{"gene":"CCR5","run_date":"2026-04-28T17:28:52","timeline":{"discoveries":[{"year":1996,"finding":"CCR5 (CC CKR5) was identified as a fusion cofactor (co-receptor) for macrophage-tropic HIV-1 entry, acting as a G protein-coupled receptor for RANTES, MIP-1alpha, and MIP-1beta; recombinant CCR5 rendered CD4-expressing nonhuman cells fusion-competent with macrophage-tropic HIV-1 envelopes.","method":"Cell fusion assay; recombinant receptor expression in nonhuman cells; mRNA detection","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — reconstitution in cell-based fusion assay, replicated simultaneously by multiple independent groups (PMIDs 8649511, 8649512, 8674119, 8751444)","pmids":["8658171","8649511","8649512","8674119","8751444"],"is_preprint":false},{"year":1996,"finding":"A 32-bp deletion in CCR5 (CCR5Δ32) causes a frameshift producing a truncated, non-functional protein that is not transported to the cell surface; homozygosity for this allele confers strong resistance to HIV-1 infection by macrophage-tropic strains.","method":"Genetic sequencing; cell-surface expression assay; in vitro HIV infection assay of primary CD4+ T cells from homozygous individuals","journal":"Cell / Nature","confidence":"High","confidence_rationale":"Tier 1-2 — loss-of-function genetics confirmed by surface expression and infection assays, replicated by multiple independent groups","pmids":["8756719","8751444"],"is_preprint":false},{"year":1996,"finding":"CCR5 was molecularly cloned and functionally characterized as a GPCR that binds RANTES, MIP-1beta, and MIP-1alpha with high affinity and generates inositol phosphates in response to these chemokines; it is expressed in lymphoid organs, peripheral blood leukocytes, macrophages, and T cells.","method":"Molecular cloning; radioligand binding assays; inositol phosphate signaling assay in transfected cells; Northern blot expression analysis","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstitution with functional signaling assay, corroborated by independent cloning study","pmids":["8663314","8639485"],"is_preprint":false},{"year":1996,"finding":"CD4 binding to gp120 dramatically enhances the affinity of gp120 for CCR5; the gp120-CD4 complex specifically binds CCR5 and inhibits binding of natural CCR5 ligands MIP-1alpha and MIP-1beta; the V3 loop of gp120 is required for this interaction.","method":"Competitive binding assay (125I-MIP-1beta displacement); cell-based fusion assay; gp120 mutagenesis","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — reconstituted binding with mutagenesis, independently replicated (PMIDs 8906795, 8906796)","pmids":["8906795","8906796"],"is_preprint":false},{"year":1998,"finding":"A conserved gp120 structure adjacent to the V3 loop (CD4-induced epitope region) is critical for CCR5 binding, in addition to the V3 loop itself, indicating a two-element binding site on gp120 for CCR5.","method":"gp120 mutagenesis; CCR5 binding assay","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis with functional binding readout","pmids":["9632396"],"is_preprint":false},{"year":1999,"finding":"The N-terminal region of CCR5 undergoes post-translational modification by O-linked glycosylation and tyrosine sulfation; sulfated N-terminal tyrosines contribute to binding of MIP-1alpha, MIP-1beta, and HIV-1 gp120/CD4 complexes and are required for efficient HIV-1 entry.","method":"Sulfation inhibition (chlorate treatment); tyrosine-to-phenylalanine mutagenesis; binding assay with soluble gp120/CD4; HIV-1 infection assay","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 — PTM identification with mutagenesis and functional validation","pmids":["10089882"],"is_preprint":false},{"year":1999,"finding":"CD4 and CCR5 constitutively associate on the cell surface in the absence of gp120; this interaction involves the second extracellular loop of CCR5 and the first two domains of CD4 and can be inhibited by antibodies that also block HIV-1 infection.","method":"Co-immunoprecipitation; antibody competition assay; CD4/CCR5 truncation mutants","journal":"Proceedings of the National Academy of Sciences","confidence":"Medium","confidence_rationale":"Tier 3 — co-IP with antibody blocking evidence; single study","pmids":["10377443"],"is_preprint":false},{"year":1998,"finding":"CCR5 internalisation is induced by RANTES but not by phorbol esters, distinguishing it from CXCR4; CCR5 lacks the Ser/IleLeu motif required for phorbol-ester-induced endocytosis, indicating distinct endocytic regulation for the two co-receptors.","method":"Flow cytometry-based receptor internalization assay; pharmacological inhibitors; receptor mutant analysis","journal":"Journal of Cell Science","confidence":"High","confidence_rationale":"Tier 2 — comparative mechanistic study with pharmacological dissection and receptor mutants","pmids":["9718374"],"is_preprint":false},{"year":1998,"finding":"CCR5 functionally couples to inhibitory G proteins (Gi, specifically Gialpha2), stimulating [35S]GTPgammaS binding and inhibiting adenylyl cyclase in a pertussis-toxin-sensitive manner; brief RANTES pretreatment causes rapid receptor desensitization and prolonged exposure leads to agonist-dependent internalization.","method":"GTPγS binding assay; adenylyl cyclase inhibition assay; pertussis toxin treatment; flow cytometry for surface receptor; co-transfection with dominant Gialpha2","journal":"Journal of Cellular Biochemistry","confidence":"High","confidence_rationale":"Tier 1 — reconstituted G protein coupling assay with pharmacological validation and Gialpha2 co-expression","pmids":["9736452"],"is_preprint":false},{"year":2000,"finding":"CCR5 receptor dimerization blocks HIV-1 infection; an anti-CCR5 mAb that induces receptor dimerization (without competing with chemokine binding or triggering signaling) prevents HIV-1 replication in vitro and in vivo; chemokines also induce CCR5 dimerization and dimerization is required for their anti-HIV-1 activity.","method":"Anti-CCR5 mAb functional assay; HIV-1 replication in PBMCs; SCID mouse model; receptor dimerization detection","journal":"Proceedings of the National Academy of Sciences","confidence":"Medium","confidence_rationale":"Tier 2 — in vitro and in vivo infection assays with mechanistic mAb characterization; single lab","pmids":["10725362"],"is_preprint":false},{"year":2000,"finding":"MIP-1beta stimulation of CCR5 induces formation of a signaling complex consisting of RAFTK/Pyk2, Syk, SHP1, SHP2, and Grb2; SHP1 and SHP2 undergo enhanced tyrosine phosphorylation upon CCR5 activation; RAFTK acts upstream of Syk activation; phosphatase inhibition abolishes MIP-1beta-induced chemotaxis.","method":"Co-immunoprecipitation; Western blot for phosphorylation; dominant-negative RAFTK mutants; orthovanadate phosphatase inhibitor; chemotaxis assay","journal":"The Journal of Biological Chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP with dominant-negative epistasis and functional chemotaxis readout; single lab","pmids":["10747947"],"is_preprint":false},{"year":2001,"finding":"Eotaxin acts as an agonist for CCR5 (triggering CCR5 internalization at 100 nM) and a natural antagonist for CCR2; eotaxin displaces CCR5 ligands from monocytes and inhibits RANTES/MIP-1beta-induced migration and enzyme release via CCR5.","method":"Receptor internalization assay; 125I-MCP-1 binding competition; chemotaxis assay; calcium mobilization assay; transfected cell lines expressing CCR5 or CCR2","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal assays (binding, internalization, chemotaxis, calcium) in both transfected and primary cells","pmids":["11264152"],"is_preprint":false},{"year":2002,"finding":"CCR5 internalisation after chemokine treatment occurs via clathrin-coated pits (inhibited by sucrose; accompanied by arrestin-2 redistribution) and also through caveolae (inhibited by nystatin/filipin); CCR5 recycling is independent of the Golgi apparatus and late endosomes, and likely proceeds through early endosomes; protein synthesis is not required for receptor recovery.","method":"Pharmacological inhibitors of clathrin (sucrose) and caveolae (nystatin, filipin); vesicle transport inhibitors; GFP-arrestin-2 translocation imaging; flow cytometry","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — multiple pharmacological dissection approaches with imaging; defines two distinct internalization pathways","pmids":["11806977"],"is_preprint":false},{"year":2003,"finding":"Both CD4 and CCR5 accumulate in actin- and ezrin-containing membrane protrusions in living cells; although they extensively co-localize in these structures, they do not exist in a stable constitutive complex.","method":"High-resolution deconvolution fluorescence microscopy of living cells","journal":"Journal of Virology","confidence":"Medium","confidence_rationale":"Tier 2 — live-cell imaging with high resolution; single study","pmids":["12663805"],"is_preprint":false},{"year":2004,"finding":"CCR5 internalization and recycling require actin polymerization and activation of RhoGTPase family members in a Rho-dependent (but Rho kinase-independent) manner; cytochalasin D and Toxin B/C3 exoenzyme each block both CCR5 internalization and recycling.","method":"Actin depolymerization (cytochalasin D); RhoGTPase inhibitors (Toxin B, C3 exoenzyme); Rho kinase inhibitor (Y27632); flow cytometry for surface receptor levels","journal":"European Journal of Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological dissection in two cell types; single lab","pmids":["14717692"],"is_preprint":false},{"year":2004,"finding":"CCR5 inhibitors (including aplaviroc) bind within a predominantly lipophilic pocket at the interface of extracellular loops and the upper transmembrane domain; mutations at key CCR5 residues decreased both gp120 binding and HIV-1 infectivity, while mutations in TM4/TM5 reduced gp120 binding with lesser effects on CC-chemokine binding, indicating the CCR5 inhibitor binding site partially overlaps with but is distinct from the CC-chemokine binding site.","method":"Saturation binding assays; site-directed mutagenesis of CCR5 residues; HIV-1 infection assay; structural modeling","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — mutagenesis combined with binding and functional infection assays mapping distinct binding regions","pmids":["16476734"],"is_preprint":false},{"year":2004,"finding":"I-TAC/CXCL11 acts as a natural antagonist for CCR5: it inhibits MIP-1alpha binding to CCR5-transfected cells and monocytes, blocks RANTES/MIP-1beta-induced chemotaxis, and reduces CCR5-mediated intracellular calcium release and actin polymerization to minimal levels.","method":"Radioligand binding competition assay; chemotaxis assay; intracellular calcium measurement; actin polymerization assay; transfected cells and primary monocytes","journal":"Journal of Leukocyte Biology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal assays (binding, chemotaxis, calcium, actin) in both transfected and primary cells","pmids":["15178708"],"is_preprint":false},{"year":2006,"finding":"Microbial HSP70 binds directly to CCR5 extracellular peptides (demonstrated by surface plasmon resonance), stimulates CCR5-mediated calcium mobilization and p38 MAPK phosphorylation, and induces CCL5 production in CD40/CCR5-co-transfected cells; stimulation of IL-12 p40 by HSP70 is inhibited by the CCR5 antagonist TAK-779.","method":"Surface plasmon resonance (direct binding); calcium mobilization assay; p38 MAPK phosphorylation; transfected HEK293 cells; primary monocyte-derived DCs; CCR5 antagonist (TAK-779) competition","journal":"European Journal of Immunology","confidence":"Medium","confidence_rationale":"Tier 2 — direct binding by SPR plus functional signaling assays; single lab","pmids":["16909434"],"is_preprint":false},{"year":2008,"finding":"CCR5 and CXCR4 physically associate in a signaling complex on T cells; simultaneous expression of and cooperation between CCR5 and CXCR4 is required for chemokine-induced T cell co-stimulation at the immunological synapse; the two receptors are recruited to the immunological synapse where they deliver co-stimulatory signals.","method":"Co-immunoprecipitation; energy transfer (FRET/BRET); immunological synapse imaging; T cell activation assays in CCR5/CXCR4-expressing cells","journal":"Proceedings of the National Academy of Sciences","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP plus FRET evidence for physical interaction with functional T cell readout; single lab","pmids":["18632580"],"is_preprint":false},{"year":2010,"finding":"NMR analysis using methyl-directed transferred cross-saturation on CCR5 reconstituted in high-density lipoprotein particles revealed that valine 59 and valine 63 of MIP-1alpha are in close proximity to CCR5 in the ligand-receptor complex.","method":"NMR (methyl-directed transferred cross-saturation); CCR5 reconstituted into rHDL lipid particles for functional stability","journal":"Journal of the American Chemical Society","confidence":"High","confidence_rationale":"Tier 1 — NMR structural analysis of receptor-ligand complex with functional reconstitution","pmids":["20423099"],"is_preprint":false},{"year":2012,"finding":"CCR5 is a direct cellular receptor for Staphylococcus aureus leukotoxin ED (LukED); CCR5 is required for LukED-mediated cytotoxic killing of CCR5+ myeloid cells and T lymphocytes; CCR5 receptor antagonists (including maraviroc) block LukED-dependent cell killing; CCR5-deficient mice are largely resistant to lethal S. aureus infection.","method":"CCR5 receptor binding assay (surface plasmon resonance); cytotoxicity assay with CCR5-expressing vs. CCR5-deficient cells; pharmacological CCR5 antagonism; CCR5 knockout mouse infection model","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1-2 — direct binding by SPR, genetic KO, pharmacological inhibition, and in vivo mouse model; multiple orthogonal methods","pmids":["23235831"],"is_preprint":false},{"year":2013,"finding":"CCR5 adopts conformationally heterogeneous states at the cell surface; nucleotide-free G protein (NF-G protein)-coupled CCR5 binds native chemokines with sub-nanomolar affinity, whereas gp120/HIV-1 does not discriminate between NF-G protein-coupled and uncoupled CCR5; this conformational heterogeneity allows HIV-1 to exploit low-chemokine-affinity CCR5 conformations for entry, explaining the relatively poor antiviral activity of native chemokines.","method":"Radioligand binding assays with GTP analogs; HIV-1 infection assay; receptor endocytosis assay; CCR5 mutants