Heat shock protein 90 inhibitor attenuates renal fibrosis through degradation of transforming growth factor-β type II receptor.

The accumulation of extracellular matrix proteins in the interstitial area is the final common feature of chronic kidney diseases. Accumulating evidence suggests that transforming growth factor (TGF)-β1 promotes the development of renal fibrosis. Heat shock protein (Hsp) 90 inhibitors have been shown to repress TGF-β1 signaling, but whether they inhibit renal fibrosis is unknown. The purpose of this study is to determine the therapeutic efficacy of Hsp90 inhibitor on renal fibrosis. In TGF-β1-treated HK2 cells and unilateral ureteral obstruction (UUO) kidneys, we found that 17-allylamino-17-demethoxygeldanamycin (17AAG), an Hsp90 inhibitor, decreased the expression of α-smooth muscle actin, fibronectin, and collagen I and largely restored the expression of E-cadherin. 17AAG inhibited TGF-β1-mediated phosphorylation of Smad2, Akt, glycogen synthase kinase-3β, and extracellular signal-regulated kinase in HK2 cells. Inhibition of Hsp90 also blocked TGF-β1-mediated induction of snail1. This 17AAG-induced reduction was completely restored by simultaneous treatment with proteasome inhibitor MG132. Furthermore, 17AAG blocked the interaction between Hsp90 and TGF-β type II receptor (TβRII) and promoted ubiquitination of TβRII, leading to the decreased availability of TβRII. Smurf2-specific siRNA reversed the ability of 17AAG to inhibit TGF-β1 signaling. The effect of 17AAG on TβRII expression and renal fibrosis was confirmed in UUO kidneys. These findings suggest that Hsp90 inhibitor prevents the development of renal fibrosis via a mechanism dependent on Smurf2-mediated degradation of TβRII.