Characterization of pancreastatin receptors and signaling in adipocyte membranes

Abstract

Pancreastatin (PST), a chromogranin A derived peptide with an array of effects in different tissues, has a role as a counterregulatory hormone of insulin action in hepatocytes and adipocytes, regulating glucose, lipid and protein metabolism. We have previously characterized PST receptors and signaling in rat hepatocytes, in which PST functions as a calcium-mobilizing hormone. In the present work we have studied PST receptors as well as the signal transduction pathways generated upon PST binding in adipocyte membranes. First, we have characterized PST receptors using radiolabeled PST as a ligand. Analysis of binding data indicated the existence of one class of binding sites, with a B max of 5 fmol/mg of protein and a K d of 1 nM. In addition, we have studied the G protein system that couples the PST receptor by γ- 35S-GTP binding studies. We have found that two G protein systems are involved, pertussis toxin-sensitive and -insensitive respectively. Specific anti-G protein α subtype sera were used to block the effect of pancreastatin receptor activation. Gα q/11 and to a lesser extent Gα i1,2 are activated by PST in rat adipocyte membranes. On the other hand, adenylate cyclase activity was not affected by PST. Finally, we have studied the specific phospholipase C isoform that is activated in response to PST. We have found that PST receptor is coupled to PLC-β 3 via Gα q/11 activation in adipocyte membranes.