The NF2 tumor suppressor gene product, merlin, inhibits cell proliferation and cell cycle progression by repressing cyclin D1 expression

Genomic characterization and detection of potential therapeutic targets for peritoneal mesothelioma in current practice

Peritoneal mesothelioma (PeM) is an aggressive tumor with limited treatment options. The current study aimed to evaluate the value of next generation sequencing (NGS) of PeM samples in current practice. Foundation Medicine F1CDx NGS was performed on 20 tumor samples. This platform assesses 360 commonly somatically mutated genes in solid tumors and provides a genomic signature. Based on the detected mutations, potentially effective targeted therapies were identified. NGS was successful in 19 cases. Tumor mutational burden (TMB) was low in 10 cases, and 11 cases were microsatellite stable. In the other cases, TMB and microsatellite status could not be determined. BRCA1 associated protein 1 (BAP1) mutations were found in 32% of cases, cyclin dependent kinase inhibitor 2A/B (CDKN2A/B) and neurofibromin 2 (NF2) mutations in 16%, and ataxia-telangiectasia mutated serine/threonine kinase (ATM) in 11%. Based on mutations in the latter two genes, potential targeted therapies are available for approximately a quarter of cases (i.e., protein kinase inhibitors for three NF2 mutated tumors, and polyADP-ribose polymerase inhibitors for two ATM mutated tumors). Extensive NGS analysis of PeM samples resulted in the identification of potentially effective targeted therapies for about one in four patients. Although these therapies are currently not available for patients with PeM, ongoing developments might result in new treatment options in the future.

Identification of hub genes and drug candidates for NF2-related vestibular schwannoma by bioinformatics tools

Neurofibromatosis type 2 (NF2)-related vestibular schwannoma (NF2-VS) is a rare genetic disorder that results in bilateral acoustic neuromas. However, the exact pathogenesis of the disease is still unclear. This study aims to use bioinformatics analyses to identify potential hub genes and therapeutic. We retrieved the mRNA expression profiles (GSE108524 and GSE141801) of NF2-VS from the database, and selected the leading 25% genes with the most variance across samples for weighted correlation network analysis. Subsequently, we conducted gene ontology term and Kyoto Encyclopedia of Genes and Genomes signaling network enrichment analyses. The STRING database was employed for protein-protein interaction (PPI) axis construction. The mRNA-miRNA modulatory network was generated via the miRTarBase database. Differentially expressed genes (DEGs) were identified via the R package "limma" in both datasets, and hub genes were screened via intersection of common DEGs, candidate hub genes from the PPI axis, and candidate hub genes from the key module. Finally, common DEGs were uploaded onto the connectivity map database to determine drug candidates. Based on our observations, the blue module exhibited the most significant relation to NF2-VS, and it included the NF2 gene. Using enrichment analysis, we demonstrated that the blue modules were intricately linked to modulations of cell proliferation, migration, adhesion, junction, and actin skeleton. Overall, 356 common DEGs were screened in both datasets, and 33 genes carrying a degree > 15 were chosen as candidate hub genes in the PPI axis. Subsequently, 4 genes, namely, GLUL, CAV1, MYH11, and CCND1 were recognized as real hub genes. In addition, 10 drugs with enrichment scores < -0.7 were identified as drug candidates. Our conclusions offered a novel insight into the potential underlying mechanisms behind NF2-VS. These findings may facilitate the identification of novel therapeutic targets in the future.

Identification of hyperosmotic stress-responsive genes in Chinese hamster ovary cells via genome-wide virus-free CRISPR/Cas9 screening

Chinese hamster ovary (CHO) cells are the preferred mammalian host cells for therapeutic protein production that have been extensively engineered to possess the desired attributes for high-yield protein production. However, empirical approaches for identifying novel engineering targets are laborious and time-consuming. Here, we established a genome-wide CRISPR/Cas9 screening platform for CHO-K1 cells with 111,651 guide RNAs (gRNAs) targeting 21,585 genes using a virus-free recombinase-mediated cassette exchange-based gRNA integration method. Using this platform, we performed a positive selection screening under hyperosmotic stress conditions and identified 180 genes whose perturbations conferred resistance to hyperosmotic stress in CHO cells. Functional enrichment analysis identified hyperosmotic stress responsive gene clusters, such as tRNA wobble uridine modification and signaling pathways associated with cell cycle arrest. Furthermore, we validated 32 top-scoring candidates and observed a high rate of hit confirmation, demonstrating the potential of the screening platform. Knockout of the novel target genes, Zfr and Pnp, in monoclonal antibody (mAb)-producing recombinant CHO (rCHO) cells and bispecific antibody (bsAb)-producing rCHO cells enhanced their resistance to hyperosmotic stress, thereby improving mAb and bsAb production. Overall, the collective findings demonstrate the value of the screening platform as a powerful tool to investigate the functions of genes associated with hyperosmotic stress and to discover novel targets for rational cell engineering on a genome-wide scale in CHO cells.

PLPP/CIN-mediated NF2 S10 dephosphorylation distinctly regulates kainate-induced seizure susceptibility and neuronal death through PAK1-NF-κB-COX-2-PTGES2 signaling pathway

BACKGROUND

Pyridoxal-5'-phosphate phosphatase/chronophin (PLPP/CIN) selectively dephosphorylates serine (S) 10 site on neurofibromin 2 (NF2, also known as merlin (moesin-ezrin-radixin-like protein) or schwannomin). p21-activated kinase 1 (PAK1) is a serine/threonine protein kinase, which is involved in synaptic activity and plasticity in neurons. NF2 and PAK1 reciprocally regulate each other in a positive feedback manner. Thus, the aim of the present study is to investigate the effects of PLPP/CIN-mediated NF2 S10 dephosphorylation on PAK1-related signaling pathways under physiological and neuroinflammatory conditions, which are largely unknown.

METHODS

After kainate (KA) injection in wild-type, PLPP/CIN^-/- and PLPP/CIN^Tg mice, seizure susceptibility, PAK1 S204 autophosphorylation, nuclear factor-κB (NF-κB) p65 S276 phosphorylation, cyclooxygenase-2 (COX-2) upregulation, prostaglandin E synthase 2 (PTGES2) induction and neuronal damage were measured. The effects of 1,1'-dithiodi-2-naphthtol (IPA-3, a selective inhibitor of PAK1) pretreatment on these responses to KA were also validated.

RESULTS

PLPP/CIN overexpression increased PAK1 S204 autophosphorylation concomitant with the enhanced NF2 S10 dephosphorylation in hippocampal neurons under physiological condition. Following KA treatment, PLPP/CIN overexpression delayed the seizure on-set and accelerated PAK1 S204 phosphorylation, NF-κB p65 S276 phosphorylation, COX-2 upregulation and PTGES2 induction, which were ameliorated by PLPP/CIN deletion or IPA-3. Furthermore, IPA-3 pretreatment shortened the latency of seizure on-set without affecting seizure severity (intensity) and ameliorated CA3 neuronal death induced by KA.

CONCLUSIONS

These findings indicate that PLPP/CIN may regulate seizure susceptibility (the latency of seizure on-set) and CA3 neuronal death in response to KA through NF2-PAK1-NF-κB-COX-2-PTGES2 signaling pathway.

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.

Heterogeneous RNA editing and influence of ADAR2 on mesothelioma chemoresistance and the tumor microenvironment

We previously observed increased levels of adenosine-deaminase-acting-on-dsRNA (Adar)-dependent RNA editing during mesothelioma development in mice exposed to asbestos. The aim of this study was to characterize and assess the role of ADAR-dependent RNA editing in mesothelioma. We found that tumors and mesothelioma primary cultures have higher ADAR-mediated RNA editing compared to mesothelial cells. Unsupervised clustering of editing in different genomic regions revealed heterogeneity between tumor samples as well as mesothelioma primary cultures. ADAR2 expression levels are higher in BRCA1-associated protein 1 wild-type tumors, with corresponding changes in RNA editing in transcripts and 3'UTR. ADAR2 knockdown and rescue models indicated a role in cell proliferation, altered cell cycle, increased sensitivity to antifolate treatment, and type-1 interferon signaling upregulation, leading to changes in the microenvironment in vivo. Our data indicate that RNA editing contributes to mesothelioma heterogeneity and highlights an important role of ADAR2 not only in growth regulation in mesothelioma but also in chemotherapy response, in addition to regulating inflammatory response downstream of sensing nucleic acid structures.

