title: CREB/ATF-dependent repression of cyclin a by human T-cell leukemia virus type 1 Tax protein.
abstract: Expression of the human T-cell leukemia virus type 1 (HTLV-1) oncoprotein Tax is correlated with cellular transformation contributing to the development of adult T-cell leukemia. Tax has been shown to modulate the activities of several cellular promoters. Existing evidence suggests that Tax need not directly bind to DNA to accomplish these effects but rather that it can act through binding to cellular factors, including members of the CREB/ATF family. Exact mechanisms of HTLV-1 transformation of cells have yet to be fully defined, but the process is likely to include both activation of cellular-growth-promoting factors and repression of cellular tumor-suppressing functions. While transcriptional activation has been well studied, transcriptional repression by Tax, reported recently from several studies, remains less well understood. Here, we show that Tax represses the TATA-less cyclin A promoter. Repression of the cyclin A promoter was seen in both ts13 adherent cells and Jurkat T lymphocytes. Two other TATA-less promoters, cyclin D3 and DNA polymerase alpha, were also found to be repressed by Tax. Interestingly, all three promoters share a common feature of at least one conserved upstream CREB/ATF binding site. In electrophoretic mobility shift assays, we observed that Tax altered the formation of a complex(es) at the cyclin A promoter-derived ATF site. Functionally, we correlated removal of the CREB/ATF site from the promoter with loss of repression by Tax. Furthermore, since a Tax mutant protein which binds CREB repressed the cyclin A promoter while another mutant protein which does not bind CREB did not, we propose that this Tax repression occurs through protein-protein contact with CREB/ATF.
authors.affiliation: Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland 20892-0460, USA.
authors.forename: K V
authors.initials: KV
authors.lastname: Kibler
authors.forename: K T
authors.initials: KT
authors.lastname: Jeang
mesh_terms: D051696:Activating Transcription Factors; D000818:Animals; D001665:Binding Sites; D001798:Blood Proteins / Q000378:metabolism*; D050882:CREB-Binding Protein; D002460:Cell Line; D002461:Cell Line, Transformed; D006224:Cricetinae; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism*; D019925:Cyclin A / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D016356:Gene Products, tax / Q000378:metabolism / Q000494:pharmacology*; D015490:HTLV-I Infections / Q000821:virology; D051548:Histone Acetyltransferases; D015368:Human T-lymphotropic virus 1 / Q000472:pathogenicity / Q000502:physiology*; D006801:Humans; D019169:Jurkat Cells; D009687:Nuclear Proteins / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics / Q000502:physiology; D035381:TATA-Binding Protein Associated Factors; D015534:Trans-Activators; D035362:Transcription Factor TFIID; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D051696:Activating Transcription Factors; D001798:Blood Proteins; D017362:Cyclic AMP Response Element-Binding Protein; D019925:Cyclin A; D004268:DNA-Binding Proteins; D016356:Gene Products, tax; D009687:Nuclear Proteins; D035381:TATA-Binding Protein Associated Factors; D015534:Trans-Activators; D035362:Transcription Factor TFIID; D014157:Transcription Factors; D050882:CREB-Binding Protein; C494363:CREBBP protein, human; D051548:Histone Acetyltransferases; C069001:TATA-binding protein associated factor 250 kDa