N6-Methyladenosine in Flaviviridae Viral RNA Genomes Regulates Infection

Nandan S. Gokhale, Alexa B.R. McIntyre, Michael J. McFadden, Allison E. Roder, Edward M. Kennedy, Jorge A. Gandara, Sharon E. Hopcraft, Kendra M. Quicke, Christine Vazquez, Jason Willer, Olga R. Ilkayeva, Brittany A. Law, Christopher L. Holley, Mariano A. Garcia-Blanco, Matthew J. Evans, Mehul S. Suthar, Shelton S. Bradrick, Christopher E. Mason, and Stacy M. Horner

Cell host & microbe 20, 654–665 November 9, 2016

Speaker: Po-Chun Chang (張博淳)                      Time: 14:00~15:00 Mar. 29, 2017

Commentator: Dr. Yao Chang (張堯 老師)         Place: Room 601

Abstract:

N6-methyladenosine (m⁶A), one of internal chemical modification of mRNA, involves in many biological processes. Methyltransferases like methyltransferase-like (METTL) enzyme METTL3 and METTL14 mediate addition of m⁶A at the consensus motif DRA^mCH (where D = G/A/U, R = G > A, and H = U/C/A). Demethylases like fat mass and obesity-associated protein (FTO) remove it and m⁶A binding proteins like YTH-domain family (YTHDF) mediate m⁶A function. They function like a writer, eraser and reader. Although m⁶A is already been known contribute to many cellular functions in eukaryotic cells, information of microbial infection is still few. Previous studies have shown that viruses with nuclear replication, such as influenza A virus and adenovirus, present m⁶A in their transcriptional RNA.A recent study reported by team of authors further found that m⁶A serves as a positive regulator of HIV-1.¹ However, whether m⁶A also involves in life cycle of viruses that replicate exclusively in cytoplasm has not been investigated. According to above, in this study authors used HCV, a virus belong to Flaviviridae, to explore association between m⁶A and virus that replicate in cytoplasm. First, authors used siMETTL, siFTO and siYTHDF Huh7 cells to reveal that m⁶A machinery regulates HCV particle production but not translation or RNA replication. They further demonstrated that YTHDF protein is able to bind to HCV RNA and relocalize to lipid droplets during HCV infection. Interestingly, although HCV replicates in cytoplasm, they found that its RNA contains m⁶A during infection. Methyl-RIP followed by sequencing (MeRIP-seq) let them to map the sites of the HCV RNA genome modified by m⁶A. Overlap with YTHDF-binding sites on the viral genome, they identified one region within the viral E1 gene which contains m⁶A and is bound by YTHDF proteins at sites with consensus DRAmCH motifs. They further mapped the location of m⁶A on the RNA genomes of other members of the Flaviviridae family. In this study, they studied the role of m⁶A in Flaviviridae viruses and uncovered potential regulatory strategies to inhibit viral replication.

References:

1     Kennedy, E. M. et al. Posttranscriptional m(6)A Editing of HIV-1 mRNAs Enhances Viral Gene Expression. Cell host & microbe 19, 675-685, 2016.04.002 (2016).