Regulation of β 1 -Integrin Function in Cultured Human Vascular Smooth Muscle Cells

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Abstract
Avidity modulation and function of β 1 -integrin receptors in cultured human vascular smooth muscle cells (SMCs) were investigated using monoclonal antibody (mAb) 8A2, which binds to the β 1 subunit of integrin heterodimers and induces a high avidity state. The adhesion of SMCs to extracellular matrix proteins, but not to poly- l -lysine, was enhanced by pretreatment with mAb 8A2. A qualitative alteration of β 1 integrin was assessed with mAb 15/7, which binds to an activation-dependent epitope on the β 1 subunit. Binding of mAb 15/7 was enhanced by mAb 8A2 in a dose-dependent manner. Arg-Gly-Asp peptide and soluble fibronectin also enhanced expression of the 15/7 epitope, suggesting that the 15/7 epitope is closely related to the ligand-occupied state of β 1 integrin. Platelet-derived growth factor (PDGF)-AA and -BB increased SMC adhesion to type I collagen but did not augment mAb 15/7 binding, suggesting that PDGFs increase binding avidity by a postreceptor mechanism. In addition, mAb 8A2 inhibited PDGF-BB–induced SMC migration through Matrigel-coated filters. These results suggest that avidity modulation of β 1 integrin may play an important role in the function of SMCs.

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