Mitotic control of human papillomavirus genome-containing cells is regulated by the function of the PDZ-binding motif of the E6 oncoprotein
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Elizabeth K. Marsh1,4, Craig P. Delury1, Nicholas J. Davies1, Christopher J. Weston2, Mohammed A. L. Miah1, Lawrence Banks3, Joanna L. Parish1, Martin R. Higgs1,*, Sally Roberts1,*
1Institute of Cancer and Genomic Sciences, University of Birmingham, Birmingham, United Kingdom
2Institute of Immunology and Immunotherapy, University of Birmingham, Birmingham, United Kingdom
3International Centre for Genetic Engineering and Biotechnology, Padriciano, Trieste, Italy
4Present address: Faculty of Medicine, Dentistry and Health, University of Sheffield, Sheffield, United Kingdom
*These authors have contributed equally to this work
Sally Roberts, email: [email protected]
Keywords: human papillomavirus, E6, PDZ proteins, HPV life cycle, mitosis
Received: August 26, 2016 Accepted: December 18, 2016 Published: January 03, 2017
The function of a conserved PDS95/DLG1/ZO1 (PDZ) binding motif (E6 PBM) at the C-termini of E6 oncoproteins of high-risk human papillomavirus (HPV) types contributes to the development of HPV-associated malignancies. Here, using a primary human keratinocyte-based model of the high-risk HPV18 life cycle, we identify a novel link between the E6 PBM and mitotic stability. In cultures containing a mutant genome in which the E6 PBM was deleted there was an increase in the frequency of abnormal mitoses, including multinucleation, compared to cells harboring the wild type HPV18 genome. The loss of the E6 PBM was associated with a significant increase in the frequency of mitotic spindle defects associated with anaphase and telophase. Furthermore, cells carrying this mutant genome had increased chromosome segregation defects and they also exhibited greater levels of genomic instability, as shown by an elevated level of centromere-positive micronuclei. In wild type HPV18 genome-containing organotypic cultures, the majority of mitotic cells reside in the suprabasal layers, in keeping with the hyperplastic morphology of the structures. However, in mutant genome-containing structures a greater proportion of mitotic cells were retained in the basal layer, which were often of undefined polarity, thus correlating with their reduced thickness. We conclude that the ability of E6 to target cellular PDZ proteins plays a critical role in maintaining mitotic stability of HPV infected cells, ensuring stable episome persistence and vegetative amplification.
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