Modeling mesothelioma utilizing human mesothelial cells reveals involvement of phospholipase-C beta 4 in YAP-active mesothelioma cell proliferation

CAMK2D: a novel molecular target for BAP1-deficient malignant mesothelioma

Malignant mesothelioma (MMe) is a rare but aggressive malignancy. Although the molecular genetics of MMe is known, including BRCA1-associated protein-1 (BAP1) gene alterations, the prognosis of MMe patients remains poor. Here, we generated BAP1 knockout (BAP1-KO) human mesothelial cell clones to develop molecular-targeted therapeutics based on genetic alterations in MMe. cDNA microarray and quantitative RT-PCR (qRT-PCR) analyses revealed high expression of a calcium/calmodulin-dependent protein kinase type II subunit delta (CAMK2D) gene in the BAP1-KO cells. CAMK2D was highly expressed in 70% of the human MMe tissues (56/80) and correlated with the loss of BAP1 expression, making it a potential diagnostic and therapeutic target for BAP1-deficient MMe. We screened an anticancer drugs library using BAP1-KO cells and successfully identified a CaMKII inhibitor, KN-93, which displayed a more potent and selective antiproliferative effect against BAP1-deficient cells than cisplatin or pemetrexed. KN-93 significantly suppressed the tumor growth in mice xenografted with BAP1-deficient MMe cells. This study is the first to provide a potential molecular-targeted therapeutic approach for BAP1-deficient MMe.

NF2 alteration in mesothelioma

The NF2 tumor suppressor gene is a frequent somatically mutated gene in mesothelioma, with 30%-40% mesotheliomas showing NF2 inactivation. NF2 encodes merlin, a member of the ezrin, radixin, and moesin (ERM) family of proteins that regulate cytoskeleton and cell signaling. Recent genome analysis revealed that NF2 alteration may be a late event in mesothelioma development, suggesting that NF2 mutation confers a more aggressive phenotype to mesothelioma cells and may not be directly caused by asbestos exposure. The Hippo tumor-suppressive and mTOR prooncogenic signaling pathways are crucial cell-signaling cascades regulated by merlin. Although the exact role and timing of NF2 inactivation in mesothelioma cells remain to be elucidated, targeting the NF2/merlin-Hippo pathway may be a new therapeutic strategy for patients with mesothelioma.

SMG6 regulates DNA damage and cell survival in Hippo pathway kinase LATS2-inactivated malignant mesothelioma

Many genes responsible for Malignant mesothelioma (MM) have been identified as tumor suppressor genes and it is difficult to target these genes directly at a molecular level. We searched for the gene which showed synthetic lethal phenotype with LATS2, one of the MM causative genes and one of the kinases in the Hippo pathway. Here we showed that knockdown of SMG6 results in synthetic lethality in LATS2-inactivated cells. We found that this synthetic lethality required the nuclear translocation of YAP1 and TAZ. Both are downstream factors of the Hippo pathway. We also demonstrated that this synthetic lethality did not require SMG6 in nonsense-mediated mRNA decay (NMD) but in regulating telomerase reverse transcriptase (TERT) activity. In addition, the RNA-dependent DNA polymerase (RdDP) activity of TERT was required for this synthetic lethal phenotype. We confirmed the inhibitory effects of LATS2 and SMG6 on cell proliferation in vivo. The result suggests an interaction between the Hippo and TERT signaling pathways. We also propose that SMG6 and TERT are novel molecular target candidates for LATS2-inactivated cancers such as MM.

Polarity switching of ovarian cancer cell clusters via SRC family kinase is involved in the peritoneal dissemination

Peritoneal dissemination is a predominant pattern of metastasis in patients with advanced ovarian cancer. Despite recent progress in the management strategy, peritoneal dissemination remains a determinant of poor ovarian cancer prognosis. Using various histological types of patient‐derived ovarian cancer organoids, the roles of the apicobasal polarity of ovarian cancer cell clusters in peritoneal dissemination were studied. First, it was found that both ovarian cancer tissues and ovarian organoids showed apicobasal polarity, where zonula occludens‐1 (ZO‐1) and integrin beta 4 (ITGB4) served as markers for apical and basal sides, respectively. The organoids in suspension culture, as a model of cancer cell cluster floating in ascites, showed apical‐out/basal‐in polarity status, while once embedded in extracellular matrix (ECM), the organoids switched their polarity to apical‐in/basal‐out. This polarity switch was accompanied by the SRC kinase family (SFK) phosphorylation and was inhibited by SFK inhibitors. SFK inhibitors abrogated the adherence of the organoids onto the ECM‐coated plastic surface. When the organoids were seeded on a mesothelial cell layer, they cleared and invaded mesothelial cells. In vivo, dasatinib, an SFK inhibitor, suppressed peritoneal dissemination of ovarian cancer organoids in immunodeficient mice. These results suggest SFK‐mediated polarity switching is involved in peritoneal metastasis. Polarity switching would be a potential therapeutic target for suppressing peritoneal dissemination in ovarian cancer.

