hMLH1 Gene Expression Research Articles

The Effect of Tobacco Smoke N-Nitrosamines, NNK and NDEA, and Nicotine, on DNA Mismatch Repair Mechanism and miRNA Markers, in Hypopharyngeal Squamous Cell Carcinoma: An In Vivo Model and Clinical Evidence.

HighlightsDeregulation in MMR mechanism and miR-21, miR-155 and miR-451a are caused by chronic exposure to N-Nitrosamines, NNK and NDEA, and nicotine.Reduced hMSH2 and hMLH1 gene expression profiles and miRNA deregulations can be detected both at early stages of tobacco smoke-related carcinogenesis and in invasive cancers of the upper aerodigestive tract in smokers.MMR gene expression phenotypes are strongly linked to deregulated specific miRNAs, such as miR-21, miR-155, miR-34a and miR-451a.The activation of NF-κB may play a role in tobacco smoke-induced MMR dysfunction and carcinogenesis in the upper aerodigestive tract.Deregulation of the DNA mismatch repair (MMR) mechanism has been linked to poor prognosis of upper aerodigestive tract cancers. Our recent in vitro data have provided evidence of crosstalk between deregulated miRNAs and MMR genes, caused by tobacco smoke (TS) N-Nitrosamines, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), in hypopharyngeal cells. Here, we explored whether chronic exposure to TS components can affect MMR mechanism and miRNA profiles in hypopharyngeal mucosa. Using a mouse model (C57Bl/6J wild type) of in vivo 14-week exposure to NNK (0.2 mmol/L) and N-Nitrosodiethylamine (NDEA; 0.004 mmol/L), with or without nicotine (0.02 μmol/L), we provide direct evidence that TS components can promote dysplasia, significant downregulation of Msh2 and Mlh1 genes and deregulation of miR-21, miR-155, miR-34a, and miR-451a. By analyzing eight human specimens from tobacco smokers and eight controls, we provide clinical evidence of a significant reduction in hMSH2 and hMLH1 mRNAs in hypopharyngeal squamous cell carcinoma (HSCC). In summary, deregulation of the MMR mechanism and miRNAs is caused by chronic exposure to TS-related N-Nitrosamines, with or without nicotine, in the early stages of upper aerodigestive tract carcinogenesis, and can also be detected in human HSCC. Thus, we encourage future studies to further elucidate a possible in vivo dose-dependent effect of individual or combined N-Nitrosamines, NNK and/or NDEA, and nicotine, on the MMR mechanism and their clinical testing to elaborate prognosis and risk assessment.

The clinicopathological significance of <em>hMLH1</em> hypermethylation in non-small-cell lung cancer: a meta-analysis and literature review

The hMLH1 gene plays an essential role in DNA repair. Methylation of the hMLH1 gene is common in many types of cancer and can lead to the loss of hMLH1 expression. However, the association and clinicopathological significance between hMLH1 promoter hypermethylation and non-small-cell lung cancer (NSCLC) is elusive. Here, we investigated the correlation of hMLH1 promoter hypermethylation and NSCLC using 13 studies by comprising 1,056 lung cancer patients via a meta-analysis. We observed that 1) loss of hMLH1 protein expression was significantly associated with its promoter hypermethylation, 2) hMLH1 gene inactivation through hypermethylation contributed to the tumorigenesis of NSCLC, which could be a decisive factor for the pathogenesis of NSCLC due to its high occurrence in NSCLC tissues compared to normal lung tissues, 3) a correlation exists between histologic subtypes/disease stages (TNM I+II vs III+IV) and hypermethylation status of hMLH1 gene, and 4) NSCLC patients with hMLH1 hypermethylation and subsequent low expression levels of hMLH1 have a short overall survival period than those patients with normal expression of hMLH1 gene. hMLH1 mRNA predicts patient survival in lung cancer, and this was confirmed by using a public database. We then discussed the tumor suppressor function of hMLH1 and the clinicopathological significance of hMLH1 in NSCLC. We concluded that hMLH1 hypermethylation should be an early diagnostic marker for NSCLC and also a prognostic index for NSCLC. hMLH1 is an interesting therapeutic target in human lung cancers.

