The NF2 tumor suppressor gene product, merlin, mediates contact inhibition of growth through interactions with CD44

Unleashing precision: A review of targeted approaches in pleural mesothelioma

This review delves into the intricate landscape of pleural mesothelioma (PM), emphasizing the need for nuanced therapeutic strategies. While platinum-based chemotherapy remains a cornerstone, the advent of immune checkpoint inhibitors (ICIs), notably through the Checkmate 743 trial, has reshaped treatment paradigms. Challenges persist due to patient heterogeneity and a lack of specific biomarkers. Targeting genotypic and phenotypic alterations emerges as a promising avenue, demanding precision oncology in this rare disease. CDKN2A loss, prevalent in PM, may respond to CDK4/6 inhibitors. Defects in MMR and HR suggest tailored approaches with ICI or PARP inhibitors, respectively. Ongoing trials explore novel inhibitors and promising targets like mesothelin. Implementing these strategies requires overcoming challenges in patient selection, combination therapies, biomarker identification, and cost considerations. Collaboration is crucial for transforming these insights into impactful clinical interventions, heralding the era of personalized and precision medicine for PM.

Evolving concepts in meningioma management in the era of genomics

Meningioma is the most common type of primary brain tumor. Surgical resection followed by surveillance is the first-line treatment for the majority of symptomatic meningiomas; however, recent advances in molecular sequencing, DNA methylation, proteomics, and single-cell sequencing provide insights into further characterizing this heterogeneous group of tumors with a wide range of prognoses. A subset of these tumors are highly aggressive and cause severe morbidity and mortality. Therefore, identifying those individuals with a poor prognosis and intervening are critical. This review aims to help readers interpret the molecular profiling of meningiomas to identify patients with worse prognoses and guide the management and strategy for surveillance.

NF2: An underestimated player in cancer metabolic reprogramming and tumor immunity

Neurofibromatosis type 2 (NF2) is a tumor suppressor gene implicated in various tumors, including mesothelioma, schwannomas, and meningioma. As a member of the ezrin, radixin, and moesin (ERM) family of proteins, merlin, which is encoded by NF2, regulates diverse cellular events and signalling pathways, such as the Hippo, mTOR, RAS, and cGAS-STING pathways. However, the biological role of NF2 in tumorigenesis has not been fully elucidated. Furthermore, cross-cancer mutations may exert distinct biological effects on tumorigenesis and treatment response. In addition to the functional inactivation of NF2, the codeficiency of other genes, such as cyclin-dependent kinase inhibitor 2A/B (CDKN2A/B), BRCA1-associated protein-1 (BAP1), and large tumor suppressor 2 (LATS2), results in unique tumor characteristics that should be considered in clinical treatment decisions. Notably, several recent studies have explored the metabolic and immunological features associated with NF2, offering potential insights into tumor biology and the development of innovative therapeutic strategies. In this review, we consolidate the current knowledge on NF2 and examine the potential connection between cancer metabolism and tumor immunity in merlin-deficient malignancies. This review may provide a deeper understanding of the biological roles of NF2 and guide possible therapeutic avenues.

G6PD and ACSL3 are synthetic lethal partners of NF2 in Schwann cells

Neurofibromatosis Type II (NFII) is a genetic condition caused by loss of the NF2 gene, resulting in activation of the YAP/TAZ pathway and recurrent Schwann cell tumors, as well as meningiomas and ependymomas. Unfortunately, few pharmacological options are available for NFII. Here, we undertake a genome-wide CRISPR/Cas9 screen to search for synthetic-lethal genes that, when inhibited, cause death of NF2 mutant Schwann cells but not NF2 wildtype cells. We identify ACSL3 and G6PD as two synthetic-lethal partners for NF2, both involved in lipid biogenesis and cellular redox. We find that NF2 mutant Schwann cells are more oxidized than control cells, in part due to reduced expression of genes involved in NADPH generation such as ME1. Since G6PD and ME1 redundantly generate cytosolic NADPH, lack of either one is compatible with cell viability, but not down-regulation of both. Since genetic deficiency for G6PD is tolerated in the human population, G6PD could be a good pharmacological target for NFII.

Gene Therapy for Neurofibromatosis Type 2-Related Schwannomatosis: Recent Progress, Challenges, and Future Directions

Neurofibromatosis type 2 (NF2)-related schwannomatosis is a rare autosomal dominant monogenic disorder caused by mutations in the NF2 gene. The hallmarks of NF2-related schwannomatosis are bilateral vestibular schwannomas (VS). The current treatment options for NF2-related schwannomatosis, such as observation with serial imaging, surgery, radiotherapy, and pharmacotherapies, have shown limited effectiveness and serious complications. Therefore, there is a critical demand for novel effective treatments. Gene therapy, which has made significant advancements in treating genetic diseases, holds promise for the treatment of this disease. This review covers the genetic pathogenesis of NF2-related schwannomatosis, the latest progress in gene therapy strategies, current challenges, and future directions of gene therapy for NF2-related schwannomatosis.

Natural products - Dawn of keloid treatment

Keloids are prevalent pathological scars, often leading to cosmetic deformities and hindering joint mobility.They cause discomfort, including burning and itching, while gradually expanding and potentially posing a risk of cancer.Developing effective drugs and treatments for keloids has been a persistent challenge in the medical field. Natural products are an important source of innovative drugs and a breakthrough for many knotty disease.Herein, keywords of "natural, plant, compound, extract" were combined with "keloid" and searched in PubMed and Google Scholar, respectively. A total of 32 natural products as well as 9 extracts possessing the potential for treating keloids were ultimately identified.Current research in this field faces a significant challenge due to the lack of suitable animal models, resulting in a predominant reliance on in vitro studies.In vivo and clinical studies are notably scarce as a result.Moreover, there is a notable deficiency in research focusing on the role of nutrients in keloid formation and treatment.The appropriate dosage form (oral, topical, injectable) is crucial for the development of natural product drugs. Finally, the conclusion was hereby made that natural products, when used as adjuncts to other treatments, hold significant potential in the management of keloids.By summarizing the natural products and elucidating their mechanisms in keloid treatment, the present study aims to stimulate further discoveries and research in drug development for effectively addressing this challenging condition.

The tumor suppressor NF2 modulates TEAD4 stability and activity in Hippo signaling via direct interaction

As an output effector of the Hippo signaling pathway, the TEAD transcription factor and co-activator YAP play crucial functions in promoting cell proliferation and organ size. The tumor suppressor NF2 has been shown to activate LATS1/2 kinases and interplay with the Hippo pathway to suppress the YAP-TEAD complex. However, whether and how NF2 could directly regulate TEAD remains unknown. We identified a direct link and physical interaction between NF2 and TEAD4. NF2 interacted with TEAD4 through its FERM domain and C-terminal tail and decreased the protein stability of TEAD4 independently of LATS1/2 and YAP. Furthermore, NF2 inhibited TEAD4 palmitoylation and induced the cytoplasmic translocation of TEAD4, resulting in ubiquitination and dysfunction of TEAD4. Moreover, the interaction with TEAD4 is required for NF2 function to suppress cell proliferation. These findings reveal an unanticipated role of NF2 as a binding partner and inhibitor of the transcription factor TEAD, shedding light on an alternative mechanism of how NF2 functions as a tumor suppressor through the Hippo signaling cascade.

