β2-microglobulin induced apoptosis of tumor cells via the ERK signaling pathway by directly interacting with HFE in HER2-overexpressing breast cancer

BackgroundOur previous study demonstrated that beta 2-microglobulin (beta 2M) promoted ER+/HER2- breast cancer survival via the SGK1/Bcl-2 signaling pathway. However, the role of beta 2M has not been investigated in ER-/HER2+ breast cancer. Here, we aimed to determine the role of beta 2M in ER-/HER2+ breast cancer.MethodsThe interaction between beta 2M and HFE was confirmed by co-immunoprecipitation, mass spectrometry, yeast two-hybrid screening, and His pull-down. The knockdown and overexpression of beta 2M or HFE were performed in MDA-MB-453 cells, and ERK signaling pathway was subsequently analyzed via western blotting. Apoptotic cells were detected using flow cytometer. beta 2M, HFE, and p-ERK1/2 were examined in tumor and paired adjacent tissues via immunohistochemistry.ResultsHFE was found to be an interacting protein of beta 2M in ER-/HER2+ breast cancer cells MDA-MB-453 by co-immunoprecipitation and mass spectrometry. A yeast two-hybrid system and His-pull down experiments verified that beta 2M directly interacted with HFE. beta 2M and HFE as a complex were mainly located in the cytoplasm, with some on the cytomembrane of MDA-MB-453 cells. In addition to breast cancer cells BT474, endogenous beta 2M directly interacted with HFE in breast cancer cells MDA-MB-453, MDA-MB-231, and MCF-7. beta 2M activated the ERK signaling pathway by interacting with HFE and induced apoptosis of MDA-MB-453 cells. The expression of HFE and p-ERK1/2 showed significantly high levels in HER2-overexpressing breast cancer tumor tissue compared with adjacent normal tissue, consistent with the results obtained from the cell experiments.Conclusions beta 2M induced apoptosis of tumor cells via activation of the ERK signal pathway by directly interacting with HFE in HER2-overexpressing breast cancer.