title: Ahsg-fetuin blocks the metabolic arm of insulin action through its interaction with the 95-kD β-subunit of the insulin receptor.
abstract: We previously have shown that Ahsg, a liver glycoprotein, inhibits insulin receptor (InsR) tyrosine kinase (TK) activity and the ERK1/2 mitogenic signaling arm of insulin signaling. Here we show that Ahsg blocks insulin-stimulated GLUT4 translocation and Akt activation in intact cells (mouse myoblasts). Furthermore, Ahsg inhibits InsR autophosphorylation of highly-purified insulin holoreceptors in a cell-free, ATP-dependent system, with an IC50 within the range of single-chain Ahsg concentrations in human serum. Binding of (125)I-insulin to living cells overexpressing the InsR shows a dissociation constant (KD) of 250pM, unaltered in the presence of 300 nM Ahsg. A mutant InsR cDNA encoding the signal peptide, the β-subunit and the furin processing site, but deleting the α-subunit, was stably expressed in HEK293 cells. Treatment with peroxovanadate, but not insulin, dramatically increased the 95 kD β-subunit tyrosine phosphoryation. The level of tyrosine phosphorylation of the 95-kD β-subunit can be driven down sharply by treatment of living HEK293 transfectant cells with physiological doses of Ahsg. Treatment of myogenic cells with Ahsg blunts insulin-stimulated InsR autophosphorylation and AKT phosphorylation. Taken together, we show that Ahsg antagonizes the metabolic functions initiated by InsR activation without interference in insulin binding. The experiments suggest a direct interaction of Ahsg with the InsR ectodomain β-subunit in a mode that does not significantly alter the high-affinity binding of insulin to the holoreceptor's two complementing α-subunits.
authors: Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Wayne State University School of Medicine, Detroit, MI, USA. asg@genetics.wayne.edu
authors: Anton Scott
authors: AS
authors: Goustin
authors: Nada
authors: N
authors: Derar
authors: Abdul B
authors: AB
authors: Abou-Samra
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D002474:Cell-Free System; D051275:Glucose Transporter Type 4 / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D007700:Kinetics; D051379:Mice; D009154:Mutation; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D011972:Receptor, Insulin / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D014162:Transfection; D060749:alpha-2-HS-Glycoprotein / Q000494:pharmacology*
chemical_list: D051275:Glucose Transporter Type 4; D007328:Insulin; D021122:Protein Subunits; D060749:alpha-2-HS-Glycoprotein; D000255:Adenosine Triphosphate; D011972:Receptor, Insulin; D051057:Proto-Oncogene Proteins c-akt