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Blood. 1999 Apr 1;93(7):2360-8.

Constitutive activation of NF-kappaB in primary adult T-cell leukemia cells.

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  • 1Department of Preventive Medicine and AIDS Research, Research Field of Pathogenesis and Clinical Sciences, Institute of Tropical Medicine, Nagasaki University, Japan.


Human T-cell leukemia virus type I (HTLV-I) is an etiologic agent of adult T-cell leukemia (ATL). The viral protein Tax induces the activation and nuclear translocalization of transcription factor NF-kappaB, which is proposed to play a crucial role in the transformation of T cells by HTLV-I. However, the HTLV-I genes including Tax are not expressed significantly in primary leukemic cells from ATL patients. In this study, we examined the basis for NF-kappaB activation in freshly isolated leukemic cells from ATL patients. We found that leukemic cells from ATL patients, like HTLV-I-infected T-cell lines, display constitutive NF-kappaB DNA binding activity and increased degradation of IkappaBalpha (an inhibitor of NF-kappaB). Whereas the NF-kappaB binding activity in Tax-expressing T-cell lines consisted mostly of p50/c-Rel, fresh ATL samples contained p50/p50 and p50/p65 heterodimers. One T-cell line derived from ATL leukemic cells, TL-Om1, displayed constitutive NF-kappaB activity, as well as enhanced degradation of IkappaBalpha, despite the lack of detectable Tax expression. Interestingly, the NF-kappaB in TL-Om1 consists of p50/p50 and p50/p65 like that in fresh primary leukemic cells. Our results suggest that activation of NF-kappaB occurs through a Tax-independent mechanism in leukemic cells of ATL patients, possibly due to differential NF-kappaB subunit activation.

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