Chromosomal aberrations in colorectal cancers and liver metastases analyzed by comparative genomic hybridization

Abstract

Comparative genomic hybridization (CGH) was used to screen for changes in the number of DNA sequence copies in 30 primary colorectal cancers and 16 liver metastases, to identify regions that contain genes important for the development and progression of colorectal cancer. In primary colorectal cancer, we found frequent gains at 7p21 (36.7%), 7q31-36 (30%), 8q23-24 (43.0%), 12p (30%) Many detailed reports have been published on the carcinogenesis of colorectal cancer. Several genetic aberrations are required for tumor initiation and progression. 1 These aberrations include activation of the SRC and RAS oncogenes 2,3 along with inactivation of the FAP 4,5 and DCC 6 tumor suppressors and loss of TP53 function. 7 However, genetic changes involved in the progression and metastases of colorectal cancer remain unclear. To investigate differences in chromosomal aberrations between primary colorectal cancer and metastatic liver tumor, we used comparative genomic hybridization (CGH). CGH is based on dual-color fluorescence in situ hybridization (FISH) using differentially labeled tumors and reference DNA as a probe. 8,9 The efficacy of CGH is based on the concept that regions with an increase in the number of copies reveal sites that may contain dominantly acting oncogenes, whereas regions with a reduction may harbor putative tumorsuppressor genes. 8 Our aim was to generate a comprehensive picture of genomic and chromosomal aberrations that occur during the development of metastases of colorectal cancers and to identify those chromosomal regions that contain genes important for the development and progression of colorectal cancer.,Colorectal adenoma and adenocarcinoma have previously been analyzed by CGH, 10 as have primary and metastatic liver tumors. 11,12 These results supported ours; above all, we emphasize that some important genes appear to be contained in 20q and to play an important role in liver metastases. Furthermore, we examined the follow-up surveys of all cases and compared cases with and without loss at 18q and with gains at 8q and 20q to determine the usefulness of these genetic alterations as prognostic markers. MATERIAL AND METHODS Samples and DNA preparationPrimary tumors and metastatic liver tumors from 44 cancer patients with colorectal cancer (Table I) were classified according to the UICC system. These samples were provided by the Department of Digestive Surgery, Kyoto Prefectural University of Medicine (Kyoto, Japan). After surgical resection, tissues were frozen and stored at -80°C and DNA was extracted. CGHCGH was performed as described previously. 13 In brief, tumor DNA was labeled with FITC-dUTP and controlled DNA and extracted from a normal male with the aid of Texas red-dUTP using nick translation. Metaphase spreads were denatured at 75°C for 2.1 min in a formamide solution [70% formamide, 2 ϫ SCC (pH 7.0)] and dehydrated in an ethanol series of 70%, 85% and 100%. Labeled tumor and normal DNAs together with 10 g unlabeled cot-1 DNA was mixed with 50% formamide, 10% dextran sulfate and 2 ϫ SSC...

hTERT gene copy number is not associated with hTERT RNA expression or telomerase activity in colorectal cancer

“…Gross genetic alterations, both losses and gains, can be detected by comparative genomic hybridization (CGH) and in colorectal carcinomas aberrations, e.g., amplifications, involving a large number of chromosomes, have been identified using this technique. [27][28][29] Theoretically, amplification of the hTERT gene can be 1 mechanism for upregulation of telomerase. In our study, we could show a high frequency of colorectal cancer samples with increased copy number of the hTERT gene located on chromosome 5p15-33.…”

Aneuploidy and Cancer: From Correlation to Causation

“…The term aneusomy is used for a specific, aneuploid chromosome. Specific aneuploidies have even been linked with specific stages of carcinogenesis and with specific phenotypes of cancers such as: (1) Distinct stages of neoplastic transformation in human [62,89,[95][96][97][98][99] and in animal carcinogenesis [84]; (2) invasiveness [97,98,100]; (3) metastasis [101][102][103][104][105][106]; (4) drug-resistance [53,69,107]; (5) transplantability to foreign hosts [108]; (6) distinct cellular morphologies [109]; (7) abnormal metabolism [62,110], and (8) cancer-specific receptors for viruses [62,109].…”

Somatic copy-neutral loss of heterozygosity and copy number abnormalities in Malaysian sporadic colorectal carcinoma patients

“…Genome-wide analyses of chromosomal CN abnormalities (CNAs) have provided insight on CRC carcinogenesis, including defining the genomic events that occur during various stages, although the results are inconsistent (Aragane et al, 2001;Choi et al, 2002;He et al, 2003;Knosel et al, 2004;Diep et al, 2006;Sheffer et al, 2009;Lagerstedt et al, 2010;Poulogiannis et al, 2010;Lin et al, 2011). However, reports on the occurrence of copy-neutral LOH have been scant.…”