Novel water-soluble derivatives of docosahexaenoic acid increase diacylglycerol production mediated by phosphatidylcholine-specific phospholipase C.
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 micrograms/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 micrograms/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 micrograms/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.
Pharmacology Division, National Cancer Center Research Institute, Tokyo, Japan.
K
K
Nishio
T
T
Morikage
T
T
Ohmori
N
N
Kubota
Y
Y
Takeda
S
S
Ohta
K
K
Yazawa
N
N
Saijo
D001205:Ascorbic Acid / Q000494:pharmacology; D002289:Carcinoma, Non-Small-Cell Lung / Q000201:enzymology; D002794:Choline / Q000494:pharmacology; D004247:DNA / Q000096:biosynthesis; D004075:Diglycerides / Q000096:biosynthesis*; D004281:Docosahexaenoic Acids / Q000494:pharmacology*; D006801:Humans; D008175:Lung Neoplasms / Q000201:enzymology; D010713:Phosphatidylcholines / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism; D054467:Phospholipases A2; D012995:Solubility; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000378:metabolism*; D014867:Water
D004075:Diglycerides; D010713:Phosphatidylcholines; D014867:Water; D004281:Docosahexaenoic Acids; D004247:DNA; D010741:Phospholipases A; D054467:Phospholipases A2; D010738:Type C Phospholipases; D002794:Choline; D001205:Ascorbic Acid