Comprehensive gene expression analysis of peroxisome proliferator-treated immortalized hepatocytes: identification of peroxisome proliferator-activated receptor alpha-dependent growth regulatory genes. Cancer Res. 63:5767–5780

Chemicals known as peroxisome proliferators (PPs) are the subject of intense study because of their ability to cause hepatocellular carcinoma in laboratory rodents. These chemicals act through a family of proteins termed the peroxisome proliferator-activated receptors (PPARs), in par-ticular PPAR. It has become increasingly apparent that the role of the PPs in the development of cancer encompasses many different aspects of cell growth regulation. Immortalized hepatocytes from wild-type (PPAR/) and PPAR/ mice were generated using a temperature-sensitive SV40 virus. Characterization of the murine SV40 hepatocytes (MuSH) generated from both genotypes (MuSH/, MuSH/) show markers of differentiation such as albumin expression, but is devoid of Kupffer cell contamination. Hallmark PPAR-mediated responses such as induction of acyl-CoA oxidase mRNA by PPs are present in the MuSH/ but are absent in MuSH/ cells. In contrast to most cell culture systems, the wild-type MuSH hepatocytes retain the mitogenic activity of PPs, whereas the MuSH/ does not respond in this manner, thus making this cell culture system an ideal tool to examine growth regulatory gene expression affected by PPs. Microarray experiments per-formed on both cell types identified many genes in which regulation is dependent on the presence of PPAR, and these changes were verified with reverse transcriptase-PCR. Genes involved in carcinogenesis and control of the cell cycle that are regulated by PPs in a PPAR-dependent manner include ubiquitin COOH-terminal hydrolase 37 (also known as UCT-L5) and cyclin T1. These results show that MuSH cells reflect the biological properties of both the wild-type and PPAR-null animals and can be used to identify novel PPAR-regulated genes that could be involved in regulation of the cell cycle and carcinogenesis