Proliferative role of TRAF4 in breast cancer by upregulating PRMT5 nuclear expression.

In this study, we examined protein arginine methyltransferase 5 (PRMT5) and tumor necrosis factor receptor-associated 4 (TRAF4) expression in breast cancer to find the interaction mechanism between the two. We examined TRAF4 and PRMT5 expression by immunohistochemistry and found that their expression is positively correlated in breast cancer. Besides, PRMT5 expression was significantly associated with histological type and tumor size (p < 0.05). PRMT5 nuclear expression was significantly associated with HER2 expression (p < 0.05). PRMT5 and TRAF4 were both overexpressed in breast cancer tissues and cells, and we found that PRMT5 binds to the zinc finger structures in TRAF4 by coimmunoprecipitation and Western blotting. We also tested the potential regulatory effect between TRAF4 and PRMT5. TRAF4 upregulated PRMT5 expression, which occurred predominantly in the nucleus, on which TRAF4 promotion of cell proliferation in breast cancer is mainly dependent. PRMT5 may play an important role in activation of the NF-κB signaling pathway.

Cytoplasmic TRAF4 contributes to the activation of p70s6k signaling pathway in breast cancer.

Tumor necrosis factor receptor associated factor 4 (TRAF4) is an important adaptor protein that plays a significant role in several signaling pathways. By studying the relationship between TRAF4 and 70 kDa ribosomal protein S6 kinase (p70s6k) in vivo, we demonstrated that cytoplasmic TRAF4 was correlated with the activation of p70s6k in breast cancer. Moreover, we found that cytoplasmic TRAF4 expression in breast cancer patients was significantly associated with a poor prognosis. To determine the exact mechanism, we analyzed the interaction between TRAF4 and p70s6k and identified the Zinc fingers domain of TRAF4 was responsible for their interaction in MCF7 cells. Furthermore, we found that activation of p70s6k/S6 signaling pathway by TRAF4 requires the mammalian target of rapamycin (mTOR) activity; TRAF4 acted as a sensitizer. Tumor necrosis factor receptor associated factor 2 (TRAF2), as a binding partner of TRAF4, could also promoted activation of p70s6k signaling via upregulating cytoplasm expression of TRAF4 and played a critical role in TNFa-induced activation of p70s6k/S6 pathway. Finally, we demonstrated p70s6k/S6 signaling pathway played an important role in the promoting function of TRAF4 on cell proliferation. In summary, our work suggests a new direction for understanding the oncogenic function of TRAF4 in breast cancer.

Suppressive role of miR-502-5p in breast cancer via downregulation of TRAF2.

TRAF2 promotes cancer cell survival, proliferation and metastasis through the NF-κB pathway by directly interacting with various TNF recepors. However, the molecular mechanism of TRAF2 dysregulation in breast cancer remains to be elucidated. In the present study, miR-502-5p was predicted as a potential regulator of TRAF2. miR-502-5p was significantly downregulated in breast cancer tissues when compared to the level in paired normal breast tissues. The breast cancer cell lines including MCF-7 and MDA-MB-231 expressed a lower level of miR-502-5p when compared to the level in the non-malignant breast epithelial cell line MCF-10A. In vitro, miR-502-5p enhanced early apoptosis and inhibited proliferation of breast cancer cells. Luciferase reporter assay results showed that miR-502-5p could bind to the 3'-untranslated region of the TRAF2 gene, thus, exerting an inhibitory effect on TRAF2. Furthermore, silencing of TRAF2 exhibited effects similar to those of exogenous miR­502-5p, while overexpression of TRAF2 partially abrogated miR-502-5p-mediated suppression in breast cancer cells. In conclusion, miR-502-5p may act as a tumor-suppressor gene by targeting oncogenic TRAF2 in breast cancer and, therefore, may be a potential diagnostic and anticancer therapeutic marker for breast cancer.