Clinical and Genetic Correlation in Neurocristopathies: Bridging a Precision Medicine Gap

Neurocristopathies (NCPs) encompass a spectrum of disorders arising from issues during the formation and migration of neural crest cells (NCCs). NCCs undergo epithelial-mesenchymal transition (EMT) and upon key developmental gene deregulation, fetuses and neonates are prone to exhibit diverse manifestations depending on the affected area. These conditions are generally rare and often have a genetic basis, with many following Mendelian inheritance patterns, thus making them perfect candidates for precision medicine. Examples include cranial NCPs, like Goldenhar syndrome and Axenfeld-Rieger syndrome; cardiac-vagal NCPs, such as DiGeorge syndrome; truncal NCPs, like congenital central hypoventilation syndrome and Waardenburg syndrome; and enteric NCPs, such as Hirschsprung disease. Additionally, NCCs' migratory and differentiating nature makes their derivatives prone to tumors, with various cancer types categorized based on their NCC origin. Representative examples include schwannomas and pheochromocytomas. This review summarizes current knowledge of diseases arising from defects in NCCs' specification and highlights the potential of precision medicine to remedy a clinical phenotype by targeting the genotype, particularly important given that those affected are primarily infants and young children.

Merlin/NF2 regulates SLC7A11/xCT expression and cell viability under glucose deprivation at high cell density in glioblastoma cells

The cystine/glutamate transporter SLC7A11/xCT is highly expressed in many cancer cells and plays an important role in antioxidant activity by supplying cysteine for glutathione synthesis. Under glucose-depleted conditions, however, SLC7A11-mediated cystine uptake causes oxidative stress and cell death called disulfidptosis, a new form of cell death. We previously reported that high cell density (HD) promotes lysosomal degradation of SLC7A11 in glioblastoma cells, allowing them to survive under glucose-depleted conditions. In this study, we found that the neurofibromatosis type 2 gene, Merlin/NF2 is a key regulator of SLC7A11 in glioblastoma cells at HD. Deletion of Merlin increased SLC7A11 protein level and cystine uptake at HD, leading to promotion of cell death under glucose deprivation. Furthermore, HD significantly decreased SLC7A11 mRNA level, which was restored by Merlin deletion. This study suggests that Merlin suppresses glucose deprivation-induced cell death by downregulating SLC7A11 expression in glioblastoma cells at HD.

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.

Plasmodium falciparum exploits CD44 as a coreceptor for erythrocyte invasion

The malaria parasite Plasmodium falciparum invades and replicates asexually within human erythrocytes. CD44 expressed on erythrocytes was previously identified as an important host factor for P falciparum infection through a forward genetic screen, but little is known about its regulation or function in these cells, nor how it may be used by the parasite. We found that CD44 can be efficiently deleted from primary human hematopoietic stem cells using CRISPR/Cas9 genome editing, and that the efficiency of ex vivo erythropoiesis to enucleated cultured red blood cells (cRBCs) is not affected by lack of CD44. However, the rate of P falciparum invasion was reduced in CD44-null cRBCs relative to isogenic wild-type control cells, validating CD44 as an important host factor for this parasite. We identified 2 P falciparum invasion ligands as binding partners for CD44, erythrocyte binding antigen 175 (EBA-175) and EBA-140 and demonstrated that their ability to bind to human erythrocytes relies primarily on their canonical receptors, glycophorin A and glycophorin C, respectively. We further show that EBA-175 induces phosphorylation of erythrocyte cytoskeletal proteins in a CD44-dependent manner. Our findings support a model in which P falciparum exploits CD44 as a coreceptor during invasion of human erythrocytes, stimulating CD44-dependent phosphorylation of host cytoskeletal proteins that alter host cell deformability and facilitate parasite entry.

Hippo pathway in intestinal diseases: focusing on ferroptosis

The incidence of intestinal diseases, such as inflammatory bowel disease, gastric cancer, and colorectal cancer, has steadily increased over the past decades. The Hippo pathway is involved in cell proliferation, tissue and organ damage, energy metabolism, tumor formation, and other physiologic processes. Ferroptosis is a form of programmed cell death characterized by the accumulation of iron and lipid peroxides. The Hippo pathway and ferroptosis are associated with various intestinal diseases; however, the crosstalk between them is unclear. This review elaborates on the current research on the Hippo pathway and ferroptosis in the context of intestinal diseases. We summarized the connection between the Hippo pathway and ferroptosis to elucidate the underlying mechanism by which these pathways influence intestinal diseases. We speculate that a mutual regulatory mechanism exists between the Hippo pathway and ferroptosis and these two pathways interact in several ways to regulate intestinal diseases.

CD44 Intracellular Domain: A Long Tale of a Short Tail

CD44 is a single-chain transmembrane receptor that exists in multiple forms due to alternative mRNA splicing and post-translational modifications. CD44 is the main cell surface receptor of hyaluronan as well as other extracellular matrix molecules, cytokines, and growth factors that play important roles in physiological processes (such as hematopoiesis and lymphocyte homing) and the progression of various diseases, the predominant one being cancer. Currently, CD44 is an established cancer stem cell marker in several tumors, implying a central functional role in tumor biology. The present review aims to highlight the contribution of the CD44 short cytoplasmic tail, which is devoid of any enzymatic activity, in the extraordinary functional diversity of the receptor. The interactions of CD44 with cytoskeletal proteins through specific structural motifs within its intracellular domain drives cytoskeleton rearrangements and affects the distribution of organelles and transport of molecules. Moreover, the CD44 intracellular domain specifically interacts with various cytoplasmic effectors regulating cell-trafficking machinery, signal transduction pathways, the transcriptome, and vital cell metabolic pathways. Understanding the cell type- and context-specificity of these interactions may unravel the high complexity of CD44 functions and lead to novel improved therapeutic interventions.

YAP at the Crossroads of Biomechanics and Drug Resistance in Human Cancer

Biomechanical forces are of fundamental importance in biology, diseases, and medicine. Mechanobiology is an emerging interdisciplinary field that studies how biological mechanisms are regulated by biomechanical forces and how physical principles can be leveraged to innovate new therapeutic strategies. This article reviews state-of-the-art mechanobiology knowledge about the yes-associated protein (YAP), a key mechanosensitive protein, and its roles in the development of drug resistance in human cancer. Specifically, the article discusses three topics: how YAP is mechanically regulated in living cells; the molecular mechanobiology mechanisms by which YAP, along with other functional pathways, influences drug resistance of cancer cells (particularly lung cancer cells); and finally, how the mechanical regulation of YAP can influence drug resistance and vice versa. By integrating these topics, we present a unified framework that has the potential to bring theoretical insights into the design of novel mechanomedicines and advance next-generation cancer therapies to suppress tumor progression and metastasis.

Missense variant interaction scanning reveals a critical role of the FERM domain for tumor suppressor protein NF2 conformation and function

NF2 (moesin-ezrin-radixin-like [MERLIN] tumor suppressor) is frequently inactivated in cancer, where its NF2 tumor suppressor functionality is tightly coupled to protein conformation. How NF2 conformation is regulated and how NF2 conformation influences tumor suppressor activity is a largely open question. Here, we systematically characterized three NF2 conformation-dependent protein interactions utilizing deep mutational scanning interaction perturbation analyses. We identified two regions in NF2 with clustered mutations which affected conformation-dependent protein interactions. NF2 variants in the F2-F3 subdomain and the α3H helix region substantially modulated NF2 conformation and homomerization. Mutations in the F2-F3 subdomain altered proliferation in three cell lines and matched patterns of disease mutations in NF2 related-schwannomatosis. This study highlights the power of systematic mutational interaction perturbation analysis to identify missense variants impacting NF2 conformation and provides insight into NF2 tumor suppressor function.

