Reduced expression of MUTYH with suppressive activity against mutations caused by 8-hydroxyguanine is a novel predictor of a poor prognosis in human gastric cancer

Genetic Complexity in Recurrent Basal Cell Carcinoma: A MUTYH Variant Case Report

The MYUTH gene plays a critical role in preserving the integrity of the human genome, with mutations being identified in several different cancer diagnoses. It serves its purpose by encoding a DNA glycosylase enzyme responsible for preventing oxidative damage through the excision of adenine that is incorrectly paired with guanine or cytosine. Mutations of the MUTYH gene have been most frequently associated with MUTYH-associated polyposis (MAP) and colorectal cancer. Biallelic mutations of the MUTYH gene are implicated in MAP, and carriers of this mutation have an increased lifetime risk of developing colorectal cancer of 43% to 100%, depending on the appropriate screening and surveillance steps taken. This case describes a patient with recurrent basal cell carcinomas (BCC) and subsequent genetic testing that revealed a pathogenic monoallelic mutation of the MUTYH gene, as well as the interventions that were subsequently performed. It highlights a potentially new patient population that would benefit from early screening to assess the risk of developing colorectal cancers as well as BCC.

Comprehensive assessment of base excision repair (BER)-related lncRNAs as prognostic and functional biomarkers in lung adenocarcinoma: implications for personalized therapeutics and immunomodulation

BACKGROUND

Lung adenocarcinoma (LUAD) is the most prevalent subtype of lung cancer, and comprehending its molecular mechanisms is pivotal for advancing treatment efficacy. This study aims to explore the prognostic and functional significance of base excision repair (BER)-related long non-coding RNAs (BERLncs) in LUAD.

METHODS

A risk score model for BERLncs was developed using the least absolute shrinkage and selection operator regression and Cox regression analysis. Model validation and prognostic evaluation were performed using Kaplan-Meier and receiver-operating characteristic curve analyses. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses were conducted to elucidate the potential biological functions of BERLncs. Comparative analyses were carried out to investigate disparities in tumor mutation burden (TMB), immune infiltration, tumor immune dysfunction and exclusion (TIDE) score, chemosensitivity, and immune checkpoint gene expression between the two risk groups.

RESULTS

A predictive risk score model comprising 19 BERLncs was successfully developed. Patients were divided into high-risk and low-risk groups according to the median risk score. The high-risk subgroup exhibited significantly inferior overall survival. Functional enrichment analysis revealed pathways associated with lung cancer development, notably the neuroactive ligand-receptor interaction pathway. High-risk patients demonstrated elevated TMB, diminished TIDE scores, and an immunosuppressive tumor microenvironment, while low-risk patients displayed potential benefits from immunotherapy. Additionally, the risk model identified potential anticancer agents.

CONCLUSION

The risk score model based on BERLncs shows promise as a prognostic biomarker for LUAD patients, providing valuable insights for clinical decision-making, therapeutic strategies, and understanding of underlying biological mechanisms.

Primary Cilia Are Frequently Present in Small Cell Lung Carcinomas but Not in Non–Small Cell Lung Carcinomas or Lung Carcinoids

Most human malignant neoplasms show loss of primary cilia (PC). However, PC are known to be retained and involved in tumorigenesis in some types of neoplasms. The PC status in lung carcinomas remains largely uninvestigated. In this study, we comprehensively assessed the PC status in lung carcinomas. A total of 492 lung carcinomas, consisting of adenocarcinomas (ACs) (n = 319), squamous cell carcinomas (SCCs) (n = 152), and small cell lung carcinomas (SCLCs) (n = 21), were examined by immunohistochemical analysis using an antibody against ARL13B, a marker of PC. The PC-positive rate was markedly higher in SCLCs (81.0%) than in ACs (1.6%) and SCCs (7.9%). We subsequently performed analyses to characterize the PC-positive lung carcinomas further. PC-positive lung carcinomas were more numerous and had longer PC than normal cells. The presence of PC in these cells was not associated with the phase of the cell cycle. We also found that the PC were retained even in metastases from PC-positive lung carcinomas. Furthermore, the hedgehog signaling pathway was activated in PC-positive lung carcinomas. Because ARL13B immunohistochemistry of lung carcinoids (n = 10) also showed a statistically significantly lower rate (10.0%) of PC positivity than SCLCs, we searched for a gene(s) that might be upregulated in PC-positive SCLCs compared with lung carcinoids, but not in PC-negative carcinomas. This search, and further cell culture experiments, identified HYLS1 as a gene possessing the ability to regulate ciliogenesis in PC-positive lung carcinomas. In conclusion, our findings indicate that PC are frequently present in SCLCs but not in non-SCLCs (ACs and SCCs) or lung carcinoids, and their PC exhibit various specific pathobiological characteristics. This suggests an important link between lung carcinogenesis and PC.

Identification and characterization of primary cilia-positive salivary gland tumours exhibiting basaloid/myoepithelial differentiation

Primary cilia (PC) are non-motile, antenna-like structures on the cell surface. Many types of neoplasms exhibit PC loss, whereas in some neoplasms PC are retained and involved in tumourigenesis. To elucidate the PC status and characteristics of major salivary gland tumours (SGTs), we examined 100 major SGTs encompassing eight histopathological types by immunohistochemical analysis. PC were present in all (100%) of the pleomorphic adenomas (PAs), basal cell adenomas (BCAs), adenoid cystic carcinomas (AdCCs), and basal cell adenocarcinomas (BCAcs) examined, but absent in all (0%) of the Warthin tumours, salivary duct carcinomas, mucoepidermoid carcinomas, and acinic cell carcinomas examined. PC were also detected by electron-microscopic analysis using the NanoSuit method. It is worthy of note that the former category and latter category of tumours contained and did not contain a basaloid/myoepithelial differentiation component, respectively. The four types of PC-positive SGTs showed longer PC than normal and exhibited a characteristic distribution pattern of the PC in the ductal and basaloid/neoplastic myoepithelial components. Two PC-positive carcinomas (AdCC and BCAc) still possessed PC in their recurrent/metastatic sites. Interestingly, activation of the Hedgehog signalling pathway, shown by predominantly nuclear GLI1 expression, was significantly more frequently observed in PC-positive SGTs. Finally, we identified tau tubulin kinase 2 (TTBK2) as being possibly involved in the production of PC in SGTs. Taken together, our findings indicate that SGTs that exhibit basaloid/myoepithelial differentiation (PA, BCA, AdCC, and BCAc) are ciliated, and their PC exhibit tumour-specific characteristics, are involved in activation of the Hedgehog pathway, and are associated with TTBK2 upregulation, providing a significant and important link between SGT tumourigenesis and PC. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Designer Fluorescent Adenines Enable Real-Time Monitoring of MUTYH Activity

The human DNA base excision repair enzyme MUTYH (MutY homolog DNA glycosylase) excises undamaged adenine that has been misincorporated opposite the oxidatively damaged 8-oxoG, preventing transversion mutations and serving as an important defense against the deleterious effects of this damage. Mutations in the MUTYH gene predispose patients to MUTYH-associated polyposis and colorectal cancer, and MUTYH expression has been documented as a biomarker for pancreatic cancer. Measuring MUTYH activity is therefore critical for evaluating and diagnosing disease states as well as for testing this enzyme as a potential therapeutic target. However, current methods for measuring MUTYH activity rely on indirect electrophoresis and radioactivity assays, which are difficult to implement in biological and clinical settings. Herein, we synthesize and identify novel fluorescent adenine derivatives that can act as direct substrates for excision by MUTYH as well as bacterial MutY. When incorporated into synthetic DNAs, the resulting fluorescently modified adenine-release turn-on (FMART) probes report on enzymatic base excision activity in real time, both in vitro and in mammalian cells and human blood. We also employ the probes to identify several promising small-molecule modulators of MUTYH by employing FMART probes for in vitro screening.

