Elimination of ie1 significantly attenuates murine cytomegalovirus virulence but does not alter replicative capacity in cell culture.
The major immediate-early (MIE) genes of cytomegaloviruses (CMV) are broadly thought to be decisive regulators of lytic replication and reactivation from latency. To directly assess the role of the MIE protein IE1 during the infection of murine CMV (MCMV), we constructed an MCMV with exon 4 of the ie1 gene deleted. We found that, independent of the multiplicity of infection, the resulting recombinant virus, MCMVdie1, which fails to express the IE1 protein, was fully competent for early gene expression and replicated in different cultured cell types with identical kinetics to those of parental or revertant virus. Immunofluorescence microscopy studies revealed that MCMVdie1 was greatly impaired in its capacity to disrupt promyelocytic leukemia bodies in NIH 3T3 cells early after infection, a process that has been proposed to increase viral transcription efficiency. We examined MCMVdie1 in the murine model using both immunocompetent BALB/c and severe combined immunodeficient (SCID) mice. When MCMVdie1 was inoculated into these two types of mice, significantly lower viral titers were detected in infected organs than in those of the wild-type virus-infected animals. Moreover, the ie1-deficient MCMV exhibited a markedly reduced virulence. While all animals infected with 5 x 10(4) PFU of parental virus died by 30 days postinfection, SCID mice infected with a similar dose of MCMVdie1 did not succumb before 60 days postinfection. The in vivo defective growth phenotype of MCMVdie1 was abrogated upon rescue of ie1. These results demonstrate the significance of the ie1 gene for promoting an acute MCMV infection and virulence yet indicate that MCMV is able to grow in vivo, although impaired, in the absence of the ie1 gene.
Ghazal
Peter
P
Scottish Centre for Genomic Technology and Informatics, University of Edinburgh, Medical School, United Kingdom.
Visser
Astrid E
AE
Gustems
Montse
M
García
Rosalía
R
Borst
Eva Maria
EM
Sullivan
Kevin
K
Messerle
Martin
M
Angulo
Ana
A
D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D022202:Chromosomes, Artificial, Bacterial / Q000235:genetics; D004279:DNA, Viral / Q000235:genetics; D017353:Gene Deletion; D015870:Gene Expression; D017781:Genes, Immediate-Early; D017874:Immediate-Early Proteins / Q000235:genetics; D051379:Mice; D008807:Mice, Inbred BALB C; D016513:Mice, SCID; D018146:Muromegalovirus / Q000235:genetics* / Q000472:pathogenicity* / Q000502:physiology; D041681:NIH 3T3 Cells; D009363:Neoplasm Proteins / Q000502:physiology; D009687:Nuclear Proteins / Q000502:physiology; D010641:Phenotype; D000071156:Promyelocytic Leukemia Protein; D011995:Recombination, Genetic; D014157:Transcription Factors / Q000502:physiology; D025521:Tumor Suppressor Proteins; D014764:Viral Proteins / Q000235:genetics; D014774:Virulence / Q000235:genetics; D014779:Virus Replication / Q000235:genetics
D004279:DNA, Viral; C088645:IE1 protein, cytomegalovirus; D017874:Immediate-Early Proteins; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; C513293:Pml protein, mouse; D000071156:Promyelocytic Leukemia Protein; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D014764:Viral Proteins