CCT7

CCT7 is the eta subunit of the TRiC/CCT chaperonin complex and functions as a chaperone that directly binds nascent or aggregation-prone client proteins to promote their folding, maturation, and trafficking (PMID:27708139). It is required for proper folding and cell-surface delivery of G protein-coupled receptors, interacting with the thromboxane A2 receptor β-isoform and the β2-adrenergic receptor through their third intracellular loops and C-termini; loss of CCT7 reduces receptor expression and redirects them to juxtanuclear aggresomes, and Trp334 in the TPβ C-terminus is critical for the interaction (PMID:27708139). CCT7 stabilizes viral capsid proteins as folding clients, binding the FAdV-4 hexon and the canine parvovirus VP2 capsid protein to support their accumulation and viral replication (PMID:30691230, PMID:38384266). Through direct binding it also stabilizes and drives nuclear translocation of β-catenin, sustaining Wnt/β-catenin signaling and pluripotency in embryonic stem cells (PMID:41455472). Beyond classical chaperone clients, the isolated CCT7 apical domain inhibits tau aggregation in vitro via a fragmentation-based mechanism (PMID:40400346), and CCT7 suppresses autophagy and promotes fibroblast fibrosis by binding TRAF6 and facilitating its ubiquitination and degradation (PMID:41947340).

1. 2016 High

   Established CCT7 as a chaperone required for GPCR biogenesis, answering how nascent receptors achieve correct folding and trafficking to the cell surface.

   Evidence Yeast two-hybrid, Co-IP, in vitro pull-down, site-directed mutagenesis, and siRNA knockdown with cell-surface expression assays for TPβ and β2AR

   PMID:27708139

   Open questions at the time

   • Whether folding requires the full TRiC/CCT complex or CCT7 alone is not resolved
   • No structural model of the CCT7–receptor interface
   • Generality across other GPCR families not tested
2. 2019 Medium

   Extended CCT7 client repertoire to viral structural proteins, showing it supports adenoviral capsid protein expression and replication.

   Evidence Co-IP plus ectopic overexpression and RNAi knockdown with FAdV-4 replication readout in LMH cells

   PMID:30691230

   Open questions at the time

   • Direct folding/chaperone activity on hexon not demonstrated biochemically
   • Interaction interface on hexon not mapped
   • Single cell system
3. 2024 Medium

   Demonstrated CCT7 stabilizes a second viral capsid protein, defining a stabilization rather than mere binding mechanism via protein half-life.

   Evidence Co-IP, confocal co-localization, VP2 truncation mapping (aa 231–320), cycloheximide chase, and RNAi/inhibitor knockdown with CPV replication assay

   PMID:38384266

   Open questions at the time

   • Mechanism of stabilization (folding vs anti-degradation) not distinguished
   • Role of full chaperonin complex unclear
   • Single lab
4. 2025 Medium

   Revealed a domain-specific anti-aggregation activity, showing the isolated CCT7 apical domain modulates tau fibril formation independently of holocomplex folding cycles.

   Evidence Kinetic aggregation assays, negative-stain EM, and coarse-grained molecular dynamics simulations comparing CCT7 and CCT3 apical domains

   PMID:40400346

   Open questions at the time

   • Activity shown in vitro only, not in cells
   • Relevance to TRiC holocomplex function unknown
   • Physiological consequence for tauopathy untested
5. 2025 Medium

   Connected CCT7 to Wnt signaling and stem cell identity by showing it binds and shuttles β-catenin to maintain pluripotency.

   Evidence CCT7 knockout/knockdown in ESCs, Co-IP, nuclear translocation assay, telomere measurement, and RNA-seq/epigenetic profiling

   PMID:41455472

   Open questions at the time

   • Whether β-catenin is folded as a chaperone client or carried as a transport partner is unclear
   • Mechanism linking CCT7 loss to telomere and 2C-state changes not fully resolved
   • Single lab
6. 2026 Medium

   Identified a non-folding regulatory role in which CCT7 controls autophagy and fibrosis by promoting TRAF6 turnover.

   Evidence Co-IP, ubiquitination assay, siRNA epistasis (TRAF6 KD reversal), autophagy marker quantification, and in vivo knockdown fibrosis model

   PMID:41947340

   Open questions at the time

   • How CCT7 promotes TRAF6 ubiquitination (direct E3 recruitment?) is unknown
   • Whether this is TRiC-dependent is untested
   • Single disease context
7. 2020 Low

   Provided a phenotypic link of CCT7 to cancer cell behavior without defining a molecular mechanism.

   Evidence siRNA knockdown with proliferation, apoptosis, and invasion assays in endometrial cancer cell lines

   PMID:32983981

   Open questions at the time

   • No binding partner or pathway placement identified
   • Cell-line phenotype only
   • No in vivo validation

• It remains unresolved which CCT7 activities operate within the intact TRiC/CCT holocomplex versus as autonomous subunit functions, and how its client-folding role mechanistically relates to its TRAF6-directed degradation and β-catenin transport roles.
• No structural data on CCT7 client complexes
• Complex-dependence of non-folding roles unknown
• Unifying mechanism across diverse clients not established