MUTYH: Not just polyposis

MUTYH is a base excision repair enzyme, it plays a crucial role in the correction of DNA errors from guanine oxidation and may be considered a cell protective factor. In humans it is an adenine DNA glycosylase that removes adenine misincorporated in 7,8-dihydro-8-oxoguanine (8-oxoG) pairs, inducing G:C to T:A transversions. MUTYH functionally cooperates with OGG1 that eliminates 8-oxodG derived from excessive reactive oxygen species production. MUTYH mutations have been linked to MUTYH associated polyposis syndrome (MAP), an autosomal recessive disorder characterized by multiple colorectal adenomas. MAP patients show a greatly increased lifetime risk for gastrointestinal cancers. The cancer risk in mono-allelic carriers associated with one MUTYH mutant allele is controversial and it remains to be clarified whether the altered functions of this protein may have a pathophysiological involvement in other diseases besides familial gastrointestinal diseases. This review evaluates the role of MUTYH, focusing on current studies of human neoplastic and non-neoplastic diseases different to colon polyposis and colorectal cancer. This will provide novel insights into the understanding of the molecular basis underlying MUTYH-related pathogenesis. Furthermore, we describe the association between MUTYH single nucleotide polymorphisms (SNPs) and different cancer and non-cancer diseases. We address the utility to increase our knowledge regarding MUTYH in the light of recent advances in the literature with the aim of a better understanding of the potential for identifying new therapeutic targets. Considering the multiple functions and interactions of MUTYH protein, its involvement in pathologies based on oxidative stress damage could be hypothesized. Although the development of extraintestinal cancer in MUTYH heterozygotes is not completely defined, the risk for malignancies of the duodenum, ovary, and bladder is also increased as well as the onset of benign and malignant endocrine tumors. The presence of MUTYH pathogenic variants is an independent predictor of poor prognosis in sporadic gastric cancer and in salivary gland secretory carcinoma, while its inhibition has been shown to reduce the survival of pancreatic ductal adenocarcinoma cells. Furthermore, some MUTYH SNPs have been associated with lung, hepatocellular and cervical cancer risk. An additional role of MUTYH seems to contribute to the prevention of numerous other disorders with an inflammatory/degenerative basis, including neurological and ocular diseases. Finally, it is interesting to note that MUTYH could be a new therapeutic target and future studies will shed light on its specific functions in the prevention of diseases and in the improvement of the chemo-sensitivity of cancer cells.

Predictive value of genetic variants XRCC1 rs1799782, APEX1 rs1760944, and MUTYH rs3219489 for adjuvant concurrent chemoradiotherapy outcomes in oral squamous cell carcinoma patients

Genetic variations in DNA base excision repair (BER) genes may affect tumor sensitivity to chemotherapy and radiotherapy. Thus, we investigated the effects of single-nucleotide polymorphisms (SNPs) in key BER pathway genes on clinical outcomes in male patients who received concurrent chemoradiotherapy (CCRT). Seven SNPs from XRCC1, OGG1, APEX1, and MUTYH were genotyped using the Sequenom iPLEX MassARRAY system in samples from 319 men with advanced oral squamous cell carcinoma. The disease-free survival (DFS) rates of the MUTYH rs3219489 genotypes and those of the other genotypes differed significantly (log-rank test p = 0.027). Multivariate Cox proportional hazard analysis showed that the MUTYH rs3219489 GG genotype was associated with poor DFS (recessive model: hazard ratio [HR] = 2.01, 95% confidence interval [CI] = 1.31-3.10; p = 0.002). The CT + TT genotypes of XRCC1 rs1799782 (dominant model: HR = 0.65, 95% CI = 0.43-0.99; p = 0.044) and GG genotype of APEX1 rs1760944 (recessive model: HR = 1.64, 95% CI = 1.00-2.70; p = 0.050) were associated with overall survival (OS). Carrying the two risk genotypes, CC and GG of XRCC1 rs1799782 and APEX1 rs1760944, respectively, (HR = 2.95, 95% CI = 1.47-5.88; p = 0.002) increased mortality risk. Our findings showed that carrying the two risk genotypes of XRCC1 rs1799782 and APEX1 rs1760944 was associated with poor OS, while the GG genotype of MUTYH rs3219489 was associated with poor DFS. Patients carrying the risk genotypes may not benefit from CCRT; therefore, they will need alternative treatments.

POLQ Overexpression Is Associated with an Increased Somatic Mutation Load and PLK4 Overexpression in Lung Adenocarcinoma

DNA Polymerase Theta (POLQ) is a DNA polymerase involved in error-prone translesion DNA synthesis (TLS) and error-prone repair of DNA double-strand breaks (DSBs). In the present study, we examined whether abnormal POLQ expression may be involved in the pathogenesis of lung adenocarcinoma (LAC). First, we found overexpression of POLQ at both the mRNA and protein levels in LAC, using data from the Cancer Genome Atlas (TCGA) database and by immunohistochemical analysis of our LAC series. POLQ overexpression was associated with an advanced pathologic stage and an increased total number of somatic mutations in LAC. When H1299 human lung cancer cell clones overexpressing POLQ were established and examined, the clones showed resistance to a DSB-inducing chemical in the clonogenic assay and an increased frequency of mutations in the supF forward mutation assay. Further analysis revealed that POLQ overexpression was also positively correlated with Polo Like Kinase 4 (PLK4) overexpression in LAC, and that PLK4 overexpression in the POLQ-overexpressing H1299 cells induced centrosome amplification. Finally, analysis of the TCGA data revealed that POLQ overexpression was associated with an increased somatic mutation load and PLK4 overexpression in diverse human cancers; on the other hand, overexpressions of nine TLS polymerases other than POLQ were associated with an increased somatic mutation load at a much lower frequency. Thus, POLQ overexpression is associated with advanced pathologic stage, increased somatic mutation load, and PLK4 overexpression, the last inducing centrosome amplification, in LAC, suggesting that POLQ overexpression is involved in the pathogenesis of LAC.

