Retinoid X receptor alpha and retinoic acid receptor gamma mediate expression of genes encoding tight-junction proteins and barrier function in F9 cells during visceral endodermal differentiation

Retinoids are critical for differentiation of columnar epithelial cells and for preventing metaplasia of these cells into stratified squamous epithelial cells, in which tight junctions (TJs) are essentially absent. This implies that retinoids might play important roles in regulating the structures and functions of TJs of columnar epithelium. F9 murine embryonal carcinoma cells differentiate into epithelial cells resembling visceral endoderm bearing TJs, when grown in suspension as aggregates in the presence of retinoic acid (RA). We show that RA induces the TJ structure and expression of several TJ-associated molecules, such as ZO-1, occludin, claudin-6, and claudin-7, as well as a barrier function in the genetically engineered cell line F9:rtTA:Cre-ER(T) L32T2, which allows sophisticated genetic manipulations simply by addition of ligands (H. Chiba et al., 2000, Exp. Cell Res. 260, 334-339). Interestingly, our data indicate that a barrier for small substances is generated after that for large ones during de novo formation of TJs. We also compared the RA-induced expression of TJ components and barrier function in RXRalpha(-/-)-RARgamma(-/-) F9 cells with those in wild-type cells and show that the retinoid signals for transduction of these events are mediated by specific RXR-RAR pairs.