Somatic mutations of the KEAP1 gene in common solid cancers

Yoo N J, Kim H R, Kim Y R, An C H & Lee S H
(2012) Histopathology  60, 943–952 Somatic mutations of the KEAP1 gene in common solid cancers Aims: KEAP1 inhibits nuclear factor erythroid 2‐related factor 2 (NRF2)‐induced cytoprotection, and is considered to be a candidate tumour suppressor. Somatic mutation of NRF2 has been analysed in a wide variety of human cancers, whereas somatic mutation of KEAP1 has been reported only in lung and gall bladder cancers. The aim of our study was to investigate whether KEAP1 mutations are widespread in human cancers. Methods and results: We analysed 499 cancer tissues from lung, breast, colon, stomach, liver, larynx and prostate, and leukaemias, by single‐strand conformation polymorphism analysis. We detected somatic mutations of KEAP1 in gastric (11.1%), hepatocellular (8.9%), colorectal (7.8%), lung (4.6%), breast (2.0%) and prostate (1.3%) carcinomas. Allelic losses of the KEAP1 locus were identified in 42.9% of cancers with KEAP1 mutations, but no NRF2 mutations were detected in these cancers. The NRF2‐activated cytoprotective proteins (NAD(P)H dehydrogenase quinone 1 and glutamine‐cysteine ligase catalytic subunit) were expressed in all of the cancers with KEAP1 mutations. Conclusions: Our data show that KEAP1 mutations occur widely in solid cancers, irrespective of histological type. Biallelic inactivation of KEAP1 and increased levels of cytoprotective proteins in the cancers suggest that KEAP1 mutations might protect cancer cells from oxidative insults and play a role in the development of solid cancers.     

Decreased expression and promoter methylation of the menin tumor suppressor in pancreatic ductal adenocarcinoma

Loss of menin, a tumor suppressor coded by the MEN1 gene, is a key factor in the pathogenesis of multiple endocrine neoplasia type I and in a percentage of sporadic endocrine tumors of the pancreas and parathyroid glands. This study investigated expression of the menin protein in the normal exocrine pancreas and in pancreatic ductal adenocarcinoma (PDAC), the most common pancreatic tumor. Immunofluorescence (IF) analyses showed that menin is expressed at high levels in normal acinar and duct cells. Examination of 24 clinical samples of PDAC revealed a pronounced decrease in menin expression in all tumors examined. To identify alterations underlying this defect, we searched for disruption and epigenetic silencing of the MEN1 gene. Analysis of nine laser‐microdissected tumors revealed loss of heterozygosity of intragenic (one tumor) or adjacent (three tumors) MEN1 microsatellite markers. Methylation of CpG sites in the MEN1 promoter was documented in five of 24 tumors. IF analyses also revealed low to undetectable menin expression in the PDAC cell lines MiaPaCa‐2 and Panc‐1. Ectopic expression of menin in these cells resulted in a marked alteration of the cell cycle, with an increase in the G1/S+G2 ratio. These findings represent the first evidence that the MEN1 gene is a target of mutation and methylation in PDAC and that menin influences the cell cycle profile of duct cells. © 2009 Wiley‐Liss,Inc.     

Molecular mechanisms of the Keap1–Nrf2 pathway in stress response and cancer evolution

The Keap1–Nrf2 regulatory pathway plays a central role in the protection of cells against oxidative and xenobiotic damage. Under unstressed conditions, Nrf2 is constantly ubiquitinated by the Cul3–Keap1 ubiquitin E3 ligase complex and rapidly degraded in proteasomes. Upon exposure to electrophilic and oxidative stresses, reactive cysteine residues of Keap1 become modified, leading to a decline in the E3 ligase activity, stabilization of Nrf2 and robust induction of a battery of cytoprotective genes. Biochemical and structural analyses have revealed that the intact Keap1 homodimer forms a cherry-bob structure in which one molecule of Nrf2 associates with two molecules of Keap1 by using two binding sites within the Neh2 domain of Nrf2. This two-site binding appears critical for Nrf2 ubiquitination. In many human cancers, missense mutations in KEAP1 and NRF2 genes have been identified. These mutations disrupt the Keap1–Nrf2 complex activity involved in ubiquitination and degradation of Nrf2 and result in constitutive activation of Nrf2. Elevated expression of Nrf2 target genes confers advantages in terms of stress resistance and cell proliferation in normal and cancer cells. Discovery and development of selective Nrf2 inhibitors should make a critical contribution to improved cancer therapy.     

