Membrane toxicity of the protein kinase C inhibitor calphostin A by a free-radical mechanism.
The effects of calphostin A on cytoplasmic calcium levels, receptor-mediated calcium release, and membrane input resistance were measured in neuroblastoma cells. Calphostin A is a lipophilic, light-sensitive perylenequinone that generates singlet oxygen when illuminated. It inhibits the activity of protein kinase C (IC50 = 250 nM), but only in the presence of light. Phorbol esters normally attenuate carbachol-evoked calcium release. This effect was blocked by simultaneous exposure to light and calphostin A (40 nM) for 30 min. At higher doses (0.5-1 microM) calphostin A also approximately doubled the resting calcium level and decreased cell input resistance by 51%. These toxic effects did not occur in the dark or after preincubation with the antioxidant alpha-tocopherol. These data support the hypothesis that the calphostins act by partitioning into the membrane and producing singlet oxygen and endoperoxides which then irreversibly modify protein kinase C and other membrane proteins and lipids.
Wang
S S
SS
Department of Biological Sciences, Stanford University, Pacific Grove, CA 93950.
Mathes
C
C
Thompson
S H
SH
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D005609:Free Radicals; D016257:Fura-2; D006706:Homeostasis / Q000187:drug effects; D008566:Membranes / Q000187:drug effects; D051379:Mice; D009281:Naphthalenes; D009447:Neuroblastoma / Q000648:ultrastructure; D011083:Polycyclic Compounds / Q000633:toxicity*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors*; D017382:Reactive Oxygen Species / Q000378:metabolism; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000648:ultrastructure; D014810:Vitamin E / Q000494:pharmacology
D005609:Free Radicals; D009281:Naphthalenes; D011083:Polycyclic Compounds; D017382:Reactive Oxygen Species; C058747:calphostin A; D014810:Vitamin E; D002217:Carbachol; D011493:Protein Kinase C; D002118:Calcium; D016257:Fura-2