Three newly established immortalized mesothelial cell lines exhibit morphological phenotypes corresponding to malignant mesothelioma epithelioid, intermediate, and sarcomatoid types, respectively

Background

Malignant mesothelioma (MM) is a very aggressive tumor that develops from mesothelial cells, mainly due to asbestos exposure. MM is categorized into three major histological subtypes: epithelioid, sarcomatoid, and biphasic, with the biphasic subtype containing both epithelioid and sarcomatoid components. Patients with sarcomatoid mesothelioma usually show a poorer prognosis than those with epithelioid mesothelioma, but it is not clear how these morphological phenotypes are determined or changed during the oncogenic transformation of mesothelial cells.

Methods

We introduced the E6 and E7 genes of human papillomavirus type 16 and human telomerase reverse transcriptase gene in human peritoneal mesothelial cells and established three morphologically different types of immortalized mesothelial cell lines.

Results

HOMC-B1 cells exhibited epithelioid morphology, HOMC-A4 cells were fibroblast-like, spindle-shaped, and HOMC-D4 cells had an intermediate morphology, indicating that these three cell lines closely mimicked the histological subtypes of MM. Gene expression profiling revealed increased expression of NOD-like receptor signaling-related genes in HOMC-A4 cells. Notably, the combination treatment of HOMC-D4 cells with TGF-β and IL-1β induced a morphological change from intermediate to sarcomatoid morphology.

Conclusions

Our established cell lines are useful for elucidating the fundamental mechanisms of mesothelial cell transformation and mesothelial-to-mesenchymal transition.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02248-5.

Identification of CD24 as a potential diagnostic and therapeutic target for malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive malignancy of the pleura that is currently incurable due to the lack of an effective early diagnostic method and specific medication. The CDKN2A (p16) and NF2 genes are both frequently mutated in MPM. To understand how these mutations contribute to MPM tumor growth, we generated NF2/p16 double-knockout (DKO) cell clones using human MeT-5A and HOMC-B1 mesothelial cell lines. Cell growth and migration activities were significantly increased in DKO compared with parental cells. cDNA microarray analysis revealed differences in global gene expression profiles between DKO and parental cells. Quantitative PCR and western blot analyses showed upregulation of CD24 concomitant with increased phosphorylation of AKT, p70S6K, and c-Jun in DKO clones. This upregulation was abrogated by exogenous expression of NF2 and p16. CD24 knockdown in DKO cells significantly decreased TGF-β1 expression and increased expression of E-cadherin, an epithelial-mesenchymal transition marker. CD24 was highly expressed in human mesothelioma tissues (28/45 cases, 62%) and associated with the loss of NF2 and p16. Public data analysis revealed a significantly shorter survival time in MPM patients with high CD24 gene expression levels. These results strongly indicate the potential use of CD24 as a prognostic marker as well as a novel diagnostic and therapeutic target for MPM.

PLCB4 upregulation is associated with unfavorable prognosis in pediatric acute myeloid leukemia

Phospholipase C (PLC) is a membrane-associated enzyme that regulates several cellular behaviors including cell motility, growth, transformation and differentiation. PLC is involved in cancer migration, invasion and drug resistance. However, the expression status and prognostic role of PLCB4 in acute myeloid leukemia (AML) remain unclear. In the present study, the complete clinical and mRNA expression data of 285 pediatric patients with de novo AML were obtained from the Therapeutically Available Research to Generate Effective Treatments database. The association between PLCB4 expression and clinical and molecular features was explored. The expression of PLCB4 was significantly higher in patients with AML who relapsed compared with those with long-term complete remission. Patients with PLCB4 upregulation had significantly lower overall survival (OS) and event free survival (EFS) rate compared with those with low PLCB4 expression. Multivariate Cox's regression analyses demonstrated that high PLCB4 expression was an independent risk factor of adverse OS (P<0.01; HR, 2.081) and EFS (P<0.01; HR, 2.130). Following stratification analysis according to transplant status in cases of first complete remission, the patients with high expression of PLCB4 had significantly lower OS and EFS rate in the chemotherapy group, but not the stem cell transplant group. Furthermore, PLCB4-associated genes were identified using Spearman's rank correlation analysis. KEGG pathway analysis revealed that PLCB4 and its associated genes were mainly involved in three potential pathways, including the Rap1 signaling pathway. Overall, the findings of the present study suggest that increased PLCB4 expression is associated with poor clinical outcome in pediatric patients with AML, and thus may represent a potential prognostic biomarker and therapeutic target for AML.

