Recurrent and nonrandom DNA copy number and chromosome alterations in Myc transgenic mouse model for hepatocellular carcinogenesis: implications for human disease

Abstract

Mouse models for hepatocellular carcinoma (HCC) provide an experimental ground for dissecting the genetic and biological complexities of human liver cancer and contribute to our ability to gain insights into the relevance of candidate cancer genes. We examined, using spectral karyotyping (SKY) and array-based CGH (aCGH), seven cell lines derived from HCC spontaneously developed in transgenic Myc mice (Myc), and four cell lines established from tumors induced in nude mice by inoculation with the original Myc cells (nuMyc). All the cell lines exhibited gain of material from chromosomes 5, 6, 8, 10, 11, 15, and 19 and DNA copy-number loss from chromosomes 2, 4, 7, 9, 12, 14, and X. In addition, several recurrent chromosome reorganizations were found, including del(3), t(3;8), del(4), t(4;11), t(6;5), del(7), del(8), del(9), t(10;14), del(11), and del(16). Chromosome breakpoints underlying rearrangements clustered in the regions previously identified as important for the early stages of Myc-induced hepatocarcinogenesis. The results strongly suggest the importance of recurrent breakage and loss of chromosomes 4, 9, and 14 and gain of chromosomes 15 and 19 in mouse liver neoplasia. Genomic changes observed in Myc HCC cell lines are also recurrent in HCC developed in other transgenic mouse models, in mouse spontaneous HCC and derivative cell lines, and in preneoplastic liver lesions induced with chemical carcinogens. Overall, the present results document selective, nonrandom genomic changes involving chromosomal regions homologous to those implicated in human HCC.

Figure 1

Spectral karyotypes (a, c) and aCGH profiles (b, d) in 604D.02.T2.CL1 and 620A.03.T2.CL3 cell lines, respectively

Figure 2

Selected recurrent structural chromosome rearrangements identified in c-Myc and NuMyc cell lines. Combined use of SKY and aCGH enableed precise annotation and identification of even cryptic losses such as interstitial loss of material from chromosome 8 (a) in translocation (3;8), chromosome 11 (b) in complex reorganization involving chromosomes 4, 5 and 11, or chromosome 9 (c), or small proximal and distal deletions in chromosomes 10 and 14, respectively.

Figure 3

Variable “shortening” of chromosome 4;deletions of this chromosome occur at different breakpoints, sometimes within the same cell line. Most frequent breakpoints are located in region D2 followed by C6 and A5.

Figure 4

Cell lines isolated from tumors induced in nude mice by injection of the original c-Myc HCC cell lines show increased incidence of DNA copy-number changes. (a, b) 604D.02.T1.CL4 and nuMyc 3, (c, d) 604D.02.T2.CL1 and nuMyc 4, and (e, f) 620A.03.T2.CL3 and nuMyc