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.

The effects of bisphenol A, benzyl butyl phthalate, and di(2-ethylhexyl) phthalate on estrogen receptor alpha in estrogen receptor-positive cells under hypoxia.

Endocrine-disrupting chemicals (EDCs) are widely used in various consumer goods. Consequently, humans are constantly exposed to EDCs, which is associated with a variety of endocrine-related diseases. In this study, we demonstrated the effects of bisphenol A (BPA), benzyl butyl phthalate (BBP), and di(2-ethylhexyl) phthalate (DEHP) on estrogen receptor alpha (ERα) expression under normoxia and hypoxia. First, we confirmed the effects of EDCs on ER activity using OECD Test Guideline 455. Compared to the 100% activity induced by 1 nM 17-ß-estradiol (positive control), BPA and BBP exhibited 50% ERα activation at concentrations of 1.31 µM and 4.8 µM, respectively. In contrast, and consistent with previous reports, DEHP did not activate ERα. ERα is activated and degraded by hypoxia in breast cancer cells. BPA, BBP, and DEHP enhanced ERα-mediated transcriptional activity under hypoxia. All three EDCs decreased ERα protein levels under hypoxia in MCF-7 cells. The transcriptional activity of hypoxia-inducible factor-1 was decreased and secretion of vascular endothelial growth factor (VEGF) was increased by BPA and BBP under hypoxia in MCF-7 cells, but not by DEHP. All three EDCs decreased the ERα protein expression level in Ishikawa human endometrial adenocarcinoma cells, and DEHP caused a weak decrease in VEGF secretion under hypoxia. These results demonstrate down-regulation of ERα by EDCs may influence the pathological state associated with hypoxia.