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1 Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, Colorado 80523-1870; and 2 Institute of Physiology, University of Innsbruck, A-6010 Innsbruck, Austria
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 exposure to acidic
medium (pH 6.9, 10 mM HCO
3) or cAMP.
In contrast, prolonged treatment with PMA increased the levels of PCK
mRNA. The two effects correlated with the membrane translocation and
downregulation of the
-isozyme of protein kinase C and
were blocked by pretreatment with specific inhibitors of protein kinase
C. The rapid decrease in PCK mRNA caused by PMA occurred with a
half-life (t1/2 = 1 h) that is significantly faster than that measured during recovery
from acid medium or following inhibition of transcription
(t1/2 = 4 h). The
effect of PMA was reversed by staurosporine, which apparently acts by inhibiting a signaling pathway other than protein kinase C. Staurosporine had no effect on the half-life of the PCK mRNA, but it
stimulated the activity of a chloramphenicol acetyltransferase gene
that was driven by the initial 490 base pairs of the PCK promoter and transiently transfected 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.
protein kinase C; transcription; messenger ribonucleic acid stability; proximal tubule; phosphoenolpyruvate carboxykinase; phorbol 12-myristate 13-acetate
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