Human T-cell leukemia virus type 1 tax protein activates transcription through AP-1 site by inducing DNA binding activity in T cells.
Human T-cell leukemia virus type 1 (HTLV-1) Tax protein induces the expression of various family members of the transcription factor AP-1, such as c-Jun, JunD, c-Fos, and Fra-1, at the level of RNA expression in T cells. We examined the activity of Tax in transcription through AP-1-binding sites (AP-1 site) in T cells. Transient transfection studies showed that Tax activated the expression of a luciferase gene regulated by two copies of an AP-1 site in the human Jurkat T-cell line. Tax activates the expression of viral and cellular genes through two different enhancers: a cAMP-responsive (CRE)-like element and a kappaB element. Two Tax mutants differentially activated expression of these two elements. Tax703 preferentially activated the kappaB element but not the CRE-like one, whereas TaxM22 showed the reverse. In addition, Tax703 and Tax, but not TaxM22, converted cell growth of a mouse T-cell line from being interleukin (IL)-2-dependent to being IL-2-independent. Unlike the wild-type Tax, Tax703 and TaxM22 only weakly activated the AP-1 site in the T-cell line. Thus, Tax seems to activate the AP-1 site via mechanisms distinct from those of kappaB or CRE-like elements, and the activation of the AP-1 site is dispensable for IL-2-independent growth of CTLL-2. Electrophoretic mobility shift assays showed that Tax induced strong binding activity to an AP-1 site in CTLL-2, whereas Tax703 did not, indicating that the induction of binding activity to the AP-1 site is essential for the transcriptional activation by Tax. The binding complex induced by Tax in CTLL-2 contained JunD and Fra-2. Other AP-1 proteins were undetectable. Activation of transcription through the AP-1 site in Jurkat cells by JunD and/or Fra-2 was weak. c-Jun, JunB, and c-Fos activation was greater, although the level was still less than that with Tax. Thus, the induction of AP-1 mRNA by Tax may not be sufficient for a complete activation of AP-1 site by Tax. Our results suggest that Tax activates the transcription of cellular genes with AP-1 sites by inducing the DNA-binding activity of AP-1 proteins in T cells, a mechanism distinct from those of CRE-like and kappaB elements.
Iwai
K
K
Department of Virology, Niigata University School of Medicine, 1-757 Asahimachi-Dori, Niigata, 951-8510, Japan.
Mori
N
N
Oie
M
M
Yamamoto
N
N
Fujii
M
M
D000818:Animals; D001665:Binding Sites; D015153:Blotting, Western; D002461:Cell Line, Transformed; D002472:Cell Transformation, Viral; D004247:DNA / Q000378:metabolism*; D016356:Gene Products, tax / Q000235:genetics / Q000378:metabolism*; D016762:Genes, fos / Q000235:genetics / Q000502:physiology; D016758:Genes, jun / Q000235:genetics / Q000502:physiology; D015368:Human T-lymphotropic virus 1 / Q000378:metabolism*; D006801:Humans; D019169:Jurkat Cells; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D051379:Mice; D012333:RNA, Messenger / Q000378:metabolism; D013601:T-Lymphocytes / Q000378:metabolism*; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D014162:Transfection
D016356:Gene Products, tax; D012333:RNA, Messenger; D018808:Transcription Factor AP-1; D004247:DNA; D008156:Luciferases