Noriyasu Usami

Plakoglobin (gamma-catenin) has TCF/LEF family-dependent transcriptional activity in beta-catenin-deficient cell line.

β-Catenin is an essential element for the transcriptional activation of target genes in the Wnt signaling cascade and is also a cell adhesion molecule that couples with cadherins. Although plakoglobin (γ-catenin), a closely related homologue of β-catenin, is also known to be a cell adhesion molecule, its function as a transcriptional factor has not been revealed in detail. Using a human malignant mesothelioma cell line, NCI-H28, in which we have identified a homozygous deletion of the β-catenin gene, we studied whether plakoglobin has a T-cell factor/lymphocyte enhancer factor (TCF/LEF) family-dependent transcriptional activity. Transfection with the wild-type plakoglobin expression vector induced accumulation of plakoglobin in the nucleus. Immunoprecipitation assay with cotransfection of plakoglobin and either TCF-4 or LEF-1 detected binding of plakoglobin to TCF-4 or LEF-1. Luciferase reporter assay demonstrated transcriptional activity of the wild-type plakoglobin when transfected with TCF/LEF, although plakoglobin showed less activity than β-catenin. Exogenous plakoglobin was also shown to promote entrance of exogenous β-catenin into the nuclei. Furthermore, small interfering RNA directed against plakoglobin suppressed expression of endogenous plakoglobin and its transcriptional activity, suggesting that endogenous plakoglobin has a weak transcriptional activity. These results suggest that plakoglobin can activate the Wnt signaling cascade directly without interaction of β-catenin, and that plakoglobin has multiple functions as a transcriptional activator and a cell adhesion molecule like β-catenin.

Krüppel-Like Factor 6 Is Frequently Down-Regulated and Induces Apoptosis in Non-Small Cell Lung Cancer Cells

Krüppel-like factor 6 (KLF6) is a ubiquitously expressed zinc finger transcriptional factor, which has been suggested to be a candidate tumor suppressor gene in prostate cancer and astrocytic glioma. Because KLF6 is located at chromosome 10p15, where non-small cell lung cancers (NSCLCs) also exhibit frequent allelic loss, we hypothesized that the inactivation of KLF6 is also involved in the development of NSCLC. To determine this, we performed mutational analysis for 105 NSCLCs, including 9 cell lines and 96 primary tumors, and Northern blot analysis for 74 NSCLCs, including the 9 cell lines and 65 primary tumors. Although somatic mutations were not detected in the coding sequence of KLF6, expression of KLF6 mRNA was down-regulated in the 9 cell lines and in 55 (85%) of the 65 primary tumors compared with normal lung tissue. Treatment of two cell lines expressing KLF6 at low levels with 5-azacytidine did not induce KLF6 expression, suggesting that KLF6 down-regulation is not due to promoter hypermethylation. We also performed loss of heterozygosity (LOH) analysis using the laser capture microdissection technique, and found that 21 of 62 (34%) informative samples had LOH in the KLF6 gene locus. Comparing the LOH status with mRNA expression of KLF6, we found that 14 of the 14 (100%) samples with LOH showed KLF6 down-regulation, and that even 23 of 31 (74%) samples without LOH also showed this down-regulation. We also studied the expression of the WAF1 gene, a possible downstream gene of KLF6, and detected simultaneous down-regulation of WAF1 and KLF6 mRNA in 6 of 9 (67%) cell lines and 48 of the 55 (87%) primary tumors, although there was not a significant association between loss of KLF6 and WAF1 expression. Furthermore, colony formation assay of two NSCLC cell lines (NCI-H1299 and NCI-H2009) induced a markedly reduced colony formation by KLF6 transfection, and Annexin V staining and terminal deoxynucleotidyl transferase-mediated nick end labeling assays revealed that KLF6 induced apoptosis. Our present studies demonstrated that KLF6 is frequently down-regulated in NSCLC and suppresses tumor growth via induction of apoptosis in NSCLC, which may suggest that KLF6 is a tumor suppressor for NSCLC.

