cyclin-d1 and Hepatitis--Animal

It has been shown that a variety of cell cycle-related proteins play important roles in the process of carcinogenesis including hepatocarcinogenesis. In the present study, we evaluated mRNA and protein expression of G1 phase-related cell cycle molecules in the process of hepatocarcinogenesis, using Long-Evans Cinnamon (LEC) rats, an animal model of hepatocellular carcinoma (HCC). The expression of cyclin D1, cyclin-dependent kinase 4 (Cdk4) and Cdk6 was measured quantitatively by real-time polymerase chain reaction. Cyclin D1 mRNA expression was increased significantly in chronic hepatitis liver compared with normal liver, and then decreased in HCC and the surrounding precancerous liver of LEC rats. Levels of Cdk4 mRNA were increased significantly in HCC compared to precancerous and chronic hepatitis livers. In contrast, mRNA levels of Cdk6 did not change significantly during hepatocarcinogenesis. We also evaluated the protein levels of these G1 phase-related cell cycle molecules by Western blot analyses and confirmed similar results. Total amounts of retinoblastoma protein (pRb) in the liver did not change significantly in the process of hepatocarcinogenesis in LEC rats. However, levels of phosphorylated pRb were increased markedly in the process of hepatocarcinogenesis, and the highest in HCC compared to precancerous, chronic hepatitis and normal livers. These results indicate that cyclin D1 may be involved in the regeneration of hepatocytes rather than hepatocarcinogenesis, while Cdk4 but not Cdk6 may play an important role in the development of HCC.

Topics: Animals; Carcinoma, Hepatocellular; Cell Cycle Proteins; Cyclin D1; Cyclin-Dependent Kinase 4; Cyclin-Dependent Kinase 6; Cyclin-Dependent Kinases; G1 Phase; Hepatitis, Animal; Hepatitis, Chronic; Liver Cirrhosis; Liver Neoplasms, Experimental; Phosphorylation; Proto-Oncogene Proteins; Rats; Rats, Inbred LEC; Retinoblastoma Protein; RNA, Messenger

JunD is the most broadly expressed member of the Jun family and the AP-1 transcription factor complex. Primary fibroblasts lacking JunD displayed p53-dependent growth arrest, upregulated p19(Arf) expression, and premature senescence. In contrast, immortalized cell lines lacking JunD showed increased proliferation and higher cyclinD1 levels. These properties are reminiscent of the effects of oncogenic Ras expression on primary and established cell cultures. Furthermore, JunD(-/-) fibroblasts exhibited increased p53-dependent apoptosis upon ultraviolet irradiation and were sensitive to the cytotoxic effects of TNF-alpha. The antiapoptotic role of JunD was confirmed using an in vivo model of TNF-mediated hepatitis. We propose that JunD protects cells from senescence, or apoptotic responses to stress stimuli, by acting as a modulator of the signaling pathways that link Ras to p53.

Topics: 3T3 Cells; Animals; Apoptosis; Cell Division; Cell Line, Transformed; Cells, Cultured; Cellular Senescence; Cyclin D1; Cyclin-Dependent Kinase Inhibitor p16; Fibroblasts; Gene Deletion; Hepatitis, Animal; Hepatocytes; Lipopolysaccharides; Mice; Mice, Knockout; Proto-Oncogene Proteins c-jun; Radiation Tolerance; ras Proteins; Signal Transduction; Survival Rate; Tumor Necrosis Factor-alpha; Tumor Suppressor Protein p14ARF; Tumor Suppressor Protein p53; Ultraviolet Rays

Helicobacter hepaticus is a new bacterial species that is homologous to Helicobacter pylori, a human gastric carcinogen. H. hepaticus causes chronic active hepatitis, with progression to hepatocellular tumors. We hypothesized that chronic up-regulation of epidermal growth factor (EGF), transforming growth factor-alpha, and nuclear oncogenes (cyclin D1 and c-Myc), all known to transform by overexpression, might contribute to tumorigenesis. Livers from mice that were 6-18 months old were analyzed, including nonneoplastic and preneoplastic tissues and tumors, along with age-matched controls, by immunohistochemistry and immunoblotting. EGF and transforming growth factor-alpha were increased at the earliest stage, with a further increase in EGF in tumors. Cyclin D1, cyclin-dependent kinase 4, and c-Myc were strongly increased in all infected livers, with even greater increases in tumors. An increase in cyclin D1/cyclin-dependent kinase 4 complex was also demonstrated in tumors, and its functionality was confirmed by an increase in the hyperphosphorylated:hypophosphorylated retinoblastoma protein ratio. Our findings suggest a possible cooperation of growth factors, cell cycle proteins, and transcription factors during the development of H. hepaticus-associated liver tumors and may have relevance to human cancers associated with bacterial, viral, or parasitic infections.

Topics: Animals; Cyclin D1; Cyclin-Dependent Kinase 4; Cyclin-Dependent Kinases; Epidermal Growth Factor; Helicobacter Infections; Hepatitis, Animal; Liver Neoplasms, Experimental; Male; Mice; Mice, Inbred A; Neoplasm Proteins; Phosphorylation; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-myc; Retinoblastoma Protein; Transforming Growth Factor alpha