RNA N6-methyladenosine methyltransferase METTL3 promotes liver cancer progression through YTHDF2 dependent post-transcriptional silencing of SOCS2

Abstract

Epigenetic alterations immensely contributed to human carcinogenesis. Conventional epigenetic studies predominantly focused on DNA methylation, histone modifications, and chromatin remodeling. Recently, diverse and reversible chemical modifications on RNAs emerge as a new layer of epigenetic regulation. N6-methyladenosine (m6A) is the most abundant chemical modification on eukaryotic mRNA and is important to the regulation of mRNA stability, splicing, and translation. Using transcriptome sequencing, we discovered that METTL3 (methyltransferase like 3), a major RNA N6-adenosine methyltransferase, was significantly up-regulated in human hepatocellular carcinoma (HCC) and multiple solid tumors. Clinically, overexpression of METTL3 was associated with poor prognosis of HCC patients. Functionally, we proved that knockdown of METTL3 drastically reduced HCC cell proliferation, migration and colony formation in vitro. Knockout of METTL3 remarkably suppressed HCC tumorigenicity and lung metastasis in vivo. On the other hand, using CRISPR/dCas9-VP64 activation system, we demonstrated that overexpression of METTL3 significantly promoted HCC growth both in vitro and in vivo. Through transcriptome sequencing, m6A-Seq and m6A MeRIP qRT-PCR, we identified SOCS2 (suppressor of cytokine signaling 2) as a target of METTL3-mediated m6A modification. Knockdown of METTL3 substantially abolished SOCS2 mRNA m6A modification and augmented SOCS2 mRNA expression. We also showed that m6A-mediated SOCS2 mRNA degradation relied on m6A "reader" protein YTHDF2 dependent pathway. In conclusion, we demonstrated that METTL3 was frequently up-regulated in human HCC and contributed to HCC progression. METTL3 repressed SOCS2 expression in HCC via the m6A-YTHDF2 dependent mechanism. Thus, our findings suggested a new dimension of epigenetic alteration in liver carcinogenesis. This article is protected by copyright. All rights reserved.

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