Original ArticlesSUV39H2 promotes colorectal cancer proliferation and metastasis via tri-methylation of the SLIT1 promoter
Introduction
Colorectal cancer (CRC) strongly contributes to the morbidity and mortality of cancer patients [1]. Genetic abnormalities have been widely studied and shown to promote or drive CRC pathogenesis [[2], [3], [4], [5], [6], [7]]. However, genetic alterations occur at a low frequency and are not sufficient to explain all the mechanisms underlying CRC initiation and progression [8].
Epigenetics describes heritable phenotype changes without DNA sequence alteration [9]. The primary epigenetic mechanisms include histone posttranslational modifications (PTMs), DNA methylation, ATP-dependent nucleosome remodeling and non-coding RNA regulation [9,10]. These mechanisms mediate transcriptional programs by regulating chromatin structure and conferring cell plasticity and selective advantages during environmental stress, exerting significant influences on cellular characteristics [8]. Though it has been widely accepted that epigenetic perturbations are critical for cancer [10], the detailed effects of specific epigenetic regulators in CRC need to be further investigated.
Histone PTMs primarily occur in N-terminal “tails” [11,12], including many modification types at different histone residues [[13], [14], [15], [16], [17]]. PTMs play critical roles in DNA template events, such as transcription, DNA repair, replication, and recombination [12,18], by changing the state of the chromosome or altering the intra- and inter-nucleosome contacts. Many proteins act as readers or effectors and can promote or suppress the expression of certain genes by recognizing and binding to specific chemical modifications of the histone, translating the histone code into useful biological activities [[19], [20], [21], [22]]. A series of histone-modifying enzymes [23,24] act alone or in combination to fine-tune expression based on extracellular stimuli.
Of the PTM types, histone methylation is the most specific and well-characterized modification [12], occurring on the arginine and lysine residuals of histones H3 and H4. In this article, we focused on H3 lysine 9 (H3K9) tri-methylation, a mark for transcriptionally silent chromatin [25,26].
Suppressor of variegation 3–9 homolog 2 (SUV39H2) is the second H3K9 selective histone methyltransferase (HMT) isolated and characterized in murines [27]. SUV39H2 catalyzes H3K9 tri-methylation and inhibits gene expression [25,26,28]. It can also regulate telomere length [29,30] and genome stability and play a critical function in male germ cell and the embryogenesis of mice [31,32]. Moreover, studies have demonstrated that Suv39H2 knockout protects mice from myocardial infarction and nonalcoholic steatohepatitis [33,34]. In addition to important roles in the physiological activities of mice, evidence indicates that SUV39H2 also participates in hepatocellular carcinoma development [35]. However, the functions and mechanisms of SUV39H2 in CRC pathogenesis and progression have not been investigated to date.
In this study, we revealed that high SUV39H2 expression positively predicted poor prognosis of CRC patients. Moreover, SUV39H2 promoted CRC proliferation and metastasis in vitro and in vivo. Mechanistic exploration using gene expression microarrays and chromatin immunoprecipitation (ChIP) analysis demonstrated that SLIT guidance ligand 1 (SLIT1) was a novel downstream target of SUV39H2. Further functional rescue experiments indicated that SUV39H2 promoted CRC progression in a SLIT1-dependent manner.
Section snippets
Cell culture
The 293 T cell line and five human CRC cell lines (HCT-15, SW620, HT-29, DLD1, HCT116) were purchased from American Type Culture Collection (ATCC, Manassas, VA, USA). NCM460 and SW1116, originating from normal and colon cancer mucosal epithelium, respectively, were kindly provided by Professor Xie Dan (Cancer Institute, Sun Yat-sen University). The ATCC-recommended conditions, including a specific medium with 10% fetal bovine serum (FBS, Gibco, Grand Island, NY, USA), penicillin (100 units/ml),
SUV39H2 is frequently upregulated in CRC tissues
Analysis of 43 histone methyltransferases and demethyltransferases in the published gene expression microarray GSE8671, which includes 32 CRC neoplastic tissues and the paired normal tissues, indicated that SUV39H2 was the most highly expressed gene in neoplastic tissues compared with that in normal tissues (Fig. S1A and S1B, P < 0.001). We also conducted real-time PCR (RT-PCR) to verify the result of the microarray analysis in CRC cells lines and paired CRC tissues. The result demonstrated
Discussion
Lysine methylation catalyzed by lysine methyltransferases (KMTs), which primarily include a family of SET-domain containing proteins, has been widely studied and proven to participate in several important cellular events [[46], [47], [48], [49]]. The SUV39 family is a subfamily of KMTs that mediates H3K9 methylation, representing the repressive status of gene expression. SUV39H1 and SUV39H2, the two critical regulators, mediate H3K9 tri-methylation (H3K9me3) distributed in heterochromatin
Conflicts of interest
The authors declare no conflict of interest.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (No. 81771701, 81472252, 81772885). We thank the members of the laboratory for helpful comments on the article.
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These authors contributed equally to this work.