Sequences responsible for erythroid and lymphoid leukemia in the long terminal repeats of Friend-mink cell focus-forming and Moloney murine leukemia viruses

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.

Section: Discussionmentioning

confidence: 99%

“…Transcriptional enhancers located within the long terminal repeats (LTRs) are the primary genetic determinants of the pathogenicity of murine leukemia viruses (MuLVs) (14,15,20,27,41,50,52,98). These elements determine the viral potency and the tissue specificity of viral leukemogenicity (13,85,92,98,105).…”

mentioning

confidence: 99%

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

Zaiman

Lenz

1996

“…These results indicate that either M-MuLV has additional determinants of T-cell lymphomagenicity in addition to its enhancers or SRS MuLV has additional determinants for the broad disease spectrum in addition to its enhancers or both. Other investigators have shown that replacement of the M-MuLV enhancers with F-MuLV enhancers is sufficient to convert the disease specificity to erythroleukemia (10,11,26,28,30,47). Therefore, if other T-cell lymphomagenic determinants exist outside the LTR of M-MuLV, they must be relatively weak.…”

Section: Discussionmentioning

confidence: 99%

Tandemization of a Subregion of the Enhancer Sequences from SRS 19-6 Murine Leukemia Virus Associated with T-Lymphoid but Not Other Leukemias

Granger

Bundy

Fan

1999

Most simple retroviruses induce tumors of a single cell type when infected into susceptible hosts. The SRS 19-6 murine leukemia virus (MuLV), which originated in mainland China, induces leukemias of multiple cellular origins. Indeed, infected mice often harbor more than one tumor type. Since the enhancers of many MuLVs are major determinants of tumor specificity, we tested the role of the SRS 19-6 MuLV enhancers in its broad disease specificity. The enhancer elements of the Moloney MuLV (M-MuLV) were replaced by the 170-bp enhancers of SRS 19-6 MuLV, yielding the recombinants ΔMo+SRS+ and ΔMo+SRS− M-MuLV. M-MuLV normally induces T-lymphoid tumors in all infected mice. Surprisingly, when neonatal mice were inoculated with ΔMo+SRS+ or ΔMo+SRS−M-MuLV, all tumors were of T-lymphoid origin, typical of M-MuLV rather than SRS 19-6 MuLV. Thus, the SRS 19-6 MuLV enhancers did not confer the broad disease specificity of SRS 19-6 MuLV to M-MuLV. However, all tumors contained ΔMo+SRS M-MuLV proviruses with common enhancer alterations. These alterations consisted of tandem multimerization of a subregion of the SRS 19-6 enhancers, encompassing the conserved LVb and core sites and adjacent sequences. Moreover, when tumors induced by the parental SRS 19-6 MuLV were analyzed, most of the T-lymphoid tumors had similar enhancer alterations in the same region whereas tumors of other lineages retained the parental SRS 19-6 MuLV enhancers. These results emphasize the importance of a subregion of the SRS 19-6 MuLV enhancer in induction of T-cell lymphoma. The relevant sequences were consistent with crucial sequences for T-cell lymphomagenesis identified for other MuLVs such as M-MuLV and SL3-3 MuLV. These results also suggest that other regions of the SRS 19-6 MuLV genome contribute to its broad leukemogenic spectrum.

“…Another well-studied example is the enhancer from the Moloney MLV, which determines the selectivity of the Moloney virus for inducing T-cell lymphomas. Substitution of the Moloney virus enhancer with that from the erythroleukemogenic Friend MLV switches the disease specificity of Moloney MLV from T-cell lymphoma to erythroleukemia (9,10,22,31,38).…”

mentioning

confidence: 99%

Core-Binding Factor Influences the Disease Specificity of Moloney Murine Leukemia Virus

Lewis¹,

Stacy²,

Green

et al. 1999

The core site in the Moloney murine leukemia virus (Moloney MLV) enhancer was previously shown to be an important determinant of the T-cell disease specificity of the virus. Mutation of the core site resulted in a significant shift in disease specificity of the Moloney virus from T-cell leukemia to erythroleukemia. We and others have since determined that a protein that binds the core site, one of the core-binding factors (CBF) is highly expressed in thymus and is essential for hematopoiesis. Here we test the hypothesis that CBF plays a critical role in mediating pathogenesis of Moloney MLV in vivo. We measured the affinity of CBF for most core sites found in MLV enhancers, introduced sites with different affinities for CBF into the Moloney MLV genome, and determined the effects of these sites on viral pathogenesis. We found a correlation between CBF affinity and the latent period of disease onset, in that Moloney MLVs with high-affinity CBF binding sites induced leukemia following a shorter latent period than viruses with lower-affinity sites. The T-cell disease specificity of Moloney MLV also appeared to correlate with the affinity of CBF for its binding site. The data support a role for CBF in determining the pathogenic properties of Moloney MLV.