Mechanical strain increases protein tyrosine phosphorylation in airway smooth muscle cells

Mechanical stress contributes to normal structure and function of the lung as well as pathology in such diseases as bronchopulmonary dysplasia and adult respiratory distress syndrome. Stress-related increases in airway smooth muscle (ASM) quantity are reflected in vitro where cultured ASM cells respond to cyclic deformational strain with increased proliferation, cell reorientation, protein production, stress fibers, and focal adhesions. To understand the mechanisms of mechanical signaling in ASM cells, we investigated whether strain increased tyrosine phosphorylation of focal adhesion-related proteins. ASM cells were grown to confluence on collagen type I and subjected to 30 min of cyclic deformation strain (2 s of 25% deformation of the substratum, 2 s relaxation) and compared at various time points with identical cells not subjected to strain for phosphotyrosine content of three focal adhesion-concentrated proteins (pp125FAK, paxillin, and talin) by Western blotting. Strain caused a rapid increase in tyrosine phosphorylation of pp125FAK and paxillin. Tyrosine phosphorylation decreased by 4 h in pp125FAK after discontinuing strain but remained elevated in paxillin at 24 h. Increases in tyrosine phosphorylation of talin were not found. In separate studies, when cells were strained in the presence of tyrosine kinase inhibitors (genistein and herbimycin A), strain-induced reorientation and elongation were inhibited. Mechanochemical signal transduction appears to mediate cell morphologic changes through quantitative and possibly qualitative changes in tyrosine phosphorylation of adhesion-related proteins.