The epigenetic regulators Bmi1 and Ring1B are differentially regulated in pancreatitis and pancreatic ductal adenocarcinoma

Chronic pancreatitis and pancreatic ductal adenocarcinoma (PDAC) are associated with major changes in cell differentiation. These changes may be at the basis of the increased risk for PDAC among patients with chronic pancreatitis. Polycomb proteins are epigenetic silencers expressed in adult stem cells; up‐regulation of Polycomb proteins has been reported to occur in a variety of solid tumours such as colon and breast cancer. We hypothesized that Polycomb might play a role in preneoplastic states in the pancreas and in tumour development/progression. To test these ideas, we determined the expression of PRC1 complex proteins (Bmi1 and Ring1b) during pancreatic development and in pancreatic tissue from mouse models of disease: acute and chronic pancreatic injury, duct ligation, and in K‐Ras^G12V conditional knock‐in and caerulein‐treated K‐Ras^G12V mice. The study was extended to human pancreatic tissue samples. To obtain mechanistic insights, Bmi1 expression in cells undergoing in vitro exocrine cell metaplasia and the effects of Bmi1 depletion in an acinar cancer cell line were studied. We found that Bmi1 and Ring1B are expressed in pancreatic exocrine precursor cells during early development and in ductal and islet cells—but not acinar cells—in the adult pancreas. Bmi1 expression was induced in acinar cells during acute injury, in acinar–ductal metaplastic lesions, as well as in pancreatic intraepithelial neoplasia (PanIN) and PDAC. In contrast, Ring1B expression was only significantly and persistently up‐regulated in high‐grade PanINs and in PDAC. Bmi1 knockdown in cultured acinar tumour cells led to changes in the expression of various digestive enzymes. Our results suggest that Bmi1 and Ring1B are modulated in pancreatic diseases and could contribute differently to tumour development. Copyright © 2009 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Sineoculis homeobox homolog 1 protein overexpression as an independent biomarker for pancreatic ductal adenocarcinoma

Sineoculis homeobox homolog 1 (SIX1) is a member of the SIX gene family. It is highly expressed in cancers derived from tissues that play a fundamental role during embryogenesis. Recent studies suggest that inappropriate expression of SIX1 can both initiate tumorigenesis and promote metastasis. To investigate the clinicopathological significance of SIX1 expression in pancreatic ductal adenocarcinoma (PDAC), and to further identify its role as a potential biomarker and therapeutic target in PDAC, 103 PDAC tissue samples and 45 normal pancreatic tissue samples were immunohistochemically stained for SIX1 protein. The localization of SIX1 protein was detected in Panc-1 cancer cells using immunofluorescence staining. Correlations between SIX1 overexpression and the clinicopathological features of pancreatic cancer were evaluated using Chi-square (χ²) tests, differences in survival curves were analyzed using log-rank tests, and multivariate survival analysis was performed using the Cox proportional hazard regression model. In results, SIX1 protein showed mainly cytoplasmic/perinuclear staining pattern in PDAC with immunohistochemistry. The strongly positive rate of SIX1 protein was 60.2% (62/103) in PDAC, which was significantly higher than normal pancreatic tissue (6.7%, 3/45). SIX1 overexpression was positively correlated with tumor size, TNM stage, lymph node metastasis, and grade of PDAC (P < 0.001). SIX1 high expression levels influenced overall survival rates in G1, G2, stage I–II and stage III–IV groups of PDAC; and high expression levels had significantly lower overall survival rates than SIX1 low expression levels. In conclusion, SIX1 emerged as a significant independent prognostic factor in PDAC. SIX1 overexpression appears to be associated with PDAC, and may be a potential biomarker for early diagnosis and prognostic evaluation of PDAC.     

