title: 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.
authors.affiliation: Department of Biochemistry, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India.
authors.forename: Sarangadhara Appala Raju
authors.initials: SA
authors.lastname: Bagadi
authors.forename: Chandra Prakash
authors.initials: CP
authors.lastname: Prasad
authors.forename: Anurag
authors.initials: A
authors.lastname: Srivastava
authors.forename: Rajinder
authors.initials: R
authors.lastname: Prashad
authors.forename: Siddarth Datta
authors.initials: SD
authors.lastname: Gupta
authors.forename: Ranju
authors.initials: R
authors.lastname: Ralhan
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics*; D000328:Adult; D051017:Apoptosis Regulatory Proteins; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D018899:CpG Islands; D019175:DNA Methylation; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D035683:MicroRNAs / Q000378:metabolism; D008875:Middle Aged; D011401:Promoter Regions, Genetic; D025521:Tumor Suppressor Proteins
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; C102885:DAB2 protein, human; D035683:MicroRNAs; D025521:Tumor Suppressor Proteins