INTEGRIN ALPHA(2) CYTOPLASMIC DOMAIN DELETION EFFECTS - LOSS OF ADHESIVE ACTIVITY PARALLELS LIGAND-INDEPENDENT RECRUITMENT INTO FOCAL ADHESIONS

Chinese hamster ovary (CHO) cells transfected with the integrin alpha(2) subunit formed a stable VLA-2 heterodimer that mediated cell adhesion to collagen. Within CHO cells spread on collagen, but not fibronectin, wild-type alpha(2) subunit localized into focal adhesion complexes (FACs). In contrast, alpha(2) with a deleted cytoplasmic domain was recruited into FACs whether CHO cells were spread on collagen or fibronectin. Thus, as previously seen for other integrins, the alpha(2) cytoplasmic domain acts as a negative regulator, preventing indiscriminate integrin recruitment into FACs. Notably, ligand-independent localization of the VLA-2 alpha(2) subunit into FACs was partially prevented if only one or two amino acids were present in the alpha(2) cytoplasmic domain (beyond the conserved GFFKR motif) and was completely prevented by four to seven amino acids. The addition of two alanine residues (added to GFFKR) also partially prevented ligand-independent localization. In a striking inverse correlation, the same mutants showing increased ligand-independent recruitment into FACs exhibited diminished alpha(2)-dependent adhesion to collagen. Thus, control of VLA-2 localization may be closely related to the suppression of cell adhesion to collagen. In contrast to FAC localization and collagen adhesion results, VLA-2-dependent binding and infection by echovirus were unaffected by either alpha 2 cytoplasmic domain deletion or exchange with other cytoplasmic domains.