Inactivating a Cellular Intrinsic Immune Defense Mediated by Daxx Is the Mechanism through Which the Human Cytomegalovirus pp71 Protein Stimulates Viral Immediate-Early Gene Expression

ABSTRACT Human cytomegalovirus (HCMV) masterfully evades adaptive and innate immune responses, allowing infection to be maintained and periodically reactivated for the life of the host. Here we show that cells also possess an intrinsic immune defense against HCMV that is disarmed by the virus. In HCMV-infected cells, the promyelocytic leukemia nuclear body (PML-NB) protein Daxx silences viral immediate-early gene expression through the action of a histone deacetylase. However, this antiviral tactic is efficiently neutralized by the viral pp71 protein, which is incorporated into virions, delivered to cells upon infection, and mediates the proteasomal degradation of Daxx. This work demonstrates the mechanism through which pp71 activates viral immediate-early gene expression in HCMV-infected cells. Furthermore, it provides insight into how a PML-NB protein institutes an intrinsic immune defense against a DNA virus and how HCMV pp71 inactivates this defense.

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Faculty Opinions recommendation of Inactivating a cellular intrinsic immune defense mediated by Daxx is the mechanism through which the human cytomegalovirus pp71 protein stimulates viral immediate-early gene expression.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1032371.373046 ◽

2006 ◽

Author(s):

Jim Smiley

Keyword(s):

Gene Expression ◽

Human Cytomegalovirus ◽

Immediate Early Gene ◽

Immune Defense ◽

Early Gene ◽

Immediate Early ◽

Early Gene Expression

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Repression of human cytomegalovirus major immediate early gene expression in a monocytic cell line

Journal of General Virology ◽

10.1099/0022-1317-73-2-433 ◽

1992 ◽

Vol 73 (2) ◽

pp. 433-435 ◽

Cited By ~ 60

Author(s):

J. H. Sinclair ◽

J. Baillie ◽

L. A. Bryant ◽

J. A. Taylor-Wiedeman ◽

J. G. P. Sissons

Keyword(s):

Gene Expression ◽

Cell Line ◽

Human Cytomegalovirus ◽

Immediate Early Gene ◽

Early Gene ◽

Immediate Early ◽

Monocytic Cell ◽

Monocytic Cell Line ◽

Early Gene Expression

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Dysregulation of Cyclin E Gene Expression in Human Cytomegalovirus-Infected Cells Requires Viral Early Gene Expression and Is Associated with Changes in the Rb-Related Protein p130

Journal of Virology ◽

10.1128/jvi.74.9.4192-4206.2000 ◽

2000 ◽

Vol 74 (9) ◽

pp. 4192-4206 ◽

Cited By ~ 33

Author(s):

Anita K. McElroy ◽

Roopashree S. Dwarakanath ◽

Deborah H. Spector

Keyword(s):

Gene Expression ◽

Cell Cycle ◽

Human Cytomegalovirus ◽

Cyclin E ◽

Early Gene ◽

Immediate Early ◽

Mrna Levels ◽

Early Gene Expression ◽

Cell Extracts ◽

Infected Cells

ABSTRACT We have previously shown that many cell cycle regulatory gene products are markedly affected by infection of primary fibroblasts with human cytomegalovirus (HCMV) (F. M. Jault, J. M. Jault, F. Ruchti, E. A. Fortunato, C. Clark, J. Corbeil, D. D. Richman, and D. H. Spector, J. Virol. 69:6697–6704, 1995). One of these proteins, cyclin E, is a key determinant of cell cycle progression during G1, and its mRNA levels are significantly increased in HCMV-infected fibroblasts (B. S. Salvant, E. A. Fortunato, and D. H. Spector, J. Virol. 72:3729–3741, 1998). To determine the molecular basis of this effect, we have examined the events that occur at the endogenous cyclin E promoter during the course of infection. In vivo dimethyl sulfate footprinting of the cyclin E promoter revealed several regions of protection and hypersensitivity that were unique to infected cells. In accord with this observation, we find that the virus-induced cyclin E transcripts initiate downstream of the start site identified in mock-infected cells, in regions where these newly appearing protected and hypersensitive sites occur. Viral gene expression is required for this induction. However, the viral immediate-early proteins IE1-72 and IE2-86, either alone or in combination, cannot induce expression of the endogenous cyclin E. The virus must progress past the immediate-early phase and express an early gene product(s) for activation of cyclin E expression. Moreover, IE1-72 does not appear to be required, as infection of cells with an HCMV mutant containing a deletion in the IE1-72 gene leads to full upregulation of cyclin E expression. Using electrophoretic mobility shift assays with infected cell extracts and a region of the cyclin E promoter that includes two previously defined E2F sites as the probe, we detected the appearance of an infection-specific banding pattern. One of the infection-specific bands contained the proteins E2F-4, DP-1, and p130, which were maintained in the infected cells as uniquely phosphorylated species. These results suggest that an altered E2F-4–DP-1–p130 complex along with viral early gene expression may play a role in the transcriptional regulation of cyclin E mRNA during HCMV infection.

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