[The tip of the iceberg: multiple cutaneous sebaceous tumor in colon cancer. Muir-Torre syndrome--case report]. / A jéghegy csúcsa: multiplex faggyúmirigy-eredetu bortumor coloncarcinomában. Muir-Torre-szindróma.

Muir-Torre syndrome is a rare genodermatosis with autosomal dominant inheritance. The syndrome is considered to be a subtype of the hereditary nonpolyposis colorectal cancer (or Lynch-syndrome). In two-third of the cases, it develops as the consequence of germline mutations in mismatch-repair genes--most commonly MutS Homolog-2 and MutL Homolog-1. Its diagnosis can be established if at least one sebaceous tumor (sebaceoma, sebaceous adenoma, epithelioma, carcinoma or basal-cell carcinoma with sebaceous differentiation) and/or keratoacanthoma and at least one internal neoplasm are present. Here the authors present the history of a 52-year-old man with multiple sebaceous carcinomas on his back. Immunohistochemical analysis showed the lack of MutL Homolog-1 protein expression in the tumor cells. Detailed clinical workup in order to identify internal malignancy found malignant coecum tumor. Histopathological evaluation of the sample from the right hemicolectomy revealed mid-grade adenocarcinoma with MutL Homolog-1 and postmeiotic segregation increased-2 deficiency. The detection of the cutaneous sebaceous carcinoma and the application of the modern diagnostic methods resulted in identification of the associated colorectal cancer in an early stage; hence, definitive treatment was available for the patient.

Purification, crystallization and preliminary X-ray diffraction analysis of the human mismatch repair protein MutSß.

MutSß is a eukaryotic mismatch repair protein that preferentially targets extrahelical unpaired nucleotides and shares partial functional redundancy with MutSα (MSH2-MSH6). Although mismatch recognition by MutSα has been shown to involve a conserved Phe-X-Glu motif, little is known about the lesion-binding mechanism of MutSß. Combined MSH3/MSH6 deficiency triggers a strong predisposition to cancer in mice and defects in msh2 and msh6 account for roughly half of hereditary nonpolyposis colorectal cancer mutations. These three MutS homologs are also believed to play a role in trinucleotide repeat instability, which is a hallmark of many neurodegenerative disorders. The baculovirus overexpression and purification of recombinant human MutSß and three truncation mutants are presented here. Binding assays with heteroduplex DNA were carried out for biochemical characterization. Crystallization and preliminary X-ray diffraction analysis of the protein bound to a heteroduplex DNA substrate are also reported.

High-level production of MSH2 from Arabidopsis thaliana: a DNA mismatch repair system key subunit.

Biochemical and immunological information concerning DNA mismatch repair proteins from higher plants is currently limited, probably due to their low abundance in vivo. An initial analysis of AtMSH2 gene expression by quantitative real-time RT-PCR indicates that calli and seedlings contain 96.7 and 1.4 cDNA copies per ng RNA, respectively, confirming that this gene is predominantly expressed in rapidly dividing tissues. In order to obtain large quantities of AtMSH2, the protein was efficiently expressed in an Escherichia coli system. The expressed gene product has an in-frame N-terminal Trx-His(6)-S-tag. The fusion protein represents about 11% of the soluble protein from IPTG-induced E. coli cells. After a two-step purification procedure the final yield accounts for 0.7 mg/g cells. Digestion of this electrophoretically homogeneous recombinant protein with enterokinase results in an intact protein with only one extra amino acid introduced at the N-terminal end. Purified intact protein was used to induce polyclonal antibodies in rabbits. These antibodies cross-react with a 110-kDa protein from cauliflower inflorescences. Together, our data describe the transcript level, cloning, expression, purification, and polyclonal antibody preparation of AtMSH2. This work will surely be useful for carrying out plant mismatch repair assays in vitro and analyzing protein expression after the exposure of plants to various stresses.

Detection of mismatch repair gene germline mutation carrier among Chinese population with colorectal cancer.

BACKGROUND: Hereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal dominant syndrome. The National Cancer Institute (NCI) has recommended the Revised Bethesda guidelines for screening HNPCC. There has been a great deal of research on the value of these tests in other countries. However, literature about the Chinese population is scarce. Our objective is to detect and study microsatellite instability (MSI) and mismatch repair (MMR) gene germline mutation carriers among a Chinese population with colorectal cancer. METHODS: In 146 prospectively recruited consecutive patients with clinically proven colorectal cancer, MSI carriers were identified by analysis of tumor tissue using multiplex fluorescence polymerase chain reaction (PCR) using the NCI recommended panel and classified into microsatellite instability-low (MSI-L), microsatellite instability-high (MSI-H) and microsatellite stable (MSS) groups. Immunohistochemical staining for MSH2, MSH6 and MLH1 on tissue microarrays (TMAs) was performed, and methylation of the MLH1 promoter was analyzed by quantitative methylation specific PCR (MSP). Germline mutation analysis of blood samples was performed for MSH2, MSH6 and MLH1 genes. RESULTS: Thirty-four out of the 146 colorectal cancers (CRCs, 23.2%) were MSI, including 19 MSI-H CRCs and 15 MSI-L CRCS. Negative staining for MSH2 was found in 8 CRCs, negative staining for MSH6 was found in 6 CRCs. One MSI-H CRC was negative for both MSH6 and MSH2. Seventeen CRCs stained negatively for MLH1. MLH1 promoter methylation was determined in 34 MSI CRCs. Hypermethylation of the MLH1 promoter occurred in 14 (73.7%) out of 19 MSI-H CRCs and 5 (33.3%) out of 15 MSI-L CRCs. Among the 34 MSI carriers and one MSS CRC with MLH1 negative staining, 8 had a MMR gene germline mutation, which accounted for 23.5% of all MSI colorectal cancers and 5.5% of all the colorectal cancers. Five patients harbored MSH2 germline mutations, and three patients harbored MSH6 germline mutations. None of the patients had an MLH1 mutation. Mutations were commonly located in exon 7 and 12 of MSH2 and exon 5 of MSH6. Right colonic lesions and mucinous carcinoma were not common in MSI carriers. CONCLUSION: Our data may imply that the characteristics of HNPCC in the Chinese population are probably different from those of Western countries. Application of NCI recommended criteria may not be effective enough to identify Chinese HNPCC families. Further studies are necessary to echo or refute our results so as to make the NCI recommendation more universally applicable.