Telomere fusions in early human breast carcinoma

Abstract

Several lines of evidence suggest that defects in telomere maintenance play a significant role in the initiation of genomic instability during carcinogenesis. Although the general concept of defective telomere maintenance initiating genomic instability has been acknowledged, there remains a critical gap in the direct evidence of telomere dysfunction in human solid tumors. To address this topic, we devised a multiplex PCR-based assay, termed TAR (telomereassociated repeat) fusion PCR, to detect and analyze chromosome end-to-end associations (telomere fusions) within human breast tumor tissue. Using TAR fusion PCR, we found that human breast lesions, but not normal breast tissues from healthy volunteers, contained telomere fusions. Telomere fusions were detected at similar frequencies during early ductal carcinoma in situ and in the later invasive ductal carcinoma stage. Our results provide direct evidence that telomere fusions are present in human breast tumor tissue and suggest that telomere dysfunction may be an important component of the genomic instability observed in this cancer. Development of this robust method that allows identification of these genetic aberrations (telomere fusions) is anticipated to be a valuable tool for dissecting mechanisms of telomere dysfunction.breast cancer | retrotransposon D efects in telomere maintenance have been suggested to play significant roles in the initiation of genomic instability via breakage-fusion-bridge cycles and aneuploidy, which are associated with the development of human cancers, including breast cancer (1, 2). A critical function of the telomere is to disguise the chromosome end from being recognized as a double-strand break, to prevent aberrant chromosomal end joining and recombination events. Cells disguise telomeric DNA by encapsulating or "capping" the chromosome ends with several telomere-associated proteins and unique telomere-specific structures (3). In healthy cells, telomere length is highly regulated in a tissue-and cell typespecific manner and is dependent on mitotic turnover rate, telomerase activity, and telomerase-associated factors (4, 5).Several lines of evidence from mouse and human systems suggest that defects in telomere maintenance play an important role in the development of cancer (1, 2). Induction of telomere dysfunction by deficiency in the telomerase RNA component (mTER) in a p53 mutant mouse background results in significant levels of breast adenocarcinomas and colon carcinomas (6-8). Telomere dysfunction also has been reported in a human mammary epithelial cell culture model (9). In this model, late-passage human mammary epithelial cell escape a stress-associated senescencelike barrier and acquire genomic alterations, including telomere fusions (9). In addition, clinical studies have shown that a significant proportion of normal breast luminal cells and ductal carcinoma in situ (DCIS) tissues have shortened telomeric DNA lengths when assayed by telomere FISH (10). Several studies have reported that anaphase bridges, possibly formed...

Spontaneous telomere to telomere fusions occur in unperturbed fission yeast cells

“…Since we found far more frequent rate of telomere-to-telomere fusions (1.4 × 10 − 4 ), it is tempting to speculate that spontaneous chromosome fusions may be a relevant trigger of genome instability and carcinogenesis. Consistent with this idea, recent evidence show telomere-to-telomere fusions in human breast carcinoma (42). The disparity in frequencies between our result and the one previously reported may simply reflect differences in the experimental setup.…”

Telomeres in cancer: tumour suppression and genome instability

“…Methods to directly detect the scars of prior telomere crisis in cancer genomes have now been developed 75,149,150 . The telomere–telomere fusions that are typical of telomere crisis can be detected with a PCR-based assay that uses correctly oriented primers situated in the subtelomeric DNA of two (or more) chromosome ends 75,150 .…”

“…The telomere–telomere fusions that are typical of telomere crisis can be detected with a PCR-based assay that uses correctly oriented primers situated in the subtelomeric DNA of two (or more) chromosome ends 75,150 . Using this approach, evidence for past telomere crisis has been obtained in CLL as well as in breast cancer, colorectal adenomas and other solid tumours 75,77,78 .…”

Investigation of repetitive sequences in the human genome

“…However interstitial sequences do duplicate at termini in a rare situation, the mechanism of which is poorly understood. Two cases of direct interstitial sequences joining to telomeric sequences were described in a human cancer fusion study [140]. One was a 447 bps interstitial chromosome 4 sequence joining to 10q telomere at one side and 4p telomere at another side.…”

“…If the Telomere repeats are lost, the broken chromosome will become unstable [139][140][141], and multiple types of rearrangements can occur, including chromosome fusion [139], tips translocation [142], or direct extension of telomere repeats [141]. The manual insertion of a telomeric sequence in the interstitial region results in enhanced chromosome breakages and induces high rates of chromosome rearrangements around the insertion [143].…”