Explore the vast range of titles available.

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.

Malignant mesothelioma (MM) is one of the most aggressive tumors. We conducted bioinformatics analysis using Cancer Cell Line Encyclopedia (CCLE) datasets to identify new molecular markers in MM. Overexpression of oxytocin receptor (OXTR), which is a G‐protein–coupled receptor for the hormone and neurotransmitter oxytocin, mRNA was distinctively identified in MM cell lines. Therefore, we assessed the role of OXTR and its clinical relevance in MM. Kaplan‐Meier and Cox regression analyses were applied to assess the association between overall survival and OXTR mRNA expression using The Cancer Genome Atlas (TCGA) datasets. The function of OXTR and the efficacy of its antagonists were investigated in vitro and in vivo using MM cell lines. Consistent with the findings from CCLE datasets analysis, OXTR mRNA expression was highly increased in MM tissues compared with other cancer types in the TCGA datasets, and MM cases with high OXTR expression showed poor overall survival. Moreover, OXTR knockdown dramatically decreased MM cell proliferation in cells with high OXTR expression via tumor cell cycle disturbance, whereas oxytocin treatment significantly increased MM cell growth. OXTR antagonists, which have high selectivity for OXTR, inhibited the growth of MM cell lines with high OXTR expression, and oral administration of the OXTR antagonist, cligosiban, significantly suppressed MM tumor progression in a xenograft model. Our findings suggest that OXTR plays a crucial role in MM cell proliferation and is a promising therapeutic target that may broaden potential therapeutic options and could be a prognostic biomarker of MM. We identified high oxytocin receptor (OXTR) expression in malignant mesothelioma (MM), which was associated with poor overall survival. OXTR knockdown and administration of OXTR antagonists in vitro and in vivo experiments showed significant suppression of MM cell proliferation. These results indicate that OXTR could be a promising therapeutic target and a prognostic biomarker, enabling a personalized approach to the treatment of MM.

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.

Background/Objectives: Mesothelioma is a highly aggressive tumor with a poor prognosis that typically develops after a long latency period following asbestos exposure. Although immunotherapy combined with chemotherapy is increasingly used, the efficacy of standard treatments remains limited. This study aimed to explore ferroptosis induction as a potential therapeutic strategy for mesothelioma. Methods: We first screened microbial culture extracts collected from soil and marine environments to identify compounds with selective cytotoxicity against mesothelioma cells. Gene expression profiling was performed to investigate the mechanism of cell death induced by the identified compound. To assess intrinsic ferroptosis susceptibility, patient-derived mesothelioma cell lines and immortalized mesothelial cell lines were treated with RSL3, a GPX4 inhibitor. Results: Screening identified brefeldin A as a compound that selectively induces cell death in mesothelioma cells. Gene expression profiling revealed transcriptional changes consistent with ferroptosis induction. Treatment with RSL3 demonstrated marked variability in ferroptosis sensitivity across cell lines; the subgroup showing high sensitivity to RSL3 did not exhibit significant genetic alterations in NF2 or BAP1, but contained a significantly higher proportion of epithelioid tumors in histological classification. Conclusions: Our findings highlight ferroptosis induction as a promising antitumor mechanism in mesothelioma, particularly in the epithelioid subtype. While GPX4 inhibitors such as RSL3 are effective in vitro, further studies are needed to overcome pharmacological limitations and define molecular determinants of ferroptosis susceptibility, which may inform future personalized therapeutic strategies.

Background Mesothelioma is a neoplastic disease associated with asbestos exposure. It is highly malignant and has a poor prognosis; thus, early detection is desirable. Recent whole‐genome analysis has revealed that mesothelioma is characterized by a high frequency of mutations in a set of genes involved in the Hippo pathway, such as NF2 and LATS2. However, a rapid, simple, and precise method for finding mesothelioma with these mutations has not yet been established. Methods Clustering of Hippo pathway gene alteration groups and the differential expression of each gene in mesothelioma patients were analyzed using The Cancer Genome Atlas database. Gene expression levels in various tumors and normal tissues were analyzed using public databases. Knockdown or transient expression of YAP1 or TAZ was performed to evaluate the regulation of gene expression by these genes. NT‐proBNP was measured in the pleural effusions of 18 patients and was compared with NF2 expression in five cases where cell lines had been successfully established. Results NPPB mRNA expression was markedly higher in the group of mesothelioma patients with Hippo pathway gene mutations than in the group without them. NPPB expression was low in all normal tissues except heart, and was highest in mesothelioma. Mesothelioma patients in the high NPPB expression group had a significantly worse prognosis than those in the low NPPB expression group. NPPB expression was suppressed by knockdown of YAP1 or TAZ. NT‐proBNP was abundant in the effusions of mesothelioma patients and was particularly high in those with impaired NF2 expression. Conclusions NPPB, whose levels can be measured in pleural effusions of mesothelioma patients, has the potential to act as a biomarker to detect NF2‐Hippo pathway gene alterations and/or predict patient prognosis. Additionally, it may provide useful molecular insights for a better understanding of mesothelioma pathogenesis and for the development of novel therapies.