Genomic landscape of pleural and peritoneal mesothelioma tumours

BACKGROUND

Malignant pleural and peritoneal mesotheliomas are rare malignancies with unacceptable poor prognoses and limited treatment options. The genomic landscape is mainly characterised by the loss of tumour suppressor genes and mutations in DNA repair genes. Currently, data from next-generation sequencing (NGS) of mesothelioma tumours is restricted to a limited number of cases; moreover, data comparing molecular features of mesothelioma from the pleural and peritoneal origin with NGS are lacking.

METHODS

We analysed 1113 pleural mesothelioma and 355 peritoneal mesothelioma samples. All tumours were sequenced with the FoundationOne® or FoundationOne®CDx assay for detection of substitutions, insertion-deletions, copy-number alterations and selected rearrangements in at least 324 cancer genes.

RESULTS

This analysis revealed alterations in 19 genes with an overall prevalence of at least 2%. Alterations in BAP1, CDKN2A, CDKN2B, NF2, MTAP, TP53 and SETD2 occurred with a prevalence of at least 10%. Peritoneal, compared to pleural mesothelioma, was characterised by a lower prevalence of alterations in CDKN2A, CDKN2B and MTAP. Moreover, we could define four distinct subgroups according to alterations in BAP1 and CDKN2A/B. Alterations in Hedgehog pathway-related genes (PTCH1/2 and SUFU) and Hippo pathway-related gene (NF2) as well as KRAS, EGFR, PDGFRA/B, ERBB2 and FGFR3 were detected in both cohorts.

CONCLUSION

Here, we report the molecular aberrations from the largest cohort of patients with mesothelioma. This analysis identified a proportion of patients with targetable alterations and suggests that molecular profiling can identify new treatment options for patients with mesothelioma.

Hepatic Epigenetic Reprogramming After Liver Resection in Offspring Alleviates the Effects of Maternal Obesity

Obesity has become a public health problem in recent decades, and during pregnancy, it can lead to an increased risk of gestational complications and permanent changes in the offspring resulting from a process known as metabolic programming. The offspring of obese dams are at increased risk of developing non-alcoholic fatty liver disease (NAFLD), even in the absence of high-fat diet consumption. NAFLD is a chronic fatty liver disease that can progress to extremely severe conditions that require surgical intervention with the removal of the injured tissue. Liver regeneration is necessary to preserve organ function. A range of pathways is activated in the liver regeneration process, including the Hippo, TGFβ, and AMPK signaling pathways that are under epigenetic control. We investigated whether microRNA modulation in the liver of the offspring of obese dams would impact gene expression of Hippo, TGFβ, and AMPK pathways and tissue regeneration after partial hepatectomy (PHx). Female Swiss mice fed a standard chow or a high-fat diet (HFD) before and during pregnancy and lactation were mated with male control mice. The offspring from control (CT-O) and obese (HF-O) dams weaned to standard chow diet until day 56 were submitted to PHx surgery. Prior to the surgery, HF-O presented alterations in miR-122, miR-370, and Let-7a expression in the liver compared to CT-O, as previously shown, as well as in its target genes involved in liver regeneration. However, after the PHx (4 h or 48 h post-surgery), differences in gene expression between CT-O and HF-O were suppressed, as well as in microRNA expression in the liver. Furthermore, both CT-O and HF-O presented a similar regenerative capacity of the liver within 48 h after PHx. Our results suggest that survival and regenerative mechanisms induced by the partial hepatectomy may overcome the epigenetic changes in the liver of offspring programmed by maternal obesity.

The Hippo Signaling Pathway in Cancer: A Cell Cycle Perspective

Simple Summary

Cancer is increasingly viewed as a cell cycle disease in that the dysregulation of the cell cycle machinery is a common feature in cancer. The Hippo signaling pathway consists of a core kinase cascade as well as extended regulators, which together control organ size and tissue homeostasis. The aberrant expression of cell cycle regulators and/or Hippo pathway components contributes to cancer development, and for this reason, we specifically focus on delineating the roles of the Hippo pathway in the cell cycle. Improving our understanding of the Hippo pathway from a cell cycle perspective could be used as a powerful weapon in the cancer battlefield.

Abstract

Cell cycle progression is an elaborate process that requires stringent control for normal cellular function. Defects in cell cycle control, however, contribute to genomic instability and have become a characteristic phenomenon in cancers. Over the years, advancement in the understanding of disrupted cell cycle regulation in tumors has led to the development of powerful anti-cancer drugs. Therefore, an in-depth exploration of cell cycle dysregulation in cancers could provide therapeutic avenues for cancer treatment. The Hippo pathway is an evolutionarily conserved regulator network that controls organ size, and its dysregulation is implicated in various types of cancers. Although the role of the Hippo pathway in oncogenesis has been widely investigated, its role in cell cycle regulation has not been comprehensively scrutinized. Here, we specifically focus on delineating the involvement of the Hippo pathway in cell cycle regulation. To that end, we first compare the structural as well as functional conservation of the core Hippo pathway in yeasts, flies, and mammals. Then, we detail the multi-faceted aspects in which the core components of the mammalian Hippo pathway and their regulators affect the cell cycle, particularly with regard to the regulation of E2F activity, the G1 tetraploidy checkpoint, DNA synthesis, DNA damage checkpoint, centrosome dynamics, and mitosis. Finally, we briefly discuss how a collective understanding of cell cycle regulation and the Hippo pathway could be weaponized in combating cancer.

Deletion of Nf2 in neural crest-derived tongue mesenchyme alters tongue shape and size, Hippo signalling and cell proliferation in a region- and stage-specific manner

Objectives

The mammalian tongue develops from the branchial arches (1–4) and comprises highly organized tissues compartmentalized by mesenchyme/connective tissue that is largely derived from neural crest (NC). This study aimed to understand the roles of tumour suppressor Neurofibromin 2 (Nf2) in NC‐derived tongue mesenchyme in regulating Hippo signalling and cell proliferation for the proper development of tongue shape and size.

Materials and methods

Conditional knockout (cKO) of Nf2 in NC cell lineage was generated using Wnt1‐Cre (Wnt1‐Cre/Nf2^cKO). Nf2 expression, Hippo signalling activities, cell proliferation and tongue shape and size were thoroughly analysed in different tongue regions and tissue types of Wnt1‐Cre/Nf2^cKO and Cre^‐/Nf2^fx/fx littermates at various stages (E10.5–E18.5).

Results

In contrast to many other organs in which the Nf2/Hippo pathway activity restrains growth and cell proliferation and as a result, loss of Nf2 decreases Hippo pathway activity and promotes an enlarged organ development, here we report our observations of distinct, tongue region‐ and stage‐specific alterations of Hippo signalling activity and cell proliferation in Nf2^cKO in NC‐derived tongue mesenchyme. Compared to Cre⁻/Nf2^fx/fx littermates, Wnt1‐Cre/Nf2^cKO depicted a non‐proportionally enlarged tongue (macroglossia) at E12.5–E13.5 and microglossia at later stages (E15.5–E18.5). Specifically, at E12.5 Nf2^cKO mutants had a decreased level of Hippo signalling transcription factor Yes‐associated protein (Yap), Yap target genes and cell proliferation anteriorly, while having an increased Yap, Yap target genes and cell proliferation posteriorly, which lead to a tip‐pointed and posteriorly widened tongue. At E15.5, loss of Nf2 in the NC lineage resulted in distinct changes in cell proliferation in different regions, that is, high in epithelium and mesenchyme subjacent to the epithelium, and lower in deeper layers of the mesenchyme. At E18.5, cell proliferation was reduced throughout the Nf2^cKO tongue.