Promoter methylation and immunohistochemical expression of hMLH1 and hMSH2 in sporadic colorectal cancer: a study from India

To determine the etiological factors of human colorectal cancer (CRC) we assessed the frequency and prognostic significance of hMLH1 and hMSH2 genes in conjunction with hMLH1 and hMSH2 protein expression in 30 Indian CRC patients. The protein expression and promoter methylation of hMLH1 and hMSH2; Mismatch Repair genes (MMR) were analyzed by immunohistochemistry and methylation-specific PCR (MSP), respectively. A loss of hMLH1 expression was recognized in 4(13.3%) and loss of hMSH2 expression was recognized in 2(6.6%) of 30 CRC cases whereas 50% tumors showed reduced expression of hMLH1 and 33.3% showed reduced expression of hMSH2 protein. One tumor showed a loss of both hMLH1 and hMSH2 expression. Normal nuclear staining pattern of hMLH1 and hMSH2 was observed in almost all the adjoining and normal mucosa. Promoter hypermethylation of the hMLH1 gene was detected in 15 of 30 CRC cases (50%) and of hMSH2 gene was only in 3 of 30 CRC cases (10%). No promoter methylation of hMLH1 and hMSH2 genes was observed in adjoining and normal mucosa. Combination of methylation of hMLH1 and hMSH2 gene was observed in two tumors (6.6%). A significant correlation between histological grade of the tumor, methylation and expression of hMLH1 gene (p < 0.05) was observed. Normal expression of hMLH1 and hMSH2 was seen in all of the unmethylated tumors (100%). Nuclear staining and promoter methylation of hMLH1 and hMSH2 did not significantly influence survival. hMLH1 methylation was common and was significantly correlated with loss of hMLH1 protein expression. In contrast, hMSH2 methylation was infrequent. These findings suggest that the inactivation of MMR gene expression probably via hypermethylation may lead to inactivation of their functions which finally leads to tumor aggressiveness and the immunostaining of hMLH1 protein can be used as a prognostic factor for determining the grade of the tumor.

MicroRNA-31-5p modulates cell cycle by targeting human mutL homolog 1 in human cancer cells

MicroRNAs (miRNAs) and DNA mismatch repair (MMR) have been linked to human cancer progression. Human mutL homolog 1 (hMLH1), one of the core MMR genes, defects in lung cancer development. However, the interaction between miRNAs and MMR genes and their regulatory effect on cell cycle remain poorly understood. In this study, we investigated the role of miR-31-5p in hMLH1 gene expression and the effect of miR-31-5p on cell cycle in non-small cell lung cancer (NSCLC). We found that miR-31-5p was inversely correlated with hMLH1 expression in NSCLC cell lines and hMLH1 was a direct target of miR-31-5p. Knockdown of miR-31-5p induced a cell cycle arrest at G2/M phase and increased hMLH1 protein expression in NSCLC cells. Conversely, overexpression of miR-31-5p significantly induced cell cycle arrest at S phase and decreased hMLH1 protein expression. Furthermore, knockdown of hMLH1 upregulated miR-31-5p expression and caused cell cycle arrest at S phase. Data from this study revealed that miR-31-5p modulates cell cycle by targeting hMLH1 protein at the posttranscriptional level in NSCLC, which may represent a novel therapy strategy for lung cancer by targeting miR-31-5p.

Epigenetic promoter methylation of hmlh1 gene in human gut malignancies: A comparative study

Gastrointestinal malignancies (GIT) are a major health hazard globally. The incidence of upper GIT malignancies varies widely based on geographic location, race, and feeding habits etc. GI cancers are most prevalent in Jammu and Kashmir region of India and have multi-factorial etiology involving dietary habits, genetic factors, and gene environmental interactions. Cancer development and progression is dictated by series of alterations in genes such as tumour suppressor genes, DNA repair genes, oncogenes and others. Inactivation of the hmlh1 gene expression by aberrant promoter hypermethylation plays an important role in the progression of various cancers. The present study was a hospital based comparative case-control study and the aim was to analyse the promoter hypermethylation of CpG islands of hmlh1 gene in G cancer patients of ethnic Kashmiri origin. Methylation-specific polymerase chain reaction (MS-PCR) was used for the analysis of the promoter methylation status of hmlh1 gene. DNA was extracted from all the samples and was modified using bisulphite modification kit. The epigenetic analysis revealed that frequency of Promoter region hypermethylation of hmlh1 gene among gastrointestinal malignancies was found to be higher in colorectal cancer (60%) followed by oesophageal (50%) and then gastric cancer (46%) and statically the association of promoter region hypermethylation with GIT malignancies was found to be significant (p

HMSH2 and hMLH1 Gene Expression Patterns Differ between Lung Adenocarcinoma and Squamous Cell Carcinoma: Correlation with Patient Survival and Response to Adjuvant Chemotherapy Treatment

