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    Retrovirology. 2009 Apr 8;6:35.

    Induction of p21(CIP1/WAF1) expression by human T-lymphotropic virus type 1 Tax requires transcriptional activation and mRNA stabilization.

    Zhang L, Zhi H, Liu M, Kuo YL, Giam CZ.

    Department of Microbiology and Immunology, Uniformed Services University, Bethesda, MD 20814, USA. zhangling@mail.nih.gov

    HTLV-1 Tax can induce senescence by up-regulating the levels of cyclin-dependent kinase inhibitors p21(CIP1/WAF1) and p27(KIP1). Tax increases p27(KIP1) protein stability by activating the anaphase promoting complex/cyclosome (APC/C) precociously, causing degradation of Skp2 and inactivation of SCF(Skp2), the E3 ligase that targets p27(KIP1). The rate of p21(CIP1/WAF1) protein turnover, however, is unaffected by Tax. Rather, the mRNA of p21(CIP1/WAF1) is greatly up-regulated. Here we show that Tax increases p21 mRNA expression by transcriptional activation and mRNA stabilization. Transcriptional activation of p21(CIP1/WAF1) by Tax occurs in a p53-independent manner and requires two tumor growth factor-beta-inducible Sp1 binding sites in the -84 to -60 region of the p21(CIP1/WAF1) promoter. Tax binds Sp1 directly, and the CBP/p300-binding activity of Tax is required for p21(CIP1/WAF1) trans-activation. Tax also increases the stability of p21(CIP1/WAF1) transcript. Several Tax mutants trans-activated the p21 promoter, but were attenuated in stabilizing p21(CIP1/WAF1) mRNA, and were less proficient in increasing p21(CIP1/WAF1) expression. The possible involvement of Tax-mediated APC/C activation in p21(CIP1/WAF1) mRNA stabilization is discussed.

    PMID: 19356250 [PubMed - indexed for MEDLINE]

    PMCID: PMC2676247

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