H-7, a protein kinase C inhibitor, inhibits phorbol ester-caused ornithine decarboxylase induction but fails to inhibit phorbol ester-caused suppression of epidermal growth factor binding in primary cultured mouse epidermal cells

12-O-Tetradecanoylphorbol-13-acetate (TPA) induced ornithine decarboxylase (ODC) and suppressed ¹²⁵I-epidermal growth factor (EGF) binding in primary cultured mouse epidermal cells. TPA (30 nM)-caused ODC induction was almost completely blocked by 30 μM H-7 [1-(5-isoquinolinylsulfonyl)-2-methylpiperazine], a well known protein kinase C inhibitor, but the same concentration of H-7 failed to restore the ¹²⁵I-EGF binding suppressed by TPA (10 nM). On the other hand, sphingosine, another protein kinase C inhibitor, blocked not only TPA-caused ODC induction but also TPA-caused suppression of ¹²⁵I-EGF binding. Concentration-response curves of sphingosine of these two TPA-caused cellular responses were almost identical. 1,2-Diacylglycerols such as 1,2-dioctanoylglycerol (30-300 μM) and 1-oleoyl-2-acetylglycerol (OAG) (30-300 μM) mimicked TPA actions. Similar to the case of TPA, suppression of ¹²⁵I-EGF binding by OAG was barely inhibited by H-7, whereas sphingosine was more effective in inhibiting the OAG-casued suppression of ¹²⁵I-EGF binding than was H-7. In TPA (50 nM)-pretreated epidermal cells, TPA (10 nM) failed to suppress ¹²⁵I-EGF binding. H-7 (30 μM) did not affect TPA (30 nM)-caused translocation of protein kinase C. These results clearly demonstrate the differential inhibition by H-7 of the TPA-caused cellular responses and indicate that TPA-caused suppression of ¹²⁵-I-EGF binding to epidermal cells is mediated through protein kinase C function, which is barely inhibited by H-7.