abolishing G protein coupling","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 1-2 — mechanistic pharmacology with receptor mutants and multiple functional assays establishing conformational model","pmids":["23696662"],"is_preprint":false},{"year":2013,"finding":"Crystal structure of CCR5 at 2.7 Å resolution bound to the HIV entry inhibitor maraviroc reveals a ligand-binding site within the transmembrane bundle that is distinct from proposed major recognition sites for chemokines and gp120, providing the structural basis for allosteric inhibition; comparison with CXCR4 structure suggests charge distributions and steric hindrance from residue substitutions as determinants of HIV-1 co-receptor selectivity.","method":"X-ray crystallography at 2.7 Å; structural comparison with CXCR4; molecular modeling of co-receptor-gp120-V3 complexes","journal":"Science","confidence":"High","confidence_rationale":"Tier 1 — high-resolution crystal structure with structure-based mechanistic interpretation","pmids":["24030490"],"is_preprint":false},{"year":2014,"finding":"The CCR5 mRNA contains a programmed -1 ribosomal frameshift (-1 PRF) signal directed by an mRNA pseudoknot; at least two microRNAs stimulate -1 PRF by forming a triplex RNA structure; the -1 PRF event directs ribosomes to a premature termination codon, destabilizing CCR5 mRNA through the nonsense-mediated decay (NMD) pathway, thereby regulating CCR5 protein levels.","method":"Reporter assay for -1 PRF; RNA pseudoknot mutagenesis; miRNA transfection; NMD pathway inhibition; mRNA stability assay","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal methods (reporter assay, mutagenesis, NMD pathway) establishing a novel regulatory mechanism","pmids":["25043019"],"is_preprint":false},{"year":2018,"finding":"CCR5 forms homodimers in three distinct conformational states involving transmembrane helix 5 residues; two dimeric states correspond to unliganded receptors and the inverse agonist maraviroc stabilizes a third distinct dimeric state; CCR5 dimerization is required for targeting the receptor to the plasma membrane.","method":"Receptor cross-linking; energy transfer (BRET/FRET); functional export assay; computational docking; X-ray crystallography of dimerization interfaces","journal":"Science Signaling","confidence":"High","confidence_rationale":"Tier 1-2 — multiple complementary biophysical methods plus functional membrane targeting assay","pmids":["29739880"],"is_preprint":false},{"year":2009,"finding":"CCR5 promotes hepatic stellate cell (HSC) migration through a redox-sensitive, PI3K-dependent signaling pathway; CCR5 mediates profibrogenic effects in resident liver cells (including HSCs), distinct from CCR1 which acts in bone-marrow-derived cells, as demonstrated in CCR5/CCR1 chimeric and knockout mice.","method":"CCR5-deficient and CCR1-deficient mice; bone marrow chimera experiments; hepatic fibrosis models (CCl4, bile duct ligation); migration assay with PI3K inhibitors and antioxidants; macrophage infiltration quantification","journal":"The Journal of Clinical Investigation","confidence":"High","confidence_rationale":"Tier 2 — genetic KO, chimera experiments, and pharmacological pathway dissection; multiple orthogonal methods","pmids":["19603542"],"is_preprint":false},{"year":2012,"finding":"CCL5-CCR5 signaling in osteosarcoma cells activates MEK, ERK, and NF-κB pathways sequentially, resulting in upregulation of αvβ3 integrin expression and promotion of cell migration; CCR5 (but not CCR1 or CCR3) mediates CCL5-induced migration, as shown by mAb, inhibitor, and siRNA knockdown of CCR5.","method":"CCR5 mAb neutralization; specific kinase inhibitors (MEK, ERK, NF-κB); dominant-negative kinase mutants; CCR5 siRNA knockdown; CCL5 shRNA; migration assay; integrin expression by flow cytometry","journal":"PLoS ONE","confidence":"Medium","confidence_rationale":"Tier 2 — multiple inhibitors and genetic KD with pathway epistasis; single lab","pmids":["22506069"],"is_preprint":false},{"year":2018,"finding":"CCL4 enhances preosteoclast migration via CCR5; RANKL treatment rapidly reduces CCR5 expression on preosteoclasts via MEK and JNK signaling, and this CCR5 downregulation promotes osteoclastogenesis; IFN-γ recovers CCR5 expression and counteracts RANKL-induced CCR5 downregulation.","method":"Migration assay; osteoclast differentiation assay; MEK/JNK inhibitors; IFN-γ treatment; CCR5 expression analysis by flow cytometry/Western blot","journal":"Cell Death & Disease","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacological pathway dissection with functional osteoclastogenesis readout; single lab","pmids":["29717113"],"is_preprint":false},{"year":2021,"finding":"CCR5 activation in neurons promotes NLRP1-dependent pyroptosis after intracerebral hemorrhage via a CCR5/PKA/CREB/NLRP1 signaling axis; CCR5 activation (by rCCL5) suppresses PKA-Cα and p-CREB expression and upregulates NLRP1, ASC, caspase-1, and GSDMD; PKA activation reverses these effects; CCR5 antagonism with maraviroc reduces pyroptosis.","method":"In vivo mouse ICH model; intracerebroventricular injection of rCCL5 and 8-Bromo-cAMP; CREB inhibitor (666-15); Western blot; immunofluorescence; neurobehavioral testing; Fluoro-Jade C staining","journal":"Stroke","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo pathway epistasis with pharmacological and genetic tools; single lab","pmids":["34719258"],"is_preprint":false},{"year":2021,"finding":"Pericyte-secreted CCL5 activates CCR5 on glioblastoma cells to enable DNA-PKcs-mediated DNA damage repair (DDR), conferring resistance to temozolomide chemotherapy; disrupting CCL5-CCR5 paracrine signaling with maraviroc inhibits DDR and improves chemotherapeutic efficacy.","method":"Genetic pericyte depletion in GBM xenografts; CCR5 antagonism (maraviroc); Western blot for DNA-PKcs and DDR markers; survival analysis of tumor-bearing mice; patient-derived xenografts","journal":"Cell Research","confidence":"Medium","confidence_rationale":"Tier 2 — genetic depletion and pharmacological inhibition in vivo with defined molecular readout (DNA-PKcs); single lab","pmids":["34239070"],"is_preprint":false},{"year":2023,"finding":"Activated microglia secrete CCL3, CCL4, and CCL5 which bind and activate neuronal CCR5, promoting mTORC1 activation, inhibiting autophagy, and impairing clearance of aggregate-prone proteins; CCR5 upregulation is self-sustaining because CCL5-CCR5-mediated autophagy inhibition impairs CCR5 degradation itself; pharmacological or genetic CCR5 inhibition rescues mTORC1 hyperactivation and autophagy dysfunction in HD and tauopathy mouse models.","method":"Conditioned medium transfer (microglia to neurons); CCR5 genetic knockout and pharmacological inhibition (maraviroc); mTORC1 activity assay; autophagy flux assay; aggregate clearance; HD and tauopathy mouse models","journal":"Neuron","confidence":"High","confidence_rationale":"Tier 2 — genetic and pharmacological approaches with defined pathway (mTORC1/autophagy) in multiple disease models","pmids":["37105172"],"is_preprint":false},{"year":2023,"finding":"Several new CCR5 C-terminal phosphorylation sites were identified as necessary for stable arrestin2 complex formation; structural studies revealed a pXpp phosphorylation motif (three phosphoresidues) essential for arrestin2 binding and activation; this motif is conserved across many other GPCRs and contributes to arrestin2 vs. arrestin3 isoform specificity.","method":"X-ray crystallography of arrestin2-CCR5 phosphopeptide complexes; NMR; biochemical binding assays; functional β-arrestin recruitment assays; phosphosite mutagenesis","journal":"Molecular Cell","confidence":"High","confidence_rationale":"Tier 1 — crystal structures combined with NMR, biochemical, and functional assays identifying essential phosphorylation motif","pmids":["37244255"],"is_preprint":false},{"year":2023,"finding":"Computational free-energy simulations revealed that CCR5 forms symmetric and asymmetric homodimers using TM4-TM5 as the preferred binding interface, and also forms heterodimers with CXCR4 using TM6-TM7 interfaces; the dimeric states differ in accessibility of ligand- and G protein-binding sites, indicating dimerization as an allosteric mechanism regulating receptor activity.","method":"Coarse-grained metadynamics free-energy simulations; structural modeling","journal":"Nature Communications","confidence":"Low","confidence_rationale":"Tier 4 — computational prediction only; no experimental validation of specific dimerization interfaces","pmids":["37833254"],"is_preprint":false},{"year":2020,"finding":"eNAMPT (extracellular NAMPT/visfatin) binds CCR5 and acts as a natural antagonist: it prevents CCR5 internalization mediated by RANTES, inhibits CCR5-mediated PKC activation, and blocks RANTES-dependent calcium signaling and migration in melanoma cells without activating CCR5 signaling itself.","method":"Surface plasmon resonance (direct binding); calcium signaling assay; PKC activation assay; receptor internalization assay; migration assay; CCR5-overexpressing stable cell line","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 — direct binding by SPR plus multiple functional assays; single lab","pmids":["32098202"],"is_preprint":false},{"year":2019,"finding":"The antisense lncRNA CCR5AS protects CCR5 mRNA from degradation by interfering with interactions between the RNA-binding protein Raly and the CCR5 3' UTR; CCR5AS knockdown or enhancement correspondingly decreases or increases CCR5 expression on CD4+ T cells; CCR5AS variation at rs1015164 (an ATF1 binding site) controls CCR5AS transcription and thereby modulates HIV infection susceptibility.","method":"CCR5AS knockdown/overexpression; RNA-IP for Raly-CCR5 mRNA interaction; CCR5 surface expression by flow cytometry; HIV infection assay in CD4+ T cells","journal":"Nature Immunology","confidence":"Medium","confidence_rationale":"Tier 2 — RNA-IP with loss/gain of function and functional HIV infection readout; single study — Note: this describes regulation OF CCR5 protein expression, not the lncRNA itself as the protein product","pmids":["31209403"],"is_preprint":false}],"current_model":"CCR5 is a seven-transmembrane Gi-coupled chemokine receptor that constitutively forms homodimers (via TM5) required for plasma membrane targeting, and whose N-terminal tyrosine sulfation and second extracellular loop mediate high-affinity binding of CC-chemokines (RANTES/CCL5, MIP-1α/CCL3, MIP-1β/CCL4) and—after CD4-induced conformational change in gp120—HIV-1 entry; agonist binding triggers Gialpha2-mediated cAMP inhibition, activation of a RAFTK/Pyk2–Syk–SHP1/2–Grb2 signaling complex, and GRK-dependent phosphorylation of C-terminal residues (via a pXpp motif) that recruits arrestin2 to drive clathrin/caveolae-mediated internalization and actin/RhoGTPase-dependent recycling through early endosomes; additionally, CCR5 serves as a receptor for S. aureus LukED toxin, promotes hepatic stellate cell migration via PI3K, drives osteoclast precursor recruitment via MEK/JNK, activates mTORC1 to suppress neuronal autophagy, and mediates DNA-PKcs-dependent DNA damage repair in cancer cells, while its expression is post-transcriptionally regulated by miRNA-stimulated programmed −1 ribosomal frameshifting coupled to NMD and by the lncRNA CCR5AS."},"narrative":{"teleology":[{"year":1996,"claim":"Identification of CCR5 as both a CC-chemokine receptor and the essential coreceptor for macrophage-tropic HIV-1 entry resolved the long-standing question of what host factor — beyond CD4 — permitted HIV-1 fusion, and the simultaneous discovery of the CCR5Δ32 loss-of-function allele conferring HIV-1 resistance validated the coreceptor's non-redundant role in vivo.","evidence":"Recombinant CCR5 expression in non-human CD4+ cells reconstituted HIV-1 fusion; molecular cloning with radioligand binding and inositol phosphate assays confirmed chemokine receptor function; genotyping of exposed-uninfected individuals identified CCR5Δ32 homozygosity","pmids":["8658171","8649511","8649512","8674119","8751444","8663314","8639485","8756719"],"confidence":"High","gaps":["Structural basis of the CD4-gp120-CCR5 ternary complex was unknown","Downstream signaling pathways activated by chemokine binding were uncharacterized","Mechanism of CCR5 trafficking and desensitization was not addressed"]},{"year":1998,"claim":"Defining CCR5's G-protein coupling specificity and endocytic regulation established that the receptor signals through Giα2 in a pertussis-toxin-sensitive manner and internalizes via agonist-dependent (but not PKC-dependent) pathways, distinguishing its regulation from the related coreceptor CXCR4.","evidence":"GTPγS binding, adenylyl cyclase inhibition, and pertussis toxin sensitivity assays with Giα2 co-expression; RANTES-induced internalization with pharmacological dissection comparing CCR5 and CXCR4","pmids":["9736452","9718374"],"confidence":"High","gaps":["The specific C-terminal phosphorylation sites driving arrestin recruitment were undefined","Clathrin vs. caveolae contribution to internalization was not resolved","Downstream kinase cascades beyond Gi coupling were unknown"]},{"year":1999,"claim":"Demonstration that N-terminal tyrosine sulfation is required for high-affinity binding of both chemokines and the gp120/CD4 complex identified a critical post-translational determinant of CCR5 ligand recognition, while evidence for constitutive CD4-CCR5 association suggested preformed complexes at the cell surface.","evidence":"Tyrosine-to-phenylalanine mutagenesis and sulfation inhibition with binding and HIV-1 infection assays; co-immunoprecipitation of CD4 and CCR5 with antibody competition","pmids":["10089882","10377443"],"confidence":"High","gaps":["Whether the CD4-CCR5 pre-association is functionally required for HIV entry was debated","The stoichiometry of sulfated tyrosine contributions was not resolved","Structural details of the sulfated N-terminus engaging gp120 were lacking"]},{"year":2000,"claim":"Discovery that CCR5 dimerization blocks HIV-1 infection and that chemokine stimulation assembles a RAFTK/Pyk2–Syk–SHP1/2–Grb2 signaling complex revealed both a quaternary-structure-based antiviral mechanism and the intracellular kinase/phosphatase network mediating chemotaxis downstream of CCR5.","evidence":"Anti-CCR5 mAb inducing dimerization blocked HIV-1 replication in PBMCs and SCID mice; co-IP of signaling complex components with dominant-negative RAFTK epistasis and chemotaxis readout","pmids":["10725362","10747947"],"confidence":"Medium","gaps":["Dimerization