SORBS1

SORBS1 (CAP/ponsin) is a multi-domain scaffolding adaptor that couples receptor tyrosine kinase signaling to actin cytoskeletal remodeling and cell adhesion at the plasma membrane. Its N-terminal sorbin homology (SoHo) domain binds flotillin to target a CAP–Cbl complex to lipid raft microdomains, forming a PI3K-independent signaling branch required for insulin-stimulated glucose uptake in adipocytes (PMID:11001060). Its three C-terminal SH3 domains engage partners including paxillin (via a structurally characterized polyproline-II helix interaction), filamin C, and CrkL to organize costameres, focal adhesions, and acetylcholine receptor clusters at the neuromuscular junction (PMID:17462669, PMID:17898075, PMID:26527617). Reggies/flotillins regulate SORBS1 recruitment to focal contacts, linking it to Rho-family GTPase signaling, neurite outgrowth, and cell migration, while loss of SORBS1 in cancer cells promotes migration and epithelial-to-mesenchymal transition through JNK/c-Jun pathway activation (PMID:18722032, PMID:27791200).

1. 2000 High

   Establishing that SORBS1 functions as a lipid-raft-targeting adaptor in insulin signaling resolved how Cbl phosphorylation is spatially coupled to glucose transporter mobilization independently of PI3K.

   Evidence Yeast two-hybrid, co-IP, subcellular fractionation, and dominant-negative expression in 3T3-L1 adipocytes blocking glucose uptake

   PMID:11001060

   Open questions at the time

   • Downstream effectors linking the raft-localized CAP–Cbl–flotillin complex to GLUT4 translocation were not identified
   • Contribution of individual SH3 domains to Cbl recruitment was not dissected
2. 2002 Medium

   Classification of SORBS1, vinexin, and ArgBP2 as a SoHo/SH3-domain adaptor family unified their roles in cell adhesion and growth factor signaling under a shared domain architecture.

   Evidence Comparative domain analysis and synthesis of two-hybrid/pull-down interaction data

   PMID:11937713

   Open questions at the time

   • Functional redundancy versus specificity among family members was not experimentally tested
   • No loss-of-function comparison across family members
3. 2007 High

   Identification of SORBS1 as a costameric adaptor bridging filamin C and paxillin to the sarcolemma defined its structural role in muscle cell adhesion and myofibril-membrane linkage, with atomic-resolution structures of the paxillin-binding SH3 domain providing a mechanistic basis for partner selectivity.

   Evidence Reciprocal Y2H, mass spectrometry, co-IP, X-ray crystallography of the second SH3 domain at 0.83 Å (free) and 1.63 Å (paxillin peptide complex), overexpression phenotypes in cells, and altered expression in mdx mouse muscle and failing human hearts

   PMID:17462669 PMID:17784760 PMID:17898075

   Open questions at the time

   • Whether filamin C and paxillin binding are mutually exclusive or simultaneous was not resolved
   • Functional consequence of SORBS1 downregulation in failing hearts was correlative, not causally tested
4. 2008 Medium

   Demonstration that reggie-1/flotillin-2 recruits SORBS1 to focal contacts and that this is required for balanced Rac1/Cdc42 activation connected the lipid-raft targeting of SORBS1 to Rho-GTPase-dependent neurite outgrowth.

   Evidence Dominant-negative reggie-1 expression, Rho-GTPase pull-down assays, FAK activity measurement, and neurite outgrowth in hippocampal neurons

   PMID:18722032

   Open questions at the time

   • Direct versus indirect effect of reggie on SORBS1 localization was not distinguished
   • The GEF or GAP through which SORBS1 influences Rac1/Cdc42 was not identified
5. 2015 High

   Discovery that SORBS1 and SORBS2 interact with CrkL and are required for AChR clustering at the neuromuscular junction extended SORBS1 function from metabolic and adhesion signaling to synaptogenesis.

   Evidence CrkL interactome by mass spectrometry, co-IP, AChR clustering assay with knockdown, and in vivo synaptic immunolocalization

   PMID:26527617

   Open questions at the time

   • Relative contributions of SORBS1 versus SORBS2 at the NMJ in vivo were not genetically separated
   • Whether the SoHo domain or SH3 domains mediate CrkL interaction was not mapped
6. 2017 Medium

   Showing that SORBS1 depletion promotes migration, invasion, and EMT via JNK/c-Jun activation revealed SORBS1 as a negative regulator of mesenchymal transition in breast cancer cells.

   Evidence siRNA knockdown in breast cancer cell lines with migration/invasion assays, western blot for JNK/c-Jun and p53, EMT marker profiling, cisplatin sensitivity assay

   PMID:27791200

   Open questions at the time

   • How SORBS1 inhibits JNK activation mechanistically was not determined
   • In vivo relevance in tumor models was not tested
   • Results from a single lab and not independently replicated
7. 2020 Medium

   Identification of the SORBS1–AHNAK complex and evidence that SORBS1 counteracts AHNAK's tumor-suppressive function via ERK and ROCK1 signaling provided a context-dependent pro-proliferative role in colorectal cancer.

   Evidence Co-IP and confocal co-localization of SORBS1-AHNAK, overexpression/knockdown with colony formation and migration assays, western blot for phospho-ERK and ROCK1

   PMID:32319594

   Open questions at the time

   • Whether SORBS1–AHNAK interaction is direct or mediated by other partners was not resolved
   • Opposing roles of SORBS1 in breast (tumor-suppressive) versus colorectal (pro-tumorigenic) cancer remain mechanistically unexplained

• A unified understanding of how SORBS1's scaffolding integrates lipid raft signaling, cytoskeletal remodeling, and transcriptional pathway regulation across different tissues is still lacking.
• No knockout mouse phenotype has been reported in the timeline
• Tissue-specific isoform usage and splicing regulation are not characterized
• The mechanism by which SORBS1 influences JNK, ERK, and Rho-GTPase pathways remains indirect