Regulatory elements within the murine leukemia virus enhancer regions mediate glucocorticoid responsiveness.

Enhancer elements within nonleukemogenic (Akv) and T-cell leukemogenic (SL3-3) murine leukemia viruses demonstrate strong cell type preference in transcriptional activity. These transcription elements are additionally regulated by the synthetic glucocorticoid dexamethasone, and this pattern of regulation varies according to cell type. The sequences required for dexamethasone regulation for both Akv and SL3-3 are shown to include a 17-nucleotide consensus sequence previously termed the glucocorticoid response element (GRE). Although the GREs are identical for both viral enhancers, the sequences surrounding these elements differ, as does the spatial arrangement of the GRE sequences with respect to one another. It is proposed that the spatial arrangement of the GREs, as well as their precise sequence context, determines the difference in the response to dexamethasone of the enhancers in different cell types.