TRIB2 inhibits Wnt/β-Catenin/TCF4 signaling through its associated ubiquitin E3 ligases, β-TrCP, COP1 and Smurf1, in liver cancer cells

Tribbles homolog 2 (TRIB2) is specifically regulated by Wnt signaling in liver cancer cells but not in colon cancer cells. However, whether and how TRIB2 regulates Wnt signaling in liver cancer cells remains unclear. Here, we report that TRIB2 negatively regulates Wnt activity through a reduction in protein stability of TCF4 and β-Catenin. Mechanistically, TRIB2 associated-ubiquitin E3 ligases beta-transducin repeat-containing E3 ubiquitin protein ligase (β-TrCP), COP1 and Smad ubiquitination regulatory factor 1 (Smurf1) reduced TCF4/β-Catenin expression, and these effects could be enhanced by TRIB2. Moreover, deletion of the binding regions of these E3-ligases within the TRIB2 protein decreased ubiquitination of TCF4/β-Catenin and reduced nuclear accumulation of β-TrCP, COP1 and Smurf1, which suggested that TRIB2 regulated-Wnt activity is closely correlated with its associated E3 ligases.