Induction of protein kinase Czeta-related protein kinase by growth suppression in carcinogen-initiated epidermal cell-line WYF31 cells

In primary cultured mouse epidermal cells, protein kinase C isozyme zeta (PKCzeta) consists of multiple forms, for example, low-salt eluted PKCzeta (1-PKCzeta; 79 and 85 kDa) and high-salt eluted PKCzeta (h-PKCzeta; 79 and 85 kDa) on anion-exchange column chromatography. In this study, biochemical and biophysical differences between 1-PKCzeta and h-PKCzeta were examined by using carcinogen-initiated mouse epidermal cell-line WYF31 cells, whose growth is stimulated by tumour promoter phorbol 12-myristate 13-acetate (PMA). The binding efficiency of h-PKCzeta to anti-PKCzeta antibody-affinity column was 10 times higher than that of 1-PKCzeta. T7-tagged rat PKCzeta overexpressed in WYF31 cells was recovered only in the high-salt eluted area on the anion-exchange column. Furthermore, when rat PKCzeta was stably overexpressed in WYF31 cells, the content of h-PKCzeta increased 4 to 5 times compared to that of parental cells, but the content of 1-PKCzeta was not altered. All of these results indicate that h-PKCzeta is the product of the PKCzeta gene (referred to as PKCzeta) and that 1-PKCzeta is closely related but different from PKCzeta (referred to as PKCzeta-related kinase). Interestingly, serum starvation of WYF31 cells caused a marked increase of the content of PKCzeta-related kinase with a concomitant decrease of PKCzeta content. These changes were reversed by stimulating the cell growth with 10% foetal calf serum. Prolonged treatment of starved cells with PMA, which induces the proliferation of WYF31 cells, also caused the downregulation of PKCzeta-related kinase. These results suggest that the expression levels of PKCzeta-related kinase and PKCzeta are differently regulated, and that the increased expression of PKCzeta-related kinase might play a significant role in the growth-suppression processes of WYF31 cells.