Hexadecylphosphocholine inhibits inositol phosphate formation and protein kinase C activity.
Hexadecylphosphocholine (HePC) inhibits protein kinase C (PKC) from NIH3T3 cells in cell-free extracts with a 50% inhibitory concentration of about 7 microM. Inhibition is competitive with regard to phosphatidylserine with a Ki of 0.59 microM. In order to determine whether HePC affects PKC in intact cells, the bombesin or tetradecanoylphorbolacetate-induced, PKC-mediated activation of the Na+/H(+)-antiporter was determined. It is demonstrated that HePC causes a drastic inhibition of this enzyme indicating a similar sensitivity of PKC to HePC in intact cells compared to cell-free extracts. In addition to the effects on PKC, treatment of NIH3T3 cells with HePC depresses the bombesin-induced formation of inositol 1,4,5-trisphosphate and the concomitant mobilization of intracellular Ca2+. Dose-response curves for the inhibition of inositol 1,4,5-trisphosphate formation and Ca2+ mobilization reveal 50% inhibitory concentrations of 2 or 5 microM, respectively. Polyphosphorylated phosphoinositides accumulate in HePC-treated cells indicating that the depression of inositol 1,4,5-trisphosphate generation is not caused by an inhibition of phosphoinositide kinases. Addition of bombesin to HePC-treated cells in the presence of LiCl revealed no evidence for an accelerated rate of inositol 1,4,5-trisphosphate turnover by the phospholipid analogue. It is concluded that HePC inhibits phosphoinositidase C in intact cells. The data strongly suggest that the growth-inhibitory effect of HePC is at least in part explained by the interference with mitogenic signal transduction.
Uberall
F
F
Institute of Medical Chemistry and Biochemistry, University of Innsbruck, Austria.
Oberhuber
H
H
Maly
K
K
Zaknun
J
J
Demuth
L
L
Grunicke
H H
HH
D001839:Bombesin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects; D007295:Inositol Phosphates / Q000096:biosynthesis*; D008094:Lithium / Q000494:pharmacology; D010767:Phosphorylcholine / Q000031:analogs & derivatives* / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors*; D017923:Sodium-Hydrogen Exchangers; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000378:metabolism / Q000473:pathology
D002352:Carrier Proteins; D007295:Inositol Phosphates; D017923:Sodium-Hydrogen Exchangers; D010767:Phosphorylcholine; C039128:miltefosine; D008094:Lithium; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D001839:Bombesin