Correlating breakage-fusion-bridge events with the overall chromosomal instability and in vitro karyotype evolution in prostate cancer

Abstract

Chromosomal instability (CIN) is thought to underlie the generation of chromosomal changes and genomic heterogeneity during prostatic tumorigenesis. The breakage-fusion-bridge (BFB) cycle is one of the CIN mechanisms responsible for characteristic mitotic abnormalities and the occurrence of specific classes of genomic rearrangements. However, there is little detailed information concerning the role of BFB and CIN in generating genomic diversity in prostate cancer. In this study we have used molecular cytogenetic methods and array comparative genomic hybridization analysis (aCGH) of DU145, PC3, LNCaP, 1532T and 1542T to investigate the in vitro role of BFB as a CIN mechanism in karyotype evolution. Analysis of mitotic structures in all five prostate cancer cell lines showed increased frequency of anaphase bridges and nuclear strings. Structurally rearranged dicentric chromosomes were observed in all of the investigated cell lines, and Spectral Karyotyping (SKY) analysis was used to identify the participating rearranged chromosomes. Multicolor banding (mBAND) and aCGH analysis of some of the more complex chromosomal rearrangements and associated amplicons identified inverted duplications, most frequently involving chromosome 8. Chromosomal breakpoint analysis showed there was a higher frequency of rearrangement at centromeric and pericentromeric genomic regions. The distribution of inverted duplications and ladder-like amplifications was mapped by mBAND and by aCGH. Adjacent spacing of focal amplifications and microdeletions were observed, and focal amplification of centromeric and end sequences was present, particularly in the most unstable line DU145. SKY analysis of this line identified chromosome segments fusing with multiple recipient chromosomes (jumping translocations) identifying potential dicentric sources. Telomere free end analysis indicated loss of DNA sequence. Moreover, the cell lines with the shortest telomeres had the most complex karyotypes, suggesting that despite the expression of telomerase, the reduced telomere length could be driving the observed BFB events and elevated levels of CIN in these lines.