mTORC2 Regulates Amino Acid Metabolism in Cancer by Phosphorylation of the Cystine-Glutamate Antiporter xCT.

Mutations in cancer reprogram amino acid metabolism to drive tumor growth, but the molecular mechanisms are not well understood. Using an unbiased proteomic screen, we identified mTORC2 as a critical regulator of amino acid metabolism in cancer via phosphorylation of the cystine-glutamate antiporter xCT. mTORC2 phosphorylates serine 26 at the cytosolic N terminus of xCT, inhibiting its activity. Genetic inhibition of mTORC2, or pharmacologic inhibition of the mammalian target of rapamycin (mTOR) kinase, promotes glutamate secretion, cystine uptake, and incorporation into glutathione, linking growth factor receptor signaling with amino acid uptake and utilization. These results identify an unanticipated mechanism regulating amino acid metabolism in cancer, enabling tumor cells to adapt to changing environmental conditions.

The Clinical Course and Treatment of a Case of Refractory Systemic Juvenile Myasthenia Gravis Successfully Treated with Thymectomy.

Juvenile myasthenia gravis (JMG) exhibits a more favorable response to glucocorticoids and has a better prognosis than adult myasthenia gravis. However, no established treatment exists for refractory JMG. Although thymectomy has been performed in several patients with refractory systemic JMG, there are few detailed clinical descriptions of patients who underwent thymectomy. Here, we present the case of a 10-year-old boy with refractory systemic JMG who was successfully treated with thymectomy. The patient developed symptoms, including dysphagia, malaise, diurnal ptosis, and weakness in the trunk muscles, and he was diagnosed with generalized JMG. Despite undergoing various treatments, including steroids, tacrolimus, steroid pulse therapy, intravenous immunoglobulin, azathioprine (AZT), and rituximab, his symptoms did not improve. Therefore, he underwent a thoracoscopic thymectomy 24 months after disease onset. Thymectomy led to remission, as demonstrated by a significant reduction in the quantitative myasthenia gravis score and anti-acetylcholine receptor antibody levels, which persisted for 43 months after surgery. Our case demonstrates the effectiveness of thymectomy in systemic JMG patients with positive anti-acetylcholine receptor antibodies, despite therapeutic failure with AZT and rituximab, within 2 years of disease onset.

Metabolic and epigenetic reprogramming in the pathogenesis of glioblastoma: Toward the establishment of "metabolism-based pathology".

Molecular genetic approaches are now mandatory for cancer diagnostics, especially for brain tumors. Genotype-based diagnosis has predominated over the phenotype-based approach, with its prognostic and predictive powers. However, comprehensive genetic testing would be difficult to perform in the clinical setting, and translational research is required to histologically decipher the peculiar biology of cancer. Of interest, recent studies have demonstrated discrete links between oncogenotypes and the resultant metabolic phenotypes, revealing cancer metabolism as a promising histologic surrogate to reveal specific characteristics of each cancer type and indicate the best way to manage cancer patients. Here, we provide an overview of our research progress to work on cancer metabolism, with a particular focus on the genomically well-characterized malignant tumor glioblastoma. With the use of clinically relevant animal models and human tissue, we found that metabolic reprogramming plays a major role in the aggressive cancer biology by conferring therapeutic resistance to cancer cells and rewiring their epigenomic landscapes. We further discuss our future endeavor to establish "metabolism-based pathology" on how the basic knowledge of cancer metabolism could be leveraged to improve the management of patients by linking cancer cell genotype, epigenotype, and phenotype through metabolic reprogramming.

The metabolomic landscape plays a critical role in glioma oncogenesis.

