MST2 silencing induces apoptosis and inhibits tumor growth for estrogen receptor alpha-positive MCF-7 breast cancer.

Mammalian sterile 20-like kinase 1/2 (MST1/2) plays an important role in cell growth and apoptosis and functions as a tumor suppressor. Previously, we showed that MST2 overexpression activates Estrogen receptor alpha (ERα) in human breast cancer MCF-7 cells in the absence of a ligand. Here, we examined the role of MST2 in the growth of ER-positive MCF-7 cells. Cell cycle, apoptosis, and mammosphere formation assay method were implemented to detect the biological effects of MST2 ablation on the growth of MCF-7 cells in vitro. The effect of MST2-siRNA on MCF-7 cells tumor growth in vivo was studied in tumor-bearing mouse model. Kaplan-Meier plotter analysis was used to determine the effect of MST2 on overall survival in breast cancer patients. MST2 overexpression increased cell viability marginally. The ablation of MST2 using siRNA dramatically suppressed the viability of the MCF-7 cells, but not ER-negative MDA-MB-231 breast cancer cells. Furthermore, MST2 knockdown increased caspase-dependent apoptosis and led to decreased mammosphere formation. Treatment of MCF-7 tumor-bearing mice with MST2 siRNA significantly inhibited tumor growth. The tumor weight was reduced further when tamoxifen was added. Patients with ER-positive breast cancer with low MST2 expression had better overall survival than did those with high MST2 expression in Kaplan-Meier survival analyses using public datasets. Our results provide new insight into the role of MST2, a key component of the Hippo signaling pathway, in mediating breast cancer progression.