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Background. Differentiation programs are hormonally regulated in the reproductive tissues and appear to fail in cancer. We searched for the genetic elements involved and found a novel hormone-induced differentiation factor APRIN, which was mapped on chromosome 13, next to BRCA2. Deletions (loss of heterozygosity) in the BRCA2 region in prostate, breast, ovarian and other cancers indicated a cryptic suppressor gene in the APRIN area. Objective. Deletions targeting the APRIN gene may indicate that the loss of APRIN is a critical factor in cancer progression. The objective of the present work is to investigate this hypothesis. Based on our previous studies, we extended our analysis of APRIN expression in reproductive cancers and analyzed the genetic and epigenetic mechanisms of silencing. Methods. We used clinical samples from invasive ductal breast adenocarcinomas, prostate adenocarcinomas and ovarian cancer to assess APRIN expression. Our immunohistochemistry results were compared with microarray and SAGE data. We also analyzed APRIN expression in vitro, in cell lines from reproductive cancers. In samples where APRIN expression was absent, we performed both genetic and epigenetic analyses to study the molecular mechanisms. In the extensive CpG island of the APRIN promoter methylation can repress promoter activity. We performed promoter methylation studies using various techniques and innovative applications. R e s u l t s. Our data indicated downregulation or silencing of APRIN expression in up to 90% of the clinical samples we analyzed. In contrast, in normal tissues in the same samples and in control biopsies APRIN was highly expressed. Microarray and SAGE data were also consistent with our immuno-histochemistry results and showed that in most breast and ovarian cancer cell lines APRIN was lost or downregulated. In prostate adenocarcinomas, however, APRIN losses were less manifest and showed clonal morphology. We found DNA methylation in the APRIN promoter in samples where APRIN was silenced. Conclusions. APRIN, a conserved chromatin factor is highly expressed in the nervous and reproductive systems. We showed that it is a mediator in hormonally regulated differentiation in reproductive organs. We also showed that early on in the oncogenic process, the loss of APRIN expression contributes to reproductive and other malignancies through epigenetic mechanisms. Our results will help to establish novel epigenetic markers in early diagnosis and prognosis.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]