Hgfr/Met oncogene acts as target for gene amplification in DMBA-induced rat sarcomas: Free chromatin fluorescence in situ hybridization analysis of amplicon arrays in homogeneously staining regions

Analysis of chromosome rearrangements in tumors is an important means for r evealing genetic pathways underlying tumorigenesis and tumor progression. I n five of 17 DMBA-induced rat sarcomas, cytogenetic analysis had disclosed homogeneously staining regions (hsrs), which are generally accepted to be c ytogenetic signs of gene amplification. Using comparative genomic hybridiza tion (CGH), regional increases in DNA copy number of the proximal part of r at chromosome (RNO) 4 were detected in four of the tumors harboring hsrs. A mplification of the Hgfr/Met oncogene, located at RNO4q21.2, was detected b y fluorescence in situ hybridization (FISH) in five tumors. In four of them . a number of flanking genes located in the close vicinity of Hgfr/Met, inc luding Cov1 (q21.1), Wnt2 (q21.2-q21.3), and Cftr (q21.3), also were amplif ied, though amplification was seen in a lower fraction of the cells than wa s Hgfr/Met amplification. In the fifth tumor (BL150T), Hgfr/Met was amplifi ed in all cells and was the sole amplified gene of those tested. In additio n, the Hgfr/Met FISH signals in BL150T were tightly clustered and formed co mpact and intense spots compared with the signals seen in the other four tu mors. Application of the free chromatin FISH technique to BL150T showed tha t the genomic Hgfr/Met probe stained the extended chromatin fibers of up to 1.5 Mb with an almost uninterrupted signal, indicating that the BL150T amp licon was build up solely of Hgfr/Met gene sequences. Our results suggest t hat the Hgfr/Met oncogene is the primary target for amplification in a subs et of rat DMBA sarcomas. (C) 2001 Wiley-Liss, Inc.