Expression of connective tissue growth factor induced by transforming growth factor-beta in human renal epithelial cells

Objective: To investigate the effect of transforming growth factor-β(TGF-β) on th e expression of connective tissue growth factor (CTGF) in human renal proximal t ubular epithelial cell line IK-2. Methodology:The mRNA and protein expression of CTGF in HK-2 cells was measured by rever se transcriptase-polymerase chain reaction (RT-PCR) and western blot, resp ectively. The effect of TGF-β 1 on the phenotypic transformation of HK-2 cel ls was observed by light microscopy, and the α-smooth muscle actin (α-SMA) e xpression in HK-2 cells was detected by immunofluorescence. Results:A basal level of CTGF mRNA and protein expression was detected in HK-2 cells. T he mRNA expression of CTGF in HK-2 cells was begun to increase by stimulati ng with 1 ng/ml TGF-β 1 (increased 2.4 times) and reached the peak at the co ncentration of 5 ng/ml (increased 3.34 times).The TGF-β 1 enhanced their expr ession in a time-dependent manner, with the maximal response at a concentration of 5 ng/ml and the best stimulating time course at 12~24 hour. At 24 hour, the mRNA expression of CTGF was increased by 3.19 times. In untreated cells, they s howed a typical cubical cobblestone phenotype and had negligible α-SMA, wherea s a more elongated fibroblastic appearance and α-SMA staining was noticeably i ncreased in the cells treated with TGF-β 1. However, the time course of HK-2 cells phenotypic transformation (72 hours after treatment with 5 ng/ml TGF-β 1 ) was much latter than that of CTGF mRNA and protein expression beginning to increase and reaching its peak (30 minutes and 24 hours after treatment with 5 ng/ml TGF-β 1, respectively). Conclusion:These results demonstrate that TGF-βdirectly induces CTGF expression in cultur ed human proximal tubular epithelial cells without myofibroblastic transdifferen tiation.