N6-methyladenosine modification of HCMV IE1 transcript promotes the repressive state of viral genome to achieve latent infection.

Abstract

Human cytomegalovirus (HCMV) is a prevalent pathogen that chronically infects the majority of human population. Among the many features that allow such widespread HCMV infection, one is its ability to maintain a transcriptionally dormant immune-evasive state called latency by suppressing its own major immediate early promoter (MIEP) via epigenetic alterations. In this study, we show a mechanism of MIEP regulation in which the major immediate early (MIE) gene product, immediate early 1 (IE1) transcript, downregulates its own promoter activity in an m⁶A modification-dependent manner. We found that the loss of the m⁶A writer, METTL3, in host cells impedes latency establishment in these cells. Through transcriptome-wide m⁶A profiling of latently infected monocytes, we identified that the major immediate early gene product IE1 transcript is m⁶A-modified during latent infection. Using IE1-specific m⁶A-abolished mutants, we found that m⁶A modification of the IE1 transcript was necessary for the efficient repression of MIEP, and these mutant viruses exhibited a significant defect in establishing latency and progressed toward lytic-like infection in the human monocytic cell line (THP-1) and primary CD14+ monocytes. Our findings demonstrate that HCMV exploits the host m⁶A machinery to suppress its own lytic program to establish latency and uncover an unexpected role of immediate early gene messenger RNA (mRNA) in regulating its own expression.