title: Role of glucocorticoid receptor binding sites in the human immunodeficiency virus type 1 long terminal repeat in steroid-mediated suppression of HIV gene expression.
abstract: Dexamethasone inhibited human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR)-directed gene expression in cells of T and B lymphoblastoid lineages, but not in monocytic cells. Suppression required an intact glucocorticoid receptor (GR), as it was amplified by transfection of lymphocytes with a plasmid encoding the human GR and blocked by the receptor antagonist RU486. These results were in direct contrast to the effects of dexamethasone on a murine leukemia retrovirus promoter where, consistent with the findings of others, activation of gene expression was obtained. Potential regions of the HIV-1 LTR mediating these effects were sought, with sequence homologies predicting two new glucocorticoid response element half-sites, GRE-II (nucleotides -6 to -1) and GRE-III (+ 15 to + 20), downstream from a previously identified GR DNA binding domain, GRE-I (-264 to -259). Mutational analyses documented the loss of inhibitory activity attendant on changes in GRE-III and the independence of steroid-mediated effects from GRE-I and GRE-II. Consistent with these findings, electrophoretic mobility shift assays revealed a difference in binding of cellular factors to GRE-III in cells of T and B lymphocyte vs. monocytic lineages. Binding sites for the cellular transcription factor leader binding protein (LBP-1) were found to overlap with GRE-III, and LBP-1 interacted with this element in the HIV LTR only in T and B lymphocytic extracts. We hypothesize that GRE-III sequence-specific effects, including modulation of LBP-GR interactions, underlie the negative regulatory effect of glucocorticoids on HIV-1 gene expression, with some specificity for cell type.
authors.affiliation: Department of Medicine, Cornell University Medical College, New York, New York 10021, USA.
authors.forename: D
authors.initials: D
authors.lastname: Mitra
authors.forename: S K
authors.initials: SK
authors.lastname: Sikder
authors.forename: J
authors.initials: J
authors.lastname: Laurence
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D002460:Cell Line; D004279:DNA, Viral / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology*; D015967:Gene Expression Regulation, Viral / Q000187:drug effects*; D016325:HIV Long Terminal Repeat / Q000187:drug effects*; D015497:HIV-1 / Q000187:drug effects* / Q000235:genetics; D006801:Humans; D015735:Mifepristone / Q000494:pharmacology; D008969:Molecular Sequence Data; D011965:Receptors, Glucocorticoid / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
chemical_list: D004279:DNA, Viral; D011965:Receptors, Glucocorticoid; D015735:Mifepristone; D003907:Dexamethasone