EXPRESSION AND FUNCTION OF BETA(1) INTEGRINS ON ADHERENT AND NONADHERENT EHRLICH ASCITES TUMOR-CELLS

Differences in integrin-mediated cell-matrix adhesion between two type s of Ehrlich ascites tumor (EAT) cells, adherent and nonadherent EAT c ells, have been studied. The adherent EAT (a-EAT) cells adhere to and spread on laminin- or fibronectin-coated plates, whereas the nonadhere nt EAT (na-EAT) cells do not, The adhesion of a-EAT cells to laminin o r fibronectin requires the presence of both Ca2+ and Mg2+. Anti-human fibronectin receptor (alpha(5) beta(1) integrin) antiserum blocks a-EA T cells from adhering to both laminin- and fibronectin-coated plates, An RGD-containing peptide (GRGDSP) inhibits the adhesion of a-EAT cell s to fibronectin-coated but not to laminin-coated plates. Taken togeth er, these data suggest that a-EAT cells interact with laminin and fibr onectin via different beta(1) integrins. As determined by immunofluore scence flow cytometry assay, both a-EAT and na-EAT cells express simil ar amounts of surface antigen(s) recognized by the same anti-alpha(5) beta(1) integrin polyclonal antibody that blocks a-EAT cells from adhe ring to laminin and fibronectin. The alpha(5) and beta(1) subunits exp ressed on both types of EAT cells appear to have the same molecular we ight when analyzed by immunoblotting. The same amount of I-125-labeled membrane protein was isolated from both types of EAT cells on immobil ized laminin and fibronectin affinity columns, These data indicate tha t na-EAT cells express similar amounts of cell surface integrins, and these integrins, when isolated, react with laminin and fibronectin in the same manner as the integrins of a-EAT cells, even though na-EAT ce lls are unable to adhere to laminin and fibronectin. Previous work has shown that both types of EAT cells express Neu5Ac alpha 2, 3 Gal-beta 1, 4 GlcNAc residues on their cell surface and that they both react w ith Maackia amurensis lectin which specifically recognizes this carboh ydrate structure, Here we show that both types of EAT cells attach to M. amurensis lectin-coated surfaces, but only a-EAT cells spread; this suggests that the differences between these two types of cells in res ponding to extra cellular matrix molecules may reside in some differen ces within the cell. (C) 1995 Academic Press, Inc.