PHYSICAL AND FUNCTIONAL INTERACTION BETWEEN THE HUMAN T-CELL LYMPHOTROPIC VIRUS TYPE-1 TAX(1) PROTEIN AND THE CCAAT BINDING-PROTEIN NF-Y

Tax(1), a potent activator of human T-cell lymphotropic virus type 1 ( HTLV-1) transcription, has been shown to modulate expression of many c ellular genes. Tax(1) does not bind DNA directly but regulates transcr iption through protein-protein interactions with sequence-specific tra nscription factors. Using the yeast two-hybrid system to screen for pr oteins which interact with Tax(1), we isolated the B subunit of the CC AAT binding protein NF-Y from a HeLa cDNA library. The interaction of Tax(1) with NF-YB was specific in that NF-YB did not interact with a v ariety of other transcription factors, including human immunodeficienc y virus Tat, human papillomavirus E6, and Bicoid, or with the M7 (amin o acids (CP)-C-29-AS) Tax(1) mutant. However, NF-YB did interact,vith the C-terminal Tax(1) mutants M22 ((130)TL-AS) and M47 ((319)LL-RS). W e also show that in vitro-translated NF-YB specifically bound to a glu tathione S-transferase-Tax(1) fusion protein. Further, Tax(1) coimmuno precipitated with NF-Y from nuclear extracts of HTLV-1-transformed cel ls, providing evidence for in vivo interaction of Tax(1) and NF-YB. We further demonstrate that Tax(1) specifically activated the NF-Y-respo nsive DQ beta promoter, as well as a minimal promoter which contains o nly the Y-box element. In addition, mutation of the Y-box element alon e abrogated Tax(1)-mediated activation. Taken together, these data ind icate that Tax(1) interacts with NF-Y through the B subunit and that t his interaction results in activation of the major histocompatibility complex class II promoter. Through activation of this and other NF-Y d riven promoters, the Tax(1)-NF-Y interaction may play a critical role in causing cellular transformation and HTLV-1 pathogenesis.