Circ_0007031 enhances tumor progression and promotes 5-fluorouracil resistance in colorectal cancer through regulating miR-133b/ABCC5 axis

Colorectal cancer (CRC) remains one of the most commonly diagnosed malignancies worldwide. Circular RNAs (circRNAs) are being found to play crucial roles in human cancer, including CRC. The purpose of this study was to explore the function and mechanism of circ_0007031 on CRC progression and 5-fluorouracil (5-FU) resistance. The levels of circ_0007031, ATP-binding cassette subfamily C member 5 (ABCC5) and miR-133b were assessed by quantitative real-time polymerase chain reaction (qRT-PCR) or western blot. Cell survival and proliferation were detected by the 3-(4,5-dimethylthiazol-2yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay. Cell colony formation was evaluated using a standard colony formation assay. Transwell assays were performed to determine cell migration and invasion. Targeted correlations among circ_0007031, miR-133b and ABCC5 were verified by dual-luciferase reporter, RNA immunoprecipitation (RIP) and RNA pulldown assays. Animal experiments were performed to observe the role of circ_0007031 in vivo. Our data indicated that circ_0007031 up-regulation was associated with CRC resistance to 5-FU. Circ_0007031 knockdown repressed CRC cell proliferation, migration and invasion and enhanced 5-FU sensitivity. Circ_0007031 directly interacted with miR-133b. Moreover, circ_0007031 knockdown regulated CRC cell progression and 5-FU sensitivity by miR-133b. ABCC5 was a direct target of miR-133b, and circ_0007031 mediated ABCC5 expression via acting as a miR-133b sponge. Furthermore, miR-133b overexpression regulated CRC cell progression and sensitivity to 5-FU by down-regulating ABCC5. Additionally, circ_0007031 knockdown suppressed tumor growth in vivo. Our current work had led to the identification of circ_0007031 knockdown that repressed CRC cell malignant progression and enhanced 5-FU sensitivity via regulating ABCC5 expression by sponging miR-133b.

Loss of Mediator complex subunit 13 (MED13) promotes resistance to alkylation through cyclin D1 upregulation

Alkylating drugs are among the most often used chemotherapeutics. While cancer cells frequently develop resistance to alkylation treatments, detailed understanding of mechanisms that lead to the resistance is limited. Here, by using genome-wide CRISPR-Cas9 based screen, we identify transcriptional Mediator complex subunit 13 (MED13) as a novel modulator of alkylation response. The alkylation exposure causes significant MED13 downregulation, while complete loss of MED13 results in reduced apoptosis and resistance to alkylating agents. Transcriptome analysis identified cyclin D1 (CCND1) as one of the highly overexpressed genes in MED13 knock-out (KO) cells, characterized by shorter G1 phase. MED13 is able to bind to CCND1 regulatory elements thus influencing the expression. The resistance of MED13 KO cells is directly dependent on the cyclin D1 overexpression, and its down-regulation is sufficient to re-sensitize the cells to alkylating agents. We further demonstrate the therapeutic potential of MED13-mediated response, by applying combinatory treatment with CDK8/19 inhibitor Senexin A. Importantly, the treatment with Senexin A stabilizes MED13, and in combination with alkylating agents significantly reduces viability of cancer cells. In summary, our findings identify novel alkylation stress response mechanism dependent on MED13 and cyclin D1 that can serve as basis for development of innovative therapeutic strategies.

Merlin cooperates with neurofibromin and Spred1 to suppress the Ras-Erk pathway

The Ras-Erk pathway is frequently overactivated in human tumors. Neurofibromatosis types 1 and 2 (NF1, NF2) are characterized by multiple tumors of Schwann cell origin. The NF1 tumor suppressor neurofibromin is a principal Ras-GAP accelerating Ras inactivation, whereas the NF2 tumor suppressor merlin is a scaffold protein coordinating multiple signaling pathways. We have previously reported that merlin interacts with Ras and p120RasGAP. Here, we show that merlin can also interact with the neurofibromin/Spred1 complex via merlin-binding sites present on both proteins. Further, merlin can directly bind to the Ras-binding domain (RBD) and the kinase domain (KiD) of Raf1. As the third component of the neurofibromin/Spred1 complex, merlin cannot increase the Ras-GAP activity; rather, it blocks Ras binding to Raf1 by functioning as a 'selective Ras barrier'. Merlin-deficient Schwann cells require the Ras-Erk pathway activity for proliferation. Accordingly, suppression of the Ras-Erk pathway likely contributes to merlin's tumor suppressor activity. Taken together, our results, and studies by others, support targeting or co-targeting of this pathway as a therapy for NF2 inactivation-related tumors.

RNA editing in mesothelioma: a look forward

RNA editing is a post-transcriptional process increasing transcript diversity, thereby regulating different biological processes. We recently observed that mutations resulting from RNA editing due to hydrolytic deamination of adenosine increase during the development of mesothelioma, a rare cancer linked to chronic exposure to asbestos. This review gathers information from the published literature and public data mining to explore several aspects of RNA editing and their possible implications for cancer growth and therapy. We address possible links between RNA editing and particular types of mesothelioma genetic and epigenetic alterations and discuss the relevance of an edited substrate in the context of current chemotherapy or immunotherapy.

Systematic Analysis of Aberrant Biochemical Networks and Potential Drug Vulnerabilities Induced by Tumor Suppressor Loss in Malignant Pleural Mesothelioma

Background: Malignant pleural mesothelioma (MPM) is driven by the inactivation of tumor suppressor genes (TSGs). An unmet need in the field is the translation of the genomic landscape into effective TSG-specific therapies. Methods: We correlated genomes against transcriptomes of patients' MPM tumors, by weighted gene co-expression network analysis (WGCNA). The identified aberrant biochemical networks and potential drug targets induced by tumor suppressor loss were validated by integrative data analysis and functional interrogation. Results: CDKN2A/2B loss activates G2/M checkpoint and PI3K/AKT, prioritizing a co-targeting strategy for CDKN2A/2B-null MPM. CDKN2A deficiency significantly co-occurs with deletions of anti-viral type I interferon (IFN-I) genes and BAP1 mutations, that enriches the IFN-I signature, stratifying a unique subset, with deficient IFN-I, but proficient BAP1 for oncolytic viral immunotherapies. Aberrant p53 attenuates differentiation and SETD2 loss acquires the dependency on EGFRs, highlighting the potential of differentiation therapy and pan-EGFR inhibitors for these subpopulations, respectively. LATS2 deficiency is linked with dysregulated immunoregulation, suggesting a rationale for immune checkpoint blockade. Finally, multiple lines of evidence support Dasatinib as a promising therapeutic for LATS2-mutant MPM. Conclusions: Systematic identification of abnormal cellular processes and potential drug vulnerabilities specified by TSG alterations provide a framework for precision oncology in MPM.

Targeting Hippo signaling pathway by phytochemicals in cancer therapy

The current era of cancer research has been continuously advancing upon identifying novel aspects of tumorigenesis and the principal mechanisms behind the unleashed proliferation, invasion, drug resistance and immortality of cancer cells in hopes of exploiting these findings to achieve a more effective treatment for cancer. In pursuit of this goal, the identification of the first components of an extremely important regulatory pathway in Drosophila melanogaster that largely determines cell fate during the developmental stages, ended up in the discovery of the highly sophisticated Hippo signaling cascade. Soon after, it was revealed that deregulation of the components of this pathway either via mutations or through epigenetic alterations can be observed in a vast variety of tumors and these alterations greatly contribute to the neoplastic transformation of cells, their survival, growth and resistance to therapy. As more hidden aspects of this pathway such as its widespread entanglement with other major cellular signaling pathways are continuously being uncovered, many researchers have sought over the past decade to find ways of therapeutic interventions targeting the major components of the Hippo cascade. To date, various approaches such as the use of exogenous targeting miRNAs and different molecular inhibitors have been recruited herein, among which naturally occurring compounds have shown a great promise. On such a basis, in the present work we review the current understanding of Hippo pathway and the most recent evidence on targeting its components using natural plant-derived phytochemicals.

