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PubMed2003

Mlh1 can function in antibody class switch recombination independently of Msh2.

Mismatch repair proteins participate in antibody class switch recombination, although their roles are unknown. Previous nucleotide sequence analyses of switch recombination junctions indicated that the roles of Msh2 and the MutL homologues, Mlh1 and Pms2, differ. We now asked if Msh2 and Mlh1 function in the same pathway during switch recombination. Splenic B cells from mice deficient in both these proteins were induced to undergo switching in culture. The frequency of switching is reduced, similarly to that of B cells singly deficient in Msh2 or Mlh1. However, the nucleotide sequences of the Smu-Sgamma3 junctions resemble junctions from Mlh1- but not from Msh2-deficient cells, suggesting Mlh1 functions either independently of or before Msh2. The substitution mutations within S regions that are known to accompany switch recombination are increased in Msh2- and Mlh1 single-deficient cells and further increased in the double-deficient cells, again suggesting these proteins function independently in class switch recombination. The finding that MMR functions to reduce mutations in switch regions is unexpected since MMR proteins have been shown to contribute to somatic hypermutation of antibody variable region genes.

Adaptor Proteins, Signal Transducing↗
PubMed1999

MLH1 promoter methylation and gene silencing is the primary cause of microsatellite instability in sporadic endometrial cancers.

Defective DNA mismatch repair in human tumors leads to genome-wide instability of microsatellite repeats and a molecular phenotype referred to as microsatellite instability (MSI). MSI has been reported in a variety of cancers and is a consistent feature of tumors from patients with hereditary non-polyposis colorectal cancer. Approximately 20% of cancers of the uterine endometrium, the fifth most common cancer of women world-wide, exhibit MSI. Although the frequency of MSI is higher in endometrial cancers than in any other common malignancy, the genetic basis of MSI in these tumors has remained elusive. We investigated the role that methylation of the MLH1 DNA mismatch repair gene plays in the genesis of MSI in a large series of sporadic endometrial cancers. The MLH1 promoter was methylated in 41 of 53 (77%) MSI-positive cancers investigated. In MSI-negative tumors on the other hand, there was evidence for limited methylation in only one of 11 tumors studied. Immunohistochemical investigation of a subset of the tumors revealed that methylation of the MLH1 promoter in MSI-positive tumors was associated with loss of MLH1 expression. Immunohistochemistry proved that two MSI-positive tumors lacking MLH1 methylation failed to express the MSH2 mismatch repair gene. Both of these cancers came from women who had family and medical histories suggestive of inherited cancer susceptibility. These observations suggest that epigenetic changes in the MLH1 locus account for MSI in most cases of sporadic endometrial cancers and provide additional evidence that the MSH2 gene may contribute substantially to inherited forms of endometrial cancer.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Mutations in the MutSalpha interaction interface of MLH1 can abolish DNA mismatch repair.

MutLalpha, a heterodimer of MLH1 and PMS2, plays a central role in human DNA mismatch repair. It interacts ATP-dependently with the mismatch detector MutSalpha and assembles and controls further repair enzymes. We tested if the interaction of MutLalpha with DNA-bound MutSalpha is impaired by cancer-associated mutations in MLH1, and identified one mutation (Ala128Pro) which abolished interaction as well as mismatch repair activity. Further examinations revealed three more residues whose mutation interfered with interaction. Homology modelling of MLH1 showed that all residues clustered in a small accessible surface patch, suggesting that the major interaction interface of MutLalpha for MutSalpha is located on the edge of an extensive beta-sheet that backs the MLH1 ATP binding pocket. Bioinformatic analysis confirmed that this patch corresponds to a conserved potential protein-protein interaction interface which is present in both human MLH1 and its E.coli homologue MutL. MutL could be site-specifically crosslinked to MutS from this patch, confirming that the bacterial MutL-MutS complex is established by the corresponding interface in MutL. This is the first study that identifies the conserved major MutLalpha-MutSalpha interaction interface in MLH1 and demonstrates that mutations in this interface can affect interaction and mismatch repair, and thereby can also contribute to cancer development.

Adaptor Proteins, Signal Transducing↗
PubMed2000

MSH4 acts in conjunction with MLH1 during mammalian meiosis.

MSH4 is a meiosis-specific MutS homolog. In yeast, it is required for reciprocal recombination and proper segregation of homologous chromosomes at meiosis I. MLH1 (MutL homolog 1) facilitates both mismatch repair and crossing over during meiosis in yeast. Germ-line mutations in the MLH1 human gene are responsible for hereditary nonpolyposis cancer, but the analysis of MLH1-deficient mice has revealed that MLH1 is also required for reciprocal recombination in mammals. Here we show that hMSH4 interacts with hMLH1. The two proteins are coimmunoprecipitated regardless of the presence of DNA or ATP, suggesting that the interaction does not require the binding of MSH4 to DNA. The domain of hMSH4 responsible for the interaction is in the amino-terminal part of the protein whereas the region that contains the ATP binding site and helix-turn-helix motif does not bind to hMLH1. Immunolocalization analysis shows that MSH4 is present at sites along the synaptonemal complex as soon as homologous chromosomes synapse. The number of MSH4 foci decreases gradually as pachynema progresses. During this transition, MLH1 foci begin to appear and colocalize with MSH4. These results suggest that MSH4 is first required for chromosome synapsis and that this MutS homologue is involved later with MLH1 in meiotic reciprocal recombination.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Germline MSH2 and MLH1 mutational spectrum including large rearrangements in HNPCC families from Poland (update study).

Germline mutations in the DNA mismatch repair genes MSH2 and MLH1 account for a significant proportion of hereditary non-polyposis colorectal cancer (HNPCC) families. One approach by which development of an efficient DNA-testing procedure can be implemented is to describe the nature and frequency of common mutations in particular ethnic groups. Two hundred and twenty-six patients from families matching the Amsterdam II diagnostic criteria or suspected HNPCC criteria were screened for MSH2 and MLH1 germline mutations. Fifty different pathogenic mutations were found, 25 in MSH2 and 25 in MLH1. Twenty-four of these had not previously been described in other populations. Among our 78 families with MSH2 or MLH1 mutations, 54 (69.2%) were affected by recurrent mutations including 38 found at least twice in our own series. Two of the most frequent alterations were a substitution of A to T at the splice donor site of intron 5 of MSH2 and a missense change (A681T) of MLH1 found in 10 and eight families, respectively. Among large deletions detected by the multiplex ligation-dependent probe amplification assay, exon 9 deletions in the MSH2 gene were found in two families. Our results indicate that a screening protocol specific for the Polish population that is limited to the detection of all reported mutations will result in the identification of the majority of changes present in MLH1 and MSH2 genes in Polish HNPCC kindreds.

Adaptor Proteins, Signal Transducing↗
PubMed1996

Mutation screening of MSH2 and MLH1 mRNA in hereditary non-polyposis colon cancer syndrome.

Germline mutations in four human mismatch repair genes (MSH2, MLH1, PMS1, and PMS2) have been reported to cause hereditary non-polyposis colon cancer syndrome (HNPCC). The identification of germline mutations in HNPCC kindreds allows precise diagnosis and accurate predictive testing. To investigate further the genetic epidemiology of HNPCC and the nature and frequency of germline mutations in this disorder, we studied 17 English HNPCC kindreds for germline mutations in MSH2 and MLH1. A previous genetic linkage study had suggested that most English HNPCC families will have mutations in one of these genes. Mutation analysis was performed in a three step process. (1) mRNA extracted from lymphoblastoid cell lines was analysed for gross rearrangements, (2) the in vitro transcription-translation (IVTT) assay was then performed to detect protein truncating mutations, and (3) partial cDNA sequencing of MSH2 or MLH1 was undertaken in families (n = 6) linked to MSH2 or MLH1 but without a detectable mutation. Seven different germline mutations were identified in eight of 17 (47%) kindreds (five in MSH2 and three in MLH1). In three cases there was a deletion of a single exon in MSH2 mRNA, three mutations resulted in a truncated protein product, and two missense mutations were identified by direct sequencing. Six mutations were novel. No precise correlation between genotype and phenotype was observed, although a MSH2 missense (Thr905Arg) mutation was associated with a susceptibility to multiple colorectal polyps. Age related risks for colorectal and uterine cancer were similar for MSH2 and MLH1 mutations.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Involvement of mammalian MLH1 in the apoptotic response to peroxide-induced oxidative stress.

MLH1 is an integral part of the mismatch repair complex, and the loss of this protein is associated with the acquisition of a mutator phenotype, microsatellite instability, and a predisposition to cancer. Deficiencies in the mismatch repair complex, including the loss of MLH1, result in elevated resistance to specific inducers of DNA damage, yet the mechanisms involved in this DNA-damage resistance are largely unknown. Abnormal cellular responses to DNA damage can lead to the selection of cells with a greater propensity for neoplastic transformation and might also reduce the effectiveness of certain chemotherapeutic drugs. It is therefore important to identify agents that provide selective pressure for growth of MLH1-deficient cells and to characterize further the pathways involved. In this study, we show that both human epithelial and mouse embryo fibroblast cell lines lacking the MLH1 protein are more resistant to two inducers of oxidative stress, hydrogen peroxide and tert-butyl hydroperoxide. Our analyses suggest that the observed differences in cellular viability are mediated primarily through apoptotic pathways and not through deficiencies in cell cycle checkpoint controls. Additional characterization of the signaling pathways for hydrogen peroxide-induced apoptosis in MLH1-proficient cells demonstrates the involvement of increased mitochondrial permeability, the release of cytochrome c, and caspase 3 activation. Together, our data indicate that cells lacking MLH1 may possess a selective growth advantage under oxidatively stressed conditions via the disregulation of apoptosis, possibly involving the mitochondria.

Adaptor Proteins, Signal Transducing↗
PubMed2003

[Is immunohistochemistry for MLH1 and MSH2 proteins a useful method for detection of microsatellite instability in sporadic colorectal cancer?].

BACKGROUND/AIMS: In order to identify microsatellite instability (MSI), the test based on the polymerase chain reaction (PCR) can be used. However, PCR is not routinely performed in all hospital laboratories. Recently, immunohistochemistry (IHC) for MLH1 and MSH2 proteins has been reported as a rapid and useful method for MSI. However, the efficacy of IHC in the detection of the MSI has not been well established. The aim of this study was to evaluate the usefulness of IHC in the detection of the MSI by comparing it with the test results using PCR in colorectal cancer (CRC). METHODS: Paraffin-embedded normal and tumor tissues from seventy-five patients who underwent surgical resection of CRC were used. Abnormal expression of MLH1 and MSH2 protein was determined by IHC using MLH1 and MSH2 antibodies. Normal and tumor DNAs were obtained from thirty CRC tissues that showed abnormal expression of MLH1 and MSH2 proteins by IHC. The MSI status was confirmed by PCR using five markers. RESULTS: Thirty tumors showed abnormal expression of MLH1 and MSH2 proteins by IHC, but only three tumors out of them were confirmed to have MSI by PCR. CONCLUSIONS: This result suggests that IHC with MLH1 and MSH2 antibodies does not seem to be a useful method to identify MSI in CRC, therefore PCR is required for detection of the MSI.

Adaptor Proteins, Signal Transducing↗
PubMedDate not supplied

Altered expression and new mutations in DNA mismatch repair genes MLH1 and MSH2 in melanoma brain metastases.

Brain metastases, including those of malignant melanoma (known for its high genomic instability), are the most common intracranial tumors. The main objective of this study was to investigate expression and mutation in the DNA mismatch repair system in melanoma brain metastases. Expression of MLH1, MSH2, PMS1 and PMS2 was investigated immunohistochemically in 31 melanoma metastatic tumors. Mutational analysis of MLH1 and MSH2 was performed in 17 melanoma brain metastases. Loss of MLH1 and MSH2 expression was found in 10/31 and 12/31 tumors. PMS1 (27/31) and PMS2 (28/31) expression was preserved in the majority of lesions. Potential missense mutation was found in MSH2 (exon 13) in 2/17 melanomas. Mutation in the intron sequence between exon 14 and 15 of MLH1 (exon 15) was observed in 4/17 cases. Our results indicate that the two major DNA mismatch repair genes, MLH1 and MSH2, are more frequently affected by alterations in the DNA mismatch repair system than the helper genes PMS1 and PMS2. The presence of mutations of MSH2 and MLH1 in melanoma brain metastases, which has not been found in primary melanomas, indicates the high genomic instability of melanoma brain metastases.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Immunohistochemistry and microsatellite instability testing for selecting MLH1, MSH2 and MSH6 mutation carriers in hereditary non-polyposis colorectal cancer.

Hereditary non-polyposis colorectal cancer (HNPCC) represents 1-3% of all colorectal cancers. HNPCC is caused by a constitutional defect in a mismatch repair (MMR) gene, most commonly affecting the genes MLH1, MSH2 and MSH6. The MMR defect results in an increased cancer risk, with the greatest lifetime risk for colorectal cancer and other cancers associated to HNPCC. The HNPCC-associated tumor phenotype is generally characterized by microsatellite instability (MSI) and immunohistochemical loss of expression of the affected MMR protein. The aim of this study was to determine the sensitivity of IHC for MLH1, MSH2 and MSH6, and MSI analysis in tumors from known MMR gene mutation carriers. Fifty-eight paired normal and tumor samples from HNPCC families enrolled in our high-risk colorectal cancer registry were studied for the presence of germline mutations in MLH1, MSH2 and MSH6 by DGGE and direct sequencing. MSI analysis and immunostaining for MLH1, MSH2 and MSH6 were evaluated. Of the 28 patients with a real pathogenic mutation, loss of immunohistochemical expression for at least 1 of these MMR proteins was found, and all except 1 have MSI-H. Sensitivity by MSI analysis was 96%. IHC analysis had a sensitivity of 100% in detecting MMR deficiency in carriers of a pathogenic MMR mutation, and can be used to predict which gene is expected to harbor the mutation for MLH1, MSH2 and MSH6. This study suggests that both analyses are useful for selecting high-risk patients because most MLH1, MSH2 and MSH6 gene carriers will be detected by this 2-step approach. This practical method should have immediate application in the clinical work of patients with inherited colorectal cancer syndromes.

Adaptor Proteins, Signal Transducing↗
PubMed2006

[Two novel germline mutations of MLH1 in hereditary nonpolyposis colorectal cancer family].

OBJECTIVE: To explore germline mutations of MLH1 in hereditary nonpolyposis colorectal cancer (HNPCC), and to investigate the pathobiology of novel detectable mutations of MLH1. METHOD: RNA was extracted from the peripheral blood of 12 patients from 12 different families fulfilling the Amsterdam II Criteria of HNPCC. Germline mutations of MLH1 were determined by RT-PCR with gene specific primers, heat-resistance reverse transcriptase and long-template PCR polymerase, followed by cDNA sequencing analysis. PCR-Genescan analysis was used to further investigate microsatellite instability with a panel of 5 microsatellite markers (BAT26, BAT25, D5S346, D2S123 and Mfd15), along with immunohistochemistry staining to detect the expression of MLH1 protein in the tumor tissues. RESULTS: Four germline mutations were found in 4 patients, 2 of which were previously reported GTT-->GAT mutation at codon 384 of exon 12, and the other two were novel mutations: CGC-->TGC at codon 217 of exon 8 and CCG-->CTG at codon 581 of exon 16. Two tumors with the novel mutations had high frequency microsatellite instability showing more than 2 instable loci (RER + phenotype), and both tumors lost their MLH1 protein expression. CONCLUSION: The two novel germline mutations of MLH1 identified in this study, i.e. CGC-->TGC at codon 217 of exon 8 and CCG-->CTG at codon 581 of exon 16, are very likely to have pathological significance.

Adaptor Proteins, Signal Transducing↗
PubMed2006

A novel MLH1 mutation harbored as a germ line aberration by a young woman of an HNPCC-like family and exhibited by a CML patient when occurring prior to the initiation of the blast phase concomitant with a c-MYC amplification.

Germ line mutations in the MLH1 and MSH2 genes account for the majority of hereditary nonpolyposis colorectal cancer (HNPCC) families. Here, we describe a family that does not meet the international criteria for HNPCC, of which a young woman harbors a missense mutation (D132H). This novel germ line mutation has not previously been reported. Of the mismatch repair (MMR) genes, MLH1 has been shown to play an important role in hematologic malignancies. The novel mutation was also revealed to be a somatic aberration occurring prior to the initiation of the blast phase in a chronic myelogenous leukemia (CML) patient. Among the possible MLH1 partners involved in signaling MMR or apoptosis is the proto-oncogene c-MYC, which is closely related to cellular proliferation. We further revealed a concomitant c-MYC dramatic amplification in the CML-MLH1-mutation carrier patient, also occurring at the pre-blast phase. Our data contribute further to characterizing the mutational spectrum of the MLH1 gene. Furthermore, given the role of c-MYC and its interaction with MLH1, taken together with the mutational status of both genes revealed at the pre-blast phase in the CML patient, a plausible increased genetic instability might be expected to take place, possibly contributing to blast triggering. Our results may provide additional insight into the complex interplay between the MMR system and other cellular pathways.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Methylation pattern of different regions of the MLH1 promoter and silencing of gene expression in hereditary and sporadic colorectal cancer.

