MODULATION OF ALPHA-6 BETA-1 INTEGRIN EXPRESSION DURING DIFFERENTIATION OF F9 MURINE EMBRYONAL CARCINOMA-CELLS TO PARIETAL ENDODERM/

In vitro differentiation of the murine embryonal carcinoma (EC) cell l ine F9 parallels that of the early blastocyst, where visceral (VE) and parietal endoderm (PE) diverge from a common precursor, the primitive endoderm. This differentiation pathway is induced by retinoic acid (R A) and dibutyryl cyclicAMP (dcAMP) and is accompanied by progressive a nd dramatic changes in cell morphology and functions. Within 7 days of treatment the cells organize their cytoskeleton and synthesize large amounts of extracellular matrix proteins, becoming fully differentiate d migratory cells; all these changes are likely to involve integrins e xpression and organization. We have investigated the changes in beta 1 integrin expression, its maturation, and organization on the cell sur face in association with alpha 6, during the transition from undiffere ntiated F9 stem cells to migrating PE cells. By Western blotting and i mmunoprecipitation we showed a gradual decrease in the amount of the b eta 1 subunit on the cell surface and a parallel progressive accumulat ion of immature protein, indicating that the control of beta 1 express ion during F9 cells differentiation occurs first at posttranslational level and then at the level of transcription. Moreover, the induction of differentiation produces a marked decrease of alpha 6B and its asso ciation to a high molecular weight protein, while alpha 6A level incre ases. By immunofluorescence we found that upon differentiation there i s a relocation of the beta 1 and alpha 6B integrin subunits from cell- cell contacts to focal contacts where they colocalize with vinculin. O n the contrary alpha 6A, weakly present in F9 stem cells, is present i n the focal contacts of PE cells and along the stress fibers. We sugge st different roles for the two alpha 6 isoforms. (C) 1997 Academic Pre ss.