Overexpression of MYC and EZH2 cooperates to epigenetically silence MST1 expression

Abstract

Hippo-like MST1 protein kinase regulates cell growth, organ size, and carcinogenesis. Reduction or loss of MST1 expression is implicated in poor cancer prognosis. However, the mechanism leading to MST1 silencing remains elusive. Here, we report that both MYC and EZH2 function as potent suppressors of MST1 expression in human prostate cancer cells. We demonstrated that concurrent overexpression of MYC and EZH2 correlated with the reduction or loss of MST1 expression, as shown by RT-qPCR and immunoblotting. Methylation sensitive PCR and bisulfite genomic DNA sequencing showed that DNA methylation caused MST1 silencing. Pharmacologic and RNAi experiments revealed that MYC and EZH2 silenced MST1 expression by inhibiting its promoter activity, and that EZH2 was a mediator of the MYC-induced silencing of MST1. In addition, MYC contributed to MST1 silencing by partly inhibiting the expression of microRNA-26a/b, a negative regulator of EZH2. As shown by ChIP assays, EZH2-induced DNA methylation and H3K27me3 modification, which was accompanied by a reduced H3K4me3 mark and RNA polymerase II occupancy on the MST1 promoter CpG region, were the underlying cause of MST1 silencing. Moreover, potent pharmacologic inhibitors of MYC or EZH2 suppressed prostate cancer cell growth in vitro, and the knockdown of MST1 caused cells' resistance to MYC and EZH2 inhibitor-induced growth retardation. These findings indicate that MYC, in concert with EZH2, epigenetically attenuates MST1 expression and suggest that the loss of MST1/Hippo functions is critical for the MYC or EZH2 mediation of cancer cell survival.

YAP1 and AR interactions contribute to the switch from androgen-dependent to castration-resistant growth in prostate cancer

“…Previously, we reported that C4-2 cells express significantly lower levels of MST1 than LNCaP cells 48 . Results from this report and the above findings suggest that MST1 is a potent negative regulator of the YAP1–AR interaction.…”

“…Here we showed that androgen increased YAP1 nuclear localization and YAP1–AR interactions in CS LNCaP cells. Nevertheless, these molecular events cannot be reversed by androgen depletion in CR C4-2 cells, which express about 40–50% less MST1 than LNCaP 48 . Our laboratory previously reported that reduction or loss of MST1 might play a prominent role in PC progression 48,52 .…”

“…Nevertheless, these molecular events cannot be reversed by androgen depletion in CR C4-2 cells, which express about 40–50% less MST1 than LNCaP 48 . Our laboratory previously reported that reduction or loss of MST1 might play a prominent role in PC progression 48,52 . Herein, we showed that loss of MST1 functions strongly correlated with increases in AI interactions of YAP1 and AR proteins in CRPC cells and that knockdown of MST1 in CS LNCaP cells promoted androgen-dependent and AI YAP1–AR interactions (Fig.…”

Notable roles of EZH2 and DNMT1 in epigenetic dormancy of the SHP1 gene during the progression of chronic myeloid leukaemia

“…For example, it was reported that MYC and EZH2 function as potent suppressors of levels of macrophage stimulating 1 (MST1) expression in human prostate cancer cells Pharmacological and RNAi experiments revealed that MYC and EZH2 inhibit the promoter activity of MST1 and thus silence expression, and that EZH2 is a mediator of the MYC-induced silencing of MST1 (21).…”

Epigenetics Territory and Cancer

“…hSNF5, a core subunit of SWI/SNF induces demethylation of p16 INK4A to promote transcriptional activation. Overexpression of EZH2, like MYC shortens the G 1 phase of the cell cycle, results in accumulation of cells in the S phase of the cell cycle, and confers a proliferative advantage by suppression of Macrophage Stimulating 1 (MST1) (Kuser-Abali et al 2014). Induction of hSNF5 causes removal of DNMT3b from the p16 INK4A promoter that can explain alterations of methylation in this region .…”