Differences in expression between transcripts using alternative promoters of hMLH1 gene and their correlation with microsatellite instability.
hMLH1 is involved in DNA mismatch repair and its defects cause hereditary non-polyposis colorectal cancer (HNPCC) as well as other types of cancer. A defective DNA mismatch repair system results in genetic instability, also referred to as microsatellite instability (MSI), which is a good indicator of HNPCC. Using in silico analysis of oligo-capping cDNA sequences, we initially identified a splicing (variant type 2) whose second exon is 5 bp shorter than that of a genuine hMLH1 transcript (variant type 1) and a transcript using alternative promoter (variant type 3) whose transcription starts about 300 bases downstream of variant type 1. We then compared the expression level of variant types 1 and 3 among six colorectal cancer cell lines using real-time PCR. As a result, we found that the cell lines that completely suppress the expression of variant type 1 by hypermethylation expressed variant type 3 to a certain extent. This result suggests that the expression of variant types 1 and 3 did not completely follow the same transcription mechanism. We also found that the cell lines showing MSI to be positive either expressed variant type 3 more than type 1 or expressed only variant type 3. These results showed the potential applicability of mRNA expression analysis to molecular diagnostic tests of MSI-positive cancer types.
Takahashi
Ryosuke
R
Advanced Research Laboratory, Hitachi, Ltd., Saitama 350-0395, Japan.
Nagai
Keiichi
K
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics*; D001483:Base Sequence; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000235:genetics*; D019175:DNA Methylation; D018076:DNA, Complementary / Q000737:chemistry; D006801:Humans; D053842:Microsatellite Instability; D008969:Molecular Sequence Data; D000070957:MutL Protein Homolog 1; D009687:Nuclear Proteins / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis
D048868:Adaptor Proteins, Signal Transducing; D018076:DNA, Complementary; C501486:MLH1 protein, human; D009687:Nuclear Proteins; D012333:RNA, Messenger; D000070957:MutL Protein Homolog 1