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 ß2 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.

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.

Brigatinib causes tumor shrinkage in both NF2-deficient meningioma and schwannoma through inhibition of multiple tyrosine kinases but not ALK.

Neurofibromatosis Type 2 (NF2) is an autosomal dominant genetic syndrome caused by mutations in the NF2 tumor suppressor gene resulting in multiple schwannomas and meningiomas. There are no FDA approved therapies for these tumors and their relentless progression results in high rates of morbidity and mortality. Through a combination of high throughput screens, preclinical in vivo modeling, and evaluation of the kinome en masse, we identified actionable drug targets and efficacious experimental therapeutics for the treatment of NF2 related schwannomas and meningiomas. These efforts identified brigatinib (ALUNBRIG®), an FDA-approved inhibitor of multiple tyrosine kinases including ALK, to be a potent inhibitor of tumor growth in established NF2 deficient xenograft meningiomas and a genetically engineered murine model of spontaneous NF2 schwannomas. Surprisingly, neither meningioma nor schwannoma cells express ALK. Instead, we demonstrate that brigatinib inhibited multiple tyrosine kinases, including EphA2, Fer and focal adhesion kinase 1 (FAK1). These data demonstrate the power of the de novo unbiased approach for drug discovery and represents a major step forward in the advancement of therapeutics for the treatment of NF2 related malignancies.

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.

The peripheral nervous system in hematopoietic stem cell aging.

Hematopoietic stem cell performance and identity, crucial for homeostasis of the blood-forming system, is governed by extrinsic factors found in the bone marrow microenvironment. Communication within hematopoietic stem cell niches occurs via soluble factors or cell-to-cell contacts between niche and blood-forming cells - which in turn are influenced by systemic factors distributed by the bone marrow extracellular fluid. Although hematopoietic cell-intrinsic aging contributes to the aging phenotype of the hematopoietic system, the architecture and cellular composition of the bone marrow microenvironment have emerged to be highly dynamic during aging and suggested as a major driver for the functional limitations of the blood system observable in old individuals. Recent attention has been paid to the interface between the peripheral nervous system and blood-forming cells in the bone marrow in several clinical contexts and in aging - the latter is reviewed here.

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 α4ß1 (very late antigen-4, VLA-4) on osteosarcoma cells and CD44 upregulated levels of integrin VLA-4 ß1 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.

C-Fiber Loss as a Possible Cause of Neuropathic Pain in Schwannomatosis.

Schwannomatosis is the third form of neurofibromatosis and characterized by the occurrence of multiple schwannomas. The most prominent symptom is chronic pain. We aimed to test whether pain in schwannomatosis might be caused by small-fiber neuropathy. Twenty patients with schwannomatosis underwent neurological examination and nerve conduction studies. Levels of pain perception as well as anxiety and depression were assessed by established questionnaires. Quantitative sensory testing (QST) and laser-evoked potentials (LEP) were performed on patients and controls. Whole-body magnetic resonance imaging (wbMRI) and magnetic resonance neurography (MRN) were performed to quantify tumors and fascicular nerve lesions; skin biopsies were performed to determine intra-epidermal nerve fiber density (IENFD). All patients suffered from chronic pain without further neurological deficits. The questionnaires indicated neuropathic symptoms with significant impact on quality of life. Peripheral nerve tumors were detected in all patients by wbMRI. MRN showed additional multiple fascicular nerve lesions in 16/18 patients. LEP showed significant faster latencies compared to normal controls. Finally, IENFD was significantly reduced in 13/14 patients. Our study therefore indicates the presence of small-fiber neuropathy, predominantly of unmyelinated C-fibers. Fascicular nerve lesions are characteristic disease features that are associated with faster LEP latencies and decreased IENFD. Together these methods may facilitate differential diagnosis of schwannomatosis.

Neurofibromatosis type 2 and multiple sclerosis.

Comorbidity of neurofibromatosis type 2 (NF2) and multiple sclerosis (MS) has rarely been reported. Since immunological mechanisms have been implicated in Nf2, coexistence of the two entities may offer insights into schwannoma pathogenesis with respect to the impact of the immune system. We present the case of a woman with a de novo mutation in the NF2 gene who later developed MS. In addition, we found a significantly higher count of T cells in a laryngeal schwannoma of this patient as compared to a schwannoma removed from a NF2 patient without MS. This finding correlated with a higher growth rate in the case of NF+MS.

The NF2 tumor suppressor merlin interacts with Ras and RasGAP, which may modulate Ras signaling.