interface residues were not mapped","Whether RAFTK-Syk axis operates in all CCR5-expressing cell types was untested","Relationship between dimerization and G-protein coupling was unknown"]},{"year":2002,"claim":"Pharmacological dissection showed that CCR5 internalizes through both clathrin-coated pits (with arrestin-2 redistribution) and caveolae, and recycles through early endosomes independently of the Golgi, establishing dual endocytic pathways and a rapid recycling itinerary.","evidence":"Sucrose (clathrin inhibitor), nystatin/filipin (caveolae inhibitors), GFP-arrestin-2 imaging, and vesicle transport inhibitors in flow-cytometry-based internalization/recycling assays","pmids":["11806977"],"confidence":"High","gaps":["Relative quantitative contribution of clathrin vs. caveolae pathways was not determined","Sorting signals on CCR5 directing each pathway were not identified","Whether the two pathways lead to different signaling outcomes was unknown"]},{"year":2004,"claim":"Identification that actin polymerization and RhoGTPase activation are required for both CCR5 internalization and recycling, combined with mapping of the small-molecule inhibitor binding pocket at the TM/extracellular-loop interface, connected cytoskeletal dynamics to receptor trafficking and defined pharmacologically targetable receptor architecture.","evidence":"Cytochalasin D, Toxin B, and C3 exoenzyme blocked internalization and recycling; site-directed mutagenesis of CCR5 with saturation binding and HIV-1 infection assays mapped inhibitor-binding residues","pmids":["14717692","16476734"],"confidence":"High","gaps":["RhoGTPase family member specificity was not resolved","Structure of the inhibitor-bound receptor at atomic resolution was not yet available","How actin-dependent trafficking feeds back to signaling was unexplored"]},{"year":2012,"claim":"Identification of CCR5 as the direct receptor for S. aureus leukotoxin LukED expanded CCR5's biological role beyond chemokine sensing and HIV-1 entry to bacterial pathogenesis, demonstrating that CCR5 deficiency protects against lethal staphylococcal infection.","evidence":"SPR direct binding; cytotoxicity in CCR5+ vs. CCR5-deficient cells; maraviroc blockade; CCR5 knockout mouse S. aureus infection model","pmids":["23235831"],"confidence":"High","gaps":["Structural basis of LukED recognition of CCR5 vs. chemokine recognition was unknown","Whether LukED triggers CCR5 signaling before pore formation was not addressed","Relevance to human staphylococcal disease outcomes was not established"]},{"year":2013,"claim":"The 2.7 Å crystal structure of CCR5 bound to maraviroc revealed that allosteric inhibitors occupy a pocket within the transmembrane bundle distinct from chemokine and gp120 binding sites, while pharmacological studies showed that HIV-1 gp120 exploits low-chemokine-affinity CCR5 conformations, explaining the limited antiviral efficacy of native chemokines.","evidence":"X-ray crystallography at 2.7 Å resolution; radioligand binding with GTP analogs and G-protein-uncoupled CCR5 mutants; HIV-1 infection assays","pmids":["24030490","23696662"],"confidence":"High","gaps":["Structure of CCR5 in complex with a chemokine or gp120 was not determined","Active-state receptor structure with G protein was unavailable","Dynamics of conformational switching between states in live cells were unresolved"]},{"year":2014,"claim":"Discovery that microRNAs stimulate programmed −1 ribosomal frameshifting on CCR5 mRNA via an RNA pseudoknot, directing the transcript to nonsense-mediated decay, uncovered a novel post-transcriptional mechanism controlling CCR5 protein levels.","evidence":"Reporter assays for −1 PRF; pseudoknot mutagenesis; miRNA transfection; NMD pathway inhibition and mRNA stability measurements","pmids":["25043019"],"confidence":"High","gaps":["Identity and regulation of the specific miRNAs in physiological contexts were incompletely defined","Whether −1 PRF-NMD regulation operates in all CCR5-expressing cell types was untested","Interplay between this mechanism and lncRNA CCR5AS-mediated stabilization was unknown"]},{"year":2018,"claim":"Biophysical characterization established that CCR5 homodimerizes via TM5 in three conformational states, with dimerization required for plasma-membrane targeting; this resolved the structural basis of earlier observations that dimerization modulates both HIV-1 entry and signaling.","evidence":"Cross-linking, BRET/FRET, computational docking, and functional membrane export assays; maraviroc stabilized a distinct dimeric state","pmids":["29739880"],"confidence":"High","gaps":["How dimerization state switches in response to different ligands in real time was not captured","Whether TM5 dimerization interface is the sole interface in vivo was not fully resolved","Impact of dimerization on arrestin recruitment and G-protein selectivity was not tested"]},{"year":2019,"claim":"Identification of the antisense lncRNA CCR5AS as a stabilizer of CCR5 mRNA — by blocking Raly-mediated degradation — added a second post-transcriptional layer of CCR5 regulation and linked the SNP rs1015164 to HIV susceptibility via ATF1-dependent CCR5AS transcription.","evidence":"CCR5AS knockdown/overexpression; RNA-IP for Raly-CCR5 mRNA interaction; CCR5 surface expression by flow cytometry; HIV infection assay in CD4+ T cells","pmids":["31209403"],"confidence":"Medium","gaps":["Whether CCR5AS regulation operates in non-lymphoid CCR5-expressing cells was untested","Interplay between CCR5AS and the −1 PRF/NMD pathway was unexplored","Whether Raly binding is the sole mechanism of CCR5AS action was not determined"]},{"year":2023,"claim":"Structural identification of a conserved pXpp C-terminal phosphorylation motif essential for arrestin-2 recruitment, combined with functional studies in neurons showing CCR5-mediated mTORC1 activation suppresses autophagy and impairs aggregate-prone protein clearance, expanded the mechanistic understanding of CCR5 desensitization and revealed a pathogenic role in neurodegeneration.","evidence":"Crystal structures of arrestin-2–CCR5 phosphopeptide complexes with NMR and phosphosite mutagenesis; conditioned-medium transfer from microglia to neurons with CCR5 KO and maraviroc in HD and tauopathy mouse models","pmids":["37244255","37105172"],"confidence":"High","gaps":["Full-length CCR5–arrestin-2 complex structure is not available","Whether mTORC1 activation is mediated through Gi or arrestin-biased signaling is unresolved","Clinical relevance of CCR5 antagonism in human neurodegenerative disease is untested"]},{"year":null,"claim":"Key unresolved questions include the atomic-resolution structure of CCR5 in complex with a native chemokine or gp120/CD4, the full signaling wiring diagram distinguishing G-protein-dependent from arrestin-biased pathways across different cell types, and whether the multiple post-transcriptional regulatory mechanisms (−1 PRF/NMD, lncRNA CCR5AS) are coordinated or independent.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structure of agonist-bound or G-protein-coupled CCR5 is available","Cell-type-specific signaling bias between Gi and arrestin pathways is undefined","Coordination between −1 PRF/NMD and CCR5AS post-transcriptional mechanisms is unexplored"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[0,2,3,8]},{"term_id":"GO:0120274","term_label":"virus coreceptor activity","supporting_discovery_ids":[0,1,3,4,5]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[1,6,13,24]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[12]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[12]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2,8,10,25,26,28,30]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[0,1,18,20]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[0,1,3,4,5,20,29]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[30]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[28]}],"complexes":["CCR5 homodimer","CCR5–CXCR4 heterodimer"],"partners":["CXCR4","CD4","ARRB1","PYK2","SYK","PTPN6","PTPN11","GRB2"],"other_free_text":[]},"mechanistic_narrative":"CCR5 is a Gi-coupled seven-transmembrane chemokine receptor that transduces signals from CC-chemokines (CCL3, CCL4, CCL5) and serves as the principal coreceptor for macrophage-tropic HIV-1 entry. Agonist binding triggers Giα2-mediated inhibition of adenylyl cyclase, assembly of a RAFTK/Pyk2–Syk–SHP1/2–Grb2 signaling complex, and GRK-dependent C-terminal phosphorylation at a conserved pXpp motif that recruits arrestin-2 for clathrin- and caveolae-mediated internalization followed by actin/RhoGTPase-dependent recycling through early endosomes [PMID:9736452, PMID:10747947, PMID:37244255, PMID:11806977, PMID:14717692]. HIV-1 gp120, after CD4-induced conformational change, engages a bipartite site involving the sulfated N-terminal tyrosines and the second extracellular loop of CCR5, exploiting conformational states distinct from those preferentially bound by native chemokines; the 2.7 Å crystal structure shows that maraviroc occupies an allosteric pocket within the transmembrane bundle separate from chemokine and gp120 recognition sites, while homodimerization via TM5 is required for plasma-membrane targeting [PMID:10089882, PMID:9632396, PMID:24030490, PMID:29739880, PMID:23696662]. Beyond its immune-cell chemotactic role and HIV-1 coreceptor function — abrogated by the CCR5Δ32 loss-of-function allele [PMID:8756719] — CCR5 acts as a receptor for S. aureus LukED leukotoxin [PMID:23235831], promotes hepatic stellate cell migration via PI3K [PMID:19603542], enables DNA-PKcs-dependent DNA damage repair in glioblastoma [PMID:34239070], and activates neuronal mTORC1 to suppress autophagy and impair clearance of aggregate-prone proteins [PMID:37105172]."},"prefetch_data":{"uniprot":{"accession":"P51681","full_name":"C-C chemokine receptor type 5","aliases":["CHEMR13","HIV-1 fusion coreceptor"],"length_aa":352,"mass_kda":40.5,"function":"Receptor for a number of inflammatory CC-chemokines including CCL3/MIP-1-alpha, CCL4/MIP-1-beta and RANTES and subsequently transduces a signal by increasing the intracellular calcium ion level. May play a role in the control of granulocytic lineage proliferation or differentiation. 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\"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Macrophage-tropic HIV-1 isolates across multiple clades (A, B, E, F) utilize CC-CKR5 for entry, but a strict correlation between macrophage tropism and CC-CKR5 utilization could not be established, suggesting an additional cofactor may determine entry into primary macrophages.\",\n      \"method\": \"Single-round replication-competent reporter virus infection of stable cell lines co-expressing CD4 and chemokine receptors\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro entry assay with defined genetic constructs\",\n      \"pmids\": [\"8995695\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"CCR5 endocytosis is induced by the beta-chemokine RANTES but not by phorbol esters, and CCR5 lacks the Ser/IleLeu sequence required for phorbol ester-induced CXCR4 endocytosis, demonstrating distinct internalization mechanisms for CCR5 versus CXCR4.\",\n      \"method\": \"Receptor internalization assays with specific inhibitors and mutant constructs in T cells\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mechanistic dissection with mutants and pharmacological tools, replicated across cell types\",\n      \"pmids\": [\"9718374\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"CCR5 functionally couples to inhibitory G proteins (Gi, specifically Gialpha2), inhibiting adenylyl cyclase and reducing cAMP; this signaling is pertussis toxin-sensitive. CCR5 also undergoes agonist-dependent (RANTES-induced) desensitization and internalization.\",\n      \"method\": \"[35S]GTPgammaS binding assay, adenylyl cyclase inhibition assay, flow cytometry for surface receptor levels, pertussis toxin treatment in CHO and NG108-15 cells\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — direct in vitro functional assays with multiple orthogonal methods\",\n      \"pmids\": [\"9736452\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"CD4 is constitutively associated with CCR5 on the cell surface in the absence of gp120, likely via the second extracellular loop of CCR5 and the first two domains of CD4; this association can be inhibited by CCR5- and CD4-specific antibodies that block HIV-1 infection.\",\n      \"method\": \"Co-immunoprecipitation of CD4 with CCR5 and CXCR4; antibody inhibition of HIV-1 infection\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP with domain mapping and functional antibody inhibition\",\n      \"pmids\": [\"10377443\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"An anti-CCR5 mAb that induces receptor dimerization without competing for chemokine binding or triggering signaling blocks HIV-1 replication; chemokines also induce CCR5 dimerization and this dimerization is required for their anti-HIV-1 activity.\",\n      \"method\": \"HIV replication assay in PBMCs and SCID mice; Ca2+ influx and chemotaxis assays; in vivo SCID mouse model\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional assays in vitro and in vivo, single lab\",\n      \"pmids\": [\"10725362\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"CCR5 activation by MIP-1beta induces tyrosine phosphorylation of SHP1 and SHP2, activates Syk kinase, and forms a signaling complex with RAFTK/Pyk2, Syk, SHP1, and Grb2; RAFTK acts upstream of CCR5-mediated Syk activation and SHP1/SHP2 phosphorylation mediated by RAFTK is independent. SHP phosphatase activity is required for MIP-1beta-induced chemotaxis.\",\n      \"method\": \"Western blot for tyrosine phosphorylation, dominant-negative mutant overexpression (RAFTK mutants), phosphatase inhibitor (orthovanadate), co-immunoprecipitation in CCR5 L1.2 transfectants and primary T cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods including dominant-negative constructs, Co-IP, and functional chemotaxis assay\",\n      \"pmids\": [\"10747947\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Eotaxin (CCL11) acts as an agonist for CCR5 (triggering internalization at 100 nM) and as a natural antagonist for CCR2 (inhibiting MCP-1-induced chemotaxis and enzyme release without activating CCR2), demonstrating eotaxin's promiscuous receptor interactions.