sufficiency rescue plus phosphorylation assay; single lab in Dictyostelium (ortholog model)","pmids":["20923836"],"is_preprint":false},{"year":2007,"finding":"In Dictyostelium, Hip1r is phosphorylated and localizes to plasma membrane puncta that also contain epsin; both phosphorylation and restricted localization require epsin. Hip1r-null cells form fruiting bodies with morphologically defective (round) spores with decreased viability, and double epsin/Hip1r-null spores are identical to Hip1r single-null spores, placing Hip1r downstream of epsin.","method":"Null mutant genetics, phosphorylation assay, colocalization imaging, double-null epistasis, spore morphology and viability assay","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with multiple readouts; single lab in Dictyostelium ortholog","pmids":["17971415"],"is_preprint":false},{"year":2009,"finding":"HIP1R interacts with BCL2L10 (Diva/BCL-B) identified by yeast two-hybrid and confirmed by co-immunoprecipitation and Far-Western analysis in 293T cells; both ANTH and THATCH domains of HIP1R contribute to BCL2L10 binding. Ectopic HIP1R expression induces moderate apoptosis with mitochondrial membrane potential loss and caspase-9 activation; BAK (but not BAX) is required for HIP1R-induced cell death; BCL2L10 associates with caspase-9, and this association is augmented by HIP1R overexpression.","method":"Yeast two-hybrid, co-immunoprecipitation, Far-Western analysis, domain-deletion mapping, flow cytometry (apoptosis, mitochondrial potential), caspase activation assay, BAK/BAX knockdown","journal":"Cellular physiology and biochemistry","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — yeast two-hybrid confirmed by co-IP and Far-Western, plus functional apoptosis assays; single lab","pmids":["19255499"],"is_preprint":false},{"year":2021,"finding":"The ANTH domain of HIP1R (and CALM and Sla2) binds ubiquitin via a unique C-terminal region within the ANTH domain not found in ENTH domains; structural studies revealed µM-affinity Ub binding. In yeast functional assays, combined loss of Ub-binding by ANTH-domain proteins together with other Ub-binding domains impairs Ub-dependent internalization of a GPCR (Ste2 engineered to rely exclusively on Ub), but not Ub-independent internalization.","method":"Structural studies (binding mode characterization), in vitro ubiquitin-binding assay with µM affinity determination, genetic loss-of-function epistasis in yeast with Ub-signal-dependent internalization reporter","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 / Moderate — structural characterization of Ub-binding site combined with mutagenesis and genetic epistasis in yeast; multiple orthogonal approaches in single study","pmids":["34821552"],"is_preprint":false},{"year":2018,"finding":"Knockdown of HIP1R impairs endocytosis of activated EGFR and reduces downstream ERK and Akt activation in hippocampal neurons; a dominant-negative HIP1R fragment (aa 633-822) interacts with EGFR and disrupts HIP1R-EGFR interaction-mediated dendritic outgrowth, establishing HIP1R as a mediator of EGFR endocytosis and downstream signaling required for dendritic branching.","method":"siRNA knockdown, EGFR endocytosis assay, Western blotting for ERK/Akt phosphorylation, dominant-negative fragment co-immunoprecipitation with EGFR, neuronal morphology analysis","journal":"Frontiers in molecular neuroscience","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — siRNA plus dominant-negative plus co-IP, multiple readouts; single lab","pmids":["30574069"],"is_preprint":false},{"year":2022,"finding":"HIP1R interacts with PTEN in thyroid cancer cells (by co-immunoprecipitation); knockdown of HIP1R reduces intracellular PTEN but upregulates membrane-bound PTEN, suggesting HIP1R mediates PTEN endocytosis. Flurbiprofen disrupts the HIP1R–PTEN interaction and enhances PTEN membrane binding, and its anti-proliferative effect is attenuated by HIP1R or PTEN knockdown.","method":"Co-immunoprecipitation (HIP1R–PTEN), siRNA knockdown, PTEN subcellular fractionation/immunofluorescence, cell proliferation assay, pharmacological intervention","journal":"European journal of medical research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single co-IP plus indirect localization readout; single lab, limited mechanistic follow-up","pmids":["35209947"],"is_preprint":false},{"year":2025,"finding":"The small molecule MS1-96 directly binds PD-L1 (KD = 2.58 µM) and enhances the interaction between HIP1R and PD-L1, shifting PD-L1 intracellular trafficking away from recycling endosomes toward late endosomes and lysosomes for degradation; HIP1R knockdown abolishes MS1-96-driven PD-L1 degradation, confirming HIP1R is required for this lysosomal trafficking route. MS1-96 also induces abnormal N-glycosylation of PD-L1, destabilizing the protein.","method":"Surface plasmon resonance / binding affinity measurement (KD), co-immunoprecipitation, HIP1R siRNA knockdown, subcellular trafficking assays (colocalization with recycling vs. late endosome markers), N-glycosylation analysis, T cell killing assay, in vivo mouse tumor model","journal":"Acta pharmacologica Sinica","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding affinity measurement plus HIP1R knockdown rescue and trafficking assays; single lab with multiple orthogonal methods","pmids":["41184620"],"is_preprint":false},{"year":2024,"finding":"Sla2 (Hip1R yeast orthologue) has two independent binding sites for clathrin light chain (CLC): one conserved between Fungi and Metazoa (including Hip1R), and a second found only in Fungi. Pan1p competes with CLC for the conserved binding site on Sla2. Cryo-EM structural model of Sla2 actin-binding domains in regulatory context was presented.","method":"Cryo-EM structural modeling, molecular biophysics binding assays, AI-assisted interaction prediction confirmed by experimental biophysics, competition assay (Pan1 vs CLC)","journal":"bioRxiv (preprint)","confidence":"Medium","confidence_rationale":"Tier 1-2 / Weak — cryo-EM plus biophysics competition assay; preprint, single lab, not yet peer-reviewed","pmids":[],"is_preprint":true}],"current_model":"HIP1R is a multi-domain endocytic adaptor that bridges clathrin-coated pits to the actin cytoskeleton: its central coiled-coil domain binds clathrin light chain (which, in turn, negatively regulates Hip1R's actin-binding THATCH domain), its ANTH domain binds 3-phosphoinositides and ubiquitin (to recognize ubiquitinated cargo), and its C-terminal proline-rich region binds cortactin's SH3 domain to inhibit actin barbed-end elongation, collectively ensuring that actin assembly at endocytic sites is transient and directional; additionally, HIP1R targets PD-L1 and EGFR to lysosomal degradation via its lysosomal targeting signal, prolongs growth factor receptor half-life, and in gastric parietal cells is required for tubulovesicle formation and normal acid secretion."