Figure 4.

UBTD1 is down-regulated and regulates YAP degradation by the ubiquitin-proteasome system independent of the Hippo signaling pathway by matrix stiffness in HCC cells. (A) UBTD1 was significantly down-regulated with increasing matrix stiffness in HCC cells. (B) UBTD1 overexpression inhibited while UBTD1 knockdown promoted YAP expression in HCC cells. (C) YAP protein degradation in Hep3B was assessed by WB in the presence of CHX. (D) UBTD1 overexpression promoted the YAP degradation rate and was analyzed following treatment with CHX (50 μg/mL). (E) Low stiffness reduced the YAP protein level and its effect was reversed by a proteasome inhibitor MG-132 (20 μM). (F) MG132 reversed UBTD1 overexpression-induced YAP decrease. (G) Hippo signaling cascade LATS1/2 and MST1/2 phosphorylation was not affected by UBTD1 overexpression. *P < 0.05.