Defective repair capacity of variant proteins of the DNA glycosylase NTHL1 for 5-hydroxyuracil, an oxidation product of cytosine

The NTHL1 gene encodes DNA glycosylase, which is involved in base excision repair, and biallelic mutations of this gene result in NTHL1-associated polyposis (NAP), a hereditary disease characterized by colorectal polyposis and multiple types of carcinomas. However, no proper functional characterization of variant NTHL1 proteins has been done so far. Herein, we report functional evaluation of variant NTHL1 proteins to aid in the accurate diagnosis of NAP. First, we investigated whether it would be appropriate to use 5-hydroxyuracil (5OHU), an oxidation product of cytosine, for the evaluation. In the supF forward mutation assay, 5OHU caused an increase of the mutation frequency in human cells, and the C→T mutation was predominant among the 5OHU-induced mutations. In addition, in DNA cleavage activity assay, 5OHU was excised by NTHL1 as well as four other DNA glycosylases (SMUG1, NEIL1, TDG, and UNG2). When human cells overexpressing the five DNA glycosylases were established, it was found that each of the five DNA glycosylases, including NTHL1, had the ability to suppress 5OHU-induced mutations. Based on the above results, we performed functional evaluation of eight NTHL1 variants using 5OHU-containing DNA substrate or shuttle plasmid. The DNA cleavage activity assay showed that the variants of NTHL1, Q90X, Y130X, R153X, and Q287X, but not R19Q, V179I, V217F, or G286S, showed defective repair activity for 5OHU and two other oxidatively damaged bases. Moreover, the supF forward mutation assay showed that the four truncated-type NTHL1 variants showed a reduced ability to suppress 5OHU-induced mutations in human cells. These results suggest that the NTHL1 variants Q90X, Y130X, R153X, and Q287X, but not R19Q, V179I, V217F, or G286S, were defective in 5OHU repair and the alleles encoding them were considered to be pathogenic for NAP.

Lentivirus-mediated shRNA targeting MUTYH inhibits malignant phenotypes of bladder cancer SW780 cells

Objectives

MUTYH is a protein-coding gene that takes part in base excision repair. Many previous studies have reported that MUTYH is directly related to hereditary adenomatous polyposis and colorectal cancer and is also associated with other cancers. However, the relationship between MUTYH and bladder cancer (BC) is unknown.

Materials and methods

The expression of MUTYH and clinical characteristics of BC were collected from databases including The Cancer Genome Atlas and Cancer Cell Line Encyclopedia. RNA sequencing and quantitative real-time PCR were used to detect MUTYH expression in SW780 BC cells. The level of MUTYH was stably downregulated by lentivirus-mediated vector in SW780 cells. Cell proliferation was evaluated using Cell Counting Kit-8 assay and 5-ethynyl-20-deoxyuridine assay, migration was detected using scratch assay and Transwell assay, and apoptosis was determined using ELISA.

Results

MUTYH was upregulated in BC tissues and SW780 cells and its expression level was positively associated with the stage and grade of carcinomas. MUTYH was successfully downregulated in SW780 cells by transducing with a lentivirus-mediated shRNA targeting MUTYH. MUTYH knockdown inhibited the proliferation and migration and induced apoptosis in SW780 cells.

Conclusion

Our data suggest that MUTYH is a new participant in bladder urothelial carcinoma. MUTYH may play a role as a biomarker and therapeutic target in BC.

Genetic Investigation of Polymorphic OGG1 and MUTYH Genes Towards Increased Susceptibility in Lung Adenocarcinoma and its Impact on Overall Survival of Lung Cancer Patients Treated with Platinum Based Chemotherapy

Genes OGG1 and MUTYH are the two primary genes in Base excision repair pathway. OGG1 hydrolyzes the sugar phosphate backbone and remove the damaged base creating abasic site. MUTYH complements OGG1 as it particularly remove adenine mispaired with 8-oxo-G. Both OGG1 and MUTYH act as a check for the mis-incorporation of bases may be due to damages incurred on DNA. DNA isolation for 326 lung cancer cases and 330 controls was followed by genotyping making use of PCR-RFLP. Logistic regression was done to analyze the risk towards lung cancer. Patients were followed through telephonic conversation. Kaplan meier and Cox-regression were used for survival analysis. OGG1 presented a high risk towards lung cancer (CG: OR = 2.44, p = 0.0003; CG + GG: OR = 1.88, p = 0.0093). On the same lines adenocarcinoma for OGG1 were potent risk factors towards lung cancer (CG: OR = 4.72, p = 0.0002; CG + GG: OR = 3.63, p = 0.0018). Single allelic carriers for MUTYH gene imposed a high risk towards overall lung susceptibility and for all the three histology. Stratified analysis for chemotherapeutic drugs revealed administration of Cisplatin/Carboplatin + Pemtrexed for OGG1Ser ³²⁶ Cys showed a better survival (MST CG vs. CC: 9.1 vs. 0.56, p = <0.0001; HR =0.051, p = 0.0025). Whereas, MUTYH Gln³²⁴His showed a smaller survival for mutant genotype (CC) (MST CC vs. GG: 4.0 vs. 9.4, p = 0.05; HR = 1.75, p = 0.26). Single allelic carriers for both OGG1 and MUTYH were risk factors towards lung cancer. The risk was amplified on combining both OGG1 and MUTYH.

Mutation Spectrum Induced by 8-Bromoguanine, a Base Damaged by Reactive Brominating Species, in Human Cells

To date, the types of mutations caused by 8-bromoguanine (8BrG), a major base lesion induced by reactive brominating species during inflammation, in human cells and the 8BrG repair system remain largely unknown. In this study, we performed a supF forward mutation assay using a shuttle vector plasmid containing a single 8BrG in three kinds of human cell lines and revealed that 8BrG in DNA predominantly induces a G → T mutation but can also induce G → C, G → A, and delG mutations in human cells. Next, we tested whether eight kinds of DNA glycosylases (MUTYH, MPG, NEIL1, OGG1, SMUG1, TDG, UNG2, and NTHL1) are capable of repairing 8BrG mispairs with any of the four bases using a DNA cleavage activity assay. We found that both the SMUG1 protein and the TDG protein exhibit DNA glycosylase activity against thymine mispaired with 8BrG and that the MUTYH protein exhibits DNA glycosylase activity against adenine mispaired with 8BrG. These results suggest that 8BrG induces some types of mutations, chiefly a G → T mutation, in human cells, and some DNA glycosylases are involved in the repair of 8BrG.