Establishment and characterization of four malignant pleural mesothelioma cell lines from Japanese patients

Malignant pleural mesothelioma (MPM) is an asbestos‐related malignancy that is highly resistant to current therapeutic modalities. We established four MPM cell lines (ACC‐MESO‐1, ACC‐MESO‐4, Y‐MESO‐8A and Y‐MESO‐8D) from Japanese patients, with the latter two from the same patient with biphasic‐like characteristics of MPM, showing epithelial and sarcomatous phenotypes, respectively, in cell culture. These cells grew well in RPMI‐1640 medium supplemented with 10% fetal bovine serum under 5% CO2. Mutation and expression analyses demonstrated that the tumor suppressor gene NF2, which is known to be one of the most frequently mutated in MPM, is mutated in ACC‐MESO‐1. We detected homozygous deletion of p16INK4A/p14ARF in all four MPM cell lines. However, mutations of other tumor suppressor genes, including TP53, and protooncogenes, including KRAS, NRAS, BRAF, EGFR and HER2, were not found in these cell lines. Polymerase chain reaction amplification of the simian virus 40 sequence did not detect any products. We also analyzed genetic alterations of six other MPM cell lines and confirmed frequent mutations of NF2 and p16INK4A/p14ARF. To characterize the biological differences between Y‐MESO‐8A and Y‐MESO‐8D, we carried out cDNA microarray analysis and detected genes that were differentially expressed in these two cell lines. Thus, our new MPM cell lines seem to be useful as new models for studying various aspects of the biology of human MPM as well as materials for the development of future therapies. (Cancer Sci 2006; 97)

Genetic alteration of the β-catenin gene (CTNNB1) in human lung cancer and malignant mesothelioma and identification of a new 3p21.3 homozygous deletion

The β-catenin gene (CTNNB1) has been shown to be genetically mutated in various human malignancies. To determine whether the β-catenin gene is responsible for oncogenesis in thoracic malignancies, we searched for the mutation in 166 lung cancers (90 primary tumors and 76 cell lines), one blastoma and 10 malignant mesotheliomas (two primary tumors and eight cell lines). Among the lung cancers, including 43 small cell lung cancers (SCLCs) and 123 non-small cell lung cancers (NSCLCs), we identified four alterations in exon 3, which is the target region of mutation for stabilizing β-catenin. One primary adenocarcinoma had a somatic mutation from C to G, leading to an amino acid substitution from Ser to Cys at codon 37. Among the cell lines, SCLC NCI-H1092 had a mutation from A to G, leading to an Asp to Gly substitution at codon 6, NSCLC HCC15 had a mutation from C to T, leading to a Ser to Phe substitution at codon 45, and NSCLC NCI-H358 had a mutation from A to G, leading to a Thr to Ala substitution at codon 75. One blastoma also had a somatic mutation from C to G, leading to a Ser to Cys substitution at codon 37. Among the 10 malignant mesotheliomas, we identified a homozygous deletion in the NCI-H28 cell line. Cloning of the rearranged fragment from NCI-H28 indicated that all the exons except exon 1 of the β-catenin gene are deleted and that the deletion junction is 13 kb downstream from exon 1. Furthermore, Northern blot analysis of 26 lung cancer and eight mesothelioma cell line RNAs detected ubiquitous expression of the β-catenin messages except NCI-H28, although Western blot analysis showed that relatively less amounts of protein products were expressed in some of lung cancer cell lines. Our findings suggest that the β-catenin gene is infrequently mutated in lung cancer and that the NCI-H28 homozygous deletion of the β-catenin gene might indicate the possibility of a new tumor suppressor gene residing in this region at 3p21.3, where various types of human cancers show frequent allelic loss.

Epigenetic Profiles Distinguish Malignant Pleural Mesothelioma from Lung Adenocarcinoma

Malignant pleural mesothelioma (MPM) is a fatal thoracic malignancy, the epigenetics of which are poorly defined. We performed high-throughput methylation analysis covering 6,157 CpG islands in 20 MPMs and 20 lung adenocarcinomas. Newly identified genes were further analyzed in 50 MPMs and 56 adenocarcinomas via quantitative methylation-specific PCR. Targets of histone H3 lysine 27 trimethylation (H3K27me3) and genetic alterations were also assessed in MPM cells by chromatin immunoprecipitation arrays and comparative genomic hybridization arrays. An average of 387 genes (6.3%) and 544 genes (8.8%) were hypermethylated in MPM and adenocarcinoma, respectively. Hierarchical cluster analysis showed that the two malignancies have characteristic DNA methylation patterns, likely a result of different pathologic processes. In MPM, a separate subset of genes was silenced by H3K27me3 and could be reactivated by treatment with a histone deacetylase inhibitor alone. Integrated analysis of these epigenetic and genetic alterations revealed that only 11% of heterozygously deleted genes were affected by DNA methylation and/or H3K27me3 in MPMs. Among the DNA hypermethylated genes, three (TMEM30B, KAZALD1, and MAPK13) were specifically methylated only in MPM and could serve as potential diagnostic markers. Interestingly, a subset of MPM cases (4 cases, 20%) had very low levels of DNA methylation and substantially longer survival, suggesting that the epigenetic alterations are one mechanism affecting progression of this disease. Our findings show a characteristic epigenetic profile of MPM and uncover multiple distinct epigenetic abnormalities that lead to the silencing of tumor suppressor genes in MPM and could serve as diagnostic or prognostic targets.