Lipid kinase PIP5Kα contributes to Hippo pathway activation via interaction with Merlin and by mediating plasma membrane targeting of LATS1

BACKGROUND

The Hippo pathway plays a critical role in controlled cell proliferation. The tumor suppressor Merlin and large tumor suppressor kinase 1 (LATS1) mediate activation of Hippo pathway, consequently inhibiting the primary effectors, Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ). Phosphatidylinositol 4,5-bisphosphate (PIP2), a lipid present in the plasma membrane (PM), binds to and activates Merlin. Phosphatidylinositol 4-phosphate 5-kinase α (PIP5Kα) is an enzyme responsible for PIP2 production. However, the functional role of PIP5Kα in regulation of Merlin and LATS1 under Hippo signaling conditions remains unclear.

METHODS

PIP5Kα, Merlin, or LATS1 knockout or knockdown cells and transfected cells with them were used. LATS1, YAP, and TAZ activities were measured using biochemical methods and PIP2 levels were evaluated using cell imaging. Low/high cell density and serum starvation/stimulation conditions were tested. Colocalization of PIP5Kα and PIP2 with Merlin and LATS1, and their protein interactions were examined using transfection, confocal imaging, immunoprecipitation, western blotting, and/or pull-down experiments. Colony formation and adipocyte differentiation assays were performed.

RESULTS

We found that PIP5Kα induced LATS1 activation and YAP/TAZ inhibition in a kinase activity-dependent manner. Consistent with these findings, PIP5Kα suppressed cell proliferation and enhanced adipocyte differentiation of mesenchymal stem cells. Moreover, PIP5Kα protein stability and PIP2 levels were elevated at high cell density compared with those at low cell density, and both PIP2 and YAP phosphorylation levels initially declined, then recovered upon serum stimulation. Under these conditions, YAP/TAZ activity was aberrantly regulated by PIP5Kα deficiency. Mechanistically, either Merlin deficiency or LATS1 deficiency abrogated PIP5Kα-mediated YAP/TAZ inactivation. Additionally, the catalytic domain of PIP5Kα directly interacted with the band 4.1/ezrin/radixin/moesin domain of Merlin, and this interaction reinforced interaction of Merlin with LATS1. In accordance with these findings, PIP5Kα and PIP2 colocalized with Merlin and LATS1 in the PM. In PIP5Kα-deficient cells, Merlin colocalization with PIP2 was reduced, and LATS1 solubility increased.

CONCLUSIONS

Collectively, our results support that PIP5Kα serves as an activator of the Hippo pathway through interaction and colocalization with Merlin, which promotes PIP2-dependent Merlin activation and induces local recruitment of LATS1 to the PIP2-rich PM and its activation, thereby negatively regulating YAP/TAZ activity. Video Abstract.

The genetic landscape and possible therapeutics of neurofibromatosis type 2

Neurofibromatosis type 2 (NF2) is a genetic condition marked by the development of multiple benign tumors in the nervous system. The most common tumors associated with NF2 are bilateral vestibular schwannoma, meningioma, and ependymoma. The clinical manifestations of NF2 depend on the site of involvement. Vestibular schwannoma can present with hearing loss, dizziness, and tinnitus, while spinal tumor leads to debilitating pain, muscle weakness, or paresthesias. Clinical diagnosis of NF2 is based on the Manchester criteria, which have been updated in the last decade. NF2 is caused by loss-of-function mutations in the NF2 gene on chromosome 22, leading the merlin protein to malfunction. Over half of NF2 patients have de novo mutations, and half of this group are mosaic. NF2 can be managed by surgery, stereotactic radiosurgery, monoclonal antibody bevacizumab, and close observation. However, the nature of multiple tumors and the necessity of multiple surgeries over the lifetime, inoperable tumors like meningiomatosis with infiltration of the sinus or in the area of the lower cranial nerves, the complications caused by the operation, the malignancies induced by radiotherapy, and inefficiency of cytotoxic chemotherapy due to the benign nature of NF-related tumors have led a march toward exploring targeted therapies. Recent advances in genetics and molecular biology have allowed identifying and targeting of underlying pathways in the pathogenesis of NF2. In this review, we explain the clinicopathological characteristics of NF2, its genetic and molecular background, and the current knowledge and challenges of implementing genetics to develop efficient therapies.

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.

Deletion of Cd44 Inhibits Metastasis Formation of Liver Cancer in Nf2-Mutant Mice

Primary liver cancer is the third leading cause of cancer-related death worldwide. An increasing body of evidence suggests that the Hippo tumor suppressor pathway plays a critical role in restricting cell proliferation and determining cell fate during physiological and pathological processes in the liver. Merlin (Moesin-Ezrin-Radixin-like protein) encoded by the NF2 (neurofibromatosis type 2) gene is an upstream regulator of the Hippo signaling pathway. Targeting of Merlin to the plasma membrane seems to be crucial for its major tumor-suppressive functions; this is facilitated by interactions with membrane-associated proteins, including CD44 (cluster of differentiation 44). Mutations within the CD44-binding domain of Merlin have been reported in many human cancers. This study evaluated the relative contribution of CD44- and Merlin-dependent processes to the development and progression of liver tumors. To this end, mice with a liver-specific deletion of the Nf2 gene were crossed with Cd44-knockout mice and subjected to extensive histological, biochemical and molecular analyses. In addition, cells were isolated from mutant livers and analyzed by in vitro assays. Deletion of Nf2 in the liver led to substantial liver enlargement and generation of hepatocellular carcinomas (HCCs), intrahepatic cholangiocarcinomas (iCCAs), as well as mixed hepatocellular cholangiocarcinomas. Whilst deletion of Cd44 had no influence on liver size or primary liver tumor development, it significantly inhibited metastasis formation in Nf2-mutant mice. CD44 upregulates expression of integrin β2 and promotes transendothelial migration of liver cancer cells, which may facilitate metastatic spreading. Overall, our results suggest that CD44 may be a promising target for intervening with metastatic spreading of liver cancer.

Plasmodium falciparum exploits CD44 as a co-receptor for erythrocyte invasion

The malaria parasite Plasmodium falciparum invades and replicates asexually within human erythrocytes. CD44 expressed on erythrocytes was previously identified as an important host factor for P. falciparum infection through a forward genetic screen, but little is known about its regulation or function in these cells, nor how it may be utilized by the parasite. We found that CD44 can be efficiently deleted from primary human hematopoietic stem cells using CRISPR/Cas9 genome editing, and that the efficiency of ex-vivo erythropoiesis to enucleated cultured red blood cells (cRBCs) is not impacted by lack of CD44. However, the rate of P. falciparum invasion was substantially reduced in CD44-null cRBCs relative to isogenic wild-type (WT) control cells, validating CD44 as an important host factor for this parasite. We identified two P. falciparum invasion ligands as binding partners for CD44, Erythrocyte Binding Antigen-175 (EBA-175) and EBA-140, and demonstrated that their ability to bind to human erythrocytes relies primarily on their canonical receptors-glycophorin A and glycophorin C, respectively. We further show that EBA-175 induces phosphorylation of erythrocyte cytoskeletal proteins in a CD44-dependent manner. Our findings support a model where P. falciparum exploits CD44 as a co-receptor during invasion of human erythrocytes, stimulating CD44-dependent phosphorylation of host cytoskeletal proteins that alter host cell deformability and facilitate parasite entry.

