Reversal of human cytomegalovirus major immediate-early enhancer/promoter silencing in quiescently infected cells via the cyclic AMP signaling pathway

J Virol. 2007 Jun;81(12):6669-81. doi: 10.1128/JVI.01524-06. Epub 2007 Feb 14.

Abstract

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Cell Line
  • Cyclic AMP / metabolism*
  • Cytomegalovirus / genetics*
  • DNA, Viral / genetics
  • Enhancer Elements, Genetic*
  • Gene Silencing*
  • Genes, Immediate-Early*
  • Humans
  • Interferon-gamma / metabolism
  • Models, Genetic
  • Phosphorylation
  • Promoter Regions, Genetic*
  • RNA, Viral / genetics
  • Serine / chemistry
  • Signal Transduction

Substances

  • DNA, Viral
  • RNA, Viral
  • Serine
  • Interferon-gamma
  • Cyclic AMP