WDR62 overexpression is associated with a poor prognosis in patients with lung adenocarcinoma

Human WDR62, which is localized in the cytoplasm including the centrosome, is known to be responsible for primary microcephaly; however, the role of WDR62 abnormality in cancers remains largely unknown. In this study, we aimed to reveal the pathological role of WDR62 abnormality in lung adenocarcinoma (LAC). We first examined the WDR62 mRNA expression level of LAC (n = 64) using a QRT-PCR analysis and found that WDR62 mRNA transcripts were significantly overexpressed in LAC (P = 0.0432, Wilcoxon matched pairs test). An immunohistochemical analysis for LAC (n = 237) showed that WDR62 proteins were also significantly overexpressed in LAC (P < 0.0001, Mann-Whitney U test). A Kaplan-Meier analysis demonstrated that patients with LAC who exhibit WDR62 overexpression have a short overall survival (P = 0.0378, log-rank test), and a multivariate analysis revealed that WDR62 overexpression was an independent predictor of a poor survival outcome among LAC patients (hazard ratio, 2.032; 95% confidence interval, 1.071-3.777; P = 0.0305). Next, we examined the functional effect of WDR62 overexpression on the lung cancer cell line H1299. WDR62-overexpressing lung cancer cells exhibited an increase in cell growth. Moreover, the concurrent overexpression of WDR62 and TPX2, a WDR62-interacting protein that is also overexpressed in LAC, induced centrosome amplification in the lung cells. Finally, we disclosed that the concurrent overexpression of WDR62 and TPX2 is common in diverse human cancers, using data from the Cancer Genome Atlas. These results suggested that WDR62 overexpression is associated with a poor prognosis in patients with LAC and leads to an increase in the malignant potential of lung cells.

Abnormal Expressions of DNA Glycosylase Genes NEIL1, NEIL2, and NEIL3 Are Associated with Somatic Mutation Loads in Human Cancer

The effects of abnormalities in the DNA glycosylases NEIL1, NEIL2, and NEIL3 on human cancer have not been fully elucidated. In this paper, we found that the median somatic total mutation loads and the median somatic single nucleotide mutation loads exhibited significant inverse correlations with the median NEIL1 and NEIL2 expression levels and a significant positive correlation with the median NEIL3 expression level using data for 13 cancer types from the Cancer Genome Atlas (TCGA) database. A subset of the cancer types exhibited reduced NEIL1 and NEIL2 expressions and elevated NEIL3 expression, and such abnormal expressions of NEIL1, NEIL2, and NEIL3 were also significantly associated with the mutation loads in cancer. As a mechanism underlying the reduced expression of NEIL1 in cancer, the epigenetic silencing of NEIL1 through promoter hypermethylation was found. Finally, we investigated the reason why an elevated NEIL3 expression level was associated with an increased number of somatic mutations in cancer and found that NEIL3 expression was positively correlated with the expression of APOBEC3B, a potent inducer of mutations, in diverse cancers. These results suggested that the abnormal expressions of NEIL1, NEIL2, and NEIL3 are involved in cancer through their association with the somatic mutation load.

NEIL1 p.Gln282Stop variant is predominantly localized in the cytoplasm and exhibits reduced activity in suppressing mutations

Human NEIL1 protein is a DNA glycosylase known to be involved in the repair of oxidized DNA lesions. A c.C844T germline variant of the NEIL1 gene has recently been identified in the Japanese population, however, the p.Q282Stop-type protein produced from this variant gene has not yet been characterized. In this study to determine whether the NEIL1 c.C844T variant might be a defective allele, we investigated the subcellular localization of the p.Q282Stop-type protein and its ability to suppress the development of mutations in mammalian cells. In contrast to the nuclear localization of wild-type (WT) NEIL1, the p.Q282Stop-type protein tagged with GFP or FLAG was localized predominantly in the cytoplasm of human H1299 cells. Mutant forms of the putative nuclear localization signal (NLS, amino acid sequences 359 to 378) of NEIL1-GFP resulted in predominant cytoplasmic localization of the mutants, suggesting that the abnormal localization of p.Q282Stop-type NEIL1 may also be caused by a loss of the putative NLS in the protein. Next, V79 mammalian cell lines inducibly expressing WT NEIL1 or p.Q282Stop-type NEIL1 were established using the piggyBac transposon vector system, and the mutation frequency was compared between the cell lines by HPRT assay. The frequency of mutations induced by glucose oxidase, an oxidative stress inducer, was higher in the p.Q282Stop-type NEIL1-transposed cells than that in the WT NEIL1-transposed cells. Finally, the Cancer Genome Atlas (TCGA) data showed an increased number of somatic mutations in primary carcinomas containing a truncating NEIL1 mutation. These results suggest that p.Q282Stop-type NEIL1 is predominantly localized in the cytoplasm, possibly due to a loss of the NLS, and possesses a reduced ability to suppress the onset of mutations, both findings suggesting that NEIL1 c.C844T is a defective allele.

BSND and ATP6V1G3: Novel Immunohistochemical Markers for Chromophobe Renal Cell Carcinoma

Differentiating between chromophobe renal cell carcinoma (RCC) and other RCC subtypes can be problematic using routine light microscopy. This study aimed to identify novel immunohistochemical markers useful for a differential diagnosis between chromophobe RCC and other RCC subtypes. We selected 3 genes (including BSND and ATP6V1G3) that showed specific transcriptional expression in chromophobe RCC using expression data (n = 783) from The Cancer Genome Atlas (TCGA) database. A subsequent immunohistochemical examination of 186 RCCs obtained in our patient series resulted in a strong diffuse positivity of BSND and ATP6V1G3 proteins (both of which are involved in the regulation of membrane transport) in all the chromophobe RCC specimens (23/23 cases, 100%) but not in the clear cell RCC specimens (0/153 cases, 0%) or the papillary RCC specimens (0/10 cases, 0%). BSND and ATP6V1G3 protein expressions were also detected in renal oncocytoma (13/14 cases, 92.9%) and in the distal nephron, including the collecting duct, in the normal kidney. A computational analysis of TCGA data suggested that DNA methylation was involved in the differential expression pattern of both genes among RCC subtypes. Finally, an immunohistochemical analysis showed lung carcinomas were negative (0/85 cases, 0%) for the expression of both proteins. These results suggest that BSND and ATP6V1G3 are excellent novel immunohistochemical markers for differentiating between chromophobe RCC and other subtypes of RCC, including clear cell and papillary RCCs.

SASS6 overexpression is associated with mitotic chromosomal abnormalities and a poor prognosis in patients with colorectal cancer

Spindle assembly abnormal protein 6 homolog (SASS6) plays an important role in the regulation of centriole duplication. To date, the genetic alteration of SASS6 has not been reported in human cancers. In the present study, we examined whether SASS6 expression is abnormally regulated in colorectal cancers (CRCs). Increased SASS6 mRNA and protein expression levels were observed in 49 (60.5%) of the 81 primary CRCs and 11 (57.9%) of the 19 primary CRCs, respectively. Moreover, the upregulation of SASS6 mRNA expression was statistically significant (P=0.0410). Next, using DLD-1 colon cancer cells inducibly expressing SASS6, SASS6 overexpression was shown to induce centrosome amplification, mitotic abnormalities such as chromosomal misalignment and lagging chromosome, and chromosomal numerical changes. Furthermore, SASS6 overexpression was associated with anaphase bridge formation, a type of mitotic structural abnormality, in primary CRCs (P<0.01). SASS6 upregulation in colon cancer was also revealed in the Cancer Genome Atlas (TCGA) data and was shown to be an independent predictor of poor survival (multivariate analysis: hazard ratio, 2.805; 95% confidence interval, 1.244‑7.512; P=0.0112). Finally, further analysis of the TCGA data demonstrated SASS6 upregulation in a modest manner in 8 of 11 cancer types other than colon cancer, and SASS6 upregulation was found to be associated with a poor survival outcome in patients with kidney renal cell carcinoma and lung adenocarcinoma. Our present findings revealed that the upregulation of SASS6 expression is involved in the pathogenesis of CRC and is associated with a poor prognosis among patients with colon cancer. They also suggest that SASS6 upregulation is a genetic abnormality relatively common in human cancer.