We recently showed that the mRNA levels of mismatch repair (MMR) proteins in non-small cell lung carcinoma (NSCLC) tissue specimens and the phenotypic translation of molecular MMR data refines the biology of the MMR system with consequent diagnostic implications in the clinical assessment of lung cancer patients. hMLH1 and hMSH2 mRNA expression was previously evaluated by qPCR for 29 NSCLC patients (13 with squamous cell carcinoma [SQC] and 16 with adenocarcinoma [ADC]) and MMR mRNA levels were converted into clinically distinct phenotypic entities. In this study, we evaluated the correlation of the hMSH2 and hMLH1 mRNA phenotypes with patient survival and their response to adjuvant chemotherapy. hMSH2 and hMLH1 mRNA phenotypic distribution differed between SQC and ADC. The MMR phenotypes differed also between advanced and early stage SQC. SQC patients with an increased hMSH2 expression had a better outcome than patients with a reduced hMSH2 expression. However, ADC patients with an increased hMSH2 expression had a poor outcome compared to those with low hMSH2 levels. SQC patients with a high hMSH2 expression exhibited a better response to adjuvant chemotherapy, whereas ADC patients with high hMSH2 levels had a poor response. ADC patients with low hMSH2 levels showed good response to adjuvant chemotherapy compared to SQC patients bearing the same phenotypic profile. Our findings show that MMR mRNA phenotypes may be added to the known biological differences between SQC and ADC. hMLH1 and hMSH2 phenotypes distributed differently according to the NSCLC stage. Distinct MMR mRNA phenotypes in SQC and ADC corresponded to patient response to adjuvant chemotherapy.

Abstract 783: Combination treatment with epigallocatechin-3-gallate and sulforaphane sensitize ovarian cancer cells to cisplatin

Abstract Objective: A number of tumor suppressor genes (TSGs), responsible for drug resistance in high stages of ovarian cancers, were silenced due to epigenetic mechanisms. Epigallocatechin-3-gallate (EGCG), which is a major component of green tea, is known for its role as a DNA methyltransferase (DNMT) inhibitor. Sulforaphane (SFN), which is derived from broccoli, is known for its role as a histone deacetylation inhibitor. Both of these compounds have anti-cancer effects in a number of cancers including ovarian. The objective of the study is to test whether EGCG and SFN combination treatment can sensitize ovarian cancer cells to cisplatin treatment. Methods: EGCG, SFN and cisplatin combination treatments were applied to A2780/CP20 (cisplatin-resistant) and A2780 (cisplatin-sensitive) cells to determine their effects on sensitization. Cell viability was measured via MTT assay. Flow cytometry analysis was adopted to reveal cell cycle arrest and apoptosis. Real time quantitative PCR was employed to analyze changes in gene expression in response to the combination treatment. Results: For A2780/CP20 cells, 50% inhibiting concentrations (IC50) to cisplatin was lowered from 13 µM to less than 1 µM with combination treatment. For A2780 cells, IC50 was decreased from 3 µM to 1.5 with combination treatment. Apoptosis analyses revealed that SFN can induce apoptosis in A2780/CP20 and A2780 cells, EGCG or cisplatin can potentiate the effect in both cell types. Cell cycle analyses revealed that 28.58% of A2780/CP20 cells were arrested in G2/M phase with SFN treatment alone compared with 14.3% of vehicle treated cells. Additionally, combination treatment leads to an increase to 52.14% of cells in G2/M phase arrest. Furthermore, we found that 20.45% of A2780 cells were arrested in G2/M phase with SFN treatment compared with 8.02% of vehicle-treated cells, while, combination treatment led to a slight increase to 29.33% of cells in the G2/M phase. There is also a synergistic effect on G2/M phase arrest when EGCG, SFN or cisplatin were used together compared with alone in both cell types. On the molecular level, mRNAs of p21 and hMLH1 were upregulated (18.5 and 28.4 fold respectively, P&amp;lt;0.01) in response to SFN treatment in A2780/CP20. Combination treatment leads to an increase to 35 and 76 fold on their expression (P&amp;lt;0.01). In A2780 cells, mRNA of p21 was upregulated (463 fold, P&amp;lt;0.01) in response to SFN treatment compared with vehicle treatment and combination treatment leads to an increase to 888 fold (P&amp;lt;0.01). No significant change in hMLH1 gene expression was detected in A2780 cells. Conclusion: EGCG and SFN can sensitize ovarian cancer cells to cisplatin treatment through enhanced G2/M cell cycle arrest and apoptosis which may occur via upregulation of p21. Upregulation of hMLH1 in A2780/CP20 cells may be responsible for the added sensitivity to cisplatin. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 783. doi:1538-7445.AM2012-783

