Connective tissue growth factor induces collagen I expression in human lung fibroblasts through the Rac1/MLK3/JNK/AP-1 pathway

Abstract

Connective tissue growth factor (CTGF) plays an important role in lung fibrosis. In this study, we investigated the role of Rac1, mixed-lineage kinase 3 (MLK3), c-Jun N-terminal kinase (JNK), and activator protein-1 (AP-1) in CTGF-induced collagen I expression in human lung fibroblasts. CTGF caused concentration- and time-dependent increases in collagen I expression. CTGF-induced collagen I expression was inhibited by the dominant negative mutant (DN) of Rac1 (RacN17), MLK3DN, MLK3 inhibitor (K252a), JNK1DN, JNK2DN, a JNK inhibitor (SP600125), and an AP-1 inhibitor (curcumin). Treatment of cells with CTGF caused activation of Rac1, MLK3, JNK, and AP-1. The CTGF-induced increase in MLK3 phosphorylation was inhibited by RacN17. Treatment with RacN17 and the MLK3DN inhibited CTGF-induced JNK phosphorylation. CTGF caused increases in c-Jun phosphorylation and the recruitment of c-Jun and c-Fos to the collagen I promoter. Furthermore, stimulation of cells with the CTGF resulted in increases in AP-1-luciferase activity; this effect was inhibited by Rac1N17, MLK3DN, JNK1DN, and JNK2DN. Moreover, CTGF-induced α-smooth muscle actin (α-SMA) expression was inhibited by the procollagen I small interfering RNA (siRNA). These results suggest for the first time that CTGF acting through Rac1 activates the MLK3/JNK signaling pathway, which in turn initiates AP-1 activation and recruitment of c-Jun and c-Fos to the collagen I promoter and ultimately induces collagen I expression in human lung fibroblasts.

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“…In yet another study, CTGF was found to increase phosphorylation of five phosphoproteins including SAPK/JNK58. Retrospectively, there are a number of reports which indicate the regulation of CTGF by SAPK/JNK signalling wherein CTGF has been shown to produce its effects in the presence of active SAPK/JNK pathway5960.…”

TMF and glycitin act synergistically on keratinocytes and fibroblasts to promote wound healing and anti-scarring activity

“…46 As a result, connective tissue growth factor (CTGF), a known downstream mediator of TGF-β, induces proliferation of myofibroblasts and expression of collagen types I and III. 47 Sisco et al 48 reported that inhibition of CTGF activity limited hypertrophic scarring via the suppression of myofibroblasts, collagen and tissue inhibitor of metalloproteinase (TIMP)-1 expression. The repression of apoptosis, mechanobiology, angiogenesis, and inflammatory responses can also contribute to a reduction in scarring.…”

Fibrosis without fibroblast TGF-β receptors?

“…Mechanisms involving co-regulation with TGF-β and cooperation with autocrine TGF-β have been reported, but it is possible that TGF-β-independent mechanisms, such as mitogen-activated protein kinase- and AP-1-mediated collagen transcription, exist. 4 Dissection of these signaling intricacies involving AP-1 is made difficult, however, by imponderables such as codependency of AP-1 and SMADs in classical TGF-β signaling.…”