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Functional effects of the MLH1-93G>A polymorphism on MLH1/EPM2AIP1 promoter activity

Sheron Perera1, Miralem Mrkonjic, James B Rawson

  • 1Department of Laboratory Medicine and Pathobiology, University of Toronto, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, 1 King's College Circle, Toronto, ON, Canada.

Oncology Reports
|January 6, 2011
PubMed

Insights

A common genetic variation in the MLH1 promoter influences both MLH1 and EPM2AIP1 gene activity, potentially impacting colorectal cancer (CRC) and other cancers with microsatellite instability (MSI). This polymorphism affects gene transcription and protein binding.

Area of Science:

  • Genetics
  • Molecular Biology
  • Oncology

Background:

  • Defective DNA mismatch repair (MMR) causes microsatellite instability (MSI), a hallmark of colorectal cancer (CRC).
  • A previously identified MLH1 promoter polymorphism (-93G>A) strongly correlates with MSI tumors, suggesting a role in CRC development.
  • The MLH1 promoter is bi-directional, also regulating the EPM2AIP1 gene on the antisense strand.

Purpose of the Study:

  • To investigate the functional impact of the MLH1-93G>A promoter polymorphism on MLH1 and EPM2AIP1 gene transcription.
  • To determine if this polymorphism affects protein binding to the MLH1 promoter region.

Main Methods:

  • Transfection of various cancer and non-tumorigenic cell lines with MLH1 luciferase promoter constructs.
  • Assessment of promoter activity for both forward (MLH1) and reverse (EPM2AIP1) orientations.
  • Electrophoretic mobility shift assays (EMSAs) to analyze differential nuclear factor binding.

Main Results:

  • The -93G allele exhibited higher MLH1 promoter activity across all tested cell lines (CRC, endometrial cancer, normal colon).
  • The -93A allele showed increased EPM2AIP1 promoter activity in HCT116 and HEC-1-A cells.
  • EMSA results indicated that the polymorphism alters the binding affinity of nuclear factors in this promoter region.

Conclusions:

  • The MLH1-93G>A polymorphism functionally modulates the transcriptional efficiency of both MLH1 and EPM2AIP1.
  • This genetic variation may contribute to the development or progression of cancers characterized by MSI.
  • Understanding this polymorphism's effect is crucial for cancer research and potential therapeutic strategies.

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