Genome organization and the role of centromeres in evolution of the erythroleukaemia cell line HEL

Abstract

The human erythroleukaemia (HEL) cell line has a highly rearranged genome. We matched whole chromosome analysis with cytogenomic microarray data to build a detailed description of these rearrangements. We used a combination of single nucleotide polymorphism array and multiple fluorescence in situ hybridization approaches, and compared our array data with publicly available data for different sublines of HEL. B allele frequencies revealed the fate of each homologue for most chromosomes. At least two instances of the breakage-fusion-bridge cycle appear to have facilitated amplification of oncogenes and deletion of tumour suppressor genes. Because our study included centromere identification, we found that some abnormal chromosomes had centromeres that did not match the identity of the rest of the chromosome. This study highlights the variety of complementary methods required to understand remodelling of the genome in cancer and uncover some of the mechanisms involved. We present evidence of centromere capture as a means of preserving broken chromosome segments. Testing for another highly repetitive DNA region, the nucleolus organizer region, helped identify the steps involved in chromosome 9 copy number aberrations. Increased use of techniques for identifying centromeres and other repetitive DNA regions will add to our understanding of genome remodelling and evolution. The pattern of chromosome 20 aberration in HEL supports an association of 20q11.21 amplification with erythroleukaemia (acute myeloid leukaemia subtype M6) in the context of 20q12 deletion. The differences between the karyotypes in different HEL sublines highlight the constantly evolving genomes of cultured cell lines.