Proteomic analysis of CTGF-activated lung fibroblasts: identification of IQGAP1 as a key player in lung fibroblast migration

Bogatkevich GS, Ludwicka-Bradley A, Singleton CB, Bethard JR, Silver RM. Proteomic analysis of CTGF- activated lung fibroblasts: identification of IQGAP1 as a key player in lung fibroblast migration. Am J Physiol Lung Cell Mol Physiol 295: L603-L611, 2008. First published August 1, 2008; doi: 10.1152/ajplung.00530.2007.-Connective tissue growth factor ( CTGF, CCN2) is overexpressed in lung fibroblasts isolated from patients with interstitial lung disease (ILD) and systemic sclerosis (SSc, scleroderma) and is considered to be a molecular marker of fibrosis. To understand the significance of elevated CTGF, we investigated the changes in lung fibroblast proteome in response to CTGF overexpression. Using 2-dimensional gel electrophoresis followed by in-gel proteolytic digestion and mass spectrometric analysis, we identified 13 proteins affected by CTGF. Several of the CTGF- induced proteins, such as pro-alpha ( I) collagen and cytoskeletal proteins vinculin, moesin, and ezrin, are known to be elevated in pulmonary fibrosis, whereas 9 of 13 proteins have not been studied in pulmonary fibrosis and are, therefore, novel CTGF- responsive molecules that may have important roles in ILD. Our study demonstrates that 1 of the novel CTGF- induced proteins, IQ motif containing GTPase activating protein ( IQGAP) 1, is elevated in lung fibroblasts isolated from scleroderma patients with ILD. IQGAP1 is a scaffold protein that plays a pivotal role in regulating migration of endothelial and epithelial cells. Scleroderma lung fibroblasts and normal lung fibroblasts treated with CTGF demonstrated increased rate of migration in a wound healing assay. Depletion of IQGAP1 expression by small interfering RNA inhibited CTGF- induced migration and MAPK ERK1/2 phosphorylation in lung fibroblasts. MAPK inhibitor U0126 decreased CTGF- induced cell migration and did not interfere with CTGF- induced IQGAP1 expression, suggesting that MAPK pathway is downstream of IQGAP1. These findings further implicate the importance of CTGF in lung tissue repair and fibrosis and propose that CTGF- induced migration of lung fibroblasts to the damaged tissue is mediated via IQGAP1 and MAPK signaling pathways.