Article

MLH3 mutation in endometrial cancer

Department of Obstetrics and Gynecology, Washington University in St. Louis, San Luis, Missouri, United States
Cancer Research (Impact Factor: 9.28). 09/2006; 66(15):7502-8. DOI: 10.1158/0008-5472.CAN-06-0248
Source: PubMed

ABSTRACT MLH3 is a recently described member of the DNA mismatch repair gene family. Based on its interaction with the MutL homologue MLH1, it was postulated that MLH3 might play a role in tumorigenesis. Germ line and somatic mutations in MLH3 have been identified in a small fraction of colorectal cancers, but the role of MLH3 in colorectal cancer tumorigenesis remains controversial. We investigated MLH3's role in endometrial tumorigenesis through analysis of tumor and germ line DNA from 57 endometrial cancer patients who were at increased risk for having inherited cancer susceptibility. Patients with known MSH2 or MSH6 mutations were excluded as well as those who had MLH1-methylated tumors. Sixteen different variants were identified by single-strand conformational variant analysis. Of the 12 missense changes identified, three were somatic mutations. One patient had a germ line missense variant and loss of heterozygosity (LOH) in her tumor specimen. There was no evidence of MLH3 promoter methylation based on combined bisulfite restriction analysis. The identification of inherited missense variants, somatic missense mutations (present in 3 of 57 tumors), and LOH in the tumor from a patient with a germ line missense change suggest a role for MLH3 in endometrial tumorigenesis.