Cancer genomics of lung cancer including malignant mesothelioma: A brief overview of current status and future prospects

Cancer as a genetic disease is by now well recognized. Genomic analysis of cancer cells, therefore, has greatly enhanced our ability to identify genetic alterations associated with various cancer types, including both lympho-hematopoietic as well as solid tumors. Chronic myeloid leukemia (CML), based on the specific diagnostic genetic abnormality has served as a prototype disease to clearly demonstrate the significance of the genomic analysis of cancer in identifying targeted therapy. Such a success has provided extra ordinary opportunities to investigate the role of genetic abnormalities and the pathways amenable to targeted therapy, not only in blood cancers but solid tumors such as Lung, Brain, Colon, Renal, Breast cancers as well as other epithelial and mesenchymal tumors. The main focus of this presentation is to illustrate the role of genomic analysis in targeting lung cancer, based on abnormalities or the pathways deregulated in tumor cells from individual patients. Lung cancer is one of the most common epithelial cancers associated with chronic inflammation due to cigarette smoking and other environmental carcinogens, and includes four distinct histologic type; non-small cell lung cancer (NSCLC); small cell lung cancer (SCLC) and squamous cell lung cancer. According to current estimates, 1.3 million cases of lung cancer are expected to be diagnosed worldwide annually, resulting in one million deaths. Since the discovery that patient's tumors with specific mutations in the EGFR may be sensitive to targeted therapeutic approach and the subsequent realization that the such mutations in the gene are not as prevalent, several cancer centers including ours initiated intense efforts to find other mutations or genomic alterations, which may serve as targets of specific therapy. Such efforts have successfully resulted in a battery of genes such as KRAS, ALK, C-MET, HER-2/neu, ROS1, etc., which have helped oncologists to triage the patients for personalized therapies. A significant proportion of patients with lung cancer, however, do not show any of the above genetic abnormalities. Approximately 90% of lung cancers exhibit RB1 mutation/deletion and or KRAS mutations, therefore, the signaling pathways, which regulate multistep tumorigenesis in lung cancer, are important for the treatment of histologic subtypes of lung cancer, which includes NSCLC & SCLC. Equally important was the findings that similar signaling pathways are also shared by other solid tumor types. We have investigated the role of these pathways to target these cancers and develop new strategies to treat lung, brain and related cancers. In addition, our translational studies in other tumor types such as NF2 related malignancies, specifically, Malignant Mesothelioma (MM), in which NF2 related pathway amenable to targeted therapies was identified. Selected examples representing experimental approaches will be discussed to illustrate the critical role of translational research in developing novel therapeutics for the successful and durable responses in some of these cancer types.

Cyclin D1 immunohistochemical staining to separate benign from malignant mesothelial proliferations

The separation of benign from malignant mesothelial proliferations is a morphologically difficult problem. Mutations/deletions of components of the Hippo pathway are frequent in malignant mesotheliomas, and one downstream effect of aberrant Hippo signaling is increased production of cyclin D1. We examined expression of cyclin D1 nuclear staining in two tissue microarrays containing 52 reactive epithelial mesothelial proliferations, 51 reactive spindle cell mesothelial proliferations, 54 epithelial mesotheliomas, and 22 sarcomatous/desmoplastic mesotheliomas. When present, cyclin D1 staining was always strong, hence the arrays were scored as 0, 1-25%, 26-50%, 51-75%, and 76-100% staining. Both arrays showed a similar pattern. Reactive epithelial proliferations generally showed no staining (42/52 cases) or 1-25% staining (10/52 cases) with no cases showing >25% staining. Overall for reactive epithelial proliferations the maximum staining was 14.8% and mean 1.1 ± 2.9%. For epithelial mesotheliomas 39/54 (72%) cases demonstrated >25% staining, with 8/54 in the 26-50% staining range, 9/54 in the 51-75% range, and 22/54 in the >75% range. Combinations of staining using cyclin D1 >50% plus BAP1 or MTAP loss in epithelial mesotheliomas produced about a 10% increase in sensitivity. Reactive spindle cell proliferations showed a broader range of staining with 27/51 in the 1-25% range, 5/51 in the 26-50% range, and 1/51 >50%. Eleven of 22 sarcomatous/desmoplastic mesotheliomas scored 50% or greater. We conclude that for epithelial mesothelial proliferations, the finding of >50% of tumor cells staining supports a diagnosis of epithelial mesothelioma with 100% specificity but only modest (57%) sensitivity.

Enhanced Dendritic Actin Network Formation in Extended Lamellipodia Drives Proliferation in Growth-Challenged Rac1P29S Melanoma Cells

Actin assembly supplies the structural framework for cell morphology and migration. Beyond structure, this actin framework can also be engaged to drive biochemical signaling programs. Here, we describe how the hyperactivation of Rac1 via the P29S mutation (Rac1^P29S) in melanoma hijacks branched actin network assembly to coordinate proliferative cues that facilitate metastasis and drug resistance. Upon growth challenge, Rac1^P29S-harboring melanoma cells massively upregulate lamellipodia formation by dendritic actin polymerization. These extended lamellipodia form a signaling microdomain that sequesters and phospho-inactivates the tumor suppressor NF2/Merlin, driving Rac1^P29S cell proliferation in growth suppressive conditions. These biochemically active lamellipodia require cell-substrate attachment but not focal adhesion assembly and drive proliferation independently of the ERK/MAPK pathway. These data suggest a critical link between cell morphology and cell signaling and reconcile the dichotomy of Rac1's regulation of both proliferation and actin assembly by revealing a mutual signaling axis wherein actin assembly drives proliferation in melanoma.

G-quadruplex–forming GGA repeat region functions as a negative regulator of the Ccnb1ip1 enhancer

An enhancer located upstream of the transcriptional start site of Ccnb1ip1 containing two GGA-rich regions and a 14-GGA repeat (GGA)14 region has been previously identified. Three copies of four GGA repeats in the c-myb promoter that form a tetrad:heptad:heptad:tetrad (T:H:H:T) dimerized G-quadruplex (G4) structure reportedly functions as both a transcriptional repressor and activator. Here, the secondary structures of the two GGA-rich and (GGA)14 regions were analyzed using circular dichroism spectral analysis, which indicated that the two GGA-rich DNAs formed parallel-type G4 structures, whereas (GGA)14 DNA formed the T:H:H:T dimerized G4 structure. Reporter assays demonstrated that individual regions did not show enhancer activity; however, the deletion of the (GGA)14 region resulted in 1.5-fold higher enhancer activity than that of the whole enhancer. These results indicate that the (GGA)14 region that forms the T:H:H:T dimerized G4 structure functions as a negative regulator of the Ccnb1ip1 enhancer.

Inactivation of Bap1 Cooperates with Losses of Nf2 and Cdkn2a to Drive the Development of Pleural Malignant Mesothelioma in Conditional Mouse Models

Pleural malignant mesothelioma is a therapy-resistant cancer affecting the serosal lining of the thoracic cavity. Mutations/deletions of BAP1, CDKN2A, and NF2 are the most frequent genetic lesions in human malignant mesothelioma. We introduced various combinations of these deletions in the pleura of conditional knockout (CKO) mice, focusing on the contribution of Bap1 loss. While homozygous CKO of Bap1, Cdkn2a, or Nf2 alone gave rise to few or no malignant mesotheliomas, inactivation of Bap1 cooperated with loss of either Nf2 or Cdkn2a to drive development of malignant mesothelioma in approximately 20% of double-CKO mice, and a high incidence (22/26, 85%) of malignant mesotheliomas was observed in Bap1;Nf2;Cdkn2a (triple)-CKO mice. Malignant mesothelioma onset was rapid in triple-CKO mice, with a median survival of only 12 weeks, and malignant mesotheliomas from these mice were consistently high-grade and invasive. Adenoviral-Cre treatment of normal mesothelial cells from Bap1;Nf2;Cdkn2a CKO mice, but not from mice with knockout of one or any two of these genes, resulted in robust spheroid formation in vitro, suggesting that mesothelial cells from Bap1;Nf2;Cdkn2a mice have stem cell-like potential. RNA-seq analysis of malignant mesotheliomas from triple-CKO mice revealed enrichment of genes transcriptionally regulated by the polycomb repressive complex 2 (PRC2) and others previously implicated in known Bap1-related cellular processes. These data demonstrate that somatic inactivation of Bap1, Nf2, and Cdkn2a results in rapid, aggressive malignant mesotheliomas, and that deletion of Bap1 contributes to tumor development, in part, by loss of PRC2-mediated repression of tumorigenic target genes and by acquisition of stem cell potential, suggesting a potential avenue for therapeutic intervention. SIGNIFICANCE: Combinatorial deletions of Bap1, Nf2, and Cdkn2a result in aggressive mesotheliomas, with Bap1 loss contributing to tumorigenesis by circumventing PRC2-mediated repression of oncogenic target genes.

A proteasome-resistant fragment of NIK mediates oncogenic NF-κB signaling in schwannomas

Schwannomas are common, highly morbid and medically untreatable tumors that can arise in patients with germ line as well as somatic mutations in neurofibromatosis type 2 (NF2). These mutations most commonly result in the loss of function of the NF2-encoded protein, Merlin. Little is known about how Merlin functions endogenously as a tumor suppressor and how its loss leads to oncogenic transformation in Schwann cells (SCs). Here, we identify nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB)-inducing kinase (NIK) as a potential drug target driving NF-κB signaling and Merlin-deficient schwannoma genesis. Using a genomic approach to profile aberrant tumor signaling pathways, we describe multiple upregulated NF-κB signaling elements in human and murine schwannomas, leading us to identify a caspase-cleaved, proteasome-resistant NIK kinase domain fragment that amplifies pathogenic NF-κB signaling. Lentiviral-mediated transduction of this NIK fragment into normal SCs promotes proliferation, survival, and adhesion while inducing schwannoma formation in a novel in vivo orthotopic transplant model. Furthermore, we describe an NF-κB-potentiated hepatocyte growth factor (HGF) to MET proto-oncogene receptor tyrosine kinase (c-Met) autocrine feed-forward loop promoting SC proliferation. These innovative studies identify a novel signaling axis underlying schwannoma formation, revealing new and potentially druggable schwannoma vulnerabilities with future therapeutic potential.

TARBP2-Enhanced Resistance during Tamoxifen Treatment in Breast Cancer

Tamoxifen is the most widely used hormone therapy in estrogen receptor-positive (ER+) breast cancer, which accounts for approximately 70% of all breast cancers. Although patients who receive tamoxifen therapy benefit with respect to an improved overall prognosis, resistance and cancer recurrence still occur and remain important clinical challenges. A recent study identified TAR (HIV-1) RNA binding protein 2 (TARBP2) as an oncogene that promotes breast cancer metastasis. In this study, we showed that TARBP2 is overexpressed in hormone therapy-resistant cells and breast cancer tissues, where it enhances tamoxifen resistance. Tamoxifen-induced TARBP2 expression results in the desensitization of ER+ breast cancer cells. Mechanistically, tamoxifen post-transcriptionally stabilizes TARBP2 protein through the downregulation of Merlin, a TARBP2-interacting protein known to enhance its proteasomal degradation. Tamoxifen-induced TARBP2 further stabilizes SOX2 protein to enhance desensitization of breast cancer cells to tamoxifen, while similar to TARBP2, its induction in cancer cells was also observed in metastatic tumor cells. Our results indicate that the TARBP2-SOX2 pathway is upregulated by tamoxifen-mediated Merlin downregulation, which subsequently induces tamoxifen resistance in ER+ breast cancer.

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.

Synergistic effect of Nutlin-3 combined with MG-132 on schwannoma cells through restoration of merlin and p53 tumour suppressors

BACKGROUND

The great majority of sporadic vestibular schwannomas (VSs) are due to the mutations of the NF2 gene encoding merlin. Sporadic VSs exhibit variable growth patterns and only a small fraction of the tumours are fast-growing; however, the underlying mechanisms remain undefined.

METHODS

DNA sequencing and dosage analysis were used to identify the NF2 mutation status in sporadic schwannomas. The expression and sub-cellular localization of merlin and p53-MDM2 were assessed by immunoblotting, qRT-PCR and immunofluorescence. In vitro and in vivo studies were performed to reveal the effects of Nutlin-3 (a MDM2 inhibitor) and/or MG-132(a proteasome inhibitor) on schwannomas. The proliferation of schwannoma cells was assessed by CCK-8 assay, EdU staining and Flow cytometry analysis.

FINDINGS

Double genetic hits of NF2 tended to occur in fast-growing tumours, characterized by the absence of merlin. The deregulation of p53-MDM2 was demonstrated to mediate merlin-deficient tumour growth, characterized by a nuclear accumulation of stabilized MDM2, contributing to a nuclear export of p53 for degradation. Nutlin-3 blocked the proliferation of schwannoma cells via a cooperative recovery of merlin and p53, accompanied by the shuttling of both proteins from the cytoplasm to the nucleus. We further demonstrated a difference in the sensitivity to Nutlin-3 between schwannoma cells with and without merlin expression. Nutlin-3 combined with MG-132 narrowed this between-group difference and triggered stronger inhibitory effects on the growth of schwannomas through coordinated reactivation of p53.

INTERPRETATION

These findings present treatment strategies directed on the pathogenesis of sporadic schwannomas. FUND: National Natural Science Foundation of China.

Cancer driver mutations in endometriosis: Variations on the major theme of fibrogenesis

BACKGROUND

One recent study reports cancer driver mutations in deep endometriosis, but its biological/clinical significance remains unclear. Since the natural history of endometriosis is essentially gradual progression toward fibrosis, it is thus hypothesized that the six driver genes reported to be mutated in endometriosis (the RP set) may play important roles in fibrogenesis but not necessarily malignant transformation.

METHODS

Extensive PubMed search to see whether RP and another set of driver genes not yet reported (NR) to be mutated in endometriosis have any roles in fibrogenesis. All studies reporting on the role of fibrogenesis of the genes in both RP and NR sets were retrieved and evaluated in this review.

RESULTS

All six RP genes were involved in various aspects of fibrogenesis as compared with only three NR genes. These nine genes can be anchored in networks linking with their upstream and downstream genes that are known to be aberrantly expressed in endometriosis, piecing together seemingly unrelated findings.

CONCLUSIONS

Given that somatic driver mutations can and do occur frequently in physiologically normal tissues, it is argued that these mutations in endometriosis are not necessarily synonymous with malignancy or premalignancy, but the result of enormous pressure for fibrogenesis.

Deficiency of tumor suppressor Merlin facilitates metabolic adaptation by co-operative engagement of SMAD-Hippo signaling in breast cancer

The NF2 gene encodes the tumor and metastasis suppressor protein Merlin. Merlin exerts its tumor suppressive role by inhibiting proliferation and inducing contact-growth inhibition and apoptosis. In the current investigation, we determined that loss of Merlin in breast cancer tissues is concordant with the loss of the inhibitory SMAD, SMAD7, of the TGF-β pathway. This was reflected as dysregulated activation of TGF-β signaling that co-operatively engaged with effectors of the Hippo pathway (YAP/TAZ/TEAD). As a consequence, the loss of Merlin in breast cancer resulted in a significant metabolic and bioenergetic adaptation of cells characterized by increased aerobic glycolysis and decreased oxygen consumption. Mechanistically, we determined that the co-operative activity of the Hippo and TGF-β transcription effectors caused upregulation of the long non-coding RNA Urothelial Cancer-Associated 1 (UCA1) that disengaged Merlin's check on STAT3 activity. The consequent upregulation of Hexokinase 2 (HK2) enabled a metabolic shift towards aerobic glycolysis. In fact, Merlin deficiency engendered cellular dependence on this metabolic adaptation, endorsing a critical role for Merlin in regulating cellular metabolism. This is the first report of Merlin functioning as a molecular restraint on cellular metabolism. Thus, breast cancer patients whose tumors demonstrate concordant loss of Merlin and SMAD7 may benefit from an approach of incorporating STAT3 inhibitors.

Neurofibromatosis type 2 tumor suppressor protein is expressed in oligodendrocytes and regulates cell proliferation and process formation

The neurofibromatosis type 2 (NF2) tumor suppressor protein Merlin functions as a negative regulator of cell growth and actin dynamics in different cell types amongst which Schwann cells have been extensively studied. In contrast, the presence and the role of Merlin in oligodendrocytes, the myelin forming cells within the CNS, have not been elucidated. In this work, we demonstrate that Merlin immunoreactivity was broadly distributed in the white matter throughout the central nervous system. Following Merlin expression during development in the cerebellum, Merlin could be detected in the cerebellar white matter tract at early postnatal stages as shown by its co-localization with Olig2-positive cells as well as in adult brain sections where it was aligned with myelin basic protein containing fibers. This suggests that Merlin is expressed in immature and mature oligodendrocytes. Expression levels of Merlin were low in oligodendrocytes as compared to astrocytes and neurons throughout development. Expression of Merlin in oligodendroglia was further supported by its identification in either immortalized cell lines of oligodendroglial origin or in primary oligodendrocyte cultures. In these cultures, the two main splice variants of Nf2 could be detected. Merlin was localized in clusters within the nuclei and in the cytoplasm. Overexpressing Merlin in oligodendrocyte cell lines strengthened reduced impedance in XCELLigence measurements and Ki67 stainings in cultures over time. In addition, the initiation and elongation of cellular projections were reduced by Merlin overexpression. Consistently, cell migration was retarded in scratch assays done on Nf2-transfected oligodendrocyte cell lines. These data suggest that Merlin actively modulates process outgrowth and migration in oligodendrocytes.

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.

