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Induction of Bcl-x(L) expression by human T-cell leukemia virus type 1 Tax through NF-kappaB in apoptosis-resistant T-cell transfectants with Tax.


J Virol. 1999 Oct;73(10):7981-7. Unique Identifier : AIDSLINE

Human T-cell leukemia virus type 1 (HTLV-1) Tax is thought to play a pivotal role in immortalization of T cells. We have recently shown that the expression of Tax protected the mouse T-cell line CTLL-2 against apoptosis induced by interleukin-2 (IL-2) deprivation and converted its growth from being IL-2 dependent to being IL-2 independent. In this study, we demonstrate that constitutive expression of bcl-xl but not bcl-2, bcl-xs, bak, bad, or bax was associated with apoptosis resistance after IL-2 deprivation in CTLL-2 cells that expressed Tax. Transient-transfection assays showed that bcl-x promoter was transactivated by wild-type Tax. Similar effects were observed in mutant Tax retaining transactivating ability through NF-kappaB. Deletion or substitution of a putative NF-kappaB binding site identified in the bcl-x promoter significantly decreased Tax-induced transactivation. This NF-kappaB-like element was able to form a complex with NF-kappaB family proteins in vitro. Furthermore, Tax-induced transactivation of the bcl-x promoter was also diminished by the mutant IkappaBalpha, which specifically inhibits NF-kappaB activity. Our findings suggest that constitutive expression of Bcl-x(L) induced by Tax through the NF-kappaB pathway contributes to the inhibition of apoptosis in CTLL-2 cells after IL-2 deprivation.

JOURNAL ARTICLE Animal *Apoptosis/GENETICS Cell Line Gene Expression Regulation, Viral/*PHYSIOLOGY Gene Products, tax/*BIOSYNTHESIS/GENETICS Human HTLV-I/*PHYSIOLOGY Mice NF-kappa B/*GENETICS Proto-Oncogene Proteins c-bcl-2/*BIOSYNTHESIS/GENETICS Support, Non-U.S. Gov't T-Lymphocytes/PATHOLOGY/PHYSIOLOGY/*VIROLOGY Transfection


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