\",\n      \"method\": \"Receptor binding displacement assay (125I-MCP-1), receptor internalization assay, chemotaxis assay, calcium mobilization in transfected cells and primary human monocytes\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal functional assays in both transfected cells and primary human cells\",\n      \"pmids\": [\"11264152\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"CCR5 internalization after chemokine treatment occurs via the clathrin-coated pit pathway (inhibited by sucrose; associated with arrestin-2 movement) and also involves caveolae (inhibited by nystatin and filipin); CCR5 recycling is independent of the Golgi apparatus and late endosomes, proceeding through early endosomes back to the cell surface without requiring new protein synthesis.\",\n      \"method\": \"Pharmacological inhibitors (sucrose, nystatin, filipin, brefeldin A) in CHO cells stably expressing CCR5; GFP-arrestin-2 translocation imaging\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple inhibitor approaches, both clathrin and caveolae pathways tested, arrestin imaging\",\n      \"pmids\": [\"11806977\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"CD4 and CCR5 colocalize in actin- and ezrin-containing membrane protrusions in living cells but do not exist in a stable complex at these structures.\",\n      \"method\": \"High-resolution deconvolution fluorescent microscopy of living cells co-expressing fluorescently tagged CD4 and CCR5\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct live-cell imaging with sub-cellular resolution, single lab\",\n      \"pmids\": [\"12663805\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"HIV-1 gp120 activates macrophage signaling through CCR5 and CXCR4, inducing K+, Cl-, and nonselective cation currents, intracellular Ca2+ increases, and activation of Pyk2, MAPK, and PI3-kinase, leading to expression of MCP-1, MIP-1beta, and TNF-alpha.\",\n      \"method\": \"Electrophysiology, Ca2+ imaging, Western blot for kinase activation, cytokine ELISA in primary human macrophages\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple signaling readouts in primary human macrophages, single lab\",\n      \"pmids\": [\"12960231\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CCR5 internalization and recycling require actin polymerization and activation of RhoGTPase family members; Toxin B and C3 exoenzyme inhibit both internalization and recycling, but Rho kinase (ROCK) is not required. CCR5 activation leads to Rho kinase-dependent focal adhesion complex formation.\",\n      \"method\": \"Cytochalasin D (actin depolymerization), Toxin B and C3 exoenzyme (RhoGTPase inhibitors), Y27632 (ROCK inhibitor) in stably transfected CHO cells and THP-1 monocytic cells\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal pharmacological tools in two cell systems, dissects RhoGTPase vs. ROCK roles\",\n      \"pmids\": [\"14717692\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CCR5 inhibitors (including aplaviroc) bind to a predominantly lipophilic pocket at the interface of extracellular loops and upper transmembrane domain of CCR5; specific TM4/TM5 mutations decrease gp120 binding and HIV infectivity with lesser effects on CC-chemokine binding, suggesting region-specific inhibition strategies.\",\n      \"method\": \"Saturation binding assays, site-directed mutagenesis, structural analyses with CCR5 inhibitors\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — binding assays combined with site-directed mutagenesis defining the inhibitor binding pocket\",\n      \"pmids\": [\"16476734\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"I-TAC (CXCL11) acts as a natural antagonist for CCR5, inhibiting MIP-1alpha binding, RANTES- and MIP-1beta-induced cell migration, intracellular calcium release, and actin polymerization mediated by CCR5 in transfected cells and primary monocytes.\",\n      \"method\": \"Competitive binding assay, chemotaxis assay, calcium release assay, actin polymerization assay in CCR5-transfected cells and primary monocytes\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal functional assays demonstrating antagonism in both transfected and primary cells\",\n      \"pmids\": [\"15178708\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Microbial HSP70 binds to CCR5 extracellular peptides (demonstrated by surface plasmon resonance) and activates CCR5-mediated calcium mobilization and p38 MAPK phosphorylation; this interaction is blocked by the CCR5 antagonist TAK-779 and involves cooperation with CD40 to enhance CCL5 production.\",\n      \"method\": \"Surface plasmon resonance binding assay, calcium mobilization assay, p38 MAPK Western blot, CCR5 antagonist inhibition in CCR5-transfected HEK293 cells and primary DCs\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — SPR binding plus functional calcium and signaling assays, single lab\",\n      \"pmids\": [\"16909434\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"CCR5 and CXCR4 physically associate in a signaling complex at the immunological synapse; simultaneous expression and cooperation of both receptors is required for chemokine-induced T cell costimulation, demonstrating functional heterodimerization.\",\n      \"method\": \"Co-immunoprecipitation, FRET/energy transfer, functional costimulation assays in human T cells during antigen-presenting cell interactions\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP plus FRET plus functional assay demonstrating receptor cooperation\",\n      \"pmids\": [\"18632580\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"NMR analysis of CCR5 reconstituted in high-density lipoprotein particles identified valine 59 and valine 63 of MIP-1alpha as residues in close proximity to CCR5 in the ligand-receptor complex, and demonstrated that a SNP of MIP-1alpha affecting HIV-1 protection alters its affinity for CCR5.\",\n      \"method\": \"Methyl-directed transferred cross-saturation NMR of CCR5 reconstituted in rHDL lipid bilayers with MIP-1alpha ligand\",\n      \"journal\": \"Journal of the American Chemical Society\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structural analysis with functional reconstitution in lipid bilayers\",\n      \"pmids\": [\"20423099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CCR5 is an essential cellular receptor for S. aureus leukotoxin ED (LukED); LukED-dependent killing of myeloid cells and T lymphocytes requires CCR5, is blocked by CCR5 antagonists including maraviroc, and CCR5-deficient mice are largely resistant to lethal S. aureus infection.\",\n      \"method\": \"Cell cytotoxicity assay with CCR5-expressing vs. CCR5-deficient cells, receptor antagonist blockade (maraviroc), CCR5-knockout mouse infection model\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mechanistic identification of CCR5 as LukED receptor using KO cells, pharmacological blockade, and in vivo KO mice\",\n      \"pmids\": [\"23235831\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Different CCR5 conformations at the cell surface are differentially engaged by chemokines and HIV-1 gp120: chemokines bind with subnanomolar affinity to nucleotide-free G protein (NFG protein)-coupled CCR5, while gp120/HIV-1 does not discriminate between NFG protein-coupled and uncoupled CCR5. Antiviral chemokine activity is G protein-independent, and 'low-chemokine-affinity' uncoupled CCR5 conformations serve as a portal for viral entry.\",\n      \"method\": \"Radiolabeled ligand binding assays, HIV infectivity assays, CCR5 mutants abolishing G protein coupling, endocytosis assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods including mutagenesis, binding assays, and infectivity assays defining conformational selectivity\",\n      \"pmids\": [\"23696662\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The human CCR5 mRNA contains a programmed -1 ribosomal frameshift (-1 PRF) signal directed by an mRNA pseudoknot; at least two microRNAs stimulate this frameshifting, possibly via triplex RNA structure formation. A -1 PRF event directs ribosomes to a premature termination codon, destabilizing CCR5 mRNA through nonsense-mediated decay (NMD) and at least one additional mRNA decay pathway, thereby regulating CCR5 expression.\",\n      \"method\": \"Ribosomal frameshifting reporter assays, miRNA stimulation assays, pseudoknot mapping, NMD pathway inhibition, mRNA stability assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted frameshifting system with pseudoknot mapping, miRNA stimulation, and NMD pathway dissection\",\n      \"pmids\": [\"25043019\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CCR5 adopts three distinct homodimeric conformations involving residues of transmembrane helix 5; two dimeric states correspond to unliganded receptors and a third is stabilized by the inverse agonist maraviroc. CCR5 dimerization is required for targeting the receptor to the plasma membrane.\",\n      \"method\": \"Computational modeling, receptor cross-linking, FRET/energy transfer assays, functional plasma membrane export assay, x-ray crystallography-informed analysis\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple biophysical methods plus functional export assay defining three dimeric states\",\n      \"pmids\": [\"29739880\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CCL4 promotes preosteoclast migration and viability via CCR5; RANKL reduces CCR5 expression on preosteoclasts through MEK and JNK pathways, and this CCR5 downregulation promotes osteoclastogenesis. IFN-γ can restore CCR5 expression during RANKL-induced differentiation.\",\n      \"method\": \"Migration assays, viability assays, flow cytometry for CCR5 expression, MEK/JNK inhibitors, RANKL stimulation in mouse preosteoclasts\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple functional assays with pathway inhibitors defining CCR5 regulation downstream of RANKL\",\n      \"pmids\": [\"29717113\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The antisense lncRNA CCR5AS controls CCR5 mRNA stability by interfering with interactions between the RNA-binding protein Raly and the CCR5 3' UTR, protecting CCR5 mRNA from Raly-mediated degradation. CCR5AS expression is controlled by an ATF1 binding site near rs1015164. Knockdown or enhancement of CCR5AS causes corresponding changes in CCR5 expression on CD4+ T cells.\",\n      \"method\": \"lncRNA knockdown/overexpression, RNA immunoprecipitation for Raly-CCR5 mRNA interaction, flow cytometry for CCR5 surface expression, HIV infection assay, transcription factor binding site analysis\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods including RIP, functional lncRNA perturbation, and HIV infection readout\",\n      \"pmids\": [\"31209403\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CCR5 activation by CCL5 (secreted by pericytes) activates DNA-PKcs-mediated DNA damage repair (DDR) in glioblastoma cells, promoting temozolomide chemoresistance; genetic depletion of pericytes or CCR5 antagonism with maraviroc blocks pericyte-promoted DDR and improves chemotherapy efficacy.\",\n      \"method\": \"Genetic depletion of pericytes in xenografts, CCR5 antagonist (maraviroc) treatment, DDR signaling Western blot, xenograft survival assay, patient-derived xenografts\",\n      \"journal\": \"Cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic and pharmacological perturbation with defined molecular readout (DNA-PKcs activation) and in vivo validation\",\n      \"pmids\": [\"34239070\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CCR5 activation after intracerebral hemorrhage promotes neuronal pyroptosis via the CCR5/PKA/CREB/NLRP1 signaling pathway: CCR5 activation reduces PKA-Cα and p-CREB expression, upregulates NLRP1, ASC, caspase-1, GSDMD, IL-1β, and IL-18. CCR5 antagonism with maraviroc reverses these effects and improves neurological outcome.\",\n      \"method\": \"In vivo ICH mouse model, intracerebroventricular rCCL5 and 8-Br-cAMP administration, CREB inhibitor (666-15), Western blot, immunofluorescence, behavioral testing\",\n      \"journal\": \"Stroke\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological and genetic epistasis in vivo with mechanistic pathway mapping, single lab\",\n      \"pmids\": [\"34719258\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Activated microglia secrete CCL3/CCL4/CCL5 which bind and activate neuronal CCR5, promoting mTORC1 activation and inhibiting autophagy; this non-cell-autonomous inhibition of neuronal autophagy impairs clearance of aggregate-prone proteins. CCR5 upregulation is self-sustaining because CCL5-CCR5-autophagy inhibition impairs CCR5 degradation itself. Pharmacological or genetic CCR5 inhibition rescues mTORC1 hyperactivation and autophagy dysfunction in HD and tau mouse models.\",\n      \"method\": \"Microglial conditioned media on neurons, CCR5 KO/pharmacological inhibition (maraviroc), mTORC1 activity assays, autophagy flux assays, mouse models of HD and tauopathy\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal approaches (genetic KO + pharmacological inhibition + pathway assays) validated in two disease mouse models\",\n      \"pmids\": [\"37105172\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Arrestin2 binds phosphorylated CCR5 C-terminal peptides through a pXpp phosphorylation motif (three phosphoresidues essential for complex formation and arrestin2 activation); crystal structures of arrestin2-CCR5 C-terminal phosphopeptide complexes and NMR revealed the molecular basis for arrestin2 binding and activation, with implications for GPCR isoform specificity.\",\n      \"method\": \"Crystal structures of arrestin2 with CCR5 phosphopeptides, NMR, mutagenesis, biochemical and functional arrestin2 recruitment assays, identification of new CCR5 phosphorylation sites\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures combined with NMR, mutagenesis, and functional assays in a single study\",\n      \"pmids\": [\"37244255\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Computational free-energy metadynamics revealed that CCR5 homodimerizes preferentially through TM4-TM5 interfaces, forming symmetric and asymmetric dimeric structures; CCR5/CXCR4 heterodimer formation was also characterized. The identified dimeric states differ in access to ligand and G protein binding sites, suggesting dimerization allosterically regulates receptor activity.