Roy 27_7

Multiple genetic alterations are common in cancers including those of the breast. The mechanisms leading to these alterations such as point mutations, gene amplifications, deletions and replication error are often associated with frequent and consistent loss of heterozygosity (LOH) or microsatellite instability (MSI). Several cytological and molecular studies have shown high frequency loss of genetic information on the long arm of chromosome 11 (i.e., 11q) in various primary breast cancers. In the present study allelic alterations in a refined position on the long arm of chromosome 11 were studied to identify the spectrum of induced damage at different stages of malignant transformation of MCF-10F cell lines after exposure to high-LET radiation using ·-particles and exposure to estradiol by using PCR-single strand conformation polymorphism (SSCP) and fluorescence in situ hybridization (FISH) analysis. Microsatellite markers were selected from chromosome 11 (11q23-q24 loci) and it was found that frequency of allelic imbalance occurs at different stages of tumor progression with a range of 15-45% depending on the marker studied. These results strongly suggested the presence of several tumor suppressor genes in this critical region of chromosome 11 (11q23-q24). It also represents the first indication of allele loss at these loci in human breast epithelial cells induced by radiation and estrogen treatment suggesting a potential interventional target in breast carcinogenesis. Introduction Multiple genetic alterations are common in various cancers including those of the breast. Human cancers are thought to accumulate multiple genetic abnormalities as they progress from carcinoma in situ to metastatic phase (1). This process is often associated with frequent and consistent loss of heterozygosity (LOH) or microsatellite instability (MSI), which often seems to unmask recessive mutations in tumor suppressor loci (2). The involvement of tumor suppressor genes in neoplastic progression may be inferred by studies, which detect allelic losses in tumor DNA (3,4). Defining specific chromosomal regions that harbor biologically important suppressor genes may, therefore, have broad practical implications in the diagnosis and management of these tumors (5,6). The development of breast cancer is the most common malignancy in women and the second leading cause of female cancer death, surpassed only by lung cancer (7,8). In breast cancer, most genetic changes are not inherited but rather are somatically acquired in breast epithelial cells (9). There is evidence that multiple mechanisms including point mutations, gene amplifications, deletions and replication errors account for the genomic instability and mutation associated with neoplastic transformation. Acquisition of such genomic instability may represent an early step in carcinogenesis (10). Accordingly a large portions of genetic alterations are associated with the multi-step carcinogenesis of breast cancer. It is unclear whether allelic imbalance is the cause or the result of carcinogenesis but it is probably the most common genetic factor associated with cancer. There is evidence that a significant number of aberrations (i.e., allelic alterations) on chromosomal regions 1p, 1q, 3p, 6q, 7q, 11p, 13q, 16q, 17p, 17q and 18q are found in breast cancers (11,12). Ionizing radiation is effective in producing these chromosomal aberrations, which are characterized either by MSI/LOH or by multicolor fluorescence in situ hybridization (mFISH) analysis (13,14). Epidemiological data also indicates that women exposed to ionizing radiation (e.g., radiation therapy during diagnosis and treatment, A-bomb etc.) have an increased risk of breast cancer (15). The action of ionizing radiation as a DNA-damaging agent, and consequently as a mutagen, is widely considered to be the basis for its action as a carcinogen (16). Allelic alterations (MSI/LOH) are INTERNATIONAL JOURNAL OF ONCOLOGY 28: 667-674, 2006 667 Allelic imbalance at 11q23-q24 chromosome associated with estrogen and radiation-induced breast cancer progression D. ROY1, G.M. CALAF1,2, M.P. HANDE3 and T.K. HEI1 1Center for Radiological Research, College of Physicians and Surgeons, Columbia University, New York, NY, USA; 2Department of Biology and Health, Faculty of Science, and Center for the Man in the Desert, University of Tarapaca, Arica, Chile; 3Department of Physiology, Faculty of Medicine, National University of Singapore, Singapore Received July 28, 2005; Accepted September 20, 2005 _________________________________________ Correspondence to: Dr Debasish Roy, Present address: Biology Department, Brookhaven National Laboratory, #463, 50 Bell Avenue, Upton, NY 11973, USA E-mail: [email protected] Abbreviations: DMEM, Dulbecco's modified Eagle's medium; LOH, loss of heterozygosity; MSI, microsatellite instability; OD, optical density; mFISH, multicolor fluorescence in situ hybridization; PCR-SSCP, polymerase chain reaction-single strand conformation