1,25(OH)2-vitamin D3 signal transduction in chick myoblasts involves phosphatidylcholine hydrolysis

1,25-Dihydroxyvitamin D3 (1,25(OH)2D3) rapidly stimulates the biphasic formation of diacylglycerol (DAG) in chick myoblasts. Neomycin (0.5 mM), an inhibitor of phosphoinositide hydrolysis, abolished the first phase (1 min) but had no effect on the second 1,25(OH)2D3-induced DAG peak (5 min). In myoblasts prelabeled with [3H]choline, 1,25(OH)2D3 increased the release of [3H]choline (maximally at 5 min), with a concomitant decrease in phosphatidylcholine and the absence of significant changes in phosphocholine. 1,25(OH)2D3 caused a significant increase in phosphatidylethanol (PEt) formation in myoblasts in the presence of 1.5% ethanol. The effects of 1,25(OH)2D3 were time- and dose-dependent (10(-11) to 10(-8) M) and specific as 25OHD3 and 24,25(OH)2D3 failed to accumulate PEt. 12-O-Tetradecanoylphorbol-13-acetate failed to accumulate PEt. 12-O-Tetradecanoylphorbol-13-acetate also stimulated PEt formation. The combination of 1,25(OH)2D3 and 12-O-tetradecanoylphorbol-13- acetate was more effective than either compound alone. Neither the PKC inhibitor H7 nor PKC down-regulation blocked the hormone-induced increase in PEt. The effects of 1,25(OH)2D3 were, however, inhibited in the absence of extracellular Ca2+ (+EGTA) and by nifedipine and verapamil, whereas the Ca2+ ionophore A23187 also increased PEt generation. The data support the notion that 1,25(OH)2D3 triggers the hydrolysis of phosphatidylcholine in myoblasts through a Ca(2+)-dependent, PKC-independent, phospholipase D-catalyzed mechanism.