},"narrative":{"mechanistic_narrative":"HIP1R is a multi-domain endocytic adaptor that physically couples clathrin-coated pits to the actin cytoskeleton and times actin assembly so that it is transient and directional at endocytic sites [PMID:11564758, PMID:14742709]. Its central coiled-coil domain forms stable homodimers and binds clathrin light chain through a conserved 22-residue N-terminal sequence, stimulating clathrin cage assembly; light-chain binding in turn drives HIP1R into a compact conformation that suppresses its own actin engagement, making clathrin a negative regulator of the HIP1R–actin interaction [PMID:11889126, PMID:15533940, PMID:18790740]. Actin binding is mediated by the C-terminal THATCH/I-LWEQ module, whose five-helix bundle engages F-actin through a conserved surface patch and is held in check by intrasteric occlusion and an oligomerizing C-terminal latch [PMID:16415883, PMID:15581353]. HIP1R restrains actin polymerization at coated pits through two further activities: its proline-rich C-terminus binds the cortactin SH3 domain to block actin filament barbed-end elongation, and loss of HIP1R causes coated structures to remain stably and aberrantly associated with dynamin, actin, Arp2/3, and cortactin [PMID:14742709, PMID:17318189]. Its membrane-binding ANTH/ENTH domain binds 3-phosphoinositides and ubiquitin, the latter through a domain-specific site that supports ubiquitin-dependent cargo internalization [PMID:14732715, PMID:34821552]. Beyond core endocytosis, HIP1R routes receptor cargo to degradative or stabilizing fates—it prolongs growth factor receptor half-life and mediates EGFR endocytosis required for downstream ERK/Akt signaling and dendritic outgrowth [PMID:14732715, PMID:30574069], and it delivers PD-L1 to the lysosome via a lysosomal targeting signal, controlling PD-L1 abundance and tumor-cell susceptibility to T-cell killing [PMID:30397328, PMID:41184620]. In gastric parietal cells, HIP1R is required for tubulovesicle formation, normal apical canalicular membrane architecture, and acid secretory dynamics [PMID:18535670]. Conserved function is established by the yeast orthologue Sla2, which negatively regulates Arp2/3-dependent actin polymerization via Pan1p and whose actin attachment is similarly governed by clathrin light chain [PMID:17151356, PMID:21849475].","teleology":[{"year":2001,"claim":"Established HIP1R as a clathrin-coated-pit component that physically bridges the clathrin coat to F-actin, defining its core role as an endocytic adaptor.","evidence":"Co-IP, live-cell imaging, immunogold EM of unroofed cells, and in vitro clathrin assembly with structural EM","pmids":["11564758"],"confidence":"High","gaps":["Mechanism timing actin assembly to coat maturation not yet resolved","Domain responsible for actin coupling not yet mapped"]},{"year":2001,"claim":"Showed that clathrin function and HIP1R–clathrin interaction are required to organize coated pits relative to the actin cytoskeleton.","evidence":"Inducible clathrin Hub dominant-negative, pharmacological actin/myosin disruption, immunofluorescence","pmids":["11733052"],"confidence":"Medium","gaps":["Does not define which HIP1R domains mediate cytoskeletal alignment","Indirect pharmacological perturbations"]},{"year":2002,"claim":"Distinguished HIP1R from HIP1 by demonstrating direct F-actin co-sedimentation, while mapping clathrin-light-chain binding to the shared central helical domain.","evidence":"In vitro F-actin co-sedimentation, clathrin assembly assay, and AP2/clathrin-heavy-chain binding assays","pmids":["11889126"],"confidence":"High","gaps":["Structural basis of actin binding not defined","How actin and clathrin binding are coordinated not addressed"]},{"year":2004,"claim":"Defined the molecular determinant of HIP1R–clathrin coupling: a conserved light-chain N-terminal sequence whose mutation abolishes binding and assembly stimulation.","evidence":"In vitro binding with site-directed light-chain mutagenesis, clathrin assembly assay, and cellular actin imaging","pmids":["15533940"],"confidence":"High","gaps":["Does not establish how light-chain binding feeds back on actin engagement","Cellular consequence shown only by overexpression"]},{"year":2004,"claim":"Showed HIP1R actin binding through the I/LWEQ module is intrinsically autoregulated by intrasteric occlusion and stabilizes filaments, revealing built-in control over actin attachment.","evidence":"F-actin co-sedimentation with truncation mutants and depolymerization assay","pmids":["15581353"],"confidence":"Medium","gaps":["Single biochemical method type","Physiological trigger relieving occlusion not identified"]},{"year":2004,"claim":"Connected HIP1R to membrane recognition and receptor fate, showing ENTH-domain phosphoinositide binding and a role in prolonging growth factor receptor half-life.","evidence":"Lipid-binding assay with ENTH deletion mutant and receptor half-life measurement","pmids":["14732715"],"confidence":"Medium","gaps":["Mechanism linking lipid binding to receptor stabilization unresolved","Apoptosis on ENTH deletion not mechanistically explained"]},{"year":2004,"claim":"Demonstrated that HIP1R confers transience on the actin–endocytic interaction, with its depletion trapping coated structures in a stable actin/Arp2/3/cortactin-associated state.","evidence":"RNAi knockdown, FRAP, double-RNAi epistasis with cortactin, and EM of unroofed cells","pmids":["14742709"],"confidence":"High","gaps":["Molecular basis of cortactin dependence not yet defined","Did not identify the inhibitory biochemical activity"]},{"year":2006,"claim":"Provided the high-resolution structural basis of HIP1R actin binding, identifying the THATCH five-helix bundle, its F-actin surface patch, and an oligomerizing latch.","evidence":"1.9-Å crystal structure with surface-patch mutagenesis and F-actin binding assay","pmids":["16415883"],"confidence":"High","gaps":["Structure of full-length regulated protein not determined","How latch oligomerization is triggered in vivo unknown"]},{"year":2006,"claim":"Established conservation of HIP1R's negative regulation of endocytic actin polymerization, showing yeast Sla2 directly inhibits the Arp2/3 activator Pan1p.","evidence":"TAP-MS, in vitro Arp2/3 activation assay, domain mapping, and genetic epistasis in yeast","pmids":["17151356"],"confidence":"High","gaps":["Whether mammalian HIP1R inhibits an Eps15/Pan1 orthologue not tested here","Coiled-coil mechanism of Pan1 inhibition not structurally defined"]},{"year":2007,"claim":"Identified the biochemical mechanism restraining actin growth: HIP1R proline-rich binding to the cortactin SH3 domain blocks barbed-end elongation, coordinating actin with coat dynamics.","evidence":"In vitro SH3-binding and