Reversal effect of 5-Aza-dc on cisplatin-resistance in human NSCLC cells in vitro

The aim of this study was to investigate the effect of 5-aza-2'-deoxycytidine (5-Aza-dc), a methylation inhibitor, on cisplatin-resistance in non-small cell lung cancer cell line A549/DDP and to explore its possible mechanism. MTT assay was used to test the cytotoxicity of 5-Aza-dc on A549/DDP cells, and the IC(50) and cisplatin resistance index of A540/DDP cells at 48 hours after 5-Aza-dc (0 µmol/L, 20 µmol/L, 40 µmol/L) treatment at different concentrations. MSP, fluorescence quantitative RT-PCR (real-time RT-PCR) and Western blot were used to detect the hMLH1 methylation status, mRNA and protein expressions, respectively. The IC(50) value of cisplatin in A549/DDP cells was 30.15 ± 0.76 µmol/L. The MTT assay results demonstrated that during the 5-Aza-dc treatment for 48 hours, the dose of 20 µmol/L was non-toxic and 40 µmol/L was low-toxic. 5-Aza-dc at those two doses reduced IC(50) value of cisplatin to 16.54 ± 0.35 µmol/L (RI = 1.82) and 6.82 ± 0.16 µmol/L (RI = 4.42), respectively. MSP, real-time RT-PCR and Western blot showed that 5-Aza-dc at non-toxic and low-toxic doses removed the partial hMLH1-hypermethylation, and up-regulated hMLH1 mRNA and protein expressions. Low dose 5-Aza-dc can partially reverse the cisplatin-resistance in A549/DDP cells, which may be achieved through removal of hMLH1 hypermethylation and increased expression of hMLH1 gene. 5-Aza-dc may have a role in increasing the efficacy of chemotherapy for patients whose tumors are lack of hMLH1 expression because of hMLH1 promoter hypermethylation.

The correlation between serum estrogen level and the expression of mismatch repair genes in colonic mucosa

Objective To investigate the effects of estrogen on mismatch repiar gene expression in colonic mucosa in vivo. Methods A total of 42 healthy individuals underwent colonoscopy were enrolled in the study. Half an hour before colonoscopy examination, blood sample was taken for determining the serum estradiol (E2) level. N ormal colonic mucosal tissues determined by naked eye under colonoscopy examination were taken in the right hemi colon to detect HMLH1 and hMSH2 gene expression by semi-quantitative RT-PCR and immunohistochemistry staining. Then the correlation of serum E2 levels with hMLH1 and hMSH2 expression in colonic mucosa was analyzed. Results A bimodal curve was presented for the correlation between serum E2 level in healthy individuals and hMLH1 expression in colonic mucosa. A strong positive correlation of E2 level with hMLH1 expression in normal colonic mucosa was observed when serum E2 level was more than 45 pg/ml (For mRNA, P=0. 003, r=0. 701; for immunohistochemistry positivity index, P=0. 000, r=0. 874).However there was no correlation between E2 level and hMSH2 expression. Conclusion High serum E2 level might increase the hMLH1 gene expression in colonic mucosa in vivo. Key words: Estrogen; Mismatch repair; Colorectal cancer

Age Related Expression of hMLH1 but Not hMSH2 in Human Hematopoietic Stem Cells Predicts Genomic Instability.

