Plant-specific environmental and developmental signals regulate the mismatch repair protein MSH6 in Arabidopsis thaliana.

The DNA mismatch repair (MMR) is a postreplicative system that guarantees genomic stability by correcting mispaired and unpaired nucleotides. In eukaryotic nuclei, MMR is initiated by the binding of heterodimeric MutS homologue (MSH) complexes to the DNA error or lesion. Among these proteins, MSH2-MSH6 is the most abundant heterodimer. Even though the MMR mechanism and proteins are highly conserved throughout evolution, physiological differences between species can lead to different regulatory features. Here, we investigated how light, sugar, and/or hormones modulate Arabidopsis thaliana MSH6 expression pattern. We first characterized the promoter region of MSH6. Phylogenetic shadowing revealed three highly conserved regions. These regions were analyzed by the generation of deletion constructs of the MSH6 full-length promoter fused to the ß-glucuronidase (GUS) gene. Combined, our in silico and genetic analyses revealed that a 121-bp promoter fragment was necessary for MSH6 expression and contained potential cis-acting elements involved in light- and hormone-responsive gene expression. Accordingly, light exposure or sugar treatment of four-day old A. thaliana seedlings triggered an upregulation of MSH6 in shoot and root apical meristems. Appropriately, MSH6 was also induced by the stem cell inducer WUSCHEL. Further, the stimulatory effect of light was dependent on the presence of phyA. In addition, treatment of seedlings with auxin or cytokinin also caused an upregulation of MSH6 under darkness. Consistent with auxin signals, MSH6 expression was suppressed in the GATA23 RNAi line compared with the wild type. Our results provide evidence that endogenous factors and environmental signals controlling plant growth and development regulate the MSH6 protein in A. thaliana.

Deficiency of the Arabidopsis mismatch repair MSH6 attenuates Pseudomonas syringae invasion.

The MutS homolog 6 (MSH6) is a nuclear DNA mismatch repair (MMR) gene that encodes the MSH6 protein. MSH6 interacts with MSH2 to form the MutSα heterodimer. MutSα corrects DNA mismatches and unpaired nucleotides arising during DNA replication, deamination of 5-methylcytosine, and recombination between non-identical DNA sequences. In addition to correcting DNA biosynthetic errors, MutSα also recognizes chemically damaged DNA bases. Here, we show that inactivation of MSH6 affects the basal susceptibility of Arabidopsis thaliana to Pseudomonas syringae pv tomato DC3000. The msh6 T-DNA insertional mutant exhibited a reduced susceptibility to the bacterial invasion. This heightened basal resistance of msh6 mutants appears to be dependent on an increased stomatal closure, an accumulation of H2O2 and double-strand breaks (DSBs) and a constitutive expression of pathogenesis-related (NPR1 and PR1) and DNA damage response (RAD51D and SOG1) genes. Complementation of this mutant with the MSH6 wild type allele under the control of its own promoter resulted in reversal of the basal bacterial resistance phenotype and the stomatal closure back to wild type levels. Taken together, these results demonstrate that inactivation of MSH6 increases Arabidopsis basal susceptibility to the bacterial pathogen and suggests a link between DNA repair and stress signaling in plants.

An effective algorithm to detect the possibility of being MSI phenotype in endometrial cancer given the BMI status and histological subtype: a statistical study.

PURPOSE: In endometrial cancer, the incidence of mutations in mismatch repair genes (MMR) is estimated at 17-30%. Patients with alterations at this level (MSI) are known to have different clinical and anatomopathological characteristics than those without this genetic alteration (MSS). In this study, we aim to identify the MSI phenotype in patients who underwent hysterectomy for endometrial cancer. We assessed the correlation of this phenotype with anatomoclinical parameters such as obesity and histological subtype. METHODS/PATIENTS: Clinical and anatomopathological data were collected from 147 patients diagnosed with endometrial cancer and an immunohistochemical study of MMR system proteins was performed. PMS2 and MSH6 proteins were evaluated as primary screening and subsequent evaluation of MLH1 and MSH6, respectively, if the former were negative. Statistical association between the anatomopathological data and the immunohistochemical result was analyzed. RESULTS AND CONCLUSIONS: 22.4% of our patients were MSI phenotype. We obtained statistically significant differences by multivariate analysis between endometrioid subtype and higher FIGO classification grade with MSI phenotype and obesity with MSS phenotype. Given these statistical results, we propose a function for predicting the probability of being MSI phenotype taking into account the histological subtype (endometrioid/non-endometrioid carcinoma) and FIGO grade as well as obesity. This prediction may be useful prior to hysterectomy, for genetic study of the MLH1 promoter and subsequent genetic counseling.

