Regulation of tumor angiogenesis by EZH2

Epigenetic regulation of cardiovascular differentiation

Epigenetic control mechanisms play a key role in the regulation of embryonic development and tissue homeostasis and modulate cardiovascular diseases. Increasing evidence suggests that lineage commitment of stem/progenitor cells is tightly regulated by epigenetic mechanisms. These epigenetic control mechanisms include DNA and histone modifications, which modulate the chromatin structure thereby regulating access of transcription factors. Particularly, the modification of histone acetylation and methylation, which is controlled by families of histone acetylases/deacetylases and methyltransferases/demethylases, respectively, controls stem cell maintenance, differentiation, and function. This review article summarizes our current understanding of epigenetic mechanisms regulating the differentiation of cardiovascular cells, specifically endothelial cells and cardiac muscle lineages. In particular, the article will focus on the enzymes which modify histones and are involved in chromatin remodelling.

Down-regulation of miR-101 in endothelial cells promotes blood vessel formation through reduced repression of EZH2

Angiogenesis is a balanced process controlled by pro- and anti-angiogenic molecules of which the regulation is not fully understood. Besides classical gene regulation, miRNAs have emerged as post-transcriptional regulators of angiogenesis. Furthermore, epigenetic changes caused by histone-modifying enzymes were shown to modulate angiogenesis as well. However, a possible interplay between miRNAs and histone-modulating enzymes during angiogenesis has not been described. Here we show that VEGF-mediated down-regulation of miR-101 caused pro-angiogenic effects. We found that the pro-angiogenic effects are partly mediated through reduced repression by miR-101 of the histone-methyltransferase EZH2, a member of the Polycomb group family, thereby increasing methylation of histone H3 at lysine 27 and transcriptome alterations. In vitro, the sprouting and migratory properties of primary endothelial cell cultures were reduced by inhibiting EZH2 through up-regulation of miR-101, siRNA-mediated knockdown of EZH2, or treatment with 3-Deazaneplanocin-A (DZNep), a small molecule inhibitor of EZH2 methyltransferase activity. In addition, we found that systemic DZNep administration reduced the number of blood vessels in a subcutaneous glioblastoma mouse model, without showing adverse toxicities. Altogether, by identifying a pro-angiogenic VEGF/miR-101/EZH2 axis in endothelial cells we provide evidence for a functional link between growth factor-mediated signaling, post-transcriptional silencing, and histone-methylation in the angiogenesis process. Inhibition of EZH2 may prove therapeutic in diseases in which aberrant vascularization plays a role.

RNA interference in the clinic: challenges and future directions

Inherent difficulties with blocking many desirable targets using conventional approaches have prompted many to consider using RNA interference (RNAi) as a therapeutic approach. Although exploitation of RNAi has immense potential as a cancer therapeutic, many physiological obstacles stand in the way of successful and efficient delivery. This Review explores current challenges to the development of synthetic RNAi-based therapies and considers new approaches to circumvent biological barriers, to avoid intolerable side effects and to achieve controlled and sustained release.

Roles of intrinsic angiogenesis inhibitor, vasohibin, in cervical carcinomas

The aim of the present study is to clarify the critical roles of vasohibin in cervical carcinomas. We investigated the expression ratios of vasohibin and vascular endothelial growth factor (VEGF) receptor-2 on endothelium and microvessel density, lymphatic vessel density (LVD) by immunohistochemistry. Sixty-one squamous cell carcinoma (SCC), 18 mucinous adenocarcinoma (Adenocarcinoma), 38 carcinoma in situ (CIS), and 35 normal cervical epithelium were collected. We investigated the expression of vasohibin and compared it with the expression of VEGF receptor-2 (VEGFR-2, KDR/flk-1), and CD34 in the stromal endothelium. Expression of VEGF was counted using the histological score (H score). D2-40 was used as a marker for lymphatic endothelial cells to investigate LVD. The microvessel density of the normal cervical epithelium was significantly lower than that of CIS, SCC, and Adenocarcinoma (P < 0.05). The expression ratio of vasohibin in the normal cervical epithelium was significantly lower than that of SCC and Adenocarcinoma (P < 0.05). The expression ratio of VEGFR-2 of the normal cervical epithelium was significantly lower than that of SCC and Adenocarcinoma (P < 0.05). The LVD of the normal cervical epithelium was significantly lower than that of CIS, SCC, and Adenocarcinoma (P < 0.05). For normal cervical epithelium, CIS, and SCC, there was a moderate correlation between the expression percentage of vasohibin and the expression percentage of VEGFR-2 (P < 0.05, r(2) = 0.3018). This is the first study to elucidate the correlation between the expression of vasohibin in the stromal endothelial cells and the expression of VEGFR-2 in human cervical carcinomas.

Enhancer of zeste homolog 2 promotes the proliferation and invasion of epithelial ovarian cancer cells

Enhancer of zeste homolog 2 (EZH2) is the catalytic subunit of the polycomb repressive complex 2 (PRC2) that includes noncatalytic subunits suppressor of zeste 12 (SUZ12) and embryonic ectoderm development (EED). When present in PRC2, EZH2 catalyzes trimethylation on lysine 27 residue of histone H3 (H3K27Me3), resulting in epigenetic silencing of gene expression. Here, we investigated the expression and function of EZH2 in epithelial ovarian cancer (EOC). When compared with primary human ovarian surface epithelial (pHOSE) cells, EZH2, SUZ12, and EED were expressed at higher levels in all 8 human EOC cell lines tested. Consistently, H3K27Me3 was also overexpressed in human EOC cell lines compared with pHOSE cells. EZH2 was significantly overexpressed in primary human EOCs (n = 134) when compared with normal ovarian surface epithelium (n = 46; P < 0.001). EZH2 expression positively correlated with expression of Ki67 (P < 0.001; a marker of cell proliferation) and tumor grade (P = 0.034) but not tumor stage (P = 0.908) in EOC. There was no correlation of EZH2 expression with overall (P = 0.3) or disease-free survival (P = 0.2) in high-grade serous histotype EOC patients (n = 98). Knockdown of EZH2 expression reduced the level of H3K27Me3 and suppressed the growth of human EOC cells both in vitro and in vivo in xenograft models. EZH2 knockdown induced apoptosis of human EOC cells. Finally, we showed that EZH2 knockdown suppressed the invasion of human EOC cells. Together, these data demonstrate that EZH2 is frequently overexpressed in human EOC cells and its overexpression promotes the proliferation and invasion of human EOC cells, suggesting that EZH2 is a potential target for developing EOC therapeutics.