Hepatocyte nuclear factor-4alpha regulates human cellular retinol-binding protein type II gene expression in intestinal cells.

Cellular retinol-binding protein type II (CRBPII) is abundantly expressed in the small intestinal enterocytes of many vertebrates and plays important physiological roles in intestinal absorption, transport, and metabolism of vitamin A. In the present study, we investigated regulation of human CRBPII gene expression using human intestinal Caco-2 BBe cells. We found that the human CRBPII gene contained a direct repeat 1 (DR-1)-like nuclear receptor response element in the proximal promoter region and that endogenous hepatocyte nuclear factor-4alpha (HNF-4alpha) was a major transcription factor binding to the DR-1-like element. Cotransfection of HNF-4alpha expression vector transactivated the human CRBPII gene promoter activity, whereas mutation of the DR-1-like element abolished the promoter activity. Stably transfected Caco-2 BBe cells overexpressing HNF-4alpha significantly increased endogenous CRBPII gene expression and retinyl ester synthesis. Reduction of HNF-4alpha protein levels by HNF-4alpha small interference RNA decreased CRBPII gene expression. Caco-2 BBe cells treated with phorbol 12-myristate 13-acetate, a protein kinase C activator, decreased nuclear HNF-4alpha protein level and binding activity to the human CRBPII gene DR-1-like element, as well as CRBPII gene expression. Moreover, nuclear HNF-4alpha protein levels, HNF-4alpha protein binding to human CRBPII DR-1-like elements, and CRBPII gene expression level were coordinately increased during Caco-2 BBe cell differentiation. These results suggest that HNF-4alpha is an important transcriptional factor that regulates human CRBPII gene expression and provide the possibility for a novel function of HNF-4alpha in the regulation of human intestinal vitamin A absorption and metabolism.

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