TRANSCRIPTIONAL REGULATION OF THE LACTATE-DEHYDROGENASE A-SUBUNIT GENE BY THE PHORBOL ESTER 12-O-TETRADECANOYLPHORBOL-13-ACETATE

Regulation of lactate dehydrogenase (LDH) (EC 1.1.1.27) isozymes occurs through a multitude of physiological signals. Here, we show that modulation of LDH A subunit occurs via the protein kinase C pathway. Activators of protein kinase C, such as tetradecanoylphorbol acetate (TPA) and dioctanoylglycerol (DG), caused a 3-4-fold accumulation of LDH A subunit mRNA in rat C6 glioma cells. The specific protein kinase C inhibitor bisindolylmaleimide GF 109203X prevented the TPA-induced increase of LDH A subunit mRNA. To analyze the molecular basis of these effects in more detail, the transcription-modulatory effects of TPA and DG were evaluated in transient transfection assays using plasmids which contain LDH A subunit promoter fragments fused to a chloramphenicol acetyltransferase reporter gene. Both effector agents caused a marked increase of the transcriptional activity of an LDH -830/+25 bp promoter/CAT construct. In contrast, a phorbol ester which fails to activate protein kinase C, phorbol 12 beta,13 alpha-didecanoate, had no effect on the LDH promoter activity. Transient transfection analysis of LDH promoter deletion/CAT constructs, DNA/protein binding assays, including footprint and gel shift analyses, identified a TRE/AP-1 enhancer module at position -294 bp which was the target for the protein kinase C-mediated signal transduction pathway. Thus, our data demonstrate an active role of the protein kinase C signal pathway in regulating LDH A subunit gene expression which may be significant in regulating LDH isozyme patterns under various physiologic conditions.