Combined inhibition of MET and EGFR suppresses proliferation of malignant mesothelioma cells

Malignant pleural mesothelioma (MPM) is an aggressive neoplasm associated with asbestos exposure. Although expression and activation of receptor tyrosine kinases (RTKs), including MET, have been reported in most MPM, specific RTK inhibitors showed less than the expected response in MPM cells. To determine whether the lack of response of MET inhibitors was due to cooperation with other RTKs, we determined activation status of MET and other RTKs, including epidermal growth factor receptor (EGFR) family of 20 MPM cell lines, and tested whether dual RTK inhibition is an effective therapeutic strategy. We detected MET upregulation and phosphorylation (thus indicating activation) in 14 (70%) and 13 (65%) cell lines, but treatment with MET-specific inhibitors showed weak or modest effect of suppression in most of the cell lines. Phospho-RTK array analysis revealed that MET was simultaneously activated with other RTKs, including EGFR, ErbB2, ErbB3 and platelet-derived growth factor receptor-beta. Combination of MET and EGFR inhibitors triggered stronger inhibition on cell proliferation and invasion of MPM cells than that of each in vitro. These results indicated that coactivation of RTKs was essential in mesothelioma cell proliferation and/or survival, thus suggesting that simultaneous inhibition of RTKs may be a more effective strategy for the development of molecular target therapy for MPM.

Integrated analysis of genetic and epigenetic alterations reveals CpG island methylator phenotype associated with distinct clinical characters of lung adenocarcinoma

DNA methylation affects the aggressiveness of human malignancies. Cancers with CpG island methylator phenotype (CIMP), a distinct group with extensive DNA methylation, show characteristic features in several types of tumors. In this study, we initially defined the existence of CIMP in 41 lung adenocarcinomas (AdCas) through genome-wide DNA methylation microarray analysis. DNA methylation status of six CIMP markers newly identified by microarray analysis was further estimated in a total of 128 AdCas by bisulfite pyrosequencing analysis, which revealed that 10 (7.8%), 40 (31.3%) and 78 (60.9%) cases were classified as CIMP-high (CIMP-H), CIMP-low and CIMP-negative (CIMP-N), respectively. Notably, CIMP-H AdCas were strongly associated with wild-type epidermal growth factor receptor (EGFR), males and heavy smokers (P = 0.0089, P = 0.0047 and P = 0.0036, respectively). In addition, CIMP-H was significantly associated with worse prognosis; especially among male smokers, CIMP-H was an independent prognostic factor (hazard ratio 1.7617, 95% confidence interval 1.0030-2.9550, P = 0.0489). Compellingly, the existence of CIMP in AdCas was supported by the available public datasets, such as data from the Cancer Genome Atlas. Intriguingly, analysis of AdCa cell lines revealed that CIMP-positive AdCa cell lines were more sensitive to a DNA methylation inhibitor than CIMP-N ones regardless of EGFR mutation status. Our data demonstrate that CIMP in AdCas appears to be a unique subgroup that has distinct clinical traits from other AdCas. CIMP classification using our six-marker panel has implications for personalized medical strategies for lung cancer patients; in particular, DNA methylation inhibitor might be of therapeutic benefit to patients with CIMP-positive tumors.

How Long Should Small Lung Lesions of Ground-Glass Opacity be Followed?

