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 vasopressin on protein synthesis and phospholipase D (PLD) activity were investigated in L6 myoblasts. TPA stimulated a concentration-dependent increase in protein synthesis (EC(50) approx. 10 nM) during a 90 min incubation, 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 choline (EC(50) 5-10 nM). In contrast to TPA, vasopressin stimulated protein synthesis (maximum increase 30%, EC(50) approx. 10 nM) and RNA accretion after 6 h, but had no effect after 90 min. Vasopressin also increased 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 preparation of PLD (2-10 units/ml) from Streptomyces sp. to L6 cells stimulated a concentration-dependent increase in choline release and protein synthesis after both 90 min (maximum stimulation 13%) and 6 h (maximum stimulation 12%). PLD also stimulated RNA accretion after 6 h but not 90 min. The data support a role for PLD in the regulation of protein synthesis in L6 cells.