Chromosomal abnormalities and frequent p53 gene mutations seen in exon 7 in endometrial and ovarian carcinomas

ABSTRACT CHROMOSOMAL ABNORMALITIES AND FREQUENT P53 GENE MUTATIONS SEEN IN EXON 7 IN ENDOMETRIAL AND OVARIAN CARCINOMAS In organism p53 known as a tumor suppressor gene encodes a protein that controls the cell cycle. In majority of human malignancies, p53 is the target of molecular alterations as approximately 50% of human cancers are related to mutations of this gene. The causation factors, such as alterations in the genes which regulate the proliferation, differentiation and cell death are the same in all types of the cancers as well as the gynecological neoplasms. So that, loss of function or inactivation of p53 will upset the control of cell proliferation and the cells with DNA damage will survive and proliferate in an uncontrollable manner. The tumor suppressor gene p53 is located at chromosome region 17pl3 and is composed of 11 exon and 393 triplets m total. Majority of hot spots are focused on between triplets of 129-146, 171-179, 234- 260 and 270-287. These triplets include the sites between exon 5 and 8. The mutations in ovarian and endometrial cancers are more frequently seen in exon 7 (46%), especially at the triplets of 236 (5.4%), 238 (5.4%), 244 (8.1%), 248 (19%) and 259 (8.1%). However, along with molecular alterations, the presence of cytogenetic alterations affecting greater regions about 3000 to 5000 kb is a common occurence in tumor tissues. Chromosomal imbalance has also been found at high rate in most of the tumors. In our study, 23 DNA samples isolated from ovarian and endometrial cancer tissues which were obtained from patients who hospitalized at University of Çukurova, Medical Faculty, Department of Obstetrics and Gynecology. Exon 7 of p53 gene which frequently mutated in ovarian and endometrial cancers was amplified from 23 DNA samples. BspLUllI, MaeDT, Ital, Mspl and Hinfl restriction enzymes were used to determine p53 gene mutations at the points 236, 238, 244, 248 and 259 respectively by RFLP (Restriction Fragment Polymorphism) analysis. Metaphases were also obtained from cultured cancer tissues (described above) for characterization of structural and numerical chromosomal alterations. Hetrozygosity was seen in 1 case of 11 ovarian cancer (%9) at triplet 236 by BspLUllI digestion and in 5 case of 11 ovarian cancer (%45) at triplet 244 by Ital digestion. In all cases no mutations were observed at triplets 238, 248 and 259 by MaeDJ, Mspl and Hinfl digestion. No evidence of mutations were seen at triplets 238, 248 and 259 in ovarian cases and at all 5 triplets in endometrial cases analyzed for known mutations. In our cytogenetic studies performed on ovarian and endometrial cancers, abnormalities were seen most frequently on chromosome 3 then on chromosome 5 and then on chromosome 1. Clonal alterations occuring during tumorigenesis are used as a xivmarker having a diagnostic importance. These alterations are observed at lq21, lq32, 3p25, 3qll, 5pl3, 5q31, 12pl0, 12ql2, 14ql3 regions in ovarian cancer cases and at lp21, lp22, lp32, lp36, lq21, lq31, lq32, 2pl3, 2qll, 2q21, 2q35, 3pl4, 3p21, 3p23, 3q21, 3q25, 4pl5, 4q21, 5pl5, 5q22, 5q31, 6q21, 7q21, 7q22, 9q22, 9q34, 10pl3, llpl5, llq23, llq24, 12pl2, 12pl3, 12ql3, 12q24, 13ql4, 13q22, 16pl3, 17pl2, 17q21, 21pl3, Xq26, Xq27 regions in endometrial cancer cases. The cancer breakpoints and fragile sites were also investigated in ovarian (lq21, lq32, 3p21, 7q22, llq23) and endometrial (lp36, lq32, 2pl2, 3p21, 7q22, 9q34, llpl5, llq23, 12ql3, 14qll, 14q32, 16pl3, 21q22) cases. We thought that, the clonal chromosomal alterations observed in the ovarian and endometrial cases may lead to find the chromosomal locations of the major genes that play an important role in progression of these malignancies. Key words: Endometrial cancer, Cytogenetics of cancer, Mutation, Ovarian cancer, p53. XV