Introduction: Pulmonary ground-glass nodules are frequently encountered. The purpose of this study was to evaluate the natural history of them and to gain some insights on how to follow them up. Methods: We retrospectively studied patients with pulmonary nodules that met the following criteria: (1) tumor diameter of 3 cm or less, (2) ground-glass opacity proportion of 50% or more, and (3) observation without treatment for 6 months or more. Between 1999 and 2012, 108 pulmonary lesions in 61 patients fulfilled these criteria. We reevaluated their computed tomography images and analyzed changes in their size. Results: The tumors were 1 cm or lesser in size in 69 lesions, 1.1 cm to 2 cm in 34, and 2.1 cm to 3 cm in five. The proportion of solid lesions was 0% for 82 lesions, 1% to 25% for 19, and 26% to 50 % for seven. At the median observation period of 4.2 years, 29 lesions had become larger, whereas the remaining 79 had persisted without changing in size (±1 mm). The median size change in the nodules that grew was 7 mm (range, 2–32 mm). All 29 tumors began to grow within 3 years of their first observation: 1 year or lesser in 13 lesions, after 1.1 years to 2 years in 12, and after 2.1 years to 3 years in four. Conclusions: Some small lung lesions exhibiting ground-glass opacity persisted without changes in size, whereas others grew gradually. The tendency to grow was clear within the first 3 years in all cases. Therefore, we conclude that these lesions should be followed for at least 3 years.

The circadian clock gene BMAL1 is a novel therapeutic target for malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is a highly aggressive neoplasm arising from the mesothelial cells lining the parietal pleura and it exhibits poor prognosis. Although there has been significant progress in MPM treatment, development of more efficient therapeutic approaches is needed. BMAL1 is a core component of the circadian clock machinery and its constitutive overexpression in MPM has been reported. Here, we demonstrate that BMAL1 may serve as a molecular target for MPM. The majority of MPM cell lines and a subset of MPM clinical specimens expressed higher levels of BMAL1 compared to a nontumorigenic mesothelial cell line (MeT‐5A) and normal parietal pleural specimens, respectively. A serum shock induced a rhythmical BMAL1 expression change in MeT‐5A but not in ACC‐MESO‐1, suggesting that the circadian rhythm pathway is deregulated in MPM cells. BMAL1 knockdown suppressed proliferation and anchorage‐dependent and independent clonal growth in two MPM cell lines (ACC‐MESO‐1 and H290) but not in MeT‐5A. Notably, BMAL1 depletion resulted in cell cycle disruption with a substantial increase in apoptotic and polyploidy cell population in association with downregulation of Wee1, cyclin B and p21WAF1/CIP1 and upregulation of cyclin E expression. BMAL1 knockdown induced mitotic catastrophe as denoted by disruption of cell cycle regulators and induction of drastic morphological changes including micronucleation and multiple nuclei in ACC‐MESO‐1 cells that expressed the highest level of BMAL1. Taken together, these findings indicate that BMAL1 has a critical role in MPM and could serve as an attractive therapeutic target for MPM.

Loss of heterozygosity of chromosome 12p does not correlate with KRAS mutation in non‐small cell lung cancer

Activating mutations of RAS gene families have been found in a variety of human malignancies, including lung cancer, suggesting their dominant role in tumorigenesis. However, several studies have shown a frequent loss of the wild‐type KRAS allele in the tumors of murine models and an inhibition of oncogenic phenotype in tumor cell lines by transfection of wild‐type RAS, indicating that wild‐type RAS may have oncosuppressive properties. To determine whether loss of wild‐type KRAS is involved in the development of human lung cancer, we investigated the mutations of KRAS, NRAS and BRAF in 154 primary non‐small cell lung cancers (NSCLCs) as well as 10 NSCLC cell lines that have been shown to have KRAS mutations. We also determined the loss of heterozygosity status of KRAS alleles in these tumors. We detected point mutations of KRAS in 11 (7%) of 154 NSCLCs, with 10 cases at codon 12 and 1 at codon 61, but no mutations of NRAS or BRAF were found. Using the laser capture microdissection technique, we confirmed that 9 of the 11 tumors and 7 of the 10 NSCLC cell lines retained the wild‐type KRAS allele. Among the cell lines with heterozygosity of mutant and wild‐type KRAS, all of the cell lines tested for expression were shown to express more mutated KRAS than wild‐type mRNA, with higher amounts of KRAS protein also being expressed compared to the cell lines with a loss of wild‐type KRAS allele. In addition, among 148 specimens available for immunohistochemical analysis, 113 (76%) showed positive staining of KRAS, indicating that the vast majority of NSCLCs continue to express wild‐type KRAS. Our findings indicate that the wild‐type KRAS allele is occasionally lost in human lung cancer, and that the oncogenic activation of mutant KRAS is more frequently associated with an overexpression of the mutant allele than with a loss of the wild‐type allele in human NSCLC development.