Identification of BCMP11 overexpression in serous borderline ovarian tumor through microarray analysis

Abstract

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Ovarian borderline tumors account for 15% of all epithelial ovarian tumors. In spite of extensive research efforts, the pathogenesis of borderline ovarian tumor is not well understood. We evaluated the gene expression profiles of ovarian borderline tumors to identify genes whose altered expression may influence their clinical behavior. Microarray analysis on serous borderline and invasive ovarian tumors identified breast cancer membrane protein 11(BCMP11), a human homologue of the secreted Xenopus laevis protein XAG, as one of the genes overexpressed in borderline tumors. To validate the expression patterns of BCMP11 in borderline serous ovarian tumors, we performed real-time quantitative PCR and immunohistochemistry. Total messenger RNA was extracted from 10 normal ovarian surface epithelium, 25 microdissected ovarian serous borderline tumors, 6 low grade serous ovarian cancers, and 63 high grade serous ovarian cancers, amplified, and hybridized onto the Affymetrix U133 Plus 2 Oligo microarray. Real-time quantitative PCR was performed on the same RNAs used for microarray analysis. Immunohistochemical staining (IHC) was performed on 36 ovarian serous borderline tumors, 5 low grade ( grade 1 ), 25 high grade ovarian cancers, and 4 normal ovarian epithelium using an anti-BCMP11 antibody. Staining intensity was compared using a semiquantitative scoring system. The intensity of staining was scored as 0, +1, +2, or +3. A total of 110 genes showed significant higher expression in ovarian borderline tumors compared to HOSE and invasive carcinomas. Of these, BCMP11 showed the most significant differences. Real-time quantitative PCR analysis on BCMP11 showed significant overexpression in borderline tumors compared to invasive cancers. There was a significant correlation between qPCR and microarray data (r = 0.753, p < 0.0001). Immunohistochemical analyses demonstrated that BCMP11 protein expression was detected in 0 (0%, score 0) of 4 normal ovarian sections, 37 (90%, score +1, +2 or +3) of 41 borderline and low grade tumor sections and 4 (16%, score +2 or +3) of 25 ovarian cancer sections, respectively. Immunostaining was predominantly restricted to the epithelial tumor cells and especially cytoplasm. Stromal area did not show any positive staining. Our findings provide evidence for a significant association between BCMP11 expression and serous borderline and low-grade ovarian tumor and suggest that BCMP11 protein could be a useful molecular marker for these groups of tumors. Future research assessment of its function and the role of the gene in borderline tumor pathogenesis would be worthwhile.