Regulation of cellular retinol-binding protein type II gene expression by arachidonic acid analogue and 9-cis retinoic acid in Caco-2 cells

We previously showed that unsaturated fatty acids induced gene expression o f cellular retinol-binding protein type LI (CRBPII) in rat jejunum [Suruga, K., Suzuki, R., Goda, T. and Takase, S, (1995) J. Nutr. 125, 2039-2044]. I n the present study, we investigated this induction mechanism(s) using the human intestinal Caco-2 cell line. The postconfluent mature Caco-2 cells we re maintained in serum-free medium containing arachidonic acid or its analo gue, 5,8,11,14-eicosatetraynoic acid (ETYA). Northern blot analysis showed that these compounds induced CRBPII mRNA levels to rise and that this induc tion was more effective when combined with 9-cis retinoic acid. This effect was independent of cycloheximide and inhibited by actinomycin D. Nuclear r un-on assays confirmed that the ETYA and 9-cis retinoic acid-induced increa se of CRBPII mRNA levels was due to an increased rate of transcription of i ts gene. In Caco-2 cells, the transcripts of peroxisome proliferator-activa ted receptor alpha (PPAR alpha) and retinoid X receptor alpha (RXR alpha), which were activated by their ligands ETYA and 9-cis retinoic acid, respect ively, were coexpressed. The gel shift study using rat CRBPII gene nuclear receptor response elements (RXRE, RE2, RE3) revealed that several forms of nuclear proteins from Caco-2 cells specifically bound to these elements. So me of these protein/DNA complexes reacted to both anti-RXR alpha and anti-P PAR antibodies. In addition, in-vitro synthesized RXR alpha and PPAR alpha cooperatively bound to these elements as a heterodimer and these binding ac tivities were enhanced by addition of ETYA or arachidonic acid but not by a ddition of 9-cis retinoic acid. These studies suggest that fatty acid or it s analogue may regulate CRBPII gene expression through PPAR/RXR heterodimer bound to the nuclear receptor response element(s) of the CRBPII genes.