Mitochondrial aconitase gene expression is regulated by testosterone and prolactin in prostate epithelial cells

BACKGROUND. m-aconitase catalyzes the first step leading to the oxidation o f citrate via the Krebs cycle. It is a constituitive enzyme in virtually al l mammalian cells, found in excess, and is considered to be a regulatory or regulated enzyme. In contrast to these general relationships, prostate sec retory epithelial cells possess a uniquely limiting mitochondrial (m-) acon itase which minimizes the oxidation of citrate. This permits the unique pro state function of accumulating and secreting extraordinarily high levels of citrate. Previous animal studies demonstrated that testosterone and prolac tin regulate the level of m-aconitase specifically in citrate-producing pro state cells. The present studies were conducted to determine if testosteron e and prolactin regulated the expression of the m-aconitase gene in prostat e cells, and to determine the effect of the hormones on human prostate cell s. METHODS. The studies were conducted with freshly prepared rat ventral, rat lateral, and pig prostate epithelial cells, and with the human malignant ce ll lines LNCaP and PC-3. The effects of 1 nM testosterone and 3 nM prolacti n on the level of m-aconitase mRNA and on the transcription rate of m-aconi tase were determined. RESULTS. The studies revealed that both prolactin and testosterone increase the levels of m-aconitase mRNA and the transcription rates of m-aconitase in rat ventral prostate cells, pig prostate cells, and human malignant pros tate cells (LNCaP and PC-3). In contrast, both hormones decreased the level of m-aconitase mRNA and repressed m-aconitase gene transcription in rat la teral prostate cells. The hormonal regulation of m-aconitase corresponded w ith the levels of m-aconitase enzyme, m-aconitase activity, and citrate oxi dation. CONCLUSIONS. In addition to the constitutive expression of m-aconitase, the m-aconitase gene is testosterone- and prolactin-regulated in specifically targeted prostate cells. The hormonal regulation of m-aconitase gene expres sion and biosynthesis of m-aconitase provide a regulatory mechanism for the oxidation of citrate, and consequently, the level of net citrate productio n by prostate. The hormonally increased expression and biosynthesis of m-ac onitase in human malignant cells might be involved in the increased citrate oxidation associated with the development of true malignant cells in prost ate cancer.