STIMULATION OF PROTEIN-SYNTHESIS AND PHOSPHOLIPASE-D ACTIVITY BY VASOPRESSIN AND PHORBOL ESTER IN L6 MYOBLASTS

The effects of 12-O-tetradecanoylphorbol-13-acetate (TPA) and vasopres sin on protein synthesis and phospholipase D (PLD) activity were inves tigated in L6 myoblasts. TPA stimulated a concentration-dependent incr ease in protein synthesis (EC(50) approx. 10 nM) during a 90 min incub ation, but had no effect after 6 h. The maximum increase was about 15% and was mediated through changes in translation, as TPA had no effect on RNA accretion and the response was not prevented by actinomycin D. TPA also stimulated PLD activity as measured by an 8-fold increase in the formation of phosphatidylbutanol (PtdBuOH) and the release of cho line (EC(50) 5-10 nM). In contrast to TPA, vasopressin stimulated prot ein synthesis (maximum increase 30%, EC(50) approx. 10 nM) and RNA acc retion after 6 h, but had no effect after 90 min. Vasopressin also inc reased PtdBuOH production 4-5-fold (EC(50) approx. 0.5 nM) and choline release (EC(50) approx. 1 nM). The addition of a highly purified prep aration of PLD (2-10 units/ml) from Streptomyces sp. to L6 cells stimu lated a concentration-dependent increase in choline release and protei n synthesis after both 90 min (maximum stimulation 13%) and 6 h (maxim um stimulation 12%). PLD also stimulated RNA accretion after 6 h but n ot 90 min. The data support a role for PLD in the regulation of protei n synthesis in L6 cells.