Development of a New Laparoscopic Detection System for Gastric Cancer Using Near-Infrared Light-Emitting Clips with Glass Phosphor

Laparoscopic surgery is now a standard treatment for gastric cancer. Currently, the location of the gastric cancer is identified during laparoscopic surgery via the preoperative endoscopic injection of charcoal ink around the primary tumor; however, the wide spread of injected charcoal ink can make it difficult to accurately visualize the specific site of the tumor. To precisely identify the locations of gastric tumors, we developed a fluorescent detection system comprising clips with glass phosphor (Yb³⁺, Nd³⁺ doped to Bi₂O₃-B₂O₃-based glasses, size: 2 mm × 1 mm × 3 mm) fixed in the stomach and a laparoscopic fluorescent detection system for clip-derived near-infrared (NIR) light (976 nm). We conducted two ex vivo experiments to evaluate the performance of this fluorescent detection system in an extirpated pig stomach and a freshly resected human stomach and were able to successfully detect NIR fluorescence emitted from the clip in the stomach through the stomach wall by the irradiation of excitation light (λ: 808 nm). These results suggest that the proposed combined NIR light-emitting clip and laparoscopic fluorescent detection system could be very useful in clinical practice for accurately identifying the location of a primary gastric tumor during laparoscopic surgery.

Establishment and characterization of CRISPR/Cas9-mediated NF2-/- human mesothelial cell line: Molecular insight into fibroblast growth factor receptor 2 in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM), a highly refractory tumor, is currently incurable due to the lack of an early diagnosis method and medication, both of which are urgently needed to improve the survival and/or quality of life of patients. NF2 is a tumor suppressor gene and is frequently mutated in MPM. Using a CRISPR/Cas9 system, we generated an NF2‐knockout human mesothelial cell line, MeT‐5A (NF2‐KO). In NF2‐KO cell clones, cell growth, clonogenic activity, migration activity, and invasion activity significantly increased compared with those in NF2‐WT cell clones. Complementary DNA microarray analysis clearly revealed the differences in global gene expression profile between NF2‐WT and NF2‐KO cell clones. Quantitative PCR analysis and western blot analysis showed that the upregulation of fibroblast growth factor receptor 2 (FGFR2) was concomitant with the increases in phosphorylation levels of JNK, c‐Jun, and retinoblastoma (Rb) in NF2‐KO cell clones. These increases were all abrogated by the exogenous expression of NF2 in the NF2‐KO clone. In addition, the disruption of FGFR2 in the NF2‐KO cell clone suppressed cell proliferation as well as the phosphorylation levels of JNK, c‐Jun, and Rb. Notably, FGFR2 was found to be highly expressed in NF2‐negative human mesothelioma tissues (11/12 cases, 91.7%) but less expressed in NF2‐positive tissues. Collectively, these findings suggest that NF2 deficiency might play a role in the tumorigenesis of human mesothelium through mediating FGFR2 expression; FGFR2 would be a candidate molecule to develop therapeutic and diagnostic strategies for targeting MPM with NF2 loss.

TAZ activation by Hippo pathway dysregulation induces cytokine gene expression and promotes mesothelial cell transformation

Malignant mesothelioma (MM) constitutes a very aggressive tumor that is caused by asbestos exposure after long latency. The NF2 tumor suppressor gene is mutated in 40-50% of MM; moreover, one of its downstream signaling cascades, the Hippo signaling pathway, is also frequently inactivated in MM cells. Although the YAP transcriptional coactivator, which is regulated by the Hippo pathway, can function as a pro-oncogenic protein, the role of TAZ, a paralog of YAP, in MM cells has not yet been clarified. Here, we show that TAZ is expressed and underphosphorylated (activated) in the majority of MM cells compared to immortalized mesothelial cells. ShRNA-mediated TAZ knockdown highly suppressed cell proliferation, anchorage-independent growth, cell motility, and invasion in MM cells harboring activated TAZ. Conversely, transduction of an activated form of TAZ in immortalized mesothelial cells enhanced these in vitro phenotypes and conferred tumorigenicity in vivo. Microarray analysis determined that activated TAZ most significantly enhanced the transcription of genes related to "cytokine-cytokine receptor interaction." Among selected cytokines, we found that IL-1 signaling activation plays a major role in proliferation in TAZ-activated MM cells. Both IL1B knockdown and an IL-1 receptor antagonist significantly suppressed malignant phenotypes of immortalized mesothelial cells and MM cells with activated TAZ. Overall, these results indicate an oncogenic role for TAZ in MMs via transcriptional induction of distinct pro-oncogenic genes including cytokines. Among these, IL-1 signaling appears as one of the most important cascades, thus potentially serving as a target pathway in MM cells harboring Hippo pathway inactivation.

