Focal Adhesion Kinase (FAK)-related Non-kinase Inhibits Myofibroblast Differentiation through Differential MAPK Activation in a FAK-dependent Manner

Abstract

Transforming growth factor (TGF)-␤1 induces fibroblast transdifferentiation to myofibroblasts, a process that requires the involvement of integrin-mediated signaling and focal adhesion kinase (FAK). FAK-related non-kinase (FRNK) is known for its role in inhibiting integrin-mediated cell migration; however, its role in myofibroblast differentiation has not been defined. Here, we report that FRNK abrogates TGF-␤1-induced myofibroblast differentiation in vitro and in vivo. TGF-␤1 can induce ␣-smooth muscle actin (␣-SMA) expression in the presence or absence of FAK; however, TGF-␤1-induced ␣-SMA expression is reduced (ϳ73%) in FAK-deficient fibroblasts. Although both ERK and p38 MAPK activation is required for maximal TGF-␤1-induced ␣-SMA expression, ERK is the major signaling intermediate in cells that express FAK. In contrast, p38 MAPK is the dominant mediator of TGF-␤1-induced ␣-SMA expression in FAK-deficient cells. FRNK overexpression blocks TGF-␤1-induced ERK or p38 MAPK activation in the presence, and surprisingly, in the absence of FAK. The loss of FRNK was tested in vivo during experimentally induced pulmonary fibrosis in mice. FRNK knock-out mice have a greater increase in ␣-SMA-expressing cells in response to a pulmonary fibrotic stimulus in vivo, as compared with congenic wild type mice. This is the first time that FRNK loss has been shown to modify the pathobiology in any animal disease model. Together, the data demonstrate that FRNK negatively regulates myofibroblast differentiation in vitro and in vivo. These data further suggest that modulation FRNK expression may be a novel avenue for therapeutic intervention in tissue fibrosis.Deranged tissue repair and remodeling or failed termination of the normal wound healing response may result in tissue fibrosis. After injury, fibroblasts migrate into the wound, proliferate, and differentiate to "activated" fibroblasts (1-4). The differentiated or activated fibroblasts are termed myofibroblasts and are present in abundance within fibrotic lesional areas in the lung, liver, and kidney (2, 4 -6). Myofibroblasts secrete profibrotic cytokines and extracellular matrix proteins, such as collagen and fibronectin, and therefore have been presumed to act as effector cells of the fibrotic process (1, 2, 4 -7).Idiopathic pulmonary fibrosis is a devastating, untreatable, progressive fibrotic disease of the lung (8 -11). In support of the importance of myofibroblasts in the pathogenesis of lung fibrosis, these cells localize to fibroblastic foci in pulmonary fibrotic lungs, and the extent of fibroblastic foci is a major prognostic factor for patients with idiopathic pulmonary fibrosis (8 -11).The phenotypic hallmarks of myofibroblasts are the expression of ␣-SMA 2 and the incorporation of ␣-SMA into well organized cytoplasmic fibers (1, 4, 6). These fibers connect to robust, mature focal adhesions (1). ␣-SMA expression is associated with an enhanced contractile phenotype and can directly enhance the contractility of fibroblasts (12, 13). Inhibition of ␣-SMA integration in...

MiR-21 Mediates Fibrogenic Activation Of Pulmonary Fibroblasts And Lung Fibrosis

“…For example, Spry1, a negative regulator of Erk activation, was previously shown to be a miR-21 target (Thum et al, 2008). Erk activation has been demonstrated to promote the fibrogenic activities of TGF-1 (Ding et al, 2008). In our experiments, Spry1 was decreased in bleomycin-treated lungs, whereas Erk phosphorylation was increased (Fig.…”

DNA methylation in fibrosis

“…It has also been shown that TGF-β stimulates fibroblast differentiation into the myofibroblast phenotype, mediated by extracellular-signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (p38 MAPK). This change in phenotype coincides with numerous changes to gene expression (Ding et al, 2008). In cells from neonatal Sprague-Dawley rats, TGF-β induced upregulation of COL1A1 was also accompanied by decreased expression of DNMT1 and DNMT3a.…”

microRNAs in Diabetic Kidney Disease

“…In cell lines from heart, lung, and kidney with TGF-treatment, overexpression of miR-29 suppresses but inhibition of miR-29 promotes expression of fibrotic markers [70,74,75,[78][79][80][81]. Gene delivery of miR-29b either before or after established obstructive nephropathy successfully blocks progressive renal fibrosis in a mouse model of unilateral ureteral obstruction nephropathy [74], providing a strong support of anti-fibrotic properties of miR-29.…”

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