Pathogenic determinants in the U3 region of recombinant murine leukemia viruses isolated from CWD and HRS/J mice

Lawrenz-Smith, S C; Massey, Ann; Innes, Donald J.; Thomas, Christopher Y.

doi:10.1128/jvi.68.8.5174-5183.1994

Cited by 8 publications

(9 citation statements)

References 55 publications

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“…Akv is an endogenous retrovirus of AKR mice. When inoculated into newborn mice of various strains, it is nonleukemogenic, at least within the first year following inoculation (49,50). Like SL3 and Mo-MuLV, Akv contains an Ets site and a core element.…”

Section: Cbf␣2-451 and C-mybmentioning

confidence: 99%

Transcriptional activation of a retrovirus enhancer by CBF (AML1) requires a second factor: evidence for cooperativity with c-Myb

Zaiman

Lenz

1996

J Virol

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Transcriptional enhancer sequences within the long terminal repeats (LTRs) of murine leukemia viruses are the primary genetic determinants of the tissue specificity and potency of the oncogenic potential of these retroviruses. SL3-3 (SL3) is a murine leukemia virus that induces T-cell lymphomas. The LTR enhancer of this virus contains two binding sites for the transcription factor CBF (also called AML1 and PEBP2) that flank binding sites for c-Myb and the Ets family of factors. Using cotransfection assays in P19 cells, we report here that CBF and c-Myb cooperatively stimulate transcription from the SL3 LTR. By itself, c-Myb had no stimulatory effect on transcription. However, when cotransfected with a cDNA encoding one form of the ␣ subunit of CBF called CBF␣2-451, a level of transactivation higher than that seen with CBF␣2-451 alone was detected. The negative regulatory domain near the carboxyl terminus of c-Myb did not affect this activity. Electrophoretic mobility shift assays indicated that CBF and c-Myb bind to DNA independently. Therefore, it appears that the cooperative stimulation of transcription by these factors occurs at a step in the process of transcription after the two factors are bound to the enhancer. Sequences near the carboxyl terminus of CBF␣2-451 were important for cooperativity with c-Myb, consistent with previous reports that this region contains an activation domain. However, CBF␣2-451 failed to activate transcription from a version of the SL3 LTR in which the enhancer was replaced with five tandem CBF-binding sites. Thus, it appears that transcriptional activation of the SL3 enhancer by CBF requires that an appropriate heterologous transcription factor be bound to a neighboring site in the regulatory sequences.

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Section: Cbf␣2-451 and C-mybmentioning

confidence: 99%

Transcriptional activation of a retrovirus enhancer by CBF (AML1) requires a second factor: evidence for cooperativity with c-Myb

Zaiman

Lenz

1996

J Virol

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“…A slight increase in activity of the enhancer element would be expected to increase the rate of viral gene transcription and virus replication, leading to a selection of viruses whose enhancers respond to E47. Moreover, this would explain why viruses with the CWM-T15 U3 region sequences induce lymphomas more rapidly than do chimeric viruses that contain the allelic U3 region sequences of the endogenous ecotropic viruses (27). The binding of E47 to the enhancer core region may also contribute to the selection of the pathogenic U3 region found in many AKR recombinants (20,21,31,33,44,45,52).…”

Section: Discussionmentioning

confidence: 99%

“…The pCATEn(Ϫ) plasmid contains the U3 region sequences 3Ј of the enhancer, including the viral promoter. The U3 sequences 3Ј of the second NF-1/CTF site were amplified by PCR with synthesized primers (Protein and Nucleic Acid Sequencing Center, University of Virginia) that corresponded to positions 191 to 209 of the U3 region and positions 2391 to 2407 of the pCATBasic vector under conditions described previously (27). The amplified DNA was digested with the appropriate restriction enzymes and ligated to the pCATBasic vector.…”

