Retinoic acid: identification of specific receptors through which it may mediate transcriptional regulation of fibronectin gene in bovine lens epithelial cells.

To elucidate in detail the regulatory mechanisms by which the fibronectin mRNA and protein are altered by all-trans retinoic acid (RA) in bovine lens epithelial (LE) cells, we have investigated the transcription mechanism and the occurrence of nuclear receptors for RA in the nuclei of cultured LE cells. The rate of transcription of fibronectin (FN) mRNA increased by 130% in response to RA. The RA receptors in nuclear extracts prepared from LE cells show specific all-trans [3H]-RA binding sites. Saturation binding of all-trans RA to these receptors and the Scatchard plot analyses of the binding data yielded an apparent dissociation constant (Kd) of about 12 nM and Bmax of about 48 pmoles/mg protein. Bovine retinoic acid receptors (RARs) have not been reported previously. Our results demonstrate for the first time that RA regulates FN expression and that regulation is at the transcriptional level in LE cells. Thus, retinoids may have an important role in the functional adhesion of epithelium to the lens capsule.