DNA methylation status of MutS genes in ameloblastoma.

OBJECTIVES: Ameloblastoma is an odontogenic epithelial tumour with a low expression of mismatch repair system components. We aimed to investigate the methylation status of the genes MSH2, MSH3 and MSH6 (MutS group) in conventional ameloblastomas. MATERIALS AND METHODS: The ameloblastoma and dental follicle samples (n = 10 each) were collected from 20 different patients. Each ameloblastoma sample was sectioned into two fragments: one was paraffin-embedded while the other one, likewise the dental follicle samples, was fixed in RNAlater and frozen at -196°C. All frozen samples were investigated for the MutS genes methylation levels, using the enzymatic restriction digestion and quantitative real-time PCR (qPCR) assay. The ameloblastoma paraffin-embedded samples were submitted to immunohistochemical reactions for MutS proteins detection and digitally quantification. Correlation analyses were performed between the immunohistochemical results and the respective gene methylation percentage. RESULTS: There are no significant differences between the MutS genes methylation levels in the ameloblastoma and the dental follicle. However, a strong negative correlation was found between MSH2 and MSH6 gene methylation status and their respective proteins expressions evaluated by immunohistochemistry. CONCLUSION: Our results show that the genes methylations is in part responsible for decreasing the expression of MSH2 and MSH6 genes in ameloblastoma.

MutSα mismatch repair protein stability is governed by subunit interaction, acetylation, and ubiquitination.

In eukaryotes, DNA mismatch recognition is accomplished by the highly conserved MutSα (Msh2/Msh6) and MutSß (Msh2/Msh3) complexes. Previously, in the yeast Saccharomyces cerevisiae, we determined that deleting MSH6 caused wild-type Msh2 levels to drop by ∼50%. In this work, we determined that Msh6 steady-state levels are coupled to increasing or decreasing levels of Msh2. Although Msh6 and Msh2 are reciprocally regulated, Msh3 and Msh2 are not. Msh2 missense variants that are able to interact with Msh6 were destabilized when Msh6 was deleted; in contrast, variants that fail to dimerize were not further destabilized in cells lacking Msh6. In the absence of Msh6, Msh2 is turned over at a faster rate and degradation is mediated by the ubiquitin-proteasome pathway. Mutagenesis of certain conserved lysines near the dimer interface restored the levels of Msh2 in the absence of Msh6, further supporting a dimer stabilization mechanism. We identified two alternative forms of regulation both with the potential to act via lysine residues, including acetylation by Gcn5 and ubiquitination by the Not4 ligase. In the absence of Gcn5, Msh2 levels were significantly decreased; in contrast, deleting Not4 stabilized Msh2 and Msh2 missense variants with partial function. The stabilizing effect on Msh2 by either the presence of Msh6 or the absence of Not4 are dependent on Gcn5. Taken together, the results suggest that the wild-type MutSα mismatch repair protein stability is governed by subunit interaction, acetylation, and ubiquitination.

Trypanosoma brucei and Trypanosoma cruzi DNA Mismatch Repair Proteins Act Differently in the Response to DNA Damage Caused by Oxidative Stress.

