Mutated primer binding sites interacting with different tRNAs allow efficient murine leukemia virus replication.

ABSTRACT SL3-3 is a murine leukemia virus which is only weakly bone pathogenic but highly T-cell lymphomagenic. A major pathogenic determinant is the transcriptional enhancer comprising several transcription factor binding sites, among which are three identical sites for nuclear factor 1 (NF1). We have investigated the pathogenic properties of NF1 site enhancer mutants of SL3-3. Two different mutants carrying a 3-bp mutation either in all three NF1 sites or in the central site alone were constructed and assayed in inbred NMRI mice. The wild type and both mutants induced lymphomas in all mice, with a mean latency period of 9 weeks. However, there was a considerable difference in osteopetrosis induction. Wild-type SL3-3 induced osteopetrosis in 11% of the mice (2 of 19), and the triple NF1 site mutant induced osteopetrosis in none of the mice (0 of 19), whereas the single NF1 site mutant induced osteopetrosis in 56% (10 of 18) of the mice, as determined by X-ray analysis. A detailed histological examination of the femurs of the mice was carried out and found to support this diagnosis. Thus, the NF1 sites of SL3-3 are major determinants of osteopetrosis induction, without determining lymphomagenesis. This conclusion was further supported by evaluation of the bone pathogenicity of other SL3-3 enhancer variants, the lymphomagenicity of which had been examined previously. This evaluation furthermore strongly indicated that the core sites, a second group of transcription factor binding sites in the viral enhancer, are necessary for the osteopetrosis induction potential of SL3-3.

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Cooperative Effect of Gag Proteins p12 and Capsid during Early Events of Murine Leukemia Virus Replication

Journal of Virology ◽

10.1128/jvi.79.7.4159-4169.2005 ◽

2005 ◽

Vol 79 (7) ◽

pp. 4159-4169 ◽

Cited By ~ 19

Author(s):

Sook-Kyung Lee ◽

Kunio Nagashima ◽

Wei-Shau Hu

Keyword(s):

Virus Replication ◽

Murine Leukemia Virus ◽

Leukemia Virus ◽

Virus Production ◽

Cooperative Effect ◽

Gag Proteins ◽

Rous Sarcoma ◽

Reverse Transcription Step ◽

Spleen Necrosis ◽

Murine Leukemia

ABSTRACT The Gag polyprotein of murine leukemia virus (MLV) is processed into matrix (MA), p12, capsid (CA), and nucleocapsid (NC) proteins. p12 affects early events of virus replication and contains a PPPY motif important for virus release. To probe the functions of p12 in the early steps of MLV replication, we tested whether p12 can be replaced by spleen necrosis virus (SNV) p18, human immunodeficiency virus type 1 p6, or Rous sarcoma virus p2b. Analyses revealed that all chimeras generated virions at levels similar to that of MLV gag-pol; however, none of them could support MLV vector replication, and all of them exhibited severely reduced DNA synthesis upon virus infection. Because a previously reported SNV gag-MLV pol chimera, but not the MLV hybrid with SNV p18, can support replication of an MLV vector, we hypothesized that other Gag proteins act cooperatively with p12 during the early phase of virus replication. To test this hypothesis, we generated three more MLV-based chimeras containing SNV CA, p18-CA, or p18-CA-NC. We found that the MLV chimera containing SNV p18-CA or p18-CA-NC could support MLV vector replication, but the chimera containing SNV CA could not. Furthermore, viruses derived from the MLV chimera with SNV CA could synthesize viral DNA upon infection but were blocked at a post-reverse-transcription step and generated very little two long terminal repeat circle DNA, thereby producing a phenotype similar to that of the provirus formation-defective p12 mutants. Taken together, our data indicate that when p12/p18 or CA was from different viruses, despite abundant virus production and proper Gag processing, the resulting viruses were not infectious. However, when p12/p18 and CA were from the same virus, even though they were from SNV and not MLV, the resulting viruses were infectious. Therefore, these results suggest a cooperative effect of p12 and CA during the early events of MLV replication.

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The Fv-1 Gene of the Mouse and its Control of Murine Leukemia Virus Replication

Current Topics in Microbiology and Immunology ◽

10.1007/978-3-642-67341-2_3 ◽

1979 ◽

pp. 67-122 ◽

Cited By ~ 65

Author(s):

Paul Jolicoeur

Keyword(s):

Virus Replication ◽

Murine Leukemia Virus ◽

Leukemia Virus ◽

Murine Leukemia

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Cellular Transcription Factor ZASC1 Regulates Murine Leukemia Virus Transcription

Journal of Virology ◽

10.1128/jvi.00299-10 ◽

2010 ◽

Vol 84 (15) ◽

pp. 7473-7483 ◽

Cited By ~ 6

Author(s):

James W. Bruce ◽

Michael Hierl ◽

John A. T. Young ◽

Paul Ahlquist

Keyword(s):

Gene Expression ◽

Transcription Factor ◽

Cell Line ◽

Binding Sites ◽

Murine Leukemia Virus ◽

Leukemia Virus ◽

Cellular Transcription Factor ◽

Cellular Transcription ◽

Ltr Promoter ◽

Murine Leukemia

ABSTRACT To identify cellular processes involved in retroviral infection, we employed a high-volume forward genetic screen of insertionally mutagenized somatic cells using a murine leukemia virus (MLV) vector. This approach identified a clonal cell line that exhibited approximately 10-fold reduced gene expression from MLV vectors following infection despite supporting normal levels of MLV reverse transcription and integration. The defect in this cell line was specific for the MLV long terminal repeat (LTR) promoter, as normal levels of reporter gene expression were obtained from both an internal cytomegalovirus (CMV) promoter contained within an LTR-defective MLV vector and LTR expression from an avian sarcoma and leukosis virus (ASLV) vector. Complementation and shRNA knockdown experiments demonstrated that the defective gene in these cells is ZASC1 (ZNF639), a transcription factor with strong links to cancer and inherited ataxias. We demonstrated that ZASC1 is a sequence-specific DNA binding protein with three closely related binding sites located within the MLV LTR promoter, but it does not bind to the ASLV promoter. Mutating these putative ZASC1 binding sites significantly reduced levels of MLV gene expression. While wild-type ZASC1 activated expression from the MLV promoter, a green fluorescent protein-ZASC1 fusion protein showed dominant-negative inhibition of MLV gene expression. These studies identify the cellular transcription factor ZASC1 as an activator of MLV gene expression and provide tools that should be useful in studying the links between ZASC1 and human diseases.

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