YAP/TAZ activation predicts clinical outcomes in mesothelioma and is conserved in in vitro model of driver mutations

The Hippo signalling pathway is dysregulated across a wide range of cancer types and, although driver mutations that directly affect the core Hippo components are rare, a handful is found within pleural mesothelioma (PM). PM is a deadly disease of the lining of the lung caused by asbestos exposure. By pooling the largest-scale clinical datasets publicly available, we here interrogate associations between the most prevalent driver mutations within PM and Hippo pathway disruption in patients, while assessing correlations with a variety of clinical markers. This analysis reveals a consistent worse outcome in patients exhibiting transcriptional markers of YAP/TAZ activation, pointing to the potential of leveraging Hippo pathway transcriptional activation status as a metric by which patients may be meaningfully stratified. Preclinical models recapitulating disease are transformative in order to develop new therapeutic strategies. We here establish an isogenic cell-line model of PM, which represents the most frequently mutated genes and which faithfully recapitulates the molecular features of clinical PM. This preclinical model is developed to probe the molecular basis by which the Hippo pathway and key driver mutations affect cancer initiation and progression. Implementing this approach, we reveal the role of NF2 as a mechanosensory component of the Hippo pathway in mesothelial cells. Cellular NF2 loss upon physiological stiffnesses analogous to the tumour niche drive YAP/TAZ-dependent anchorage-independent growth. Consequently, the development and characterisation of this cellular model provide a unique resource to obtain molecular insights into the disease and progress new drug discovery programs together with future stratification of PM patients.

Merlin tumor suppressor function is regulated by PIP2-mediated dimerization

Neurofibromatosis Type 2 is an inherited disease characterized by Schwann cell tumors of cranial and peripheral nerves. The NF2 gene encodes Merlin, a member of the ERM family consisting of an N-terminal FERM domain, a central α-helical region, and a C-terminal domain. Changes in the intermolecular FERM-CTD interaction allow Merlin to transition between an open, FERM accessible conformation and a closed, FERM-inaccessible conformation, modulating Merlin activity. Merlin has been shown to dimerize, but the regulation and function Merlin dimerization is not clear. We used a nanobody based binding assay to show that Merlin dimerizes via a FERM-FERM interaction, orientated with each C-terminus close to each other. Patient derived and structural mutants show that dimerization controls interactions with specific binding partners, including HIPPO pathway components, and correlates with tumor suppressor activity. Gel filtration experiments showed that dimerization occurs after a PIP2 mediated transition from closed to open conformation monomers. This process requires the first 18 amino acids of the FERM domain and is inhibited by phosphorylation at serine 518. The discovery that active, open conformation Merlin is a dimer represents a new paradigm for Merlin function with implications for the development of therapies designed to compensate for Merlin loss.

Tumor Biology and Microenvironment of Vestibular Schwannoma-Relation to Tumor Growth and Hearing Loss

Vestibular schwannoma is the most common benign neoplasm of the cerebellopontine angle. It arises from Schwann cells of the vestibular nerve. The first symptoms of vestibular schwannoma include hearing loss, tinnitus, and vestibular symptoms. In the event of further growth, cerebellar and brainstem symptoms, along with palsy of the adjacent cranial nerves, may be present. Although hearing impairment is present in 95% of patients diagnosed with vestibular schwannoma, most tumors do not progress in size or have low growth rates. However, the clinical picture has unpredictable dynamics, and there are currently no reliable predictors of the tumor's behavior. The etiology of the hearing loss in patients with vestibular schwannoma is unclear. Given the presence of hearing loss in patients with non-growing tumors, a purely mechanistic approach is insufficient. A possible explanation for this may be that the function of the auditory system may be affected by the paracrine activity of the tumor. Moreover, initiation of the development and growth progression of vestibular schwannomas is not yet clearly understood. Biallelic loss of the NF2 gene does not explain the occurrence in all patients; therefore, detection of gene expression abnormalities in cases of progressive growth is required. As in other areas of cancer research, the tumor microenvironment is coming to the forefront, also in vestibular schwannomas. In the paradigm of the tumor microenvironment, the stroma of the tumor actively influences the tumor's behavior. However, research in the area of vestibular schwannomas is at an early stage. Thus, knowledge of the molecular mechanisms of tumorigenesis and interactions between cells present within the tumor is crucial for the diagnosis, prediction of tumor behavior, and targeted therapeutic interventions. In this review, we provide an overview of the current knowledge in the field of molecular biology and tumor microenvironment of vestibular schwannomas, as well as their relationship to tumor growth and hearing loss.

Hyaluronic Acid as a Modern Approach in Anticancer Therapy-Review

Hyaluronic acid (HA) is a linear polysaccharide and crucial component of the extracellular matrix (ECM), maintaining tissue hydration and tension. Moreover, HA contributes to embryonic development, healing, inflammation, and cancerogenesis. This review summarizes new research on the metabolism and interactions of HA with its binding proteins, known as hyaladherins (CD44, RHAMM), revealing the molecular basis for its distinct biological function in the development of cancer. The presence of HA on the surface of tumor cells is a sign of an adverse prognosis. The involvement of HA in malignancy has been extensively investigated using cancer-free naked mole rats as a model. The HA metabolic components are examined for their potential impact on promoting or inhibiting tumor formation, proliferation, invasion, and metastatic spread. High molecular weight HA is associated with homeostasis and protective action due to its ability to preserve tissue integrity. In contrast, low molecular weight HA indicates a pathological condition in the tissue and plays a role in pro-oncogenic activity. A systematic approach might uncover processes related to cancer growth, establish novel prognostic indicators, and identify potential targets for treatment action.

Genetic Alterations and Deregulation of Hippo Pathway as a Pathogenetic Mechanism in Bone and Soft Tissue Sarcoma

The Hippo pathway is an evolutionarily conserved modulator of developmental biology with a key role in tissue and organ size regulation under homeostatic conditions. Like other signaling pathways with a significant role in embryonic development, the deregulation of Hippo signaling contributes to oncogenesis. Central to the Hippo pathway is a conserved cascade of adaptor proteins and inhibitory kinases that converge and regulate the activity of the oncoproteins YAP and TAZ, the final transducers of the pathway. Elevated levels and aberrant activation of YAP and TAZ have been described in many cancers. Though most of the studies describe their pervasive activation in epithelial neoplasms, there is increasing evidence pointing out its relevance in mesenchymal malignancies as well. Interestingly, somatic or germline mutations in genes of the Hippo pathway are scarce compared to other signaling pathways that are frequently disrupted in cancer. However, in the case of sarcomas, several examples of genetic alteration of Hippo members, including gene fusions, have been described during the last few years. Here, we review the current knowledge of Hippo pathway implication in sarcoma, describing mechanistic hints recently reported in specific histological entities and how these alterations represent an opportunity for targeted therapy in this heterogeneous group of neoplasm.

