Alternative Promoters Drive Human Cytomegalovirus Reactivation from Latency

Abstract

Reactivation from latency requires reinitiation of viral gene expression and culminates in the production of infectious progeny. The major immediate early promoter (MIEP) of human cytomegalovirus (HCMV) drives the expression of crucial lytic cycle transactivators but is silenced during latency in hematopoietic progenitor cells (HPCs). Because the MIEP is poorly active in HPCs, it is unclear how viral transactivators are expressed during reactivation. We demonstrate that transcripts originating from alternative promoters within the canonical major immediate early locus are abundantly expressed upon reactivation, whereas MIEP-derived transcripts remain undetectable. Further, we show that these promoters are necessary for efficient reactivation in primary CD34+ HPCs. Our findings change the paradigm for HCMV reactivation by demonstrating that promoter switching governs reactivation from viral latency in a context-specific manner.

Activator protein-1 transactivation of the major immediate early locus is a determinant of cytomegalovirus reactivation from latency

“…4B) transcription. These findings are consistent with previous findings using the THP-1 culture system (16). However, AP-1 mut p -infected Kasumi-3 cells displayed impaired MIEP-, iP2-, and dP-derived transcripts compared to cultures infected with either WT or AP-1 rep (Fig.…”

“…While these alternative transcripts differ in their 5’UTR, each encodes full-length IE1 or IE2 protein (15). More recently, Collins-McMillen et al found two of these alternative transcripts derived from promoters within intron A, iP1 and iP2, are important for reactivation from latency (16). However, the contribution of transcription factor binding on the activity of these alternative promoters during reactivation is unknown.…”

“…Recently published findings from Collins-McMillen, et al detailed the requirement for iP1- and iP2-derived transcripts for viral reactivation (16). Our findings build upon these observations and begin to unravel the likely complex web of transcription factors that regulate the iP1 and iP2 promoters.…”

“…Interestingly, recent work from Collins-McMillen, et al demonstrated iP2-derived transcripts are the most abundant during both latency and reactivation. Furthermore, transactivation of both iP1 and iP2 are required for efficient viral reactivation in primary CD34 + hematopoietic progenitor cells (HPCs) (16), though the regulation of these newly identified promoters remains unknown. These findings highlight the complexity of the transcriptional control of the MIE locus.…”

FOXO Transcription Factors Activate Alternative Major Immediate Early Promoters to Induce Human Cytomegalovirus Reactivation

“…However we recently discovered two alternative promoters (iP1 and iP2, together referred to as intronic promoters) within the first intron of the canonical major immediate early locus(9). Rather than inducing MIEP activity, HCMV reactivation stimuli instead induce transcription from the iP1 and iP2 promoters, which correlates with the increase in IE1 and IE2 mRNA levels(10). Deletion of the intronic promoters significantly attenuates the production of infectious virus after reactivation, revealing that the iP1 and iP2 promoters play critical roles in IE1 and IE2 re-expression and HCMV reactivation.…”