Abstract
Polycomb group protein enhancer of zeste homolog 2 (EZH2) is a methyltransferase that correlates with the regulation of invasion and metastasis and is overexpressed in human cancers such as colorectal cancer. MicroRNA-31 (miR-31) plays an oncogenic role and is associated with BRAF mutation and poor prognosis in colorectal cancer. EZH2 is functionally considered to suppress miR-31 expression in human cancers; however, no study has reported its relationship with colon cancer. We therefore evaluated EZH2 expression using immunohistochemistry and assessed miR-31 and epigenetic alterations using 301 colorectal carcinomas and 207 premalignant lesions. Functional analysis was performed to identify the association between EZH2 and miR-31 using cancer cell lines. In the current study, negative, weak, moderate, and strong EZH2 expressions were observed in 15%, 19%, 25%, and 41% of colorectal cancers, respectively. EZH2 was inversely associated with miR-31 (P < 0.0001), independent of clinicopathological and molecular features. In a multivariate stage-stratified analysis, high EZH2 expression was related to favorable prognosis (P = 0.0022). Regarding premalignant lesions, negative EZH2 expression was frequently detected in sessile serrated adenomas/polyps (SSA/Ps) (76%; P < 0.0001) compared with hyperplastic polyps, traditional serrated adenomas, and non-serrated adenomas (25–36%). Functional analysis demonstrated that the knockdown of EZH2 increased miR-31 expression. In conclusion, an inverse association was identified between EZH2 and miR-31 in colorectal cancers. Our data also showed that upregulation of EZH2 expression may be rare in SSA/Ps. These results suggest that EZH2 suppresses miR-31 in colorectal cancer and may correlate with differentiation and evolution of serrated pathway.
Highlights
In a database comprising 301 patients with colorectal cancer, high enhancer of zeste homolog 2 (EZH2) expression was inversely associated with miR-31 expression, independent of clinicopathological and molecular features
Negative EZH2 expression was higher in sessile serrated adenoma/polyp (SSA/P) than in hyperplastic polyp (HP), traditional serrated adenoma (TSA) or non-serrated adenomas
We showed that the small interfering RNA (siRNA) knockdown of EZH2 increased miR-31 expression in colon cancer cell lines
Summary
A polycomb group protein, enhancer of zeste homolog 2 (EZH2), is a methyltransferase and the core catalytic element of polycomb repressive complex 2 (PRC2), which plays a critical role in the regulation of cancer initiation, progression, invasion, metastasis, and drug resistance [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19]. Various oncogenic transcription factors and cancer-associated non-coding RNAs regulate EZH2 expression [1,2,3,4, 6, 9, 10, 16, 17, 20, 21]. Increased EZH2 activity induces the genomewide histone H3 lysine 27 trimethylation (H3K27me3) and may act as an oncogene via the repression of tumor suppressor genes in human cancers [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16, 20, 22,23,24]. Associations have been reported between EZH2 overexpression and poor prognosis in esophageal [15], gastric [25], pancreatic [26], and bile duct cancers [4]. We performed functional analyses to identify whether EZH2 suppressed miR-31 expression in colorectal cancers
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