MSH2, associated with MSH3 or MSH6, is a central component of the eukaryotic DNA Mismatch Repair (MMR) pathway responsible for the recognition and correction of base mismatches that occur during DNA replication and recombination. Previous studies have shown that MSH2 plays an additional DNA repair role in response to oxidative damage in Trypanosoma cruzi and Trypanosoma brucei. By performing co-immunoprecipitation followed by mass spectrometry with parasites expressing tagged proteins, we confirmed that the parasites' MSH2 forms complexes with MSH3 and MSH6. To investigate the involvement of these two other MMR components in the oxidative stress response, we generated knockout mutants of MSH6 and MSH3 in T. brucei bloodstream forms and MSH6 mutants in T. cruzi epimastigotes. Differently from the phenotype observed with T. cruzi MSH2 knockout epimastigotes, loss of one or two alleles of T. cruzi msh6 resulted in increased susceptibility to H2O2 exposure, besides impaired MMR. In contrast, T. brucei msh6 or msh3 null mutants displayed increased tolerance to MNNG treatment, indicating that MMR is affected, but no difference in the response to H2O2 treatment when compared to wild type cells. Taken together, our results suggest that, while T. cruzi MSH6 and MSH2 are involved with the oxidative stress response in addition to their role as components of the MMR, the DNA repair pathway that deals with oxidative stress damage operates differently in T. brucei.

Analysis of mismatch repair (MMR) proteins expression in a series of malignant pleural mesothelioma (MPM) patients.

BACKGROUND: Promising results have been reported with immune checkpoint inhibitors (ICI) in a small proportion of MPM patients. MMR deficiency (dMMR) has been well described in several malignancies and was approved as a biomarker for anti-PD-1 inhibitors. Next generation sequencing (NGS) data demonstrated that 2% of MPM harbor microsatellite instability. The aim of this study is to characterize MMR by immunohistochemistry (IHC) in a series of MPM including a subset of patients treated with immunotherapy. METHODS: Tumors of 159 MPM p diagnosed between 2002 and 2017 were reviewed. Formalin-fixed, paraffin-embedded tissue was stained for MLH1, MSH2, MSH6 and PMS2 and tumors were classified as dMMR (MMR protein expression negative) and MMR intact (all MMR proteins positively expressed). We retrospectively collected clinical outcomes under standard chemotherapy and experimental immunotherapy in the entire cohort. RESULTS: MMR protein expression was analyzed in 158 samples with enough tissue and was positive in all of the cases. Twenty two patients received ICI with anti-CTLA4 or anti-PD-1 blockade in clinical trials, 58% had a response or stable disease for more than 6 m, with median progression-free survival (PFS) of 5.7 m (2.1-26.1 m). The median overall survival (mOS) in all population was 15 months (m) (13.5-18.8 m). In a multivariable model factors associated to improved mOS were PS 0, neutrophil-lymphocyte ratio (NLR) < 5 and epithelioid histology (p < 0.001). CONCLUSIONS: In our series we were unable to identify any MPM patient with dMMR by IHC. Further studies are needed to elucidate potential predictive biomarkers of ICI benefit in MPM.

The role of double-strand break repair, translesion synthesis, and interstrand crosslinks in colorectal cancer progression-clinicopathological data and survival.

BACKGROUND AND OBJECTIVES: DNA repair is a new and important pathway that explains colorectal carcinogenesis. This study will evaluate the prognostic value of molecular modulation of double-strand break repair (XRCC2 and XRCC5); DNA damage tolerance/translesion synthesis (POLH, POLK, and POLQ), and interstrand crosslink repair (DCLRE1A) in sporadic colorectal cancer (CRC). METHODS: Tumor specimens and matched healthy mucosal tissues from 47 patients with CRC who underwent surgery were assessed for gene expression of XRCC2, XRCC5, POLH, POLK, POLQ, and DCLRE1A; protein expression of Polk, Ku80, p53, Ki67, and mismatch repair MLH1 and MSH2 components; CpG island promoter methylation of XRCC5, POLH, POLK, POLQ, and DCLRE1A was performed. RESULTS: Neoplastic tissues exhibited induction of POLK (P < .001) and DCLRE1A (P < .001) expression and low expression of POLH (P < .001) and POLQ (P < .001) in comparison to healthy paired mucosa. Low expression of POLH was associated with mucinous histology and T1-T2 tumors (P = .038); low tumor expression of POLK was associated with distant metastases (P = .042). CRC harboring POLK promoter methylation exhibited better disease-free survival (DFS) (P = .005). CONCLUSIONS: This study demonstrated that low expression or unmethylated POLH and POLK were related to worse biological behavior tumors. However, POLK methylation was associated with better DFS. POLK and POLH are potential prognostic biomarkers in CRC.

