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Epigenetic inactivation of CHFR in human tumors
Minoru Toyota1, Yasushi Sasaki, Ayumi Satoh
1Department of Molecular Biology, Cancer Research Institute, Sapporo Medical University, Sapporo 060-8556, Japan.
Abstract:
Cell-cycle checkpoints controlling the orderly progression through mitosis are frequently disrupted in human cancers. One such checkpoint, entry into metaphase, is regulated by the CHFR gene encoding a protein possessing forkhead-associated and RING finger domains as well as ubiquitin-ligase activity. Although defects in this checkpoint have been described, the molecular basis and prevalence of CHFR inactivation in human tumors are still not fully understood. To address this question, we analyzed the pattern of CHFR expression in a number of human cancer cell lines and primary tumors. We found CpG methylation-dependent silencing of CHFR expression in 45% of cancer cell lines, 40% of primary colorectal cancers, 53% of colorectal adenomas, and 30% of primary head and neck cancers. Expression of CHFR was precisely correlated with both CpG methylation and deacetylation of histones H3 and H4 in the CpG-rich regulatory region. Moreover, CpG methylation and thus silencing of CHFR depended on the activities of two DNA methyltransferases, DNMT1 and DNMT3b, as their genetic inactivation restored CHFR expression. Finally, cells with CHFR methylation had an intrinsically high mitotic index when treated with microtubule inhibitor. This means that cells in which CHFR was epigenetically inactivated constitute loss-of-function alleles for mitotic checkpoint control. Taken together, these findings shed light on a pathway by which mitotic checkpoint is bypassed in cancer cells and suggest that inactivation of checkpoint genes is much more widespread than previously suspected.
Insights
The CHFR gene, crucial for cell division checkpoints, is epigenetically silenced in many cancers via DNA methylation. This inactivation leads to uncontrolled cell division, contributing to cancer development.
Area of Science:
- Molecular Biology
- Cancer Research
- Epigenetics
Background:
- Cell-cycle checkpoints are vital for preventing genomic instability in human cancers.
- The CHFR gene regulates entry into metaphase, a critical stage of mitosis.
- Understanding CHFR inactivation mechanisms in tumors is crucial for cancer research.
Purpose of the Study:
- To investigate the molecular basis and prevalence of CHFR gene silencing in human cancers.
- To determine the role of epigenetic modifications in CHFR inactivation.
- To assess the functional consequences of CHFR loss-of-function in cancer cells.
Main Methods:
- Analysis of CHFR gene expression in cancer cell lines and primary tumors.
- Assessment of CpG methylation and histone modifications in the CHFR regulatory region.
- Investigation of DNA methyltransferases (DNMT1 and DNMT3b) involvement.
- Evaluation of mitotic index in cells with CHFR methylation.
Main Results:
- CHFR expression was silenced in 45% of cancer cell lines and significant percentages of primary colorectal cancers, adenomas, and head and neck cancers.
- CHFR silencing correlated with CpG methylation and histone H3/H4 deacetylation.
- DNMT1 and DNMT3b activities were essential for CHFR methylation and silencing.
- Cells with methylated CHFR exhibited a high mitotic index when exposed to microtubule inhibitors.
Conclusions:
- Epigenetic inactivation of the CHFR gene, through CpG methylation, is a common event in human cancers.
- CHFR silencing contributes to bypassing mitotic checkpoints, promoting uncontrolled cell proliferation.
- These findings reveal a significant pathway for mitotic checkpoint evasion in cancer and suggest widespread inactivation of checkpoint genes.