Inactivation of the tumor suppressor NF2/merlin underlies neurofibromatosis type 2 (NF2) and some sporadic tumors. Previous studies have established that merlin mediates contact inhibition of proliferation; however, the exact mechanisms remain obscure and multiple pathways have been implicated. We have previously reported that merlin inhibits Ras and Rac activity during contact inhibition, but how merlin regulates Ras activity has remained elusive. Here we demonstrate that merlin can directly interact with both Ras and p120RasGAP (also named RasGAP). While merlin does not increase the catalytic activity of RasGAP, the interactions with Ras and RasGAP may fine-tune Ras signaling. In vivo, loss of RasGAP in Schwann cells, unlike the loss of merlin, failed to promote tumorigenic growth in an orthotopic model. Therefore, modulation of Ras signaling through RasGAP likely contributes to, but is not sufficient to account for, merlin's tumor suppressor activity. Our study provides new insight into the mechanisms of merlin-dependent Ras regulation and may have additional implications for merlin-dependent regulation of other small GTPases.

Metabolic enzyme PDK3 forms a positive feedback loop with transcription factor HSF1 to drive chemoresistance.

Background & Aims: Dysregulation of metabolism plays an important role in the development and progression of cancers, while the underlying mechanisms remain largely unknown. This study aims to explore the regulation and relevance of glycolysis in chemoresistance of gastric cancer. Methods: Biochemical differences between chemoresistant and chemosensitive cancer cells were determined by metabolism profiling, microarray gene expression, PCR or western blotting. Cancer cell growth in vitro or in vivo were analyzed by viability, apoptosis and nude mice assay. Immunoprecipation was used to explore the interaction of proteins with other proteins or DNAs. Results: By metabolic and gene expression profiling, we found that pyruvate dehydrogenase kinase 3 (PDK3) was highly expressed to promote glycolysis in chemoresistant cancer cells. Its genetic or chemical inhibition reverted chemoresistance in vitro and in vivo. It was transcriptionally regulated by transcription factor HSF1 (Heat shock factor 1). Interestingly, PDK3 can localize in the nucleus and interact with HSF1 to disrupt its phosphorylation by GSK3ß. Since HSF1 was subjected to FBXW7-catalyzed polyubiquitination in a phosphorylation-dependent manner, PDK3 prevented HSF1 from proteasomal degradation. Thus, metabolic enzyme PDK3 and transcription factor HSF1 forms a positive feedback loop to promote glycolysis. As a result, inhibition of HSF1 impaired enhanced glycolysis and reverted chemoresistance both in vitro and in vivo. Conclusions: PDK3 forms a positive feedback loop with HSF1 to drive glycolysis in chemoresistance. Targeting this mitonuclear communication may represent a novel approach to overcome chemoresistance.

Preclinical assessment of MEK1/2 inhibitors for neurofibromatosis type 2-associated schwannomas reveals differences in efficacy and drug resistance development.

BACKGROUND: Neurofibromatosis type 2 (NF2) is a genetic tumor-predisposition disorder caused by NF2/merlin tumor suppressor gene inactivation. The hallmark of NF2 is formation of bilateral vestibular schwannomas (VS). Because merlin modulates activity of the Ras/Raf/mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) pathway, we investigated repurposing drugs targeting MEK1 and/or MEK2 as a treatment for NF2-associated schwannomas. METHODS: Mouse and human merlin-deficient Schwann cell lines (MD-MSC/HSC) were screened against 6 MEK1/2 inhibitors. Efficacious drugs were tested in orthotopic allograft and NF2 transgenic mouse models. Pathway and proteome analyses were conducted. Drug efficacy was examined in primary human VS cells with NF2 mutations and correlated with DNA methylation patterns. RESULTS: Trametinib, PD0325901, and cobimetinib were most effective in reducing MD-MSC/HSC viability. Each decreased phosphorylated pERK1/2 and cyclin D1, increased p27, and induced caspase-3 cleavage in MD-MSCs. Proteomic analysis confirmed cell cycle arrest and activation of pro-apoptotic pathways in trametinib-treated MD-MSCs. The 3 inhibitors slowed allograft growth; however, decreased pERK1/2, cyclin D1, and Ki-67 levels were observed only in PD0325901 and cobimetinib-treated grafts. Tumor burden and average tumor size were reduced in trametinib-treated NF2 transgenic mice; however, tumors did not exhibit reduced pERK1/2 levels. Trametinib and PD0325901 modestly reduced viability of several primary human VS cell cultures with NF2 mutations. DNA methylation analysis of PD0325901-resistant versus -susceptible VS identified genes that could contribute to drug resistance. CONCLUSION: MEK inhibitors exhibited differences in antitumor efficacy resistance in schwannoma models with possible emergence of trametinib resistance. The results support further investigation of MEK inhibitors in combination with other targeted drugs for NF2 schwannomas.