barbed-end elongation assays, siRNA rescue with deletion mutant, and live imaging","pmids":["17318189"],"confidence":"High","gaps":["How barbed-end inhibition is relieved at scission not defined","Quantitative contribution versus other inhibitors unknown"]},{"year":2007,"claim":"Placed Hip1r downstream of epsin for membrane localization and phosphorylation, with developmental consequences for spore formation in Dictyostelium.","evidence":"Null-mutant genetics, phosphorylation and colocalization assays, double-null epistasis, spore viability","pmids":["17971415"],"confidence":"Medium","gaps":["Kinase phosphorylating Hip1r not identified","Relevance to mammalian HIP1R regulation untested"]},{"year":2008,"claim":"Resolved the regulatory logic of HIP1R: it homodimerizes via its coiled coil, and clathrin light-chain binding drives a compact conformation that suppresses THATCH actin binding.","evidence":"Biophysics of recombinant coiled coils, in vivo co-IP for oligomerization, and actin binding +/- clathrin light chain","pmids":["18790740"],"confidence":"High","gaps":["Structural model of the compact conformation not determined","Cellular timing of the conformational switch not directly observed"]},{"year":2008,"claim":"Defined an in vivo physiological role: HIP1R is required for parietal-cell tubulovesicle formation, canalicular membrane integrity, and acid secretion.","evidence":"Hip1r knockout mouse with EM, localization, acid secretion assay, and gastrin double-knockout epistasis","pmids":["18535670"],"confidence":"High","gaps":["Molecular link between endocytic adaptor function and tubulovesicle biogenesis unresolved","Cause of parietal-cell apoptosis not defined"]},{"year":2009,"claim":"Linked HIP1R to apoptotic machinery via interaction with BCL2L10, with ANTH and THATCH domains contributing to binding and a BAK-dependent death pathway.","evidence":"Yeast two-hybrid, co-IP, Far-Western, domain mapping, apoptosis/caspase assays, and BAK/BAX knockdown","pmids":["19255499"],"confidence":"Medium","gaps":["Physiological relevance of the apoptotic role unclear","Death observed largely on ectopic overexpression"]},{"year":2010,"claim":"Established epsin's ENTH domain as sufficient to restore Hip1r membrane localization and phosphorylation, defining an upstream regulator of Hip1r positioning.","evidence":"Dictyostelium null analysis, ENTH-domain rescue, phosphorylation mobility shift, double-null epistasis","pmids":["20923836"],"confidence":"Medium","gaps":["Mechanism of ENTH-driven phosphorylation unknown","Mammalian conservation of epsin–HIP1R axis untested"]},{"year":2011,"claim":"Extended the clathrin-light-chain regulatory mechanism in yeast, showing CLC controls endocytic progression by gating Sla2–actin attachment through the THATCH domain.","evidence":"Synthetic genetic array, F-actin sedimentation with CLC and Sla2, and THATCH-dependent epistasis","pmids":["21849475"],"confidence":"High","gaps":["Direct demonstration in mammalian cells not provided here","Timing of CLC release during endocytosis not resolved"]},{"year":2018,"claim":"Defined a degradative cargo-targeting function: HIP1R delivers PD-L1 to lysosomes, controlling its abundance and tumor susceptibility to T-cell killing.","evidence":"Reciprocal co-IP, RNAi with PD-L1 flow cytometry, T-cell cytotoxicity co-culture, and PD-LYSO chimeric peptide","pmids":["30397328"],"confidence":"High","gaps":["The lysosomal targeting signal sequence determinant not fully mapped here","How PD-L1 is selected as cargo unresolved"]},{"year":2018,"claim":"Showed HIP1R mediates EGFR endocytosis and downstream ERK/Akt signaling required for dendritic branching, linking its adaptor role to receptor signaling output.","evidence":"siRNA knockdown, EGFR endocytosis assay, ERK/Akt Western blots, dominant-negative co-IP, neuronal morphology","pmids":["30574069"],"confidence":"Medium","gaps":["Reconciliation with earlier receptor-stabilization role not addressed","Direct vs indirect EGFR interaction not fully resolved"]},{"year":2021,"claim":"Identified a ubiquitin-binding site within the ANTH domain that supports ubiquitin-dependent cargo internalization, adding cargo recognition to HIP1R's membrane functions.","evidence":"Structural characterization, in vitro µM-affinity Ub binding, and genetic epistasis with a Ub-dependent GPCR reporter in yeast","pmids":["34821552"],"confidence":"High","gaps":["Mammalian ubiquitinated cargo not directly identified","Functional only in combination with other Ub-binding proteins"]},{"year":2022,"claim":"Reported a HIP1R–PTEN interaction proposing HIP1R-mediated PTEN endocytosis in thyroid cancer cells.","evidence":"Co-IP, siRNA knockdown, PTEN fractionation/IF, proliferation assay, and flurbiprofen intervention","pmids":["35209947"],"confidence":"Low","gaps":["Single co-IP with indirect localization readout, not independently validated","Direct endocytosis of PTEN not demonstrated"]},{"year":2025,"claim":"Mechanistically dissected the PD-L1 degradation route, showing HIP1R is required to shift PD-L1 from recycling endosomes toward late endosomes/lysosomes, exploitable by a small molecule.","evidence":"SPR binding (KD), co-IP, HIP1R siRNA rescue, recycling vs late-endosome colocalization, N-glycosylation analysis, T-cell killing, in vivo tumor model","pmids":["41184620"],"confidence":"Medium","gaps":["How HIP1R diverts cargo between recycling and degradative routes not defined","Generality beyond PD-L1 not tested"]},{"year":null,"claim":"How clathrin-light-chain-driven conformational switching, ubiquitin/lipid cargo recognition, and actin-restraining activities are temporally integrated during a single endocytic event in mammalian cells remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of full-length regulated HIP1R in a coat context","Mammalian ubiquitinated cargo repertoire undefined","Trigger relieving actin inhibition at scission unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[2,5,7]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1,4]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[8]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[4,6,11]},{"term_id":"GO:0038024","term_label":"cargo receptor activity","supporting_discovery_ids":[13,17]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,9,10]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,2,9]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[0,1]},{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[13,20]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,1,4,8]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[13,20]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[18]}],"complexes":["clathrin-coated pit"],"partners":["CLTB","CTTN","EGFR","CD274","BCL2L10","PTEN"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O75146","full_name":"Huntingtin-interacting protein 1-related protein","aliases":["Huntingtin-interacting protein 12","HIP-12"],"length_aa":1068,"mass_kda":119.4,"function":"Component of clathrin-coated pits and vesicles, that may link the endocytic machinery to the actin cytoskeleton. 