Loss of heterozygosity of the mannose 6-phosphate/insulin-like growth factor II receptor and p53 genes in human hepatocellular carcinoma

The JNK inhibitor SP600129 enhances apoptosis of HCC cells induced by the tumor suppressor WWOX

BACKGROUND/AIMS

The FRA16D fragile site gene WWOX is a tumor suppressor that participates in p53-mediated apoptosis. The c-jun N-terminal kinase JNK1 interacts with WWOX and inhibits apoptosis. We investigated the function of WWOX in human hepatocellular carcinoma (HCC) and the effect of JNK inhibition on WWOX-mediated apoptosis.

METHODS

Allelic imbalance on chromosome 16 was analyzed in 73 HCCs using 53 microsatellite markers. WWOX mRNA in HCC cell lines and primary HCCs was measured by real-time RT-PCR. Effects of WWOX on proliferation and apoptosis and the interaction between WWOX and JNK inhibition were examined.

RESULTS

Loss on chromosome 16 occurred in 34 of 73 HCCs. Of 11 HCC cell lines, 2 had low, 7 intermediate, and 2 had high WWOX mRNA. Of 51 primary tumors, 23 had low WWOX mRNA. Forced expression of WWOX in SNU387 cells decreased FGF2-mediated proliferation and enhanced apoptosis induced by staurosporine and the JNK inhibitor SP600129. Conversely, knockdown of WWOX in SNU449 cells using shRNA targeting WWOX increased proliferation and resistance to SP600129-induced apoptosis.

CONCLUSIONS

WWOX induces apoptosis and inhibits human HCC cell growth through a mechanism enhanced by JNK inhibition.

Insulin-like growth factor 2 and its receptors (IGF 1R and IGF 2R/mannose 6-phosphate) in endometrial adenocarcinoma

OBJECTIVE

To investigate the consequences of IGF proteins dysfunction in development of endometrial adenocarcinomas.

METHODS

The expression of IGF 2 and IGF 1R was correlated with the expression of IGF 2R and apoptosis rate in 59 human endometrial adenocarcinomas, 10 endometrial hyperplasias and 7 normal tissues. The presence of mutations in the IGF 2R gene was followed in 46 adenocarcinomas. We also examined the effect of IGF 1 receptor blockage on cancer cell proliferation. In groups of either IGF 2-positive or IGF 2-negative tumors (stages III and IV) the expression of IGF 1 and IGF 1R was correlated with cell proliferation index and telomerase activity.

RESULTS

The expression of IGF 2 and IGF 1R was much higher in malignant tissue of stages III and IV than in tumors of stages I and II and normal or hyperplastic endometrium. This correlated with a decreased apoptosis rate and IGF 2R expression. Eight adenocarcinomas expressed biallelic mutation of the IGF 2R gene. The specific inhibition of IGF 1R and IGF 2 decreased tumor cell proliferation in IGF 2/IGF 1R-positive tumors. Furthermore, the positive correlation between increased expression of IGF 1 and IGF 1R proteins and increased telomerase activity and cell proliferation index was found in both IGF 2-negative and IGF 2-positive tumors.

CONCLUSION

Our data suggest that IGF 1, IGF 2 and their receptors are involved in the progression of endometrial adenocarcinomas. As cancer cell proliferation can be abrogated by blocking mRNA or protein products of these genes, tumors with extensive involvement of the IGF 2 pathway would be candidates for the therapeutics strategies aimed at interference with this pathway.

Reliable safety assessment depends on species differences in epigenetic mechanisms of gene regulation

The potential carcinogenic hazard of chemical agents to humans is presently based primarily on the results of long-term animal bioassays. The validity of this toxicologic approach to human risk assessment depends on two fundamental assumptions. First, the results of an animal bioassay are directly applicable to humans (interspecies extrapolation). Second, the doses used in an animal bioassay are relevant for estimating risk at known or expected human exposure levels (dose extrapolation). Although progress has been made over the past four decades in understanding the mode of action of chemical carcinogens, it is increasingly important to determine mechanistically the relevance of these modes of action in humans. There is now evidence that M6P/IGF2R functions as a novel tumor-suppressor gene in a variety of human and rodent cancers. M6p/Igf2r is imprinted in rodents and expressed only from the maternal allele after embryonic implantation. In contrast, both alleles are functional in humans. This marked species difference in M6P/IGF2R imprinting has important implications for human carcinogen risk assessment since only one rather than two alleles needs to be mutated in rodents to completely inactivate the function of this tumor suppressor gene. This striking species difference in the imprint status of M6P/IGF2R clearly demonstrates that we need to understand better variations in epigenetic mechanisms of gene regulation between rodents and humans to perform accurately chemical safety assessments.

