Modulation of insulin receptor signalling by pancreastatin in HTC hepatoma cells.
Pancreastatin, a neuropeptide derived from chromogranin A, has a glycogenolytic and counterregulatory effect to insulin in the rat liver. This effect is mediated by calcium and protein kinase C activity. Our aim was to study the possible cross-talk between pancreastatin and the insulin signalling system, by using the well-studied insulin sensitive rat hepatoma HTC cells. First, we checked the counterregulatory effect of pancreastatin on insulin action. Pancreastatin dose-dependently inhibited insulin stimulated glycogen synthesis. This effect was not due to competition for insulin receptors. Moreover, when protein kinase C activation was blocked with staurosporine, this effect of pancreastatin was not observed. Next, we found a dose-dependent inhibition of insulin receptor autophosphorylation by pancreastatin. In addition, phosphorylation of the major substrates of insulin receptor in HTC, i. e. insulin-receptor substrate (IRS)-1/IRS-2 and p62 was also blunted and so was its association with p85 regulatory subunit of phosphatidylinositol-3-kinase. Moreover, the insulin activation of S6 kinase was also blocked by pancreastatin. Again, all these inhibitory effects of pancreastatin were prevented by staurosporine. Furthermore, pancreastatin produced Ser/Thr phosphorylation of insulin receptor by a staurosporine-sensitive mechanism. Finally, we checked the pancreastatin activation of protein kinase C in HTC cells and found that a "classical" isoform of this protein is translocated to the plasma membrane. These findings suggest that pancreastatin could exert its anti-insulin effect in the hepatocyte by interrupting the stimulation of early insulin receptor signalling as a result of phosphorylation. This interaction might have a role in the mechanisms of insulin resistance.
Sánchez-Margalet
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Department of Medical Biochemistry and Molecular Biology, School of Medicine, Virgen Macarena Hospital, University of Seville, Spain.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D053379:Chromogranin A; D007328:Insulin / Q000031:analogs & derivatives / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology*; D007700:Kinetics; D008114:Liver Neoplasms, Experimental; D010187:Pancreatic Hormones / Q000494:pharmacology*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D011972:Receptor, Insulin / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D019311:Staurosporine / Q000494:pharmacology
D053379:Chromogranin A; D007328:Insulin; D010187:Pancreatic Hormones; C008147:insulin, iodo-; C050836:pancreastatin; D011972:Receptor, Insulin; D011493:Protein Kinase C; D019311:Staurosporine; D002118:Calcium