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Molecular and Cellular Biology, November 2000, p. 8580-8589, Vol. 20, No. 22
0270-7306/00/$04.00+0

Distinct p300-Responsive Mechanisms Promote Caspase-Dependent Apoptosis by Human T-Cell Lymphotropic Virus Type 1 Tax Protein

Christophe Nicot* and Robert Harrod

Basic Research Laboratory, Division of Basic Sciences, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892

Received 2 May 2000/Returned for modification 9 June 2000/Accepted 21 August 2000

The dysregulation of cellular apoptosis pathways has emerged as a critical early event associated with the development of many types of human cancers. Numerous viral and cellular oncogenes, aside from their inherent transforming properties, are known to induce programmed cell death, consistent with the hypothesis that genetic defects are required to support tumor survival. Here, we report that nuclear expression of the CREB-binding protein (CBP)/p300-binding domain of the human T-cell lymphotropic virus type 1 (HTLV-1) transactivator, Tax, triggers an apoptotic death-inducing signal during short-term clonal analyses, as well as in transient cell death assays. Coexpression of the antiapoptotic factor Bcl-2 increased serum stimulation; incubation with the chemical caspase inhibitor z-Val-Ala-DL-Asp fluoromethylketone antagonized Tax-induced cell death. The CBP/p300-binding defective Tax mutants K88A and V89A exhibited markedly reduced cytotoxic effects compared to the wild-type Tax protein. Importantly, nuclear expression of the minimal CBP/p300-binding peptide of Tax induced apoptosis in the absence of Tax-dependent transcriptional activities, while its K88A counterpart did not cause cell death. Further, Tax-mediated apoptosis was effectively prevented by ectopic expression of the p300 coactivator. We also report that activation of the NF-kappa B transcription pathway by Tax, under growth arrest conditions, results in apoptosis that occurs independent of direct Tax coactivator effects. Our results allude to a novel pivotal role for the transcriptional coactivator p300 in determining cell fate and raise the possibility that dysregulated coactivator usage may pose an early barrier to transformation that must be selectively overcome as a prerequisite for the initiation of neoplasia.

* Corresponding author. Mailing address: Basic Research Laboratory, Division of Basic Sciences, National Cancer Institute, National Institutes of Health, Building 41, Room D804, 9000 Rockville Pike, Bethesda, MD 20892. Phone: (301) 402-0303. Fax: (301) 402-0055. E-mail: cbeben{at}helix.nih.gov.

Molecular and Cellular Biology, November 2000, p. 8580-8589, Vol. 20, No. 22
0270-7306/00/$04.00+0


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