REPS2

REPS2 (POB1) is a multidomain scaffold protein that acts as a negative regulator of growth factor receptor signalling, restraining proliferative, survival, and stemness programs across multiple cancer cell types (PMID:12771942, PMID:35995867, PMID:40514427). Its central proline-rich domain carries adjacent binding motifs for 14-3-3 and for the SH3 domains of Amphiphysin II and Grb2, and engagement of these motifs is required for REPS2 to suppress EGFR (but not transferrin receptor) endocytosis, with 14-3-3 bridging REPS2 to EGFR (PMID:18647389); by blocking EGFR internalisation REPS2 dampens downstream AKT/NF-κB, p38MAPK, and ERK1/2 signalling (PMID:35995867). Its EH domain directly binds the NPF motif of the NF-κB subunit p65 in a PMA-inducible manner, providing a second route to NF-κB modulation (PMID:15184881). REPS2 additionally constrains small-GTPase signalling, acting upstream of the RalBP1/RAC1/CDC42 axis and the FAK/Cdc42 axis, where its loss drives proliferation, EMT, and cytoskeletal reorganisation (PMID:27120794, PMID:35690292), and it promotes p62 (SQSTM1)-dependent autophagy-lysosomal degradation of β-catenin within a REPS2–p62–β-catenin complex to attenuate Wnt signalling and cancer stemness (PMID:40514427). REPS2 expression is transcriptionally activated by LXR through an LXRE in its promoter (PMID:35995867). No structural model of full-length REPS2 or its assembled signalling complexes has been characterized in the available corpus.

1. 2003 Medium

   Established REPS2 as a functional negative regulator of growth factor/Ral signalling rather than a passive structural protein, by linking its overexpression to a measurable cellular consequence.

   Evidence Transient overexpression in prostate cancer cells with apoptosis and TPA-response-element luciferase reporter readouts

   PMID:12771942

   Open questions at the time

   • No direct biochemical mechanism resolved
   • Relies on overexpression rather than endogenous loss-of-function
   • Connection to specific receptor not defined
2. 2004 Medium

   Defined a direct molecular link between REPS2 and NF-κB by showing its EH domain binds an NPF motif in p65, explaining how REPS2 can modulate an inflammatory/survival transcription factor.

   Evidence Yeast and mammalian two-hybrid, co-IP, and structure-guided mutagenesis with PMA stimulation

   PMID:15184881

   Open questions at the time

   • Single lab
   • Functional consequence on NF-κB target genes not fully quantified
   • Stimulus dependence beyond PMA unexplored
3. 2008 High

   Identified the receptor-selective mechanism of REPS2 in endocytosis, mapping the proline-rich motifs required for it to inhibit EGFR (but not transferrin receptor) internalisation and naming the bridging partners.

   Evidence Phage display, peptide arrays, mutagenesis, co-IP, and dominant-negative EGFR endocytosis assay

   PMID:18647389

   Open questions at the time

   • 14-3-3 bridging of EGFR proposed but not structurally resolved
   • Endogenous regulation versus dominant-negative fragment not distinguished
   • Spatial/temporal step of endocytosis affected not defined
4. 2011 Low

   Extended REPS2's RalBP1 partnership to a drug-resistance phenotype by implicating it in modulating RalBP1-mediated efflux of chemotherapeutics.

   Evidence Review summary citing prior molecular interaction data

   PMID:21907823

   Open questions at the time

   • Review without new primary experiment in abstract
   • Direct effect of REPS2 on efflux kinetics not shown here
   • Mechanism of RalBP1 inhibition unspecified
5. 2016 Medium

   Placed REPS2 in a defined oncogenic regulatory circuit, showing it is a direct miR-675-5p target acting upstream of RalBP1/RAC1/CDC42 to control cell cycle, proliferation, and metastasis.

   Evidence miRNA target validation, siRNA knockdown rescue, cell cycle/proliferation/invasion assays, and xenografts

   PMID:27120794

   Open questions at the time

   • Direct biochemical inhibition of RalBP1 by REPS2 not shown in this study
   • Single lab
   • Downstream RAC1/CDC42 activation not directly assayed
6. 2022 Medium

   Connected REPS2 to a second small-GTPase axis (FAK/Cdc42) and to a transcriptional activator (LXR), establishing how REPS2 levels are set and how its loss promotes EMT and growth.

   Evidence siRNA knockdown with G-protein pulldown and FAK inhibitor rescue in lens epithelial cells; ChIP and promoter assays plus EGFR endocytosis/signalling readouts in HCC cells

   PMID:35690292 PMID:35995867

   Open questions at the time

   • Whether FAK/Cdc42 regulation is direct or downstream of receptor endocytosis unclear
   • LXR-driven REPS2 induction tested in limited cell contexts
   • In vivo relevance of LXR–REPS2 axis not fully established
7. 2025 Medium

   Revealed a degradative mechanism by which REPS2 suppresses Wnt/stemness signalling, showing it scaffolds β-catenin to p62 for autophagy-lysosomal turnover.

   Evidence Genome-wide CRISPR/Cas9 screen, co-IP of REPS2–p62–β-catenin complex, autophagy/lysosome inhibition, and in vitro/in vivo assays

   PMID:40514427

   Open questions at the time

   • Domain of REPS2 mediating p62/β-catenin engagement not mapped
   • Single lab
   • Selectivity for β-catenin over other autophagy cargo unaddressed

• It remains unresolved how REPS2's distinct scaffolding activities (EGFR endocytosis, NF-κB, RalBP1/Cdc42 axes, and β-catenin degradation) are coordinated and which are direct versus secondary consequences of receptor regulation.
• No structural model of full-length REPS2 or its complexes
• No unified model linking endocytic and degradative roles
• Physiological versus disease-context functions not separated