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Updated: Oct 1, 2026
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Published on: July 28, 2010
Expression of the hMSH6 mismatch-repair protein in colon cancer and HeLa cells
H Klingler1, C Hemmerle, F Bannwart
1Institute of Medical Radiobiology, University of Zürich, Switzerland.
Principles:
10 to 15% of human colon cancers are associated with an inherited or somatic defect of the DNA Mismatch Repair (MMR) system, which has evolved to correct biosynthetic errors such as nucleotide mis-incorporations or misalignments arising during DNA replication in the S phase of the cell-cycle. Although expression of the MMR genes was expected to be cell-cycle dependent, we and others observed that the MMR proteins hMSH2 and hMLH1 are expressed constitutively in proliferating cells.
Methods:
In this study we extend our observations to another essential MMR protein, hMSH6. We used immunohistochemistry to evaluate the expression pattern of this protein in human colorectal mucosa and tumours, as well as in synchronised HeLa-S3 cells, in which we analysed its steady-state levels during the cell-cycle.
Results:
We show that the immunohistochemical pattern of expression of hMSH6 in normal colorectal crypts and in colon cancers differs significantly from that of the other MMR proteins, with a much lower percentage of replicating cells being hMSH6-positive. This implies that hMSH6 could be cell-cycle regulated. In order to test this hypothesis in a model system, we synchronised HeLa-S3 cells with mitotic shake-off and found that the hMSH6 protein was detectable throughout the cell-cycle, but that its steady-state level increased when cells progressed from G1 to S-phase.
Discussion:
The increase of hMSH6 steadystate level when cells enter S-phase was expected, since MMR acts during DNA replication. However, the overall low level of oscillations of hMSH6 during the cell-cycle in this cellular model apparently does not fit the immunohistochemical phenotype. We believe that this discrepancy is due to the fact that human cell lines proliferate at a much higher rate than normal and neoplastic colorectal cells in vivo.
Insights
The DNA Mismatch Repair (MMR) protein hMSH6 shows increased levels during the S-phase of the cell cycle. However, its expression pattern in colorectal cells differs from other MMR proteins, suggesting complex regulation in vivo.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- DNA Mismatch Repair (MMR) system corrects DNA replication errors.
- Defects in MMR are linked to 10-15% of human colon cancers.
- MMR proteins hMSH2 and hMLH1 are constitutively expressed.
Purpose of the Study:
- Investigate the cell-cycle expression pattern of the MMR protein hMSH6.
- Compare hMSH6 expression in normal and cancerous colorectal tissues.
- Analyze hMSH6 steady-state levels during the cell cycle in a model system.
Main Methods:
- Immunohistochemistry used on human colorectal mucosa and tumors.
- Synchronized HeLa-S3 cells analyzed for hMSH6 levels during the cell cycle.
- Mitotic shake-off employed for cell cycle synchronization.
Main Results:
- hMSH6 expression pattern differs from other MMR proteins in colorectal cells.
- A lower percentage of replicating cells were hMSH6-positive in vivo.
- hMSH6 levels increased as HeLa-S3 cells progressed from G1 to S-phase.
Conclusions:
- hMSH6 levels increase during S-phase, consistent with its role in DNA replication.
- Discrepancy between in vitro and in vivo expression patterns may be due to differing proliferation rates.
- Further research needed to reconcile cell-cycle regulation and observed expression phenotypes.
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