The Hgfr/Met oncogene is the target for gene amplification in DMBA-induced rat sarcomas

Abstract

Analysis of chromosome rearrangements in tumors is an important means for revealing genetic pathways underlying tumorigenesis and tumor progression. In a set of 17 rat sarcomas induced by exposure to 7,12-dimethylbenz[a]anthracene (DMBA), we had previously found homogeneously staining regions (which are generally accepted as cytogenetic signs of gene amplification) in 5 tumors, using cytogenetic analysis. By employing comparative genomic hybridization, we detected regional increases in DNA copy number of the proximal part of rat chromosome 4 (RNO4) in the tumors harboring homogeneously staining regions. We detected amplification of the Hgfr/Met oncogene, located at RNO4q21.2, by fluorescence in situ hybridization (FISH) in all five tumors. In four of them, several flanking genes located in the near vicinity of Hgfr/Met, including Cav1 (q21.1), Wnt2 (q21.2?q21.3) and Cftr (q21.3), were also amplified, although amplification was seen in a smaller fraction of the cells than Hgfr/Met amplification. In the fifth tumor (BL150T), Hgfr/Met was amplified in all cells and was the sole amplified gene of those tested. In addition the Hgfr/Met FISH signals in BL150T were tightly clustered and formed compact and intense spots compared with the signals seen in the other four tumors. Application of the free chromatin FISH technique to BL150T showed that the genomic Hgfr/Met probe stained the extended chromatin fibers of up to 1.5 megabases with an almost uninterrupted signal, indicating that the BL150T amplicon was build up solely from Hgfr/Met gene sequences. Our results indicate that the Hgfr/Met oncogene may be the primary target for amplification in a subset of rat DMBA sarcomas.