Institute of Medical Biochemistry, University of Oslo, Norway
Abstract:
We have investigated the possibility that adenylyl cyclase (AC) activity and membrane protein levels of the -subunits of the stimulatory and inhibitory G-proteins of AC (Gs and Gi?2) in cultured prolactin-producing rat pituitary adenoma cells (GH3 cells) are modulated by phospholipase C (PLC)-generated second messengers. Pretreatment of cells (6–48 h) with ionomycin (1 μM) or 1-oleoyl-2-acetylglycerol (OAG; 1μM) showed that ionomycin regulated Gs levels in a time-dependent, biphasic manner; a two-fold increase followed a 40% initial reduction, while OAG lowered Gs levels by more than 50% at all time-points. Gi?2 levels remained unchanged by both pretreatments. OAG, but not ionomycin, increased basal AC activity without increasing enzyme protein levels. Alterations in AC responsiveness to peptide hormones (e.g. thyroliberin and vasoactive intestinal peptide) correlated to membrane Gs protein -subunit content. These results demonstrate the involvement of G-protein translation regulation as one mechanism of ‘cross-talk’ between the PLC- and AC-dependent signalling pathways.