In JB6 epidermal cells, induction of fos proto-oncogene expression by phorbol 12-myristate 13-acetate can be inhibited by the protein kinase C (PKC) inhibitor H7 [1-5(isoquinolinesulphonyl)-2-methylpiperazine]. The compound causes also a dose-dependent suppression of fos precursor RNA splicing which, however, appears to react somewhat less sensitively to H7 than does PKC activity. This indicates that H7-induced accumulation of fos precursor RNA is not due to inhibition of PKC. Support for this interpretation comes from the finding that other inhibitors of PKC, such as N-(2-guanidinoethyl)-5-isoquinolinesulphonamide dihydrochloride, sphingosine, staurosporine or N-(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide, do not suppress splicing when applied at PKC-inhibiting concentrations.
