[PMC free article] [PubMed] [Google Scholar] 19

[PMC free article] [PubMed] [Google Scholar] 19. was greatly reduced in YAP1shRNA1 cells compared with vector control cells (N.S.shRNA) (Figure ?(Figure2A2A and ?and2B).2B). Furthermore, YAP1 downregulation reduced the expression of CTGF, a well-characterized YAP-targeted gene, at the protein and mRNA level (Figure ?(Figure2A2A and ?and2C).2C). The impact of YAP1 silencing on cell proliferation was also assessed. As shown in Figure ?Figure2D,2D, YAP1 knockdown significantly Mifepristone (Mifeprex) reduced cell proliferation compared with the N.S.shRNA cells at 48 ( 0.0001) and 72 hours ( 0.05). Open in a separate window Figure 2 Genetic inhibition of YAP1 impairs cell proliferationMDA-MB-231 cells stably expressing a short hairpin RNA against YAP1 (YAP1shRNA1) were subjected to (A) immunoblot graph shows the intensity of the bands normalized to the N.S.shRNA lane] and (B-C) qRT-PCR analysis to evaluate protein and mRNA levels of YAP1 and its molecular target, CTGF. (D) Cell proliferation in N.S.shRNA and YAP1shRNA cells was evaluated at the indicated time points. Values shown are the means + SE (standard error) of three independent experiments. * 0.05, ** 0.001, *** 0.0001, n.s. = not significant. We also determined the influence of YAP1 inhibition on MDA-MB-231 cell migration by performing wound healing and transwell migration assays. YAP1 knockdown significantly ( 0.05) impaired the wound healing capacity, as well as transwell migration (Figure 3AC3C) in MDA-MB-231 cells. A decrease in migration could be a reflection of reversion from mesenchymal state to epithelial state following YAP1 downregulation. YAP1 downregulation resulted in the conversion of cells from a mesenchymal to an epithelial-like morphology with a cobblestone-like appearance, suggesting a potential reversion to an epithelial state (data not shown). Expression of Slug and ERK, critical regulators of cell migration and invasion in TNBC cells showed a marked decrease upon YAP1 downregulation (Figure ?(Figure3D)3D) [33, 34]. Although no obvious difference in vimentin levels was detected, reduction in the expression levels of pERK1/2 and Slug could partly explain the impaired migration upon YAP1 downregulation. However, while Slug expression is crucial for the repression of E-cadherin, we did not observe any recovery in the expression of E-cadherin following YAP1 downregulation (data not shown) [35]. This could be because the E-cadherin promoter is hypermethylated in MDA-MB-231 cells, and de-repression of the E-cadherin promoter could require participation of factors not regulated by YAP1 [36]. Altogether our results show that YAP1 inhibition in TNBC cells results in reduced cell proliferation and migration with potential transition from a mesenchymal to an epithelial state. Open in a separate window Figure 3 YAP1 silencing impairs MDA-MB-231 cell migrationYAP1shRNA1 or N.S.shRNA cells were (A) evaluated at 0, and 24 h, for wound healing (B, C) migration ability via Matrigel-based transwell assay, and (D) immunoblot analysis of vimentin, Slug, and ERK. Data represent the average of three independent experiments. Error bars represent SEM (standard Mifepristone (Mifeprex) error of the mean). * 0.05. Inhibition of YAP1 radiosensitizes TNBC cells Studies have shown that YAP1 plays a role in radioresistance [30, 31]. We investigated the effect of YAP1 silencing using shRNA and siRNA on the radiosensitivity of TNBC cell lines (MDA-MB-231, MDA-MB-468, and SUM159PT) Sav1 by assessing their clonogenic potential. MDA-MB-231-YAP1shRNA1 cells were significantly more sensitive to the cytotoxic effects of radiation than N.S.shRNA cells (Figure ?(Figure4A,4A, 0.05). The degree of radiosensitization was quantified from the survival Mifepristone (Mifeprex) curves by comparing the surviving fractions at the radiation dose of 2 Gy (SF2) and by calculating the dose enhancement factor (DEF), i.e. the ratio of radiation doses to achieve a given survival level. Significant differences in survival between.