Molecular credentialing of rodent bladder carcinogenesis models

Abstract

Cancer of the urinary bladder is often a result of exposure to chemical carcinogens. Models of this disease have been developed by exposing rodents to N-butyl-N-(4-hydroxybutyl)-nitrosamine (OH-BBN). The resultant tumors are histologically similar to human disease, but little is known about genetic similarities to the latter. Such knowledge would help identify or corroborate genes found important in human bladder cancer and suggest biologically appropriate mechanistic studies. We address this need by comparing gene expression profiles associated with urothelial carcinoma for three different species: mouse, rat, and human. We find that many human genes homologous to those differentially expressed in carcinogen-induced rodent tumors are also differentially expressed in human disease and are preferentially associated with progression from non-muscle-invasive to muscle-invasive disease. We also find that overall gene expression profiles of rodent tumors correspond more closely with those of invasive human tumors rather than non-muscle-invasive tumors. Finally, we provide a list of genes that are likely candidates for driving this disease process by virtue of their concordant regulation in tumors of all three species.

Figure 1

(A) Diagrammatic representation of the analysis workflow and results. (B) Venn diagrams showing the numbers of genes differentially regulated in human, mouse, and rat and concordantly regulated. Shown are genes overexpressed or underexpressed in tumors compared to normal urothelium. Asterisk (*) indicates genes whose pattern of expression is shown in Figure 2.

Figure 2

Patterns of expression for genes differentially regulated in human, mouse, and rat bladder tumors as a function of human bladder state. The average normalized log2(gene expression) value for normal urothelium, non-muscle-invasive and muscle-invasive cancers are plotted for each tissue type. Data for all significantly and differentially expressed probe sets for the genes identified with an asterisk (*) in Figure 1B are plotted here. Line color codes relate to the gene expression pattern as a function of tumorigenicity and progression as shown in Table 2 (genes in bold). For example, genes with red lines are significantly differentially expressed between normal urothelium and noninvasive tumor and between noninvasive tumor and invasive human tumor.

Figure 3

Hierarchical clustering of rodent homologs with human cancer. Fold changes between gene expression values in human non-muscle-invasive and muscle-invasive tumors are hierarchically clustered with “mouse” (A) and “rat” (B) gene expression profiles. The probe sets in the “rodent” gene profiles are assigned published [12,13] fold change values (cancer vs normal) corresponding to the homologous rodent genes. Probe sets overexpressed in cancer are colored red, whereas underexpressed probe sets are colored green. HG-U133A probe sets are listed on the right, the stage and grade of the tumors characterized on the chips are shown on the bottom, and the color bar near the top of the figure represents the classification of the tumor: red indicates non-muscle-invasive tumors, blue indicates muscle-invasive tumors, and green indicates the mouse (A) or the rat profile (B).