Study On The Relationship Between DBC2, CHEK2 Gene Mutation And The Early Onset And Sporadic Breast Cancer From Shanghai In China

Backgroud: The development of breast cancer is related to various kinds of factors. It has been demonstrated that there are about 5～10% patients belonging to hereditary breast cancer in the overall cases,while there are 90～95% patients belonging to sporadic ones. DBC2(deleted in breast cancer) are one of the tumor suppressor gene,it located at human chromosome 8p21 and its total length is 20.5Kbp,DBC2 is also named Rhobtb2.DBC2 is an atypical Rho GTPase,its common function is to prevent the proliferation of abnormal cells which is related to the developing of tumor. The growth of breast cell line can be inhibited when DBC2 gene is introducted in it,while the growth of tumor cell can't be restricted when DBC2 gene has natural mutation in the breast cancer. All of foundings suggest that DBC2 gene may play an important role as an gene impressor in breast cancer. DBC2 can regulates a lot of important procedure,including the formation of actin and cytoskeleton,transcription of gene,progression of cell-cycle and membrane-trafficking pathways etc. It is a novel direct target of E2F1 with important roles in cell cycle and apoptosis. Biological studies of RhoBTB2 activity have demonstrated that overexpression of RhoBTB2 can lead to growth inhibition in breast cancer cell lines, whereas point mutants derived from primary tumors have lost this ability. As a tumor suppressor gene which is related to sporadic breast cancer, DBC2 was found lost in about 60% breast cancer patients. As more than 90% breast cancer cases is belonging to sporadic one,the discovery of DBC2 may play an important role in the therapy of breast cancer.Checkpoint kinase 2 (CHEK2, Chk2) emerges as an important signal transducer of cellular responses to DNA damage and a candidate tumor suppressor whose defects contribute to molecular pathogenesis of diverse types of human malignancies, both sporadic and hereditary. In 2002, scientist identified CHEK2 1100delC variant in a large breast cancer pedigree and further found the variant in 5.1% of individuals with breast cancer from 718 Western-European and North-American families without BRCA1 or BRCA2 mutations and in 1.1% in healthy individuals. They estimated that the 1100delC variant results in an approximately twofold increase of breast cancer risk in women. The CHEK2 Breast Cancer Case-Control Consortium studied the 1100delC allele in 10860 breast cancer cases and 9065 controls from 10 case-control studies in five countries and found the variant in 1.9% of all cases and 0.7% of controls (OR 2.34; 95% CI 1.72-3.20). This large study confirmed that the 1100delC allele confers about twofold elevated breast cancer risk that was also observed in women unselected for family history. A trend for a higher breast cancer odds ratio was also seen for earlier ages of onset and carriers in breast cancer families who develop breast cancer at an earlier age than noncarriers.At present, the onset of breast cancer has become more and more earlier(the age of onset is below 40); especially in China,the onset of breast cancer has been 10-15years earlier than that in weatern countries So,it is critical to identify the high-risk population and find out the different expression of these two genes from other people. The related research has not been carried out in our country.This study is to detect the mutation of DBC2 and CHEK2 gene and to evaluate the relationship between the gene mutation and the early onset and sporadic breast cancer patients from Shanghai in China who have no BRCA1/2 mutations.[objective] The investigation is to investigate the the mutation of DBC2 and CHEK2 gene in the early onset and sporadic breast cancer patients from Shanghai in China who have no BRCA1/2 mutations,and analyze the potential relationship between the mutation and genetic susceptibility of breast cancer in China.[method] The genome DNA extraction in peripheral blood from 45 early onset and sporadic breast cancer cases who have no BRCA1/2 mutations and 30 controls is performed. After PCR amplification was carried out in the 5th ,9th exon of DBC2 and the 10th exon of CHEK2,the PCR production was sequenced. All have been done to analyze the relationship between the gene mutation and breast cancer.[result](1) There is a novel missense mutation +7776C>T(P . Leu288Phe) we have detected,located in the 5th exon of DBC2 in 8 cases out of 45 early onset and sporadic breast cancer cases. The mutation rate is 17.78%, but there is no mutation in the control group. We have not detected any SNP sites in the 9th exon and controls (The mutation rate is 0).After Fisher's exact test, we conclude that the mutation rate of 5 exon in cases is higher than control groups(one-sided p value is 0.0186,two-sided p value is 0.0371).(2) By compareing the characterictics of patients who have the mutation in the 5th exon of DBC2 with that who have not,we found that there are no variability in age of onset (P> 0.05) , rate of positive ER(two-sided p value is 0.2693) , Her-2(two-sided p value is 1.0888).(3) We have not found any SNP site of 9th exon in DBC2 gene in both groups,there is no variability of mutation rate between two groups.(4) We have not found the CHEK2c. 1100delC mutatin in both groups,but we found four same SNP sites in 10 exon of CHEK2 gene in both groups, and the type of mutation,nucleotide base transformation and the mutation site are the same,there is no difference of mutation rate between two groups.[conclusion](1) The novel mutation rate of +7776OT in 5th exon of DBC2 gene is higher in breast caner cases than the control groups. It may be the special mutation site in the early onset and sporadic breast cancer patients of China. And may contribute to the predisposition for the early onset and sporadic breast cancer and be a mutation site of high risk gene of breast cancer in the early onset and sporadic breast cancer in China . Thus,we could build a platform to screen the susceptible population of breast cancer patients, which would benefit to some aspects of society and economy. A further study would be needed to confirm the results. The study on the function of the mutation site and the screen to the first degree relative of patient who has the positive mutation will be continued.(2) There is no difference between the patient with or without the mutation in the age of onset, rate of positive ER, PR and Her-2.The bias may caused by the small size of samples and may be corrected by the enlargment of the sample size in further study .The collection of large samples would contribute to get the distribution tendency of more information about the disease which have the mutation.(3) The mutation in 9th exon of DBC2 gene is rare in the early onset and sporadic breast cancer in Shanghai .The reason may be the sample size is relatively small and be prone to selection bias. The large sample research will be done to illuminate the distribution and effect of this gene mutation in Chinese group.(4) CHEK2 c.1100delC is rare variant for the early onset and sporadic breast cancer of Shanghai population in China and may not contribute to predisposition for sporadic breast cancer. The three novel SNP sites we have detected are gene polymorphism in China population,we suppose that they have no pathology significance. A further study in large sample is needed to confirm the results.