TRAF2 regulates the cytoplasmic/nuclear distribution of TRAF4 and its biological function in breast cancer cells

Although numerous studies have shown that tumor necrosis factor receptor-associated factor 4 (TRAF4) plays an important role in the carcinogenesis of many tumor types, its exact molecular mechanism remains elusive. In this study, we examined the regulation function of TRAF2 to the cytoplasmic/nuclear distribution of TRAF4 in the breast cancer cell line. Using cell immunofluorescent staining, we found that TRAF2 and TRAF4 were co-localized to the cytoplasm in MCF-7 cells. Co-immunoprecipitation showed that TRAF2 could interact with TRAF4 in MCF-10A, MCF-7 and MDA-MB-231 cell lines. Western blotting showed TRAF2 depletion by targeted siRNA in MDA-MB-231 cells led to reduced TRAF4 expression in the cytoplasm and augmented TRAF4 expression in the nucleus. Cytoplasmic expression of TRAF4 was augmented and nuclear expression was reduced when MCF-7 cells were transfected with hTRAF2pLPCX-HA-Flag/P874. MCF-7 cells expressing hTRAF2pLPCX-HA-Flag/P874 had enhanced cell proliferation rates. The nuclear expression of NF-κB significantly increased after TNF-α treatment. When hTRAF2pLPCX-HA-Flag/P874 and the siRNA-TRAF4 plasmid were cotransfected, the nuclear expression of NF-κB was significantly reduced compared with cells transfected with hTRAF2pLPCX-HA-Flag/P874 only. In conclusion, TRAF2 appears to interact with TRAF4 and affect the localization of TRAF4 in breast cancer cell lines. The overexpression of TRAF2 augmented the cytoplasmic expression of TRAF4 which promoted cell proliferation and inhibited cell apoptosis by activating NF-κB nuclear transcription. TRAF4 may play an important role in the activation of NF-κB via TRAF2.