Antisense oligonucleotides targeting exon 11 are able to partially rescue the NF2-related schwannomatosis phenotype in vitro

NF2-related schwannomatosis (NF2-related SWN) is an autosomal dominant condition caused by loss of function variants in the NF2 gene, which codes for the protein Merlin and is characterized by the development of multiple tumors of the nervous system. The clinical presentation of the disease is variable and related to the type of the inherited germline variant. Here, we tested if phosphorodiamidate morpholino oligomers (PMOs) could be used to correct the splice signaling caused by variants at ±13 within the intron-exon boundary region and showed that the PMOs designed for these variants do not constitute a therapeutic approach. Furthermore, we evaluated the use of PMOs to decrease the severity of the effects of NF2 truncating variants with the aim of generating milder hypomorphic isoforms in vitro through the induction of the in-frame deletion of the exon-carrying variant. We were able to specifically induce the skipping of exons 4, 8, and 11 maintaining the NF2 gene reading frame at cDNA level. Only the skipping of exon 11 produced a hypomorphic Merlin (Merlin-e11), which is able to partially rescue the observed phenotype in primary fibroblast cultures from NF2-related SWN patients, being encouraging for the treatment of patients harboring truncating variants located in exon 11.

Carcinogenesis resistance in the longest-lived rodent, the naked mole-rat

Certain mammalian species are resistant to cancer, and a better understanding of how this cancer resistance arises could provide valuable insights for basic cancer research. Recent technological innovations in molecular biology have allowed the study of cancer-resistant mammals, despite the fact that they are not the classical model animals, which are easily studied using genetic approaches. Naked mole-rats (NMRs; Heterocephalus glaber) are the longest-lived rodent, with a maximum lifespan of more than 37 years, and almost never show spontaneous carcinogenesis. NMRs are currently attracting much attention from aging and cancer researchers, and published studies on NMR have continued to increase over the past decade. Cancer development occurs via multiple steps and involves many biological processes. Recent research on the NMR as a model for cancer resistance suggests that they possess various unique carcinogenesis-resistance mechanisms, including efficient DNA repair pathways, cell-autonomous resistance to transformation, and dampened inflammatory response. Here, we summarize the molecular mechanisms of carcinogenesis resistance in NMR, which have been uncovered over the past two decades, and discuss future perspectives.

CD44 Contributes to the Regulation of MDR1 Protein and Doxorubicin Chemoresistance in Osteosarcoma

Osteosarcoma is the most common type of pediatric bone tumor. Despite great advances in chemotherapy during the past decades, the survival rates of osteosarcoma patients remain unsatisfactory. Drug resistance is one of the main reasons, leading to treatment failure and poor prognosis. Previous reports correlated expression of cluster of differentiation 44 (CD44) with drug resistance and poor survival of osteosarcoma patients, however the underlying mechanisms are poorly defined. Here, we investigated the role of CD44 in the regulation of drug chemoresistance, using osteosarcoma cells isolated from mice carrying a mutation of the tumor suppressor neurofibromatosis type 2 (Nf2) gene. CD44 expression was knocked-down in the cells using CRISPR/Cas9 approach. Subsequently, CD44 isoforms and mutants were re-introduced to investigate CD44-dependent processes. Sensitivity to doxorubicin was analyzed in the osteosarcoma cells with modified CD44 expression by immunoblot, colony formation- and WST-1 assay. To dissect the molecular alterations induced by deletion of Cd44, RNA sequencing was performed on Cd44-positive and Cd44-negative primary osteosarcoma tissues isolated from Nf2-mutant mice. Subsequently, expression of candidate genes was evaluated by quantitative reverse transcription PCR (qRT-PCR). Our results indicate that CD44 increases the resistance of osteosarcoma cells to doxorubicin by up-regulating the levels of multidrug resistance (MDR) 1 protein expression, and suggest the role of proteolytically released CD44 intracellular domain, and hyaluronan interactions in this process. Moreover, high throughput sequencing analysis identified differential regulation of several apoptosis-related genes in Cd44-positive and -negative primary osteosarcomas, including p53 apoptosis effector related to PMP-22 (Perp). Deletion of Cd44 in osteosarcoma cells led to doxorubicin-dependent p53 activation and a profound increase in Perp mRNA expression. Overall, our results suggest that CD44 might be an important regulator of drug resistance and suggest that targeting CD44 can sensitize osteosarcoma to standard chemotherapy.

Molecular Alterations in Malignant Pleural Mesothelioma: A Hope for Effective Treatment by Targeting YAP

Malignant pleural mesothelioma is a rare and aggressive neoplasm, which has primarily been attributed to the exposure to asbestos fibers (83% of cases); yet, despite a ban of using asbestos in many countries, the incidence of malignant pleural mesothelioma failed to decline worldwide. While little progress has been made in malignant pleural mesothelioma diagnosis, bevacizumab at first, then followed by double immunotherapy (nivolumab plus ipilumumab), were all shown to improve survival in large phase III randomized trials. The morphological analysis of the histological subtyping remains the primary indicator for therapeutic decision making at an advanced disease stage, while a platinum-based chemotherapy regimen combined with pemetrexed, either with or without bevacizumab, is still the main treatment option. Consequently, malignant pleural mesothelioma still represents a significant health concern owing to poor median survival (12-18 months). Given this context, both diagnosis and therapy improvements require better knowledge of the molecular mechanisms underlying malignant pleural mesothelioma's carcinogenesis and progression. Hence, the Hippo pathway in malignant pleural mesothelioma initiation and progression has recently received increasing attention, as the aberrant expression of its core components may be closely related to patient prognosis. The purpose of this review was to provide a critical analysis of our current knowledge on these topics, the main focus being on the available evidence concerning the role of each Hippo pathway's member as a promising biomarker, enabling detection of the disease at earlier stages and thus improving prognosis.

Self-Sustained Regulation or Self-Perpetuating Dysregulation: ROS-dependent HIF-YAP-Notch Signaling as a Double-Edged Sword on Stem Cell Physiology and Tumorigenesis

Organ development, homeostasis, and repair often rely on bidirectional, self-organized cell-niche interactions, through which cells select cell fate, such as stem cell self-renewal and differentiation. The niche contains multiplexed chemical and mechanical factors. How cells interpret niche structural information such as the 3D topology of organs and integrate with multiplexed mechano-chemical signals is an open and active research field. Among all the niche factors, reactive oxygen species (ROS) have recently gained growing interest. Once considered harmful, ROS are now recognized as an important niche factor in the regulation of tissue mechanics and topology through, for example, the HIF-YAP-Notch signaling pathways. These pathways are not only involved in the regulation of stem cell physiology but also associated with inflammation, neurological disorder, aging, tumorigenesis, and the regulation of the immune checkpoint molecule PD-L1. Positive feedback circuits have been identified in the interplay of ROS and HIF-YAP-Notch signaling, leading to the possibility that under aberrant conditions, self-organized, ROS-dependent physiological regulations can be switched to self-perpetuating dysregulation, making ROS a double-edged sword at the interface of stem cell physiology and tumorigenesis. In this review, we discuss the recent findings on how ROS and tissue mechanics affect YAP-HIF-Notch-PD-L1 signaling, hoping that the knowledge can be used to design strategies for stem cell-based and ROS-targeting therapy and tissue engineering.

Hyaluronan network: a driving force in cancer progression

Hyaluronan is one of the most abundant macromolecules of the extracellular matrix and regulates several physiological cell and tissue properties. However, hyaluronan has been shown to accumulate together with its receptors in various cancers. In tumors, accumulation of hyaluronan system components (hyaluronan synthesizing/degrading enzymes and interacting proteins) associates with poor outcomes of the patients. In this article, we review the main roles of hyaluronan in normal physiology and cancer, and further discuss the targeting of hyaluronan system as an applicable therapeutic strategy.

