Mutation and expression of the p53 gene during chemical hepatocarcinogenesis in F344 rats

Regulation of expression of drug-metabolizing enzymes by oncogenic signaling pathways in liver tumors: a review

Mutations in genes encoding key players in oncogenic signaling pathways trigger specific downstream gene expression profiles in the respective tumor cell populations. While regulation of genes related to cell growth, survival, and death has been extensively studied, much less is known on the regulation of drug-metabolizing enzymes (DMEs) by oncogenic signaling. Here, a comprehensive review of the available literature is presented summarizing the impact of the most relevant genetic alterations in human and rodent liver tumors on the expression of DMEs with a focus on phases I and II of xenobiotic metabolism. Comparably few data are available with respect to DME regulation by p53-dependent signaling, telomerase expression or altered chromatin remodeling. By contrast, DME regulation by constitutive activation of oncogenic signaling via the RAS/RAF/mitogen-activated protein kinase (MAPK) cascade or via the canonical WNT/β-catenin signaling pathway has been analyzed in greater depth, demonstrating mostly positive-regulatory effects of WNT/β-catenin signaling and negative-regulatory effects of MAPK signaling. Mechanistic studies have revealed molecular interactions between oncogenic signaling and nuclear xeno-sensing receptors which underlie the observed alterations in DME expression in liver tumors. Observations of altered DME expression and inducibility in liver tumors with a specific gene expression profile may impact pharmacological treatment options.

High mobility group box associated with cell proliferation appears to play an important role in hepatocellular carcinogenesis in rats and humans

To identify genes important in hepatocellular carcinogenesis, especially processes involved in malignant transformation, we focused on differences in gene expression between adenomas and carcinomas by DNA microarray. Eighty-one genes for which expression was specific in carcinomas were analyzed using Ingenuity Pathway Analysis software and Gene Ontology, and found to be associated with TP53 and regulators of cell proliferation. In the genes associated with TP53, we selected high mobility group box (HMGB) for detailed analysis. Immunohistochemistry revealed expression of HMGBs in carcinomas to be significantly higher than in other lesions among both human and rat liver, and a positive correlation between HMGBs and TP53 was detected in rat carcinomas. Knock-down of HMGB 2 expression in a rat hepatocellular carcinoma cell line by RNAi resulted in inhibition of cell growth, although no effects on invasion were evident in vitro. These results suggest that acquisition of malignant potential in the liver requires specific signaling pathways related to high cell proliferation associated with TP53. In particular, HMGBs appear to have an important role for progression and cell proliferation associated with loss of TP53 function in rat and in human hepatocarcinogenesis.

Correlation analysis of liver tumor-associated genes with liver regeneration

AIM: To study at transcriptional level the similarities and differences of the physiological and biochemical activities between liver tumor (LT) and regenerating liver cells.

METHODS: LT-associated genes and their expression changes in LT were obtained from databases and scientific articles, and their expression profiles in rat liver regeneration (LR) were detected using Rat Genome 230 2.0 array. Subsequently their expression changes in LT and LR were compared and analyzed.

RESULTS: One hundred and twenty one LT-associated genes were found to be LR-associated. Thirty four genes were up-regulated, and 14 genes were down-regulated in both LT and regenerating liver; 20 genes up-regulated in LT were down-regulated in regenerating liver; 21 up-regulated genes and 16 down-regulated genes in LT were up-regulated at some time points and down-regulated at others during LR.

CONCLUSION: Results suggested that apoptosis activity suppressed in LT was still active in regenerating liver, and there are lots of similarities and differences between the LT and regenerating liver at the aspects of cell growth, proliferation, differentiation, migration and angiogenesis.

p53 immunostaining pattern in Brazilian patients with hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is an important type of cancer etiologically related to some viruses, chemical carcinogens and other host or environmental factors associated to chronic liver injury in humans. The tumor suppressor gene p53 is mutated in highly variable levels (0-52%) of HCC in different countries.

OBJECTIVE

The objective of the present study was to compare the frequency of aberrant immunohistochemical expression of p53 in HCC occurring in cirrhotic or in non-cirrhotic patients as well as in liver cell dysplasia and in adenomatous hyperplasia. We studied 84 patients with HCC or cirrhosis.

RESULTS

We detected p53 altered immuno-expression in 58.3% of patients in Grade III-IV contrasting to 22.2% of patients in Grade I-II (p = 0.02). Nontumorous areas either in the vicinity of HCC or in the 30 purely cirrhotic cases showed no nuclear p53 altered expression, even in foci of dysplasia or adenomatous hyperplasia. No significant difference was found among cases related to HBV, HCV or alcohol.

CONCLUSION

The high frequency of p53 immunoexpression in this population is closer to those reported in China and Africa, demanding further studies to explain the differences with European and North American reports.