Hpv E5: An Enigmatic Oncoprotein

Mucosal papillomaviruses contain a short open reading frame (ORF) at the 3' end of the early region, termed E5. The E5 protein is a hydrophobic, membrane-integrated protein that localizes to the endoplasmic reticulum, Golgi apparatus, endosomes and the nuclear envelope. Structural similarity to the bovine papillomavirus (BPV-1) E5 protein prompted an examination of the transforming abilities of human papillomavirus (HPV) E5, which revealed E5 to be a third oncoprotein encoded by HPV. In comparison to E6 and E7, less is understood of the role that E5 plays in host transformation and the HPV life cycle. Although recent findings have increased our knowledge of E5, the field is controversial and there is much work to be accomplished before we fully understand the many functions of this protein. This chapter summarizes our latest understanding of the HPV E5 protein and its interactions with host cells, demonstrating that this protein is indeed of critical importance for HPV and worthy of further investigation.