Human Papillomavirus-Induced Chromosomal Instability and Aneuploidy in Squamous Cell Cancers

Abstract

Chromosomal instability (CIN) and aneuploidy are hallmarks of cancer. CIN is defined as a continuous rate of chromosome missegregation events over the course of multiple cell divisions. CIN causes aneuploidy, a state of abnormal chromosome content differing from a multiple of the haploid. Human papillomavirus (HPV) is a well-known cause of squamous cancers of the oropharynx, cervix, and anus. The HPV E6 and E7 oncogenes have well-known roles in carcinogenesis, but additional genomic events, such as CIN and aneuploidy, are often required for tumor formation. HPV+ squamous cancers have an increased frequency of specific types of CIN, including polar chromosomes. CIN leads to chromosome gains and losses (aneuploidies) specific to HPV+ cancers, which are distinct from HPV- cancers. HPV-specific CIN and aneuploidy may have implications for prognosis and therapeutic response and may provide insight into novel therapeutic vulnerabilities. Here, we review HPV-specific types of CIN and patterns of aneuploidy in squamous cancers, as well as how this impacts patient prognosis and treatment.

Keywords: aneuploidy; chromosomal instability; chromosome; human papillomavirus; squamous cell carcinoma.

Figure 1

HPV16 E6 and E7 expression in immortalized normal oral keratinocytes (NOKs) induces CIN. (A) NOKs expressing the control pLXSN vector (left) or HPV16 E6 and E7 (middle and right) in metaphase. E6 and E7 expression cause polar chromosomes (middle panel, arrowhead) and centrosome amplification leading to multipolar spindles (right panel, asterisks). Centrosomes at spindle poles are indicated by staining with pericentrin (green). (B) NOKs expressing the control pLXSN vector (left) or HPV16 E6 and E7 (middle and right) in anaphase. E6 and E7 expression results in chromosome missegregation, including lagging chromosomes (middle; arrowhead) or chromosome bridges (right; arrowhead). (C) Micronucleus in NOKs expressing HPV16 E6 and E7 in interphase (right; arrowhead). NOKs expressing the control pLXSN vector or HPV16 E6 and E7 were fixed with paraformaldehyde, incubated with anti-tubulin or anti-pericentrin antibodies, and counterstained with DAPI as in [10] (blue, DAPI; red, tubulin; green, pericentrin). All images were acquired using a Nikon Eclipse Ti-E 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. Scale bar, 10 μm.

Figure 2

HPV E6 and E7 induce many different types of CIN via unique mechanisms. Created with BioRender.com.

Figure 3

Squamous cell carcinomas show different patterns of aneuploidy depending on HPV status. Integrated Genomics Viewer (IGV) plot of somatic copy number alterations by HPV status for squamous cancer tumor types associated with HPV. Data are sorted by HPV status; tumor type is specified but not clustered. Blue indicates copy number loss, red indicates copy number gain, white indicates copy number neutral, and gray indicates no data available. Sex chromosome copy number data were not available for ASCC. CESC (TCGA, n = 242); HNSCC (TCGA, n = 501); ASCC (DFCI, n = 60). ASCC tumor sample copy number data were made available by Mouw et al. [78]. CESC and HNSCC tumor sample copy number data were made available by The Cancer Genome Atlas [75].