Protein Kinase C Mediates Prolactin Regulation of Mitochondrial Aspartate Aminotransferase Gene Expression in...

Prolactin stimulates citrate accumulation in prostate cells by increasing the expression of mitochondrial aspartate aminotransferase (mAAT). In this study, we further investigated the mechanism of prolactin regulation of mAAT expression in rat lateral prostate and LNCaP and PC-3 prostate cancer cells. Prolactin and 12-O-tetra-decanoylphorbol 13-acetate (TPA) increased the mAAT mRNA level twofold to fourfold. In addition, prolactin and TPA increased protein kinase C (PKC) activity in prostate cells 20% to 60% and 40% to 210%, respectively. The effects of both prolactin and TPA on mAAT mRNA were eliminated by downregulation of PKC. The effect of prolactin and TPA on gene transcription was determined using mAAT-chloramphenicol acetyltransferase (CAT) reporter-gene constructs, transiently transfected into PC-3 cells. The 59 untranslated region of the precursor form (pmAAT) of the mAAT gene contains five sequences that are homologous to the consensus TPA response elements (TRE). Reporter constructs with various combinations of these sequences were used to assay prolactin stimulation of CAT transcription in PC-3 cells. Prolactin increased CAT expression in PC-3 cells transfected with a reporter gene containing four of the TRE consensus sequences. Another CAT reporter gene, which contained two of the putative TREs, was also stimulated by prolactin, but a third reporter, containing the two other TRE sequences, was not induced by prolactin. These results suggest that prolactin regulates mAAT at the transcriptional level. Moreover, because both prolactin and TPA induced PKC activity, and because the effects of prolactin and TPA were eliminated when PKC was downregulated, we postulate that the prolactin effect on mAAT expression is mediated via the diacylglycerol PKC signal transduction pathway in rat lateral prostate and human prostate cancer cells.