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coiled-coil domain; it localizes to clathrin-coated pits in vivo; it promotes clathrin cage assembly in vitro; it is a rod-shaped apparent dimer with globular heads at either end and can assemble clathrin-coated vesicles and F-actin into higher order structures.\",\n      \"method\": \"Co-immunoprecipitation, live-cell fluorescence imaging (Hip1R-YFP / DsRed-clathrin LC), immunogold EM of unroofed cells, in vitro clathrin assembly assay, electron microscopy of protein architecture\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple orthogonal methods (live imaging, EM, in vitro assembly assay, overexpression) in a single rigorous study; foundational paper replicated by subsequent work\",\n      \"pmids\": [\"11564758\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Hip1R depletion by RNAi causes clathrin-coated structures to become stably associated with dynamin, actin, Arp2/3, and cortactin (rather than transiently), and this stabilization depends on cortactin; demonstrating that Hip1R makes the actin–endocytic machinery interaction transient and functional. FRAP showed dynamic actin filament assembly can occur at CCSs.\",\n      \"method\": \"RNAi knockdown, fluorescence microscopy, FRAP, double RNAi depletion epistasis, EM of unroofed cells\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean RNAi with defined phenotypic readout, epistasis (double depletion), and live-cell FRAP; replicated conceptually by multiple subsequent studies\",\n      \"pmids\": [\"14742709\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"HIP12 (HIP1R) co-sediments with F-actin in vitro (unlike HIP1, which shows no actin interaction). Both HIP1 and HIP1R stimulate clathrin assembly through their central helical domain, and this domain binds directly to clathrin light chain. HIP1R does not bind to AP2 nor to the terminal domain of clathrin heavy chain with high affinity (unlike HIP1).\",\n      \"method\": \"F-actin co-sedimentation assay, in vitro clathrin assembly assay, direct binding assays for clathrin heavy chain terminal domain and AP2 alpha ear\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution assays with multiple binding partners; single lab but multiple orthogonal biochemical methods\",\n      \"pmids\": [\"11889126\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"HIP1R binds clathrin light chains via the conserved 22-amino acid sequence of the light chain N-terminus; HIP1R prefers light chains associated with clathrin heavy chain; mutations in the conserved light-chain sequence that abolish HIP1R binding block HIP1R-stimulated clathrin assembly in vitro; overexpression of the HIP1R-binding light-chain fragment disrupts cellular actin distribution.\",\n      \"method\": \"In vitro binding assays, site-directed mutagenesis of clathrin light chain, in vitro clathrin assembly assay, overexpression in cells with actin imaging\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis combined with in vitro assembly assay and cell imaging; single lab with multiple orthogonal approaches\",\n      \"pmids\": [\"15533940\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The C-terminal proline-rich domain of Hip1R binds the SH3 domain of cortactin; this Hip1R–cortactin complex inhibits actin assembly by blocking actin filament barbed-end elongation. Hip1R deleted for the cortactin-binding site cannot fully rescue the abnormal actin structures at endocytic sites caused by Hip1R siRNA. In vivo, maximum recruitment of Hip1R, clathrin, and cortactin to endocytic sites is coincident and all disappear together upon vesicle formation.\",\n      \"method\": \"In vitro binding assay (proline-rich domain / SH3 interaction), actin assembly assay (barbed-end elongation), siRNA rescue with deletion mutant, live-cell fluorescence imaging\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro barbed-end elongation assay plus siRNA rescue with domain-deletion mutant plus live imaging; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"17318189\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The 1.9-Å crystal structure of the HIP1R THATCH domain reveals a unique five-helix bundle; a large sequence-conserved surface patch formed primarily by helices 3 and 4 mediates F-actin binding, as shown by point mutations at seven contiguous patch residues that significantly reduce F-actin binding. The THATCH domain also has a conserved C-terminal latch capable of oligomerizing the core, modulating F-actin engagement.\",\n      \"method\": \"X-ray crystallography (1.9 Å), site-directed mutagenesis of surface-patch residues, F-actin binding assay\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution crystal structure validated by mutagenesis and functional F-actin binding assay; rigorous single study\",\n      \"pmids\": [\"16415883\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Hip1 and Hip1R coiled-coil domains form stable homodimers in vitro with no propensity to heterodimerize; homodimers are also predominant in vivo. Clathrin light chain binding induces a compact conformation of Hip1R and significantly reduces actin binding by the THATCH domain, establishing clathrin as a negative regulator of Hip1R–actin interactions.\",\n      \"method\": \"Biophysical analysis of recombinant coiled-coil domains (sedimentation, gel filtration), in vivo co-immunoprecipitation for oligomerization, actin binding assay in the presence/absence of clathrin light chain\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro reconstitution with biophysics plus in vivo validation; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"18790740\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Hip1R (Hip12) binds F-actin through its I/LWEQ module, but actin binding is regulated by intrasteric occlusion — a conserved structural element within the module inhibits the primary actin-binding determinants in the native protein. The I/LWEQ module also contains a dimerization motif and stabilizes actin filaments against depolymerization.\",\n      \"method\": \"F-actin co-sedimentation assay with full-length and truncated proteins, actin depolymerization assay\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro biochemical reconstitution; single lab, single method type\",\n      \"pmids\": [\"15581353\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"HIP1R ENTH domain binds 3-phosphoinositides (preferentially phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 3,5-bisphosphate); deletion of the ENTH domain abolishes lipid binding and induces apoptosis. Full-length HIP1R prolongs the half-life of growth factor receptors after ligand-induced endocytosis.