Construction of cloning-friendly minigenes for mammalian expression of full-length human NF1 isoforms.

The neurofibromatosis type 1 (NF1) tumor suppressor gene is one of the most frequently mutated genes in human tumors. Research on the NF1 proteins has been partially hindered by the difficulties in cloning and propagating the full-length coding cDNAs. We have now established a condition for propagating the natural open reading frames (ORFs) and have assembled the ORFs for human NF1 type 1 and 2 isoforms. Furthermore, we were able to eliminate the cDNA cloning toxicity by introducing a mini-intron. These NF1 minigenes were expressed similarly to the intronless version and could be used to purify full-length NF1 proteins. The NF1 isoforms expressed from the minigenes showed Ras-GAP activity in vivo and in vitro, while the type 1 was more potent. Our constructs expand currently available full-length NF1 constructs and should be valuable tools in expediting the understanding of NF1, particularly the isoform-specific functions and regulation.

Traditional and systems biology based drug discovery for the rare tumor syndrome neurofibromatosis type 2.

Neurofibromatosis 2 (NF2) is a rare tumor suppressor syndrome that manifests with multiple schwannomas and meningiomas. There are no effective drug therapies for these benign tumors and conventional therapies have limited efficacy. Various model systems have been created and several drug targets have been implicated in NF2-driven tumorigenesis based on known effects of the absence of merlin, the product of the NF2 gene. We tested priority compounds based on known biology with traditional dose-concentration studies in meningioma and schwann cell systems. Concurrently, we studied functional kinome and gene expression in these cells pre- and post-treatment to determine merlin deficient molecular phenotypes. Cell viability results showed that three agents (GSK2126458, Panobinostat, CUDC-907) had the greatest activity across schwannoma and meningioma cell systems, but merlin status did not significantly influence response. In vivo, drug effect was tumor specific with meningioma, but not schwannoma, showing response to GSK2126458 and Panobinostat. In culture, changes in both the transcriptome and kinome in response to treatment clustered predominantly based on tumor type. However, there were differences in both gene expression and functional kinome at baseline between meningioma and schwannoma cell systems that may form the basis for future selective therapies. This work has created an openly accessible resource (www.synapse.org/SynodosNF2) of fully characterized isogenic schwannoma and meningioma cell systems as well as a rich data source of kinome and transcriptome data from these assay systems before and after treatment that enables single and combination drug discovery based on molecular phenotype.

Heat Shock Factor 1 Epigenetically Stimulates Glutaminase-1-Dependent mTOR Activation to Promote Colorectal Carcinogenesis.

Heat shock factor 1 (HSF1) generally exhibits its properties under stress conditions. In tumors, HSF1 has a pleiotropic feature in regulating growth, survival, and aggressiveness of cancer cells. In this study, we found HSF1 was increased in colorectal cancer (CRC) and had a positive correlation with shorter disease-free survival (DFS). Knockdown of HSF1 in CRC cells attenuated their growth while inhibiting mTOR activation and glutamine metabolism. HSF1 inhibited the expression of microRNA137 (MIR137), which targeted GLS1 (glutaminase 1), thus stimulating GLS1 protein expression to promote glutaminolysis and mTOR activation. HSF1 bound DNA methyltransferase DNMT3a and recruited it to the promoter of lncRNA MIR137 host gene (MIR137HG), suppressing the generation of primary MIR137. The chemical inhibitor of HSF1 also reduced cell growth, increased apoptosis, and impaired glutamine metabolism in vitro. Moreover, both chemical inhibition and genetic knockout of HSF1 succeeded in increasing MIR137 expression, reducing GLS1 expression, and alleviating colorectal tumorigenesis in azoxymethane (AOM)/dextran sulfate sodium (DSS) mice. In conclusion, HSF1 expression was increased and associated with poor prognosis in CRC. By recruiting DNMT3a to suppress the expression of MIR137 that targets GLS1 mRNA, HSF1 stimulated GLS1-dependent mTOR activation to promote colorectal carcinogenesis. Therefore, targeting HSF1 to attenuate glutaminolysis and mTOR activation could be a promising approach for CRC treatment.

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.

