Constitutive Activation of NF-κB in Primary Adult T-Cell Leukemia Cells

Abstract

AbstractHuman 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-κB, 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-κB 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-κB DNA binding activity and increased degradation of IκBα (an inhibitor of NF-κB). Whereas the NF-κB 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-κB activity, as well as enhanced degradation of IκBα, despite the lack of detectable Tax expression. Interestingly, the NF-κB in TL-Om1 consists of p50/p50 and p50/p65 like that in fresh primary leukemic cells. Our results suggest that activation of NF-κB occurs through a Tax-independent mechanism in leukemic cells of ATL patients, possibly due to differential NF-κB subunit activation.