Activation of mitogen‐activated protein kinase by protein kinase C isotypes α, βI and γ, but not ϵ

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Abstract
Treatment of CHO.T cells with either PMA or insulin led to the activation of MAP kinase by ∼3‐fold, and p90 rsk by ∼ 4‐fold. Over‐expression of the α, β I or γ isoforms of protein kinase C caused a substantial enhancement of the effect of PMA on the activation of MAP kinase and p90 rsk , however, the effect of insulin was unchanged. Over‐expression of the ϵ isoform of protein kinase C did not alter the effect of either PMA or insulin on the activation of MAP kinase and p90 rsk . The results suggest that protein kinase C isotypes α, β I and γ, but not ϵ, can mediate MAP kinase activation by PMA, and strongly support the hypothesis that protein kinase C isoforms can initiate distinct signalling pathways.