Inhibitory role of TRIP-Br1 oncoprotein in hypoxia-induced apoptosis in breast cancer cell lines.

TRIP-Br1 oncoprotein is known to be involved in many vital cellular functions. In this study, we examined the role of TRIP-Br1 in hypoxia-induced cell death. Exposure to the overcrowded and CoCl2-induced hypoxic conditions increased TRIP-Br1 expression at the protein level in six breast cancer cell lines (MCF7, MDA-MB-231, T47D, Hs578D, BT549, and MDA-MB-435) but resulted in no significant change in three normal cell lines (MCF10A, MEF and NIH3T3). Our result revealed that CoCl2-induced hypoxia stimulated apoptosis and autophagy, in which TRIP-Br1 expression was found to be upregulated. Interestingly, TRIP-Br1 silencing in the MCF7 and MDA-MB-231 cancer cells accelerated apoptosis and destabilization of XIAP under the CoCl2-induced hypoxic condition, implying that TRIP-Br1 may render cancer cells resistant to apoptosis through the stabilization of XIAP. We also propose that TRIP-Br1 seems to be upregulated at least partly as a result of the inhibition of PI3K/AKT signaling pathway and the overexpression of HIF-1α. In conclusion, our findings suggest that TRIP-Br1 functions as an oncogenic protein by providing cancer cells resistance to the hypoxia-induced cell death.