The tax protein of human T-cell leukemia virus type 1 mediates the transactivation of the c-sis/platelet-derived growth factor-B promoter through interactions with the zinc finger transcription factors Sp1 and NGFI-A/Egr-1.
Transcriptional up-regulation of the c-sis/platelet-derived growth factor-B (PDGF-B) proto-oncogene by the Tax protein of human T-cell leukemia virus type 1 has been implicated as one possible mechanism of cellular transformation by human T-cell leukemia virus type 1. In previous work, we identified an essential site in the c-sis/PDGF-B promoter, Tax-responsive element 1 (TRE1), necessary for transactivation by Tax. We also identified Sp1, Sp3, and NGFI-A/Egr-1 as the primary nuclear transcription factors binding to TRE1 which mediate Tax responsiveness. In the present work, we have investigated the mechanism(s) whereby Tax transactivates the c-sis/PDGF-B proto-oncogene. In vitro transcription assays showed that Tax was able to significantly increase the transcriptional activity of a template containing the -257 to +74 region of the c-sis/PDGF-B promoter. Electrophoretic mobility shift assay analysis showed that Tax increased the DNA binding activity of both Sp1 and NGFI-A/Egr-1 using a TRE1 probe. Analysis of Tax mutants showed that two mutants, IEXC29S and IEXL320G, were unable to significantly transactivate the c-sis/PDGF-B promoter. Finally, co-immunoprecipitation analysis revealed that Tax is able to stably bind to both Sp1 and NGFI-A/Egr-1. Interestingly, co-immunoprecipitation analysis also revealed that Tax mutant IEXC29S is unable to interact with NGFI-A/Egr-1, whereas Tax mutant IEXL320G is able to interact with NGFI-A/Egr-1.
Trejo
S R
SR
Division of Molecular Oncology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Fahl
W E
WE
Ratner
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L
D001483:Base Sequence; D001665:Binding Sites; D016384:Consensus Sequence; D004268:DNA-Binding Proteins / Q000378:metabolism*; D051766:Early Growth Response Protein 1; D016356:Gene Products, tax / Q000378:metabolism*; D017930:Genes, Reporter; D015368:Human T-lymphotropic virus 1 / Q000378:metabolism*; D006801:Humans; D017874:Immediate-Early Proteins; D008156:Luciferases; D009838:Oligodeoxyribonucleotides; D010982:Platelet-Derived Growth Factor / Q000096:biosynthesis* / Q000235:genetics; D011401:Promoter Regions, Genetic; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis* / Q000235:genetics; D020574:Proto-Oncogene Proteins c-sis; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D013601:T-Lymphocytes; D013698:Templates, Genetic; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D014407:Tumor Cells, Cultured; D016335:Zinc Fingers
D004268:DNA-Binding Proteins; C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; D016356:Gene Products, tax; D017874:Immediate-Early Proteins; C000715470:MAS1 protein, human; D009838:Oligodeoxyribonucleotides; D010982:Platelet-Derived Growth Factor; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D020574:Proto-Oncogene Proteins c-sis; D011993:Recombinant Fusion Proteins; D016329:Sp1 Transcription Factor; D014157:Transcription Factors; D008156:Luciferases