Overproduction of NFKB2 (lyt-10) and c-Rel: a mechanism for HTLV-I Tax-mediated trans-activation via the NF-kappa B signalling pathway. 
Molecular, biochemical and epidemiological evidence implicate HTLV-I as an etiologic agent of adult T cell leukemia (ATL). The Tax protein of HTLV-I, a positive transcriptional activator of HTLV-I gene expression, is a viral oncogene that also increases transcription of cellular genes including GM-CSF, IL-2R alpha and IL-2. One of the cellular targets of the trans-activating effects of Tax is the NF-kappa B/Rel family of transcription factors, pleiotropic regulators of immunoregulatory, cytokine and viral gene expression. In this report, we demonstrate that NFKB2 (lyt-10) and c-Rel are overexpressed in HTLV-I infected and Tax-expressing cells and, together, account for the majority of the constitutive NF-kappa B binding activity in these cells before and after PMA stimulation. Most importantly, we show a Tax-dependent correlation between expression of NFKB2(p100) and processing to the DNA binding NFKB2(p52) form, induction of c-Rel, and trans-activation of NF-kappa B-mediated gene expression. Furthermore, the NFKB2 precursor is physically associated with c-Rel and with Tax in HTLV-I infected cells. We propose that NFKB2 synthesis and processing allows continuous nuclear expression of an otherwise cytoplasmic protein and, in conjunction with overexpression of c-Rel, NFKB2 alters the NF-kappa B signalling pathway and contributes to leukemic transformation of T cells by HTLV-I.