Abstract
BACKGROUND: Vitamin A and its derivatives, the retinoids, are essential for normal embryonic development and maintenance of cell differentiation. beta, beta-carotene 15,15'-monooxygenase 1 (BCMO1) catalyzes the central cleavage of beta-carotene to all-trans retinal and is the key enzyme in the intestinal metabolism of carotenes to vitamin A. However, human and various rodent species show markedly different efficiencies in intestinal BCMO1-mediated carotene to retinoid conversion. The aim of this study is to identify potentially human-specific regulatory control mechanisms of BCMO1 gene expression. RESULTS: We identified and functionally characterized the human BCMO1 promoter sequence and determined the transcriptional regulation of the BCMO1 gene in a BCMO1 expressing human intestinal cell line, TC-7. Several functional transcription factor-binding sites were identified in the human promoter that are absent in the mouse BCMO1 promoter. We demonstrate that the proximal promoter sequence, nt -190 to +35, confers basal transcriptional activity of the human BCMO1 gene. Site-directed mutagenesis of the myocyte enhancer factor 2 (MEF2) and peroxisome proliferator-activated receptor (PPAR) binding elements resulted in decreased basal promoter activity. Mutation of both promoter elements abrogated the expression of intestinal cell BCMO1. Electrophoretic mobility shift and supershift assays and transcription factor co-expression in TC-7 cells showed MEF2C and PPARgamma bind to their respective DNA elements and synergistically transactivate BCMO1 expression. CONCLUSION: We demonstrate that human intestinal cell BCMO1 expression is dependent on the functional cooperation between PPARgamma and MEF2 isoforms. The findings suggest that the interaction between MEF2 and PPAR factors may provide a molecular basis for interspecies differences in the transcriptional regulation of the BCMO1 gene.