\",\n      \"method\": \"Coarse-grained metadynamics free-energy simulation; results cross-referenced with experimental dimerization data\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — computational prediction; mechanistic implications not yet validated by direct experiment\",\n      \"pmids\": [\"37833254\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"CCR5 mediates profibrogenic effects in resident liver cells (hepatic stellate cells), promoting HSC migration through a redox-sensitive, PI3K-dependent pathway; CCR5-deficient HSCs show strongly suppressed CC chemokine-induced migration. In chimeric mouse studies, CCR5 in resident liver cells (not bone marrow-derived cells) drives hepatic fibrosis.\",\n      \"method\": \"CCR5-deficient mouse model, bone marrow chimeras, HSC migration assays with PI3K inhibitors and ROS scavengers, experimental liver fibrosis models\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO combined with chimeric mouse epistasis and defined biochemical pathway (PI3K, redox) in primary HSCs\",\n      \"pmids\": [\"19603542\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CCL5-CCR5 interaction in osteosarcoma cells activates MEK, ERK, and NF-κB signaling pathways, resulting in upregulation of αvβ3 integrin expression and enhanced cell migration; CCR5 (but not CCR1 or CCR3) mediates these CCL5 effects.\",\n      \"method\": \"CCR5 mAb, pharmacological inhibitors, CCR5 siRNA knockdown, dominant-negative signaling mutants, migration and invasion assays in human osteosarcoma cells\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple pathway inhibitors and receptor-specific knockdown with defined functional readout\",\n      \"pmids\": [\"22506069\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"eNAMPT (extracellular nicotinamide phosphoribosyltransferase) binds CCR5 and acts as a natural antagonist: it does not activate ERK or Ca2+ release but prevents CCR5 internalization by RANTES and inhibits CCR5-mediated PKC activation and RANTES-dependent calcium signaling and migration.\",\n      \"method\": \"Surface plasmon resonance binding assay, calcium imaging, PKC activation assay, receptor internalization assay, migration assay in HeLa CCR5-overexpressing cells and B16 melanoma cells\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — SPR binding confirmed; multiple functional assays demonstrating antagonism, single lab\",\n      \"pmids\": [\"32098202\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CCR5 is a seven-transmembrane Gi-coupled GPCR that serves as the principal coreceptor for macrophage-tropic HIV-1 entry (acting in concert with CD4), signals through Gi proteins to inhibit adenylyl cyclase and activate downstream cascades including MAPK, PI3K, Pyk2/RAFTK, SHP1/SHP2, and Syk, undergoes agonist-induced internalization via clathrin-coated pits and caveolae in an actin/RhoGTPase-dependent manner, is regulated at the mRNA level by a miRNA-stimulated programmed ribosomal frameshift coupled to NMD and by the lncRNA CCR5AS, forms homodimers (three conformations, TM5-dependent) required for plasma membrane delivery and stabilized distinctly by inverse agonists, recruits arrestin2 through a defined pXpp phosphomotif on its C-terminal tail, and in pathological contexts drives HIV entry, hepatic stellate cell migration, microglial-to-neuronal autophagy inhibition via mTORC1, and DNA damage repair-mediated chemoresistance in glioblastoma through CCL5-CCR5-DNA-PKcs signaling.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1996,\n      \"finding\": \"CCR5 (CC CKR5) was identified as a fusion cofactor (co-receptor) for macrophage-tropic HIV-1 entry, acting as a G protein-coupled receptor for RANTES, MIP-1alpha, and MIP-1beta; recombinant CCR5 rendered CD4-expressing nonhuman cells fusion-competent with macrophage-tropic HIV-1 envelopes.\",\n      \"method\": \"Cell fusion assay; recombinant receptor expression in nonhuman cells; mRNA detection\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution in cell-based fusion assay, replicated simultaneously by multiple independent groups (PMIDs 8649511, 8649512, 8674119, 8751444)\",\n      \"pmids\": [\"8658171\", \"8649511\", \"8649512\", \"8674119\", \"8751444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"A 32-bp deletion in CCR5 (CCR5Δ32) causes a frameshift producing a truncated, non-functional protein that is not transported to the cell surface; homozygosity for this allele confers strong resistance to HIV-1 infection by macrophage-tropic strains.\",\n      \"method\": \"Genetic sequencing; cell-surface expression assay; in vitro HIV infection assay of primary CD4+ T cells from homozygous individuals\",\n      \"journal\": \"Cell / Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — loss-of-function genetics confirmed by surface expression and infection assays, replicated by multiple independent groups\",\n      \"pmids\": [\"8756719\", \"8751444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"CCR5 was molecularly cloned and functionally characterized as a GPCR that binds RANTES, MIP-1beta, and MIP-1alpha with high affinity and generates inositol phosphates in response to these chemokines; it is expressed in lymphoid organs, peripheral blood leukocytes, macrophages, and T cells.\",\n      \"method\": \"Molecular cloning; radioligand binding assays; inositol phosphate signaling assay in transfected cells; Northern blot expression analysis\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution with functional signaling assay, corroborated by independent cloning study\",\n      \"pmids\": [\"8663314\", \"8639485\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"CD4 binding to gp120 dramatically enhances the affinity of gp120 for CCR5; the gp120-CD4 complex specifically binds CCR5 and inhibits binding of natural CCR5 ligands MIP-1alpha and MIP-1beta; the V3 loop of gp120 is required for this interaction.\",\n      \"method\": \"Competitive binding assay (125I-MIP-1beta displacement); cell-based fusion assay; gp120 mutagenesis\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted binding with mutagenesis, independently replicated (PMIDs 8906795, 8906796)\",\n      \"pmids\": [\"8906795\", \"8906796\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"A conserved gp120 structure adjacent to the V3 loop (CD4-induced epitope region) is critical for CCR5 binding, in addition to the V3 loop itself, indicating a two-element binding site on gp120 for CCR5.\",\n      \"method\": \"gp120 mutagenesis; CCR5 binding assay\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis with functional binding readout\",\n      \"pmids\": [\"9632396\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The N-terminal region of CCR5 undergoes post-translational modification by O-linked glycosylation and tyrosine sulfation; sulfated N-terminal tyrosines contribute to binding of MIP-1alpha, MIP-1beta, and HIV-1 gp120/CD4 complexes and are required for efficient HIV-1 entry.\",\n      \"method\": \"Sulfation inhibition (chlorate treatment); tyrosine-to-phenylalanine mutagenesis; binding assay with soluble gp120/CD4; HIV-1 infection assay\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — PTM identification with mutagenesis and functional validation\",\n      \"pmids\": [\"10089882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"CD4 and CCR5 constitutively associate on the cell surface in the absence of gp120; this interaction involves the second extracellular loop of CCR5 and the first two domains of CD4 and can be inhibited by antibodies that also block HIV-1 infection.\",\n      \"method\": \"Co-immunoprecipitation; antibody competition assay; CD4/CCR5 truncation mutants\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — co-IP with antibody blocking evidence; single study\",\n      \"pmids\": [\"10377443\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"CCR5 internalisation is induced by RANTES but not by phorbol esters, distinguishing it from CXCR4; CCR5 lacks the Ser/IleLeu motif required for phorbol-ester-induced endocytosis, indicating distinct endocytic regulation for the two co-receptors.\",\n      \"method\": \"Flow cytometry-based receptor internalization assay; pharmacological inhibitors; receptor mutant analysis\",\n      \"journal\": \"Journal of Cell Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — comparative mechanistic study with pharmacological dissection and receptor mutants\",\n      \"pmids\": [\"9718374\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"CCR5 functionally couples to inhibitory G proteins (Gi, specifically Gialpha2), stimulating [35S]GTPgammaS binding and inhibiting adenylyl cyclase in a pertussis-toxin-sensitive manner; brief RANTES pretreatment causes rapid receptor desensitization and prolonged exposure leads to agonist-dependent internalization.\",\n      \"method\": \"GTPγS binding assay; adenylyl cyclase inhibition assay; pertussis toxin treatment; flow cytometry for surface receptor; co-transfection with dominant Gialpha2\",\n      \"journal\": \"Journal of Cellular Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted G protein coupling assay with pharmacological validation and Gialpha2 co-expression\",\n      \"pmids\": [\"9736452\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"CCR5 receptor dimerization blocks HIV-1 infection; an anti-CCR5 mAb that induces receptor dimerization (without competing with chemokine binding or triggering signaling) prevents HIV-1 replication in vitro and in vivo; chemokines also induce CCR5 dimerization and dimerization is required for their anti-HIV-1 activity.\",\n      \"method\": \"Anti-CCR5 mAb functional assay; HIV-1 replication in PBMCs; SCID mouse model; receptor dimerization detection\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vitro and in vivo infection assays with mechanistic mAb characterization; single lab\",\n      \"pmids\": [\"10725362\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"MIP-1beta stimulation of CCR5 induces formation of a signaling complex consisting of RAFTK/Pyk2, Syk, SHP1, SHP2, and Grb2; SHP1 and SHP2 undergo enhanced tyrosine phosphorylation upon CCR5 activation; RAFTK acts upstream of Syk activation; phosphatase inhibition abolishes MIP-1beta-induced chemotaxis.\",\n      \"method\": \"Co-immunoprecipitation; Western blot for phosphorylation; dominant-negative RAFTK mutants; orthovanadate phosphatase inhibitor; chemotaxis assay\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP with dominant-negative epistasis and functional chemotaxis readout; single lab\",\n      \"pmids\": [\"10747947\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Eotaxin acts as an agonist for CCR5 (triggering CCR5 internalization at 100 nM) and a natural antagonist for CCR2; eotaxin displaces CCR5 ligands from monocytes and inhibits RANTES/MIP-1beta-induced migration and enzyme release via CCR5.\",\n      \"method\": \"Receptor internalization assay; 125I-MCP-1 binding competition; chemotaxis assay; calcium mobilization assay; transfected cell lines expressing CCR5 or CCR2\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal assays (binding, internalization, chemotaxis, calcium) in both transfected and primary cells\",\n      \"pmids\": [\"11264152\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"CCR5 internalisation after chemokine treatment occurs via clathrin-coated pits (inhibited by sucrose; accompanied by arrestin-2 redistribution) and also through caveolae (inhibited by nystatin/filipin); CCR5 recycling is independent of the Golgi apparatus and late endosomes, and likely proceeds through early endosomes; protein synthesis is not required for receptor recovery.\",\n      \"method\": \"Pharmacological inhibitors of clathrin (sucrose) and caveolae (nystatin, filipin); vesicle transport inhibitors; GFP-arrestin-2 translocation imaging; flow cytometry\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple pharmacological dissection approaches with imaging; defines two distinct internalization pathways\",\n      \"pmids\": [\"11806977\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Both CD4 and CCR5 accumulate in actin- and ezrin-containing membrane protrusions in living cells; although they extensively co-localize in these structures, they do not exist in a stable constitutive complex.\",\n      \"method\": \"High-resolution deconvolution fluorescence microscopy of living cells\",\n      \"journal\": \"Journal of Virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — live-cell imaging with high resolution; single study\",\n      \"pmids\": [\"12663805\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CCR5 internalization and recycling require actin polymerization and activation of RhoGTPase family members in a Rho-dependent (but Rho kinase-independent) manner; cytochalasin D and Toxin B/C3 exoenzyme each block both CCR5 internalization and recycling.\",\n      \"method\": \"Actin depolymerization (cytochalasin D); RhoGTPase inhibitors (Toxin B, C3 exoenzyme); Rho kinase inhibitor (Y27632); flow cytometry for surface receptor levels\",\n      \"journal\": \"European Journal of Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological dissection in two cell types; single lab\",\n      \"pmids\": [\"14717692\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CCR5 inhibitors (including aplaviroc) bind within a predominantly lipophilic pocket at the interface of extracellular loops and the upper transmembrane domain; mutations at key CCR5 residues decreased both gp120 binding and HIV-1 infectivity, while mutations in TM4/TM5 reduced gp120 binding with lesser effects on CC-chemokine binding, indicating the CCR5 inhibitor binding site partially overlaps with but is distinct from the CC-chemokine binding site.\",\n      \"method\": \"Saturation binding assays; site-directed mutagenesis of CCR5 residues; HIV-1 infection assay; structural modeling\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mutagenesis combined with binding and functional infection assays mapping distinct binding regions\",\n      \"pmids\": [\"16476734\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"I-TAC/CXCL11 acts as a natural antagonist for CCR5: it inhibits MIP-1alpha binding to CCR5-transfected cells and monocytes, blocks RANTES/MIP-1beta-induced chemotaxis, and reduces CCR5-mediated intracellular calcium release and actin polymerization to minimal levels.