Expression of integrin subunit β1B in integrin β1-deficient GD25 cells does not interfere with αVβ3 functions

We have expressed the beta 1B integrin subunit in beta 1-deficient GD25 cells to examine beta 1B functions without the interference of endogenous beta 1A expression. As previously reported [Retta et al, 1998, Mot Biol Cell 9, 715-731], the beta 1B integrins did not mediate cell adhesion under normal culture conditions, while the presence of 0.3 mM Mn2+ allowed beta 1B integrins to support adhesion. Mn2+, aS well as the small soluble peptide GRGDS, induced a beta 1B conformation, which was recognized by the mAb 9EG7, a marker for active or ligand-bound integrins, beta 1B integrins were found to localize to a subset of focal contacts in a ligand-independent manner on fibronectin, but not on vitronectin, However, clustering of beta 1B did not induce tyrosine phosphorylation of FAK, p130(Cas), or paxillin, as studied by beta 1B-mediated adhesion, to fibronectin in the presence of Mn2+ or to anti-beta 1 antibody in DMEM, Induction of ligand-occupied conformation by the GRGDS peptide during the adhesion to anti-beta 1 antibody also failed to trigger FAK phosphorylation, Stimulation of tyrosine phosphorylation on FAK, p130(Cas) and paxillin by adhesion via integrin alpha Y beta 3 to fibronectin or vitronectin was not disturbed in GD25-beta 1B cells compared to the untransfected GD25 cells, nor were any negative effects of beta 1B observed on alpha V beta 3-mediated cell attachment, spreading, and actin organization, or on the cell proliferation rate. These results show that the reported negative effects of beta 1B on adhesive events do not apply to alpha V beta 3-dependent interactions and suggest that they may specifically act on beta 1 integrins. (C) 2000 Academic Press.