Purification and characterisation of the E7 oncoproteins of the high-risk human papillomavirus types 16 and 18.

E7 proteins are major oncoproteins of human papillomaviruses (HPVs) which play a key role in virus-associated cervical carcinogenesis. The E7 oncoprotein of HPV-16 has been shown to interact with a variety of cellular target proteins and these interactions are considered essential for the transforming properties of this oncoprotein. Several additional HPV types associated etiologically to cervical cancer have been described, the second most common being HPV-18. Less is known about the biochemical functions and interactions of HPV-18 E7. As a first step to determine biochemical properties common to the E7 proteins of the high-risk HPV types 16 and 18 these E7 proteins were expressed in bacteria and purified to homogeneity. Purified E7 proteins were used to investigate the in vitro interaction with the pocket protein p107 and insulin-like growth factor-binding protein-3 (IGFBP-3) that are known to interact with the amino-terminal and the carboxyl-terminal part of IGFBP-3, respectively. Both purified E7 proteins interacted strongly with p107 and, as demonstrated here for the first time, HPV-18 E7 was capable of binding to IGFBP-3, albeit to a lesser extent than HPV-16 E7. These findings suggest that the purified recombinant E7 proteins retain, at least in part, their biochemical activities.