title: Mouse mammary tumor virus superantigen expression is reduced by glucocorticoid treatment.
abstract: Expression of mouse mammary tumor virus (MMTV)-encoded superantigens in B lymphocytes are required for viral transmission and pathogenesis. Due to problems with detection and quantification of the superantigen protein, most reports about the mechanism of superantigen expression from the viral sag gene rely on the quantitative analysis of putative sag mRNAs. The description of multiple promoters as a source of putative sag mRNA has complicated the situation even further. All conclusions about the level of superantigen protein expression based on these data remain circumstantial. To test the effect of the glucocorticoid hormone dexamethasone on the total superantigen expression from an infectious MMTV provirus we used a quantitative assay that is based on a superantigen-luciferase fusion protein. MMTV gene expression from the major promoter in the 5' long terminal repeat (LTR) is strongly induced in the presence of glucocorticoid hormones. We now demonstrate that, in the presence of dexamethasone, sag gene expression is reduced despite increased transcription from the MMTV 5' LTR and increased amounts of putative sag mRNA initiated at the LTR promoter. These data show that the expression of the MMTV sag gene does not correlate with the activity of the major LTR promoter and thus differs from all other MMTV genes.
authors.affiliation: Deutsches Krebsforschungszentrum, Forschungsschwerpunkt Angewandte Tumorvirologie F0400, 69120 Heidelberg, Germany.
authors.forename: V A
authors.initials: VA
authors.lastname: Tovar Sepúlveda
authors.forename: B
authors.initials: B
authors.lastname: Berdel
authors.forename: J M
authors.initials: JM
authors.lastname: Coffin
authors.forename: F U
authors.initials: FU
authors.lastname: Reuss
mesh_terms: D000818:Animals; D002460:Cell Line; D003907:Dexamethasone / Q000494:pharmacology / Q000627:therapeutic use; D015967:Gene Expression Regulation, Viral / Q000187:drug effects*; D017930:Genes, Reporter / Q000235:genetics; D005814:Genes, Viral / Q000235:genetics*; D005938:Glucocorticoids / Q000494:pharmacology* / Q000627:therapeutic use; D006412:Hematopoietic Stem Cells / Q000187:drug effects / Q000378:metabolism / Q000821:virology; D008324:Mammary Tumor Virus, Mouse / Q000187:drug effects* / Q000235:genetics / Q000276:immunology*; D051379:Mice; D011401:Promoter Regions, Genetic / Q000235:genetics; D011533:Proviruses / Q000187:drug effects / Q000235:genetics / Q000276:immunology; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D012367:RNA, Viral / Q000032:analysis / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics; D018089:Superantigens / Q000235:genetics*; D020079:Terminal Repeat Sequences / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects / Q000235:genetics; D014162:Transfection
chemical_list: D005938:Glucocorticoids; D012333:RNA, Messenger; D012367:RNA, Viral; D011993:Recombinant Fusion Proteins; D018089:Superantigens; D003907:Dexamethasone