Structure of the E6/E6AP/p53 complex required for HPV-mediated degradation of p53

Abstract

Summary The p53 pro-apoptotic tumor suppressor is mutated or functionally altered in most cancers. In epithelial tumors induced by “high-risk” mucosal Human Papillomaviruses (hrm-HPVs), including human cervical carcinoma and a growing number of head-and-neck cancers 1, p53 is degraded by the viral oncoprotein E6 2. In this process, E6 binds to a short LxxLL consensus sequence within the cellular ubiquitin ligase E6AP 3. Subsequently, the E6/E6AP heterodimer recruits and degrades p53 4. Neither E6 nor E6AP are separately able to recruit p53 3,5, and the precise mode of assembly of E6, E6AP and p53 is unknown. Here, we solved the crystal structure of a ternary complex comprising full-length HPV16 E6, the LxxLL motif of E6AP and the core domain of p53. The LxxLL motif of E6AP renders the conformation of E6 competent for interaction with p53 by structuring a p53-binding cleft on E6. Mutagenesis of critical positions at the E6-p53 interface disrupts p53 degradation. The E6-binding site of p53 is distal from previously described DNA- and protein-binding surfaces of the core domain. This suggests that, in principle, E6 may avoid competition with cellular factors by targeting both free and bound p53 molecules. The E6/E6AP/p53 complex represents a prototype of viral hijacking of both the ubiquitin-mediated protein degradation pathway and the p53 tumor suppressor pathway. The present structure provides a framework for the design of inhibitory therapeutic strategies against HPV-mediated oncogenesis.

Low risk HPV‑6E6 induces apoptosis in bone marrow‑derived dendritic cells

“…However, it has also been identified that low-risk HPV-E6 binds to the C-terminal region of p53, which does not initiate p53 degradation (16). The results of the present study support the latter observation and suggest that low-risk HPV-E6 cannot degrade p53, which may be the primary reason that infection with low-risk HPV does not lead to the development of malignant cancer (17,18). Furthermore, DC exposure to low-risk HPV-6E6 induces apoptosis via the upregulation of apoptosis-associated proteins, including p53, Bax, Bak and cytochrome c. This is supported by the results of a study by Manjarrez et al (19) who demonstrated that p53 levels were higher in papillomatosis than in normal larynxes.…”

Novel ß-HPV49 Transgenic Mouse Model of Upper Digestive Tract Cancer

“…We found that Arg55 and Arg131 of HPV16 E6, which provide crucial contacts to acidic residues of the LxxLL peptide of E6AP (25), are conserved (at least as positively charged residues) in HPV49 E6, but not in HPV38 E6. Similarly, the key p53-binding residue Asp49 (26) is conserved in HPV49, whereas it becomes an Asn residue in HPV38 E6 ( Supplementary Fig. S3).…”

HPV-mediated inactivation of tumor suppressor p53

“…More recently, we were able to solve the crystal structure of a minimal ternary complex, comprising HPV16 E6, e6ap and the core (or DNA binding) domain of p53 (called p53core from hereon) 6 (Fig. 1, top and middle).…”