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    • "The MSI status was stable in carriers with the mutations G933C, W1276R or E1451K (Liu et al. 2003), whereas R647C was associated with the MSI-H phenotype (Taylor et al. 2006). In the Wu et al. (2001) study, 77 % of tumors (including tumors associated with the mutations Q24E, R647C, S817G, A1394T and E1451K) showed the MSI-H phenotype with the marker panel D3S1283, D9S171, D17S250, D3S2456, and D6S1279, whereas using the Bethesda panel, only 39% of tumors showed the MSI-H phenotype. "
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    ABSTRACT: Mismatch repair (MMR) mechanisms repair DNA damage occurring during replication and recombination. To date, five human MMR genes, MSH2, MHS6, MSH3, MLH1 and PMS2 are known to be involved in the MMR function. Human MMR proteins form 3 different heterodimers: MutSα (MSH2 and MSH6) and MutSβ (MSH2 and MSH3), which are needed for mismatch recognition and binding, and MutLα (MLH1 and PMS2), which is needed for mediating interactions between MutS homologues and other MMR proteins. The other two MutL homologues, MLH3 and PMS1, have been shown to heterodimerize with MLH1. However, the heterodimers MutLγ (MLH1and MLH3) and MutLβ (MLH1 and PMS1) are able to correct mismatches only with low or no efficiency, respectively. A deficient MMR mechanism is associated with the hereditary colorectal cancer syndrome called hereditary nonpolyposis colorectal cancer (HNPCC) or Lynch syndrome. HNPCC is the most common hereditary colorectal cancer syndrome and accounts for 2-5% of all colorectal cancer cases. HNPCC-associated mutations have been found in 5 MMR genes: MLH1, MSH2, MSH6, PMS2 and MLH3. Most of the mutations have been found in MLH1 and MSH2 (~90%) and are associated with typical HNPCC, while mutations in MSH6, PMS2 and MLH3 are mainly linked to putative HNPCC families lacking the characteristics of the syndrome. More data of MLH3 mutations are needed to assess the significance of its mutations in HNPCC. In this study, were functionally characterized 51 nontruncating mutations in the MLH1, MLH3 and MSH2 genes to address their pathogenic significance and mechanism of pathogenicity. Of the 36 MLH1 mutations, 22 were deficient in more than one assay, 2 variants were impaired only in one assay, and 12 variants behaved like the wild type protein, whereas all seven MLH3 mutants functioned like the wild type protein in the assays. To further clarify the role and relevance of MLH3 in MMR, we analyzed the subcellular localization of the native MutL homologue proteins. Our immunofluorescence analyses indicated that when all the three MutL homologues are natively expressed in human cells, endogenous MLH1 and PMS2 localize in the nucleus, whereas MLH3 stays in the cytoplasm. The coexpression of MLH3 with MLH1 results in its partial nuclear localization. Only one MSH2 mutation was pathogenic in the in vitro MMR assay. Our study on MLH1 mutations could clearly distinguish nontruncating alterations with severe functional defects from those not or only slightly impaired in protein function. However, our study on MLH3 mutations suggest that MLH3 mutations per se are not sufficient to trigger MMR deficiency and the continuous nuclear localization of MLH1 and PMS2 suggest that MutLα has a major activity in MMR in vivo. Together with our functional assays, this confirms that MutLγ is a less efficient MMR complex than MutLα. Solujen toimintaa ohjaavat DNA ja siinä sijaitsevat geenit. DNA:han kertyy virheitä niin ympäristöstä kuin solujen toiminnan tuloksenakin. Solun erilaiset DNA:n korjausmenetelmät pyrkivät korjaamaan nämä DNA:han kertyneet virheet. DNA:n kahdentumisen aikana syntyviä pieniä DNA emäspariutumavirheitä korjaa ns. mismatch repair (MMR) mekanismi. Toiselta vanhemmalta peritty mutaatio jossain viidestä MMR proteiinia koodaavasta geenistä (MLH1, MSH2, MSH6, PMS2 tai MLH3) altistavat kantajan perinnölliselle ei-polypoottiselle paksusuolisyövälle (hereditary nonpolyposis colorectal cancer HNPCC), joka kattaa noin 2-5 % kaikista paksusuolisyöpätapauksista. HNPCC on vallitsevasti periytyvä syöpäoireyhtymä, jossa peritty altistava mutaatio aiheuttaa yksilölle huomattavasti suurentuneen riskin sairastua syöpään. Sairastumisikä on noin 40 vuotta, joka on noin 20 vuotta alhaisempi kuin ei periytyvissä syövissä. Tyypillisimmät geenimutaatiot löytyvät MLH1 ja MSH2 geeneistä kun taas MSH6, PMS2 ja MLH3 geenien mutaatiot ovat harvinaisempia ja liitetään useimmiten epätyypillisiin HNPCC oireisiin. Erityisesti löydettyjen MLH3 mutaatioiden vaikutusta MMR mekanismiin ja yhteyttä HNPCC:hen tulee selvittää tarkemmin. Syövälle altistavien eli patogeenisten mutaatioiden löytäminen ja niiden erottelu ei-altistavista varianteista on tärkeää potilaiden neuvonnan ja seurannan takia. Geenien mutaatiot, jotka muuttavat proteiinia merkittävästi, kuten lyhentävät proteiinia, ovat selvästi patogeenisiä. Kuitenkin suuri ja koko ajan kasvava määrä erilaisia pieniä yhden emäsparin geenivirheitä, ns. missense mutaatioita, on löydetty ja näiden DNA muutosten vaikutus proteiinin toimintaan on usein hankala selvittää ilman erilaisia biokemiallisia menetelmiä. Tässä tutkimuksessa pyrittiin erilaisin biokemiallisin testein määrittämään ovatko syöpäpotilailta löydetyt MMR geenien missense tyyppiset mutaatiot patogeenisiä. Työssä oli mukana 36 MLH1 geenin mutaatiota, joista 22 osoittautui patogeenisiksi useammassa kuin yhdessä testissä ja kaksi mutaatiota yhdessä testissä. Tulokset tarjoavat tietoa, jota voidaan hyödyntää mutaatioiden kantajien ja heidän perheidensä perinnöllisyysneuvonnassa sekä seurannassa. Työssä tutkittiin myös seitsemän MLH3 geenin mutaatiota, joista yksikään ei osoittautunut patogeeniseksi sekä kahdeksan MSH2 mutaatioita, joista yksi osoittautui patogeeniseksi. Lisäksi työssä tutkittiin MLH1:n, PMS2:n ja MLH3:n kulkeutumista tumaan, jossa DNA:n korjaus tapahtuu. Tulokset vahvistivat käsitystä siitä, että MLH1 ja PMS2 ovat MMR mekanismissa tärkeitä, kun taas MLH3:n rooli sekä MMR mekanismissa että HNPCC:ssä näyttäisi olevan vähäisempi.
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