Expression of MMR system genes is correlated to NF-kB in patients with oral squamous cell carcinoma.

AIMS: The aim of this study was to evaluate the mismatch repair gene expression and their correlation with NF-kB in patients with oral squamous cell carcinoma (SCC). METHODS: Total RNA was isolated from 28 biopsy samples. A control group was composed of 20 volunteers. Differential expression of hMSH2, hMSH6 and NF-kB genes was accessed by quantitative PCR. RESULTS: There is increased expression of all the analysed genes when the patients were smokers and alcoholics. In addition, there is increased expression of hMSH2 when SCC was removed from the base of the tongue. There was a correlation between NF-kB and hMSH2 and hMSH6 as well as between repair genes hMSH2 and hMSH6 expression levels. There is increased expression of the hMSH2 gene in patients with SCC, especially in the alcoholics. CONCLUSIONS: There is a strong indication that NF-kB gene was expressed along with the studied repair genes, evidencing the possibility that this system can be activated by the inflammatory pathway.

Prognostic significance of hMSH2, hMSH3, and hMSH6 expression in ameloblastoma.

OBJECTIVE: The aim of this study was to investigate hMutS proteins in developing human tooth, ameloblastomas, and ameloblastic carcinoma and to determine whether the expression of these proteins has any prognostic potential. STUDY DESIGN: Ten cases of developing human tooth, 39 ameloblastomas, and 2 ameloblastic carcinomas were used to determine the distribution of the proteins during the process of carcinogenesis. Simultaneously, another sample of 73 ameloblastomas was arranged in tissue microarray, and their clinical, microscopic, and radiographic features; treatment outcome; presence of BRAF-V600E mutation; and follow-up data were assessed to determine the prognostic relevance of the expression of hMutS (hMSH2, hMSH3, hMSH6) and Ki-67. hMSH2 and hMSH6 were significantly downexpressed in ameloblastomas (P = .0059) compared with developing human tooth (P < .0001). RESULTS: hMSH2, hMSH3 expression were significantly associated with BRAF-V600E mutation (P < .05). Simultaneous overexpression of hMutS was associated with recurrence (P = .035); however, these did not predict the disease-free survival of patients (P > .05). CONCLUSIONS: hMutS proteins are downregulated in ameloblastoma; moreover, simultaneous overexpression of these proteins in ameloblastoma was associated with recurrence but did not predict disease-free survival.

Link between immunoexpression of hMLH1 and hMSH2 proteins and clinical-epidemiological aspects of actinic cheilitis.

BACKGROUND: The studies found in the literature associate the immunoexpression of hMLH1 and hMSH2 proteins with histologic aspects, but do not correlate it with clinical and epidemiological data. OBJECTIVE: To evaluate the immunoexpression of hMLH1 and hMSH2 in actinic cheilitis, correlating it with clinical characteristics. METHODS: We analyzed 40 cases. Histological and immunohistochemical analyses were performed. The following clinical variables were evaluated: gender, age range, ethnicity, clinical aspect and occupational sunlight exposure. Statistical evaluation included the Student t-test, while the significance level was set at 5%. RESULTS: Greater immunoexpression of hMLH1 and hMSH2 was observed in females, individuals aged over 40, and mixed-race/black patients. Furthermore, the immunoexpression of these proteins was greater in actinic cheilitis with a white-colored appearance and in patients without occupational sunlight exposure. No statistical differences were observed for the variables studied. CONCLUSION: This study uncovered variations of hMLH1 and hMSH2 protein expression upon evaluation of clinical aspects in actinic cheilitis.

