Decades of research on the human papillomavirus oncogenes, E6 and E7, have given us huge amounts of data on their expression, functions and structures. We know much about the very many cellular proteins and pathways that they influence in one way or another. However, much of this information is quite discrete, referring to one activity examined under one condition. It is now time to join the dots to try to understand a larger picture: how, where and when do all these interactions occur... and why? Examining these questions will also show how many of the yet obscure cellular processes work together for cellular and tissue homeostasis in health and disease.

The high-risk Human Papillomavirus (HPV) E6 oncoprotein is known to contribute to human malignancy by targeting several of its cellular substrates through the ubiquitin-mediated degradation pathway. Previous studies have revealed that E6 interacts with the E6AP ubiquitin-protein ligase and directs its ubiquitylation activity toward several specific cellular proteins, one of the most important of which is p53. However, the role of E6AP in the degradation of many other E6 substrates is still ambiguous because loss of E6AP also induces a loss of E6 expression. To examine this further, we used CRISPR-edited E6AP knockout cells to perform E6 degradation assays in the presence of a catalytically inactive mutant form of E6AP, thus ensuring the stabilization of E6 but with the ligase itself being functionally inactive. Using this system, we found that E6 can mediate the degradation of several PDZ domain-containing proteins independently of E6AP ubiquitin ligase activity. This study thus opens up ways to investigate other possible components of the cellular ubiquitin proteasome pathway that E6 might utilize to target these substrates.

Human papillomavirus (HPV) is the leading cause of cervical cancer and has been implicated in several other cancer types including vaginal, vulvar, penile, and oropharyngeal cancers. Despite the recent availability of a vaccine, there are still over 310,000 deaths each year worldwide. Current treatments for HPV-mediated cancers show limited efficacy, and would benefit from improved understanding of disease mechanisms. Recently, we developed a Drosophila ‘HPV 18 E6’ model that displayed loss of cellular morphology and polarity, junctional disorganization, and degradation of the major E6 target Magi; we further provided evidence that mechanisms underlying HPV E6-induced cellular abnormalities are conserved between humans and flies. Here, we report a functional genetic screen of the Drosophila kinome that identified IKK$$\beta$$ β —a regulator of NF-κB—as an enhancer of E6-induced cellular defects. We demonstrate that inhibition of IKK$$\beta$$ β reduces Magi degradation and that this effect correlates with hyperphosphorylation of E6. Further, the reduction in IKK$$\beta$$ β suppressed the cellular transformation caused by the cooperative action of HPVE6 and the oncogenic Ras. Finally, we demonstrate that the interaction between IKK$$\beta$$ β and E6 is conserved in human cells: inhibition of IKK$$\beta$$ β blocked the growth of cervical cancer cells, suggesting that IKK$$\beta$$ β may serve as a novel therapeutic target for HPV-mediated cancers.

This is the first demonstration that E6AP can directly help stabilize the HPV E7 oncoprotein, in a manner similar to that observed with HPV E6. This redefines how E6 and E7 can cooperate and potentially modulate each other’s activity and further highlights the essential role played by E6AP in the viral life cycle and malignancy.