A Functional interaction between the human papillomavirus 16 transcription/replication factor E2 and the DNA damage response protein TopBP1.

The human papillomavirus (HPV) transcription/replication factor E2 is essential for the life cycle of HPVs. E2 protein binds to DNA target sequences in the viral long control regions to regulate transcription of the viral genome. It also enhances viral DNA replication by interacting with the viral replication factor E1 and recruiting it to the origin of replication and may also play a more direct role in replication. The cellular proteins with which E2 interacts to carry out these functions are largely unknown. To identify these proteins a yeast two-hybrid screen was carried out with the transcription/replication domain of HPV16 E2. This screen identified several candidate interacting partners for E2 including TopBP1 (topoisomerase II beta-binding protein 1). TopBP1 has eight BRCA1 carboxyl-terminal domains that are found in proteins regulating the DNA damage response, transcription, and replication. Here we demonstrate that HPV16 E2 and TopBP1 interact in vitro and in vivo and that TopBP1 can enhance the ability of E2 to activate transcription and replication. This is the first time that TopBP1 has been shown to function as a transcriptional coactivator and that E2 interacts with TopBP1. Removal of the amino-terminal domain of TopBP1 abolishes coactivation of transcription and replication. This interaction may have functional consequences upon the viral life cycle.