Interaction between the HPV-16 E2 transcriptional activator and p53

The HPV-16 E2 protein is a major regulator of viral DNA replication and gen e expression. Through interactions with the viral origin binding protein, E l, it localizes El to the origin of replication and stimulates the initiati on of viral DNA replication. However, several recent reports have described a number of diverse activities of E2 relating to the induction of apoptosi s through both p53 dependent and independent mechanisms, and to induction o f growth arrest in both the G1 and G2M phases of the cell cycle. Recent stu dies have also shown that p53 can specifically inhibit HPV DNA replication, albeit through an unknown mechanism. Since p53 has been described in the r eplication centres of Herpes Viruses, Adenovirus and SV40 we decided to inv estigate whether any of the above activities of E2 may be related to an ass ociation with p53. We show, in a series of in vitro assays, specific intera ction between p53 and HPV-16 E2 via residues in the carboxy terminal half o f the E2 protein. Mutational analysis of p53 indicates that sequences in bo th the DIVA binding and oligomerization domains are essential for the inter action, and a mutant of p53 which is unable to bind E2 is also unable to in hibit HPV DNA replication. Finally, using an inducible system of p53 expres sion we also show that E2 will complex with p53 in vivo. These results rais e the intriguing possibility that p53 may also be involved in HPV DNA repli cation centres, and also provides explanations for some of the diverse acti vities reported for the HPV E2 proteins.