PMA AND STAUROSPORINE AFFECT EXPRESSION OF THE PCK GENE IN LLC-PK1-F+CELLS

The addition of phorbol 12-myristate 13-acetate (PMA) to renal LLC-PK1 -F+ cells caused a rapid decrease in the level of phosphoenolpyruvate carboxykinase (PCK) mRNA and reversed the stimulatory effects of expos ure to acidic medium (pH 6.9, 10 mM HCO3-) or cAMP. In contrast, prolo nged treatment with PMA increased the levels of PCK mRNA. The two effe cts correlated with the membrane translocation and downregulation of t he alpha-isozyme of protein kinase C and were blocked by pretreatment with specific inhibitors of protein kinase C. The rapid decrease in PC K mRNA caused by PMA occurred with a half-life (t(1/2) = 1 h) that is significantly faster than that measured during recovery from acid medi um or following inhibition of transcription (t(1/2) = 4 h). The effect of PMA was reversed by staurosporine, which apparently acts by inhibi ting a signaling pathway other than protein kinase C. Staurosporine ha d no effect on the half-life of the PCK mRNA, but it stimulated the ac tivity of a chloramphenicol acetyltransferase gene that was driven by the initial 490 base pairs of the PCK promoter and transiently transfe cted into LLC-PK1-F+ cells. This effect was additive to that of cAMP, and neither stimulation was reversed by PMA. The stimulatory effect of staurosporine was mapped to the cAMP response element (CRE-1) and P3( II) element of the PCK promoter. The data indicate that, in LLC-PK1-F cells, activation of protein kinase C decreases the stability of the PCK mRNA, whereas transcription of the PCK gene may be suppressed by a kinase that is inhibited by staurosporine.