In vitro inhibition of rat brain protein kinase C by rhodamine 6G. Profound effects of the lipid cofactor on the inhibition of the enzyme.
Rhodamine 6G inhibited protein kinase C (PKC) when the enzyme was activated by Ca2+ plus phosphatidylserine, 12-O-tetradecanoyl-phorbol-13-acetate (TPA) or mezerein plus phosphatidylserine, Ca2+ plus arachidonic acid, or arachidonic acid alone. Rhodamine 6G did not affect protein kinase C activity in the absence of lipid cofactor and, thus, does not appear to inhibit the enzyme through direct interactions with the active site. The inhibitory potency of the drug was affected dramatically by the nature of the lipid cofactor. Thus, 50 microM rhodamine 6G inhibited the Ca2+ plus arachidonic acid dependent protein kinase activity approximately 50%, whereas 800 microM rhodamine 6G was required to cause 50% inhibition of the Ca2+ plus phosphatidylserine dependent protein kinase activity. These results, along with studies demonstrating a reversal of inhibition by high lipid concentrations, provide evidence that rhodamine 6G exerts its inhibitory effect on PKC through drug-lipid interactions. The dramatic effect of the lipid cofactor on the potency of rhodamine 6G as a PKC inhibitor suggests that the lipid environment of the cell may profoundly affect the abilities of rhodamine 6G and related cationic lipophilic drugs to inhibit PKC in vivo.
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000494:pharmacology; D001921:Brain / Q000201:enzymology*; D008055:Lipids / Q000494:pharmacology*; D010766:Phosphorylation; D011479:Protamines / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors*; D051381:Rats; D012235:Rhodamines / Q000494:pharmacology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014966:Xanthenes / Q000494:pharmacology*
D000970:Antineoplastic Agents; D001095:Arachidonic Acids; D008055:Lipids; D011479:Protamines; D012235:Rhodamines; D014966:Xanthenes; C026188:rhodamine 6G; D016718:Arachidonic Acid; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate