hMLH1 Mutations Research Articles

Hereditary and Familial Colon Cancer

Between 2% to 5% of all colon cancers arise in the setting of well-defined inherited syndromes, including Lynch syndrome, familial adenomatous polyposis, MUTYH-associated polyposis, and certain hamartomatous polyposis conditions. Each is associated with a high risk of colon cancer. In addition to the syndromes, up to one-third of colon cancers exhibit increased familial risk, likely related to inheritance. A number of less penetrant, but possibly more frequent susceptibility genes have been identified for this level of inheritance. Clarification of predisposing genes allows for accurate risk assessment and more precise screening approaches. This review examines the colon cancer syndromes, their genetics and management, and also the common familial colon cancers with current genetic advances and screening guidelines.

Establishment and characterization of 13 human colorectal carcinoma cell lines: mutations of genes and expressions of drug-sensitivity genes and cancer stem cell markers

Thirteen human colorectal cancer (CRC) cell lines were established from 10 primary tumors and 3 metastatic tumors obtained from 13 Korean patients. Characteristics of the cell lines including morphology in vivo and in vitro; mutations of the K-ras, p53, APC and MMR genes and microsatellite instability (MSI) status in vitro were determined. Expression of drug-sensitivity genes including MDR1, MXR, MRP1 and COX2 was also analyzed. The cell lines were unique as judged by DNA fingerprinting using 16 short tandem repeats. Eleven of the cell lines grew as adherent populations and the remaining two as floating aggregates. None of the cell lines were contaminated with Mycoplasma or bacteria. All cell lines showed high viability with relatively long doubling times. Six cell lines contained mutations at K-ras. Seven cell lines displayed p53 gene missense, nonsense and frameshift mutations. MSI was found in three cell lines and two cell lines with an MSI-high phenotype-possessed hMLH1 mutations. Nine cell lines had an APC mutation. MRP1 was highly expressed in all cell lines, and high expression of MDR1, MXR and COX2 evident in eight, six and six cell lines, respectively. Embryonal stem cell markers (MELK, SOX4 and OCT4) were expressed in most of cell lines. The cancer stem cell biomarkers CD133, CD44 and Lgr5 were expressed in 12, 13 and 13 cell lines, respectively. The presently well-characterized CRC cell lines should be useful in investigations of the biological characteristics of CRC, particularly for investigations related to gene alterations associated with CRC and biology of cancer stem cells.

Flanking sequence specificity determines coding microsatellite heteroduplex and mutation rates with defective DNA mismatch repair (MMR)

The activin type II receptor (ACVR2) contains 2 identical microsatellites in exon 3 and 10, but only the exon 10 microsatellite is frameshifted in MMR-defective colonic tumors. The reason for this selectivity is not known. We hypothesized that ACVR2 frameshifts were influenced by DNA sequences surrounding the microsatellite. We constructed plasmids in which exon 3 or 10 of ACVR2 were cloned +1bp out-of-frame of EGFP, allowing −1bp frameshift to express EGFP. Plasmids were stably-transfected into MMR-deficient cells, subsequent non-fluorescent cells sorted, cultured, and harvested for mutation analysis. We swapped DNA sequences flanking the exon 3 and 10 microsatellites to test our hypothesis. Native ACVR2 exon 3 and 10 microsatellites underwent heteroduplex formation (A7/T8) in hMLH1−/− cells, but only exon 10 microsatellites fully mutated (A7/T7) in both hMLH1−/− and hMSH6−/− backgrounds, showing selectivity for exon 10 frameshifts and inability of exon 3 heteroduplexes to fully mutate. Substituting nucleotides flanking the exon 3 microsatellite for nucleotides flanking the exon 10 microsatellite significantly reduced heteroduplex and full mutation in hMLH1−/− cells. When the exon 3 microsatellite was flanked by nucleotides normally surrounding the exon 10 microsatellite, fully-mutant exon 3 frameshifts appeared. Mutation selectivity for ACVR2 lies partly with flanking nucleotides surrounding each microsatellite.

Dietary factors, genetic and epigenetic influences in colorectal cancer.

Genetic influences, together with epigenetic components and dietary factors, play a fundamental role in the initiation and progression of cancer by causing a number of deregulations. Colorectal cancer (CRC) is a disease influenced by dietary factors, for which established genetic and epigenetic alterations have been identified. Within CRC, there are hereditary syndromes that present mutations in the germ-line hMLH1, and also alterations in the methylation of the promoters. Epigenetics has also been established as a pathway of carcinogenesis. In the present review, we analyzed studies conducted to discern the different pathways leading to established CRC, stressing the importance of identifying factors that may predict CRC at an early stage, since it is mostly a silent disease observed at the clinical level in advanced stages.

HMLH1 and hMSH2 gene mutations in a population susceptible to gastric cancer

hMLH1 and hMSH2 gene mutations in a population susceptible to gastric cancer

Assessing pathogenicity of MLH1 variants by co-expression of human MLH1 and PMS2genes in yeast

BackgroundLoss of DNA mismatch repair (MMR) in humans, mainly due to mutations in the hMLH1 gene, is linked to hereditary nonpolyposis colorectal cancer (HNPCC). Because not all MLH1 alterations result in loss of MMR function, accurate characterization of variants and their classification in terms of their effect on MMR function is essential for reliable genetic testing and effective treatment. To date, in vivo assays for functional characterization of MLH1 mutations performed in various model systems have used episomal expression of the modified MMR genes. We describe here a novel approach to determine accurately the functional significance of hMLH1 mutations in vivo, based on co-expression of human MLH1 and PMS2 in yeast cells.MethodsYeast MLH1 and PMS1 genes, whose protein products form the MutLα complex, were replaced by human orthologs directly on yeast chromosomes by homologous recombination, and the resulting MMR activity was tested.ResultsThe yeast strain co-expressing hMLH1 and hPMS2 exhibited the same mutation rate as the wild-type. Eight cancer-related MLH1 variants were introduced, using the same approach, into the prepared yeast model, and their effect on MMR function was determined. Five variants (A92P, S93G, I219V, K618R and K618T) were classified as non-pathogenic, whereas variants T117M, Y646C and R659Q were characterized as pathogenic.ConclusionResults of our in vivo yeast-based approach correlate well with clinical data in five out of seven hMLH1 variants and the described model was thus shown to be useful for functional characterization of MLH1 variants in cancer patients found throughout the entire coding region of the gene.

Alternative splicing of hMLH1 in childhood acute lymphoblastic leukaemia and characterisation of the variably expressed Δ9/10 isoform as a dominant negative species

Mismatch repair (MMR) deficiency is a common feature of acute lymphoblastic leukaemia (ALL) cell lines and in some cases is due to the mutations of hMLH1 which affect mRNA splicing. Therefore, we have analysed alternative splicing of hMLH1 in a cohort of children with ALL. We show that alternative splicing of hMLH1 is highly variable in normal and leukaemic cells and can occur by exon skipping or by the use of an alternative splice site, both serving to down-regulate the amount of full-length hMLH1 mRNA/protein produced. Aberrant splicing was found in one child with an aggressive leukaemia in which there was a predominant hMLH1Δ6 form and an associated loss of wild-type hMLH1 protein but this was not accompanied by microsatellite instability. Functional analysis of one of the most abundant spliced forms, hMLH1Δ9/10, was shown to have a significant dominant negative effect on the functionality of the MMR pathway but again was similarly expressed in ALL and normal cells.

Unusual presentation of Lynch Syndrome

Lynch Syndrome/HNPCC is a syndrome of cancer predisposition linked to inherited mutations of genes participating in post-replicative DNA mismatch repair (MMR). The spectrum of cancer associated with Lynch Syndrome includes tumours of the colorectum, endometrium, ovary, upper gastrointestinal tract and the urothelium although other cancers are rarely described. We describe a family of Lynch Syndrome with an hMLH1 mutation, that harbours an unusual tumour spectrum and its diagnostic and management challenges.

A novel germline mutation of hMLH1 in a Korean hereditary non-polyposis colorectal cancer family

Hereditary non-polyposis colorectal cancer (HNPCC) is an inherited disease caused by a germline mutation of the mismatch repair (MMR) genes, and the distinctive feature is that colorectal and extracolonic malignancies occur early in life. We report on the case of a Korean HNPCC family with endometrial cancer, with the goal of elucidating the involvement of an MMR deficiency. Although the family history did not fulfill the Amsterdam criteria II, blood samples were subjected to genetic testing by the revised Bethesda guidelines. Immunohistochemistry and direct sequencing of the genomic DNA identified a C insertion at the 1780th base in exon 16 of hMLH1, a pathogenic mutation that has not been reported before. By this mutation, premature termination at codon 592 resulted with an estimated deletion of 21% of the C-terminus of the hMLH1 protein. For early detection of the disease, the family was examined by colonoscopy and a gynecologic examination. The expression of hMLH1 in colon tissues was analyzed by Western blot analysis. We observed that the C-terminus portion of the hMLH1 protein was truncated in the HNPCC family members. Two young family members with no clinical symptoms were newly diagnosed with colorectal cancer by colonoscopy and a pathological examination. Hereby, we identified a novel pathogenic germline mutation of hMLH1 in a Korean HNPCC family. The loss of C-terminus of hMLH1 protein was thus considered to possibly play a role in the development of HNPCC with other tumors. Our findings might be useful for early diagnosis and management of the HNPCC family.

I219V Polymorphism in hMLH1 Gene in Patients Affected with Ulcerative Colitis

hMLH1 gene, lying on chromosome 3p21-23, is a key factor of the mismatch repair (MMR) complex, which amends DNA replication errors. MMR alterations are involved in the development of both hereditary and sporadic forms of colorectal carcinoma related to ulcerative colitis (UC). I219V Polymorphism is located on exon 8 of hMLH1 and provides an aminoacidic substitution of isoleucine to valine, on the protein codon 219. This may affect the speed and fidelity of protein synthesis because of a tRNA paucity or changes in the mRNA secondary structure. Most of the hereditary nonpolyposis colon cancer-associated missense mutations of hMLH1 cause structural changes of the amino- or carboxy-terminal regions, involving the domains that interact with ATP and hPMS2. In this study, we analyzed the hMLH1 I219V polymorphism frequency in colectomized patients with UC. Venous blood from 100 ulcerative patients and 97 apparently healthy subjects has been collected. Out of 100 patients affected with UC, 75 noncolectomized showed an alternating course of disease, while 25 did not respond to the common drugs, and underwent colectomy. Genotyping was performed by polymerase chain reaction and following enzymatic digestion by BccI. No significant differences were found between patients with UC and controls both for genotype and allele frequencies. However, our data show a significant association when colectomized and noncolectomized patients are compared. The frequencies of G homozygosity were 28% in colectomized and 10.7% in noncolectomized patients (p < 0.05, chi(2) = 4.4, Odds ratio = 3.3). The allele frequencies of allele A were 52% in colectomized and 68% in noncolectomized patients; while those of allele G were 48% and 32%, respectively. I219V polymorphism in hMLH1 could influence the clinical course of the disease and lead to resistance to therapy.

Die Rolle epigenetischer Veränderungen in kolorektalen Karzinomen und ihren Vorläuferläsionen

Colorectal carcinomas are the third most common malignant tumours worldwide with an incidence of 570,000 per year. According to their molecular mechanisms, sporadic colorectal carcinomas can be divided into two different phenotypes. The genetic phenotype, 50 to 70 % of all sporadic colorectal carcinomas, is characterised by a chromosomal instability (CIN) with the classical adenoma-carcinoma sequence due to alteration of the APC-βcatenin pathway with p53 mutations, SMAD alterations and LOH (loss of heterozygositiy) of 5q, 17 p 18q. On the other, the CpG island methylator phenotype (CIMP + ) was described with an epigenetic inactivation of tumour suppressor genes that are typically inactivated by germline mutations in familiar cancer syndromes, e. g., Rb, VHL, hMLH1, p16 or BRCA. Colorectal carcinomas of the CIMP + type often show a high microsatellite instability (MSI + ) caused by aberrant promoter methylation of the missmatch repair gene hMLH1. Further CIMP + are located in the proximal right-side colon and show a poor grading with mucinous or signet-cell differentiation.

The G67E mutation in hMLH1 is associated with an unusual presentation of Lynch syndrome

Germline mutations in the mismatch repair (MMR) genes are associated with Lynch syndrome, also known as hereditary non-polyposis colorectal cancer (HNPCC) syndrome. Here, we characterise a variant of hMLH1 that confers a loss-of-function MMR phenotype. The mutation changes the highly conserved Gly67 residue to a glutamate (G67E) and is reminiscent of the hMLH1-p.Gly67Arg mutation, which is present in several Lynch syndrome cohorts. hMLH1-Gly67Arg has previously been shown to confer loss-of-function (Shimodaira et al, 1998), and two functional assays suggest that the hMLH1-Gly67Glu protein fails to sustain normal MMR functions. In the first assay, hMLH1-Gly67Glu abolishes the protein's ability to interfere with MMR in yeast. In the second assay, mutation of the analogous residue in yMLH1 (yMLH1-Gly64Glu) causes a loss-of-function mutator phenotype similar to yMLH1-Gly64Arg. Despite these molecular similarities, an unusual spectrum of tumours is associated with hMLH1-Gly67Glu, which is not typical of those associated with Lynch syndrome and differs from those found in families carrying the hMLH1-Gly67Arg allele. This suggests that hMLH1 may have different functions in certain tissues and/or that additional factors may modify the influence of hMLH1 mutations in causing Lynch syndrome.

Die Rolle epigenetischer Veränderungen in kolorektalen Karzinomen und ihren Vorläuferläsionen

Colorectal carcinomas are the third most common malignant tumours worldwide with an incidence of 570,000 per year. According to their molecular mechanisms, sporadic colorectal carcinomas can be divided into two different phenotypes. The genetic phenotype, 50 to 70 % of all sporadic colorectal carcinomas, is characterised by a chromosomal instability (CIN) with the classical adenoma-carcinoma sequence due to alteration of the APC-betacatenin pathway with p53 mutations, SMAD alterations and LOH (loss of heterozygositiy) of 5q, 17 p 18q. On the other, the CpG island methylator phenotype (CIMP+) was described with an epigenetic inactivation of tumour suppressor genes that are typically inactivated by germline mutations in familiar cancer syndromes, e. g., Rb, VHL, hMLH1, p16 or BRCA. Colorectal carcinomas of the CIMP+ type often show a high microsatellite instability (MSI+) caused by aberrant promoter methylation of the missmatch repair gene hMLH1. Further CIMP+ are located in the proximal right-side colon and show a poor grading with mucinous or signet-cell differentiation.

Differences and evolution of the methods for the assessment of microsatellite instability

Microsatellite instability (MSI) originates from the systematic accumulation of uncorrected deletion/insertion in repetitive DNA tracts in cancer cells with a deficient mismatch repair system. Among colorectal cancers, the MSI signature identifies hereditary cases arising in patients with germline mutations in hMLH1, hMSH2, PMS2 and a fraction of those with hMSH6 mutations, as well as sporadic cancers with epigenetic hMLH1 promoter hypermethylation. Considering the specific pathogenesis, pathological features, natural history and response to 5-fluoro-uracil-based chemotherapy of the MSI cancers, confusion about the genetic markers for MSI recognition seems surprising. In this clinically relevant field, an agreement has not been reached concerning the use of di- or mononucleotide markers for MSI assessment. The Revised Bethesda Guidelines still recommend a panel of markers consisting of mono- and dinucleotides, despite being questioned whether it is congruous to continue to use dinucleotide markers for MSI identification. In any event, no single marker is accurate enough for MSI testing, and an awareness of their pros and cons is required for proper interpretation of results. In recent years, several papers have reported different prevalence of MSI in unrelated series, largely depending on the detection and classification method, suggesting that MSI test interpretation also requires the understanding of the phenomenon rather than simply the crude satisfaction of panel recommendations. Inaccuracies can otherwise lead to under- or overdiagnosis and inaccurate disease classification, which always have a negative impact on the clinical practice of medicine.

Mutation of hMLH1 and hMSH2 genes in hereditary nonpolyposis colorectal cancer: analysis of 76 probands

To investigate the mutations of the mismatch repair genes hMLH1 and hMSH2 in hereditary nonpolyposis colorectal cancer (HNPCC). The DNA samples of 76 probands of HNPCC families underwent PCR amplification and sequencing on 35 exons in hMLH1 and hMSH2 genes. (1) The overall mutation rate of the hMLH1 and hMSH2 genes was 33% (25/76). (2) 22 mutations were found, 16 in the hMLH1 gene and 6 in the hMSH2 gene. (3) The spectrum of mutation type included frame shift, nonsense, splice site, and missense mutations. Missense mutation was the most common mutation type. The hMLH1 and hMSH2 mutations in Chinese HNPCC families show a wide spectrum. It seems that hMLH1 gene is involved more frequently than hMSH2 gene. A certain number of HNPCC families can be benefited from the genetic screening for mutation of the mismatch repair genes.

In vitro functional analysis of missense mutations in hMLH1 and hMSH2 identified in Danish patients with colorectal cancer

In vitro functional analysis of missense mutations in hMLH1 and hMSH2 identified in Danish patients with colorectal cancer

Clinical value of screening hereditary nonpolyposis colorectal cancer in China with protocol recommended by NCCN guidelines

To investigate the effect of the protocol recommended by NCCN-2007 on the diagnosis of hereditary nonpolyposis colorectal cancer (HNPCC) in China. NCCN protocol consists of identifying HNPCC characteristics according to the revised Bethesda Guidelines,genetic counseling with immunohistochemistry and finally genetic testing. Four hundred and nineteen patients diagnosed as colorectal cancer from January 2002 to February 2006 were selected. The hMLH1 and hMSH2 immunostaining were implemented for 90 patients who fulfilled the revised Bethesda Guidelines, in whom 8 patients fulfilling the Amsterdam II (Criteria were classified as group A and the other 82 patients as group B. The frozen tissues were collected from patients who showed loss of hMLH1 or hMSH2 protein expression, then RNA was extracted, and RT-PCR and cDNA sequencing were adopted to detect the germline mutations of hMLH1 and hMSH2. Tumor tissues from 18 patients showed loss of hMLH1 or hMSH2 protein expression (5 patients in group A and 13 in group B). Finally, 21 patients(8 in group A and 13 in group B showed loss expression of MMR protein) were diagnosed as HNPCC, including 2 cases of hMLH1 and 1 case of hMSH2 mutations. These 3 cases with cDNA mutations did not fulfill the Amsterdam II( Criteria, and were finally diagnosed as HNPCC. The protocol recommended by NCCN-2007 offers a useful approach to identify HNPCC patients,and reduces the possibility of missed diagnosis of HNPCC.

A novel mutation in hMLH1 gene in a Uruguayan Hereditary non-polyposis colorectal cancer (HNPCC-Lynch syndrome) family

22203 Background: HNPCC is the most common colorectal cancer syndrome and is associated with germ-line mutations in DNA mismatch repair genes (MMR). To date, more than 700 MMR gene mutations have been identified. The MMR gene mutation spectrum may vary across different populations and be influenced by founder mutations that prevail in specific ethnic groups. Uruguay is a small country without considerable genetic diversity and whose population is mainly originated from Southern Europe. We have previously reported an unexpectedly low frequency of molecularly defined HNPCC cases despite advanced methodology used for mutation detection, which may suggest the involvement of novel susceptibility genes. Methods: Ten Amsterdam positive families, seven of them without microsatellite instability (MSI) in their proband´s tumours, where thoroughly evaluated for mutations in hMLH1 and hMSH2 by Single-Strand Conformation Polymorphism (SSCP) and direct sequencing of genomic DNA from peripheral blood performed in the proband. Results: We identified a novel hMLH1 mutation (c.289T>G - Y97D) in a 37 year-old colorectal cancer patient from a family with eleven affected members, Amsterdam I positive criteria and without MSI. The affected family members are descendant of a Spanish family and the mean colon cancer diagnosis was 54 years old. This mutation has not been reported to the available databases (InSiGHT or the Newfoundland database). Conclusions: We identified a novel punctual germ-line mutation in hMLH1 in an HNPCC patient with microsatellite stable colorectal cancer. Absence of MSI in HNPCC patients is found only in 10–15% of cases. Southern Europe people represent mixed populations in which no particular mutation has been enriched and therefore it is not surprising that Uruguayan mutations differ from those found in Southern Europeans. However, novel mutations and the reported unexpectedly low frequency of molecularly defined HNPCC cases can be explained by a different mutational spectrum in the Uruguayan population which should be further investigated. No significant financial relationships to disclose.

Genetic Instability Is Not a Requirement for Tumor Development

The idea, originating in the early years of the 20th century, that each cancer is an independent somatic evolutionary process has been abundantly confirmed by modern molecular approaches ( [1][1]– [3][2]). Genetic and epigenetic changes that increase the chance of outgrowth of the developing tumor

The interplay between hMLH1 and hMRE11: Role in MMR and the effect of hMLH1 mutations

Our previous studies indicate that hMRE11 plays a role in MMR, and this function of hMRE11 is most likely mediated by the hMLH1–hMRE11 interaction. Here, we explored the functional implications of the hMLH1–hMRE11 interaction in MMR and the effects of hMLH1 mutations on their interaction. Our in vitro MMR assay demonstrated that the dominant-negative hMRE11452–634 mutant peptide (i.e., harboring only the hMLH1-interacting domain) imparted a significant reduction in both 3′ excision and 3′-directed MMR activities. Furthermore, the expression of hMRE11452–634, and to a lesser extent hMRE111–634 (ATLD1), impaired G2/M checkpoint control in response to MNU and cisplatin treatments, rendering cells resistant to killings by these two anticancer drugs. Analysis of 38 hMLH1 missense mutations showed that the majority of mutations caused significant (>50%) reductions in their interaction with hMRE11, suggesting a potential link between aberrant protein interaction and the pathogenic effects of hMLH1 variants.