The TGFβ1-Induced Fibronectin in Human Renal Proximal Tubular Epithelial Cells Is p38 MAP Kinase Dependent and Smad Independent

Abstract

Background/Aim: Transforming growth factor beta 1 (TGFβ1) is a fibrokine implicated in the progression of renal fibrosis. Following TGFβ1 receptor activation, a number of signalling pathways are stimulated. This study investigates the role of p38 mitogen-activated protein (MAP) kinase and Smad pathways in the TGFβ1-induced fibronectin (FN) production. Methods: Transformed human proximal tubular epithelial cells of the line HKC were used. Secreted FN was analyzed by enzyme-linked immunosorbent assay and Smad proteins by Western blotting. Chemical inhibitors were used to study the role of p38 MAP kinase and the TGFβ receptor ALK5. The Smad pathway was studied using a cell line overexpressing Smad7 and small interfering RNAs (siRNA). The FN mRNA expression was assessed by reverse transcription-polymerase chain reaction. Results: TGFβ1 produced a significant increase in FN secretion in both HKC and Smad7-HKC cells, and the p38 MAP kinase inhibitor SB202190 markedly reduced this (n = 3, p < 0.05 and p < 0.01). ALK5 inhibition also reduced the TGFβ1-induced FN (n = 3, p < 0.05). Smad knockdown using the siRNA did not reduce the TGFβ1-induced FN secretion. TGFβ1 induced FN mRNA expression in HKC cells, and SB202190 decreased this induction (n = 5, p < 0.05). Conclusions: These results suggest that TGFβ1-induced FN production in HKC cells is p38 MAP kinase dependent and Smad independent. Targeting p38 MAP kinase may be of therapeutic value in renal fibrosis.