Cancer cells depend on metabolic reprogramming for survival, undergoing profound shifts in nutrient sensing, nutrient uptake and flux through anabolic pathways, in order to drive nucleotide, lipid, and protein synthesis and provide key intermediates needed for those pathways. Although metabolic enzymes themselves can be mutated, including to generate oncometabolites, this is a relatively rare event in cancer. Usually, gene amplification, overexpression, and/or downstream signal transduction upregulate rate-limiting metabolic enzymes and limit feedback loops, to drive persistent tumor growth. Recent molecular-genetic advances have revealed discrete links between oncogenotypes and the resultant metabolic phenotypes. However, more comprehensive approaches are needed to unravel the dynamic spatio-temporal regulatory map of enzymes and metabolites that enable cancer cells to adapt to their microenvironment to maximize tumor growth. Proteomic and metabolomic analyses are powerful tools for analyzing a repertoire of metabolic enzymes as well as intermediary metabolites, and in conjunction with other omics approaches could provide critical information in this regard. Here, we provide an overview of cancer metabolism, especially from an omics perspective and with a particular focus on the genomically well characterized malignant brain tumor, glioblastoma. We further discuss how metabolomics could be leveraged to improve the management of patients, by linking cancer cell genotype, epigenotype, and phenotype through metabolic reprogramming.

Clinical features and difficulty in diagnosis of Langerhans cell histiocytosis in the hypothalamic-pituitary region.

Langerhans cell histiocytosis (LCH) is a multi-organ disorder that rarely involves the hypothalamic-pituitary region (HPR). HPR-LCH presents with severe progressive pituitary dysfunction and its prognosis is poor. The definitive diagnosis of LCH is considerably difficult and complicated owing to the occurrence of several diseases with similar manifestations in the HPR and its location in the deepest portion of the anterior skull base, in close proximity to important normal structures, severely limiting the size of the biopsy specimen. Chemotherapy is the established treatment modality for LCH; hence, timely and accurate diagnosis of LCH is essential for early therapeutic intervention. We retrospectively reviewed clinical features and biopsy procedures in four patients with HPR-LCH (all female, 28-44 years old) from 2009 to 2020. Maximum diameter of supra-sellar lesions was 23-35 mm and 2 cases had skip lesions. All patients demonstrated central diabetes insipidus, hyper-prolactinemia, and severe anterior pituitary dysfunction. Two of the patients had progressive disease. Furthermore, four patients presented body weight gain, two visual disturbance, and two impaired consciousness. The duration from onset to diagnosis of LCH was 3 to 10 (average 7.25) years. In total, eight operations were performed until final diagnosis. The percentage of correct diagnosis by biopsy was 50% (4/8). Clinical features of HPR-LCH are very similar to those of other HPR diseases, and their symptoms are progressive and irreversible. Clinicians should consider repeated biopsy with a more aggressive approach if the lesion is refractory to steroid therapy, in order to ensure accurate diagnosis and appropriate treatment.

IgG4-related brain pseudotumor mimicking CNS lymphoma. A case report.

Here, we report a case of IgG4-related brain pseudotumor (IgG4-BP) in a 39-year-old woman, mimicking central nervous system (CNS) lymphoma. She presented with headache, fever, and fatigue. Her medical history was notable for appearance of a tumefactive brain lesion seven years before. Brain biopsy performed at the age of 32 revealed nonspecific inflammatory changes, and her condition improved with oral low-dose steroid therapy. Magnetic resonance imaging performed at the age of 39 identified a hyperintensity lesion with edema located at the medial temporal lobe region adjacent to the inferior horn of the left lateral ventricle on fluid-attenuated inversion recovery images, which showed gadolinium-contrast enhancement on T1-weighted images and a slightly hyperintensity signal on diffusion-weighted images. Methionine-positron emission tomography (PET) depicted a high methionine uptake in the lesion. Additionally, soluble levels of interleukin (IL)-2 receptor (sIL-2R) and IL-10 were increased in cerebrospinal fluid (CSF). Based on these findings, we suspected CNS lymphoma and performed partial resection of the brain lesion. Pathological examination revealed prominent lymphocytic infiltration associated with plasma cell infiltration. Most of the plasma cells were immunoreactive for IgG4. Storiform fibrosis and partially obliterative phlebitis were concomitantly observed. Thus, the patient was diagnosed as having IgG4-BP. To the best of our knowledge, this is the first case report of IgG4-BP with detailed findings obtained by CSF testing, methionine-PET, and pathological examination. Because IgG4-related diseases can present as a pseudotumor that mimics CNS lymphoma, it is essential to carefully differentiate IgG4-BP from CNS lymphoma.

[Molecular Diagnostic Approaches for Diffuse Gliomas Based on Updated WHO Classification and cIMPACT-NOW Proposals].

