Increased extracellular matrix (ECM) deposition and airway smooth muscle (ASM) mass are major contributors to airway remodeling in asthma. Recently, we have demonstrated that the ECM protein collagen I, which is increased surrounding asthmatic ASM, induces a proliferative, hypocontractile ASM phenotype. Little is known, however, on the signaling pathways involved. Using bovine tracheal smooth muscle, we investigated the role of focal adhesion kinase (FAK) and downstream signaling pathways in collagen I-induced ASM phenotype modulation. Phosphorylation of FAK was increased during adhesion to both uncoated and collagen I-coated culture dishes, without differences between these matrices. No differences in cellular adhesion were found either. Inhibition of FAK activity by overexpression of the FAK deletion mutants FAT (focal adhesion targeting domain) and FRNK (FAK-related non-kinase) attenuated adhesion. After attachment, FAK phosphorylation was time-dependently increased in cells cultured on collagen I, whereas no activation was found on an uncoated plastic matrix. In addition, collagen I time- and concentration-dependently increased cell proliferation, which was fully inhibited by FAT and FRNK. Similarly, the specific pharmacological FAK inhibitor PF-573,228 as well as specific inhibitors of p38 MAPK and Src also fully inhibited collagen I-induced proliferation, whereas partial inhibition was observed by inhibition of PI3-kinase and MEK. The inhibition of cell proliferation by these inhibitors was associated with attenuation of the collagen I-induced hypocontractility. Collectively, the results indicate that induction of a proliferative, hypocontractile ASM phenotype by collagen I is mediated by FAK and downstream signaling pathways.
- The American Society for Pharmacology and Experimental Therapeutics