Inhibition of phorbol ester binding and protein kinase C activity by heavy metals.
Other laboratories have reported biphasic effects of heavy metals on protein kinase C activity: stimulation followed by inhibition at higher concentrations. We demonstrate that these earlier findings most likely resulted from a combination of the effect of the heavy metals to liberate Ca2+ from Ca2+-EGTA buffer systems and the direct inhibitory effects of the metals on protein kinase C. Simulations of such interactions substantiate this conclusion. When soluble protein kinase C is prepared without the addition of Ca2+ or chelator, heavy metals (Cd2+, Cu2+, Hg2+, Zn2+, in the 10 microM range) inhibit the activity of, and the binding of regulatory ligands to, protein kinase C. Heavy metals inhibit the extent of [3H]phorbol dibutyrate binding without affecting the affinity of the interaction, an inhibition that is not surmounted by excess phospholipid. Heavy metals also inhibit the phospholipid-dependent catalytic activity of protein kinase C in a manner that excess phosphatidylserine can overcome. The inhibition of enzyme activity by heavy metals cannot be surmounted by excess Ca2+ or Mg2+. The inhibitory effects of heavy metals are not confined to protein kinase C. Heavy metals also inhibit cyclic AMP binding to cyclic AMP-dependent protein kinase and the catalytic activity of that kinase, but in a distinctly different pattern.
Speizer
L A
LA
Department of Pharmacology, University of California, San Diego School of Medicine, La Jolla 92093.
Watson
M J
MJ
Kanter
J R
JR
Brunton
L L
LL
D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D029742:Caenorhabditis elegans Proteins; D002118:Calcium / Q000494:pharmacology; D002352:Carrier Proteins; D002460:Cell Line; D003300:Copper / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D007700:Kinetics; D008345:Manganese / Q000494:pharmacology; D008628:Mercury / Q000494:pharmacology; D008670:Metals / Q000494:pharmacology*; D015240:Phorbol 12,13-Dibutyrate / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism*; D011955:Receptors, Drug / Q000187:drug effects / Q000378:metabolism*; D015032:Zinc / Q000494:pharmacology
D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D008670:Metals; D011955:Receptors, Drug; C083141:phorbol ester binding protein; C027776:phorbol ester receptor; D002104:Cadmium; D015240:Phorbol 12,13-Dibutyrate; D008345:Manganese; D004533:Egtazic Acid; D003300:Copper; D011493:Protein Kinase C; D008628:Mercury; D015032:Zinc; D002118:Calcium