Regulation of
Phospholipase D Activity in Human Hepatocacinoma Cells by Protein Kinases and D-sphingosine
HUANG Yong, ZHANG Xia-Ying and CHEN Hui-Li
( Key Laboratory of Glycoconjugate Research, Ministry of Health, Department
of Biochemistry,
Shanghai Medical University, Shanghai 200032, China )
Abstract 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, PKCα and PKCβI may be the
main isotypes of PKC in the regulation of PLD.
Key Words Phospholipase D; inhibitors of protein
kinase; D-sphingosine; PKC subtype
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