Tripartite motif protein 52 (TRIM52) promoted fibrosis in LX-2 cells through PPM1A-mediated Smad2/3 pathway.

To investigate the roles of tripartite motif containing 52 (TRIM52) in human hepatic fibrosis in vitro, human hepatic stellate cell line LX-2 cells were transfected with hepatitis B virus (HBV) replicon to establish HBV-induced fibrosis in LX-2 cells, and then treated with small interfering RNA-mediated knockdown of TRIM52 (siTRIM52). LX-2 cells without HBV replicon transfection were treated with lentiviruses-mediated overexpression of TRIM52 and phosphatase magnesium dependent 1A (PPM1A). Fibrosis response of LX-2 cells were assessed by the production of hydroxyproline (Hyp) and collagen I/III, as well as protein levels of α-smooth muscle actin (α-SMA). PPM1A and phosphorylated (p)-Smad2/3 were measured to assess the mechanism. The correlation between TRIM52 and PPM1A was determined using co-immunoprecipitation, and whether and how TRIM52 regulated the degradation of PPM1A were determined by ubiquitination assay. Our data confirmed HBV-induced fibrogenesis of LX-2 cells, as evidenced by significant increase in Hyp and collagen I/III and α-SMA, which was associated with reduction of PPM1A and elevation of transforming growth factor-β (TGF-β), p-Smad2/3, and p-Smad3L. However, those changes induced by HBV were significantly attenuated with additional siTRIM52 treatment. Similar to HBV, overexpression of TRIM52 exerted promoted effect in the fibrosis of LX-2 cells. Interestingly, TRIM52 induced the fibrogenesis of LX-2 cells and the activation of TGF-β/Smad pathway were significantly reversed by PPM1A overexpression. Furthermore, our data confirmed TRIM52 as a deubiquitinase that influenced the accumulation of PPM1A protein, and subsequently regulated the fibrogenesis of LX-2 cells. TRIM52 was a fibrosis promoter in hepatic fibrosis in vitro, likely through PPM1A-mediated TGF-β/Smad pathway.