Independent amplification of two gene clusters on chromosome 4 in rat endometrial cancer: Identification and molecular characterization

The BDII rat is genetically predisposed to hormone-dependent endometrial ad enocarcinoma and was used to model human cancer. Tumors arising spontaneous ly in strain crosses involving BDII rats were analyzed by means of comparat ive genome hybridization. The most common aberration was amplification of t he proximal region of rat chromosome 4, centered around bands q12-q22. The copy numbers of 15 cancer-related genes from the region were examined in ti ssue cultures of 11 endometrial carcinomas (10 endometrial adenocarcinomas and 1 endometrial squamous cell carcinoma) and one peritoneal mesothelioma. Amplification in rat chromosome 4 was detected in six tumors (50 %), five of which carried two separate amplified regions, situated at 4q12-q13 and 4 q21-q22, interrupted by a nonamplified segment at 4q13-q21.1. The genes Cdk 6 (cyclin-dependent kinase 6) and Met (hepatocyte growth factor receptor) w ere located in the core of each amplified region and were amplified most re currently and at the highest levels among the genes tested. Using fluoresce nce in situ hybridization on tumor metaphases, it was observed that the amp lified Cdk6 and Met sequences were situated on typical homogeneously staini ng regions (HSRs). In three tumors, both genes were amplified in the same H SRs, whereas in two tumors, the amplified sequences of each gene were situa ted in separate HSRs. In addition, Cdk6 and Met amplification was consisten tly associated with a corresponding increase in gene expression, suggesting that the two genes might represent the targets for the amplifications. In the sixth tumor, which carried amplified sequences of Met but not of Cdk6, coexpression of Met and the normally silent hepatocyte growth factor gene ( Hgf; the ligand of Met) was observed. This finding suggests that an autocri ne signaling circuit might be operating in this particular tumor. Taken tog ether, our findings suggest that up-regulation of Cdk6 and/or Met may contr ibute to the development of endometrial cancers in the BDII rat.