CLCA2 as a novel immunohistochemical marker for differential diagnosis of squamous cell carcinoma from adenocarcinoma of the lung

Recent progress in targeted therapy for lung cancer has revealed that accurate differential diagnosis between squamous cell carcinoma (SCC) and adenocarcinoma (ADC) of the lung is essential. To identify a novel immunohistochemical marker useful for differential diagnosis between the two subtypes of lung cancer, we first selected 24 SCC-specific genes and 6 ADC-specific genes using data (case number, 980) from the Cancer Genome Atlas (TCGA) database. Among the genes, we chose the CLCA2 gene, which is involved in chloride conductance and whose protein expression in lung cancer is yet to be characterized, and evaluated its protein expression status in 396 cases of primary lung cancer at Hamamatsu University Hospital. Immunohistochemical analysis revealed a significantly higher CLCA2 expression level in the SCCs than in the ADCs (P < 0.0001) and also a significantly higher frequency of CLCA2 protein expression in the SCCs (104/161, 64.6%) as compared with that in the ADCs (2/235, 0.9%) (P < 0.0001; sensitivity 64.6%, specificity 99.1%). The CLCA2 protein expression status was associated with the histological tumor grade in the SCCs. These results suggest that CLCA2 might be a novel excellent immunohistochemical marker for differentiating between primary SCC and primary ADC of the lung.

Human DNA glycosylase enzyme TDG repairs thymine mispaired with exocyclic etheno-DNA adducts

Lipid peroxidation directly reacts with DNA and produces various exocyclic etheno-base DNA adducts, some of which are considered to contribute to carcinogenesis. However, the system for repairing them in humans is largely unknown. We hypothesized that etheno-DNA adducts are repaired by base excision repair initiated by DNA glycosylase. To test this hypothesis, we examined the activities of the DNA glycosylase proteins OGG1, SMUG1, TDG, NEIL1, MUTYH, NTH1, MPG, and UNG2 against double-stranded oligonucleotides containing 1,N(6)-ethenoadenine (εA), 3,N(4)-ethenocytosine (εC), butanone-ethenocytosine (BεC), butanone-ethenoguanine (BεG), heptanone-ethenocytosine (HεC), or heptanone-ethenoguanine (HεG) using a DNA cleavage assay. We found that TDG is capable of removing thymine that has mispaired with εC, BεC, BεG, HεC, or HεG in vitro. We next examined the effect of TDG against etheno-DNA adducts in human cells. TDG-knockdown cells exhibited the following characteristics: (a) higher resistance to cell death caused by the induction of etheno-DNA adducts; (b) lower repair activity for εC; and (c) a modest acceleration of mutations caused by εC, compared with the rate in control cells. All these characteristics suggest that TDG exerts a repair activity against etheno-DNA adducts in human cells. These results suggest that TDG has novel repair activities toward etheno-DNA adducts.

PLK4 overexpression and its effect on centrosome regulation and chromosome stability in human gastric cancer

Polo-like kinase 4 (PLK4) is a centrosomal protein that is involved in the regulation of centrosome duplication. This study aimed to determine whether the genetic abnormality of PLK4 is involved in human gastric cancer. First, we examined the status of PLK4 mRNA expression in 7 gastric cancer cell lines and 48 primary gastric cancers using an RT-PCR analysis. The upregulation of PLK4 mRNA expression was detected in 57.1 % (4/7) of the gastric cancer cell lines, and a novel PLK4 variant with exon 4, but without exon 5, was identified. In the primary gastric cancers, the upregulation of PLK4 mRNA expression in the cancerous cells was detected in 50.0 % (24/48) of the cases, and this upregulation was statistically significant (P value = 0.0139). Next, we established AGS gastric cancer cells capable of inducibly expressing PLK4 using the piggyBac transposon vector system and showed that PLK4 overexpression induced centrosome amplification and chromosome instability using immunofluorescence and FISH analyses, respectively. Furthermore, PLK4 overexpression suppressed primary cilia formation. Our current findings suggested that PLK4 is upregulated in a subset of primary gastric cancers and that PLK4 overexpression induces centrosome amplification and chromosome instability and causes the suppression of primary cilia formation.

Impaired 8-hydroxyguanine repair activity of MUTYH variant p.Arg109Trp found in a Japanese patient with early-onset colorectal cancer

PURPOSE

The biallelic inactivation of the 8-hydroxyguanine repair gene MUTYH leads to MUTYH-associated polyposis (MAP), which is characterized by colorectal multiple polyps and carcinoma(s). However, only limited information regarding MAP in the Japanese population is presently available. Since early-onset colorectal cancer (CRC) is a characteristic of MAP and might be caused by the inactivation of another 8-hydroxyguanine repair gene, OGG1, we investigated whether germline MUTYH and OGG1 mutations are involved in early-onset CRC in Japanese patients.

METHODS

Thirty-four Japanese patients with early-onset CRC were examined for germline MUTYH and OGG1 mutations using sequencing.

RESULTS

Biallelic pathogenic mutations were not found in any of the patients; however, a heterozygous p.Arg19∗  MUTYH variant and a heterozygous p.Arg109Trp MUTYH variant were detected in one patient each. The p.Arg19∗ and p.Arg109Trp corresponded to p.Arg5∗ and p.Arg81Trp, respectively, in the type 2 nuclear-form protein. The defective DNA repair activity of p.Arg5∗ is apparent, while that of p.Arg81Trp has been demonstrated using DNA cleavage and supF forward mutation assays.

CONCLUSION

These results suggest that biallelic MUTYH or OGG1 pathogenic mutations are rare in Japanese patients with early-onset CRC; however, the p.Arg19∗ and p.Arg109Trp MUTYH variants are associated with functional impairments.

