Age of host and transplantation-site microenvironment inf luence the tumorigenic potential of neoplastically transformed liver epithelial cells. Tumorigenic BAG2-GN6TF rat liver epithelial cells consistently form tumors at ectopic sites, but differentially express tumorigenicity or hepatocytic differentiation in the liver depending on host age and route of cell transplantation into the liver.

We have previously mapped a liver tumor suppressor locus to human chromosome 11p11.2-p12 using a functional model of tumor suppression. Using this model system, we have employed a candidate gene approach to identify potential liver tumor suppressor genes. Thirty-eight known genes have been positioned in human 11p11.2-p12 by the Human Genome Project. Here we show that four of these genes (guanine nucleotide binding protein gamma 3; mitochondrial carrier homolog 2; p53-induced protein (PIG11), and pRDI-BF1-rIZ1 domain containing 11) localized to the minimal liver tumor suppressor region within 11p11.2-p12. In fact, all of these genes mapped to human 11p11.2, allowing refinement of the liver tumor suppressor region to this cytogenetic band. Three of the four genes (mitochondrial carrier homolog 2, PIG11, and pRDI-BF1-rIZ1 domain containing 11) were uniformly expressed by an index panel of suppressed microcell hybrid cell lines, identifying them as candidate liver tumor suppressor genes. In a preliminary analysis of four human hepatocellular carcinoma cell lines (HepG2, Hep3B, SNU398, and SNU449), the transcript for PIG11 was lost or significantly decreased in two of these cell lines (HepG2 and Hep3B), suggesting the potential involvement of PIG11 in some human hepatocellular carcinomas. The results of this study extended our previous knowledge of genes located in the minimal liver tumor suppressor region of human 11p11.2 and identified several candidate liver tumor suppressor genes from this region. Further characterization of these candidates will provide new insight into the role of human 11p11.2 in the molecular pathogenesis of human liver cancer.

We have previously described a functional model for identification of human liver tumor suppressor genes in which human chromosome 11 was introduced into rat liver epithelial tumor cell lines via microcell-mediated chromosome transfer, producing microcell hybrid (MCH) cell lines that exhibit suppression of tumorigenicity in vivo. Chromosome deletion mapping studies identified a 950-kb region of 11p11.2-p12 that was retained in all suppressed MCH cell lines, suggesting that this region may harbor one or more genes with liver tumor suppressor function. In this study, we generated a comprehensive transcription map of the 11p11.2-p12 liver tumor suppressor region through examination of 142 expressed sequence tag (EST) markers among a group of suppressed MCH cell lines. Of 142 ESTs examined, 19 were localized within the 11p11.2-p12 liver tumor suppressor region. RT-PCR analysis of gene expression for these 19 ESTs among an index panel of suppressed MCH cell lines (n = 3) identified 11 potential candidate liver tumor suppressor genes. Examination of candidate gene expression among six additional suppressed MCH cell lines reduced the number of potential candidate genes to three (stSG30184, stSG10014, and stSG29748). Northern blot analysis of suppressed MCH cell lines and derived tumor cell lines suggested stSG30184 as the best candidate liver tumor suppressor gene. The 3.7 kb stSG30184 transcript was expressed by all suppressed MCH cell lines, but expression was extinguished coordinately with reexpression of tumorigenicity by these cells, consistent with a tumor suppressor gene. Subsequent characterization of this EST indicates that it is a novel transcript with expression in a broad range of tissue types. Further characterization of the genes identified in this study will provide a greater understanding of their role in the molecular pathogenesis of neoplastic liver disease.

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