Inactivation of p21-Activated Kinase 2 (Pak2) Inhibits the Development of Nf2-Deficient Tumors by Restricting Downstream Hedgehog and Wnt Signaling

Because loss of the NF2 tumor suppressor gene results in p21-activated kinase (Pak) activation, PAK inhibitors hold promise for the treatment of NF2-deficient tumors. To test this possibility, we asked if loss of Pak2, a highly expressed group I PAK member, affects the development of malignant mesothelioma in Nf2;Cdkn2a-deficient (NC) mice and the growth properties of NC mesothelioma cells in culture. In vivo, deletion of Pak2 resulted in a markedly decreased incidence and delayed onset of both pleural and peritoneal malignant mesotheliomas in NC mice. In vitro, Pak2 deletion decreased malignant mesothelioma cell viability, migration, clonogenicity, and spheroid formation. RNA-sequencing analysis demonstrated downregulated expression of Hedgehog and Wnt pathway genes in NC;Pak2-/- mesothelioma cells versus NC;Pak2+/+ mesothelioma cells. Targeting of the Hedgehog signaling component Gli1 or its target gene Myc inhibited cell viability and spheroid formation in NC;P+/+ mesothelioma cells. Kinome profiling uncovered kinase changes indicative of EMT in NC;Pak2-/- mesothelioma cells, suggesting that Pak2-deficient malignant mesotheliomas can adapt by reprogramming their kinome in the absence of Pak activity. The identification of such compensatory pathways offers opportunities for rational combination therapies to circumvent resistance to anti-PAK drugs.

IMPLICATIONS

We provide evidence supporting a role for PAK inhibitors in treating NF2-deficient tumors. NF2-deficient tumors lacking Pak2 eventually adapt by kinome reprogramming, presenting opportunities for combination therapies to bypass anti-PAK drug resistance.

Lung Hyaluronasome: Involvement of Low Molecular Weight Ha (Lmw-Ha) in Innate Immunity

Hyaluronic acid (HA) is a major component of the extracellular matrix. It is synthesized by hyaluronan synthases (HAS) into high-molecular-weight chains (HMW-HA) that exhibit anti-inflammatory and immunomodulatory functions. In damaged, infected, and/or inflamed tissues, HMW-HA are degraded by hyaluronidases (HYAL) or reactive oxygen species (ROS) to give rise to low-molecular-weight HAs (LMW-HAs) that are potent pro-inflammatory molecules. Therefore, the size of HA regulates the balance of anti- or pro-inflammatory functions. The activities of HA depend also on its interactions with hyaladherins. HA synthesis, degradation, and activities through HA/receptors interactions define the hyaluronasome. In this review, a short overview of the role of high and low-molecular-weight HA polymers in the lungs is provided. The involvement of LMW-HA in pulmonary innate immunity via the activation of neutrophils, macrophages, dendritic cells, and epithelial cells is described to highlight LMW-HA as a therapeutic target in inflammatory respiratory diseases. Finally, the possibilities to counter LMW-HA’s deleterious effects in the lungs are discussed.

mTOR Signaling and Potential Therapeutic Targeting in Meningioma

Meningiomas are the most frequent primary tumors arising in the central nervous system. They typically follow a benign course, with an excellent prognosis for grade I lesions through surgical intervention. Although radiotherapy is a good option for recurrent, progressive, or inoperable tumors, alternative treatments are very limited. mTOR is a protein complex with increasing therapeutical potential as a target in cancer. The current understanding of the mTOR pathway heavily involves it in the development of meningioma. Its activation is strongly dependent on PI3K/Akt signaling and the merlin protein. Both factors are commonly defective in meningioma cells, which indicates their likely function in tumor growth. Furthermore, regarding molecular tumorigenesis, the kinase activity of the mTORC1 complex inhibits many components of the autophagosome, such as the ULK1 or Beclin complexes. mTOR contributes to redox homeostasis, a vital component of neoplasia. Recent clinical trials have investigated novel chemotherapeutic agents for mTOR inhibition, showing promising results in resistant or recurrent meningiomas.

A Ponceau S Staining-Based Dot Blot Assay for Rapid Protein Quantification of Biological Samples

Despite the availability of a wide range of commercial kits, protein quantification is often unreliable, especially for tissue-derived samples, leading to uneven loading in subsequent experiments. Here we show that the widely used Bicinchoninic Acid (BCA) assay tends to underestimate protein concentrations of tissue samples. We present a Ponceau S staining-based dot-blot assay as an alternative for protein quantification. This method is simple, rapid, more reliable than the BCA assay, compatible with biological samples lysed in RIPA or 2x SDS gel-loading buffer, and also inexpensive.

p21-Activated kinase 1 (PAK1) in aging and longevity: An overview

The p21-activated kinases (PAKs) belong to serine/threonine kinases family, regulated by ∼21 kDa small signaling G proteins RAC1 and CDC42. The mammalian PAK family comprises six members (PAK1-6) that are classified into two groups (I and II) based on their domain architecture and regulatory mechanisms. PAKs are implicated in a wide range of cellular functions. PAK1 has recently attracted increasing attention owing to its involvement in oncogenesis, tumor progression, and metastasis as well as several life-limiting diseases and pathological conditions. In Caenorhabditis elegans, PAK1 functions limit the lifespan under basal conditions by inhibiting forkhead transcription factor DAF-16. Interestingly, PAK depletion extended longevity and attenuated the onset of age-related phenotypes in a premature-aging mouse model and delayed senescence in mammalian fibroblasts. These observations implicate PAKs as not only oncogenic but also aging kinases. Therefore, PAK-targeting genetic and/or pharmacological interventions, particularly PAK1-targeting, could be a viable strategy for developing cancer therapies with relatively no side effects and promoting healthy longevity. This review describes PAK family proteins, their biological functions, and their role in regulating aging and longevity using C. elegans. Moreover, we discuss the effect of small-molecule PAK1 inhibitors on the lifespan and healthspan of C. elegans.

AMOTL2 mono-ubiquitination by WWP1 promotes contact inhibition by facilitating LATS activation

This work reveals a novel function of WWP1 E3 ligase in the mono-ubiquitination of AMOTL2, which enables the binding and activation of LATS kinases upon contact inhibition.

Contact inhibition is a key cellular phenomenon that prevents cells from hyper-proliferating upon reaching confluence. Although not fully characterized, a critical driver of this process is the Hippo signaling pathway, whose downstream effector yes-associated protein plays pivotal roles in cell growth and differentiation. Here, we provide evidence that the E3 ligase WWP1 (WW-domain containing protein 1) mono-ubiquitinates AMOTL2 (angiomotin-like 2) at K347 and K408. Mono-ubiquitinated AMOTL2, in turn, interacts with the kinase LATS2, which facilitates recruitment of the upstream Hippo pathway component SAV1 and ultimately promotes yes-associated protein phosphorylation and subsequent cytoplasmic sequestration and/or degradation. Furthermore, contact inhibition induced by high cell density promoted the localization and stabilization of WWP1 at cell junctions, where it interacted with Crumbs polarity proteins. Notably, the Crumbs complex was functionally important for AMOTL2 mono-ubiquitination and LATS activation under high cell density conditions. These findings delineate a functionally important molecular mechanism in which AMOTL2 mono-ubiquitination by WWP1 at cell junctions and LATS activation are tightly coupled to upstream cell density cues.