\",\n      \"method\": \"Lipid-binding assay (ENTH domain deletion mutant), receptor half-life measurement by pulse-chase/Western blotting\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct lipid-binding assay with domain-deletion mutant plus receptor stability experiment; single lab, two orthogonal approaches\",\n      \"pmids\": [\"14732715\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Expression of the Hub fragment of clathrin heavy chain (dominant-negative) dissociates Hip1R from coated pits, and disrupts the linear alignment of clathrin-coated pits with the actin cytoskeleton; cytochalasin D (actin disassembly) and BDM (myosin inhibition) also disrupt coated-pit alignment, indicating that proper clathrin function and Hip1R–clathrin interaction are required for cytoskeletal organization of coated pits.\",\n      \"method\": \"Inducible expression of clathrin Hub dominant-negative, immunofluorescence microscopy, pharmacological actin disruption\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — dominant-negative approach combined with pharmacological treatments and imaging; single lab, multiple perturbations\",\n      \"pmids\": [\"11733052\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Hip1r is expressed in gastric parietal cells, localizing predominantly with F-actin to canalicular membranes. Hip1r-deficient mice show loss of tubulovesicles and abnormal apical canalicular membranes in parietal cells, altered acid secretory dynamics, and increased parietal cell apoptosis; normalization of proliferation and gland height in double gastrin/Hip1r knockout mice indicates that elevated gastrin drives glandular hypertrophy secondary to Hip1r loss.\",\n      \"method\": \"Hip1r knockout mouse model, electron microscopy, immunofluorescence/localization, acid secretion assay in isolated gastric glands, double knockout epistasis\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean knockout mouse with multiple orthogonal readouts (EM, secretion assay, double-KO epistasis); rigorous in vivo study\",\n      \"pmids\": [\"18535670\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Yeast Hip1R homologue Sla2p directly inhibits Pan1p (yeast Eps15-related Arp2/3 activator) Arp2/3 complex activation activity in vitro; the coiled-coil region of Sla2p is required for Pan1p inhibition; a pan1 partial loss-of-function mutation suppresses temperature sensitivity, endocytic defects, and actin phenotypes of sla2 coiled-coil deletion mutants, placing Sla2p upstream of Pan1p in negative regulation of actin polymerization during endocytosis.\",\n      \"method\": \"Tandem affinity purification–mass spectrometry (Pan1p interactors), in vitro Arp2/3 activation assay, domain-deletion mapping, genetic epistasis (double mutants)\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro reconstitution of inhibition plus genetic epistasis; single lab but orthogonal biochemical and genetic approaches\",\n      \"pmids\": [\"17151356\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"In yeast, clathrin light chain (CLC) N-terminus binding to Sla2 (Hip1R orthologue) inhibits Sla2 interaction with F-actin in actin sedimentation assays; CLC N-terminus deletion suppresses endocytic defects of rvs and vrp1 mutants in a manner requiring the Sla2 THATCH actin-binding domain, suggesting that CLC regulates endocytic progression by controlling Sla2–actin attachments.\",\n      \"method\": \"Synthetic genetic array analysis, F-actin sedimentation assay with CLC and Sla2, genetic epistasis with THATCH domain requirement\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro actin sedimentation plus systematic genetic epistasis in yeast; replicates and extends mammalian findings\",\n      \"pmids\": [\"21849475\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"HIP1R physically interacts with PD-L1 and delivers PD-L1 to the lysosome via a lysosomal targeting signal; depletion of HIP1R in tumor cells causes PD-L1 accumulation and suppresses T cell-mediated cytotoxicity; a chimeric peptide (PD-LYSO) incorporating HIP1R's lysosomal-sorting signal and PD-L1-binding sequence depletes PD-L1.\",\n      \"method\": \"Co-immunoprecipitation (HIP1R–PD-L1), RNAi knockdown with flow cytometry for PD-L1 levels, T cell cytotoxicity co-culture assay, chimeric peptide functional study\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP, RNAi with functional readout (T cell killing), and peptide rescue experiment; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"30397328\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In Dictyostelium, epsin is required for membrane recruitment and phosphorylation of Hip1r; epsin-null cells phenocopy Hip1r-null cells for actin/clathrin dynamics defects; the ENTH domain of epsin is sufficient to restore Hip1r phosphorylation and restricted plasma-membrane localization, establishing epsin as an upstream regulator of Hip1r localization and phosphorylation.\",\n      \"method\": \"Dictyostelium null mutant analysis, fluorescence imaging of Hip1r localization, phosphorylation detection by mobility shift, ENTH domain rescue experiment, epistasis of double-null cells\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis plus domain-sufficiency rescue plus phosphorylation assay; single lab in Dictyostelium (ortholog model)\",\n      \"pmids\": [\"20923836\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"In Dictyostelium, Hip1r is phosphorylated and localizes to plasma membrane puncta that also contain epsin; both phosphorylation and restricted localization require epsin. Hip1r-null cells form fruiting bodies with morphologically defective (round) spores with decreased viability, and double epsin/Hip1r-null spores are identical to Hip1r single-null spores, placing Hip1r downstream of epsin.\",\n      \"method\": \"Null mutant genetics, phosphorylation assay, colocalization imaging, double-null epistasis, spore morphology and viability assay\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with multiple readouts; single lab in Dictyostelium ortholog\",\n      \"pmids\": [\"17971415\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"HIP1R interacts with BCL2L10 (Diva/BCL-B) identified by yeast two-hybrid and confirmed by co-immunoprecipitation and Far-Western analysis in 293T cells; both ANTH and THATCH domains of HIP1R contribute to BCL2L10 binding. Ectopic HIP1R expression induces moderate apoptosis with mitochondrial membrane potential loss and caspase-9 activation; BAK (but not BAX) is required for HIP1R-induced cell death; BCL2L10 associates with caspase-9, and this association is augmented by HIP1R overexpression.