Protein complexes involving alpha(V)beta(3) integrins, nonmuscle myosin heavy chain-A, and focal adhesion kinase form in thrombospondin-treated smooth muscle cells

alpha(nu)beta(3) integrins have been implicated in regulating vascular heal ing in animal models of arterial injury. Because the specific cellular even ts mediated by alpha(nu)beta(3), integrins are not completely understood, w e examined alpha(nu)beta(3), integrin-dependent cytoplasmic events in cultu red human smooth muscle cells (SMC) following treatment with thrombospondin -l (TSP), a glycoprotein concentrated at sites of blood vessel injury. TSP treatment elicited a time-dependent association of nonmuscle myosin heavy c hain-A (NMHC-A) with alpha(nu)beta(3) integrins, NMHC-A also associated wit h focal adhesion kinase (FAK) in TSP-treated SMC FAK, a nonreceptor kinase implicated in integrin-mediated signaling, was phosphorylated on tyrosine i n growth-arrested SMC, but levels of tyrosine phosphorylation increased fol lowing treatment with TSP, To test whether NMHC-A was regulated by vascular injury, we examined expression in baboon brachial arteries. In uninjured a rteries, NMHC-A staining was present in the media. In arteries injured by b alloon withdrawal, medial NMHC-A expression was increased with intense stai ning at specific sites. In summary, heteromeric protein complexes involving alpha(nu)beta(3) integrins, NMHC-A, and FAK form following treatment of hu man SR IC with TSP, These results suggest that the formation of protein sig naling complexes is one mechanism whereby alpha(nu)beta(3) integrins influe nce intracellular signaling pathways.