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HLTF gene silencing in human colon cancer
Helen R Moinova1, Wei-Dong Chen, Lanlan Shen
1Cancer Center and Department of Medicine at Case Western Reserve University, Cleveland, OH 44106, USA.
Abstract:
Chromatin remodeling enzymes are increasingly implicated in a variety of important cellular functions. Various components of chromatin remodeling complexes, including several members of the SWI/SNF family, have been shown to be disrupted in cancer. In this study we identified as a target for gene inactivation in colon cancer the gene for helicase-like transcription factor (HLTF), a SWI/SNF family protein. Loss of HLTF expression accompanied by HLTF promoter methylation was noted in nine of 34 colon cancer cell lines. In these cell lines HLTF expression was restored by treatment with the demethylating agent 5-azacytidine. In further studies of primary colon cancer tissues, HLTF methylation was detected in 27 of 63 cases (43%). No methylation of HLTF was detected in breast or lung cancers, suggesting selection for HLTF methylation in colonic malignancies. Transfection of HLTF suppressed 75% of colony growth in each of three different HLTF-deficient cell lines, but showed no suppressive effect in any of three HLTF-proficient cell lines. These findings show that HLTF is a common target for methylation and epigenetic gene silencing in colon cancer and suggest HLTF is a candidate colon cancer suppressor gene.
Insights
Helicase-like transcription factor (HLTF) is frequently silenced by promoter methylation in colon cancer. Restoring HLTF expression suppressed tumor cell growth, identifying it as a potential colon cancer suppressor gene.
Area of Science:
- Epigenetics
- Cancer Biology
- Molecular Oncology
Background:
- Chromatin remodeling enzymes, including SWI/SNF family proteins, play critical roles in cellular functions and are frequently disrupted in cancer.
- The helicase-like transcription factor (HLTF) is a member of the SWI/SNF family.
Purpose of the Study:
- To investigate the role of HLTF as a target for gene inactivation in colon cancer.
- To determine the frequency and significance of HLTF promoter methylation in colon malignancies.
Main Methods:
- Analysis of HLTF expression and promoter methylation in colon cancer cell lines and primary tissues.
- Treatment of HLTF-deficient cell lines with a demethylating agent (5-azacytidine) to assess gene expression restoration.
- Functional studies involving transfection of HLTF into HLTF-deficient and proficient cell lines to evaluate its effect on colony growth.
Main Results:
- Loss of HLTF expression due to promoter methylation was observed in 9 of 34 colon cancer cell lines.
- HLTF methylation was detected in 43% (27 of 63) of primary colon cancer tissues, but not in breast or lung cancers.
- Restoration of HLTF expression by 5-azacytidine confirmed the role of methylation in gene silencing.
- Transfection of HLTF significantly suppressed colony growth in HLTF-deficient cell lines but not in HLTF-proficient ones.
Conclusions:
- HLTF is a common target for epigenetic gene silencing via promoter methylation in colon cancer.
- HLTF functions as a tumor suppressor gene in the colon.
- HLTF methylation is a specific event selected for in colon cancer development.