TRAF4, a new substrate of SIAH1, participates in chemotherapy resistance of breast cancer cell by counteracting SIAH1-mediated downregulation of β-catenin.

Abstract

TRAF4 plays an important role in the development and progression of breast cancer, but its impact on chemotherapy resistance is as yet, however, poorly understood. Western blotting, immunoprecipitation, and immunofluorescence staining were used to identify and verify that TRAF4 was a novel substrate of SIAH1 and prevented SIAH1-mediated β-catenin degradation. Cell proliferation analysis and Flow cytometry analysis were utilized to detect TRAF4's function on the growth-inhibitory effect of etoposide. Immunohistochemistry was used to detect the expression of TRAF4, SIAH1, and β-catenin. Statistical analysis was used to analyze the relationships between them with clinical parameters and curative effect of chemotherapy pathologically. Our results suggested that TRAF4 prevents SIAH1-mediated β-catenin degradation. TRAF4 was a novel substrate of SIAH1 and the TRAF domain of TRAF4 was critical for binding to SIAH1. TRAF4 reduced the growth-inhibitory effect of etoposide via reducing the number of S-phase cells and suppressing cell apoptosis. Concordantly, we found that breast cancer patients with a low-TRAF4 expression benefited most from chemotherapy, who had higher tumor volume reduction rate and better pathological response, while, the high-TRAF4 expression group had lower tumor volume reduction rate and poor pathological response. TRAF4 was a novel substrate of SIAH1 and prevented SIAH1-mediated β-catenin degradation, which explains the protective effect of TRAF4 on β-catenin during cell stress and links TRAF4 to chemotherapy resistance in tumors. These findings implicated a novel pathway for the oncogenic function of TRAF4.