Comprehensive and definitive molecular cytogenetic characterization of HeLa cells by spectral karyotyping

We revisited the cytogenetic alterations of the cervical adenocarcinoma cel l Line HeLa through the use of spectral karyotyping (SKY), comparative geno mic hybridization (CGH), and fluorescence in situ hybridization (FISH), SKY analysis unequivocally characterized all abnormal chromosomes. Chromosomal breakpoints were primarily assigned by simultaneous assessment of SKY pain ted chromosomes and inverted il,4,6-diamidino-2-phenylindole banding from t he same cell. Twenty clonally abnormal chromosomes were found. Comparison w ith previously reported HeLa G-banding karyotypes revealed a remarkably sta ble cytogenetic constitution because 18 of 20 markers that were found were present before. The classification of 12 markers was refined in this study. Our assignment of the remaining six markers was consistent with those desc ribed in the literature, The CGH map of chromosomal copy number gains and losses strikingly matched the SKY results and was, in a few instances, decisive for assigning breakpo ints. The combined use of molecular cytogenetic methods SKY, CGH, and FISH with site-specific probes, in addition to inverted 4,6-diamidino-2-phenylin dole or conventional G-banding analysis, provides the means to fully assess the genomic abnormalities in cancer cells. Human papillomaviruses (HPVs) a re frequently integrated into the cellular DNA in cervical cancers, We mapp ed by FISH five HPV18 integration sites: three on normal chromosomes 8 at 8 q24 and two on derivative chromosomes, der(5)t(5;22;8)(q11;q11q13;q24) and der(22)t(8; 22)(q24;q13), which have chromosome 8q24 material. An 8q24 copy number increase was detected by CGH, Dual-color FISH with a c-MYC probe ma pping to 8q24 revealed colocalization with HPV18 at all integration sites, indicating that dispersion and amplification of the c-MYC gene sequences oc curred after and was most likely triggered by the viral insertion at a sing le integration site. Numerical and structural chromosomal aberrations ident ified by SKY, genomic imbalances detected by CGH, as well as FISH localizat ion of HPV18 integration at the c-MYC locus in HeLa cells are common and re presentative for advanced stage cervical cell carcinomas. The HeLa genome h as been remarkably stable after years of continuous cultivation; therefore, the genetic alterations detected may have been present in the primary tumo r and reflect events that are relevant to the development of cervical cance r.