ase, which instead was present in the cytoplasm on HCC cells. Forty-five-50 weeks after initiation, 8 moderately differentiated and 2 poorly differentiated HCC were collected from F344 rats. Three well-differentiated and 7 moderately differentiated HCC were collected at 6067 weeks from BN rats. 3.2 Identification of deregulated genes in DN and HCC Gene expression profiles showed 105 upregulated and 94 downregulated genes in F344 HCC, with respect to Neuromedin N custom synthesis normal liver, 70% of which were also upregulated, and 46% were downregulated in F344 DN, respectively. Most genes involved in signal transduction and HCC progression were upregulated in DN and/or HCC, whereas tumor growth inhibitors Gadd45g, Gnmt, Dusp1, and Dmbt1, were downregulated in DN and/or HCC of F344 rats. In HCC of BN rats 126 genes were upregulated and 88 were downregulated. Upregulated genes included different growth-related and signal transduction genes. Notably, growth inhibitors such as Dmbt1, Dusp1, Fath1, Gadd45g, Gnmt, Klf6, and Pp2ca were upregulated in BN nodules and/or HCC. Changes in gene expression regarded 23 upregulated and 26 downregulated genes in BN nodules, only 55% of which were also deregulated in BN HCC. 3.3 Unsupervised hierarchical clustering of gene expression reveals two distinct classes of DN in rats with different susceptibility Evaluation of gene expression profiles of F344 normal liver versus BN liver showed about 2-fold higher expression of Gng10 and Rapgef2 in BN than F344 rat liver, and 2.23.1 fold higher 
expression of Cyp7b1, Decr1 and Gsta2 in F344 liver. This indicates the existence of close similar expression patterns between F344 and BN normal livers. Therefore, direct interstrain comparison of DN and HCC expression profiles was made, using BN normal liver as a reference. Unsupervised hierarchical cluster analysis of gene expression data from normal livers, DN, and HCC of F344 and BN rats revealed two distinctive gene expression patterns, the first of which included normal liver of F344 and BN rats and DN of BN rats, and the second one DN of F344 rats, and HCC of both strains. When the data were analyzed using high statistical stringency, expression of 91 DN genes was significantly different between BN and F344 rats, whereas no interstrain difference in expression of these genes occurred in normal livers. Sixty-nine known genes, among the 91 annotated genes differentially expressed, exhibited a wide range of functions according to GeneOntology database. Most genes involved in “metabolic process”, “response to stimulus”, “response to xenobiotics”, “oxidative stress”, “signal transduction”, and “cell proliferation” Author Manuscript Author Manuscript Author Manuscript Author Manuscript Cell Oncol. Author manuscript; available in PMC 2015 July 28. Frau et al. Page 5 were more expressed in F344 than BN DN, whereas oncosuppressors and cytochrome P450 isoforms were more expressed in BN than F344 DN. Interstrain comparison for gene expression in HCC showed significant differences for 55 genes, most of which, involved in “metabolic process”, “cell proliferation” and “signal transduction”, and all oncosuppressors were more expressed in BN than F344 HCC. Only ~20% of genes differently expressed with respect to normal liver exhibited a uniform behavior in PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19846406 DN and HCC of BN rats, whereas about 70% of genes showed a uniform pattern in F344 rat lesions. The BN/F344 expression ratios of genes differently expressed in DN and HCC, were plausible with the expressi