Prognostic and predictive values of Nrf2, Keap1, p16 and E-cadherin expression in ovarian epithelial carcinoma

Objectives: Despite considerable interest in the Nuclear factor-erythroid 2-related factor 2 (Nrf2)/Kelch-like ECH-associated protein-1 (Keap1), p16 and epithelial cadherin (E-cadherin) activation in carcinoma progression, contradictory results regarding association of Nrf2/Keap1/E-cadherin and p16 expression with clinico-pathological features and prognosis have been reported. The predictive value of these markers in ovarian carcinoma is unknown. Methods/Materials: In this retrospective study, 108 cases were evaluated immunohistochemically with antibodies to Nrf2, Keap1, estrogen receptor (ER), p16 and E-cadherin. The results were compared with histological and clinical data, disease-free survival (DFS) and overall survival (OS). Results: A cohort of 108 ovarian carcinomas (47 serous, 23 mucinous, 13 endometrioid and 25 clear cell), including 68 FIGO stage I-II cases and 40 FIGO stage III-IV cases was studied. The age of patients (P=0.005), FIGO stage (P<0.001), immunohistochemical expression of Keap1 (P<0.000), E-cadherin (P=0.045), p53 (P=0.003), p16 (P<0.001) and ER (P=0.004) were significant factors between different histological subtypes. Patients with serous carcinoma were older in age, presented with more advanced stage disease, worst prognosis, highest Keap1 expression and least percentage of E-cadherin immunoreactivity. In univariate analysis, FIGO staging (P=0.000 for DFS; P=0.000 for OS), Nrf2 (P=0.010 for DFS; P=0.001 for OS), and p16 (P=0.004 for DFS; P=0.019 for OS) were associated with worse prognosis. After multivariate analysis, FIGO staging and Nrf2 remained significance prognostic factors. Conclusions: There were differences in the expression of Nrf2, Keap1, p16 and E-cadherin between different ovarian carcinoma subtypes. In multivariate analysis, FIGO stage and Nrf2 expression were associated with poorer DFS and OS.     

Nitro-fatty acids and cyclopentenone prostaglandins share strategies to activate the Keap1-Nrf2 system: a study using green fluorescent protein transgenic zebrafish

Nitro‐fatty acids are electrophilic fatty acids produced in vivo from nitrogen peroxide that have many physiological activities. We recently demonstrated that nitro‐fatty acids activate the Keap1‐Nrf2 system, which protects cells from damage owing to electrophilic or oxidative stresses via transactivating an array of cytoprotective genes, although the molecular mechanism how they activate Nrf2 is unclear. A number of chemical compounds with different structures have been reported to activate the Keap1‐Nrf2 system, which can be categorized into at least six classes based on their sensing pathways. In this study, we showed that nitro‐oleic acid (OA‐NO₂), one of major nitro‐fatty acids, activates Nrf2 in the same manner that of a cyclopentenone prostaglandin 15‐deoxy‐Δ^12,14‐prostaglandin J₂ (15d‐PGJ₂) using transgenic zebrafish that expresses green fluorescent protein (GFP) in response to Nrf2 activators. In transgenic embryos, GFP was induced in the whole body by treatment with OA‐NO₂, 15d‐PGJ₂ or diethylmaleate (DEM), but not with hydrogen peroxide (H₂O₂), when exogenous Nrf2 and Keap1 were co‐overexpressed. Induction by OA‐NO₂ or 15d‐PGJ₂ but not DEM was observed, even when a C151S mutation was introduced in Keap1. Our results support the contention that OA‐NO₂ and 15d‐PGJ₂ share an analogous cysteine code as electrophiles and also have similar anti‐inflammatory roles.     

DNA methylation analysis of the HIF‐1α prolyl hydroxylase domain genes PHD1, PHD2, PHD3 and the factor inhibiting HIF gene FIH in invasive breast carcinomas

Huang K T, Mikeska T, Dobrovic A & Fox S B
(2010) Histopathology 57, 451–460
DNA methylation analysis of the HIF‐1α prolyl hydroxylase domain genes PHD1, PHD2, PHD3 and the factor inhibiting HIF gene FIH in invasive breast carcinomas Aims: Hypoxia‐inducible factor‐1 (HIF‐1) activity is regulated by prolyl hydroxylase (PHD1, PHD2, PHD3) and factor inhibiting HIF‐1 (FIH) that target the α subunit of HIF‐1 (HIF‐1α) for proteosomal degradation. We hypothesised that the elevated HIF‐1α level is due in some tumours to epigenetic silencing by DNA hypermethylation of the promoter region of one or more of the PHDs and FIH genes. The aims were to define the presence or absence of promoter methylation of PHDs and FIH in cell lines of various sources and breast carcinomas and, if present, determine its effect on mRNA and protein expression. Methods and results: Tumour cell lines (n = 20) and primary invasive breast carcinomas (n = 168) were examined for promoter region DNA methylation using methylation‐sensitive high‐resolution melting. There was evidence of PHD3 but not of PHD1, PHD2 or FIH DNA methylation in breast cancer (SkBr3) and leukaemic (HL60 and CCRF‐CEM) cell lines, but there was no evidence of methylation in any of 168 breast cancers. Only the high‐level PHD3 methylation seen in leukaemic cell lines correlated with absent mRNA and protein expression. Conclusions: Methylation‐induced epigenetic silencing of PHD1, PHD2, PHD3 and FIH is unlikely to underlie up‐regulated HIF‐1α expression in human breast cancer but may play a role in other tumour types.     