Abstract 3235Poster Board III-172DNA damage repair pathways have been shown to be important for hematopoietic function and longevity. A number of studies focusing on the loss of DNA damage repair genes have reported age related loss of hematopoietic stem cells, reduced hematopoietic function, and increased rates of hematologic cancer. A poorly studied pathway with respect to its effect on hematopoietic function is the mismatch repair (MMR) pathway. Microsatellite instability (MSI), one marker of MMR failure, has been observed in acute lymphoblastic leukemia, myelodysplastic syndrome, and lymphocytes obtained from the peripheral blood of the elderly. Further, studies investigating MMR pathway disruption in mice show an increased incidence of age related hematologic disorders and failure to repopulate in competitive transplant experiments. These reports led to the formation of the hypothesis that age related loss of MMR in a subset hematopoietic stem/progenitor cells (HSC) leads to a progenitor population with a mutator phenotype potentially leading to cell death or leukemogenesis.To test this hypothesis we clonally expanded HSC from cord blood, bone marrow, and bone core samples from various aged individuals most of whom had normal CBCs. These colony forming units (CFU) were then tested for MSI at five microsatellite loci previously used in the diagnosis of the MMR defective disease HNPCC (BAT 25, BAT 26, D2S123, D5S346, and D17S250). These results showed a statistically significant increase in high grade instability (measured as MSI observed at >20% of loci tested) in CFU obtained from individuals over the age of 50 compared to those in the age range between 0 and 50 years (p=0.0034). Next we sought to determine if loss of gene expression in MMR genes could account for the observed MSI. Gene expression of two genes known to be transcriptionally downregulated in MMR failure, hMLH1 and hMSH2, were assessed by qRT-PCR in CFU obtained from pure CD34+ immunomagnetic separations of HSC from various aged donors. Further, individual CD34+ cells from these same donors were fixed to slides and immunostained for hMLH1 and hMSH2. We observed a significant loss of hMLH1 gene expression in a subset of HSC obtained from older donors above age 42, but no pattern of loss of hMSH2 gene expression. The age related loss of MMR in HSC suggests that MMR pathway proficiency is important for hematopoiesis. These results suggest that loss of MMR might precede myelodysplastic syndromes and leukemia in older individuals. DisclosuresNo relevant conflicts of interest to declare.

P3.42. Promoter methylation and protein expression of hMLH1 gene in oral cancer. Preliminary report

P3.42. Promoter methylation and protein expression of hMLH1 gene in oral cancer. Preliminary report

Phenotypic mismatch repair hMSH2 and hMLH1 gene expression profiles in primary non-small cell lung carcinomas

Background Defects in the human DNA mismatch repair genes (MMR) hMSH2 and hMLH1 are responsible for the development of sporadic and hereditary colorectal cancers. The role of MMR genes in the pathogenesis of lung cancer has not been elucidated. The aim of this study was to address the phenotypic mRNA expression profiles of mismatch DNA repair system in lung cancer. Materials and methods We evaluated the mRNA levels of the hMSH2 and hMLH1 components of the mismatch DNA repair (MMR) system in 29 unselected frozen pairs of primary non-small cell lung carcinomas (NSCLCs) and their adjacent normal tissue (ANTs) specimens by quantitative real-time PCR analysis relative to housekeeping Porphobilinogen deaminase ( hPBGD) mRNA. To simplify and potentially improve the analysis of data, we defined for each individual MMR mRNA two possible phenotypes: a regular (R 2: hMSH2/hPBGD mRNAs ≥ 1 and R 1: hMLH1/hPBGD mRNAs ≥ 1) and a reduced (r 2: hMSH2/hPBGD mRNAs < 1 and r 1: hMLH1/hPBGD mRNAs < 1). The presence of MMR gene expression was evaluated after conversion of the molecular mRNA levels into clinically distinct phenotypic entities by these working criteria, based on the hypothesis that reduced mRNA and protein levels result in lower or non-functional MMR. Results Phenotyping defined four distinct MMR system expression profiles, R 2R 1, r 2R 1, R 2r 1 and r 2r 1 by ascending tumor progression rate and identified a previously unrecognized disease-associated phenotypic entity (r 2r 1). The phenotype-based biological aspects of the MMR system suggested that its two components: (1) function independently and (2) are not directly involved in the onset of the transformation process, since healthy lung tissue was devoid of r 2r 1 phenotypes. Conclusion These findings link MMR mRNA levels of paired lung tissue specimens to patients’ clinical condition and suggest that phenotypic translation of molecular MMR data refines the biology of the MMR system with consequent diagnostic implications in the clinical assessment of lung cancer patients.

Histone H3 lysine 9 methylation is associated with the expression of hMLH1 and DNA methylation in gastric cancer cells

To identify the association of his tone H3 lysine 9 (H3-K9) methylation with DNA methylation and the expression of the mismatch repair gene hMLH1 in human gastric cancer cells. Gastric cancer cells of the lines BGC-823 and MGC-803 were cultured and treated with 5-Aza-2'-deoxycytidine (5-Aza-dC), a demethylation agent, for 72 hour. Chromatin immunoprecipitation (ChIP) assay was used to assess the status of histone H3 lysine 9 methylation in the promoter regions of hMLH1 gene. Methylation-specific PCR (MSP) was used to evaluate the effect of 5-Aza-dC on DNA methylation status. RT-PCR was used to examine the hMLH1 gene expression. In the MGC-803 cells, silenced hMLH1 gene was characterized by DNA methylation and histone H3-K9 hypermethylation; 5-Aza-dC demethylated the DNA and reduced the histone H3-K9 methylation at silenced loci and resulted in reactivation of hMLH1 gene therein. Contrary to the MGC-803 cells, BGC-823 cells expressed hMLH1 gene with DNA demethylation and histone H3-K9 hypomethylation; and 5-Aza-dC had no effects on the gene expression, DNA methylation, and histone H3-K9 methylation therein. Hypermethylation of DNA in the promoter region is related to transcriptional silencing of hMLH1 gene. Histone H3-K9 methylation in different regions of the promoter studied correlates with DNA methylation status of hMLH1 gene in gastric cancer cells. Alteration of DNA methylation affects histone H3-K9 methylation. 5-Aza-dC can control hMLH1 expression, DNA methylation, and histone H3-K9 methylation in the promoter.

