In vivo effects of doxorubicin on kinase C in cultured cells

The ability of doxorubicin to inhibit kinase C in vivo in cultured BALB/c 3T3 mouse fibroblasts was determined by the phosphorylation of the myristoylated alanine-rich C kinase substrate (MARCKS) and the induction of c-fos transcription following treatment with 200 nM phorbol 12-myristate 13-acetate. A concentration of 60 μM doxorubicin did not inhibit MARCKS phosphorylation but completely inhibited c-fos expression. The inhibition of c-fos expression was not specifically mediated via kinase C, since both the total RNA synthesis as measured by [3H]-uridine uptake and the fraction of serum-induced c-fos expression that was not attributable to kinase C were inhibited by doxorubicin. The present data do not support the hypothesis that the cytotoxic effect of doxorubicin is attributable to the inhibition of kinase C in vivo.