Focal Adhesion Kinase Regulates Collagen I–Induced Airway Smooth Muscle Phenotype Switching

Abstract

Increased extracellular matrix (ECM) deposition and airway smooth muscle (ASM) mass are major contributors to airway remodeling in asthma. Recently, we demonstrated that the ECM protein collagen I, which is increased surrounding asthmatic ASM, induces a proliferative, hypocontractile ASM phenotype. Little is known, however, about 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. Nor were any differences found in cellular adhesion. Inhibition of FAK activity by overexpression of the FAK deletion mutants FAT (focal adhesion targeting domain) and FRNK (FAK-related nonkinase) attenuated adhesion. After attachment, FAK phosphorylation increased in a time-dependent manner in cells cultured on collagen I, whereas no activation was found on an uncoated plastic matrix. In addition, collagen I increased in a time-and concentrationdependent manner the cell proliferation, which was fully inhibited by FAT and FRNK. Similarly, the specific pharmacologic FAK inhibitor benzyl)amino)-5-trifluoromethylpyrimidin-2-yl) amino)-3,4-dihydro-1H-quinolin-2-one] as well as specific inhibitors of p38 mitogen-activated protein kinase (MAPK) and Src also fully inhibited collagen I-induced proliferation, whereas partial inhibition was observed by inhibition of phosphatidylinositol-3-kinase (PI3-kinase) and mitogen-activated protein kinase kinase (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.

Microfibrillar-associated protein 4 modulates airway smooth muscle cell phenotype in experimental asthma

“…To our knowledge, only one study so far addressed the role of FAK in integrin signalling in ASM, showing that FAK promotes collagen I induced bovine ASM proliferation together with activation of PI3K and ERK 32. Both these pathways regulate growth factor-induced ASM growth, though PI3K seems to be more important in asthmatic ASM 33.…”

Periodic Mechanical Stress Stimulates the FAK Mitogenic Signal in Rat Chondrocytes Through ERK1/2 Activity

“…Focal adhesion kinase (FAK) is known to be tightly linked to integrin-associated mechanotransduction [2,3,4]. Accumulating evidence supports an important role of FAK in several signal transduction pathways that affect cellular biological processes, including proliferation, migration and survival [5,6,7]. Several researchers have established that mechanical stimulation activates FAK signaling in a number of cell types [8,9].…”

Beyond TGFβ – Novel ways to target airway and parenchymal fibrosis

“…Collectively, these findings indicate that integrins, ECM proteins and matrikines form an interesting target for the treatment of fibrotic lung disease. Moreover targeting of intracellular signalling pathways downstream of integrins, such as focal adhesion kinase (FAK) and integrin-linked kinase (ILK), may also have potential to prevent fibrosis as well as airway remodelling [59,60].…”