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, Far-Western analysis, domain-deletion mapping, flow cytometry (apoptosis, mitochondrial potential), caspase activation assay, BAK/BAX knockdown\",\n      \"journal\": \"Cellular physiology and biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — yeast two-hybrid confirmed by co-IP and Far-Western, plus functional apoptosis assays; single lab\",\n      \"pmids\": [\"19255499\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The ANTH domain of HIP1R (and CALM and Sla2) binds ubiquitin via a unique C-terminal region within the ANTH domain not found in ENTH domains; structural studies revealed µM-affinity Ub binding. In yeast functional assays, combined loss of Ub-binding by ANTH-domain proteins together with other Ub-binding domains impairs Ub-dependent internalization of a GPCR (Ste2 engineered to rely exclusively on Ub), but not Ub-independent internalization.\",\n      \"method\": \"Structural studies (binding mode characterization), in vitro ubiquitin-binding assay with µM affinity determination, genetic loss-of-function epistasis in yeast with Ub-signal-dependent internalization reporter\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — structural characterization of Ub-binding site combined with mutagenesis and genetic epistasis in yeast; multiple orthogonal approaches in single study\",\n      \"pmids\": [\"34821552\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Knockdown of HIP1R impairs endocytosis of activated EGFR and reduces downstream ERK and Akt activation in hippocampal neurons; a dominant-negative HIP1R fragment (aa 633-822) interacts with EGFR and disrupts HIP1R-EGFR interaction-mediated dendritic outgrowth, establishing HIP1R as a mediator of EGFR endocytosis and downstream signaling required for dendritic branching.\",\n      \"method\": \"siRNA knockdown, EGFR endocytosis assay, Western blotting for ERK/Akt phosphorylation, dominant-negative fragment co-immunoprecipitation with EGFR, neuronal morphology analysis\",\n      \"journal\": \"Frontiers in molecular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — siRNA plus dominant-negative plus co-IP, multiple readouts; single lab\",\n      \"pmids\": [\"30574069\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"HIP1R interacts with PTEN in thyroid cancer cells (by co-immunoprecipitation); knockdown of HIP1R reduces intracellular PTEN but upregulates membrane-bound PTEN, suggesting HIP1R mediates PTEN endocytosis. Flurbiprofen disrupts the HIP1R–PTEN interaction and enhances PTEN membrane binding, and its anti-proliferative effect is attenuated by HIP1R or PTEN knockdown.\",\n      \"method\": \"Co-immunoprecipitation (HIP1R–PTEN), siRNA knockdown, PTEN subcellular fractionation/immunofluorescence, cell proliferation assay, pharmacological intervention\",\n      \"journal\": \"European journal of medical research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single co-IP plus indirect localization readout; single lab, limited mechanistic follow-up\",\n      \"pmids\": [\"35209947\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The small molecule MS1-96 directly binds PD-L1 (KD = 2.58 µM) and enhances the interaction between HIP1R and PD-L1, shifting PD-L1 intracellular trafficking away from recycling endosomes toward late endosomes and lysosomes for degradation; HIP1R knockdown abolishes MS1-96-driven PD-L1 degradation, confirming HIP1R is required for this lysosomal trafficking route. MS1-96 also induces abnormal N-glycosylation of PD-L1, destabilizing the protein.\",\n      \"method\": \"Surface plasmon resonance / binding affinity measurement (KD), co-immunoprecipitation, HIP1R siRNA knockdown, subcellular trafficking assays (colocalization with recycling vs. late endosome markers), N-glycosylation analysis, T cell killing assay, in vivo mouse tumor model\",\n      \"journal\": \"Acta pharmacologica Sinica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding affinity measurement plus HIP1R knockdown rescue and trafficking assays; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"41184620\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Sla2 (Hip1R yeast orthologue) has two independent binding sites for clathrin light chain (CLC): one conserved between Fungi and Metazoa (including Hip1R), and a second found only in Fungi. Pan1p competes with CLC for the conserved binding site on Sla2. Cryo-EM structural model of Sla2 actin-binding domains in regulatory context was presented.\",\n      \"method\": \"Cryo-EM structural modeling, molecular biophysics binding assays, AI-assisted interaction prediction confirmed by experimental biophysics, competition assay (Pan1 vs CLC)\",\n      \"journal\": \"bioRxiv (preprint)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 / Weak — cryo-EM plus biophysics competition assay; preprint, single lab, not yet peer-reviewed\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"HIP1R is a multi-domain endocytic adaptor that bridges clathrin-coated pits to the actin cytoskeleton: its central coiled-coil domain binds clathrin light chain (which, in turn, negatively regulates Hip1R's actin-binding THATCH domain), its ANTH domain binds 3-phosphoinositides and ubiquitin (to recognize ubiquitinated cargo), and its C-terminal proline-rich region binds cortactin's SH3 domain to inhibit actin barbed-end elongation, collectively ensuring that actin assembly at endocytic sites is transient and directional; additionally, HIP1R targets PD-L1 and EGFR to lysosomal degradation via its lysosomal targeting signal, prolongs growth factor receptor half-life, and in gastric parietal cells is required for tubulovesicle formation and normal acid secretion.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"HIP1R is a multi-domain endocytic adaptor that physically couples clathrin-coated pits to the actin cytoskeleton and times actin assembly so that it is transient and directional at endocytic sites [#0, #1]. Its central coiled-coil domain forms stable homodimers and binds clathrin light chain through a conserved 22-residue N-terminal sequence, stimulating clathrin cage assembly; light-chain binding in turn drives HIP1R into a compact conformation that suppresses its own actin engagement, making clathrin a negative regulator of the HIP1R\\u2013actin interaction [#2, #3, #6]. Actin binding is mediated by the C-terminal THATCH/I-LWEQ module, whose five-helix bundle engages F-actin through a conserved surface patch and is held in check by intrasteric occlusion and an oligomerizing C-terminal latch [#5, #7]. HIP1R restrains actin polymerization at coated pits through two further activities: its proline-rich C-terminus binds the cortactin SH3 domain to block actin filament barbed-end elongation, and loss of HIP1R causes coated structures to remain stably and aberrantly associated with dynamin, actin, Arp2/3, and cortactin [#1, #4]. Its membrane-binding ANTH/ENTH domain binds 3-phosphoinositides and ubiquitin, the latter through a domain-specific site that supports ubiquitin-dependent cargo internalization [#8, #17]. Beyond core endocytosis, HIP1R routes receptor cargo to degradative or stabilizing fates\\u2014it prolongs growth factor receptor half-life and mediates EGFR endocytosis required for downstream ERK/Akt signaling and dendritic outgrowth [#8, #18], and it delivers PD-L1 to the lysosome via a lysosomal targeting signal, controlling PD-L1 abundance and tumor-cell susceptibility to T-cell killing [#13, #20]. In gastric parietal cells, HIP1R is required for tubulovesicle formation, normal apical canalicular membrane architecture, and acid secretory dynamics [#10]. Conserved function is established by the yeast orthologue Sla2, which negatively regulates Arp2/3-dependent actin polymerization via Pan1p and whose actin attachment is similarly governed by clathrin light chain [#11, #12].