Proteasome inhibitor inhibits proliferation and induces apoptosis in renal interstitial fibroblasts

Background: The ubiquitin proteasome pathway plays a pivotal role in controlling cell proliferation, apoptosis and differentiation in a variety of normal and tumor cells. This study aimed to investigate the role of a proteasome inhibitor on proliferation, apoptosis and related proteins in renal interstitial fibroblasts (NRK-49F). Methods: NRK-49F cells were induced using transforming growth factor-beta 1 (TGF-beta 1) and pretreated with the proteasome inhibitor MG-132. Cell proliferation was measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). The cell cycle and apoptosis were analyzed using flow cytometry. Apoptosis was also analyzed using a DNA ladder. The protein expression of p53, p27, p21, caspase-3, Bcl-2 and Bax was examined using western blots. Results: The results showed that TGF-beta 1 (5 ng/ml) can stimulate the proliferation of NRK-49F cells. MG-132 (0.25-5 mu M) inhibited TGF-beta 1-induced proliferation in a dose-dependent manner through Gl-arrest; TGF-beta 1 alone did not induce apoptosis (3.8 +/- 0.4% vs. 4.7 +/- 1.6%). However, pretreatment with MG-132 significantly induced apoptosis in TGF-beta 1-stimulated NRK-49F cells in a dose-dependent manner. A typical DNA ladder was also confirmed in these two groups. Western blot analysis showed that MG-132 activated p53, p21, caspase-3 and Bax, and inhibited Bcl-2 in a dose-dependent manner, while p27 expression remained unchanged. Conclusions: A proteasome inhibitor inhibited proliferation and induced apoptosis in renal interstitial fibroblasts stimulated by TGF-beta 1. The mechanism may relate to the p53, p21, caspase-3, Bcl-2 and Bax pathways. Our results suggest that a proteasome inhibitor could be a new strategy to treat renal interstitial fibrosis.