Pancreastatin, a chromogranin A-derived peptide, inhibits DNA and protein synthesis by producing nitric oxide in HTC rat hepatoma cells

Abstract

Background/Aims : Pancreastatin, a chromogranin A-derived peptide, has a counter-regulatory effect on insulin action. We have previously characterized pancreastatin receptor and signalling in rat liver and HTC hepatoma cells. A G α q/11 -PLC- β pathway leads to an increase in [Ca 2+] i, PKC and mitogen activated protein kinase (MAPK) activation. These data suggested that pancreastatin might have a role in growth and proliferation, similar to other calcium-mobilizing hormones. Methods : DNA and protein synthesis were measured as [ 3H]-thymidine and [ 3H]-leucine incorporation. Nitric oxide (NO) was determined by the Griess method and cGMP production was quantified by enzyme-linked immunoassay. Results : Contrary to the expected results, we have found that pancreastatin inhibits protein and DNA synthesis in HTC hepatoma cells. On the other hand, when the activity of NO synthase was inhibited by N -monomethyl- l -arginine (NMLA), the inhibitory effect of pancreastatin on DNA and protein synthesis was not only reverted, but a dose-dependent stimulatory effect was observed, probably due to MAPK activation, since it was prevented by PD98059. These data strongly suggested the role of NO in the inhibitory effect of pancreastatin on protein and DNA synthesis, which is overcoming the effect on MAPK activation. Moreover, pancreastatin dose-dependently increased NO production in parallel to cyclic guanosine monophosphate (cGMP). Both effects were prevented by NMLA. Finally, an indirect effect of pancreastatin through the induction of apoptosis was ruled out. Conclusions : Therefore, the NO and the cGMP produced by the NO-activated guanylate cyclase may mediate the dose-dependent inhibitory effect of pancreastatin on growth and proliferation in HTC hepatoma cells.