Human T-Lymphotropic Virus Type 1 p30 II Regulates Gene Transcription by Binding CREB Binding Protein/p300

The highly conserved coadapters CREB binding protein (CBP) and p300 form complexes with CREB as well as other DNA binding transcription factors to modulate chromatin remodeling and thus transcription. Human T-lymphotropic virus type 1 (HTLV-1) transcription is controlled, in part, by the CREB/ATF family of transcription factors which bind promoter sequences and function as complexes with the viral oncogenic protein Tax. We have reported that the nuclear localizing protein p30 II of HTLV-1 functions as a transcription factor, differentially modulates CREB-responsive promoters, and is critical for maintenance of proviral loads in rabbits. In this study, we tested whether p30 II directly interacts with CBP/p300 to modulate gene transcription. Gal4(BD)-p30 II -mediated transactivation was enhanced following exogenous expression of p300 and was competitively repressed by the p300 binding protein, adenovirus E1A, and E1ACR2 (mutated for retinoblastoma binding but retaining p300 binding). In contrast, E1ACR1 (mutated for p300 binding) failed to alter Gal4(BD)-p30 II -mediated transactivation. In addition, Gal4(BD)-p30 II -mediated transactivation was competitively inhibited by the cotransfection of CMV-p30 II -HA and CMV-Tax but could be rescued by exogenous p300. Importantly, we demonstrate that p30 II colocalizes with p300 in cell nuclei and directly binds to CBP/p300 in cells. Deletion mutants of CBP/p300 were used to localize the site critical for binding p30 II to a highly conserved KIX region. DNA binding assays confirmed the interference of p30 II with the assembly of CREB-Tax-p300/CBP multiprotein complexes on 21-bp repeat oligonucleotides in vitro. Collectively, our results demonstrate that CBP/p300 is a cellular protein target for HTLV-1 p30 II and mediates its transcriptional effects in vivo.