Expression of β1B integrin isoform in CHO cells results in a dominant negative effect on cell adhesion and motility

The integrin subunit β1B, a β1 isoform with a unique sequence at the cytoplasmic domain, forms heterodimers with integrin α chains and binds fibronectin, but it does not localize to focal adhesion sites (Balzac, F., A. Belkin, V. Koteliansky, Y. Balabanow, F. Altruda, L. Silengo, and G. Tarone. 1993. J. Cell Biol. 121:171-178). Here we analyze the functional properties of human β1B by expressing it in hamster CHO cells. When stimulated by specific antibodies, β1B does not trigger tyrosine phosphorylation of a 125- kD cytosolic protein, an intracellular signaling pathway that is activated both by the endogenous hamster or the transfected human β1A. Moreover, expression of β1B results in reduced spreading on fibronectin and laminin, but not on vitronectin. Expression of β1B also results in severe reduction of cell motility in the Boyden chamber assay. Reduced cell spreading and motility could not be accounted for by preferential association of β1B with a given integrin α subunit. These data, together with our previous results, indicate that β1B interferes with β1A function when expressed in CHO cells resulting in a dominant negative effect on cell adhesion and migration.