Impact of BRAF, MLH1 on the incidence of microsatellite instability high colorectal cancer in populations based study

We have identified an alternative pathway of tumorigenesis in sporadic colon cancer, involving microsatellite instability due to mismatched repair methylation, which may be driven by mutations in the BRAF gene (V600E). Colorectal cancer (CRC) is the most common cancer in the world, and African Americans show a higher incidence than other populations in the United States. We analyzed sporadic CRCs in Omani (of African origin, N = 61), Iranian (of Caucasian origin, N = 53) and African American (N = 95) patients for microsatellite instability, expression status of mismatched repair genes (hMLH1, hMSH2) and presence of the BRAF (V600E) mutation. In the Omani group, all tumors with BRAF mutations were located in the left side of the colon, and for African Americans, 88% [7] of tumors with BRAF mutations were found in the right side of the colon. In African Americans, 31% of tumors displayed microsatellite instability at two or more markers (MSI-H), while this rate was 26% and 13% for tumors in the Iranian and Omani groups, respectively. A majority of these MSI-H tumors were located in the proximal colon (right side) in African American and Iranian subjects, whereas most were located in the distal colon (left side) in Omani subjects. Defects in hMLH1 gene expression were found in 77% of MSI-H tumors in both African Americans and Iranians and in 38% of tumors in Omanis. BRAF mutations were observed in all subjects: 10% of tumors in African Americans (8/82), 2% of tumors in Iranians (1/53), and 19% of tumors in Omanis (11/59). Our findings suggest that CRC occurs at a younger age in Omani and Iranian patients, and these groups showed a lower occurrence of MSI-H than did African American patients. Our multivariate model suggests an important and significant role of hMLH1 expression and BRAF mutation in MSI-H CRC in these populations. The high occurrence of MSI-H tumors in African Americans may have significant implications for treatment, since patients with MSI-H lesions display a different response to chemotherapeutic agents such as 5-fluorouracil.

Differential hMLH1 Gene Expression after Temozolomide Selection Linked to Microsatellite Instability in a Subset of Hematopoietic Stem/Progenitor Cells in Old Versus Young and Cancer Versus Normal Patient Samples.

The etiology of hematologic pathologies such as leukemia, myelodysplasia, anemia, bone marrow failure, altered immune function, and how they are associated with aging, remains unclear. Our hypothesis is that these diseases are caused or aggravated by a subset of hematopoietic stem/progenitor cells (HSC) lacking effective mismatch repair (MMR) and therefore exhibiting a hypermutator phenotype. Microsatellite instability (MSI) is a marker of MMR deficiency. We used cord blood, bone marrow, and bone core samples to isolate and then clonally expand HSC for MSI analysis. Five microsatellite loci previously used in the diagnosis of the MMR defective disease HNPCC (BAT 25, BAT 26, D2S123, D5S346, and D17S250) were analyzed for insertions and deletions. We have analyzed 38 patient samples between the ages of 0 and 86 years, including 8 cancer patients. These data show an age-dependent increase in the frequency of high grade microsatellite instability (MSI-H), i.e. those CFU with microsatellite instability at >20% of loci tested. Additionally, samples obtained from individuals older than 50 years were 6 times more likely to have a > 10% frequency of MSI-H CFU than samples obtained from younger individuals, suggesting an inflection point for the onset of hematopoietic diseases. In all instances this instability is seen only within a subset of human HSC clones. To further characterize the origin of this deficiency, a method to select for MMR deficient hematopoietic cells was developed that first selected for survival of MMR deficient HSC, and then allowed for the examination of expression status of key MMR pathway genes hMLH1 and hMSH2 and their protein products. First, CD34+ HSC were isolated from various aged patient samples. To avoid possible effects of other repair pathways, the cells were treated with O6-Benzylguanine (BG) to remove O6-methylguanine DNA-methyltransferase (MGMT) activity and prevent removal of O6-methylguanine lesions. Next, temozolomide (TMZ) at concentrations of 50–125 μM was used to induce O6-methylguanine (O6-mG) lesions that persist in the presence of BG. These O6-mG lesions mispair with cytosine and are recognized as DNA mismatches by the mismatch repair (MMR) pathway inducing apoptotic cell death. TMZ selected cells that fail to recognize the mispair due to a lack of MMR survive this selection. In these TMZ resistant clones, RT-PCR amplification of hMLH1 transcripts from total RNA isolated reveal a defect in hMLH1 but not hMSH2 expression. In the one AML sample obtained thus far HSC treated with 200 uM TMZ we have observed 0 to 30% of hMLH1 expression within TMZ resistant CFU was observed when compared to untreated controls. Together this data links MSI to MMR defects of a subpopulation of hematopoietic precursors in older individuals. This is the first examination of MMR gene expression in clones of HSC that has shown specific MMR functional deficiencies. Our study suggests that a MMR pathway deficiency in a subset of stem cells could contribute to age related hematopoietic disease processes including stem cell failure and malignant transformation.

