Pertussis toxin catalyzed ADP-ribosylation of a 41 kDa G-protein impairs insulin-stimulated glucose metabolism in Bc3H-1 myocytes

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Abstract
In this study, we examined the effects of pertussis toxin (PT) on the ADP-ribosylation of guanine nucleotide binding proteins (G-proteins) and various insulinstimulated processes in cultured BC3H-1 myocytes. Treatment of intact myocytes with 0.1 μg/ml PT for 24 hours resulted in the complete ribosylation of a 41 kDa protein. The 41 kDa PT substrate was immunoprecipitated with antibodies directed against a synthetic peptide corresponding to a unique sequence in the alpha subunit of Gi-proteins. PT treatment of intact cells had no effect on insulin receptor binding or internalization. However, PT inhibited insulin-stimulated glucose transport at all insulin-concentrations tested (1–100ng/ml). Maximally stimulated glucose transport was reduced by 50% ± 15%. Insulin-stimulated glucose oxidation was also decreased by 31% ± 8%. The toxin had no significant effect on the basal rates of glucose transport and glucose oxidation. The time course of PT-induced inhibition on glucose transport correlated with the time course of the “in vivo” ADP-ribosylation of the 41 kDa protein. The results suggest that a 41 kDa PT-sensitive G-protein, identical or very similar to Gi, is involved in the regulation of glucose metabolism by insulin in BC3H-1 cells.