Detection of mutation of mismatch repair gene hMLH1 in colorectal carcinomas with microsatellite instability by two-dimensional DNA electrophoresis and DNA sequencing

Dianchun FANG; Rongquan WANG; Shiming YANG; Guiyong PENG; Tianli XIAO; Yuanhui LUO

ABSTRACT

BACKGROUND:

Microsatellite instability (MSI), an important gene change type, plays animportant role in the occurrence of tumor. Mismatch repair gene induces its occurrence. Although the effect of mismatch repair gene hMLH1 mutation in the hereditary nonpolyposis colorectal cancers (HNPCC) has been reported, its effect on the sporadic colorectal carcinoma lacks in-depth study.

OBJECTIVE:

To investigate the effect of mismatch repair gene hMLH1 mutation on colorectal carcinogenesis, and its correlation with MSI.

DESIGN:

Single-sample experiment.

SETTING:

Department of Gastroenterology, Southwest Hospital of Third Military Medical University of Chinese PLA.

PARTICIPANTS:

Seventy-six cases of sporadic colorectal carcinoma and corresponding normal tissues were obtained from surgically resected specimens of coloreetal carcinoma in Southwest Hospital between January 2001and December 2003. No patients had family history of tumor, or had received radiotherapy and chemotherapy. Patients were informed of the experiment.

METHODS:

Mutation of hMLH1 was detected by two-dimensional electrophoresis and DNA sequencing; MSI was analyzed by PCR-based methods.MAIN OUTCOME

MEASURES:

① Detection rate of hMLH1 mutation of colorectal carcinoma and MSI. ② The relationship of MSI and hMLH1 mutation.

RESULTS:

Seventy-six cases of sporadic colorectal carcinoma were studied for hMLH1 mutation and MSI. hMLH1 mutation was detected in 8 (10.5%) cases of colorectal carcinomas while MSI was detected in 20 (26.3%) cases of colorectal carcinomas. Frequency of hMLH1 mutation and MSI was significantly higher in right colorectal cancer than in left colorec tal cancer (6/26 vs 2/50, x2=4.739, P=0.029; 11/26 vs 9/50,x2=5.212,P=0.022). No association was observed between hMLH1 mutation or MSI and tumor size, differentiation, histological type, depth of invasion, metastasis or clinical pathological stages. ② MSI was divided into high-frequency group (≥ 2 loci, n=10) and low-frequency group (1 locus, n-10), and MSI negative group (n=56). 8 hMLH1 mutations were all detected in high frequency MSI group, but no mutation was found in low frequency MSI or MSI negative groups.

CONCLUSION:

hMLH1 mutation and MSI occur in cancer of the right large intestine and hMLH1 mutation is involved in carcinogenesis of some sporadic colorectal cancer with high-frequency MSI.