A Single Nucleotide Substitution (−107C → G) in the hMLH1 Promoter Found in Colorectal Cancer Population Reduces Transcriptional Activity

Inactivation of the DNA mismatch repair gene hMLH1 predisposes one to colorectal cancer. We have identified a C to G nucleotide substitution at position -107 relative to the hMLH1 gene translation initiation site in three of 163 colorectal cancer patients with an allele frequency of 0.0092 (3/326). One of the three -107G alleles occurred in one patient out of five with reduced hMLH1 expression in the tumor tissue. The -107G was not found in 63 healthy individuals. This substitution reduced transcriptional activity by 51% compared with -107C (P<0.01) and impeded the promoter-binding capacity of nuclear proteins. Although the small number of identified -107G alleles is insufficient to evaluate the contribution to the carcinogenesis and clinicopathological properties of the tumors, the effects of -107G on hMLH1 gene transcription and nuclear protein binding to the promoter sequence implicate the site, including -107C, as a crucial element interacting with the activator that maintains hMLH1 gene expression.

Sessile serrated polyp mimicry in patients with solitary rectal ulcer syndrome: is there evidence of preneoplastic change?

Abstract Context.—Solitary rectal ulcer syndrome (SRUS) is associated with erythema and ulceration of the rectal wall. Serrated lesions of the colon are divided into conventional hyperplastic polyps and a new set of lesions that are variably called sessile serrated polyps (SSPs) and sessile serrated adenomas. The SSPs are epithelial proliferative lesions that appear to act as a unique pathway to colorectal carcinogenesis. No association between SRUS and SSPs has been previously reported. Objective.—To assess a possible association between SRUS and morphologic features that mimic SSPs. Design.—Twenty-six patients with SRUS, who presented to our institution between January 1, 1999, and November 14, 2004, were retrospectively reviewed for SSP-type morphologic features by 3 pathologists. Ki-67 and hMLH1 immunohistochemical stains were used. Control tissues included 10 conventional left-sided hyperplastic polyps, 10 right-sided large SSPs, 7 adenocarcinomas with known loss of hMLH1 gene expression, and 4 norma...

Sessile Serrated Polyp Mimicry in Patients With Solitary Rectal Ulcer Syndrome: Is There Evidence of Preneoplastic Change?

Solitary rectal ulcer syndrome (SRUS) is associated with erythema and ulceration of the rectal wall. Serrated lesions of the colon are divided into conventional hyperplastic polyps and a new set of lesions that are variably called sessile serrated polyps (SSPs) and sessile serrated adenomas. The SSPs are epithelial proliferative lesions that appear to act as a unique pathway to colorectal carcinogenesis. No association between SRUS and SSPs has been previously reported. To assess a possible association between SRUS and morphologic features that mimic SSPs. Twenty-six patients with SRUS, who presented to our institution between January 1, 1999, and November 14, 2004, were retrospectively reviewed for SSP-type morphologic features by 3 pathologists. Ki-67 and hMLH1 immunohistochemical stains were used. Control tissues included 10 conventional left-sided hyperplastic polyps, 10 right-sided large SSPs, 7 adenocarcinomas with known loss of hMLH1 gene expression, and 4 normal human tonsil tissues. Ten (38%) of 26 SRUS specimens demonstrated histologic features consistent with SSPs. These features included exaggerated serration within the lower crypt compartments, crypt branching, hypermucinous appearance of epithelium, and horizontal extension of crypt bases along the muscularis mucosa. All 10 cases of SRUS had positive basal Ki-67 staining in 10% to 20% of cells. Two (20%) of the 10 cases demonstrated focal superficial loss of hMLH1 mismatch repair gene expression within areas of serrated morphologic features. One hyperplastic polyp superimposed on SRUS showed a reduced number of surface epithelial cells that express hMLH1 protein. Up to 38% of patients with SRUS have histologic changes that mimic SSPs. More importantly, 20% of these serrated lesions were found to have focal loss of hMLH1 gene expression, indicating a potential of preneoplastic change. This phenomenon may reflect an increased propensity for neoplastic progression in response to repeated trauma and repair process in certain cases of SRUS.