Crizotinib inhibits NF2-associated schwannoma through inhibition of focal adhesion kinase 1

Neurofibromatosis type 2 (NF2) is a dominantly inherited autosomal disease characterized by schwannomas of the 8th cranial nerve. The NF2 tumor suppressor gene encodes for Merlin, a protein implicated as a suppressor of multiple cellular signaling pathways. To identify potential drug targets in NF2-associated malignancies we assessed the consequences of inhibiting the tyrosine kinase receptor MET. We identified crizotinib, a MET and ALK inhibitor, as a potent inhibitor of NF2-null Schwann cell proliferation in vitro and tumor growth in vivo. To identify the target/s of crizotnib we employed activity-based protein profiling (ABPP), leading to identification of FAK1 (PTK2) as the relevant target of crizotinib inhibition in NF2-null schwannoma cells. Subsequent studies confirm that inhibition of FAK1 is sufficient to suppress tumorigenesis in animal models of NF2 and that crizotinib-resistant forms of FAK1 can rescue the effects of treatment. These studies identify a FDA approved drug as a potential treatment for NF2 and delineate the mechanism of action in NF2-null Schwann cells.

Targeting MYC sensitizes malignant mesothelioma cells to PAK blockage-induced cytotoxicity

Clinical management of malignant mesothelioma (MM) is very challenging due to marked resistance of this tumor to chemotherapy. Various mechanisms lead to a less than ideal drug concentration inside of MM cells, diminishing cytotoxicity. Consequently, single cytotoxic drugs achieve very modest response rates in MM patients, and combination regimens using standard and novel therapies have achieved only limited improvement in overall survival. Here, we demonstrate that MYC has either proliferative or pro-survival effects in MM cells during normal or stressed conditions, respectively. A MYC inhibitor 10058-F4 reduced MM cell proliferation via down regulation of cyclin D. Under serum starvation conditions, MM cells became quiescent, and the addition of MYC inhibitors triggered apoptosis in the resting MM cells. We also found that high concentrations of the PAK inhibitor PF3758309 killed MM cells, but the drug had only cytostatic effects at lower concentrations. These quiescent cells underwent apoptosis upon pharmacological inhibition of MYC. A novel MYC inhibitor KJ-Pyr-9 and a newer PAK inhibitor, FRAX597, also demonstrated marked cytotoxic cooperativity. Collectively, these findings demonstrate that targeting of MYC can sensitize MM cells and provide rationale for inhibition of MYC and PAK as a novel combinatory regimen for the treatment of this otherwise therapy-resistant, clinically incurable malignancy.

Differential NF2 Gene Status in Sporadic Vestibular Schwannomas and its Prognostic Impact on Tumour Growth Patterns

The great majority of sporadic vestibular schwannomas (VSs) are due to the inactivation of the NF2 gene. In this study, we found age-dependent differences in the clinical parameters of sporadic VSs. Young patients were characterized by progressive tumour behaviours, including earlier onset of initial symptoms, shorter symptom duration and larger tumour size. An increased rate of "two-hits" of both NF2 alleles, usually by mutation and allelic loss, was observed in young cases compared to older, and this correlated with the loss of protein and mRNA expression. In contrast, the tumours with a single mutation (referred to as 'one-hit') exhibited obvious expression levels. Moreover, a mixture of merlin-expressing tumour cells and non-expressing tumour cells was observed in 'one-hit' schwannomas, suggesting that a subset of 'one-hit' tumour cells was present in these tumours. To mimic the growth promoting effects by the second hit, we performed lentivirus-mediated NF2 knockdown in the 'one-hit' schwannoma cultures. Following the loss of NF2 expression, schwannoma cultures demonstrated increased proliferation rates. Above all, we have identified a correlation between the NF2 status and the growth patterns of sporadic VSs. The treatment decision-making, microsurgery or "wait and scan" strategy, should be carried out according to the tumour's genetic background.

Differential NF2 Gene Status in Sporadic Vestibular Schwannomas and its Prognostic Impact on Tumour Growth Patterns

The great majority of sporadic vestibular schwannomas (VSs) are due to the inactivation of the NF2 gene. In this study, we found age-dependent differences in the clinical parameters of sporadic VSs. Young patients were characterized by progressive tumour behaviours, including earlier onset of initial symptoms, shorter symptom duration and larger tumour size. An increased rate of “two-hits” of both NF2 alleles, usually by mutation and allelic loss, was observed in young cases compared to older, and this correlated with the loss of protein and mRNA expression. In contrast, the tumours with a single mutation (referred to as ‘one-hit’) exhibited obvious expression levels. Moreover, a mixture of merlin-expressing tumour cells and non-expressing tumour cells was observed in ‘one-hit’ schwannomas, suggesting that a subset of ‘one-hit’ tumour cells was present in these tumours. To mimic the growth promoting effects by the second hit, we performed lentivirus-mediated NF2 knockdown in the ‘one-hit’ schwannoma cultures. Following the loss of NF2 expression, schwannoma cultures demonstrated increased proliferation rates. Above all, we have identified a correlation between the NF2 status and the growth patterns of sporadic VSs. The treatment decision-making, microsurgery or “wait and scan” strategy, should be carried out according to the tumour’s genetic background.

Cellular prion protein (PrPC) in the development of Merlin-deficient tumours

Loss of function mutations in the neurofibromatosis Type 2 (NF2) gene, coding for a tumour suppressor, Merlin, cause multiple tumours of the nervous system such as schwannomas, meningiomas and ependymomas. These tumours may occur sporadically or as part of the hereditary condition neurofibromatosis Type 2 (NF2). Current treatment is confined to (radio) surgery and no targeted drug therapies exist. NF2 mutations and/or Merlin inactivation are also seen in other cancers including some mesothelioma, breast cancer, colorectal carcinoma, melanoma and glioblastoma. To study the relationship between Merlin deficiency and tumourigenesis, we have developed an in vitro model comprising human primary schwannoma cells, the most common Merlin-deficient tumour and the hallmark for NF2. Using this model, we show increased expression of cellular prion protein (PrP^C) in schwannoma cells and tissues. In addition, a strong overexpression of PrP^C is observed in human Merlin-deficient mesothelioma cell line TRA and in human Merlin-deficient meningiomas. PrP^C contributes to increased proliferation, cell-matrix adhesion and survival in schwannoma cells acting via 37/67 kDa non-integrin laminin receptor (LR/37/67 kDa) and downstream ERK1/2, PI3K/AKT and FAK signalling pathways. PrP^C protein is also strongly released from schwannoma cells via exosomes and as a free peptide suggesting that it may act in an autocrine and/or paracrine manner. We suggest that PrP^C and its interactor, LR/37/67 kDa, could be potential therapeutic targets for schwannomas and other Merlin-deficient tumours.

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.

Stem Cell Factor-Based Identification and Functional Properties of In Vitro-Selected Subpopulations of Malignant Mesothelioma Cells

Malignant mesothelioma (MM) is an aggressive neoplasm characterized by a poor patient survival rate, because of rapid tumor recurrence following first-line therapy. Cancer stem cells (CSCs) are assumed to be responsible for initiating tumorigenesis and driving relapse after therapeutic interventions. CSC-enriched MM cell subpopulations were identified by an OCT4/SOX2 reporter approach and were characterized by (1) increased resistance to cisplatin, (2) increased sensitivity toward the FAK inhibitor VS-6063 in vitro, and (3) a higher tumor-initiating capacity in vivo in orthotopic xenograft and allograft mouse models. Overexpression of NF2 (neurofibromatosis 2, merlin), a tumor suppressor often mutated or lost in MM, did not affect proliferation and viability of CSC-enriched MM populations but robustly decreased the viability of reporter-negative cells. In contrast, downregulation of calretinin strongly decreased proliferation and viability of both populations. In summary, we have enriched and characterized a small MM cell subpopulation that bears the expected CSC characteristics.

