Reversal of human cytomegalovirus major immediate-early enhancer/promoter silencing in quiescently infected cells via the cyclic AMP signaling pathway.
The human cytomegalovirus (HCMV) major immediate-early (MIE) enhancer contains five functional cyclic AMP (cAMP) response elements (CRE). Because the CRE in their native context do not contribute appreciably to MIE enhancer/promoter activity in lytically infected human fibroblasts and NTera2 (NT2)-derived neurons, we postulated that they might have a role in MIE enhancer/promoter reactivation in quiescently infected cells. Here, we show that stimulation of the cAMP signaling pathway by treatment with forskolin (FSK), an adenylyl cyclase activator, greatly alleviates MIE enhancer/promoter silencing in quiescently infected NT2 neuronal precursors. The effect is immediate, independent of de novo protein synthesis, associated with the phosphorylation of ATF-1 serine 63 and CREB serine 133, dependent on protein kinase A (PKA) and the enhancer's CRE, and linked to viral-lytic-cycle advancement. Coupling of FSK treatment with the inhibition of either histone deacetylases or protein synthesis synergistically activates MIE gene expression in a manner suggesting that MIE enhancer/promoter silencing is optimally relieved by an interplay of multiple regulatory mechanisms. In contrast, MIE enhancer/promoter silence is not overcome by stimulation of the gamma interferon (IFN-gamma) signaling pathway, despite the enhancer having two IFN-gamma-activated-site-like elements. We conclude that stimulation of the cAMP/PKA signaling pathway drives CRE-dependent MIE enhancer/promoter activation in quiescently infected cells, thus exposing a potential mode of regulation in HCMV reactivation.
Keller
Michael J
MJ
Department of Internal Medicine, University of Iowa Carver College of Medicine, and Veterans Affairs Medical Center, Iowa City, Iowa 52242, USA.
Wu
Allen W
AW
Andrews
Janet I
JI
McGonagill
Patrick W
PW
Tibesar
Eric E
EE
Meier
Jeffery L
JL
D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism*; D003587:Cytomegalovirus / Q000235:genetics*; D004279:DNA, Viral / Q000235:genetics; D004742:Enhancer Elements, Genetic; D020868:Gene Silencing; D017781:Genes, Immediate-Early; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism; D008957:Models, Genetic; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D012367:RNA, Viral / Q000235:genetics; D012694:Serine / Q000737:chemistry; D015398:Signal Transduction
D004279:DNA, Viral; D012367:RNA, Viral; D012694:Serine; D007371:Interferon-gamma; D000242:Cyclic AMP