\",\n      \"method\": \"Radioligand binding competition assay; chemotaxis assay; intracellular calcium measurement; actin polymerization assay; transfected cells and primary monocytes\",\n      \"journal\": \"Journal of Leukocyte Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal assays (binding, chemotaxis, calcium, actin) in both transfected and primary cells\",\n      \"pmids\": [\"15178708\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Microbial HSP70 binds directly to CCR5 extracellular peptides (demonstrated by surface plasmon resonance), stimulates CCR5-mediated calcium mobilization and p38 MAPK phosphorylation, and induces CCL5 production in CD40/CCR5-co-transfected cells; stimulation of IL-12 p40 by HSP70 is inhibited by the CCR5 antagonist TAK-779.\",\n      \"method\": \"Surface plasmon resonance (direct binding); calcium mobilization assay; p38 MAPK phosphorylation; transfected HEK293 cells; primary monocyte-derived DCs; CCR5 antagonist (TAK-779) competition\",\n      \"journal\": \"European Journal of Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct binding by SPR plus functional signaling assays; single lab\",\n      \"pmids\": [\"16909434\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"CCR5 and CXCR4 physically associate in a signaling complex on T cells; simultaneous expression of and cooperation between CCR5 and CXCR4 is required for chemokine-induced T cell co-stimulation at the immunological synapse; the two receptors are recruited to the immunological synapse where they deliver co-stimulatory signals.\",\n      \"method\": \"Co-immunoprecipitation; energy transfer (FRET/BRET); immunological synapse imaging; T cell activation assays in CCR5/CXCR4-expressing cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP plus FRET evidence for physical interaction with functional T cell readout; single lab\",\n      \"pmids\": [\"18632580\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"NMR analysis using methyl-directed transferred cross-saturation on CCR5 reconstituted in high-density lipoprotein particles revealed that valine 59 and valine 63 of MIP-1alpha are in close proximity to CCR5 in the ligand-receptor complex.\",\n      \"method\": \"NMR (methyl-directed transferred cross-saturation); CCR5 reconstituted into rHDL lipid particles for functional stability\",\n      \"journal\": \"Journal of the American Chemical Society\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structural analysis of receptor-ligand complex with functional reconstitution\",\n      \"pmids\": [\"20423099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CCR5 is a direct cellular receptor for Staphylococcus aureus leukotoxin ED (LukED); CCR5 is required for LukED-mediated cytotoxic killing of CCR5+ myeloid cells and T lymphocytes; CCR5 receptor antagonists (including maraviroc) block LukED-dependent cell killing; CCR5-deficient mice are largely resistant to lethal S. aureus infection.\",\n      \"method\": \"CCR5 receptor binding assay (surface plasmon resonance); cytotoxicity assay with CCR5-expressing vs. CCR5-deficient cells; pharmacological CCR5 antagonism; CCR5 knockout mouse infection model\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct binding by SPR, genetic KO, pharmacological inhibition, and in vivo mouse model; multiple orthogonal methods\",\n      \"pmids\": [\"23235831\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CCR5 adopts conformationally heterogeneous states at the cell surface; nucleotide-free G protein (NF-G protein)-coupled CCR5 binds native chemokines with sub-nanomolar affinity, whereas gp120/HIV-1 does not discriminate between NF-G protein-coupled and uncoupled CCR5; this conformational heterogeneity allows HIV-1 to exploit low-chemokine-affinity CCR5 conformations for entry, explaining the relatively poor antiviral activity of native chemokines.\",\n      \"method\": \"Radioligand binding assays with GTP analogs; HIV-1 infection assay; receptor endocytosis assay; CCR5 mutants abolishing G protein coupling\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mechanistic pharmacology with receptor mutants and multiple functional assays establishing conformational model\",\n      \"pmids\": [\"23696662\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Crystal structure of CCR5 at 2.7 Å resolution bound to the HIV entry inhibitor maraviroc reveals a ligand-binding site within the transmembrane bundle that is distinct from proposed major recognition sites for chemokines and gp120, providing the structural basis for allosteric inhibition; comparison with CXCR4 structure suggests charge distributions and steric hindrance from residue substitutions as determinants of HIV-1 co-receptor selectivity.\",\n      \"method\": \"X-ray crystallography at 2.7 Å; structural comparison with CXCR4; molecular modeling of co-receptor-gp120-V3 complexes\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — high-resolution crystal structure with structure-based mechanistic interpretation\",\n      \"pmids\": [\"24030490\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The CCR5 mRNA contains a programmed -1 ribosomal frameshift (-1 PRF) signal directed by an mRNA pseudoknot; at least two microRNAs stimulate -1 PRF by forming a triplex RNA structure; the -1 PRF event directs ribosomes to a premature termination codon, destabilizing CCR5 mRNA through the nonsense-mediated decay (NMD) pathway, thereby regulating CCR5 protein levels.\",\n      \"method\": \"Reporter assay for -1 PRF; RNA pseudoknot mutagenesis; miRNA transfection; NMD pathway inhibition; mRNA stability assay\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal methods (reporter assay, mutagenesis, NMD pathway) establishing a novel regulatory mechanism\",\n      \"pmids\": [\"25043019\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CCR5 forms homodimers in three distinct conformational states involving transmembrane helix 5 residues; two dimeric states correspond to unliganded receptors and the inverse agonist maraviroc stabilizes a third distinct dimeric state; CCR5 dimerization is required for targeting the receptor to the plasma membrane.\",\n      \"method\": \"Receptor cross-linking; energy transfer (BRET/FRET); functional export assay; computational docking; X-ray crystallography of dimerization interfaces\",\n      \"journal\": \"Science Signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple complementary biophysical methods plus functional membrane targeting assay\",\n      \"pmids\": [\"29739880\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"CCR5 promotes hepatic stellate cell (HSC) migration through a redox-sensitive, PI3K-dependent signaling pathway; CCR5 mediates profibrogenic effects in resident liver cells (including HSCs), distinct from CCR1 which acts in bone-marrow-derived cells, as demonstrated in CCR5/CCR1 chimeric and knockout mice.\",\n      \"method\": \"CCR5-deficient and CCR1-deficient mice; bone marrow chimera experiments; hepatic fibrosis models (CCl4, bile duct ligation); migration assay with PI3K inhibitors and antioxidants; macrophage infiltration quantification\",\n      \"journal\": \"The Journal of Clinical Investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO, chimera experiments, and pharmacological pathway dissection; multiple orthogonal methods\",\n      \"pmids\": [\"19603542\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CCL5-CCR5 signaling in osteosarcoma cells activates MEK, ERK, and NF-κB pathways sequentially, resulting in upregulation of αvβ3 integrin expression and promotion of cell migration; CCR5 (but not CCR1 or CCR3) mediates CCL5-induced migration, as shown by mAb, inhibitor, and siRNA knockdown of CCR5.\",\n      \"method\": \"CCR5 mAb neutralization; specific kinase inhibitors (MEK, ERK, NF-κB); dominant-negative kinase mutants; CCR5 siRNA knockdown; CCL5 shRNA; migration assay; integrin expression by flow cytometry\",\n      \"journal\": \"PLoS ONE\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple inhibitors and genetic KD with pathway epistasis; single lab\",\n      \"pmids\": [\"22506069\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CCL4 enhances preosteoclast migration via CCR5; RANKL treatment rapidly reduces CCR5 expression on preosteoclasts via MEK and JNK signaling, and this CCR5 downregulation promotes osteoclastogenesis; IFN-γ recovers CCR5 expression and counteracts RANKL-induced CCR5 downregulation.\",\n      \"method\": \"Migration assay; osteoclast differentiation assay; MEK/JNK inhibitors; IFN-γ treatment; CCR5 expression analysis by flow cytometry/Western blot\",\n      \"journal\": \"Cell Death & Disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacological pathway dissection with functional osteoclastogenesis readout; single lab\",\n      \"pmids\": [\"29717113\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CCR5 activation in neurons promotes NLRP1-dependent pyroptosis after intracerebral hemorrhage via a CCR5/PKA/CREB/NLRP1 signaling axis; CCR5 activation (by rCCL5) suppresses PKA-Cα and p-CREB expression and upregulates NLRP1, ASC, caspase-1, and GSDMD; PKA activation reverses these effects; CCR5 antagonism with maraviroc reduces pyroptosis.\",\n      \"method\": \"In vivo mouse ICH model; intracerebroventricular injection of rCCL5 and 8-Bromo-cAMP; CREB inhibitor (666-15); Western blot; immunofluorescence; neurobehavioral testing; Fluoro-Jade C staining\",\n      \"journal\": \"Stroke\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo pathway epistasis with pharmacological and genetic tools; single lab\",\n      \"pmids\": [\"34719258\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Pericyte-secreted CCL5 activates CCR5 on glioblastoma cells to enable DNA-PKcs-mediated DNA damage repair (DDR), conferring resistance to temozolomide chemotherapy; disrupting CCL5-CCR5 paracrine signaling with maraviroc inhibits DDR and improves chemotherapeutic efficacy.\",\n      \"method\": \"Genetic pericyte depletion in GBM xenografts; CCR5 antagonism (maraviroc); Western blot for DNA-PKcs and DDR markers; survival analysis of tumor-bearing mice; patient-derived xenografts\",\n      \"journal\": \"Cell Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic depletion and pharmacological inhibition in vivo with defined molecular readout (DNA-PKcs); single lab\",\n      \"pmids\": [\"34239070\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Activated microglia secrete CCL3, CCL4, and CCL5 which bind and activate neuronal CCR5, promoting mTORC1 activation, inhibiting autophagy, and impairing clearance of aggregate-prone proteins; CCR5 upregulation is self-sustaining because CCL5-CCR5-mediated autophagy inhibition impairs CCR5 degradation itself; pharmacological or genetic CCR5 inhibition rescues mTORC1 hyperactivation and autophagy dysfunction in HD and tauopathy mouse models.\",\n      \"method\": \"Conditioned medium transfer (microglia to neurons); CCR5 genetic knockout and pharmacological inhibition (maraviroc); mTORC1 activity assay; autophagy flux assay; aggregate clearance; HD and tauopathy mouse models\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic and pharmacological approaches with defined pathway (mTORC1/autophagy) in multiple disease models\",\n      \"pmids\": [\"37105172\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Several new CCR5 C-terminal phosphorylation sites were identified as necessary for stable arrestin2 complex formation; structural studies revealed a pXpp phosphorylation motif (three phosphoresidues) essential for arrestin2 binding and activation; this motif is conserved across many other GPCRs and contributes to arrestin2 vs. arrestin3 isoform specificity.\",\n      \"method\": \"X-ray crystallography of arrestin2-CCR5 phosphopeptide complexes; NMR; biochemical binding assays; functional β-arrestin recruitment assays; phosphosite mutagenesis\",\n      \"journal\": \"Molecular Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures combined with NMR, biochemical, and functional assays identifying essential phosphorylation motif\",\n      \"pmids\": [\"37244255\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Computational free-energy simulations revealed that CCR5 forms symmetric and asymmetric homodimers using TM4-TM5 as the preferred binding interface, and also forms heterodimers with CXCR4 using TM6-TM7 interfaces; the dimeric states differ in accessibility of ligand- and G protein-binding sites, indicating dimerization as an allosteric mechanism regulating receptor activity.\",\n      \"method\": \"Coarse-grained metadynamics free-energy simulations; structural modeling\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 — computational prediction only; no experimental validation of specific dimerization interfaces\",\n      \"pmids\": [\"37833254\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"eNAMPT (extracellular NAMPT/visfatin) binds CCR5 and acts as a natural antagonist: it prevents CCR5 internalization mediated by RANTES, inhibits CCR5-mediated PKC activation, and blocks RANTES-dependent calcium signaling and migration in melanoma cells without activating CCR5 signaling itself.\",\n      \"method\": \"Surface plasmon resonance (direct binding); calcium signaling assay; PKC activation assay; receptor internalization assay; migration assay; CCR5-overexpressing stable cell line\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct binding by SPR plus multiple functional assays; single lab\",\n      \"pmids\": [\"32098202\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The antisense lncRNA CCR5AS protects CCR5 mRNA from degradation by interfering with interactions between the RNA-binding protein Raly and the CCR5 3' UTR; CCR5AS knockdown or enhancement correspondingly decreases or increases CCR5 expression on CD4+ T cells; CCR5AS variation at rs1015164 (an ATF1 binding site) controls CCR5AS transcription and thereby modulates HIV infection susceptibility.\",\n      \"method\": \"CCR5AS knockdown/overexpression; RNA-IP for Raly-CCR5 mRNA interaction; CCR5 surface expression by flow cytometry; HIV infection assay in CD4+ T cells\",\n      \"journal\": \"Nature Immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — RNA-IP with loss/gain of function and functional HIV infection readout; single study — Note: this describes regulation OF CCR5 protein expression, not the lncRNA itself as the protein product\",\n      \"pmids\": [\"31209403\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CCR5 is a seven-transmembrane Gi-coupled chemokine receptor that constitutively forms homodimers (via TM5) required for plasma membrane targeting, and whose N-terminal tyrosine sulfation and second extracellular loop mediate high-affinity binding of CC-chemokines (RANTES/CCL5, MIP-1α/CCL3, MIP-1β/CCL4) and—after CD4-induced conformational change in gp120—HIV-1 entry; agonist binding triggers Gialpha2-mediated cAMP inhibition, activation of a RAFTK/Pyk2–Syk–SHP1/2–Grb2 signaling complex, and GRK-dependent phosphorylation of C-terminal residues (via a pXpp motif) that recruits arrestin2 to drive clathrin/caveolae-mediated internalization and actin/RhoGTPase-dependent recycling through early endosomes; additionally, CCR5 serves as a receptor for S. aureus LukED toxin, promotes hepatic stellate cell migration via PI3K, drives osteoclast precursor recruitment via MEK/JNK, activates mTORC1 to suppress neuronal autophagy, and mediates DNA-PKcs-dependent DNA damage repair in cancer cells, while its expression is post-transcriptionally regulated by miRNA-stimulated programmed −1 ribosomal frameshifting coupled to NMD and by the lncRNA CCR5AS.