Conformational flexibility determines the Nf2/merlin tumor suppressor functions

The Neurofibromatosis type 2 gene encodes the Nf2/merlin tumor suppressor protein that is responsible for the regulation of cell proliferation. Once activated, Nf2/merlin modulates adhesive signaling pathways and thereby inhibits cell growth. Nf2/merlin controls oncogenic gene expression by modulating the Hippo pathway. By responding to several physical and biochemical stimuli, Hippo signaling determines contact inhibition of proliferation as well as organ size. The large tumor suppressor (LATS) serine/threonine-protein kinase is the key enzyme in the highly conserved kinase cascade that negatively regulates the activity and localization of the transcriptional coactivators Yes-associated protein (YAP) and its paralogue transcriptional coactivator with PDZ-binding motif (TAZ). Nf2/merlin belongs to the band 4.1, ezrin, radixin, moesin (FERM) gene family that links the actin cytoskeleton to adherens junctions, remodels adherens junctions during epithelial morphogenesis and maintains organized apical surfaces on the plasma cell membrane. Nf2/merlin and ERM proteins have a globular N-terminal cloverleaf head domain, the FERM domain, that binds to the plasma membrane, a central α-helical domain, and a tail domain that binds to its head domain. Here we present the high-resolution crystal structure of Nf2/merlin bound to LATS1 which shows that LATS1 binding to Nf2/merlin displaces the Nf2/merlin tail domain and causes an allosteric shift in the Nf2/merlin α-helix that extends from its FERM domain. This is consistent with the fact that full-length Nf2/merlin binds LATS1 ~10-fold weaker compared to LATS1 binding to the Nf2/merlin-PIP₂ complex. Our data increase our understanding of Nf2/merlin biology by providing mechanistic insights into the Hippo pathway that are relevant to several diseases in particular oncogenic features that are associated with cancers.

Biological Treatments of Neurofibromatosis Type 2 and Other Skull Base Disorders

Studies of genomic alterations that occur in skull base tumors have provided information regarding biological aberrations that are necessary for the growth and maintenance of these tumors. This has led to the development and initiation of clinical trials incorporating biological treatments for many skull base tumors. The exciting developments of molecularly targeted therapy for the treatment of skull base tumors may provide noninvasive therapeutic options for patients that can be used either alone or in combination with surgery and/or radiation therapy. Future analysis and continued scientific discovery of treatments for skull base tumors can lead to improved outcomes in patients.

The CD44/COL17A1 pathway promotes the formation of multilayered, transformed epithelia

At the early stage of cancer development, oncogenic mutations often cause multilayered epithelial structures. However, the underlying molecular mechanism still remains enigmatic. By performing a series of screenings targeting plasma membrane proteins, we have found that collagen XVII (COL17A1) and CD44 accumulate in RasV12-, Src-, or ErbB2-transformed epithelial cells. In addition, the expression of COL17A1 and CD44 is also regulated by cell density and upon apical cell extrusion. We further demonstrate that the expression of COL17A1 and CD44 is profoundly upregulated at the upper layers of multilayered, transformed epithelia in vitro and in vivo. The accumulated COL17A1 and CD44 suppress mitochondrial membrane potential and reactive oxygen species (ROS) production. The diminished intracellular ROS level then promotes resistance against ferroptosis-mediated cell death upon cell extrusion, thereby positively regulating the formation of multilayered structures. To further understand the functional role of COL17A1, we performed comprehensive metabolome analysis and compared intracellular metabolites between RasV12 and COL17A1-knockout RasV12 cells. The data imply that COL17A1 regulates the metabolic pathway from the GABA shunt to mitochondrial complex I through succinate, thereby suppressing the ROS production. Moreover, we demonstrate that CD44 regulates membrane accumulation of COL17A1 in multilayered structures. These results suggest that CD44 and COL17A1 are crucial regulators for the clonal expansion of transformed cells within multilayered epithelia, thus being potential targets for early diagnosis and preventive treatment for precancerous lesions.

Crispr/Cas-based modeling of NF2 loss in meningioma cells

BACKGROUND

Alterations of the neurofibromatosis type 2 gene (NF2) occur in more than fifty percent of sporadic meningiomas. Meningiomas develop frequently in the setting of the hereditary tumor syndrome NF2. Investigation of potential drug-based treatment options has been limited by the lack of appropriate in vitro and in vivo models.

NEW METHODS

Using Crispr/Cas gene editing, of the malignant meningioma cell line IOMM-Lee, we generated a pair of cell clones characterized by either stable knockout of NF2 and loss of the protein product merlin or retained merlin protein (transfected control without gRNA).

RESULTS

IOMM-Lee cells lacking NF2 showed reduced apoptosis and formed bigger colonies compared to control IOMM-Lee cells. Treatment of non-transfected IOMM-Lee cells with the focal adhesion kinase (FAK) inhibitor GSK2256098 resulted in reduced colony sizes. Orthotopic mouse xenografts showed the formation of convexity tumors typical for meningiomas with NF2-depleted and control cells.

COMPARISON WITH EXISTING METHODS

No orthotopic meningioma models with genetically-engineered cell pairs are available so far.

CONCLUSION

Our model based on Crispr/Cas-based gene editing provides paired meningioma cells suitable to study functional consequences and therapeutic accessibility of NF2/merlin loss.

A microtubule-LUZP1 association around tight junction promotes epithelial cell apical constriction

Apical constriction is critical for epithelial morphogenesis, including neural tube formation. Vertebrate apical constriction is induced by di-phosphorylated myosin light chain (ppMLC)-driven contraction of actomyosin-based circumferential rings (CRs), also known as perijunctional actomyosin rings, around apical junctional complexes (AJCs), mainly consisting of tight junctions (TJs) and adherens junctions (AJs). Here, we revealed a ppMLC-triggered system at TJ-associated CRs for vertebrate apical constriction involving microtubules, LUZP1, and myosin phosphatase. We first identified LUZP1 via unbiased screening of microtubule-associated proteins in the AJC-enriched fraction. In cultured epithelial cells, LUZP1 was found localized at TJ-, but not at AJ-, associated CRs, and LUZP1 knockout resulted in apical constriction defects with a significant reduction in ppMLC levels within CRs. A series of assays revealed that ppMLC promotes the recruitment of LUZP1 to TJ-associated CRs, where LUZP1 spatiotemporally inhibits myosin phosphatase in a microtubule-facilitated manner. Our results uncovered a hitherto unknown microtubule-LUZP1 association at TJ-associated CRs that inhibits myosin phosphatase, contributing significantly to the understanding of vertebrate apical constriction.

PLPP/CIN-mediated NF2-serine 10 dephosphorylation regulates F-actin stability and Mdm2 degradation in an activity-dependent manner

Neurofibromin 2 (NF2, also known as merlin) is a tumor suppressor protein encoded by the neurofibromatosis type 2 gene NF2. NF2 is also an actin-binding protein that functions in an intrinsic signaling network critical for actin dynamics. Although protein kinase A (PKA)-mediated NF2-serin (S) 10 phosphorylation stabilizes filamentous actin (F-actin), the underlying mechanisms of NF2-S10 dephosphorylation and the role of NF2 in seizures have been elusive. Here, we demonstrate that pyridoxal-5′-phosphate phosphatase/chronophin (PLPP/CIN) dephosphorylated NF2-S10 site as well as cofilin-S3 site. In addition, NF2-S10 dephosphorylation reversely regulated murine double minute-2 (Mdm2) and postsynaptic density 95 (PSD95) degradations in an activity-dependent manner, which increased seizure intensity and its progression in response to kainic acid (KA). In addition, NF2 knockdown facilitated seizure intensity and its progress through F-actin instability independent of cofilin-mediated actin dynamics. Therefore, we suggest that PLPP/CIN may be a potential therapeutic target for epileptogenesis and NF2-associated diseases.