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High SOX2 and OCT4 levels reveal a subpopulation of MM cells with CSC properties

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EGFP + MM cells are more resistant to cis-Pt, but more sensitive toward VS-6063

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EGFP + MM cells show a higher tumor-initiating capacity in xeno- and allograft models

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Calretinin downregulation, but not NF2 expression affects EGFP + MM cell viability

Loss of tumor suppressor Merlin results in aberrant activation of Wnt/β-catenin signaling in cancer

The expression of the tumor suppressor Merlin is compromised in nervous system malignancies due to genomic aberrations. We demonstrated for the first time, that in breast cancer, Merlin protein expression is lost due to proteasome-mediated elimination. Immunohistochemical analysis of tumor tissues from patients with metastatic breast cancer revealed characteristically reduced Merlin expression. Importantly, we identified a functional role for Merlin in impeding breast tumor xenograft growth and reducing invasive characteristics. We sought to determine a possible mechanism by which Merlin accomplishes this reduction in malignant activity. We observed that breast and pancreatic cancer cells with loss of Merlin show an aberrant increase in the activity of β-catenin concomitant with nuclear localization of β-catenin. We discovered that Merlin physically interacts with β-catenin, alters the sub-cellular localization of β-catenin, and significantly reduces the protein levels of β-catenin by targeting it for degradation through the upregulation of Axin1. Consequently, restoration of Merlin inhibited β-catenin-mediated transcriptional activity in breast and pancreatic cancer cells. We also present evidence that loss of Merlin sensitizes tumor cells to inhibition by compounds that target β-catenin-mediated activity. Thus, this study provides compelling evidence that Merlin reduces the malignant activity of pancreatic and breast cancer, in part by suppressing the Wnt/β-catenin pathway. Given the potent role of Wnt/β-catenin signaling in breast and pancreatic cancer and the flurry of activity to test β-catenin inhibitors in the clinic, our findings are opportune and provide evidence for Merlin in restraining aberrant activation of Wnt/β-catenin signaling.

Co-occurring Mutations of Tumor Suppressor Genes, LATS2 and NF2, in Malignant Pleural Mesothelioma

Purpose: To better define malignant pleural mesothelioma (MPM) heterogeneity and identify molecular subtypes of MPM, we focus on the tumor suppressor gene LATS2, a member of the Hippo signaling pathway, which plays a key role in mesothelial carcinogenesis.Experimental Design: Sixty-one MPM primary cultures established in our laboratory were screened for mutations in LATS2 Gene inactivation was modeled using siRNAs. Gene and protein expressions were analyzed by quantitative RT-PCR, Western blot analysis, and reverse phase protein array. Cell proliferation, viability, apoptosis, mobility, and invasion were determined after siRNA knockdown or YAP (verteporfin), mTOR (rapamycin), and mTOR/PI3K/AKT (PF-04691502) inhibitor treatment.Results: The LATS2 gene was altered in 11% of MPM by point mutations and large exon deletions. Genetic data coupled with transcriptomic data allowed the identification of a new MPM molecular subgroup, C2^LN, characterized by a co-occurring mutation in the LATS2 and NF2 genes in the same MPM. MPM patients of this subgroup presented a poor prognosis. Coinactivation of LATS2 and NF2 leads to loss of cell contact inhibition between MPM cells. Hippo signaling pathway activity, mTOR expression, and phosphorylation were altered in the C2^LN MPM subgroup. MPMs of this new subgroup show higher sensitivity to PF-04691502 inhibitor. The MOK gene was identified as a potential biomarker of the C2^LN MPM subgroup and PF-04691502 sensitivity.Conclusions: We identified a new MPM molecular subgroup that shares common genetic and transcriptomic characteristics. Our results made it possible to highlight a greater sensitivity to an anticancer compound for this MPM subgroup and to identify a specific potential biomarker. Clin Cancer Res; 23(12); 3191-202. ©2016 AACR.

The Conundrum of Genetic "Drivers" in Benign Conditions

Advances in deep genomic sequencing have identified a spectrum of cancer-specific passenger and driver aberrations. Clones with driver anomalies are believed to be positively selected during carcinogenesis. Accumulating evidence, however, shows that genomic alterations, such as those in BRAF, RAS, EGFR, HER2, FGFR3, PIK3CA, TP53, CDKN2A, and NF1/2, all of which are considered hallmark drivers of specific cancers, can also be identified in benign and premalignant conditions, occasionally at frequencies higher than in their malignant counterparts. Targeting these genomic drivers can produce dramatic responses in advanced cancer, but the effects on their benign counterparts are less clear. This benign-malignant phenomenon is well illustrated in studies of BRAF V600E mutations, which are paradoxically more frequent in benign nevi (∼80%) than in dysplastic nevi (∼60%) or melanoma (∼40%-45%). Similarly, human epidermal growth factor receptor 2 is more commonly overexpressed in ductal carcinoma in situ (∼27%-56%) when compared with invasive breast cancer (∼11%-20%). FGFR3 mutations in bladder cancer also decrease with tumor grade (low-grade tumors, ∼61%; high-grade, ∼11%). “Driver” mutations also occur in nonmalignant settings: TP53 mutations in synovial tissue from rheumatoid arthritis and FGFR3 mutations in seborrheic keratosis. The latter observations suggest that the oncogenicity of these alterations may be tissue context–dependent. The conversion of benign conditions to premalignant disease may involve other genetic events and/or epigenetic reprogramming. Putative driver mutations can also be germline and associated with increased cancer risk (eg, germline RAS or TP53 alterations), but germline FGFR3 or NF2 abnormalities do not predispose to malignancy. We discuss the enigma of genetic “drivers” in benign and premalignant conditions and the implications for prevention strategies and theories of tumorigenesis.

Inflammation-Related IL1β/IL1R Signaling Promotes the Development of Asbestos-Induced Malignant Mesothelioma

Exposure to asbestos is causally associated with the development of malignant mesothelioma, a cancer of cells lining the internal body cavities. Malignant mesothelioma is an aggressive cancer resistant to all current therapies. Once inhaled or ingested, asbestos causes inflammation in and around tissues that come in contact with these carcinogenic fibers. Recent studies suggest that inflammation is a major contributing factor in the development of many types of cancer, including malignant mesothelioma. The NALP3/NLRP3 inflammasome, including the component ASC, is thought to be an important mediator of inflammation in cells that sense extracellular insults, such as asbestos, and activate a signaling cascade resulting in release of mature IL1β and recruitment of inflammatory cells. To determine if inflammasome-mediated inflammation contributes to asbestos-induced malignant mesothelioma, we chronically exposed Asc-deficient mice and wild-type littermates to asbestos and evaluated differences in tumor incidence and latency. The Asc-deficient mice showed significantly delayed tumor onset and reduced malignant mesothelioma incidence compared with wild-type animals. We also tested whether inflammation-related release of IL1β contributes to tumor development in an accelerated mouse model of asbestos-induced malignant mesothelioma. Nf2(+/-);Cdkn2a(+/-) mice exposed to asbestos in the presence of anakinra, an IL1 receptor (IL1R) antagonist, showed a marked delay in the median time of malignant mesothelioma onset compared with similarly exposed mice given vehicle control (33.1 weeks vs. 22.6 weeks, respectively). Collectively, these studies provide evidence for a link between inflammation-related IL1β/IL1R signaling and the development of asbestos-induced malignant mesothelioma. Furthermore, these findings provide rationale for chemoprevention strategies targeting IL1β/IL1R signaling in high-risk, asbestos-exposed populations. Cancer Prev Res; 9(5); 406-14. ©2016 AACR.

Role of Merlin/NF2 inactivation in tumor biology

Merlin (Moesin-ezrin-radixin-like protein, also known as schwannomin) is a tumor suppressor protein encoded by the neurofibromatosis type 2 gene NF2. Loss of function mutations or deletions in NF2 cause neurofibromatosis type 2 (NF2), a multiple tumor forming disease of the nervous system. NF2 is characterized by the development of bilateral vestibular schwannomas. Patients with NF2 can also develop schwannomas on other cranial and peripheral nerves, as well as meningiomas and ependymomas. The only potential treatment is surgery/radiosurgery, which often results in loss of function of the involved nerve. There is an urgent need for chemotherapies that slow or eliminate tumors and prevent their formation in NF2 patients. Interestingly NF2 mutations and merlin inactivation also occur in spontaneous schwannomas and meningiomas, as well as other types of cancer including mesothelioma, glioma multiforme, breast, colorectal, skin, clear cell renal cell carcinoma, hepatic and prostate cancer. Except for malignant mesotheliomas, the role of NF2 mutation or inactivation has not received much attention in cancer, and NF2 might be relevant for prognosis and future chemotherapeutic approaches. This review discusses the influence of merlin loss of function in NF2-related tumors and common human cancers. We also discuss the NF2 gene status and merlin signaling pathways affected in the different tumor types and the molecular mechanisms that lead to tumorigenesis, progression and pharmacological resistance.