Hepatitis B virus integration, fragile sites, and hepatocarcinogenesis

Chronic liver disease associated with long term hepatitis B virus (HBV) infection contributes importantly to the development of hepatocellular carcinoma (HCC). A salient feature of these chronic infections is the integration of subgenomic HBV DNA fragments into many different locations within the host DNA, suggesting that integration is random. Although this may promote genetic instability during liver regeneration which accompanies a bout of chronic liver disease, the actual role of integrated HBV DNA in hepatocarcinogenesis is uncertain. Importantly, most integration events retain the HBV open reading frame encoding the HBx antigen (HBxAg), which is the virus contribution to HCC. In addition, many integration events reported in the literature occur near or within fragile sites or other cancer associated regions of the human genome that are prone to instability in tumor development and progression. Genetic instability associated with integration potentially alters the expression of oncogenes, tumor suppressor genes, and microRNAs (miRNAs) that may contribute importantly to tumorigenesis. If so, then selected integration events may alter pathways that are rate limiting in hepatocarcinogenesis, thereby providing targets with diagnostic/prognostic potential and for therapeutic intervention.

Gastric cancer: the role of insulin-like growth factor 2 (IGF 2) and its receptors (IGF 1R and M6-P/IGF 2R)

Insulin-like growth factor 2 (IGF 2) appears to be involved in the progression of many tumours. It binds to at least two different types of receptor: IGF type 1 (IGF 1R) and mannose 6-phosphate/IGF type 2 (M6-P/IGF 2R). Ligand binding to IGF 1R provokes mitogenic and anti-apoptotic effects. M6-P/IGF 2R has a tumour suppressor function--it mediates IGF 2 degradation. Mutation of M6-P/IGF 2R causes both diminished growth suppression and augmented growth stimulation. The aim of this study was to investigate the role of IGF 2 and its receptors (IGF 1R and IGF 2R) in human gastric cancer. The expression of IGF 2 and its receptors was measured in order to analyse the possible correlation between the activity of these genes and cell proliferation in two different gastric tumour types: diffuse and intestinal. The effect of IGF 1 receptor blockage on cell proliferation and anchorage-independent cell growth was also examined. Increased expression of IGF 2 and IGF 1R genes (at the mRNA and protein level) was found in gastric cancer when compared with non-tumour tissue. Furthermore, there was a significant difference between IGF 2 expression in the more aggressive diffuse type and that in the intestinal type of gastric cancer. Moreover, the IGF 2 peptide level in the culture media obtained from the diffuse type of cancer cells was significantly higher when compared with the intestinal type. The level of IGF 2 peptide in the conditioned media strongly correlated with [3H]thymidine incorporation and cell proliferation. On the contrary, IGF 2R mRNA expression was much higher in the intestinal type of cancer than in the diffuse type. In addition, IGF 2R protein expression was substantially lower with progression of the diffuse cancer type to a higher stage. The alphaIR3 monoclonal antibody strongly inhibited [3H]thymidine incorporation and decreased the number of colonies in soft agar of cells overexpressing IGF 2. These findings suggest that members of the IGF family are involved in the pathogenesis of gastric cancer, probably by autocrine/paracrine stimulation of cell growth. Such tumours might be excellent candidates for therapeutic strategies aimed at interference with this pathway.

M6P/IGF2R tumor suppressor gene mutated in hepatocellular carcinomas in Japan

Mannose 6-phosphate/insulin-like growth factor II receptor (M6P/IGF2R) tumor suppressor- gene mutation is an early event in human hepatocellular carcinoma (HCC) formation in the United States, but its role in hepatocarcinogenesis in Japan is unclear. We therefore determined M6P/IGF2R mutation frequency in HCCs from patients who resided in the southern, central, and northern regions of Japan. Ten single nucleotide polymorphisms were used to identify HCCs and dysplastic liver nodules with M6P/IGF2R loss of heterozygosity. The retained allele in these tumors was also assessed for point mutations and deletions in the M6P/IGF2R ligand binding domains by direct sequencing of polymerase chain reaction (PCR) amplified DNA products. Fifty-eight percent (54 of 93) of the patients were heterozygous at the M6P/IGF2R locus, and 67% (43 of 64) of the HCCs and 75% (3 of 4) of the dysplastic nodules had loss of heterozygosity. The remaining allele in 21% of the HCCs contained either M6P/IGF2R missense mutations or deletions, whereas such mutations were not found in the dysplastic lesions. In conclusion, M6P/IGF2R is mutated in HCCs from throughout Japan with a frequency similar to that in the United States. Loss of heterozygosity in dysplastic liver nodules provides additional evidence that M6P/IGF2R haploid insufficiency is an early event in human hepatocarcinogenesis.