QUANTITATIVE SWITCH IN INTEGRIN EXPRESSION ACCOMPANIES DIFFERENTIATION OF F9 CELLS TREATED WITH RETINOIC ACID

F9 embryonal carcinoma cells resemble epithelial cells when in monolay er culture. After treatment with retinoic acid these cells differentia te into fibroblastic-like cells in a sequence that has been modeled as the mammalian equivalent of the differentiation from stem cells of th e inner cell. mass to parietal endoderm. This study examined the chang es in integrin subtypes that accompany retinoic acid-induced different iation of F9 cells. Although several integrins were found to be presen t on the surface of F9 cells and retinoic acid-induced (RA) cells, the two dominant integrins were alpha 3 beta 1 and alpha 5 beta 1. Differ entiation of F9 cells resulted in about 10- to 25-fold increase in the amount of alpha 3 beta 1 integrin protein as measured by immunoprecip itation of cell surface labeled material. There was a corresponding se veral-fold reduction of alpha 5 beta 1 protein. The concentration of a lpha 3 mRNA was about the same in F9 and RA cells while the concentrat ion of alpha 5 mRNA dropped several-fold after retinoic acid treatment . Thus alpha 3 regulation appeared to be largely posttranscriptional w hile the drop in alpha 5 protein may have been a result of transcripti onal down-regulation. Quantitative measurement of adhesion suggested t hat most of the F9 and RA cell-substrate adhesion to fibronectin or la minin is mediated by these integrins. They are the dominant integrins present, and antibodies to either these integrins or to the substrate blocked the adhesion. Despite the large switch in integrin subtype pro tein expression there was little difference between the two cell types in initial cell interactions when adhesive affinities were measured q uantitatively. Also there was no difference between the two phenotypes in rate of initial adhesive strengthening. The phenotypic difference was first observed with later events in the attachment and spreading o f the RA-treated cells to the substrate, These results show that retin oic acid treatment alters the amounts of alpha 5 and alpha 3 integrin subunits during the F9 to RA phenotypic switch. The data show that the se integrins are important in the cell-substrate adhesion to fibronect in and laminin. They show, however, that the phenotypic changes observ ed with differentiation are not associated with the initial preferenti al adhesions to the substrate, but rather with consequences that alter the cytoskeletal architecture of the cell. (C) 1994 Wiley-Liss, Inc.