Relative importance of elements within the SL3-3 virus enhancer for T-cell specificity

Abstract

Elements within the enhancer of T-lymphomagenic SL3-3 virus were examined for their contributions to transcriptional activity in T lymphocytes and non-T cells. A region containing two sequences homologous to the enhancer core consensus sequence and a sequence homologous to the binding site for factor LVb was found to have the largest effect on activity. Evidence was obtained that suggests that the activity of this region was greater in T lymphocytes than in non-T cells and that multiple elements within it were necessary for activity. A second region, containing sequences homologous to the binding site of factor NF-I and the glucocorticoid response element, had about a twofold effect on transcription in both T lymphocytes and non-T cell lines. The twofold effect was seen whether the region containing the cores and LVb site was present or not. These results indicate that the most important region for the specificity of SL3-3 enhancer activity and, presumably, for viral leukemogenicity comprises the core elements and the LVb site. DNA-protein-binding studies demonstrated that one cellular factor, S/A-CBF, bound to both core elements, while a second cellular factor, S-CBF, bound to only one of them. In combination with earlier studies, this indicates that cells contain multiple factors that bind to the critical region.

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

“…Mutation of either a c-Myb-or CBF-binding site inhibited the activity of the TCR␦ and TCR␥ enhancers in T cells (36,39). Mutation of the c-Myb-or CBF-binding sites inhibited the activity of the SL3 enhancer in T cells (6,34,54,55,64,94,106). The cotransfection experiments presented here are important because they explicitly show that c-Myb and CBF␣2-451 are capable of driving transcription through these sites.…”

“…In all cases, identical mutations were simultaneously generated in each of the 72-bp repeats of the SL3 enhancer. Mutations in each of the three binding sites as well as in core I were previously found to inhibit the transcriptional activity of the SL3 LTR in T lymphocytes (6,34,54,55,64,94,106). In addition, mutation of the Myb site was found to nearly eliminate the lymphomagenicity of SL3 (66).…”

“…SL3-3 (SL3) is an MuLV that induces T-cell lymphomas (74). Deletion analysis defined a minimal portion of the SL3 enhancer that is necessary for its preferential transcriptional activity in T lymphocytes (34,55). This stretch of about 40 nucleotides contains binding sites for multiple transcription factors.…”

“…This stretch of about 40 nucleotides contains binding sites for multiple transcription factors. These include two binding sites for the factor CBF (55,94). CBF is also called PEBP2 or AML1 (18,24,43,45,59,72,99).…”

Stability of AML1 (core) site enhancer mutations in T lymphomas induced by attenuated SL3-3 murine leukemia virus mutants

“…The exact mecha-nisms by which virus enhancer structures determine disease induction are not known. First, the enhancer effect on provirus transcription may determine the level of expression of a viral gene product in the target cell or the virus load in target tissues (17,27). However, in the case of thymic lymphomagenesis it was found that infection of target tissue is not sufficient for subsequent disease development (11,12).…”