DNA methylation and mRNA expression of HLA‐DQA1 alleles in type 1 diabetes mellitus

Type 1 diabetes (T1D) belongs among polygenic multifactorial autoimmune diseases. The highest risk is associated with human leucocyte antigen (HLA) class II genes, including HLA‐DQA1 gene. Our aim was to investigate DNA methylation of HLA‐DQA1 promoter alleles (QAP) and correlate methylation status with individual HLA‐DQA1 allele expression of patients with T1D and healthy controls. DNA methylation is one of the epigenetic modifications that regulate gene expression and is known to be shaped by the environment.Sixty one patients with T1D and 39 healthy controls were involved in this study. Isolated DNA was treated with sodium bisulphite and HLA‐DQA1 promoter sequence was amplified using nested PCR. After sequencing, DNA methylation of HLA‐DQA1 promoter alleles was analysed. Individual mRNA HLA‐DQA1 relative allele expression was assessed using two different endogenous controls (PPIA, DRA). We have found statistically significant differences in HLA‐DQA1 allele 02:01 expression (PPIA normalization, P_corr = 0·041; DRA normalization, P_corr = 0·052) between healthy controls and patients with T1D. The complete methylation profile of the HLA‐DQA1 promoter was gained with the most methylated allele DQA1*02:01 and the least methylated DQA1*05:01 in both studied groups. Methylation profile observed in patients with T1D and healthy controls was similar, and no correlation between HLA‐DQA1 allele expression and DNA methylation was found. Although we have not proved significant methylation differences between the two groups, detailed DNA methylation status and its correlation with expression of each HLA‐DQA1 allele in patients with T1D have been described for the first time.     

Methylation profiles of hereditary and sporadic ovarian cancer

Bol G M, Suijkerbuijk K P M, Bart J, Vooijs M, van der Wall E & van Diest P J
(2010) Histopathology 57, 363–370
Methylation profiles of hereditary and sporadic ovarian cancer Aims: Tumour suppressor gene silencing through promoter hypermethylation plays an important role in oncogenesis. Carcinogenesis of hereditary cancers usually differs from that of their sporadic counterparts, but methylation has hardly been studied in hereditary ovarian cancer. The aim of this study was to investigate promoter methylation of a set of common tumour suppressor genes in BRCA1‐related ovarian cancer in comparison with sporadic ovarian cancer. Methods and results: Methylation‐specific multiplex ligation‐dependent probe amplification was used to assess the extent of promoter methylation of 24 different tumour suppressor genes in BRCA1‐associated (n = 25) and matched sporadic ovarian tumours (n = 50). A cumulative methylation index (CMI) was calculated and differences between individual genes were analysed. There was no significant difference in cumulative methylation between BRCA1‐associated and sporadic ovarian carcinomas (median CMI 108; CMI 110; P = 0.86). Also, methylation patterns of individual genes did not show distinct differences after correction for multiple comparisons. CDH13, GSTP1 and RASSF1 were frequently methylated in both sporadic and hereditary ovarian cancers. BRCA1 methylation occurred in 14% of sporadic tumours, but was not detected in BRCA1‐associated tumours. Conclusions: CDH13, GSTP1 and RASSF1 are frequently methylated in both sporadic and BRCA1‐associated ovarian cancers. Interestingly, methylation of BRCA1, while frequent in sporadic ovarian cancer, never occurred in the hereditary group. BRCA1‐associated ovarian cancers mimic their sporadic counterparts in extent and pattern of promoter methylation of several common tumour suppressor genes. This finding could have implications for future chemotherapy regimens based on epigenetic changes.