The updated 2016 World Health Organization(WHO)classification of tumors of the central nervous system(CNS)has incorporated molecular parameters into the histopathological diagnosis of the tumor in the name of "integrated diagnosis." It has enabled more prognostically precise diagnoses of brain tumor entities; however, its practical application has also raised concerns about whether genotypes predominate over phenotypes in tumor diagnostics. In response, cIMAPCT-NOW(the Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy-"Not Official WHO")was established to provide a forum for evaluating and recommending proposed changes to future CNS tumor classifications. cIMPACT has thus far published seven updates on the proposal and clarification of existing and new terms and entities. Herein, we highlight the current status of clinical application of the 2016 WHO classification and cIMPACT proposals, and the future endeavor to incorporate comprehensive genomic and epigenomic profiling of CNS tumors with the aid of artificial intelligence technology for better clinical decision-making to achieve the goal of precision medicine for each patient with brain tumors.

mTORC2 links growth factor signaling with epigenetic regulation of iron metabolism in glioblastoma.

In cancer, aberrant growth factor receptor signaling reprograms cellular metabolism and global gene transcription to drive aggressive growth, but the underlying mechanisms are not well-understood. Here we show that in the highly lethal brain tumor glioblastoma (GBM), mTOR complex 2 (mTORC2), a critical core component of the growth factor signaling system, couples acetyl-CoA production with nuclear translocation of histone-modifying enzymes including pyruvate dehydrogenase and class IIa histone deacetylases to globally alter histone acetylation. Integrated analyses in orthotopic mouse models and in clinical GBM samples reveal that mTORC2 controls iron metabolisms via histone H3 acetylation of the iron-related gene promoter, promoting tumor cell survival. These results nominate mTORC2 as a critical epigenetic regulator of iron metabolism in cancer.

Diffuse gliomas to date and beyond 2016 WHO Classification of Tumours of the Central Nervous System.

The updated 2016 World Health Organization (WHO) Classification of Tumours of the Central Nervous System (CNS) has incorporated molecular parameters into pathological diagnosis, for the first time in the molecular era. While it has led to the more precise diagnoses of well-understood entities and the better comprehension of less-understood entities, its practical application has also created some concerns whether or not genotypes predominate over phenotypes in tumor diagnostics. In response to these concerns, the Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy-Not Official WHO (cIMAPCT-NOW) was established under the sponsorship of the International Society of Neuropathology to provide a forum to evaluate and recommend proposed changes to future CNS tumor classifications. cIMPACT has thus far published five updates on the proposal and clarification of existing and new terms and entities. Also, recent studies have shown that WHO grading based on histology has lost its prognostic relevance, which necessitates novel, improved grading criteria. We herein highlight the current status of clinical application of WHO 2016 classification and cIMPACT proposals, and the future endeavor to incorporate DNA methylation profiling of the CNS tumors for better clinical decision-making to achieve a goal of precision medicine for each patient with brain tumors.

Astrocytes release glutamate via cystine/glutamate antiporter upregulated in response to increased oxidative stress related to sporadic amyotrophic lateral sclerosis.

A vast body of evidence implicates increased oxidative stress and extracellular glutamate accumulation in the pathomechanism of sporadic amyotrophic lateral sclerosis (ALS). Cystine/glutamate antiporter (xCT) carries extracellular cystine uptake and intracellular glutamate release (cystine/glutamate exchange) in the presence of oxidative stress. The aim of the present study was to determine the involvement of xCT in ALS. Immunohistochemical observations in the spinal cord sections demonstrated that xCT was mainly expressed in astrocytes, with staining more intense in 12 sporadic ALS patients as compared to 12 age-matched control individuals. Western blot and densitometric analyses of the spinal cord samples revealed that the relative value of xCT/ß-actin optical density ratio was significantly higher in the ALS group as compared to the control group. Next, we conducted cell culture experiments using a human astrocytoma-derived cell line (1321N1) and a mouse motor neuron/neuroblastoma hybrid cell line (NSC34). In 1321N1 cells, the normalized xCT expression levels in cell lysates were significantly increased by H2 O2 treatment. Glutamate concentrations in 1321 N1 cell culture-conditioned media were significantly elevated by H2 O2 treatment, and the H2 O2 -driven elevations were completely canceled by the xCT inhibitor erastin pretreatment. In motor neuron-differentiated NSC34 cells (NSC34d cells), both the normalized xCT expression levels in the cell lysates and glutamate concentrations in the cell-conditioned media were constant with or without H2 O2 treatment. The present results provide in vivo and in vitro evidence that astrocytes upregulate xCT expression to release glutamate in response to increased oxidative stress associated with ALS, contributing to extracellular glutamate accumulation.

