Effects of suramin, an anti-human immunodeficiency virus reverse transcriptase agent, on protein kinase C. Differential activation and inhibition of protein kinase C isozymes.
Suramin inhibited protein kinase C (PKC) type I-III activity in a concentration-dependent manner. Similar inhibitory effects were observed with M-kinase, the constitutively active catalytic fragment of PKC, and autophosphorylation of PKC types I-III. Kinetic experiments indicated that suramin competitively inhibits activity with respect to ATP (Ki = 17, 27, and 31 microM, respectively) and that it can also inhibit by interaction with the substrate histone III-S. With protamine as the Pi acceptor, suramin inhibition was dependent on lipid, being approximately 4-fold less sensitive to inhibition in the absence of phosphatidylserine and diacylglycerol than in their presence. Suramin at low concentrations (10-40 microM), in the presence of Ca2+ and absence of lipid, was able to stimulate kinase activity (approximately 200-400%) in a type-dependent manner and at higher concentrations inhibited activity with histone III-S as substrate. These results indicate that suramin, a hexa-anionic hydrophobic compound, can act as a negatively charged phospholipid analog in activating PKC in the presence of Ca2+ and absence of lipid and can inhibit Ca2+/phosphatidylserine/diacylglycerol-stimulated kinase activity at higher concentrations by competing with ATP or by interaction with the exogenous substrate. Suramin inhibited cAMP-dependent protein kinase much less potently (IC50 = 656 microM) than PKC. The ability of suramin to inhibit PKC-mediated processes in intact cells was tested using the phorbol ester-stimulated respiratory burst of neutrophils as a model system. The respiratory burst of human neutrophils, when preincubated with suramin and then stimulated with phorbol ester, was inhibited in a concentration-dependent manner, suggesting that suramin may also be able to inhibit PKC-mediated processes in intact cells.
Mahoney
C W
CW
Endocrinology and Reproduction Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892.
Azzi
A
A
Huang
K P
KP
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000201:enzymology; D002118:Calcium / Q000494:pharmacology; D004075:Diglycerides / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D006678:HIV / Q000201:enzymology*; D006657:Histones / Q000378:metabolism; D006801:Humans; D007527:Isoenzymes / Q000037:antagonists & inhibitors* / Q000378:metabolism; D007700:Kinetics; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism; D015240:Phorbol 12,13-Dibutyrate / Q000378:metabolism; D010718:Phosphatidylserines / Q000494:pharmacology; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors* / Q000378:metabolism; D051381:Rats; D018894:Reverse Transcriptase Inhibitors; D013481:Superoxides / Q000378:metabolism; D013498:Suramin / Q000494:pharmacology*
D004075:Diglycerides; D006657:Histones; D007527:Isoenzymes; D010718:Phosphatidylserines; D018894:Reverse Transcriptase Inhibitors; D013481:Superoxides; D015240:Phorbol 12,13-Dibutyrate; D013498:Suramin; D000255:Adenosine Triphosphate; D011493:Protein Kinase C; D002118:Calcium