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"CCR5 is a Gi-coupled seven-transmembrane chemokine receptor that transduces signals from CC chemokines (CCL3, CCL4, CCL5) to regulate leukocyte migration, immune activation, and tissue homeostasis, and that serves as the principal coreceptor—together with CD4—for macrophage-tropic HIV-1 entry. Ligand binding triggers pertussis toxin–sensitive inhibition of adenylyl cyclase and activates downstream cascades including MAPK, PI3K, Pyk2/RAFTK, Syk, and SHP1/SHP2, while agonist-induced internalization proceeds through both clathrin-coated pits and caveolae in an actin- and RhoGTPase-dependent manner, with arrestin2 recruited via a defined pXpp phosphomotif on the receptor's C-terminal tail [PMID:9736452, PMID:10747947, PMID:11806977, PMID:14717692, PMID:37244255]. CCR5 forms TM5-dependent homodimers in at least three conformational states—required for plasma membrane delivery and differentially stabilized by the inverse agonist maraviroc—and heterodimerizes with CXCR4 at the immunological synapse to enable chemokine-driven T cell costimulation [PMID:29739880, PMID:18632580]. Beyond its role as the HIV-1 coreceptor and a target for S. aureus leukotoxin ED [PMID:8658171, PMID:23235831], CCR5 signaling drives hepatic stellate cell migration and fibrosis via a redox-sensitive PI3K pathway, promotes glioblastoma chemoresistance through CCL5–CCR5–DNA-PKcs-mediated DNA damage repair, and inhibits neuronal autophagy via mTORC1 activation downstream of microglial chemokine release [PMID:19603542, PMID:34239070, PMID:37105172].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"The identity of the macrophage-tropic HIV-1 coreceptor was unknown; reconstitution of CCR5 expression in CD4+ non-human cells conferred susceptibility to M-tropic HIV-1 fusion, establishing CCR5 as the principal HIV-1 entry coreceptor.\",\n      \"evidence\": \"Cell fusion assay with recombinant CCR5 in non-human cells plus mRNA tissue distribution\",\n      \"pmids\": [\"8658171\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of gp120–CCR5 interaction undefined\", \"Whether additional cofactors contribute to macrophage entry unresolved\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"The G protein coupling and core signaling output of CCR5 were undefined; direct biochemical assays demonstrated Gi/Giα2-coupled inhibition of adenylyl cyclase (pertussis toxin–sensitive) and agonist-induced desensitization/internalization, establishing CCR5 as a canonical inhibitory GPCR.\",\n      \"evidence\": \"[35S]GTPγS binding, adenylyl cyclase inhibition, flow cytometry in CHO/NG108-15 cells\",\n      \"pmids\": [\"9736452\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream effector kinases not yet mapped\", \"Mechanism of desensitization not molecularly defined\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Whether CCR5 shares the same internalization mechanism as CXCR4 was unknown; demonstration that RANTES but not PMA drives CCR5 endocytosis, and that CCR5 lacks the Ser/IleLeu motif needed for PKC-driven internalization, established receptor-specific trafficking determinants.\",\n      \"evidence\": \"Receptor internalization assays with inhibitors and mutant constructs in T cells\",\n      \"pmids\": [\"9718374\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endocytic pathway (clathrin vs. caveolae) not yet distinguished\", \"Arrestin involvement not tested\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Whether CD4 and CCR5 exist as a preformed complex was unresolved; co-immunoprecipitation showed constitutive CD4–CCR5 association involving the CCR5 second extracellular loop, suggesting a pre-assembled entry platform for HIV-1.\",\n      \"evidence\": \"Reciprocal co-IP with domain mapping and antibody-blocking HIV-1 infection assays\",\n      \"pmids\": [\"10377443\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Later live-cell imaging questioned stability of this complex (PMID:12663805)\", \"Stoichiometry and affinity of CD4–CCR5 association undefined\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"The signaling intermediates connecting CCR5 to chemotaxis were unknown; identification of a RAFTK/Pyk2–Syk–SHP1/SHP2–Grb2 signaling complex downstream of CCR5, with SHP phosphatase activity required for MIP-1β–induced chemotaxis, mapped a major effector cascade.\",\n      \"evidence\": \"Co-IP, dominant-negative RAFTK, phosphatase inhibitors, chemotaxis assays in CCR5 transfectants and primary T cells\",\n      \"pmids\": [\"10747947\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How this cascade integrates with Gi-mediated cAMP suppression not determined\", \"Whether this complex operates identically in macrophages versus T cells untested\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"The endocytic route of CCR5 was debated; pharmacological dissection showed dual internalization via clathrin-coated pits and caveolae, with recycling through early endosomes independent of the Golgi, and arrestin-2 translocation confirmed adaptor recruitment.\",\n      \"evidence\": \"Sucrose, nystatin, filipin, brefeldin A inhibitors; GFP-arrestin-2 imaging in CHO-CCR5 cells\",\n      \"pmids\": [\"11806977\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of each pathway in primary immune cells unknown\", \"Phosphorylation sites mediating arrestin recruitment not mapped\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Whether cytoskeletal remodeling is required for CCR5 trafficking was untested; actin depolymerization and RhoGTPase inhibition blocked both internalization and recycling, while ROCK was dispensable for trafficking but required for focal adhesion formation, separating trafficking from adhesion outputs.\",\n      \"evidence\": \"Cytochalasin D, Toxin B, C3 exoenzyme, Y27632 in CHO-CCR5 and THP-1 cells\",\n      \"pmids\": [\"14717692\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific Rho family member(s) responsible not identified\", \"Role of Rac/Cdc42 versus RhoA not distinguished\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Whether CCR5 and CXCR4 function cooperatively was unknown; FRET and co-IP demonstrated physical heterodimerization at the immunological synapse, with both receptors required for chemokine-induced T cell costimulation, revealing functional cross-talk between coreceptors.\",\n      \"evidence\": \"Co-IP, FRET, functional costimulation assays in human T cells during APC interaction\",\n      \"pmids\": [\"18632580\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and dynamics of heterodimer in vivo undefined\", \"Whether heterodimerization modulates HIV-1 tropism switching untested\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"The cell-type-specific role of CCR5 in liver fibrosis was unclear; bone marrow chimera experiments with CCR5-KO mice showed that CCR5 in resident hepatic stellate cells—not hematopoietic cells—drives fibrosis through redox-sensitive PI3K-dependent migration.\",\n      \"evidence\": \"CCR5-KO mice, bone marrow chimeras, PI3K/ROS inhibitors, HSC migration assays, liver fibrosis models\",\n      \"pmids\": [\"19603542\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream redox sensor not identified\", \"Whether CCR5 promotes stellate cell activation beyond migration not tested\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Beyond HIV-1, no bacterial ligand for CCR5 was known; identification of CCR5 as the essential receptor for S. aureus leukotoxin ED, with protection of CCR5-deficient mice from lethal infection, expanded CCR5's role to bacterial pathogenesis.\",\n      \"evidence\": \"Cytotoxicity assays in CCR5-expressing vs. KO cells, maraviroc blockade, CCR5-KO mouse infection\",\n      \"pmids\": [\"23235831\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of LukED–CCR5 binding undefined\", \"Whether other leukotoxins also use CCR5 untested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Whether HIV-1 gp120 and chemokines engage the same CCR5 conformations was unknown; binding studies with G protein-coupling mutants showed chemokines preferentially bind nucleotide-free G protein–coupled CCR5, while gp120 is conformation-indiscriminate, explaining how 'uncoupled' CCR5 serves as the viral entry portal.\",\n      \"evidence\": \"Radiolabeled ligand binding, HIV infectivity assays, G protein-uncoupling CCR5 mutants\",\n      \"pmids\": [\"23696662\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural resolution of conformation-selective binding not achieved\", \"In vivo relevance of conformational selection for viral tropism not demonstrated\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"How CCR5 mRNA abundance is post-transcriptionally controlled was unknown; discovery of a microRNA-stimulated programmed −1 ribosomal frameshift coupled to nonsense-mediated decay established a novel translational regulatory mechanism governing CCR5 expression levels.\",\n      \"evidence\": \"Frameshifting reporter assays, pseudoknot mapping, miRNA stimulation, NMD inhibition, mRNA stability assays\",\n      \"pmids\": [\"25043019\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the specific miRNAs driving frameshifting in vivo not fully established\", \"Quantitative contribution of −1 PRF relative to transcriptional regulation in primary cells unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"The oligomeric state of CCR5 at the plasma membrane was structurally undefined; biophysical analyses revealed three TM5-dependent homodimeric conformations, with dimerization required for plasma membrane delivery and the inverse agonist maraviroc stabilizing a distinct dimeric state.\",\n      \"evidence\": \"Cross-linking, FRET, functional PM export assay, crystallography-informed modeling\",\n      \"pmids\": [\"29739880\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional significance of each dimeric state for signaling or HIV entry not delineated\", \"Whether dimerization is dynamically regulated by ligands in real time not shown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Whether non-coding RNA regulates CCR5 mRNA stability was unknown; identification of the antisense lncRNA CCR5AS, which protects CCR5 mRNA from Raly-mediated degradation, established a second post-transcriptional regulatory layer controlling CCR5 surface expression and HIV susceptibility.\",\n      \"evidence\": \"lncRNA knockdown/overexpression, Raly RNA immunoprecipitation, flow cytometry, HIV infection assays\",\n      \"pmids\": [\"31209403\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CCR5AS and miRNA-driven −1 PRF pathways interact or operate independently unknown\", \"Cell-type-specific regulation of CCR5AS not mapped\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"How tumor microenvironment cells confer chemoresistance via CCR5 was unclear; pericyte-secreted CCL5 was shown to activate CCR5–DNA-PKcs signaling in glioblastoma cells, promoting DNA damage repair and temozolomide resistance reversed by maraviroc.\",\n      \"evidence\": \"Pericyte genetic depletion in xenografts, maraviroc treatment, DNA-PKcs signaling assays, patient-derived xenograft survival\",\n      \"pmids\": [\"34239070\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream targets of DNA-PKcs in this context not identified\", \"Whether this mechanism operates in other CCR5-expressing tumors unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"The structural basis of arrestin recruitment to CCR5 was unresolved; crystal structures of arrestin2 bound to CCR5 C-terminal phosphopeptides revealed a pXpp phosphomotif as the essential recognition element, explaining GPCR-arrestin isoform selectivity.\",\n      \"evidence\": \"X-ray crystallography, NMR, mutagenesis, biochemical arrestin recruitment assays\",\n      \"pmids\": [\"37244255\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length CCR5–arrestin2 complex structure not yet solved\", \"How pXpp motif specificity extends to other GPCRs not experimentally validated\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"A non-cell-autonomous neurodegenerative mechanism through CCR5 was unknown; microglial CCL3/4/5 was shown to activate neuronal CCR5–mTORC1, inhibiting autophagy and impairing aggregate-prone protein clearance, with a self-sustaining loop where autophagy inhibition prevents CCR5 degradation.\",\n      \"evidence\": \"Conditioned media, CCR5 KO/maraviroc, mTORC1 and autophagy flux assays, HD and tauopathy mouse models\",\n      \"pmids\": [\"37105172\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific mTORC1 substrate(s) mediating autophagy inhibition downstream of CCR5 not identified\", \"Whether this pathway contributes to other proteinopathies beyond HD and tauopathy untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A high-resolution structure of full-length CCR5 in complex with a G protein heterotrimer, arrestin, or gp120/CD4 has not been determined, leaving the allosteric coupling between dimerization interfaces, the ligand-binding pocket, and intracellular effector engagement incompletely understood at atomic resolution.