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.

Rheb is a unique member of the Ras superfamily GTP-binding proteins. We as well as others previously have shown that Rheb is a critical component of the TSC/TOR signaling pathway. In fission yeast, Rheb is encoded by the rhb1 gene. Rhb1p is essential for growth and directly interacts with Tor2p. In this article, we report identification of 22 single amino acid changes in the Tor2 protein that enable growth in the absence of Rhb1p. These mutants also exhibit decreased mating efficiency. Interestingly, the mutations are located in the C-terminal half of the Tor2 protein, clustering mainly within the FAT and kinase domains. We noted some differences in the effect of a mutation in the FAT domain (L1310P) and in the kinase domain (E2221K) on growth and mating. Although the Tor2p mutations bypass Rhb1p's requirement for growth, they are incapable of suppressing Rhb1p's requirement for resistance to stress and toxic amino acids, pointing to multiple functions of Rhb1p. In mammalian systems, we find that mammalian target of rapamycin (mTOR) carrying analogous mutations (L1460P or E2419K), although sensitive to rapamycin, exhibits constitutive activation even when the cells are starved for nutrients. These mutations do not show significant difference in their ability to form complexes with Raptor, Rictor, or mLST8. Furthermore, we present evidence that mutant mTOR can complex with wild-type mTOR and that this heterodimer is active in nutrient-starved cells.

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.

Junctional adhesion molecule (JAM) is a Ca2+-independent immunoglobulin-like cell-cell adhesion molecule which localizes at tight junctions (TJs). Claudin is a key cell-cell adhesion molecule that forms TJ strands at TJs. JAM is associated with claudin through their cytoplasmic tail-binding protein, ZO-1. JAM is furthermore associated with Par-3, a cell polarity protein which forms a ternary complex with Par-6 and atypical protein kinase C. Nectin is another Ca2+-independent immunoglobulin-like cell-cell adhesion molecule which localizes at adherens junctions (AJs). Nectin is associated with E-cadherin through their respective cytoplasmic tail-binding proteins, afadin and catenins, and involved in the formation of AJs cooperatively with E-cadherin. We show here that nectin is furthermore involved in the localization of JAM at TJs. During the formation of the junctional complex consisting of AJs and TJs in Madin-Darby canine kidney (MDCK) cells, JAM was recruited to the nectin-based cell-cell adhesion sites. This recruitment of JAM was inhibited by nectin inhibitors, which inhibited the trans-interaction of nectin. Microbeads coated with the extracellular fragment of nectin, that interacted with cellular nectin, also recruited JAM to the bead-MDCK cell contact sites. Furthermore, when cadherin-deficient L fibroblasts stably expressing both exogenous JAM and nectin (nectin-JAM-L cells) were co-cultured with L fibroblasts expressing only nectin (nectin-L cells), JAM was concentrated at the cell-cell adhesion sites between nectin-JAM-L and nectin-L cells without the trans-interaction of JAM. Analyses of the localization and immunoprecipitation of JAM revealed that it was associated with nectin through afadin and ZO-1. These results suggest that nectin has a role in the localization of JAM at TJs in the process of the formation of the junctional complex in epithelial cells.

Nectin is a Ca2+‐independent Ig‐like cell–cell adhesion molecule that forms homo‐ and hetero‐trans‐dimers (trans‐interaction). Nectin first forms cell–cell adhesions and then recruits cadherin to the nectin‐based cell–cell adhesion sites to form AJ cooperatively with cadherin. In addition, the trans‐interaction of nectin and nectin induces the activation of Cdc42 and Rac small G proteins, which enhances the formation of AJ. The activation of Cdc42 and Rac by the trans‐interaction of nectin and nectin is mediated by c‐Src, another small G protein, Rap1, a Cdc42‐GEF, FRG, and a Rac‐GEF, Vav2. Necl‐5/Tage4/PVR/CD155 is another Ca2+‐independent Ig‐like molecule, which does not homophilically trans‐interact, but heterophilically trans‐interacts with nectin‐3, one member of the nectin family. We show here that the trans‐interaction of Necl‐5 and nectin‐3 bidirectionally induces the activation of Cdc42 and Rac. Similarly to the activation of Cdc42 and Rac by the trans‐interaction of nectin and nectin, the trans‐interaction of Necl‐5 and nectin‐3 first recruits and activates c‐Src at the Necl‐5/nectin‐3‐based cell–cell contact sites. c‐Src then phosphorylates FRG and Vav2, and the tyrosine‐phosphorylated FRG and Vav2 are recruited to the Necl‐5/nectin‐3‐based cell–cell contact sites. The trans‐interaction of Necl‐5 and nectin‐3 also activates Rap1 through C3G, a Rap‐GEF, and this activation of Rap1 is required for the activation of Cdc42 and Rac. These results indicate that the trans‐interactions of Necl‐5 and nectin‐3 and of nectin and nectin induce the activation of Cdc42 and Rac through the common signaling molecules c‐Src, Rap1, FRG, and Vav2. (Cancer Sci 2005; 96: 578 –589)