Abstract
The papillomavirus E2 protein is involved in the maintenance of persistent infection and known to bind either to cellular factors or directly to mitotic chromosomes in order to partition the viral genome into the daughter cells. However, how the HPV-16 E2 protein acts to facilitate partitioning of the viral genome remains unclear. In this study, we found that serine 243 of HPV-16 E2, located in the hinge region, is crucial for chromosome binding during mitosis. Bromodomain protein 4 (Brd4) has been identified as a cellular binding target through which the E2 protein of bovine papillomavirus type 1 (BPV-1) tethers the viral genome to mitotic chromosomes. Mutation analysis showed that, when the residue serine 243 was substituted by glutamic acid or aspartic acid, whose negative charges mimic the effect of constitutive phosphorylation, the protein still can interact with Brd4 and colocalize with Brd4 in condensed metaphase and anaphase chromosomes. However, substitution by the polar uncharged residues asparagine or glutamine abrogated Brd4 and mitotic chromosome binding. Moreover, following treatment with the inhibitor JQ1 to release Brd4 from the chromosomes, Brd4 and E2 formed punctate foci separate from the chromosomes, further supporting the hypothesis that the association of the HPV-16 E2 protein with the chromosomes is Brd4-dependent. In addition, the S243A E2 protein has a shorter half-life than the wild type, indicating that phosphorylation of the HPV-16 E2 protein at serine 243 also increases its half-life. Thus, phosphorylation of serine 243 in the hinge region of HPV-16 E2 is essential for interaction with Brd4 and required for host chromosome binding.
Highlights
Papillomaviruses (PVs) are small, double-stranded DNA viruses that infect squamous epithelial cells and cause persistently infected lesions known as papillomas or warts
Based on the results of MALDI-TOF analysis, we found two phosphoacceptor residues at serine 207 and serine 243 in the hinge region, which is located from positions 202 to 286 in the human papillomavirus (HPV)-16 E2 protein (Fig. 1B; Fig. S1)
To elucidate whether these two residues are critical for chromosome binding by the HPV-16 E2 protein, we substituted each of these serine residues with alanine in the background of the full-length HPV-16 protein, to eliminate phosphorylation, and examined the localization of these E2 proteins on the mitotic chromosomes by confocal microscopy
Summary
Papillomaviruses (PVs) are small, double-stranded DNA viruses that infect squamous epithelial cells and cause persistently infected lesions known as papillomas or warts. The viral E2 protein plays an important role in ensuring that the viral genomes are retained within the nucleus of the infected cell and are partitioned into the daughter cells during each round of cell division, by tethering the viral DNA to the host chromosomes. This mechanism helps maintain persistent infection of the host cells, so that the dividing basal cells can provide a reservoir of infected cells that migrate up to replenish the overlying, virus-producing, differentiated layers [4,5,6]. The N-terminal transactivation domain is important for the regulation of transcription and interacts with many cellular transcriptional regulatory factors, including TFIIB, NAP-1, p300/CBP, p/CAF, GR, NRIP and Brd4 [10,11,12,13,14,15,16,17]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
