CK2 Phosphorylation of Human Papillomavirus 16 E2 on Serine 23 Promotes Interaction with TopBP1 and Is Critical for E2 Interaction with Mitotic Chromatin and the Viral Life Cycle

During the human papillomavirus 16 (HPV16) life cycle, the E2 protein interacts with host factors to regulate viral transcription, replication, and genome segregation/retention. Our understanding of host partner proteins and their roles in E2 functions remains incomplete. Here we demonstrate that CK2 phosphorylation of E2 on serine 23 promotes interaction with TopBP1 in vitro and in vivo and that E2 is phosphorylated on this residue during the HPV16 life cycle. We investigated the consequences of mutating serine 23 on E2 functions. E2-S23A (E2 with serine 23 mutated to alanine) activates and represses transcription identically to E2-WT (wild-type E2), and E2-S23A is as efficient as E2-WT in transient replication assays. However, E2-S23A has compromised interaction with mitotic chromatin compared with E2-WT. In E2-WT cells, both E2 and TopBP1 levels increase during mitosis compared with vector control cells. In E2-S23A cells, neither E2 nor TopBP1 levels increase during mitosis. Introduction of the S23A mutation into the HPV16 genome resulted in delayed immortalization of human foreskin keratinocytes (HFK) and higher episomal viral genome copy number in resulting established HFK. Remarkably, S23A cells had a disrupted viral life cycle in organotypic raft cultures, with a loss of E2 expression and a failure of viral replication. Overall, our results demonstrate that CK2 phosphorylation of E2 on serine 23 promotes interaction with TopBP1 and that this interaction is critical for the viral life cycle. IMPORTANCE Human papillomaviruses are causative agents in around 5% of all cancers, with no specific antiviral therapeutics available for treating infections or resultant cancers. In this report, we demonstrate that phosphorylation of HPV16 E2 by CK2 promotes formation of a complex with the cellular protein TopBP1 in vitro and in vivo. This complex results in stabilization of E2 during mitosis. We demonstrate that CK2 phosphorylates E2 on serine 23 in vivo and that CK2 inhibitors disrupt the E2-TopBP1 complex. Mutation of E2 serine 23 to alanine disrupts the HPV16 life cycle, hindering immortalization and disrupting the viral life cycle, demonstrating a critical function for this residue.

Comparison of clinical performance of two high-throughput liquid bead microarray assays, GeneFinder and CareGENE, for cervical screening in the general population

Recently, a clinical need for an improved human papilloma virus (HPV) test that covers a broad range of genotypes has emerged as a valuable primary screening tool for cervical lesions. The liquid bead microarray (LBMA) assay is a recently developed high-throughput platform covering a broad range of genotypes. Here, we compared the clinical performance of two recently developed LBMA assays, GeneFinder^TM HPV Liquid Bead Microarray (GeneFinder) and CareGENE^TM HPV genotyping kit-O (CareGENE), in the Korean general population. A total of 3,148 cervical swabs were tested by the GeneFinder and CareGENE assays. Cases with discrepant results between the two assays were subjected to direct sequencing as a reference method for evaluating the performance of the two LBMA assays. Among all swabs tested, 12.6% showed HPV positivity, and the prevalent HPV genotypes were HPV53, 70, 16, 39, and 51, in that order. The concordance rates between the two assays for the detection of HPV and for genotyping were 96.6% (kappa = 0.836) and 94.5% (kappa = 0.779), respectively. The two LBMA assays showed comparable sensitivity and specificity for HPV detection (GeneFinder: sensitivity 94.4% and specificity 98.7%, CareGENE: sensitivity 89.8% and specificity 99.6%) and for genotyping (GeneFinder: sensitivity 91.0% and specificity 96.6%, CareGENE: sensitivity 90.2% and specificity 99.1%). This is the first demonstration that CareGENE has comparable clinical performance to GeneFinder, which has been established to show excellent performance for screening HPV in previous studies. Both LBMA platforms are thus considered to be valuable tools for HPV detection and genotyping to improve cervical screening in the general population.