Nonrandom, widespread promoter methylation of tumor suppressor genes is a common mechanism of gene inactivation during tumorigenesis. We examined the methylation status of two distinct regions of the MLH1 promoter (proximal and distal to the transcription start site) and the MLH1 gene expression by methylation-specific PCR and immunohistochemistry. A total of 72 colorectal tumors, both with (n = 51, 22 affected by hereditary nonpolyposis colorectal cancer, HNPCC, defined according to the international clinical criteria and 29 sporadic cases) and without microsatellite instability (MSI) (n = 21) were studied. Methylation was present in at least one of the two promoter regions in 86% of the sporadic MSI cases, in 33% of the cases lacking MSI, and in 23% of the HNPCC tumors. In the HNPCC cases with a known MLH1 mutation (n = 10) none of the two promoter regions was methylated. Hypermethylation in both MLH1 promoter regions was seen in 45% of the MSI sporadic cases vs. 5% of the MSI-negative cases and 0% of the HNPCC cases. The overall concordance between the two promoter regions regarding methylation status was good (P = 0.009), but no significant correlation between methylation and suppression of the MLH1 immunohistochemical expression was found. Our data confirm that mutation and hypermethylation are mutually exclusive mechanisms in inducing mismatch repair deficiency and support the hypothesis of methylation as a process evenly distributed along the different regions of the promoter.

Adaptor Proteins, Signal Transducing↗
PubMed2005

Molecular characterization of the spectrum of genomic deletions in the mismatch repair genes MSH2, MLH1, MSH6, and PMS2 responsible for hereditary nonpolyposis colorectal cancer (HNPCC).

A systematic search by Southern blot analysis in a cohort of 439 hereditary nonpolyposis colorectal cancer (HNPCC) families for genomic rearrangements in the main mismatch repair (MMR) genes, namely, MSH2, MLH1, MSH6, and PMS2, identified 48 genomic rearrangements causative of this inherited predisposition to colorectal cancer in 68 unrelated kindreds. Twenty-nine of the 48 rearrangements were found in MSH2, 13 in MLH1, 2 in MSH6, and 4 in PMS2. The vast majority were deletions, although one previously described large inversion, an intronic insertion, and a more complex rearrangement also were found. Twenty-four deletion breakpoints have been identified and sequenced in order to determine the underlying recombination mechanisms. Most fall within repetitive sequences, mainly Alu repeats, in agreement with the differential distribution of deletions between the MSH2 and MLH1 genes: the higher number and density of Alu repeats in MSH2 corresponded with a higher incidence of genomic rearrangement at this disease locus when compared with other MMR genes. Long interspersed nuclear element (LINE) repeats, relatively abundant in, for example, MLH1, did not seem to contribute to the genesis of the deletions, presumably because of their older evolutionary age and divergence among individual repeat units when compared with short interspersed nuclear element (SINE) repeats, including Alu repeats. Moreover, Southern blot analysis of the introns and the genomic regions flanking the MMR genes allowed us to detect 6 novel genomic rearrangements that left the coding region of the disease-causing gene intact. These rearrangements comprised 4 deletions upstream of the coding region of MSH2 (3 cases) and MSH6 (1 case), a 2-kb insertion in intron 7 of PMS2, and a small (459-bp) deletion in intron 13 of MLH1. The characterization of these genomic rearrangements underlines the importance of genomic deletions in the etiology of HNPCC and will facilitate the development of PCR-based tests for their detection in diagnostic laboratories.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Polymorphisms and HNPCC: PMS2-MLH1 protein interactions diminished by single nucleotide polymorphisms.

Hereditary nonpolyposis colorectal cancer (HNPCC) is one of the most common autosomal dominant inherited diseases. Mutations in the human mismatch repair (MMR) proteins MLH1, MSH2, MSH6, PMS1, and PMS2 have been found to co-segregate with HNPCC. The MLH1 and MSH2 proteins have been demonstrated to interact with PMS1, PMS2, and MSH6 proteins. A previous study reported that missense mutations in specific regions of MLH1 can lead to defects in protein-protein interactions with PMS2. Here we report that three missense alterations previously identified as single nucleotide polymorphisms (SNPs) in PMS2 (P511K, T597S, and M622I) cause defective protein-protein interactions with MLH1, even though the alterations are not in the previously reported interaction domain. These results suggest that an additional domain in PMS2 affects MLH1-PMS2 interaction. This study also demonstrates that SNPs can result in gene alterations that indeed have a functional effect on protein phenotype. Thus, these three SNPs may ultimately represent variants with an increased risk factor for tumorgenesis in HNPCC. This study is one of the first to use a functional assay to appraise the role of SNPs and suggests that traditional definitions of polymorphisms and mutations are in need of reconsideration.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Analysis of the allele-specific expression of the mismatch repair gene MLH1 using a simple DHPLC-Based Method.

