Cloning and functional characterization of related TC10 isoforms, a subfamily of Rho proteins involved in insulin-stimulated glucose transport

Insulin stimulates glucose transport via phosphatidylinositol 3-kinase-dependent and -independent pathways. The phosphatidylinositol 3-kinase-independent pathway involves activation of the G protein TC10. A cDNA encoding the mouse homolog of TC10 was cloned, and its gene was mapped at the distal end of chromosome 17. Additionally, a second gene was discovered with ∼70% sequence identity to TC10. We refer to this gene as TC10β. Both isoforms of TC10 were activated by insulin upon transfection in 3T3L1 adipocytes. Cotransfection of cells with TC10α or β plus a dominant negative form of the c-cbl-associated protein CAP prevented the activation by insulin, implicating the CAP/Cbl pathway. Interestingly, both forms of TC10 were also localized in lipid raft fractions in transfected adipocytes. However, although overexpression of TC10α completely blocked glucose transport, TC10β only partially inhibited this process. Furthermore, TC10α overexpression disrupted adipocyte cortical actin, whereas TC10β had little if any effect. Thus, there are two isoforms of this key signaling intermediate, both of which are activated by insulin, but they may play different roles in initiating downstream effectors that influence glucose transport.