Link between immunoexpression of hMLH1 and hMSH2 proteins and clinical-epidemiological aspects of actinic cheilitis

Abstract: Background: The studies found in the literature associate the immunoexpression of hMLH1 and hMSH2 proteins with histologic aspects, but do not correlate it with clinical and epidemiological data. Objective: To evaluate the immunoexpression of hMLH1 and hMSH2 in actinic cheilitis, correlating it with clinical characteristics. Methods: We analyzed 40 cases. Histological and immunohistochemical analyses were performed. The following clinical variables were evaluated: gender, age range, ethnicity, clinical aspect and occupational sunlight exposure. Statistical evaluation included the Student t-test, while the significance level was set at 5%. Results: Greater immunoexpression of hMLH1 and hMSH2 was observed in females, individuals aged over 40, and mixed-race/black patients. Furthermore, the immunoexpression of these proteins was greater in actinic cheilitis with a white-colored appearance and in patients without occupational sunlight exposure. No statistical differences were observed for the variables studied. Conclusion: This study uncovered variations of hMLH1 and hMSH2 protein expression upon evaluation of clinical aspects in actinic cheilitis.

Correlation between cell cycle proteins and hMSH2 in actinic cheilitis and lip cancer.

This study aims to evaluate and verify the relationship between the immunoexpression of hMSH2, p53 and p21 in actinic cheilitis (AC) and lower lip squamous cell carcinoma (SCC) cases. Forty AC and 40 SCC cases were submitted to immunoperoxidase method and quantitatively analyzed. Expression was compared by Mann-Whitney test, Student t test or one-way ANOVA. To correlate the variables, Pearson's correlation coefficient was calculated. The expression of p53 and p21 showed no significant differences between histopathological grades of AC or lower lip SCC (p > 0.05). Immunoexpression of p53 was higher in SCC than in AC (p < 0.001), while p21 expression was more observed in AC when compared to SCC group (p = 0.006). The AC group revealed an inverse correlation between p53 and hMSH2 expression (r = -0.30, p = 0.006). Alterations in p53 and p21 expression suggest that these proteins are involved in lower lip carcinogenesis. Moreover, p53 and hMSH2 seem to be interrelated in early events of this process.

Profile of hMSH2 expression in breast tumors and lymph nodes: a preliminary study.

OBJECTIVE: The mismatch repair (MMR) genes play a central role for the onset of cancer. One of these genes is hMSH2. A differential hMSH2 protein expression has been detected in the mononuclear fraction of peripheral blood of patients with breast cancer when compared to healthy women. This work aims to evaluate the expression of hMSH2 in patients diagnosed with breast cancer undergoing treatment at various stages of the disease to verify its potential use as a prognostic marker. PATIENTS AND METHODS: Immunohistochemical expression of hMSH2 at different stages of breast cancer in 40 patients biopsy samples were analyzed. RESULTS: hMSH2 has a considerable increased expression in all groups of patients with tumors, when compared to patients without tumors. CONCLUSIONS: immunohistochemistry indeed can be a great tool for the diagnosis of breast cancer, as it is an easy and versatile technique.

Clinical characterization and mutation spectrum in Caribbean Hispanic families with Lynch syndrome.

Lynch syndrome (LS) is an inherited form of colorectal cancer (CRC) caused by germline mutations in the mismatch repair (MMR) genes. It accounts for approximately 5% of all CRCs. The prevalence of LS among US Hispanics is unknown. The objective of this study was to describe the germline mutations of LS in Caribbean Hispanics from Puerto Rico and Dominican Republic. A total of 89 subjects were recruited through the Puerto Rico Familial Colorectal Cancer Registry and were classified according to Amsterdam and Bethesda clinical guidelines. For those tumors with lack of expression of MMR protein, gene sequencing was ordered. A total of 35 individuals with deficient MMR system were identified: 22 had MMR mutations and 13 had tumors with absent MMR protein expression. Our results show that the mutation spectrum of Caribbean Hispanic LS patients was composed mostly of MSH2 (66.7%) mutations, followed by MLH1 (25.0%). One mutation was identified in MSH6 (8.3%). A previously unidentified mutation in MLH1 gene c.2044_2045del was found in one Caribbean Hispanic family. MMR mutation-positive individuals were found to be more likely to have a prominent family history of CRC and tumors located at the proximal colon. Compared to MSH2 mutation carriers, MLH1 mutation-positive individuals were more likely to have a strong family history of CRC and LS associated cancers. Furthermore, insurance coverage for genetic testing was found to be limited in the study population with 65.1% of the individuals recruited were denied coverage. This report presents the first description of the mutation spectrum and clinicopathologic characteristics of LS Caribbean Hispanics patients.