Progress in the Management of Malignant Pleural Mesothelioma in 2017

Malignant pleural mesothelioma (MPM) is an uncommon, almost universally fatal, asbestos-induced malignancy. New and effective strategies for diagnosis, prognostication, and treatment are urgently needed. Herein we review the advances in MPM achieved in 2017. Whereas recent epidemiological data demonstrated that the incidence of MPM-related death continued to increase in United States between 2009 and 2015, new insight into the molecular pathogenesis and the immunological tumor microenvironment of MPM, for example, regarding the role of BRCA1 associated protein 1 and the expression programmed death receptor ligand 1, are highlighting new potential therapeutic strategies. Furthermore, there continues to be an ever-expanding number of clinical studies investigating systemic therapies for MPM. These trials are primarily focused on immunotherapy using immune checkpoint inhibitors alone or in combination with other immunotherapies and nonimmunotherapies. In addition, other promising targeted therapies, including pegylated adenosine deiminase (ADI-PEG20), which focuses on argininosuccinate synthase 1-deficient tumors, and tazemetostat, an enhancer of zeste 2 polycomb repressive complex 2 subunit inhibitor of BRCA1 associated protein 1 gene (BAP1)-deficient tumors, are currently being explored.

NF2/Merlin Inactivation and Potential Therapeutic Targets in Mesothelioma

The neurofibromatosis type 2 (NF2) gene encodes merlin, a tumor suppressor protein frequently inactivated in schwannoma, meningioma, and malignant mesothelioma (MM). The sequence of merlin is similar to that of ezrin/radixin/moesin (ERM) proteins which crosslink actin with the plasma membrane, suggesting that merlin plays a role in transducing extracellular signals to the actin cytoskeleton. Merlin adopts a distinct closed conformation defined by specific intramolecular interactions and regulates diverse cellular events such as transcription, translation, ubiquitination, and miRNA biosynthesis, many of which are mediated through Hippo and mTOR signaling, which are known to be closely involved in cancer development. MM is a very aggressive tumor associated with asbestos exposure, and genetic alterations in NF2 that abrogate merlin’s functional activity are found in about 40% of MMs, indicating the importance of NF2 inactivation in MM development and progression. In this review, we summarize the current knowledge of molecular events triggered by NF2/merlin inactivation, which lead to the development of mesothelioma and other cancers, and discuss potential therapeutic targets in merlin-deficient mesotheliomas.

Targeting the Hippo Pathway Is a New Potential Therapeutic Modality for Malignant Mesothelioma

Malignant mesothelioma (MM) constitutes a very aggressive tumor that arises from the pleural or peritoneal cavities and is highly refractory to conventional therapies. Several key genetic alterations are associated with the development and progression of MM including mutations of the CDKN2A/ARF, NF2, and BAP1 tumor-suppressor genes. Notably, activating oncogene mutations are very rare; thus, it is difficult to develop effective inhibitors to treat MM. The NF2 gene encodes merlin, a protein that regulates multiple cell-signaling cascades including the Hippo pathway. MMs also exhibit inactivation of Hippo pathway components including LATS1/2, strongly suggesting that merlin-Hippo pathway dysregulation plays a key role in the development and progression of MM. Furthermore, Hippo pathway inactivation has been shown to result in constitutive activation of the YAP1/TAZ transcriptional coactivators, thereby conferring malignant phenotypes to mesothelial cells. Critical YAP1/TAZ target genes, including prooncogenic CCDN1 and CTGF, have also been shown to enhance the malignant phenotypes of MM cells. Together, these data indicate the Hippo pathway as a therapeutic target for the treatment of MM, and support the development of new strategies to effectively target the activation status of YAP1/TAZ as a promising therapeutic modality for this formidable disease.

