Browsing by Subject "Genomic instability"

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Open Access
Determining the origin of synchronous multifocal bladder cancer by exome sequencing
(BioMed Central Ltd., 2015) Acar, Ö.; Özkurt, E.; Demir, G.; Saraç, H.; Alkan C.; Esen, T.; Somel, M.; Lack, N. A.
Background: Synchronous multifocal tumours are commonly observed in urothelial carcinomas of the bladder. The origin of these physically independent tumours has been proposed to occur by either intraluminal migration (clonal) or spontaneous transformation of multiple cells by carcinogens (field effect). It is unclear which model is correct, with several studies supporting both hypotheses. A potential cause of this uncertainty may be the small number of genetic mutations previously used to quantify the relationship between these tumours. Methods: To better understand the genetic lineage of these tumours we conducted exome sequencing of synchronous multifocal pTa urothelial bladder cancers at a high depth, using multiple samples from three patients. Results: Phylogenetic analysis of high confidence single nucleotide variants (SNV) demonstrated that the sequenced multifocal bladder cancers arose from a clonal origin in all three patients (bootstrap value 100 %). Interestingly, in two patients the most common type of tumour-associated SNVs were cytosine mutations of TpC*dinucleotides (Fisher's exact test p < 10-41), likely caused by APOBEC-mediated deamination. Incorporating these results into our clonal model, we found that TpC*type mutations occurred 2-5× more often among SNVs on the ancestral branches than in the more recent private branches (p < 10-4) suggesting that TpC*mutations largely occurred early in the development of the tumour. Conclusions: These results demonstrate that synchronous multifocal bladder cancers frequently arise from a clonal origin. Our data also suggests that APOBEC-mediated mutations occur early in the development of the tumour and may be a driver of tumourigenesis in non-muscle invasive urothelial bladder cancer.
Open Access
An investigation of microRNAs mapping to breast cancer related genomic gain and loss regions
(Elsevier, 2009) Selcuklu, S. D.; Yakicier, M. C.; Erson, A. E.
Various regions of amplification or loss are observed in breast tumors as a manifestation of genomic instability. To date, numerous oncogenes or tumor suppressors on some of these regions have been characterized. An increasing body of evidence suggests that such regions also harbor microRNA genes with crucial regulatory roles in cellular processes and disease mechanisms, including cancer. Here, we investigated 35 microRNAs localized to common genomic gain and/or loss regions in breast cancers. To examine amplification or loss of these microRNAs as a result of genomic instability, we performed semiquantitative duplex polymerase chain reaction in 20 breast cancer cell lines, 2 immortalized mammary cell lines, and 2 normal DNA controls. A comprehensive DNA fold number change data for 35 microRNA genes on chromosomal gain/loss regions are presented in breast cancer cells. A 23% (8/35) of the investigated microRNAs showed significant fold number increases (greater than fourfold) compared to GAPDH in one or more of the breast cell lines. Although no homozygous deletions were detected, fold number decreases indicating potential loss regions were observed for 26% (9/35) of the investigated microRNAs. Such fold number changes may point out some of these microRNAs as potential targets of the genomic instability regions as oncogene and tumor suppressor candidates. © 2009 Elsevier Inc. All rights reserved.