Effects of temozolomide (TMZ) on the expression and interaction of heat shock proteins (HSPs) and DNA repair proteins in human malignant glioma cells.

We previously reported the association of HSPA1A and HSPB1 with high-grade astrocytomas, suggesting that these proteins might be involved in disease outcome and response to treatment. With the aim to better understand the resistance/susceptibility processes associated to temozolomide (TMZ) treatment, the current study was performed in three human malignant glioma cell lines by focusing on several levels: (a) apoptotic index and senescence, (b) DNA damage, and (c) interaction of HSPB1 with players of the DNA damage response. Three human glioma cell lines, Gli36, U87, and DBTRG, were treated with TMZ evaluating cell viability and survival, apoptosis, senescence, and comets (comet assay). The expression of HSPA (HSPA1A and HSPA8), HSPB1, O6-methylguanine-DNA methyltransferase (MGMT), MLH1, and MSH2 was determined by immunocytochemistry, immunofluorescence, and Western blot. Immunoprecipitation was used to analyze protein interaction. The cell lines exhibited differences in viability, apoptosis, and senescence after TMZ administration. We then focused on Gli36 cells (relatively unstudied) which showed very low recovery capacity following TMZ treatment, and this was related to high DNA damage levels; however, the cells maintained their viability. In these cells, MGMT, MSH2, HSPA, and HSPB1 levels increased significantly after TMZ administration. In addition, MSH2 and HSPB1 proteins appeared co-localized by confocal microscopy. This co-localization increased after TMZ treatment, and in immunoprecipitation analysis, MSH2 and HSPB1 appeared interacting. In contrast, HSPB1 did not interact with MGMT. We show in glioma cells the biological effects of TMZ and how this drug affects the expression levels of heat shock proteins (HSPs), MGMT, MSH2, and MLH1. In Gli36 cells, the results suggest that interactions between HSPB1 and MSH2, including co-nuclear localization, may be important in determining cell sensitivity to TMZ.

Low expression of MSH2 DNA repair protein is associated with poor prognosis in head and neck squamous cell carcinoma.

OBJECTIVE: This study aimed to investigate the expression of the MSH2 DNA repair protein in head and neck squamous cell carcinoma (HNSCC) in order to analyze its association with clinicopathologic factors and overall survival of patients. MATERIAL AND METHODS: Clinical data and primary lesions of HNSSC were collected from 55 patients who underwent surgical resection with postoperative radiotherapy in Montes Claros, state of Minas Gerais, Brazil, between 2000 and 2008. Immunohistochemical reactions were performed to analyze MSH2 protein expression. RESULTS: Bivariate analysis showed no significant correlation or association between MSH2 expression and clinicopathologic parameters by Mann-Whitney and Kruskal-Wallis tests. Patients with locoregional metastatic disease (OR=4.949, p<0.001) and lower MSH2 immunohistochemical expressions (OR=2.943, p=0.032) presented poorer survival for HNSCC by Cox regression models. CONCLUSIONS: Our data demonstrated that lower MSH2 expression might contribute to a higher clinic aggressiveness of HNSCC by promoting an unfavorable outcome.

Immunohistochemical analysis of mismatch proteins in carcinogenesis of the lower lip.

