Frameshift mutations and a length polymorphism in the hMSH3 gene and the spectrum of microsatellite instability in sporadic colon cancer

Hints from a Female Patient with Breast Cancer Who Later Presented with Cowden Syndrome

A 51-year-old woman presented with metachronous tumor development in bilateral breasts, thyroid, and endometrium. Additional signs and symptoms fulfilled the National Comprehensive Cancer Network criteria for Cowden syndrome. Immunohistochemistry showed loss of PTEN expression in all tumors. Single nucleotide variants, 647 germline variants (including one each in PTEN and MSH3), and 21 somatic mutations within exons were detected in all tumors after whole-exome sequencing. There were 0, 11, and 46 specific somatic mutations in bilateral breasts, thyroid, and endometrial cancers, respectively. Although PTEN mutation is key to the development of Cowden syndrome, DNA repair dysfunction might be the initial driver of mutations. Fewer mutations were required to induce initial bilateral breast carcinomas, with subsequent thyroid and endometrial carcinomas requiring more mutations for induction. When genetic screening is unavailable, breast cancer patients with clinical manifestations of Cowden syndrome must be carefully assessed for secondary malignancies, such as thyroid and endometrial carcinomas.

Mismatch repair gene MSH3 polymorphism is associated with the risk of sporadic prostate cancer

PURPOSE

The mismatch repair system is a DNA repair mechanism that corrects mispaired bases during DNA replication errors. Cancer cells deficient in MMR proteins have a 10(2) to 10(3)-fold increase in the mutation rate. Single nucleotide polymorphisms of mismatch repair genes have been shown to cause a decrease in DNA repair activity. We hypothesized that mismatch repair gene polymorphism could be a risk factor for prostate cancer and p53 Pro/Pro genotype carriers could influence MSH3 and MSH6 polymorphisms.

MATERIALS AND METHODS

DNA samples from 110 patients with prostate cancer and 110 healthy controls were analyzed by single strand conformational polymorphism and polymerase chain reaction-restriction fragment length polymorphism to determine the genotypic frequency of 5 polymorphic loci on 2 MMR genes (MSH3 and MSH6) and p53 codon72. The chi-square test was applied to compare genotype frequency between patients and controls.

RESULTS

A significant increase in the G/A+A/A genotype of MSH3 Pro222Pro was observed in patients compared to controls (OR 1.87, 95% CI 1.0-3.5). The frequency of A/G + G/G genotypes of MSH3 exon23 Thr1036Ala also tended to increase in patients (OR 1.57, 95% CI 0.92-2.72). In p53 codon72 Arg/Pro + Pro/Pro carriers the frequency of the AG + GG genotype of MSH3 exon23 was significantly increased in patients compared to controls (OR 2.1, 95% CI 1.05-4.34).

CONCLUSIONS

To our knowledge this is the first report of the association of MSH3 gene polymorphisms in prostate cancer. These results suggest that the MSH3 polymorphism may be a risk factor for prostate cancer.

Inactivation of human mutL homolog 1 and mutS homolog 2 genes in head and neck squamous cell carcinoma tumors and leukoplakia samples by promoter hypermethylation and its relation with microsatellite instability phenotype

BACKGROUND

A subset of head and neck squamous cell carcinoma (HNSCC) exhibits a microsatellite instability (MIN) phenotype. The authors correlated alterations in the mismatch-repair genes human mutL homolog 1 (hMLH1) and human mutS homolog 2 (hMSH2) in primary head and neck squamous cell carcinoma (HNSCC) tumors and in samples of leukoplakia with the MIN phenotype.

METHODS

One hundred twenty-three paired HNSCC normal and tumor tissues and 27 leukoplakia samples were examined for hypermethylation of hMLH1 and hMSH2 promoters. The hypermethylation status of the tissues was confirmed by expression studies. Sixty-three of 123 randomly selected tumors and all 27 leukplakia samples were genotyped with 8 microsatellite markers to determine MIN.

RESULTS

Fifty percent of HNSCC tumors and 63% of leukoplakia samples harbored hypermethylation at either or both hMLH1 and hMSH2 promoters. Normal tissues adjacent to methylation-positive tumors also demonstrated hypermethylation of both promoters at a high frequency (25%). A positive correlation between tobacco habit and promoter hypermethylation was observed (P = .001). A correlation was observed between MIN and the frequency of promoter hypermethylation in the leukoplakia samples, but no such trend was observed in the HNSCC tumors. It is noteworthy that patients who had a high frequency of MIN-positive tumors exhibited hypermethylation in both the affected tissues and the adjacent normal tissues (P = .007). Patients with a tobacco habit who had promoter hypermethylation at both the affected tissues and the adjacent normal tissues had tumors that mostly were MIN positive (P = .047).

CONCLUSIONS

The current results suggested that tobacco-addicted individuals are more susceptible to promoter hypermethylation of hMLH1 and hMSH2 and that, if such hypermethylation occurs in the normal squamous epithelium of the head and neck region, then those tissues are likely to develop into tumors that involve the MIN pathway.

Inactivation of the hMSH3 mismatch repair gene in bladder cancer

Deficiency in the DNA mismatch repair (MMR) is frequently involved in various cancers. The hMSH3 gene is one of the human MMR genes whose role in bladder cancer is not known. We hypothesized that down-regulation of the hMSH3 gene might be involved in bladder cancer. In this study we analyzed this gene with regard to frame-shift mutation, single nucleotide polymorphism (SNP), a 9bp repeat in exon 1, loss of heterozygosity (LOH), immunohistochemistry, and methylation status in 102 bladder cancer samples. Immunohistochemistry revealed that hMSH3 expression in bladder cancer was significant decreased compared to normal epithelium (p<0.0001). An inverse correlation with pathological grade was found. The frame-shift mutation in the (A) 8 tract was lacking in bladder cancer. There was no significantly difference between bladder cancer samples and healthy controls' with regard to SNP and the 9bp repeat. In bladder cancer, presence of the codon 222 polymorphism, LOH, and the 9bp repeats in exon 1 had a correlation with either pathological stage or pathological grade. Presence of the codon 1036 polymorphism had significant correlation with pathological stage and a trend to correlation with pathological grade. After 5-aza-dC treatment, MSH3 expression was significantly enhanced in TCC and UMUC bladder cancer cells when compared to untreated cells. This is the first report suggesting that genetic and epigenetic alterations in the human MSH3 gene might play a significant role in the progression of bladder tumors.