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 approximately 70% sequence identity to TC10. We refer to this gene as TC10beta. Both isoforms of TC10 were activated by insulin upon transfection in 3T3L1 adipocytes. Cotransfection of cells with TC10alpha or beta 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 TC10alpha completely blocked glucose transport, TC10beta only partially inhibited this process. Furthermore, TC10alpha overexpression disrupted adipocyte cortical actin, whereas TC10beta 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.
Chiang
Shian-Huey
SH
Department of Medicine, Life Sciences Institute, University of Michigan School of Medicine, Ann Arbor, MI 48109-0650, USA.
Hou
June Chunqiu
JC
Hwang
Joseph
J
Pessin
Jeffrey E
JE
Saltiel
Alan R
AR
D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D017931:DNA Primers; D005947:Glucose / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D020741:rho GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*
D017931:DNA Primers; D007328:Insulin; D020033:Protein Isoforms; C503260:Rhoq protein, mouse; D020741:rho GTP-Binding Proteins; D005947:Glucose