Amplification of Mycn, Ddx1, Rrm2, and Odc1 in rat uterine endometrial carcinomas

The BD11 rat is genetically predisposed to estrogen-dependent endometrial a denocarcinoma and represents a valuable model for this type of tumor. Tumor s arising in strain crosses involving the BD11 rats had previously been scr eened for DNA copy number changes using comparative genome hybridization (C GH). It was found that extra copies of the proximal region of rat chromosom e (RNO) 6 commonly could be detected in these tumors. Based on RH-mapping d ata and comparative mapping with mouse and human, seven cancer-related gene s were predicted to be situated in RNO6q14-q16. Rat PACs were isolated for the N-myc proto-oncogene (Mycn), apolipoprotein B (Apob), the DEAD box gene 1 (Ddx1), ornithine decarboxylase 1 (Odc1), proopiomelanocortin (Pomc1), r ibonucleotide reductase, M2 polypeptide (Rrm2), and syndecan 1 (5dc1). The localization of the genes to the region was verified by FISH (fluorescence in situ hybridization) mapping, and the detailed order among them was deter mined by dual-color FISH. By Southern blot analysis, it was found that the Mycn locus was highly amplified in two out of 10 cell cultures derived from the tumors. in one of them (designated RUT30), the amplification level of Mycn was estimated at 140 X. Two other genes were coamplified (Ddx1 and Rrm 2) at much lower levels. Similarly, in another culture (designated RUT2), M ycn was amplified more than 40x, whereas three of the other genes (Ddx1, Rr m2, and Odd) were coamplified at lower levels. Using FISH on metaphase chro mosomes from the cell cultures analyzed, the amplified sequences were shown to be located in typical HSRs. With competitive RT-PCR, distinct overexpre ssion of Mycn and Ddx1 could be demonstrated in both RUT2 and RUT30. In add ition, Mycn was overexpressed in two other tumors not exhibiting Mycn ampli fication, Taken together, our results suggest that overexpression of Mycn p lays an important role in the development of endometrial cancer in the BD11 rat. In humans, Mycn amplification has been reported mainly from tumors of neuronal origin. To our knowledge, this is the first report of Mycn amplif ication and overexpression in hormone-dependent tumors. (C) 2001 Wiley-Liss , Inc.