820 m6A mRNA demethylase FTO regulates tumorigenicity and response to anti-PD-1 immunotherapy in melanoma

Abstract

Analogous to epigenetic regulation of gene expression through the reversible DNA and histone modifications, post-transcriptional N6-methyladenosine (m6A) methylation of adenosine residues in mRNA as well as lncRNA provides an additional layer of regulation that may alter mRNA metabolism and gene expression. Recently, m6A RNA methylation research was revived by the discovery of the fat mass- and obesity-associated protein (FTO) as the first RNA demethylase, implying that m6A RNA methylation is a reversible and dynamic modification and may have critical biological functions. However the role of FTO in melanoma tumorigenicity remains unknown. Here we show that N6-methyladenosine (m6A) mRNA demethylation by FTO promotes melanoma growth and inhibits response to anti-PD-1 blockade therapy and cell killing induced by interferon gamma (IFNg). FTO is up-regulated in human melanoma, suggesting an oncogenic role of FTO in melanoma. FTO knockdown inhibited melanoma cell proliferation, migration, and invasion in vitro, which is reversed by knockdown of the m6A methyltransferases METTL3 and METTL14. FTO knockdown inhibited melanoma tumor growth in vivoin both xenograft and syngeneic melanoma mouse models. FTO is up-regulated by metabolic stress through the autophagy/NF-kB pathway. m6A immunoprecipitation sequencing (m6A-seq) and RNA-seq analyses showed that FTO knockdown increases m6A modifications in the critical melanoma-promoting genes including PDCD1, CXCR4 and SOX10, leading to increased RNA decay through the m6A reader YTHDF2. Our findings demonstrate a key role of FTO as a RNA demethylase in promoting melanoma growth, and suggest that the combination of FTO inhibition with targeted therapy or immunotherapies may improve therapeutic response.