An Overview of Asbestos and Malignant Pleural Mesothelioma: An Iranian Perspective

Asbestos refers to a group of minerals that appears naturally in the environment as bundles of fibers. The incidence rate of asbestos-related diseases has considerably increased as well as the amount of asbestos utilization in few countries. Malignant pleural mesothelioma (MPM) is a rare type of aggressive and life threatening neoplasm which arise from various serous surfaces: pleura, peritoneum, tunica vaginalis and pericardium. The first case of MPM was reported in 1947. MPM etiologically is associated to the exposure of asbestos fibers. This form of malignancy is difficult to diagnose in paraclinical work-ups because mesothelioma could occur within 10-20 years of the first-time exposure to asbestos. The burden of MPM is not yet to be wholly understood. The toxic side effects of asbestos on environment and people compelled the European countries to accept the French view upon this matter. However, this approach has not been accepted by some developing countries. This review provides a brief points and facts in relation to MPM and asbestos in Iran.

PLCB4 copy gain and PLCß4 overexpression in primary gastrointestinal stromal tumors: Integrative characterization of a lipid-catabolizing enzyme associated with worse disease-free survival

To explore the implications of lipid catabolism-associated genes in gastrointestinal stromal tumors, we reappraised transcriptomic and genomic datasets and identified copy-gained and differentially upregulated PLCB4 gene associated with tumor progression. On full sections, PLCB4 mRNA abundance and PLCß4 immunoexpression were validated in 70 cases. On tissue microarrays, PLCB4 gene copies and PLCß4 immunoexpression were both informative in 350 cases with KIT/PDGFRA/BRAF genotypes noted in 213. In GIST48 cell line, we stably silenced PLCB4 and YAP1 to characterize their functional effects and regulatory link. Compared with normal tissue, PLCB4 mRNA abundance significantly increased across tumors of various risk levels (p<0.001), and was strongly correlated with immunoexpression level (p<0.001, r=0.468). Including polysomy (12.6%) and amplification (17.4%), PLCB4 copy gain was detected in 105 (30%) cases and significantly more frequent (p<0.001) in cases exhibiting higher PLCß4 immunoexpression (82/175). Copy gain and protein overexpression were modestly associated with unfavorable genotypes (both p<0.05), strongly associated with increased size, mitosis, and risk levels defined by both the NIH and NCCN schemes (all p<0.001), and univariately predictive of shorter disease-free survival (both p<0.0001). In PLCß4-overexpressing cases, PLCB4 copy gain still predicted worse prognosis (p<0.0001). In a multivariate comparison, both overexpression (p=0.007, hazard ratio: 2.454) and copy gain (p=0.031, hazard ratio: 1.892) exhibited independent impact. In vitro, YAP1 increased PLCB4 mRNA and protein expression, and both molecules significantly promoted cell proliferation. Being driven by copy gain or YAP1, PLCß4 is a novel overexpressed enzyme regulating lipid catabolism that promotes cell proliferation and independently confers a worse prognosis.

E-cadherin expression is correlated with focal adhesion kinase inhibitor resistance in Merlin-negative malignant mesothelioma cells

Malignant mesothelioma (MM) is an aggressive tumor commonly caused by asbestos exposure after a long latency. Focal adhesion kinase (FAK) inhibitors inhibit the cell growth of Merlin-deficient MM cells; however, their clinical efficacy has not been clearly determined. The aim of this study was to evaluate the growth inhibitory effect of the FAK inhibitor VS-4718 on MM cell lines and identify biomarkers for its efficacy. Although most Merlin-deficient cell lines were sensitive to VS-4718 compared with control MeT-5A cells, a subset of these cell lines exhibited resistance to this drug. Microarray and qRT-PCR analyses using RNA isolated from Merlin-deficient MM cell lines revealed a significant correlation between E-cadherin mRNA levels and VS-4718 resistance. Merlin- and E-cadherin-negative Y-MESO-22 cells underwent apoptosis upon treatment with a low concentration of VS-4718, whereas Merlin-negative, E-cadherin-positive Y-MESO-9 cells did not undergo VS-4718-induced apoptosis. Furthermore, E-cadherin knockdown in Merlin-negative MM cells significantly sensitized cells to VS-4718 and induced apoptotic cell death upon VS-4718 treatment. Together, our results suggest that E-cadherin serves as a predictive biomarker for molecular target therapy with FAK inhibitors for patients with mesothelioma and that its expression endows MM cells with resistance to FAK inhibitors.