Soluble iron accumulation induces microglial glutamate release in the spinal cord of sporadic amyotrophic lateral sclerosis.

Previous studies on sporadic amyotrophic lateral sclerosis (SALS) demonstrated iron accumulation in the spinal cord and increased glutamate concentration in the cerebrospinal fluid. To clarify the relationship between the two phenomena, we first performed quantitative and morphological analyses of substances related to iron and glutamate metabolism using spinal cords obtained at autopsy from 12 SALS patients and 12 age-matched control subjects. Soluble iron content determined by the Ferrozine method as well as ferritin (Ft) and glutaminase C (GLS-C) expression levels on Western blots were significantly higher in the SALS group than in the control group, while ferroportin (FPN) levels on Western blots were significantly reduced in the SALS group as compared to the control group. There was no significant difference in aconitase 1 (ACO1) and tumor necrosis factor-alpha (TNFα)-converting enzyme (TACE) levels on Western blots between the two groups. Immunohistochemically, Ft, ACO1, TACE, TNFα, and GLS-C were proven to be selectively expressed in microglia. Immunoreactivities for FPN and hepcidin were localized in neuronal and glial cells. Based on these observations, it is predicted that soluble iron may stimulate microglial glutamate release. To address this issue, cell culture experiments were carried out on a microglial cell line (BV-2). Treatment of BV-2 cells with ferric ammonium citrate (FAC) brought about significant increases in intracellular soluble iron and Ft expression levels and conditioned medium glutamate and TNFα concentrations. Glutamate concentration was also significantly increased in conditioned media of TNFα-treated BV-2 cells. While the FAC-driven increases in glutamate and TNFα release were completely canceled by pretreatment with ACO1 and TACE inhibitors, respectively, the TNFα-driven increase in glutamate release was completely canceled by GLS-C inhibitor pretreatment. Moreover, treatment of BV-2 cells with hepcidin resulted in a significant reduction in FPN expression levels on Western blots of the intracellular total protein extracts. The present results provide in vivo and in vitro evidence that microglial glutamate release in SALS spinal cords is enhanced by intracellular soluble iron accumulation-induced activation of ACO1 and TACE and by increased extracellular TNFα-stimulated GLS-C upregulation, and suggest a positive feedback mechanism to maintain increased intracellular soluble iron levels, involving TNFα, hepcidin, and FPN.

Metabolic reprogramming in the pathogenesis of glioma: Update.

Cancer is a genetic disease that is currently classified not only by its tissue and cell type of origin but increasingly by its molecular composition. Increasingly, tumor classification and subtyping is being performed based upon the oncogene gains, tumor suppressor losses, and associated epigenetic and transcriptional features. However, cancers, including brain tumors, are also characterized by profound alterations in cellular metabolism. At present, even though signature mutations in known metabolic enzymes are recognized as being important, the metabolic landscape of tumors is not currently incorporated into tumor diagnostic categories. Here we describe a set of recent discoveries on metabolic reprogramming driven by mutations in the genes for the isocitrate dehydrogenase (IDH) and receptor tyrosine kinase (RTK) pathways, which are the most commonly observed aberrations in diffuse gliomas. We highlight the importance of oncometabolites to dynamically shift the epigenetic landscape in IDH-mutant gliomas, and c-Myc and mechanistic target of rapamycin (mTOR) complexes in RTK-mutated gliomas to adapt to the microenvironment through metabolic reprogramming. These signify the integration of the genetic mutations with metabolic reprogramming and epigenetic shifts in diffuse gliomas, shedding new light onto potential patient subsets, coupled with information to guide the development of new therapeutic opportunities against the deadly types of brain tumors.

mTORC2 activity in brain cancer: Extracellular nutrients are required to maintain oncogenic signaling.

