Expression of epithelial markers and retinoid-binding proteins in retinol- or retinoic acid-treated intestinal cells in vitro.

This study was undertaken with the aim of investigating the effects of retinoids on the expression of differentiated traits in intestinal cell models. The cell lines used included epithelial cells isolated from fetal rat intestines (FRIC), displaying a relatively undifferentiated phenotype, and the human colon adenocarcinoma cell lines Caco 2 and HT29, which express some of the traits of the mature enterocytes under defined culture conditions. The effects of retinoids were also studied in organ cultures of fetal rat intestine, where the epithelial-mesenchymal interactions are preserved. All-trans-retinol and all-trans-retinoic acid treatments were compared in their ability to regulate the expression of genes coding for proteins involved in retinoid metabolism and for cytoskeletal proteins. The results have shown that the effects of the two retinoids were qualitatively similar. A specific induction of the cellular retinol-binding protein CRBP I mRNA was observed following retinoid treatment in one of the two FRIC lines examined (FRIC B) and in organ culture. The expression of the retinoic acid receptors RAR alpha and gamma was not affected by treatment in any of the cultures examined, while RAR beta was expressed only by the organ cultures and was transcriptionally induced by retinoic acid treatment. The retinoids also induced a reorganization of the actin cytoskeleton in the FRIC B cell line, accompanied by a decrease in the expression of two components of the microvillar cytoskeleton, ezrin and villin. The results obtained in both cell and organ cultures suggest that retinoids alone are not able to trigger the differentiation program in the intestinal epithelial cell, irrespective of the level of differentiation already achieved at the time of treatment.