Frequent loss of Dab2 protein and infrequent promoter hypermethylation in breast cancer.
ABSTRACT Disabled-2 (Dab2), a putative tumor suppressor protein, is lost in 80-90% ovarian tumors and ovarian/breast cancer cell lines. The clinical significance of Dab2 protein in breast cancer remains yet unknown. Immunohistochemical analysis of Dab2 protein showed no detectable expression in 67/91 (74%) breast tumors, while all 10 normal tissues showed presence of Dab2 protein. We hypothesized that epigenetic silencing of Dab2 may account for loss of protein in breast cancer. Methylation of Dab2 exon 1, a putative promoter, was analyzed in six breast cancer cell lines and in 54 primary breast tumors by methylation specific PCR. Methylation was observed in MDA-MB-231 and MDA-MB-157 cells and in 6 of 54 (11%) primary breast tumors that also showed loss of Dab2 protein. Expression of Dab2 transcripts was detected in all cell lines except MDA-MB-157. However, none of these six cell lines showed detectable levels of Dab2 protein by western blotting, while non-malignant mammary epithelial cell line MCF 10A showed Dab2 protein expression. To our knowledge this is the first report showing low frequency of Dab2 (putative) promoter methylation (11%) in primary breast tumors. Frequent loss of Dab2 protein (74%) suggest that hypermethylation of Dab2 promoter may only be one of the mechanisms accounting for its loss in breast cancer. Further, in silico analysis of Dab2 3'-UTR revealed existence of miRNA complimentary to this region of the gene, suggesting microRNA mediated targeting of Dab2 mRNA might account for loss of the protein in breast cancer.
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ABSTRACT: Promoter hypermethylation of genes is implicated in the pathogenesis of many cancers, including breast cancer. Herein, we analyzed the promoter methylation status of a panel of critical growth regulatory genes, RASSF1A, RARbeta2, BRCA1 and HOXA5, in 54 breast cancers and 5 distant normal breast tissues of Indian patients. The methylation data were correlated with clinicopathological characteristics and hormone receptor status to determine the impact of methylation in breast carcinogenesis. Promoter hypermethylation of RASSF1A was observed in 39/54 (72%), HOXA5 in 36/54 (67%), BRCA1 in 15/54 (28%) and RARbeta2 in 8/54 (15%) breast cancers. Our most significant findings were the association of RASSF1A methylation with nodal metastasis (p=0.05); and RARbeta2 methylation with age (all tumors in patients in the older age group were methylated, p=0.04). Further, the interactions between DNA methylation and hormone receptor biology in breast cancer cells are beginning to be clearly understood. In this context the association of HOXA5 methylation with loss of ERalpha (p=0.009) is noteworthy.Life Sciences 07/2008; 82(25-26):1288-92. DOI:10.1016/j.lfs.2008.04.020 · 2.30 Impact Factor
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ABSTRACT: Two novel oestrogen receptor (ER) negative breast cancer cell lines, BCa-11 (familial) and BCa-15 (sporadic) were successfully established from primary tumours. Characterisation of these cell lines showed expression of epithelial specific antigen and cytokeratins confirming their epithelial lineage. Analysis of ultrastructure and anchorage independent growth confirmed the epithelial nature and transformed phenotype of these cells. Both cell lines showed loss of pRb, Dab2 and ERalpha and elevated levels of proliferation marker Ki67. In addition, BCa-11 cells showed loss of HOXA5, tumour suppressor genes p16(INK4A) and RARbeta as well as overexpression of CyclinD1. Elevation of DNMT1 and DNMT3B transcript levels, promoter hypermethylation of RASSF1A, RARbeta2, and HOXA5 further support their neoplastic origin. In conclusion, the two ERalpha negative breast cancer cell lines established herein have certain useful characteristics that may make them valuable for understanding the mechanism of oestrogen receptor negative breast tumours and testing new drugs.Cell Biology International 02/2008; 32(1):55-65. DOI:10.1016/j.cellbi.2007.08.010 · 1.64 Impact Factor
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ABSTRACT: Dysregulation of microRNAs (miRNAs) has been demonstrated to contribute to malignant progression in nasopharyngeal carcinoma (NPC). We previously reported that miR-93 was significantly upregulated in NPC based on a microarray analysis. However, the potential role and mechanism of action of miR-93 in the initiation and progression of NPC remains largely unknown. Quantitative RT-PCR demonstrated that miR-93 was significantly upregulated in NPC cell lines and clinical specimens. The MTT assay, colony formation assay, anchorage-independent growth, and Transwell migration and invasion assays showed that depletion of miR-93 inhibited NPC cell growth, invasion and migration in vitro and suppressed tumor growth in vivo. Disabled homolog-2 (Dab2) was verified as a miR-93 target gene using Luciferase reporter assays, quantitative RT-PCR and Western blotting and was involved in miR-93-regulated NPC cell growth, invasion and migration. These results indicated that miR-93 plays an important role in the initiation and progression of NPC by targeting Dab2 and the miR-93/Dab2 pathway may contribute to the development of novel therapeutic strategies for NPC in future. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.Cancer letters 04/2015; 363(2). DOI:10.1016/j.canlet.2015.04.006 · 5.02 Impact Factor