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Inactivation of SMAD4 tumor suppressor gene during gastric carcinoma progression
Li-Hui Wang1, Seok-Hyung Kim, Jung Hyun Lee
1Research Institute of Pharmaceutical Science, Department of Pharmacy, Seoul National University College of Pharmacy, Seoul, Korea.
Purpose:
Mothers against decapentaplegic homologue 4 (SMAD4) is a tumor suppressor gene associated with gastrointestinal carcinogenesis. The aim of the present study is to more precisely characterize its role in the development and progression of human gastric carcinoma.
Experimental Design:
The expression of SMAD4 was investigated in 283 gastric adenocarcinomas and related lesions, as well as in 9 gastric carcinoma cell lines. We also analyzed the methylation status of SMAD4 gene by using methylation-specific PCR, examined loss of heterozygosity (LOH) of this gene locus by using a vicinal marker, and detected exon mutation of SMAD4 through exon-by-exon amplification. Moreover, we assessed whether MG132, a proteasome inhibitor, affected the SMAD4 protein level.
Results:
We found loss of SMAD4 protein expression in the cytoplasm (36 of 114, 32%) and in the nucleus (46 of 114, 40%) of gastric cancer cells. The loss of nuclear SMAD4 expression in primary tumors correlated significantly with poor survival, and was an independent prognostic marker in multivariate analysis. We also found a substantial decrease in SMAD4 expression at both the RNA and protein level in several human gastric carcinoma cell lines. In addition, we found that LOH (20 of 70, 29%) and promoter hypermethylation (4 of 73, 5%) were associated with the loss of SMAD4 expression. SMAD4 protein levels were also affected in certain gastric carcinoma cell lines following incubation with MG132.
Conclusion:
Taken together, our results indicate that the loss of SMAD4, especially loss of nuclear SMAD4 expression, is involved in gastric cancer progression. The loss of SMAD4 in gastric carcinomas was due to several mechanisms, including LOH, hypermethylation, and proteasome degradation.
Insights
Loss of nuclear SMAD4 expression in gastric cancer is linked to poor survival and indicates the gene
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- Mothers against decapentaplegic homologue 4 (SMAD4) is a known tumor suppressor gene.
- SMAD4 plays a critical role in gastrointestinal carcinogenesis.
- Its precise function in human gastric carcinoma development and progression requires further elucidation.
Purpose of the Study:
- To investigate the role of SMAD4 in human gastric carcinoma.
- To analyze SMAD4 expression patterns in gastric tumors and cell lines.
- To identify mechanisms contributing to SMAD4 loss in gastric cancer.
Main Methods:
- Investigated SMAD4 expression in 283 gastric adenocarcinomas and 9 cell lines.
- Analyzed SMAD4 gene methylation status using methylation-specific PCR.
- Assessed loss of heterozygosity (LOH) and exon mutations of SMAD4.
- Evaluated the effect of proteasome inhibitor MG132 on SMAD4 protein levels.
Main Results:
- Loss of SMAD4 protein expression observed in cytoplasm (32%) and nucleus (40%) of gastric cancer cells.
- Loss of nuclear SMAD4 expression significantly correlated with poor survival and served as an independent prognostic marker.
- Decreased SMAD4 expression at RNA and protein levels noted in gastric carcinoma cell lines.
- LOH (29%) and promoter hypermethylation (5%) were associated with SMAD4 expression loss.
- MG132 affected SMAD4 protein levels in certain cell lines.
Conclusions:
- Loss of SMAD4, particularly nuclear expression, is implicated in gastric cancer progression.
- Mechanisms for SMAD4 loss include LOH, promoter hypermethylation, and proteasome degradation.
- SMAD4 is a crucial factor in gastric carcinogenesis, with its loss impacting patient prognosis.
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