Functional analysis of stress responsive gene BRE (brain and reproductive organ expressed): A potentially processed-modulator for steroid action

Genes that modulate the action of hormones and cytokines play critical roles in stress response, survival, growth and differentiation of cells. We had previously identified a new gene that was responsive to DNA damage and retinoic acid. This gene highly expressed in rat brain and reproductive organs and so called BRE. Recent studies indicated that BRE could bind to the p55 TNF receptor. Meanwhile, over expression of BRE inhibited TNF induced NF-kappaB activation. These studies indicated that BRE might be a modulator of TNF action. However, the function of this gene has not been well defined yet.; To further investigate the function of BRE, we screened BRE in 50 human tissues using multiple-tissue Dot-blot and Northern blot. Besides brain and testis, BRE was found to express strongly in the adrenal cortex. In situ hybridization results indicated that BRE mRNA expressed strongly in the zona glomerulosa of the adrenal cortex. It also expressed in the glial and neuronal cells of the brain, and in the Leydig cells of the testis. Immunohistochemical staining results generally agreed with the in situ hybridization results. While in rat ovary, BRE also expressed in the cumulus oophorus of zona granulosa and the theca interna of the theca folliculi. BRE protein was also found in the granulosa lutein cells of corpus luteum. These BRE up-regulated tissues and cells are well known as steroidogenic sites. Therefore, tissue specific expression of BRE indicated that BRE is associated with steroid hormone production.; In a study of pituitary hormones in regulating steroidogenesis, BRE, was found overtly expressed in rat adrenals with impaired steroidogenesis (rats chronically treated with nitrate or nitrite), suggesting a regulation by ACTH. BRE expression was down regulated in adrenal neoplasia including adrenal adenoma and pheochromocytoma. On the other hand, decreased expression for BRE was found in the zona fasciculata and reticularis and Leydig cells, respectively in dexamethasone- and testosterone-treated rats. In vitro , BRE expression was up-regulated by hCG in time and dose dependent manners in mouse Leydig Tumor cells (mLTC-1), which was sensitive to the protein synthesis-inhibitor cycloheximide. Western blot studies revealed BRE-specific proteins of 30, 42 and 60kDa polypeptides in HeLa cells, and only the 30 and 60kDa proteins in mLTC-1, the former being hCG responsive. The modulation of BRE expression again indicated that BRE might play a role in steroidogenesis.; BRE has many characteristics similar to the sterol metabolizing proteins StAR and SCP2, which may be the putative phospholipid interaction sites for mitochondria and peroxisome, and perform the role of transporting cholesterol to inner mitochondrial membrane for side chain cleavage reaction. Computer analysis indicated that the N-terminal of BRE contains an amphipathic amino acid motif comprising alpha-helical segments, a potential mitochondrial presequence, and was confirmed by using GFP as expression marker. BRE also has three peroxisomal targeting signals and several protein kinase phosphorylation sites. These motifs are crucial for cholesterol activation and transport.; These data, taken together, indicated that the function of the stress-responsive gene BRE is apparently associated with steroid hormone production and action. BRE may play an important role in steroidogenesis. The potential roles of BRE in immuno-endocrine interaction and apoptosis are also discussed.