Quantitative measures of allele-specific gene expression allow the indirect detection of mutations or sequence variants in regulatory elements or in other non-coding regions that may result in significant physiological or pathological changes of gene expression and may contribute to Mendelian or multifactorial disorders. We have devised a simple method, based on RT-PCR and single nucleotide primer extension (SNuPE) with unlabelled dideoxynucleotides, followed by DHPLC (denaturing high performance liquid chromatography). We established optimal conditions for separation of the extended products corresponding to the alleles of the c.655A>G (p.Ile219Val) SNP, which is the most frequent exonic polymorphism of MLH1. We then genotyped 99 unrelated control subjects and measured the allele-specific MLH1 expression in the 40 heterozygous controls found in this group. This method allowed us to define a narrow range of normal biallelic expression of MLH1, each allele contributing between 44.7% and 55.3% of the total expression. We then measured the allele-specific expression in hereditary nonpolyposis colorectal cancer (HNPCC) patients with MLH1 mRNAs bearing different stop-codon or frame-shift mutations, or in-frame deletions, in order to detect the effects of nonsense-mediated mRNA decay (NMD). Defects that induce mRNA instability were identified unambiguously and the data were consistent with current models of NMD. This study provides a sensitive tool to identify indirectly MLH1 defects that may escape detection in genomic DNA screenings but result in a quantitative change at the mRNA level.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Identification of six novel MSH2 and MLH1 germline mutations in HNPCC.

Germline mutations in mismatch repair genes are responsible for hereditary nonpolyposis colorectal cancer (HNPCC), the most common hereditary cancer-susceptibility syndrome. We report six novel germline mutations, three in MSH2 and three in MLH1. All but one mutation have been found in families fulfilling the criteria of the Bethesda guidelines; two of them additionally fulfilled the Amsterdam criteria. We identified two nonsense mutations in MSH2 (c.1764T>G [p.Y588X], c.2579C>A [p.S860X]), one duplication of four nucleotides causing premature stop codon (MLH1: c.821_824dupAAGC [p.A275fsX307]), one splice site mutation resulting in skipping of exon 8 from the MLH1 transcript (c.677+3A>G), one duplication of 18 nucleotides leading to duplication of six amino acids in the mismatch-binding domain of MSH2 (c.4_21dup [p.A2_E7dup) and one missense mutation in the PMS2 interaction domain of MLH1 (c.1756G>C [p.A586P]). The three latter mutations were not found in 73, 90 and 94 healthy control individuals, respectively. The corresponding tumors from all patients showed a high level of microsatellite instability (MSI-H). Immunohistochemistry (IH) revealed complete loss of expression of the affected protein in the tumor cells from the patients with the nonsense, splice-site and missense mutation. The tumor from the patient with the c.821_824dupAAGC mutation showed a reduced, rather than lost, expression of the MLH1-protein.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Distinct patterns of germ-line deletions in MLH1 and MSH2: the implication of Alu repetitive element in the genetic etiology of Lynch syndrome (HNPCC).

A relatively high frequency of germ-line genomic rearrangements in MLH1 and MSH2 has been reported among Lynch Syndrome (HNPCC) patients from different ethnic populations. To investigate the underlying molecular mechanisms, we characterized the DNA breakpoints of 11 germ-line deletions, six for MLH1 and five for MSH2. Distinct deletion patterns were found for the two genes. The five cases of MSH2 deletions result exclusively from intragenic unequal recombination mediated by repetitive Alu sequences. In contrast, five out of the six MLH1 deletions are due to recombinations involving sequences of no significant homology (P=0.015). A detailed analysis of the DNA breakpoints in the two genes, previously characterized by other groups, validated the observation that Alu-mediated unequal recombination is the main type of deletion in MSH2 (n=34), but not in MLH1 (n=21) (P<0.0001). Plotting the distribution of known DNA breakpoints among the introns of the two genes showed that, the highest breakpoint density is co-localized with the highest Alu density. Our study suggests that Alu is a promoting factor for the genomic recombinations in both MLH1 and MSH2, and the local Alu density may be involved in shaping the deletion pattern.

Adaptor Proteins, Signal Transducing↗