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Full-length CCR5–effector complex structures lacking\", \"How three dimeric states differentially regulate signaling versus viral entry unresolved\", \"Integration of transcriptional, lncRNA, and −1 PRF regulatory layers in vivo not quantified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 3, 10, 18]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 25]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 4, 9, 20]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [8]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [3, 6, 10, 24, 25, 29]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 15, 17]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 1, 23]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [25]}\n    ],\n    \"complexes\": [\n      \"CCR5 homodimer\",\n      \"CCR5-CXCR4 heterodimer\",\n      \"CD4-CCR5 complex\"\n    ],\n    \"partners\": [\n      \"CD4\",\n      \"CXCR4\",\n      \"ARRB1\",\n      \"PYK2\",\n      \"SYK\",\n      \"PTPN6\",\n      \"PTPN11\",\n      \"GRB2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"CCR5 is a Gi-coupled seven-transmembrane chemokine receptor that transduces signals from CC-chemokines (CCL3, CCL4, CCL5) and serves as the principal coreceptor for macrophage-tropic HIV-1 entry. Agonist binding triggers Giα2-mediated inhibition of adenylyl cyclase, assembly of a RAFTK/Pyk2–Syk–SHP1/2–Grb2 signaling complex, and GRK-dependent C-terminal phosphorylation at a conserved pXpp motif that recruits arrestin-2 for clathrin- and caveolae-mediated internalization followed by actin/RhoGTPase-dependent recycling through early endosomes [PMID:9736452, PMID:10747947, PMID:37244255, PMID:11806977, PMID:14717692]. HIV-1 gp120, after CD4-induced conformational change, engages a bipartite site involving the sulfated N-terminal tyrosines and the second extracellular loop of CCR5, exploiting conformational states distinct from those preferentially bound by native chemokines; the 2.7 Å crystal structure shows that maraviroc occupies an allosteric pocket within the transmembrane bundle separate from chemokine and gp120 recognition sites, while homodimerization via TM5 is required for plasma-membrane targeting [PMID:10089882, PMID:9632396, PMID:24030490, PMID:29739880, PMID:23696662]. Beyond its immune-cell chemotactic role and HIV-1 coreceptor function — abrogated by the CCR5Δ32 loss-of-function allele [PMID:8756719] — CCR5 acts as a receptor for S. aureus LukED leukotoxin [PMID:23235831], promotes hepatic stellate cell migration via PI3K [PMID:19603542], enables DNA-PKcs-dependent DNA damage repair in glioblastoma [PMID:34239070], and activates neuronal mTORC1 to suppress autophagy and impair clearance of aggregate-prone proteins [PMID:37105172].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Identification of CCR5 as both a CC-chemokine receptor and the essential coreceptor for macrophage-tropic HIV-1 entry resolved the long-standing question of what host factor — beyond CD4 — permitted HIV-1 fusion, and the simultaneous discovery of the CCR5Δ32 loss-of-function allele conferring HIV-1 resistance validated the coreceptor's non-redundant role in vivo.\",\n      \"evidence\": \"Recombinant CCR5 expression in non-human CD4+ cells reconstituted HIV-1 fusion; molecular cloning with radioligand binding and inositol phosphate assays confirmed chemokine receptor function; genotyping of exposed-uninfected individuals identified CCR5Δ32 homozygosity\",\n      \"pmids\": [\"8658171\", \"8649511\", \"8649512\", \"8674119\", \"8751444\", \"8663314\", \"8639485\", \"8756719\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the CD4-gp120-CCR5 ternary complex was unknown\", \"Downstream signaling pathways activated by chemokine binding were uncharacterized\", \"Mechanism of CCR5 trafficking and desensitization was not addressed\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Defining CCR5's G-protein coupling specificity and endocytic regulation established that the receptor signals through Giα2 in a pertussis-toxin-sensitive manner and internalizes via agonist-dependent (but not PKC-dependent) pathways, distinguishing its regulation from the related coreceptor CXCR4.\",\n      \"evidence\": \"GTPγS binding, adenylyl cyclase inhibition, and pertussis toxin sensitivity assays with Giα2 co-expression; RANTES-induced internalization with pharmacological dissection comparing CCR5 and CXCR4\",\n      \"pmids\": [\"9736452\", \"9718374\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The specific C-terminal phosphorylation sites driving arrestin recruitment were undefined\", \"Clathrin vs. caveolae contribution to internalization was not resolved\", \"Downstream kinase cascades beyond Gi coupling were unknown\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Demonstration that N-terminal tyrosine sulfation is required for high-affinity binding of both chemokines and the gp120/CD4 complex identified a critical post-translational determinant of CCR5 ligand recognition, while evidence for constitutive CD4-CCR5 association suggested preformed complexes at the cell surface.\",\n      \"evidence\": \"Tyrosine-to-phenylalanine mutagenesis and sulfation inhibition with binding and HIV-1 infection assays; co-immunoprecipitation of CD4 and CCR5 with antibody competition\",\n      \"pmids\": [\"10089882\", \"10377443\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the CD4-CCR5 pre-association is functionally required for HIV entry was debated\", \"The stoichiometry of sulfated tyrosine contributions was not resolved\", \"Structural details of the sulfated N-terminus engaging gp120 were lacking\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Discovery that CCR5 dimerization blocks HIV-1 infection and that chemokine stimulation assembles a RAFTK/Pyk2–Syk–SHP1/2–Grb2 signaling complex revealed both a quaternary-structure-based antiviral mechanism and the intracellular kinase/phosphatase network mediating chemotaxis downstream of CCR5.\",\n      \"evidence\": \"Anti-CCR5 mAb inducing dimerization blocked HIV-1 replication in PBMCs and SCID mice; co-IP of signaling complex components with dominant-negative RAFTK epistasis and chemotaxis readout\",\n      \"pmids\": [\"10725362\", \"10747947\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Dimerization interface residues were not mapped\", \"Whether RAFTK-Syk axis operates in all CCR5-expressing cell types was untested\", \"Relationship between dimerization and G-protein coupling was unknown\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Pharmacological dissection showed that CCR5 internalizes through both clathrin-coated pits (with arrestin-2 redistribution) and caveolae, and recycles through early endosomes independently of the Golgi, establishing dual endocytic pathways and a rapid recycling itinerary.\",\n      \"evidence\": \"Sucrose (clathrin inhibitor), nystatin/filipin (caveolae inhibitors), GFP-arrestin-2 imaging, and vesicle transport inhibitors in flow-cytometry-based internalization/recycling assays\",\n      \"pmids\": [\"11806977\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative quantitative contribution of clathrin vs. caveolae pathways was not determined\", \"Sorting signals on CCR5 directing each pathway were not identified\", \"Whether the two pathways lead to different signaling outcomes was unknown\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Identification that actin polymerization and RhoGTPase activation are required for both CCR5 internalization and recycling, combined with mapping of the small-molecule inhibitor binding pocket at the TM/extracellular-loop interface, connected cytoskeletal dynamics to receptor trafficking and defined pharmacologically targetable receptor architecture.\",\n      \"evidence\": \"Cytochalasin D, Toxin B, and C3 exoenzyme blocked internalization and recycling; site-directed mutagenesis of CCR5 with saturation binding and HIV-1 infection assays mapped inhibitor-binding residues\",\n      \"pmids\": [\"14717692\", \"16476734\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"RhoGTPase family member specificity was not resolved\", \"Structure of the inhibitor-bound receptor at atomic resolution was not yet available\", \"How actin-dependent trafficking feeds back to signaling was unexplored\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identification of CCR5 as the direct receptor for S. aureus leukotoxin LukED expanded CCR5's biological role beyond chemokine sensing and HIV-1 entry to bacterial pathogenesis, demonstrating that CCR5 deficiency protects against lethal staphylococcal infection.\",\n      \"evidence\": \"SPR direct binding; cytotoxicity in CCR5+ vs. CCR5-deficient cells; maraviroc blockade; CCR5 knockout mouse S. aureus infection model\",\n      \"pmids\": [\"23235831\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of LukED recognition of CCR5 vs. chemokine recognition was unknown\", \"Whether LukED triggers CCR5 signaling before pore formation was not addressed\", \"Relevance to human staphylococcal disease outcomes was not established\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"The 2.7 Å crystal structure of CCR5 bound to maraviroc revealed that allosteric inhibitors occupy a pocket within the transmembrane bundle distinct from chemokine and gp120 binding sites, while pharmacological studies showed that HIV-1 gp120 exploits low-chemokine-affinity CCR5 conformations, explaining the limited antiviral efficacy of native chemokines.\",\n      \"evidence\": \"X-ray crystallography at 2.7 Å resolution; radioligand binding with GTP analogs and G-protein-uncoupled CCR5 mutants; HIV-1 infection assays\",\n      \"pmids\": [\"24030490\", \"23696662\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of CCR5 in complex with a chemokine or gp120 was not determined\", \"Active-state receptor structure with G protein was unavailable\", \"Dynamics of conformational switching between states in live cells were unresolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Discovery that microRNAs stimulate programmed −1 ribosomal frameshifting on CCR5 mRNA via an RNA pseudoknot, directing the transcript to nonsense-mediated decay, uncovered a novel post-transcriptional mechanism controlling CCR5 protein levels.\",\n      \"evidence\": \"Reporter assays for −1 PRF; pseudoknot mutagenesis; miRNA transfection; NMD pathway inhibition and mRNA stability measurements\",\n      \"pmids\": [\"25043019\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity and regulation of the specific miRNAs in physiological contexts were incompletely defined\", \"Whether −1 PRF-NMD regulation operates in all CCR5-expressing cell types was untested\", \"Interplay between this mechanism and lncRNA CCR5AS-mediated stabilization was unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Biophysical characterization established that CCR5 homodimerizes via TM5 in three conformational states, with dimerization required for plasma-membrane targeting; this resolved the structural basis of earlier observations that dimerization modulates both HIV-1 entry and signaling.\",\n      \"evidence\": \"Cross-linking, BRET/FRET, computational docking, and functional membrane export assays; maraviroc stabilized a distinct dimeric state\",\n      \"pmids\": [\"29739880\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How dimerization state switches in response to different ligands in real time was not captured\", \"Whether TM5 dimerization interface is the sole interface in vivo was not fully resolved\", \"Impact of dimerization on arrestin recruitment and G-protein selectivity was not tested\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identification of the antisense lncRNA CCR5AS as a stabilizer of CCR5 mRNA — by blocking Raly-mediated degradation — added a second post-transcriptional layer of CCR5 regulation and linked the SNP rs1015164 to HIV susceptibility via ATF1-dependent CCR5AS transcription.\",\n      \"evidence\": \"CCR5AS knockdown/overexpression; RNA-IP for Raly-CCR5 mRNA interaction; CCR5 surface expression by flow cytometry; HIV infection assay in CD4+ T cells\",\n      \"pmids\": [\"31209403\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether CCR5AS regulation operates in non-lymphoid CCR5-expressing cells was untested\", \"Interplay between CCR5AS and the −1 PRF/NMD pathway was unexplored\", \"Whether Raly binding is the sole mechanism of CCR5AS action was not determined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Structural identification of a conserved pXpp C-terminal phosphorylation motif essential for arrestin-2 recruitment, combined with functional studies in neurons showing CCR5-mediated mTORC1 activation suppresses autophagy and impairs aggregate-prone protein clearance, expanded the mechanistic understanding of CCR5 desensitization and revealed a pathogenic role in neurodegeneration.\",\n      \"evidence\": \"Crystal structures of arrestin-2–CCR5 phosphopeptide complexes with NMR and phosphosite mutagenesis; conditioned-medium transfer from microglia to neurons with CCR5 KO and maraviroc in HD and tauopathy mouse models\",\n      \"pmids\": [\"37244255\", \"37105172\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length CCR5–arrestin-2 complex structure is not available\", \"Whether mTORC1 activation is mediated through Gi or arrestin-biased signaling is unresolved\", \"Clinical relevance of CCR5 antagonism in human neurodegenerative disease is untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the atomic-resolution structure of CCR5 in complex with a native chemokine or gp120/CD4, the full signaling wiring diagram distinguishing G-protein-dependent from arrestin-biased pathways across different cell types, and whether the multiple post-transcriptional regulatory mechanisms (−1 PRF/NMD, lncRNA CCR5AS) are coordinated or independent.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structure of agonist-bound or G-protein-coupled CCR5 is available\", \"Cell-type-specific signaling bias between Gi and arrestin pathways is undefined\", \"Coordination between −1 PRF/NMD and CCR5AS post-transcriptional mechanisms is unexplored\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 2, 3, 8]},\n      {\"term_id\": \"GO:0120274\", \"supporting_discovery_ids\": [0, 1, 3, 4, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 6, 13, 24]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [12]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2, 8, 10, 25, 26, 28, 30]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [0, 1, 18, 20]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 1, 3, 4, 5, 20, 29]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [30]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [28]}\n    ],\n    \"complexes\": [\n      \"CCR5 homodimer\",\n      \"CCR5–CXCR4 heterodimer\"\n    ],\n    \"partners\": [\n      \"CXCR4\",\n      \"CD4\",\n      \"ARRB1\",\n      \"PYK2\",\n      \"SYK\",\n      \"PTPN6\",\n      \"PTPN11\",\n      \"GRB2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}