The effect of ascorbic acid 6-docosahexaenoate (DHA-VC) on the phospholipase-C-mediated hydrolysis of phosphatidylcholine was investigated. In human non-small cell lung cancer cells (PC-14) exposed to DHA-VC for 24 hr, a dose-dependent increase in phosphatidylcholine-specific phospholipase C (PC-PLC) activity was seen. PC-PLC activity in whole-cell homogenate of PC- 14 cells was increased about 2.5-fold by 2 hr of treatment with DHA-VC (20 μg/ml). Treatment with DHA-VC also augmented PC-PLC activity in the crude membrane extract. On the other hand, DHA-VC inhibited the activity of phospholipase A2 (ID50 = 800 μg/ml). Another water-soluble analog, choline docosahexaenoate, also stimulated PC-PLC activity. To explore the effect of DHA-VC on phosphatidylcholine turnover, we analyzed phospholipids labeled with [14C] choline or [3H]myristate by thin-layer chromatography, and found that the amount of [14C]- and [3H]-labeled phosphatidylcholine was constant in the presence of DHA-VC. These results suggest that phosphatidylcholine turnover was not influenced by DHA-VC. DHA-VC treatment increased protein kinase C activity of the cells in the late phase (120 min), suggesting that DHA-VC-induced diacylglycerol production mediated by PC-PLC causes protein kinase C activation. Considering that significant inhibition of DNA synthesis occurred 12 hr after 2 hr of treatment with DHA-VC (20 μg/ml), DHA-VC-induced PC-PLC activation seems to be an early event in DHA- VC-induced cytotoxicity, which suggests that the effects of DHA-VC on signal transduction pathways may play an important role in the cytotoxicity of DHA- VC.
|ジャーナル||Proceedings of the Society for Experimental Biology and Medicine|
|出版ステータス||Published - 1993|
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