The prognostic significance of BAP1, NF2, and CDKN2A in malignant peritoneal mesothelioma

Cytoreductive surgery and hyperthermic intraperitoneal chemoperfusion for patients with malignant peritoneal mesothelioma has resulted in improved disease control and increased survival. Despite these results, there are significant perioperative risks associated with this aggressive procedure that necessitate consideration of prognostic markers during patient selection. The molecular pathogenesis of peritoneal mesothelioma remains relatively unknown, but extrapolation of findings from their pleural counterpart would suggest frequent alterations in CDKN2A, NF2, and BAP1. Homozygous deletions in CDKN2A portend a worse overall survival in peritoneal mesothelioma. However, the prevalence and prognostic significance of NF2 and BAP1 abnormalities has not been studied. Dual-color fluorescence in situ hybridization using CDKN2A and NF2 locus-specific probes and BAP1 immunohistochemistry identified homozygous CDKN2A deletions (n=25, 29%), hemizygous NF2 loss (n=30, 35%), and/or loss of BAP1 protein expression (n=49, 57%) in 68 of 86 (79%) peritoneal mesotheliomas. Homozygous CDKN2A deletions or hemizygous NF2 loss correlated with shorter progression-free survival (P<0.02) and poor overall survival (P<0.03). Moreover, the significance of these findings was cumulative. Patients harboring both homozygous CDKN2A deletions and hemizygous NF2 loss had a 2-year progression-free survival rate of 9% with a median of 6 months (P<0.01) and overall survival rate of 18% with a median of 8 months (P<0.01). By multivariate analysis, combined homozygous CDKN2A deletions and hemizygous NF2 loss was a negative prognostic factor for both progression-free survival and overall survival, independent of patient age, peritoneal cancer index, completeness of cytoreduction, and extent of invasion. In contrast, loss of BAP1 was not associated with clinical outcome. In summary, homozygous deletions in CDKN2A and hemizygous loss of NF2 as detected by fluorescence in situ hybridization would confer a poor clinical outcome and may guide future treatment decisions for patients with peritoneal mesothelioma.

Group I Paks as therapeutic targets in NF2-deficient meningioma

Neurofibromatosis type 2 (NF2) is an autosomal dominant disorder characterized by the development of multiple tumors in the central nervous system, most notably schwannomas and meningiomas. Mutational inactivation of NF2 is found in 40-60% of sporadic meningiomas, but the molecular mechanisms underlying malignant changes of meningioma cells remain unclear. Because group I p21-activated kinases (Paks) bind to and are inhibited by the NF2-encoded protein Merlin, we assessed the signaling and anti-tumor effects of three group-I specific Pak inhibitors - Frax597, 716 and 1036 - in NF2-/- meningiomas in vitro and in an orthotopic mouse model. We found that these Pak inhibitors suppressed the proliferation and motility of both benign (Ben-Men1) and malignant (KT21-MG1) meningiomas cells. In addition, we found a strong reduction in phosphorylation of Mek and S6, and decreased cyclin D1 expression in both cell lines after treatment with Pak inhibitors. Using intracranial xenografts of luciferase-expressing KT21-MG1 cells, we found that treated mice showed significant tumor suppression for all three Pak inhibitors. Similar effects were observed in Ben-Men1 cells. Tumors dissected from treated animals exhibited an increase in apoptosis without notable change in proliferation. Collectively, these results suggest that Pak inhibitors might be useful agents in treating NF2-deficient meningiomas.

Merlin negative regulation by miR-146a promotes cell transformation

Inactivation of the tumor suppressor Merlin, by deleterious mutations or by protein degradation via sustained growth factor receptor signaling-mediated mechanisms, results in cell transformation and tumor development. In addition to these mechanisms, here we show that, miRNA-dependent negative regulation of Merlin protein levels also promotes cell transformation. We provide experimental evidences showing that miR-146a negatively regulates Merlin protein levels through its interaction with an evolutionary conserved sequence in the 3´ untranslated region of the NF2 mRNA. Merlin downregulation by miR-146a in A549 lung epithelial cells resulted in enhanced cell proliferation, migration and tissue invasion. Accordingly, stable miR-146a-transfectant cells formed tumors with metastatic capacity in vivo. Together our results uncover miRNAs as yet another negative mechanism controlling Merlin tumor suppressor functions.

Role of cyclins D1 and D3 in vestibular schwannoma

BACKGROUND

Vestibular schwannomas in younger patients have been observed to be larger in size and grow more quickly.

OBJECTIVE

This study aimed to evaluate the expression of three important cell cycle proteins, cyclin D1, cyclin D3 and Ki-67, in vestibular schwannoma patients separated into two age groups: ≤ 40 years or > 40 years.

METHOD

Immunohistochemical detection of cyclin D1, cyclin D3 and Ki-67 was undertaken in 180 surgically resected vestibular schwannomas.

RESULTS

The proliferation index of vestibular schwannomas was statistically higher in the ≤ 40 years age group compared to that in the > 40 years age group (mean of 4.52 vs 3.27, respectively; p = 0.01). Overexpression of cyclin D1 and cyclin D3 was found in 68 per cent and 44 per cent of tumours, respectively.

CONCLUSION

There was an increased Ki-67 proliferation index in the younger age group that appears to correlate with clinical behaviour. Vestibular schwannomas in both age groups show increased expression of cyclin D1 and cyclin D3.

Schwannomas exhibit distinct size-dependent gene-expression patterns

AIM

Neurofibromatosis type 2 (NF2)-associated vestibular schwannomas have variable size at presentation which presents a unique challenge in NF2 patient management. Therefore, we investigated the molecular signature characteristic of the differences in size for improved individualized precise therapy.

MATERIALS & METHODS

RNA expression analysis was performed on 15 small and 27 large NF2-associated vestibular schwannoma tumors using a microarray analyzing over 47,000 transcripts.

RESULTS

A signature of 11 genes was found to be correlated with NF2 tumor size.

CONCLUSION

We have identified the genetic hallmark that differentiates large NF2-associated tumors from smaller tumors. This is the first time that these genes have been shown to be the hallmark for NF2 tumor size.

Using the neurofibromatosis tumor predisposition syndromes to understand normal nervous system development

Development is a tightly regulated process that involves stem cell self-renewal, differentiation, cell-to-cell communication, apoptosis, and blood vessel formation. These coordinated processes ensure that tissues maintain a size and architecture that is appropriate for normal tissue function. As such, tumors arise when cells acquire genetic mutations that allow them to escape the normal growth constraints. In this regard, the study of tumor predisposition syndromes affords a unique platform to better understand normal development and the process by which normal cells transform into cancers. Herein, we review the processes governing normal brain development, discuss how brain cancer represents a disruption of these normal processes, and highlight insights into both normal development and cancer made possible by the study of tumor predisposition syndromes.

The p53/mouse double minute 2 homolog complex deregulation in merlin-deficient tumours

Deficiency of the tumour suppressor merlin leads to the development of schwannomas, meningiomas and ependymomas occurring spontaneously or as a part of the hereditary disease Neurofibromatosis type 2 (NF2). Merlin loss is also found in a proportion of other cancers like mesothelioma, melanoma, breast cancer and glioblastoma. The tumour suppressor/transcription factor p53 regulates proliferation, survival and differentiation and its deficiency plays a role in the development of many tumours. 53 can be negatively regulated by FAK, PI3K/AKT and MDM2 and possibly positively regulated by merlin in different cell lines. In this study we investigated the role of p53 in merlin-deficient tumours. Using our in vitro model of primary human schwannoma cells we have previously demonstrated that FAK is overexpressed/activated and localises into the nucleus of schwannoma cells increasing proliferation. AKT is strongly activated via platelet-derived growth factor (PDGF) - and insulin-like growth factor 1 (IGF1) - receptors increasing survival. Here we investigated p53 regulation and its role in proliferation and survival of human primary schwannoma cells using western blotting, immunocytochemistry, immunohistochemistry and proliferation, survival and transcription factor assays. In human primary schwannoma cells p53 was found to be downregulated while MDM2 was upregulated leading to increased cell proliferation and survival. p53 is regulated by merlin involving FAK, AKT and MDM2. Merlin reintroduction into schwannoma cells increased p53 levels and activity, and treatment with Nutlin-3, a drug which increases p53 stability by disrupting the p53/MDM2 complex, decreased tumour growth and reduced cell survival. These findings are important to dissect the mechanisms responsible for the development of merlin-deficient tumours and to identify new therapeutic targets. We suggest that Nutlin-3, possibly in combination with FAK or PI3K inhibitors, can be employed as a novel treatment for schwannoma and other merlin-deficient tumours.