title: Transactivation of cellular genes involved in nucleotide metabolism by the regulatory IE1 protein of murine cytomegalovirus is not critical for viral replicative fitness in quiescent cells and host tissues.
abstract: Despite its high coding capacity, murine CMV (mCMV) does not encode functional enzymes for nucleotide biosynthesis. It thus depends on cellular enzymes, such as ribonucleotide reductase (RNR) and thymidylate synthase (TS), to be supplied with deoxynucleoside triphosphates (dNTPs) for its DNA replication. Viral transactivation of these cellular genes in quiescent cells of host tissues is therefore a parameter of viral fitness relevant to pathogenicity. Previous work has shown that the IE1, but not the IE3, protein of mCMV transactivates RNR and TS gene promoters and has revealed an in vivo attenuation of the mutant virus mCMV-DeltaIE1. It was attractive to propose the hypothesis that lack of transactivation by IE1 and a resulting deficiency in the supply of dNTPs are the reasons for growth attenuation. Here, we have tested this hypothesis with the mutant virus mCMV-IE1-Y165C expressing an IE1 protein that selectively fails to transactivate RNR and TS in quiescent cells upon transfection while maintaining the capacity to disperse repressive nuclear domains (ND10). Our results confirm in vivo attenuation of mCMV-DeltaIE1, as indicated by a longer doubling time in host organs, whereas mCMV-IE1-Y165C replicated like mCMV-WT and the revertant virus mCMV-IE1-C165Y. Notably, the mutant virus transactivated RNR and TS upon infection of quiescent cells, thus indicating that IE1 is not the only viral transactivator involved. We conclude that transactivation of cellular genes of dNTP biosynthesis is ensured by redundancy and that attenuation of mCMV-DeltaIE1 results from the loss of other critical functions of IE1, with its function in the dispersal of ND10 being a promising candidate.
authors.affiliation: Institute for Virology, Johannes Gutenberg-University, Hochhaus am Augustusplatz, 55101 Mainz, Germany. Matthias.Reddehase@uni-mainz.de
authors.forename: Vanessa
authors.initials: V
authors.lastname: Wilhelmi
authors.forename: Christian O
authors.initials: CO
authors.lastname: Simon
authors.forename: Jürgen
authors.initials: J
authors.lastname: Podlech
authors.forename: Verena
authors.initials: V
authors.lastname: Böhm
authors.forename: Torsten
authors.initials: T
authors.lastname: Däubner
authors.forename: Simone
authors.initials: S
authors.lastname: Emde
authors.forename: Dennis
authors.initials: D
authors.lastname: Strand
authors.forename: Angélique
authors.initials: A
authors.lastname: Renzaho
authors.forename: Niels A W
authors.initials: NA
authors.lastname: Lemmermann
authors.forename: Christof K
authors.initials: CK
authors.lastname: Seckert
authors.forename: Matthias J
authors.initials: MJ
authors.lastname: Reddehase
authors.forename: Natascha K A
authors.initials: NK
authors.lastname: Grzimek
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D005347:Fibroblasts / Q000166:cytology / Q000502:physiology; D005786:Gene Expression Regulation; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism*; D008099:Liver / Q000166:cytology / Q000821:virology; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D018146:Muromegalovirus / Q000235:genetics / Q000502:physiology*; D041681:NIH 3T3 Cells; D009711:Nucleotides / Q000378:metabolism*; D010455:Peptides / Q000235:genetics / Q000378:metabolism; D017354:Point Mutation; D011401:Promoter Regions, Genetic; D016415:Sequence Alignment; D015533:Transcriptional Activation; D014779:Virus Replication
chemical_list: C088645:IE1 protein, cytomegalovirus; D017874:Immediate-Early Proteins; D009711:Nucleotides; D010455:Peptides