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Human Cytomegalovirus Can Procure Deoxyribonucleotides for Viral DNA Replication in the Absence of Retinoblastoma Protein Phosphorylation
- Source :
- Journal of Virology. 90:8634-8643
- Publication Year :
- 2016
- Publisher :
- American Society for Microbiology, 2016.
-
Abstract
- Viral DNA replication requires deoxyribonucleotide triphosphates (dNTPs). These molecules, which are found at low levels in noncycling cells, are generated either by salvage pathways or through de novo synthesis. Nucleotide synthesis utilizes the activity of a series of nucleotide-biosynthetic enzymes (NBEs) whose expression is repressed in noncycling cells by complexes between the E2F transcription factors and the retinoblastoma (Rb) tumor suppressor. Rb-E2F complexes are dissociated and NBE expression is activated during cell cycle transit by cyclin-dependent kinase (Cdk)-mediated Rb phosphorylation. The DNA virus human cytomegalovirus (HCMV) encodes a viral Cdk (v-Cdk) (the UL97 protein) that phosphorylates Rb, induces the expression of cellular NBEs, and is required for efficient viral DNA synthesis. A long-held hypothesis proposed that viral proteins with Rb-inactivating activities functionally similar to those of UL97 facilitated viral DNA replication in part by inducing the de novo production of dNTPs. However, we found that dNTPs were limiting even in cells infected with wild-type HCMV in which UL97 is expressed and Rb is phosphorylated. Furthermore, we revealed that both de novo and salvage pathway enzymes contribute to viral DNA replication during HCMV infection and that Rb phosphorylation by cellular Cdks does not correct the viral DNA replication defect observed in cells infected with a UL97-deficient virus. We conclude that HCMV can obtain dNTPs in the absence of Rb phosphorylation and that UL97 can contribute to the efficiency of DNA replication in an Rb phosphorylation-independent manner. IMPORTANCE Transforming viral oncoproteins, such as adenovirus E1A and papillomavirus E7, inactivate Rb. The standard hypothesis for how Rb inactivation facilitates infection with these viruses is that it is through an increase in the enzymes required for DNA synthesis, which include nucleotide-biosynthetic enzymes. However, HCMV UL97, which functionally mimics these viral oncoproteins through phosphorylation of Rb, fails to induce the production of nonlimiting amounts of dNTPs. This finding challenges the paradigm of the role of Rb inactivation during DNA virus infection and uncovers the existence of an alternative mechanism by which UL97 contributes to HCMV DNA synthesis. The ineffectiveness of the UL97 inhibitor maribavir in clinical trials might be better explained with a fuller understanding of the role of UL97 during infection. Furthermore, as the nucleoside analog ganciclovir is the current drug of choice for treating HCMV, knowing the provenance of the dNTPs incorporated into viral DNA may help inform antiviral therapeutic regimens.
- Subjects :
- 0301 basic medicine
Human cytomegalovirus
viruses
Deoxyribonucleotides
Immunology
Cytomegalovirus
Viral Plaque Assay
Virus Replication
Retinoblastoma Protein
Microbiology
03 medical and health sciences
Cyclin-dependent kinase
Virology
medicine
Humans
Phosphorylation
Cells, Cultured
DNA synthesis
biology
DNA replication
Retinoblastoma protein
DNA virus
Maribavir
Cell cycle
medicine.disease
Molecular biology
Virus-Cell Interactions
Phosphotransferases (Alcohol Group Acceptor)
030104 developmental biology
Insect Science
DNA, Viral
biology.protein
Protein Processing, Post-Translational
Subjects
Details
- ISSN :
- 10985514 and 0022538X
- Volume :
- 90
- Database :
- OpenAIRE
- Journal :
- Journal of Virology
- Accession number :
- edsair.doi.dedup.....0ea7e451303c8b08f1f9b17f92eb15df