Fig 2: Overexpression of MST1 regulates cell cycle and apoptosis in breast cancer cell lines. Flow cytometry was used to determine the effects of MST1 overexpression on (A) MCF-7 and (B) SKBR3 cell apoptosis. Flow cytometry was used to analyze the cell cycle distribution of MST1-overexpressing (C) MCF-7 and (D) SKBR3 cells. *P<0.05. LV, lentivirus; MST1, mammalian STE20-like protein kinase 1; NC, negative control; PI, propidium iodide.

Fig 3: Overexpression of MST1 regulates the proliferation, migration and apoptosis of BCa cell lines. (A) Transfection efficiency of MCF-7 and SKBR3 cells transfected with LV-MST1 was determined using reverse transcription-quantitative PCR. (B) Cell Counting Kit-8 and (C) EdU incorporation assays (magnification, ×200) were performed to determine the effects of MST1 overexpression on the proliferation of BCa cells. (D) Wound healing assays were conducted to determine the effects of MST1 overexpression on BCa cell migration (magnification, ×100). *P<0.05, **P<0.01. MST1, mammalian STE20-like protein kinase 1; BCa, breast cancer; LV, lentivirus; OD, optical density; NC, negative control; EdU, 5-Ethynyl-2'-deoxyuridine.

Fig 4: Hippo signaling pathway inhibitors reverse the effects of MST1 on breast cancer cells. (A) Reverse transcription-quantitative PCR was performed to analyze the expression levels of MST1 in the LV-MST1 and LV-MST1 + XMU-MP-1 groups of MCF-7 and SKBR3 cell lines. (B) Cell Counting Kit-8 assay was performed to detect the effect of LV-MST1 + XMU-MP-1 on the proliferation of MCF-7 and SKBR3 cell lines. (C) EdU incorporation assays were performed to determine the effects of LV-MST1 + XMU-MP-1 on the intake of EdU in MCF-7 and SKBR3 cell lines (magnification, ×200). (D) Wound healing assay was performed to detect the effects of LV-MST1 + XMU-MP-1 on the migration of MCF-7 and SKBR3 cell lines (magnification, ×100). *P<0.05, **P<0.01 (vs. LV-MST1 in part C). EdU, 5-Ethynyl-2'-deoxyuridine; LV, lentivirus; MST1, mammalian STE20-like protein kinase 1; NC, negative control; OD, optical density.

Fig 5: Potential mechanism through which MST1 was hypothesized to regulate the Hippo signaling pathway in breast cancer cells. Western blotting was used to analyze the protein expression levels of Ki-67, Bcl-2, Bax and intermediates of the Hippo signaling pathway, YAP and LATS1, in (A) MCF-7 and (B) SKBR3 cells following the transfection with LV-MST1 in the presence or absence of XMU-MP-1 treatment. *P<0.05. LATS1, large tumor suppressor kinase 1; LV, lentivirus; MST1, mammalian STE20-like protein kinase 1; YAP, YY1 associated protein 1.