Human Papillomavirus 31 Tyrosine 102 Regulates Interaction with E2 Binding Partners and Episomal Maintenance.

Several serine and threonine residues of the papillomavirus early E2 protein have been found to be phosphorylated. In contrast, only one E2 tyrosine phosphorylation site in BPV-1 (tyrosine 102) and one in HPV-16/31 (tyrosine 138) site have been characterized. Between BPV-1 and HPV-31 E2, 8 of the 11 tyrosines are conserved in the N-terminal domain, suggesting that phosphorylation of tyrosines has an essential role in E2 biology. In this study, we examine the effect of Y102 phosphorylation on HPV-31 E2 biology. Y102 proteins mutated either to the potential phospho-mimetic glutamic acid (Y102E) or to the nonphosphorylated homologue phenylalanine (Y102F) remain nuclear; however, Y102E is more associated with the nuclear matrix fraction. This is consistent with the inability of Y102E to bind TopBP1. Both BPV-1 and HPV-31 Y102E are similar in that neither binds the C terminus of Brd4, but in all other aspects the mutant behaves differently between the two families of papillomaviruses. BPV-1 Y102E was unable to bind E1 and did not replicate in a transient assay, while HPV-31 Y102E binds E1 and was able to replicate, albeit at lower levels than wild type. To examine the effect of E2 mutations under more native-like infection conditions, a neomycin-selectable marker was inserted into L1/L2 of the HPV-31 genome, creating HPV-31neo. This genome was maintained in every cell line tested for at least 50 days posttransfection/infection. Y102E in both transfection and infection conditions was unable to maintain high episome copy numbers in epithelial cell lines. Posttranslational modifications by phosphorylation can change protein activities, binding partners, or localization. Tyrosine 102 is conserved between delta papillomavirus BPV-1 and alpha papillomavirus HPV-31 E2. We characterized mutations of HPV-31 E2 for interactions with relevant cellular binding partners and replication in the context of the viral genome.