Expression of Drop1, a gene encoding a 350 kDa protein, is downregulated in epithelial malignancies

2713 In a study employing differential display analysis to identify differentially expressed genes in ovarian carcinomas, we found an 11 kb mRNA coding for a 350 kDa Protein suppressed in over 70% of ovarian and mammary carcinomas. Its expression is downregulated 20-1000 fold in these tumors. cDNA arrays of matched pairs of tumor and normal tissue showed that the mRNA of Drop 1 is downregulated in more than 80% of epithelial tumors, such as ovary (>80%), breast (>50%), kidney (>90%), lung (>70%) and pancreas (85%). Incubation of cell lines expressing Drop 1 at a low lever with methyltransferase inhibitors resulted in an increase in Drop 1expression of up to 18-fold. This indicates that Drop 1 can be downregulated through methylation of the promoter. Mouse monoclonal antibodies raised to a C-terminal fragment of Drop1recognized a 350 kDa protein on Western Blots as well as a nucleus-associated protein on cytospins. Drop 1 is associated with the polar region of the mitotic spindle during mitosis. An N-terminal fragment of Drop 1 fused to GFP and expressed in COS-7 cells also shows association with the nucleus. This location as well as the structural homology to dystrophin make Drop1 an interesting candidate for processes involved in the integration of the nuclear structure during the cell cycle. RNAi knockdown experiments and yeast two hybrid screening are in progress to elucidate Drop1 function.