CXCL12 Induces Connective Tissue Growth Factor Expression in Human Lung Fibroblasts through the Rac1/ERK, JNK, and AP-1 Pathways

Abstract

CXCL12 (stromal cell-derived factor-1, SDF-1) is a potent chemokine for homing of CXCR4+ fibrocytes to injury sites of lung tissue, which contributes to pulmonary fibrosis. Overexpression of connective tissue growth factor (CTGF) plays a critical role in pulmonary fibrosis. In this study, we investigated the roles of Rac1, extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and activator protein-1 (AP-1) in CXCL12-induced CTGF expression in human lung fibroblasts. CXCL12 caused concentration- and time-dependent increases in CTGF expression and CTGF-luciferase activity. CXCL12-induced CTGF expression was inhibited by a CXCR4 antagonist (AMD3100), small interfering RNA of CXCR4 (CXCR4 siRNA), a dominant negative mutant of Rac1 (RacN17), a mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitor (PD98059), a JNK inhibitor (SP600125), a p21-activated kinase inhibitor (PAK18), c-Jun siRNA, and an AP-1 inhibitor (curcumin). Treatment of cells with CXCL12 caused activations of Rac1, Rho, ERK, and c-Jun. The CXCL12-induced increase in ERK phosphorylation was inhibited by RacN17. Treatment of cells with PD98059 and SP600125 both inhibited CXCL12-induced c-Jun phosphorylation. CXCL12 caused the recruitment of c-Jun and c-Fos binding to the CTGF promoter. Furthermore, CXCL12 induced an increase in α-smooth muscle actin (α-SMA) expression, a myofibroblastic phenotype, and actin stress fiber formation. CXCL12-induced actin stress fiber formation and α-SMA expression were respectively inhibited by AMD3100 and CTGF siRNA. Taken together, our results suggest that CXCL12, acting through CXCR4, activates the Rac/ERK and JNK signaling pathways, which in turn initiates c-Jun phosphorylation, and recruits c-Jun and c-Fos to the CTGF promoter and ultimately induces CTGF expression in human lung fibroblasts. Moreover, overexpression of CTGF mediates CXCL12-induced α-SMA expression.

The cytokines of pulmonary fibrosis: Much learned, much more to learn

“…Another chemokine, CXCL12, also known as stromal cellderived factor (SDF-1), attracts fibrocytes to injured lungs and induces CTGF expression in pulmonary fibroblasts, which are both dependent on its cell-surface receptor CXCR4, thus contributing to lung fibrosis [190,191]. A more detailed overview of the roles of chemokines in fibrosis can be found elsewhere [189,190].…”

Inhibition of Rac1 Signaling Downregulates Inflammasome Activation and Attenuates Lung Injury in Neonatal Rats Exposed to Hyperoxia

“…It is known that Rac1 signaling regulates CTGF expression [16,23]. Lin et al [16] showed that CXCL-12 activates Rac1 signaling which induces the expression of CTGF in human lung fibroblasts.…”

“…Lin et al [16] showed that CXCL-12 activates Rac1 signaling which induces the expression of CTGF in human lung fibroblasts. CTGF is the downstream mediator of TGFβ-induced adventitial remodeling in carotid angioplasty [24].…”

“…In fact, treatment with NSC23766, a specific Rac1 inhibitor, decreases leukocyte infiltration and lung injury in animal models [14,15]. Rac1 also regulates the expression of connective tissue growth factor (CTGF), which is a key factor in the pathogenesis of pulmonary vascular remodeling and fibrosis [16]. …”

Role of CXCL12/CXCR4-Mediated Circulating Fibrocytes in Pulmonary Fibrosis

“…The downstream intracellular signaling transduction pathways including Phosphatidylinositol 3-kinase (PI3K)/Akt/ mammalian target of rapamycin (mTOR), Rac1/extracellular signal-regulated kinase (ERK), mitogen-activated protein kinase (MAPK), p38MAPK, stress-activated protein kinase (SAPK), c-Jun N-terminal kinase (JNK)/ activator protein-1 (AP-1), Janus kinase/signal transducers and activators of transcription (JAK/STAT). 45,46 CXCR4 is the predominant chemokine receptor on human fibrocytes. More and more evidence have indicated that substantial numbers of CXCR4 + fibrocytes can migrate and accumulate in lung in response to CXCL12 during pulmonary fibrosis.…”