Possible association between tumor-suppressor gene mutations and hMSH2/hMLH1 inactivation in alveolar soft part sarcoma

Alveolar soft part sarcoma (ASPS) is a rare soft tissue tumor of unknown origin and pathogenesis. We clinicopathologically analyzed 16 cases of ASPS and screened for the genetic alterations of various tumor-suppressor genes and oncogenes, including p53, adenomatous polyposis coli ( APC), E-cadherin, and β-catenin, in 11 cases of ASPS. We also examined the expression of hMSH2/hMLH1 of DNA mismatch repair genes by immunohistochemistry, and promoter hypermethylation of these DNA mismatch repair genes by methylation-specific polymerase chain reaction (MS-PCR) to elucidate any possible association between mutation status of these genes and inactivation of the hMSH2/hMLH1 genes. Furthermore, microsatellite instability (MSI) analysis and loss of heterozygosity (LOH) on chromosome 5q analysis were used for some cases of ASPS where DNA derived from normal tissue was available. The 5-year overall survival rate for all of the patients in this study was 68.6%. The 5-year overall survival rates for patients presenting with localized ASPS and for patients with distant metastases were 83.3% and 47.6%, respectively. The high nuclear grade of tumor cells was a significantly adverse prognostic factor ( P = 0.0085). Single-strand conformation polymorphism analysis followed by DNA direct sequencing revealed 4 point mutations of the p53 gene in 3 of 11 cases (27.3%), composed of 3 missense mutations and 1 silent mutation. In addition, 1 case with the E-cadherin missense mutation and 1 case with the APC missense mutations were observed, respectively. None of the cases harbored mutation of exon 3 of the β-catenin gene. Loss of expression of the hMSH2 and hMLH1 genes was observed in 2 (18.2%) and 3 (27.3%) of 11 cases, respectively. All 3 cases with loss of hMLH1 gene expression harbored mutations of the p53 gene. There was a statistically significant correlation between the genetic alteration positive in these tumor-suppressor genes and loss of hMLH1 gene expression ( P = 0.024). Methylation-specific PCR did not reveal hypermethylation of the hMSH2/hMLH1 promoter region in any of the cases examined. Three of 8 (37.5%) ASPS cases showed low MSI, and 2 of these 3 cases showed immunohistochemical lack of expression for either hMSH2 or hMLH1. LOH on 5q was present in 2 of 6 (33.3%) informative cases, and both cases showed LOH on the D5S346 marker, a microsatellite marker near the APC locus. Thus, inactivation of hMSH2/hMLH1 of DNA mismatch repair genes seems to have an important role to play in the mutagenesis of the tumor-suppressor genes in ASPS.

The role of mismatch repair in small-cell lung cancer cells

The role of mismatch repair (MMR) in small-cell lung cancer (SCLC) is controversial, as the phenotype of a MMR-deficiency, microsatellite instability (MSI), has been reported to range from 0 to 76%. We studied the MMR pathway in a panel of 21 SCLC cell lines and observed a highly heterogeneous pattern of MMR gene expression. A significant correlation between the mRNA and protein levels was found. We demonstrate that low hMLH1 gene expression was not linked to promoter CpG methylation. One cell line (86MI) was found to be deficient in MMR and exhibited resistance to the alkylating agent MNNG. Surprisingly, MSI was not detected in 86MI and it appears to express all the major MMR components hMSH2, hMSH6, hMLH1, hPMS2, hMSH3, hMLH3, MBD4 (MED1) and hExo1. These data are consistent with at least two possibilities: (1) A missense mutation in one of the MMR genes, which dissociates MSI from drug resistance, or (2) inactivation of a second pathway that leads to MMR-deficiency and MNNG resistance, but induces negligible levels of MSI. We conclude that MMR deficiency is largely not associated with the pathogenesis of SCLC.