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Established HIP1R as a clathrin-coated-pit component that physically bridges the clathrin coat to F-actin, defining its core role as an endocytic adaptor.\",\n      \"evidence\": \"Co-IP, live-cell imaging, immunogold EM of unroofed cells, and in vitro clathrin assembly with structural EM\",\n      \"pmids\": [\"11564758\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism timing actin assembly to coat maturation not yet resolved\", \"Domain responsible for actin coupling not yet mapped\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Showed that clathrin function and HIP1R\\u2013clathrin interaction are required to organize coated pits relative to the actin cytoskeleton.\",\n      \"evidence\": \"Inducible clathrin Hub dominant-negative, pharmacological actin/myosin disruption, immunofluorescence\",\n      \"pmids\": [\"11733052\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not define which HIP1R domains mediate cytoskeletal alignment\", \"Indirect pharmacological perturbations\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Distinguished HIP1R from HIP1 by demonstrating direct F-actin co-sedimentation, while mapping clathrin-light-chain binding to the shared central helical domain.\",\n      \"evidence\": \"In vitro F-actin co-sedimentation, clathrin assembly assay, and AP2/clathrin-heavy-chain binding assays\",\n      \"pmids\": [\"11889126\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of actin binding not defined\", \"How actin and clathrin binding are coordinated not addressed\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Defined the molecular determinant of HIP1R\\u2013clathrin coupling: a conserved light-chain N-terminal sequence whose mutation abolishes binding and assembly stimulation.\",\n      \"evidence\": \"In vitro binding with site-directed light-chain mutagenesis, clathrin assembly assay, and cellular actin imaging\",\n      \"pmids\": [\"15533940\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not establish how light-chain binding feeds back on actin engagement\", \"Cellular consequence shown only by overexpression\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Showed HIP1R actin binding through the I/LWEQ module is intrinsically autoregulated by intrasteric occlusion and stabilizes filaments, revealing built-in control over actin attachment.\",\n      \"evidence\": \"F-actin co-sedimentation with truncation mutants and depolymerization assay\",\n      \"pmids\": [\"15581353\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single biochemical method type\", \"Physiological trigger relieving occlusion not identified\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Connected HIP1R to membrane recognition and receptor fate, showing ENTH-domain phosphoinositide binding and a role in prolonging growth factor receptor half-life.\",\n      \"evidence\": \"Lipid-binding assay with ENTH deletion mutant and receptor half-life measurement\",\n      \"pmids\": [\"14732715\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking lipid binding to receptor stabilization unresolved\", \"Apoptosis on ENTH deletion not mechanistically explained\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Demonstrated that HIP1R confers transience on the actin\\u2013endocytic interaction, with its depletion trapping coated structures in a stable actin/Arp2/3/cortactin-associated state.\",\n      \"evidence\": \"RNAi knockdown, FRAP, double-RNAi epistasis with cortactin, and EM of unroofed cells\",\n      \"pmids\": [\"14742709\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of cortactin dependence not yet defined\", \"Did not identify the inhibitory biochemical activity\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Provided the high-resolution structural basis of HIP1R actin binding, identifying the THATCH five-helix bundle, its F-actin surface patch, and an oligomerizing latch.\",\n      \"evidence\": \"1.9-\\u00c5 crystal structure with surface-patch mutagenesis and F-actin binding assay\",\n      \"pmids\": [\"16415883\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of full-length regulated protein not determined\", \"How latch oligomerization is triggered in vivo unknown\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Established conservation of HIP1R's negative regulation of endocytic actin polymerization, showing yeast Sla2 directly inhibits the Arp2/3 activator Pan1p.\",\n      \"evidence\": \"TAP-MS, in vitro Arp2/3 activation assay, domain mapping, and genetic epistasis in yeast\",\n      \"pmids\": [\"17151356\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether mammalian HIP1R inhibits an Eps15/Pan1 orthologue not tested here\", \"Coiled-coil mechanism of Pan1 inhibition not structurally defined\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identified the biochemical mechanism restraining actin growth: HIP1R proline-rich binding to the cortactin SH3 domain blocks barbed-end elongation, coordinating actin with coat dynamics.\",\n      \"evidence\": \"In vitro SH3-binding and barbed-end elongation assays, siRNA rescue with deletion mutant, and live imaging\",\n      \"pmids\": [\"17318189\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How barbed-end inhibition is relieved at scission not defined\", \"Quantitative contribution versus other inhibitors unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Placed Hip1r downstream of epsin for membrane localization and phosphorylation, with developmental consequences for spore formation in Dictyostelium.\",\n      \"evidence\": \"Null-mutant genetics, phosphorylation and colocalization assays, double-null epistasis, spore viability\",\n      \"pmids\": [\"17971415\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Kinase phosphorylating Hip1r not identified\", \"Relevance to mammalian HIP1R regulation untested\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Resolved the regulatory logic of HIP1R: it homodimerizes via its coiled coil, and clathrin light-chain binding drives a compact conformation that suppresses THATCH actin binding.