A novel somatic FGFR3 mutation in primary lung cancer

The recent discovery of mutations and fusions of oncokinase genes in a subset of lung cancers (LCs) is of considerable clinical interest, since LCs containing such mutations or fusion transcripts are reportedly sensitive to kinase inhibitors. To better understand the role of the recently identified fibroblast growth factor receptor 3 (FGFR3) mutations and fusions in pulmonary carcinogenesis, we examined 214 LCs for mutations in the mutation cluster region of the FGFR3 gene using sequencing analysis. We also examined 190 LCs for the FGFR3-TACC3 and FGFR3-BAIAP2L1 fusion transcripts using reverse transcription-polymerase chain reaction (RT-PCR) analysis. Although the expression of FGFR3-TACC3 and FGFR3-BAIAP2L1 fusion transcripts was not detected in any of the carcinomas, somatic FGFR3 mutations were detected in two (0.9%) LCs. The two mutations were the same, i.e., p.R248H. That was a novel mutation occurring in the same codon as p.R248C, for which an oncogenic potential has previously been shown. Increased FGFR3 expression was shown in the two LCs containing the FGFR3 p.R248H mutation using qPCR. Histologically, both carcinomas were squamous cell carcinomas, therefore the incidence of the FGFR3 mutation among the squamous cell carcinoma cases was calculated as 3.2% (2/63). When we examined other co-occurring genetic abnormalities, one case exhibited a p53 p.R273C mutation, while the other case exhibited PIK3CA and SOX2 amplifications. The above results suggest that an FGFR3 p.R248H mutation is involved in the carcinogenesis of a subset of LCs and may contribute to the elucidation of the characteristics of FGFR3 mutation-positive LCs in the future.

Regulation of human MutYH DNA glycosylase by the E3 ubiquitin ligase mule

Oxidation of DNA is a frequent and constantly occurring event. One of the best characterized oxidative DNA lesions is 7,8-dihydro-8-oxoguanine (8-oxo-G). It instructs most DNA polymerases to preferentially insert an adenine (A) opposite 8-oxo-G instead of the appropriate cytosine (C) thus showing miscoding potential. The MutY DNA glycosylase homologue (MutYH) recognizes A:8-oxo-G mispairs and removes the mispaired A giving way to the canonical base excision repair that ultimately restores undamaged guanine (G). Here we characterize for the first time in detail a posttranslational modification of the human MutYH DNA glycosylase. We show that MutYH is ubiquitinated in vitro and in vivo by the E3 ligase Mule between amino acids 475 and 535. Mutation of five lysine residues in this region significantly stabilizes MutYH, suggesting that these are the target sites for ubiquitination. The endogenous MutYH protein levels depend on the amount of expressed Mule. Furthermore, MutYH and Mule physically interact. We found that a ubiquitination-deficient MutYH mutant shows enhanced binding to chromatin. The mutation frequency of the ovarian cancer cell line A2780, analyzed at the HPRT locus can be increased upon oxidative stress and depends on the MutYH levels that are regulated by Mule. This reflects the importance of tightly regulated MutYH levels in the cell. In summary our data show that ubiquitination is an important regulatory mechanism for the essential MutYH DNA glycosylase in human cells.

Mammalian MutY homolog (MYH or MUTYH) protects cells from oxidative DNA damage

MutY DNA glycosylase homologs (MYH or MUTYH) reduce G:C to T:A mutations by removing misincorporated adenines or 2-hydroxyadenines paired with guanine or 8-oxo-7,8-dihydroguanine (8-oxo-G). Mutations in the human MYH (hMYH) gene are associated with the colorectal cancer predisposition syndrome MYH-associated polyposis. To examine the function of MYH in human cells, we regulated MYH gene expression by knockdown or overproduction. MYH knockdown human HeLa cells are more sensitive to the killing effects of H2O2 than the control cells. In addition, hMYH knockdown cells have altered cell morphology, display enhanced susceptibility to apoptosis, and have altered DNA signaling activation in response to oxidative stress. The cell cycle progression of hMYH knockdown cells is also different from that of the control cells following oxidative stress. Moreover, hMYH knockdown cells contain higher levels of 8-oxo-G lesions than the control cells following H2O2 treatment. Although MYH does not directly remove 8-oxo-G, MYH may generate favorable substrates for other repair enzymes. Overexpression of mouse Myh (mMyh) in human mismatch repair defective HCT15 cells makes the cells more resistant to killing and refractory to apoptosis by oxidative stress than the cells transfected with vector. In conclusion, MYH is a vital DNA repair enzyme that protects cells from oxidative DNA damage and is critical for a proper cellular response to DNA damage.

TNK2 gene amplification is a novel predictor of a poor prognosis in patients with gastric cancer

BACKGROUNDS AND OBJECTIVES

We previously examined the amplification status of 10 kinase genes (PIK3CA, EPHB3, TNK2, PTK7, EGFR, MET, ERBB2, HCK, SRC, and AURKA) in gastric cancer (GC). This study aimed to determine the prognostic significance of these gene amplifications in GC.

METHODS

A survival analysis was performed for GC patients. Since TNK2 amplification was identified as a prognostic marker in the analysis, we also examined the functional effect of TNK2 overexpression on gastric cells.

RESULTS

A Kaplan-Meier analysis showed that the prognosis of patients with GC exhibiting TNK2 or AURKA amplification was significantly poorer than the prognosis of patients with GC without TNK2 or AURKA amplification. A further multivariate analysis revealed that TNK2 amplification was an independent predictor of a poor survival outcome among patients with GC (hazard ratio, 3.668; 95% confidence interval, 1.513-7.968; P = 0.0056). TNK2-overexpressing GC cells showed an increase in cell migration and non-anchored cell growth. Finally, microarray and pathway analyses revealed the aberrant regulation of some cancer-related pathways in TNK2-overexpressing GC cells.

CONCLUSIONS

These results suggested that TNK2 amplification is an independent predictor of a poor prognosis in patients with GC and leads to an increase in the malignant potential of GC cells.

SGOL1 variant B induces abnormal mitosis and resistance to taxane in non-small cell lung cancers

Mitosis is the most conspicuous cell cycle phase and Shugoshin-like 1 (SGOL1) is a key protein in protecting sister chromatids from precocious separation during mitosis. We studied the role of SGOL1 and its splice variants in non-small cell lung cancer (NSCLC) using 82 frozen NSCLC tissue samples. SGOL1-B expression was prevalent in smokers, in cases with a wild-type (WT) EGFR status, and in cases with the focal copy number amplification of genes that are known to be important for defining the biological behaviors of NSCLC. The overexpression of SGOL1-B1 in an NSCLC cell line induced aberrant chromosome missegregation, precociously separated chromatids, and delayed mitotic progression. A higher level of SGOL1-B mRNA was related to taxane resistance, while the forced downregulation of SGOL1-B increased the sensitivity to taxane. These results suggest that the expression of SGOL1-B causes abnormal mitosis and taxane resistance in NSCLC cells.

