Studies on the gene expression and physiological roles of cellular retinol-binding protein, type II in small intestine

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1) Dietary fatty acids which modulate jejunal cellular retinol binding protein type II (CRBP (II)) and nuclear factors of retinoid receptor (RXR) and peroxisome proliferator-activated receptor (PPAR) were explored using rats. All unsaturated fatty acids (oleic, linoleic and linolenic) enhanced the CRBP (II) mRNA levels, but not the RXR_<alpha> and PPAR_<alpha> levels.2) We investigated whether arachidonic acids and peroxisome proliferators (clofibric acid and eicosatetraynoic acid (ETYA)) enhance gene expression of CRBP (II) and RXR_<alpha> & PPAR_<alpha> in human intestinal cell line, Caco-2 cells. The cells exposed to clofibric acid, arachidonic acid and ETYA enhanced CRBP (II) mRNA expression, but not RXR_<alpha> and PPAR_<alpha> mRNAs. Additive effect on CRBP (II) gene expression by ETYA in combination with 9-cis retinoic acid were observed in Caco-2 cells.3) It was observed by gel shift assay that jejunum nuclear extracts from rats fed high fat (corn oil) diet bound to nucler receptor response elements (RXRE & RE3) in a 5'flanking region of the rat CRBP (II) gen, and the binding was prevented with RXR antibody. The binding level of the nuclear extracts to the DNA response elements were elevated in rats fed the high fat diet.4) Gel shift assay revealed that the increased CRBP (II) mRNA level in ETYA-treatmented Caco-2 cells were related to the enhanced nuclear interaction of the receptor response elements (RE3) with nuclear extracts from the cells. Actinomycin D treatment of the Caco-2 cells brought about a inhibition of the the CRBP (II) mRNA expressio n by ETYA,suggesting a increased binding of RXR/PPAR omplex to a 5'flanking region by the ETYA reatment may enhance CRBP (II) gene level5) Effects of feeding excessbeta-carotene on CRBP (II) and vitamin A levels were investigated. Feeding excessbeta-carotene did not increase jejunum CRBP (II) levels and jejunal contents of unesterified retinol and retinyl palmitate in rats.