Signal transduction involved in CTGF-induced production of chemokines in mesangial cells

Abstract

This study investigates the regulatory role of connective tissue growth factor (CTGF) on production of fractalkine, monocyte-chemoattractant protein-1 (MCP-1) and regulated on activation, normal T cell expressed and secreted (RANTES) in human mesangial cells, and explore the mechanisms of CTGF action. Cultured human mesangial cells were treated with CTGF. Expressions of mRNA and proteins of fractalkine, MCP-1 and RANTES were analyzed by real-time polymerase chain reaction (PCR) and by enzyme-linked immunosorbent assay, respectively. Expressions of phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2), phosphoinositide 3-kinase (PI3-K) and protein kinase B (PKB) were assessed by Western blotting. Activities of nuclear factor-KB (NF-KB) were determined by NF-kappaB luciferase reporter assay. CTGF enhanced the mRNA expressions and protein release of fractalkine, MCP-1 and RANTES, and the expressions of phosphorylated ERK1/2, PI3-K and PKB, and activities of NF-KB. Blockade of ERK1/2 inhibited the CTGF-induced expression ofphosphorylated ERK1/2 and NF-kappaB, and partially decreased the expressions of the above chemokines. PI3-K blockade downregulated the CTGF-stimulated expressions of phosphorylated PI3-K, PKB and NF-kappaB but not phosphorylated ERK1/2, partially decreased the expressions of the above chemokines. NF-kappaB blockade abrogated the CTGF-activated NF-kappaB and partially decreased the expressions of the above chemokines. Soluble heparin and K252a, an inhibitor of Trk, blocked CTGF-induced production of the above chemokines and the activation of the above signaling proteins. These results demonstrated that CTGF induces production of fractalkine, MCP-1 and RANTES via ERK1/2 and PI3-K/PKB/NF-kappaB-dependent signal pathway mediated by cell surface heparin sulfate proteoglycans and the tyrosine kinase receptor TrkA in human mesangial cells.