AIM: This study investigated the immunohistochemical expression of hMLH1 and hMSH2 proteins in lower lip squamous cell carcinoma (SCC) and actinic cheilitis (AC), to contribute to the understanding of the development of lower lip cancer. METHODS AND RESULTS: Forty cases of lower lip AC and SCC were studied. Quantitative immunohistochemical analysis was undertaken by counting 1000 cells (positive and negative) in each lesion. Statistical evaluation included Student's t-test and one-way ANOVA. For SCC and AC, the mean number of hMLH1- and hMSH2-positive cells decreased with advanced stage of the lesion. The largest mean number of immunostained cells was observed in AC cases without dysplasia or with mild dysplasia (hMLH1: 721.23 ± 88.116; hMHS2: 781.50 ± 156.93). Intermediate values were obtained for AC with moderate or severe dysplasia (hMLH1: 532.86 ± 197.72; hMHS2: 611.14 ± 172.48). Lower lip SSCs presented the smallest number of positive cells (hMLH1: 255.03 ± 199.47; hMHS2: 518.38 ± 265.68). A statistically significant difference was observed between groups (P < 0.001). CONCLUSIONS: The results support the hypothesis that changes in the immunoexpression of these mismatch proteins are related to the process of carcinogenesis of the lower lip.

Mismatch recognition function of Arabidopsis thaliana MutSγ.

Genetic stability depends in part on an efficient DNA lesion recognition and correction by the DNA mismatch repair (MMR) system. In eukaryotes, MMR is initiated by the binding of heterodimeric MutS homologue (MSH) complexes, MSH2-MSH6 and MSH2-MSH3, which recognize and bind mismatches and unpaired nucleotides. Plants encode another mismatch recognition protein, named MSH7. MSH7 forms a heterodimer with MSH2 and the protein complex is designated MutSγ. We here report the effect the expression of Arabidopsis MSH2 and MSH7 alone or in combination exert on the genomic stability of Saccharomyces cerevisiae. AtMSH2 and AtMutSγ proteins failed to complement the hypermutator phenotype of an msh2 deficient strain. However, overexpressing AtMutSγ in MMR proficient strains generated a 4-fold increase in CAN1 forward mutation rate, when compared to wild-type strains. Can(r) mutation spectrum analysis of AtMutSγ overproducing strains revealed a substantial increase in the frequency of base substitution mutations, including an increased accumulation of base pair changes from G:C to A:T and T:A to C:G, G:C or A:T. Taken together, these results suggest that AtMutSγ affects yeast genomic stability by recognizing specific mismatches and preventing correction by yeast MutSα and MutSß, with subsequent inability to interact with yeast downstream proteins needed to complete MMR.

Case-case study of factors associated to hMLH1, hMSH2, and hMSH6 protein expression among endometrial cancer patients of the University District Hospital of San Juan, Puerto Rico.

UNLABELLED: Lynch syndrome (LS) is an autosomal dominant disorder caused by DNA mismatch repair (MMR) system deficiencies. Women affected by LS present a 40% to 60% lifetime risk of endometrial cancer (EC). OBJECTIVE: This case-case study aims to determine the frequency of the hMLH1, hMSH2, and hMSH6 MMR proteins and the factors (age, family history of cancer [FHC] related to LS, and body mass index [BMI]) associated to their absence in EC patients attending the University District Hospital of San Juan, Puerto Rico. MATERIALS AND METHODS: Twenty cases were preliminary evaluated for the MMR protein expression by immunohistochemistry testing and classified as positive cases (presence of protein) or negative cases (absence of protein). The statistical analysis was based on the logistic regression model using the maximum likelihood estimation (MLE). The Bayesian approach was used to determine the posterior probability (posterior Pr[odds ratio {OR} > 1]). RESULTS: Results showed absence for at least 1 MMR protein in 25% of the cases, 15% for hMLH1, and 10% for hMSH2. None of the cases showed an absence for hMSH6. The MLE demonstrated that women diagnosed with EC before the age of 50 (OR: 12.4; 95% confidence interval [CI] = 0.5-322.7), having FHC related to LS (OR: 17.7; 95% CI = 0.6-534.6), and having lower BMI (OR: 2.38; 95% CI = 0.39-14.28) present higher odds than their counterparts of lacking an MMR protein, once adjusted for potential predictors (P > 0.05). The posterior probability that an excess risk of lacking an MMR protein occurs was 95% or greater for each predictor. CONCLUSIONS: Our study in this Hispanic population supports previous studies in that younger age, FHC, and lower BMI are associated with increased odds of having an absence of MMR protein expression. Further studies with larger sample sizes should be performed.