Regulation of Phospholipase D Activity in Human Hepatocacinoma Cells by Protein Kinases and D-sphingosine.
The effects of some inhibitors of protein kinase C(PKC) and tyrosine protein kinase(TPK)as well as the antibodies to PKC isotypes on the activity of phosphatidylcholine-specific phospholipase D(PLD)in 7721 human hepatocarcinoma cells were determined in order to study the regulation of PKC and TPK on PLD in these cells. It was found that all of the four inhibitors of PKC (chelerythrine, H-7, calphostin C and stausporine) and two inhibitors of TPK (tyrphostin 46 and genistein) partially inhibited the basal activity of PLD. Among them, the inhibition rates of staurosporine and calphostin C were the highest. The effects of TPK inhibitors were less than that of PKC inhibitors. When the inhibitors of PKC and TPK were added in combination, the inhibitory effect was greater than that used separately. A well known physiological inhibitor of PKC, D-sphingosine, did not show any inhibition, but did show stimulation on PLD activity. The mechanism is probably related to the transformation of D-sphingosine to D-sphingosine 1-phosphate, a stimulator of PLD via the activation TPK (and probably also PKC). The stimulating effects of both D-sphingosine and D-sphingosine 1-phosphate were blocked by TPK inhibitors and other PKC inhibitors. Among the 3 common PKC isotypes in human hepatocarcinoma cells, PKCalpha and PKCbetaI may be the main isotypes of PKC in the regulation of PLD.
Key Laboratory of Glycoconjugate Research, Ministry of Health, Department of Biochemistry, Shanghai Medical University, Shanghai 200032, China. hlchen@shmu.edu.cn
Yong
Y
Huang
Xia-Ying
XY
Zhang
Hui-Li
HL
Chen