Section: Methodsmentioning

confidence: 99%

“…Previous studies by Holland et al have shown that the Bxv-1 U3 region sequences of the AKR recombinant virus MCF 247 contains leukemogenic determinants that are absent in the allelic sequences of the AKR endogenous ecotropic virus (20). Our laboratory has reported that an ecotropic virus that con-tained the CWM-T15 U3 region induced lymphomas with a higher frequency and shorter latency than did a virus that was isogenic except that the U3 region was derived from the endogenous ecotropic parent, Emv-1 (27). The pathogenicity of the CWM-T15 or Bxv-1-related U3 region sequences probably explains why recombinant viruses that acquire these sequences have a selective advantage in vivo.…”

mentioning

confidence: 91%

“…Another interpre-tation of the results is that subtle but biologically significant differences in the activity of the two enhancers were obscured by the inherent variability and lack of sensitivity of the transient-expression assays. For instance, the CWM-T15 and Emv-1 enhancers both support viral replication and pathogenicity, but the CWM-T15 U3 region of sequences reduce tumor latency by about 20%, or 3 months (27). If one assumes that this reduction is related to a proportional increase in the activity of the CWM-T15 enhancer, this small difference would easily have been missed in the transient-expression assays.…”

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The E47 transcription factor binds to the enhancer sequences of recombinant murine leukemia viruses and influences enhancer function

Lawrenz-Smith

Thomas

1995

J Virol

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The genomes of most recombinant murine leukemia viruses (MuLVs) inherit pathogenic U3 region sequences from the endogenous xenotropic provirus Bxv-1. However, the U3 regions of about one-third of recombinant MuLVs from CWD mice, such as CWM-T15, have nonecotropic substitutions that are probably derived from an endogenous polytropic provirus. The CWM-T15 U3 region sequences contain five nucleotide substitutions compared with the less pathogenic sequences of the endogenous ecotropic virus parent, Emv-1. Three of these substitutions are located immediately 3 of the enhancer core, and two form part of an E-box motif that is also found in the Bxv-1 sequence. A series of electromobility shift assays revealed that nuclear extracts from S194 cells and the basic helix-loop-helix transcription factor E47 could distinguish between oligonucleotides that contained the core region sequences of CWM-T15 or Emv-1. The E47 homodimers appeared to bind to the CWM-T15 E-box motif and when expressed at high levels in cells transactivated the CWM-T15 but not the Emv-1 enhancer. Taken together, these results suggest that E47 or related basic helix-loop-helix proteins that are expressed in lymphoid cells bind to and transactivate the CWM-T15 enhancer in vivo. This transactivation may explain why the CWM-T15 and Bxv-1 U3 regions accelerate the onset of lymphoid neoplasms and why related enhancer core region sequences are preferentially incorporated into the genomes of recombinant MuLVs and are found in other leukemogenic mammalian retroviruses. * Corresponding author. Phone: (904) 953-7126. Fax: (904) 953-7117. 4142

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Nuclear Factors That Bind to the U3 Region of Two Murine Myeloid Leukemia-Inducing Retroviruses, Cas-Br-E and Graffi

Barat

Rassart

1998

Virology

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Cas-Br-E and Graffi are two myeloid leukemia-inducing murine viruses. Cas-Br-E induces, in NIH-Swiss mice, mostly non-T, non-B leukemia composed of very immature cells with no specific characteristics (Bergeron et al. (1993). Leukemia 7, 954-962). The Graffi murine leukemia virus causes exclusively myeloid leukemia, but the tumor cells are clearly of granulocytic nature (Ru et al. (1993). J. Virol. 67, 4722). We were interested to understand the role of the long terminal repeat (LTR) U3 region in the myeloid specificity of these two retroviruses. We used DNase I footprinting and gel mobility shift assays to identify a number of protein binding sites within Cas-Br-E and Graffi U3 regions. The pattern of protected regions is highly similar for the two viruses. Some factors identified in other murine leukemia viruses, like the core binding factor, also bind to Cas-Br-E and Graffi LTR; however, other binding sites seem specific for these two viruses. Only one difference between them was noted, at the 5' end of the U3 region. Transcriptional activity of both LTRs was also analyzed in various cell lines and compared with other murine leukemia viruses. The results show a slight myeloid specificity for the two LTRs, and indicate that the Graffi enhancer is quite strong in a broad range of cell types.

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Pathogenic determinants in the U3 region of recombinant murine leukemia viruses isolated from CWD and HRS/J mice

Cited by 8 publications

References 55 publications

Transcriptional activation of a retrovirus enhancer by CBF (AML1) requires a second factor: evidence for cooperativity with c-Myb

Transcriptional activation of a retrovirus enhancer by CBF (AML1) requires a second factor: evidence for cooperativity with c-Myb

The E47 transcription factor binds to the enhancer sequences of recombinant murine leukemia viruses and influences enhancer function

Nuclear Factors That Bind to the U3 Region of Two Murine Myeloid Leukemia-Inducing Retroviruses, Cas-Br-E and Graffi

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