Identification and association study with lung cancer for novel insertion polymorphisms of human endogenous retrovirus

Sequences of human endogenous retroviruses (HERVs) are members of the long terminal repeat (LTR) retrotransposon family. Although the expression of HERV has long been a topic of investigation, HERV-insertion polymorphisms are not well known, and a genetic association between HERV-insertion polymorphisms and cancer has never been reported. To identify novel HERV loci in the genome from cancer tissues, we carried out the inverse PCR method targeting a conserved LTR region of HML-2, which is the most recently acquired HERV group. Novel two insertions, HML-2_sLTR(1p13.2) and HML-2_sLTR(19q12), were identified as insertionally polymorphic solo LTRs. Furthermore, a significant prevalence of HML-2_sLTR(1p13.2) homozygosity was detected in female never-smoking patients aged 60 years and over who had lung adenocarcinoma [versus the other genotyping; odds ratio (OR): 1.97; 95% confidence interval (CI): 1.01-3.81]. In another cohort consisting of female never-smoking patients with lung adenocarcinoma, a prevalence of HML-2_sLTR(1p13.2) homozygosity tended to be high in patients aged 60 years and over (versus the other genotyping; OR: 2.03; 95% CI: 0.96-4.29), whereas a low prevalence of HML-2_sLTR(1p13.2) homozygosity was detected in patients <60 years old (versus the other genotyping; OR: 0.31; 95% CI: 0.11-0.94). Our results suggest that HML-2_sLTR(1p13.2) is involved with the susceptibility to lung adenocarcinoma in female never-smokers in an age-dependent manner and that other HERV polymorphisms related to human diseases might remain to be identified in the human genome.

MUTYH-associated colorectal cancer and adenomatous polyposis

MUTYH-associated polyposis (MAP) was first described in 2002. MUTYH is a component of a base excision repair system that protects the genomic information from oxidative damage. When the MUTYH gene product is impaired by bi-allelic germline mutation, it leads to the mutation of cancer-related genes, such as the APC and/or the KRAS genes, via G to T transversion. MAP is a hereditary colorectal cancer syndrome inherited in an autosomal-recessive fashion. The clinical features of MAP include the presence of 10-100 adenomatous polyps in the colon, and early onset of colorectal cancer. Ethnic and geographical differences in the pattern of the MUTYH gene mutations have been suggested. In Caucasian patients, c.536A>G (Y179C) and c.1187G>A (G396D) mutations are frequently detected. In the Asian population, Y179C and G396D are uncommon, whereas other variants are suggested to be the major causes of MAP. We herein review the literature on MUTYH-associated colorectal cancer and adenomatous polyposis.

Role of MUTYH in human cancer

MUTYH, a human ortholog of MutY, is a post-replicative DNA glycosylase, highly conserved throughout evolution, involved in the correction of mismatches resulting from a faulty replication of the oxidized base 8-hydroxyguanine (8-oxodG). In particular removal of adenine from A:8-oxodG mispairs by MUTYH activity is followed by error-free base excision repair (BER) events, leading to the formation of C:8-oxodG base pairs. These are the substrate of another BER enzyme, the OGG1 DNA glycosylase, which then removes 8-oxodG from DNA. Thus the combined action of OGG1 and MUTYH prevents oxidative damage-induced mutations, i.e. GC->TA transversions. Germline mutations in MUTYH are associated with a recessively heritable colorectal polyposis, now referred to as MUTYH-associated polyposis (MAP). Here we will review the phenotype(s) associated with MUTYH inactivation from bacteria to mammals, the structure of the MUTYH protein, the molecular mechanisms of its enzymatic activity and the functional characterization of MUTYH variants. The relevance of these results will be discussed to define the role of specific human mutations in colorectal cancer risk together with the possible role of MUTYH inactivation in sporadic cancer.

Impaired suppressive activities of human MUTYH variant proteins against oxidative mutagenesis

AIM: To investigate the suppressive activity of MUTYH variant proteins against mutations caused by oxidative lesion, 8-hydroxyguanine (8OHG), in human cells.

METHODS: p.R154H, p.M255V, p.L360P, and p.P377L MUTYH variants, which were previously found in patients with colorectal polyposis and cancer, were selected for use in this study. Human H1299 cancer cell lines inducibly expressing wild-type (WT) MUTYH (type 2) or one of the 4 above-mentioned MUTYH variants were established using the piggyBac transposon vector system, enabling the genomic integration of the transposon sequence for MUTYH expression. MUTYH expression was examined after cumate induction using Western blotting analysis and immunofluorescence analysis. The intracellular localization of MUTYH variants tagged with FLAG was also immunofluorescently examined. Next, the mutation frequency in the supF of the shuttle plasmid pMY189 containing a single 8OHG residue at position 159 of the supF was compared between empty vector cells and cells expressing WT MUTYH or one of the 4 MUTYH variants using a supF forward mutation assay.

RESULTS: The successful establishment of human cell lines inducibly expressing WT MUTYH or one of the 4 MUTYH variants was concluded based on the detection of MUTYH expression in these cell lines after treatment with cumate. All of the MUTYH variants and WT MUTYH were localized in the nucleus, and nuclear localization was also observed for FLAG-tagged MUTYH. The mutation frequency of supF was 2.2 × 10^-2 in the 8OHG-containing pMY189 plasmid and 2.5 × 10^-4 in WT pMY189 in empty vector cells, which was an 86-fold increase with the introduction of 8OHG. The mutation frequency (4.7 × 10^-3) of supF in the 8OHG-containing pMY189 plasmid in cells overexpressing WT MUTYH was significantly lower than in the empty vector cells (P < 0.01). However, the mutation frequencies of the supF in the 8OHG-containing pMY189 plasmid in cells overexpressing the p.R154H, p.M255V, p.L360P, or p.P377L MUTYH variant were 1.84 × 10^-2, 1.55 × 10^-2, 1.91 × 10^-2, and 1.96 × 10^-2, respectively, meaning that no significant difference was observed in the mutation frequency between the empty vector cells and cells overexpressing MUTYH mutants.

CONCLUSION: The suppressive activities of p.R154H, p.M255V, p.L360P, and p.P377L MUTYH variants against mutations caused by 8OHG are thought to be severely impaired in human cells.

Detection of kinase amplifications in gastric cancer archives using fluorescence in situ hybridization

To test the feasibility of using bacterial artificial chromosomes (BAC) containing kinases for pathological diagnosis using fluorescence in situ hybridization (FISH), 10 BAC probes containing a gene amplified in 5% or more of a pilot cohort were selected from a previous survey using arbitrarily selected BAC clones harboring 100 kinases. In this report, we describe the prevalence and association with the clinicopathological profile of these selected 10 BAC probes in 365 gastric cancer tissues. FISH analyses using these 10 BAC probes containing loci encoding EGFR, ERBB2(HER2), EPHB3, PIK3CA, MET, PTK7, ACK1, STK15, SRC, and HCK showed detectable amplifications in paraffin-embedded tissue in 2.83% to 13.6% of the gastric cancer tissues. Considerable numbers of the cases showed the co-amplification of two or more of the probes that were tested. BAC probes located within a genome neighborhood, such as PIK3CA, EPHB3, and ACK1 at 3q26-29 or HCK, SRC, and STK15 at 20q11-13.1, were often co-amplified in the same cases, but non-random co-amplifications of genes at distant genomic loci were also observed. These findings provide basic information regarding the creation of a strategy for personalizing gastric cancer therapy, especially when using multiple kinase inhibitors.

