The Causes and Consequences of DNA Damage and Chromosomal Instability Induced by Human Papillomavirus

Abstract

High-risk human papillomaviruses (HPVs) are the main cause of cervical, oropharyngeal, and anogenital cancers, which are all treated with definitive chemoradiation therapy when locally advanced. HPV proteins are known to exploit the host DNA damage response to enable viral replication and the epithelial differentiation protocol. This has far-reaching consequences for the host genome, as the DNA damage response is critical for the maintenance of genomic stability. HPV+ cells therefore have increased DNA damage, leading to widespread genomic instability, a hallmark of cancer, which can contribute to tumorigenesis. Following transformation, high-risk HPV oncoproteins induce chromosomal instability, or chromosome missegregation during mitosis, which is associated with a further increase in DNA damage, particularly due to micronuclei and double-strand break formation. Thus, HPV induces significant DNA damage and activation of the DNA damage response in multiple contexts, which likely affects radiation sensitivity and efficacy. Here, we review how HPV activates the DNA damage response, how it induces chromosome missegregation and micronuclei formation, and discuss how these factors may affect radiation response. Understanding how HPV affects the DNA damage response in the context of radiation therapy may help determine potential mechanisms to improve therapeutic response.

Keywords: DNA damage response; alternative end-joining; chromosomal instability (CIN); human papillomavirus (HPV); mitosis; radiation.

Figure 1

Human papillomavirus oncoproteins can activate the DNA damage response directly (top) or indirectly by inducing chromosomal instability (CIN, bottom). Viral-induced DSBs can also directly activate the DDR pathways. HPV E6 and E7 induce specific types of chromosomal instability, including misaligned and lagging chromosomes, chromosome bridges, multipolar spindles, and micronuclei formation, each of which can activate DDR pathways. Radiation and chemotherapeutic drugs induce DSBs, which also increase CIN and activate the DDR. Created with BioRender.com.

Figure 2

Representative immunofluorescent images revealing how chromosome missegregation can be associated with DNA damage in HPV+ cells. Images are of untreated 93-VU-147T (HPV16+) head and neck cancer cells undergoing mitosis with evidence of chromosomal instability (CIN) in the form of micronuclei, misaligned chromosomes, chromosome bridges (indicated by arrows), or multipolar spindles (spindles denoted by asterisks). Recognition of DSBs by ATM leads to the phosphorylation of the histone H2AX yielding γH2AX. The top three panels represent examples of interphase or mitotic cells with CIN that are not associated with DNA damage, while the bottom four panels represent examples of CIN that are associated with DSBs and γH2AX signaling. Thus, CIN is not always associated with DNA damage. The 93-VU-147T cells were fixed with paraformaldehyde, incubated with anti-tubulin or anti-γH2AX antibodies, and counterstained with DAPI. (Blue, DAPI; pink, alpha-tubulin; green, γH2AX). All images were acquired using a Nikon Eclipse Ti2-E (Nikon, Yokohama, Japan) inverted fluorescence microscope with a 100×/1.4 numerical aperture oil objective. Images are maximum projections of 0.2 μm z-stacks that have been deconvolved.