ABSTRACT: Human papillomavirus (HPV) induced immortalization of human foreskin keratinocytes (HFK) is a two-step process, including 1) the bypass of replicative senescence and acquisition of an extended lifespan, and 2) the outgrowth of immortal cells. Our previous study showed that the immortalization capacity of HPV is type dependent, as reflected by the presence or absence of a crisis period before reaching immortality. In the present study we determined how the HPV-type specific immortalization capacity relates to DNA damage induction and overall genomic instability. Early passage HFKs transduced with HPV types 16, 18, 31, 33, 35, 45, 51, 59, 66 and 70 showed an increased number of double strand DNA breaks compared to controls, without significant differences between the various HPV-types. However, immortal descendants of HPV-transduced HFKs that underwent a crisis period (HPV45-, 51-, 59-, 66- and 70-transduced HFKs) showed significantly more chromosomal aberrations compared to those without a crisis period (HPV16-, 18-, 31-, and 35-transduced HFKs) (p<0.01). In particular, regions on chromosome 5p, 8, and 9q were significantly more frequently altered in cells with crisis. Interestingly, the hTERT locus at 5p was exclusively gained in cell lines with crisis. Chromothripsis was detected in one of the HPV16-immortalized cell lines in which multiple rearrangements within chromosome 8 resulted in a gain of c-MYC. In conclusion, the present study shows that upon HPV-induced immortalization, the number of chromosomal aberrations is inversely related to the immortalization capacity of the virus type. This suggests that hrHPV types with reduced immortalization capacity in vitro, as reflected by a crisis period, require more genetic host cell aberrations to trigger immortalization. DNA copy number analysis of human keratinocytes transformed by high-risk HPV
