β2-microglobulin has a different regulatory molecular mechanism between ER+ and ER- breast cancer with HER2-

BackgroundPrevious studies have demonstrated that 2-microglobulin (2M) promotes the growth and survival of a variety of cancer cells and has different regulatory effects on the expression of Bcl-2 and HER2 in HER2(-) breast cancer cells. However, 2M-mediated signaling in ER+ and ER- breast cancer with HER2(-) remains unclear.Methods2M expression vector and siRNA were transfected into two types of HER2(-) breast cancer cells, and the possible relevant signaling molecules were subsequently analyzed by real-time PCR and western blotting. These signaling molecules were also analyzed by real-time PCR and immunohistochemistry (IHC) in two types of HER2(-) breast cancer tissues, and the associations between 2M and these signaling molecules were assessed using Spearman's correlation analysis.Results2M silencing downregulated p-SGK1/SGK1 levels and Bcl-2 expression, and 2M overexpression downregulated p-CREB/CREB and significantly upregulated p-SGK1/SGK1 levels and Bcl-2 expression, and both resulting processes did not affect HER2, HIF-1, VEGF, and ERK signaling in ER+ breast cancer cells with HER2(-). 2M silencing upregulated p-CREB/CREB and VEGF protein and significantly downregulated p-ERK/ERK levels, and 2M overexpression downregulated p-CREB/CREB and VEGF, significantly upregulated p-ERK/ERK levels, and both resulting processes did not affect HIF-1 and SGK1 signaling in ER- breast cancer cells with HER2(-). 2M expression was positively correlated with p-CREB, p-SGK1, and Bcl-2 expression and had no correlation with HIF-1, VEGF, and p-ERK1/2, whereas p-SGK1 exhibited a significantly positive correlation with Bcl-2 expression in cancer tissues of patients with luminal A breast cancer, which coincide with the results obtained from the same molecular types of breast cancer cells except CREB signaling. However, 2M expression did not show a significant correlation with HIF-1, p-CREB, VEGF, p-SGK1, p-ERK1/2, and Bcl-2 expression in cancer tissues of patients with basal-like breast cancer, which was discordant with the results obtained from the same molecular types of breast cancer cells.Conclusions2M has a different molecular regulatory mechanism between ER+ and ER- breast cancer with HER2(-), and it may promote tumor survival through the SGK1/Bcl-2 signaling pathway in ER+ breast cancer with HER2(-) and has no regulatory effects on ER- breast cancer with HER2(-).