Cancer-associated variants and a common polymorphism of MUTYH exhibit reduced repair of oxidative DNA damage using a GFP-based assay in mammalian cells

Biallelic germline mutations in the base excision repair enzyme gene MUTYH lead to multiple colorectal adenomas and carcinomas referred to as MUTYH-associated polyposis. MUTYH removes adenine misincorporated opposite the DNA oxidation product, 8-oxoguanine (OG), thereby preventing accumulation of G:C to T:A transversion mutations. The most common cancer-associated MUTYH variant proteins when expressed in bacteria exhibit reduced OG:A mismatch affinity and adenine removal activity. However, direct evaluation of OG:A mismatch repair efficiency in mammalian cells has not been assessed due to the lack of an appropriate assay. To address this, we developed a novel fluorescence-based assay of OG:A repair and measured the repair capacity of MUTYH-associated polyposis variants expressed in Mutyh-/- mouse embryonic fibroblasts (MEFs). The repair of a single site-specific synthetic lesion in a green fluorescent protein reporter leads to green fluorescent protein expression with co-expression of a red fluorescent protein serving as the transfection control. Cell lines that stably express the MUTYH-associated polyposis variants G382D and Y165C have significantly lower OG:A repair versus wild-type MEFs and MEFs expressing human wild-type MUTYH. The MUTYH allele that encodes the Q324H variant is found at a frequency above 40% in samples from different ethnic groups and has long been considered phenotypically silent but has recently been associated with increased cancer risk in several clinical studies. In vitro analysis of Q324H MUTYH expressed in insect cells showed that it has reduced enzyme activity similar to that of the known cancer variant G382D. Moreover, we find that OG:A repair in MEFs expressing Q324H was significantly lower than wild-type controls, establishing that Q324H is functionally impaired and providing further evidence that this common variant may lead to increased cancer risk.

Lipid peroxidation-induced DNA adducts in human gastric mucosa

DNA adducts are a major cause of DNA mutation and DNA mutation-related diseases, but the simultaneous identification of multiple DNA adducts has been a challenge for a decade. An adductome approach using consecutive liquid chromatography and double mass spectrometry after micrococcal nuclease treatment has paved the way to demonstrations of numerous DNA adducts in a single experiment and is expected to contribute to the comprehensive understanding of overall environmental and endogenous exposures to possible mutagens in individuals. In this report, we applied an adductome approach to gastric mucosa samples taken at the time of a gastrectomy for gastric cancer in Lujiang, China, and in Hamamatsu, Japan. Seven lipid peroxidation-related DNA adducts [1,N6-etheno-2'-deoxyadenosine, butanone-etheno-2'-deoxycytidine (BεdC), butanone-etheno-2'-deoxy-5-methylcytidine, butanone-etheno-2'-deoxyadenosine (BεdA), heptanone-etheno-2'-deoxycytidine, heptanone-etheno-2'-deoxyadenosine (HεdA) and heptanone-etheno- 2'-deoxyguanosine] were identified in a total of 22 gastric mucosa samples. The levels of these adducts ranged from 0 to 30,000 per 10(9) bases. Although the presence of Helicobacter pylori DNA in the mucosa was not related to these adducts level, the levels of BεdC, BεdA and HεdA were higher in the Japanese gastric mucosa samples. The profiles of these 7 adduct levels among the 21 cases were capable of discriminating between the possible origins (China or Japan) of the gastric mucosa samples. Our report is the first demonstration of lipid peroxidation-related DNA adducts in the human stomach, and these observations warrant further investigation in the context of the significance of DNA adducts in human gastric carcinogenesis.

MUTYH-associated polyposis (MAP), the syndrome implicating base excision repair in inherited predisposition to colorectal tumors

In 2002, Al-Tassan and co-workers described for the first time a recessive form of inherited polyposis associated with germline mutations of MUTYH, a gene encoding a base excision repair (BER) protein that counteracts the DNA damage induced by the oxidative stress. MUTYH-associated polyposis (MAP) is now a well-defined cancer susceptibility syndrome, showing peculiar molecular features that characterize disease progression. However, some aspects of MAP, including diagnostic criteria, genotype-phenotype correlations, pathogenicity of variants, as well as relationships between BER and other DNA repair pathways, are still poorly understood. A deeper knowledge of the MUTYH expression pattern is likely to refine our understanding of the protein role and, finally, to improve guidances for identifying and handling MAP patients.

The CRKL gene encoding an adaptor protein is amplified, overexpressed, and a possible therapeutic target in gastric cancer

Background

Genomic DNA amplification is a genetic factor involved in cancer, and some oncogenes, such as ERBB2, are highly amplified in gastric cancer. We searched for the possible amplification of other genes in gastric cancer.

Methods and Results

A genome-wide single nucleotide polymorphism microarray analysis was performed using three cell lines of differentiated gastric cancers, and 22 genes (including ERBB2) in five highly amplified chromosome regions (with a copy number of more than 6) were identified. Particular attention was paid to the CRKL gene, the product of which is an adaptor protein containing Src homology 2 and 3 (SH2/SH3) domains. An extremely high CRKL copy number was confirmed in the MKN74 gastric cancer cell line using fluorescence in situ hybridization (FISH), and a high level of CRKL expression was also observed in the cells. The RNA-interference-mediated knockdown of CRKL in MKN74 disclosed the ability of CRKL to upregulate gastric cell proliferation. An immunohistochemical analysis revealed that CRKL protein was overexpressed in 24.4% (88/360) of the primary gastric cancers that were analyzed. The CRKL copy number was also examined in 360 primary gastric cancers using a FISH analysis, and CRKL amplification was found to be associated with CRKL overexpression. Finally, we showed that MKN74 cells with CRKL amplification were responsive to the dual Src/BCR-ABL kinase inhibitor BMS354825, likely via the inhibition of CRKL phosphorylation, and that the proliferation of MKN74 cells was suppressed by treatment with a CRKL-targeting peptide.

Conclusion

These results suggested that CRKL protein is overexpressed in a subset of gastric cancers and is associated with CRKL amplification in gastric cancer. Furthermore, our results suggested that CRKL protein has the ability to regulate gastric cell proliferation and has the potential to serve as a molecular therapy target for gastric cancer.

Genetic aspects of gastric cancer instability

Unravelling the molecular mechanisms underlying gastric carcinogenesis is one of the major challenges in cancer genomics. Gastric cancer is a very complex and heterogeneous disease, and although much has been learned about the different genetic changes that eventually lead to its development, the detailed mechanisms still remain unclear. Malignant transformation of gastric cells is the consequence of a multistep process involving different genetic and epigenetic changes in numerous genes in combination with host genetic background and environmental factors. The majority of gastric adenocarcinomas are characterized by genetic instability, either microsatellite instability (MSI) or chromosomal instability (CIN). It is believed that chromosome destabilizations occur early in tumour progression. This review summarizes the most common genetic alterations leading to instability in sporadic gastric cancers and its consequences.