TRANS ACTIVATION BY THE FULL-LENGTH E2 PROTEINS OF HUMAN PAPILLOMAVIRUS TYPE-16 AND BOVINE PAPILLOMAVIRUS TYPE-1 IN-VITRO AND IN-VIVO - COOPERATION WITH ACTIVATION DOMAINS OF CELLULAR TRANSCRIPTION FACTORS

Papillomaviral E2 genes encode proteins that regulate viral transcript ion. While the full-length bovine papillomavirus type 1 (BPV-1) E2 pep tide is a strong trans activator, the homologous full-length E2 produc t of human papillomavirus type 16 (HPV-16) appeared to vary in functio n in previous studies. Here we show that when expressed from comparabl e constructs, the full-length E2 products of HPV-16 and BPV-1 trans ac tivate a simple E2- and Sp1-dependent promoter up to similar to 100-fo ld in human keratinocytes and other epithelial cells as well as human and animal fibroblasts. Vaccinia virus expressed, purified full-length HPV-16 rind BPV-1 E2 proteins bound a consensus E2 site with high spe cific affinities (K-d = similar to 10(-9) M) and stimulated in vitro t ranscription up to six- to eightfold. In vivo and in vitro trans activ ation by either E2 protein required cooperation with another activator , such as Sp1, or other factors that interact with papillomavirus prom oters, such as AP-1, Oct-1, nuclear factor 1/CTF, transcriptional enha ncer factor 1, or USF. The glutamine-rich domain B of Sp1 or the mutua lly unrelated activation domains of other transcription factors were n ecessary and sufficient for cooperation with either E2 factor. We conc lude that like BPV-1 E2, the HPV-16 E2 protein has the potential to fu nction as a strong activator of viral gene expression in cooperation w ith cellular transcription factors.