The role of N6-methyladenosine in translational control of the immune response

• Applicant: Dr. Jan Mauer
• Subject Area: Immunology ; Biochemistry ; Cell Biology
• Term: from 2015 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 280429966

• Final Report Year: 2019

Final Report Abstract

Internal bases in RNA can be subjected to modifications that influence the fate of transcripts in cells. One of the most prevalent modified bases is found at the 5′ end of RNA, at the first encoded nucleotide adjacent to the N7-methylguanosine cap. I showed that this nucleotide, N6,2′-O-dimethyladenosine (m6Am), is a reversible modification that influences cellular RNA fate and function. The first part of my project was focused on investigating m6Am in mRNA. Using a transcriptome-wide map of m6Am I found that m6Am-initiated mRNAs are markedly more stable and more efficiently translated than mRNAs that begin with other nucleotides. Moreover, I found that m6Am is selectively demethylated by fat mass and obesity-associated protein (FTO). FTO preferentially demethylates m6Am rather than its previously assigned target N6- methyladenosine (m6A) and reduces the stability of m6Am mRNAs. Together, my findings show that the cap-associated modified nucleotide m6Am is a dynamic and reversible epitranscriptomic modification. In the second part of my project, I discovered that small nuclear RNAs (snRNAs), which are core components of the pre-mRNA splicing machinery, carry an FTO-regulated m6Am residue as their starting nucleotide. In contrast to the high stoichiometry m6Am in mRNAs, snRNA m6Am is only detected in FTO deficient cells. I found that snRNA biogenesis involves the formation of an initial m1-isoform with a single-methylated adenosine (2′-O-methyladenosine, Am), which is then converted to a dimethylated m2-isoform (m6Am). The relative m1- and m2- isoform levels are determined by the RNA demethylase FTO, which selectively demethylates the m2-isoform. Furthermore, I demonstrated that FTO is inhibited by the oncometabolite 2-hydroxyglutarate, resulting in increased m2-snRNA levels. Cells that exhibit high m2-snRNA levels show altered patterns of alternative splicing. Together, these data reveal that FTO controls a previously unknown central step of snRNA processing involving reversible methylation. To summarize, my work suggests that reversible epitranscriptomic information is stored in the extended 5’ cap of mRNAs and snRNAs. These findings have wide-spread implications for our understanding of RNA metabolism and represent a potential bridge between aberrant splicing and cancer development.

Publications

• Reversible methylation of m6Am in the 5' cap controls mRNA stability. Nature, 2017
  Mauer J, Luo X, Blanjoie A, Jiao X, Grozhik AV, Patil DP, Linder B, Pickering BF, Vasseur JJ, Chen Q, Gross SS, Elemento O, Debart F, Kiledjian M, Jaffrey SR
  
• FTO, m6Am, and the hypothesis of reversible epitranscriptomic mRNA modifications. Review, FEBS Lett. 2018
  Mauer J, Jaffrey SR
  
• FTO controls reversible m6Am RNA methylation during snRNA biogenesis. Nat Chem Biol. 2019
  Mauer J, Sindelar M, Despic V, Guez T, Hawley BR, Vasseur JJ, Rentmeister A, Gross SS, Pellizzoni L, Debart F, Goodarzi H, Jaffrey SR