Abstract
BackgroundBreast cancer (BC) displays striking genetic, epigenetic and phenotypic diversity. N6-methyladenosine (m6A) in mRNA has emerged as a crucial epitranscriptomic modification that controls cancer self-renewal and cell fate. However, the key enzymes of m6A expression and function in human breast carcinogenesis remain unclear.MethodsThe expression of m6A methylases (METTL3, METTL14 and WTAP) and demethylases (FTO and ALKBH5) were analyzed by using ONCOMINE and The Cancer Genome Atlas databases and in 36 pairs of BC and adjacent non-cancerous tissue. The level of m6A in BC patients was detected by ELISA, and the function of m6A was analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, colony formation assay and transwell assay. The database of bc-GenExMiner v4.0, Kaplan-Meier Plotter and cBioPortal were queried for correlation, mutation and prognosis analysis of BC.ResultsThe m6A methylases and demethylases were dysregulated in several major malignant tumors. Specifically, the expression of all m6A methylases was reduced in BC as compared with normal controls, but the demethylase ALKBH5 was induced in ONCOMINE databases and confirmed in clinical patients. METTL14 expression was positively correlated with METTL3 expression, and both showed high expression in normal breast-like and luminal-A and -B BC. Functionally, reducing m6A expression by overexpressing METTL14 and/or knockdown of ALKBH5 could inhibit breast cell viability, colony formation and cell migration. Furthermore, Kaplan-Meier, meta-analysis and univariate Cox assay showed that the expression of m6A members including METTL3, METTL14, WTAP and FTO but not their gene mutation and amplification, was tightly associated with cancer progression and poor survival.ConclusionsChanges of m6A modulators reduced m6A may promote tumorigenesis and predict poor prognosis in BC.
Highlights
Breast cancer (BC) displays striking genetic, epigenetic and phenotypic diversity
Reduced m6A level and methylase expression in BC ONCOMINE database analysis revealed that m6A enzymes were distinctively dysregulated in several major malignant tumors
The above results were verified in our clinical BC patients: with 77.87, 80.19, 69.04 and 81.49% reduction of mRNA expression of methyltransferase-like 3 (METTL3), Methyltransferase-like 14 (METTL14), Wilms tumor 1-associated protein (WTAP) and fat-mass– and obesity-associated protein (FTO) and 1.71-fold induction of AlkB family member 5 (ALKBH5) mRNA expression in tumor tissue as compared with non-tumor tissue (Fig. 2a-e)
Summary
Breast cancer (BC) displays striking genetic, epigenetic and phenotypic diversity. N6-methyladenosine (m6A) in mRNA has emerged as a crucial epitranscriptomic modification that controls cancer self-renewal and cell fate. The key enzymes of m6A expression and function in human breast carcinogenesis remain unclear. A new concept of the “epitranscriptome” was introduced as a result of transcriptome-wide mapping of N6-methyladenosine (m6A), involved in a diverse set of mRNA transcription, splicing, nuclear export, localization, translation, and stability functions [1]. Writers are methyltransferase-like 3 (METTL3), METTL14 and Wilms tumor 1-associated protein (WTAP). METTL14, together with METTL3, forms a stable heterodimer of methyltransferase complex that mediates cellular m6A deposition on mammalian mRNAs. Knockdown of METTL3 or METTL14 substantially decreases m6A mRNA levels [2].
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