Developmental role of hyaluronic acid and its application in salivary gland tissue engineering

Dry mouth, or xerostomia, caused by salivary gland dysfunction significantly impacts oral/systemic health and quality of life. Although in vitro-generated artificial salivary glands have been considered as the fundamental solution, its structural complexity is difficult to reproduce using current biomaterials. Therefore, understanding and recapitulating the roles of biomacromolecules in salivary gland organogenesis is needed to solve these problems. Hyaluronic acid (HA) is a macromolecule abundant during salivary gland organogenesis, but its role remains unknown. Here, we verify the effects of HA on salivary gland organogenesis and artificial organ germ formation in solubilized and substrate-immobilized forms. In embryonic submandibular glands (eSMG), we found dense HA layers encapsulating proliferative c-Kit+ progenitor cells that were expressing CD44, an HA receptor. The blockage of HA synthesis, or degradation of HA, impaired eSMG growth by ablating the c-Kit+ progenitor cell population. We also found that high-molecular-weight (HMW) HA has a significant role in eSMG growth. Based on these findings, we discovered that HA is also crucial for in vitro formation of salivary gland organ germs, one of the most promising candidates for salivary gland tissue regeneration. We significantly enhanced salivary gland organ germ formation by supplementing HMW HA in solution; this effect was further increased when the HMW HA was immobilized on the substrate by polydopamine/HA co-immobilization. Our study suggests that the current use of HA in salivary gland tissue engineering can be further optimized.

Role of CD44 in breast cancer

Breast cancer (BC) is among the most prevalent type of malignancy affecting females worldwide. BC is classified into different types according to the status of the expression of receptors such as estrogen receptor (ER), human epidermal growth factor receptor 2 (HER2), and progesterone receptor (PR). Androgen receptor (AR) appears to be a promising therapeutic target of BC. Binding of 5α-dihydrotestosterone (DHT) to AR controls the expression of microRNA (miRNA) molecules in BC, consequently, affecting protein expression. One of these proteins is the transmembrane glycoprotein cluster of differentiation 44 (CD44). Remarkably, CD44 is a common marker of cancer stem cells in BC. It functions as a co-receptor for a broad diversity of extracellular matrix ligands. Several ligands, primarily hyaluronic acid (HA), can interact with CD44 and mediate its functions. CD44 promotes a variety of functions independently or in cooperation with other cell-surface receptors through activation of varied signaling pathways like Rho GTPases, Ras-MAPK, and PI3K/AKT pathways to regulate cell adhesion, migration, survival, invasion, and epithelial-mesenchymal transition. In this review, we present the relations between AR, miRNA, and CD44 and their roles in BC.

Pathomechanisms in schwannoma development and progression

Schwannomas are tumors of the peripheral nervous system, consisting of different cell types. These include tumorigenic Schwann cells, axons, macrophages, T cells, fibroblasts, blood vessels, and an extracellular matrix. All cell types involved constitute an intricate “tumor microenvironment” and play relevant roles in the development and progression of schwannomas. Although Nf2 tumor suppressor gene-deficient Schwann cells are the primary tumorigenic element and principle focus of current research efforts, evidence is accumulating regarding the contributory roles of other cell types in schwannoma pathology. In this review, we aim to provide an overview of intra- and intercellular mechanisms contributing to schwannoma formation.

“Genes load the gun, environment pulls the trigger.”

-George A. Bray

Cluster of differentiation 44 promotes osteosarcoma progression in mice lacking the tumor suppressor Merlin

Merlin is a versatile tumor suppressor protein encoded by the NF2 gene. Several lines of evidence suggest that Merlin exerts its tumor suppressor activity, at least in part, by forming an inhibitory complex with cluster of differentiation 44 (CD44). Consistently, numerous NF2 mutations in cancer patients are predicted to perturb the interaction of Merlin with CD44. We hypothesized that disruption of the Merlin-CD44 complex through loss of Merlin, unleashes putative tumor- or metastasis-promoting functions of CD44. To evaluate the relevance of the Merlin-CD44 interaction in vivo, we compared tumor growth and progression in Cd44-positive and Cd44-negative Nf2-mutant mice. Heterozygous Nf2-mutant mice were prone to developing highly metastatic osteosarcomas. Importantly, while the absence of the Cd44 gene had no effect on the frequency of primary osteosarcoma development, it strongly diminished osteosarcoma metastasis formation in the Nf2-mutant mice. In vitro assays identified transendothelial migration as the most prominent cellular phenotype dependent on CD44. Adhesion to endothelial cells was blocked by interfering with integrin α4β1 (very late antigen-4, VLA-4) on osteosarcoma cells and CD44 upregulated levels of integrin VLA-4 β1 subunit. Among other putative functions of CD44, which may contribute to the metastatic behavior, the passage through the endothelial cells also appears to be critical in vivo, as CD44 significantly promoted formation of lung metastasis upon intravenous injection of osteosarcoma cells into immunocompromised mice. Altogether, our results strongly suggest that CD44 plays a metastasis-promoting role in the absence of Merlin.

The use of non-traditional models in the study of cancer resistance-the case of the naked mole rat

Non-traditional model organisms are typically defined as any model the deviates from the typical laboratory animals, such as mouse, rat, and worm. These models are becoming increasingly important in human disease research, such as cancer, as they often display unusual biological features. Naked mole rats (NMRs) are currently one of the most popular non-traditional model, particularly in the longevity and cancer research fields. NMRs display an exceptionally long lifespan (~30 years), yet have been observed to display a low incidence of cancer, making them excellent candidates for understanding endogenous cancer resistance mechanisms. Over the past decade, many potential resistance mechanisms have been characterized. These include unique biological mechanisms involved in genome stability, protein stability, oxidative metabolism, and other cellular mechanisms such as cell cycle regulation and senescence. This review aims to summarize the many identified cancer resistance mechanisms to understand some of the main hypotheses that have thus far been generated. Many of these proposed mechanisms remain to be fully characterized or confirmed in vivo, giving the field a direction to grow and further understand the complex biology displayed by the NMR.

Hyaluronan Degradation Promotes Cancer via Hippo-YAP Signaling: An Intervention Point for Cancer Therapy

High-molecular-weight hyaluronan acts as a ligand of the tumor-suppressive Hippo signal, whereas degradation of hyaluronan from a high-molecular-weight form to a low-molecular-weight forms by hyaluronidase 2 inhibits Hippo signal activation and thereby activates the pro-oncogenic transcriptional coactivator yes-associated protein (YAP), which creates a cancer-predisposing microenvironment and drives neoplastic transformation of cells through both cell-autonomous and non-cell-autonomous mechanisms. In fact, accumulation of low-molecular-weight hyaluronan in tissue stroma is observed in many types of cancers. Since inhibition of YAP activity suppresses tumor growth in vivo, pharmacological intervention of the Hippo-YAP signal is an attractive approach for future drug development. In this review, pharmacological intervention of excessive hyaluronan degradation as a novel approach for inhibition of the Hippo-YAP signal is also discussed. Development of hyaluronidase inhibitors may provide novel therapeutic strategies for human malignant tumors.