Study Of The Expression Of Spindle Checkpoint Protein MAD2 In Carcinogenesis Of Epithelial Ovarian Tumors And Its Mechanism

IntroductionOvarian carcinomas are heterogeneous and are primarily classified by cell type into serous, mucinous, endometrioid, clear cell, and Brenner (transitional) tumors corresponding to different types of epithelia in the organs of the female reproductive tract. The tumors in each of the categories are further subdivided into three groups, benign, malignant, and intermediate (borderline tumor) to reflect their behavior. Among gynecologic malignancies, ovarian cancer accounts for the highest tumor-related mortality in women in the United States. The high case fatality rate associated with ovarian cancer is due in part to the frequent diagnosis of advanced-stage disease when the malignancy has already spread beyond the ovary. This poor prognosis is reflected in the <20% 5-year survival rate after initial diagnosis for patients with stage III and IV disease, whereas for patients with stage I or II disease >80% survive for the same period .So the mechanisms of the tumorigenesis of ovarian carcinoma should be well elucidated. The relationship between benign, borderline and malignant ovarian tumours is unclear. In a recent model, two broad categories have been proposed. Type I tumours are suggested to represent acontinuum from benign through borderline to low-grade malignancy. Type II tumours are high-grade with no recognizable intermediate lesion and are thought to represent de novo development. This model of carcinogenesis reconciles the relationship of borderline tumors to invasive carcinoma and provides a morphological and molecular framework for studies aimed at elucidating the pathogenesis of ovarian cancer. But to date, its molecular mechanism is still largely unknown.Accurate chromosomal segregation is essential for cell survival and genomic stability. Chromosomal instability (CIN) leading to an aberrant chromosome number (aneuploidy) is a hallmark of cancers. CIN presumably drives tumor progression by accelerating the rate of gain or loss of individual chromosomes. The mechanism and molecular determinants of CIN are not clearly understood, but considerable interest surrounds the possibility that lesions in spindle checkpoint are involved. The understanding of the spindle checkpoint might provide valuable insights into CIN and tumorigenesis of cancer. The spindle checkpoint prevents the onset of anaphase until all chromosomes are properly attached to the mitotic spindle. Mitotic arrest deficient (MAD2) is a key component of this checkpoint system, which ensuring the accurate partition of the genetic material. Although MAD2 gene mutations are very rare in human cancer, aberrantly reduced expression of MAD2 protein has been correlated with defective mitotic checkpoint in cancer cells.Notably, chromosomal aberrations were frequently found in ovarian cancer. But little information is available in literature about the expression of spindle checkpoint protein Mad2 in ovarian tumor tissue. Therefore, we investigate the expressions of spindle checkprotein MAD2 in serous ovarian tumorigenesis and the relationship between expression patterns of MAD2 and the clinicopathologic features of the tumors. We also research the expressions of MAD2 in epithelial ovarian carcinomas and the role of MAD2 in CIN and ovarian tumorigenesis.Methods and ResultsPart One: The expression and clinical significance of spindle checkpoint protein MAD2 in serous ovarian tumorsMethods: Immunohistochemistry and immublotting analyses were performed to analyze the distributions and expressions of MAD2 in the 19 normal ovarian tissues, 17 ovarian serous cystadenomas, 21 borderline serous cystadenomas and 40 ovarian serous carcinomas.Results: (1) MAD2 protein expressions were detected in epithelial cell nucleolus and plasma, All types had the expressions of MAD2, but there were different levels of MAD2 protein expressions, the levels of MAD2 in ovarian serous carcinomas and borderline serous cystadenomas were statistically higher than those in ovarian serous cystadenomas and normal ovarian tissues(P<0.05), and there were no differences between the ovarian serous carcinomas and borderline serous cystadenomas or between the ovarian serous cystadenomas and normal ovarian tissues(P>0.05). (2) The levels of MAD2 protein expressions were found no differences in different clinical stages( I -Hand ID-VI), different histological grades(Gi and 62-3), ascites( < 500ml and > 500ml) , CA125(normal and enhancement) and with or without metastasis to pelvic or abdominal cavity (P>0.05) in ovarian serous carcinomas.Part Two: The expression of spindle checkpoint protein MAD2 in epithelial ovarian cancers and its mechanismMethods: Expressions of MAD2 and cyclin Bl were detected by western blot technique in 42 cases of epithelial ovarian cancers (20 serous carcinomas, 7 mucinous carcinomas, 8 endometrioid carcinomas and 7 clear cell carcinomas) and the nontumorous tissues in the contralateral or ipsilateral ovaries. Cell cycle G2/Mdistribution and DNA ploidy analysis in cancer tissues was performed by flowcytometry.Results: Compared to the corresponding nontumorous tissues, 76% (32/42) epithelialovarian carcinomas presented elevated MAD2 levels. Elevated expression levels ofMAD2 was associated with increased expression levels of cyclin Bl and was relevantto the appearances of aneuploidy(P<0.05). Whereas there were no relativities betweenexpression levels of MAD2 and the percent of G2/M in cell cycles (P>0.05).Conclusions1. Overexpression of MAD2 may be early event in carcinogenesis of epithelial ovarian cancers.2. Aberrant MAD2 expression is associated with the pathway of MAD2-cyclinBl-CIN in epithelial ovarian cancers. But there may be the other pathways in the different histological types of epithelial ovarian cancers.