\",\n      \"evidence\": \"Biophysics of recombinant coiled coils, in vivo co-IP for oligomerization, and actin binding +/- clathrin light chain\",\n      \"pmids\": [\"18790740\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural model of the compact conformation not determined\", \"Cellular timing of the conformational switch not directly observed\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Defined an in vivo physiological role: HIP1R is required for parietal-cell tubulovesicle formation, canalicular membrane integrity, and acid secretion.\",\n      \"evidence\": \"Hip1r knockout mouse with EM, localization, acid secretion assay, and gastrin double-knockout epistasis\",\n      \"pmids\": [\"18535670\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular link between endocytic adaptor function and tubulovesicle biogenesis unresolved\", \"Cause of parietal-cell apoptosis not defined\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Linked HIP1R to apoptotic machinery via interaction with BCL2L10, with ANTH and THATCH domains contributing to binding and a BAK-dependent death pathway.\",\n      \"evidence\": \"Yeast two-hybrid, co-IP, Far-Western, domain mapping, apoptosis/caspase assays, and BAK/BAX knockdown\",\n      \"pmids\": [\"19255499\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological relevance of the apoptotic role unclear\", \"Death observed largely on ectopic overexpression\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Established epsin's ENTH domain as sufficient to restore Hip1r membrane localization and phosphorylation, defining an upstream regulator of Hip1r positioning.\",\n      \"evidence\": \"Dictyostelium null analysis, ENTH-domain rescue, phosphorylation mobility shift, double-null epistasis\",\n      \"pmids\": [\"20923836\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of ENTH-driven phosphorylation unknown\", \"Mammalian conservation of epsin\\u2013HIP1R axis untested\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Extended the clathrin-light-chain regulatory mechanism in yeast, showing CLC controls endocytic progression by gating Sla2\\u2013actin attachment through the THATCH domain.\",\n      \"evidence\": \"Synthetic genetic array, F-actin sedimentation with CLC and Sla2, and THATCH-dependent epistasis\",\n      \"pmids\": [\"21849475\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct demonstration in mammalian cells not provided here\", \"Timing of CLC release during endocytosis not resolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Defined a degradative cargo-targeting function: HIP1R delivers PD-L1 to lysosomes, controlling its abundance and tumor susceptibility to T-cell killing.\",\n      \"evidence\": \"Reciprocal co-IP, RNAi with PD-L1 flow cytometry, T-cell cytotoxicity co-culture, and PD-LYSO chimeric peptide\",\n      \"pmids\": [\"30397328\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The lysosomal targeting signal sequence determinant not fully mapped here\", \"How PD-L1 is selected as cargo unresolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Showed HIP1R mediates EGFR endocytosis and downstream ERK/Akt signaling required for dendritic branching, linking its adaptor role to receptor signaling output.\",\n      \"evidence\": \"siRNA knockdown, EGFR endocytosis assay, ERK/Akt Western blots, dominant-negative co-IP, neuronal morphology\",\n      \"pmids\": [\"30574069\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Reconciliation with earlier receptor-stabilization role not addressed\", \"Direct vs indirect EGFR interaction not fully resolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identified a ubiquitin-binding site within the ANTH domain that supports ubiquitin-dependent cargo internalization, adding cargo recognition to HIP1R's membrane functions.\",\n      \"evidence\": \"Structural characterization, in vitro \\u00b5M-affinity Ub binding, and genetic epistasis with a Ub-dependent GPCR reporter in yeast\",\n      \"pmids\": [\"34821552\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mammalian ubiquitinated cargo not directly identified\", \"Functional only in combination with other Ub-binding proteins\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Reported a HIP1R\\u2013PTEN interaction proposing HIP1R-mediated PTEN endocytosis in thyroid cancer cells.\",\n      \"evidence\": \"Co-IP, siRNA knockdown, PTEN fractionation/IF, proliferation assay, and flurbiprofen intervention\",\n      \"pmids\": [\"35209947\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single co-IP with indirect localization readout, not independently validated\", \"Direct endocytosis of PTEN not demonstrated\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Mechanistically dissected the PD-L1 degradation route, showing HIP1R is required to shift PD-L1 from recycling endosomes toward late endosomes/lysosomes, exploitable by a small molecule.\",\n      \"evidence\": \"SPR binding (KD), co-IP, HIP1R siRNA rescue, recycling vs late-endosome colocalization, N-glycosylation analysis, T-cell killing, in vivo tumor model\",\n      \"pmids\": [\"41184620\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How HIP1R diverts cargo between recycling and degradative routes not defined\", \"Generality beyond PD-L1 not tested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How clathrin-light-chain-driven conformational switching, ubiquitin/lipid cargo recognition, and actin-restraining activities are temporally integrated during a single endocytic event in mammalian cells remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of full-length regulated HIP1R in a coat context\", \"Mammalian ubiquitinated cargo repertoire undefined\", \"Trigger relieving actin inhibition at scission unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [2, 5, 7]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1, 4]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [4, 6, 11]},\n      {\"term_id\": \"GO:0038024\", \"supporting_discovery_ids\": [13, 17]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 9, 10]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 2, 9]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [13, 20]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 1, 4, 8]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [13, 20]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [18]}\n    ],\n    \"complexes\": [\"clathrin-coated pit\"],\n    \"partners\": [\"CLTB\", \"CTTN\", \"EGFR\", \"CD274\", \"BCL2L10\", \"PTEN\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}