2016 Children's Tumor Foundation conference on neurofibromatosis type 1, neurofibromatosis type 2, and schwannomatosis.

Organized and hosted by the Children's Tumor Foundation (CTF), the Neurofibromatosis (NF) conference is the premier annual gathering for clinicians and researchers interested in neurofibromatosis type 1 (NF1), neurofibromatosis type 2 (NF2), and schwannomatosis (SWN). The 2016 edition constituted a blend of clinical and basic aspects of NF research that helped in clarifying different advances in the field. The incorporation of next generation sequencing is changing the way genetic diagnostics is performed for NF and related disorders, providing solutions to problems like genetic heterogeneity, overlapping clinical manifestations, or the presence of mosaicism. The transformation from plexiform neurofibroma (PNF) to malignant peripheral nerve sheath tumor (MPNST) is being clarified, along with new management and treatments for benign and premalignant tumors. Promising new cellular and in vivo models for understanding the musculoskeletal abnormalities in NF1, the development of NF2 or SWN associated schwannomas, and clarifying the cells that give rise to NF1-associated optic pathway glioma were presented. The interaction of neurofibromin and SPRED1 was described comprehensively, providing functional insight that will help in the interpretation of pathogenicity of certain missense variants identified in NF1 and Legius syndrome patients. Novel promising imaging techniques are being developed, as well as new integrative and holistic management models for patients that take into account psychological, social, and biological factors. Importantly, new therapeutic approaches for schwannomas, meningiomas, ependymomas, PNF, and MPNST are being pursued. This report highlights the major advances that were presented at the 2016 CTF NF conference.

Neuropathies in the setting of Neurofibromatosis tumor syndromes: Complexities and opportunities.

The term 'Neurofibromatosis' (NF) comprises a group of rare diseases with related clinical presentations but distinct genetic conditions. All currently known types - NF1, NF2 and Schwannomatosis - predispose afflicted individuals to the development of glial cell-derived (gliogenic) tumors. Furthermore, the occurrence of neuropathic symptoms, which add to the overall neurologic disability of patients, has been described in all disease entities. We show that neuropathic symptoms are a common and clinically important, yet infrequently studied feature in the NF spectrum. However, the clinical relevance and respective underlying pathogenesis, varies greatly among the different NF types. In this review, we summarize and interpret the latest basic research findings, as well as clinical observations, in respect of Neurofibromatosis-associated neuropathies.

Vitamin A regulates Akt signaling through the phospholipid fatty acid composition.

Protein kinases, including the serine/threonine kinase Akt, mediate manifold bioactivities of vitamin A, although the mechanisms behind the sustained kinase activation are diffuse. To investigate the role of cellular lipids as targetable factors in Akt signaling, we combined mass spectrometry-based lipidomics with immunologic detection of Akt (Ser473) phosphorylation. A screening campaign revealed retinol (vitamin A alcohol) and all-trans retinoic acid (vitamin A acid) (RA) as hits that time-dependently (≥24 h) deplete phosphatidylcholine-bound polyunsaturated fatty acids (PUFA-PCs) from NIH-3T3 mouse fibroblasts while inducing Akt activation (EC50 ≈ 0.1-1 µM). Other mitogenic and stress-regulated kinases were hardly affected. Organized in a coregulated phospholipid subcluster, PUFA-PCs compensated for the RA-induced loss of cellular PUFA-PCs and diminished Akt activation when supplemented. The counter-regulation of phospholipids and Akt by RA was mimicked by knockdown of lysophosphatidylcholine acyltransferase-3 or the selective retinoid X receptor (RXR) agonist bexarotene and prevented by the selective RXR antagonist Hx531. Treatment of mice with retinol decreased the tissue ratio of PUFA-PC and enhanced basal Akt activation preferentially in brain, which was attributed to astrocytes in dissociated cortical cultures. Together, our findings show that RA regulates the long-term activation of Akt by changes in the phospholipid composition.-Pein, H., Koeberle, S. C., Voelkel, M., Schneider, F., Rossi, A., Thürmer, M., Loeser, K., Sautebin, L., Morrison, H., Werz, O., Koeberle, A. Vitamin A regulates Akt signaling through the phospholipid fatty acid composition.

Merlin controls the repair capacity of Schwann cells after injury by regulating Hippo/YAP activity.

Loss of the Merlin tumor suppressor and activation of the Hippo signaling pathway play major roles in the control of cell proliferation and tumorigenesis. We have identified completely novel roles for Merlin and the Hippo pathway effector Yes-associated protein (YAP) in the control of Schwann cell (SC) plasticity and peripheral nerve repair after injury. Injury to the peripheral nervous system (PNS) causes a dramatic shift in SC molecular phenotype and the generation of repair-competent SCs, which direct functional repair. We find that loss of Merlin in these cells causes a catastrophic failure of axonal regeneration and remyelination in the PNS. This effect is mediated by activation of YAP expression in Merlin-null SCs, and loss of YAP restores axonal regrowth and functional repair. This work identifies new mechanisms that control the regenerative potential of SCs and gives new insight into understanding the correct control of functional nerve repair in the PNS.