VITAMIN-K-3 PREFERENTIALLY INHIBITS STIMULATION OF PHOSPHOLIPASE-D MEDIATED HYDROLYSIS OF PHOSPHATIDYLETHANOLAMINE BY PROTEIN-KINASE-C ACTIVATORS IN NIH 3T3 FIBROBLASTS

Vitamin K-3 (menadione), a synthetic vitamin K congener, inhibits the growth of tumor cells. Here, we examined possible effects of vitamin K -3 On phospholipase D (PLD) activity, an enzyme which produces growth regulatory substances. In NIH 3T3 fibroblasts, vitamin K-3 (50-100 mu M) alone had no effect on PLD-catalyzed formation of phosphatidylethan ol, a marker of PLD activity, but it slightly (10-21%) inhibited the s timulatory effect of phorbol 12-myristate 13-acetate (PMA), an activat or of protein kinase C (PKC). Of the two major substrates of PLD, phos phatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEtn), vitami n K-3 (10-100 mu M) preferentially inhibited PtdEtn hydrolysis when st imulated by PMA or platelet-derived growth factor, the latter being a hormonal activator of PKC. Vitamin K-3 had no inhibitory effect on sph ingosine- or staurosporine-induced hydrolysis of PtdEtn or PtdCho. Inh ibition of PMA-induced PtdEtn hydrolysis by vitamin K-3 was effectivel y reduced by both cysteine (1 mM) and reduced glutathione (1 mM) and w as mimicked by the superoxide-generating xanthine/xanthine oxidase sys tem. The results show that vitamin K-3 preferentially inhibits the eff ects of PKC activators on PLD-mediated hydrolysis of PtdEtn by a mecha nism which may involve oxidation of thiols in a critically important r egulatory component. (C) 1994 Academic Press, Inc.