Differences in expression between transcripts using alternative promoters of hMLH1 gene and their correlation with...

Area of Science:

• Molecular Biology
• Genetics
• Oncology

Background:

• Human MLH1 (hMLH1) is crucial for DNA mismatch repair.
• Defects in hMLH1 lead to hereditary non-polyposis colorectal cancer (HNPCC) and other cancers.
• Microsatellite instability (MSI) indicates defective DNA mismatch repair and is a marker for HNPCC.

Purpose of the Study:

• To investigate the expression patterns of different hMLH1 transcript variants in colorectal cancer.
• To determine the relationship between hMLH1 variant expression and microsatellite instability (MSI).
• To assess the potential of mRNA expression analysis for MSI diagnostics.

Main Methods:

• In silico analysis of oligo-capping cDNA sequences to identify hMLH1 transcript variants (type 1, type 2, type 3).
• Real-time PCR to compare expression levels of variant type 1 and variant type 3 in six colorectal cancer cell lines.
• Analysis of hMLH1 variant expression in relation to MSI status.

Main Results:

• Identified three hMLH1 transcript variants: genuine (type 1), alternatively spliced (type 2), and alternative promoter (type 3).
• Colorectal cancer cell lines with hypermethylation-induced suppression of type 1 hMLH1 expressed type 3 to some extent, indicating different transcription mechanisms.
• MSI-positive cell lines predominantly expressed type 3 hMLH1, either more than type 1 or exclusively.

Conclusions:

• hMLH1 variant expression patterns differ, with type 3 showing distinct transcriptional regulation.
• The expression of hMLH1 variant type 3 is associated with MSI-positive colorectal cancers.
• mRNA expression analysis of hMLH1 variants holds potential for molecular diagnostic tests of MSI-positive cancers.