Structure, sequence, and promoter analysis of human disabled-2 gene (DAB2)

Disabled-2 (DAB2 for human and Dab2 for other species) is one of two mammal ian orthologues of Drosophila Disabled. DAB2 exhibits properties of a tumor suppressor gene: the expression of DAB2 is eliminated in 85-95% of breast and ovarian tumors; homozygous deletions of the gene have been found in som e of these tumors; and reintroduction of DAB2 expression suppresses tumorig enicity of carcinoma cells. To study the mechanisms of loss of expression a nd to detect possible mutations in tumors, we have investigated the genomic structure of the DAB2 gene. The complete DAB2 gene was identified and sequ enced from four overlapping BAC clones found to contain the gene. Complemen t factor 9 (C9) gene was localized next to the DAB2 gene at the 3'-end of t he BAC DNA fragments. The human DAB2 gene is about 35 kb in size and consis ts of 15 exons and 14 introns, producing an approximately 4-kb message. A s pliced variant corresponding to mouse Dab2 p93 and a 3'-end spliced variant were also identified. The translation initiation site resides in the secon d exon, and the noncoding first exon is separated from the second exon by a 14-kb intron. The 420-bp sequence 5' of exon 1 contains a CpG island (39 C pG sites). This 420-bp putative promoter was found to contain the site for transcription initiation, identified by RNase protection assay, and is suff icient for active transcription in epithelial cells. The information about the gene structure of DAB2 will enable us to analyze possible mutations and the mechanisms of loss of DAB2 expression in tumors. (C) 2000 Academic Pre ss.