Mutations in growth factor receptor signaling pathways are common in cancer cells, including the highly lethal brain tumor glioblastoma (GBM) where they drive tumor growth through mechanisms including altering the uptake and utilization of nutrients. However, the impact of changes in micro-environmental nutrient levels on oncogenic signaling, tumor growth, and drug resistance is not well understood. We recently tested the hypothesis that external nutrients promote GBM growth and treatment resistance by maintaining the activity of mechanistic target of rapamycin complex 2 (mTORC2), a critical intermediate of growth factor receptor signaling, suggesting that altered cellular metabolism is not only a consequence of oncogenic signaling, but also potentially an important determinant of its activity. Here, we describe the studies that corroborate the hypothesis and propose others that derive from them. Notably, this line of reasoning raises the possibility that systemic metabolism may contribute to responsiveness to targeted cancer therapies.

Gliosarcoma arising from oligodendroglioma, IDH mutant and 1p/19q codeleted.

Herein, we present a rare case of gliosarcoma arising from oligodendroglioma, isocitrate dehydrogenase (IDH) mutant and 1p/19q codeleted. A 36-year-old man presented with a non-enhanced calcified abnormal lesion on the right frontal lobe. The patient underwent subtotal surgical resection, PAV chemotherapy (procarbazine, nimustine (ACNU) and vincristine), and fractionated radiotherapy with 50 Gy. The pathological diagnosis was oligodendroglioma, IDH mutant and 1p/19q codeleted, World Health Organization 2016 grade II. Six years later, a new enhanced lesion appeared, and the recurrent tumor was surgically removed. Although the histopathological findings indicated gliosarcoma, the recurrent tumor still demonstrated the IDH mutation and 1p/19q codeleted. Thus, the recurrent tumor was considered to originate from oligodendroglioma, rather than being newly generated after chemoradiotherapy. Interestingly, the second recurrent tumor responded well to temozolomide chemotherapy. Based on the findings of this case, oligodendrogliomas have the potential for mesenchymal transformation on progression, while keeping their genotype.

Copper deposition in oligodendroglial cells in an autopsied case of hepatolenticular degeneration.

We present a case of hepatolenticular degeneration, so-called Wilson's disease (WD), in a 31-year-old Japanese man with broader deposition of copper in the liver, kidney and brain. The liver showed severe cirrhotic changes with macronodular pseudolobule formation, but there was little difference in immunohistochemical expression patterns of the copper transporter ATP7B between the control and present case. In the brain, there were both WD-related lesions such as the scattering of Opalski cells and changes caused by hepatic encephalopathy including the appearance of Alzheimer type II glia. Of note, we identified copper deposits in the systemic organs, including hepatocytes, renal tubules, and in broad areas of the brain. Surprisingly, as a result of further pursuit, copper accumulation in the brain was rarely identified in neuronal cells, but in Olig2-positive glial cells with double immunohistochemical staining. Together, this rare autopsied case suggests a novel cellular candidate affected by abnormal copper metabolism and the necessity to perform the systemic examination of copper deposition in WD.

Glucose-dependent acetylation of Rictor promotes targeted cancer therapy resistance.

Cancer cells adapt their signaling in response to nutrient availability. To uncover the mechanisms regulating this process and its functional consequences, we interrogated cell lines, mouse tumor models, and clinical samples of glioblastoma (GBM), the highly lethal brain cancer. We discovered that glucose or acetate is required for epidermal growth factor receptor vIII (EGFRvIII), the most common growth factor receptor mutation in GBM, to activate mechanistic target of rapamycin complex 2 (mTORC2) and promote tumor growth. Glucose or acetate promoted growth factor receptor signaling through acetyl-CoA-dependent acetylation of Rictor, a core component of the mTORC2 signaling complex. Remarkably, in the presence of elevated glucose levels, Rictor acetylation is maintained to form an autoactivation loop of mTORC2 even when the upstream components of the growth factor receptor signaling pathway are no longer active, thus rendering GBMs resistant to EGFR-, PI3K (phosphoinositide 3-kinase)-, or AKT (v-akt murine thymoma viral oncogene homolog)-targeted therapies. These results demonstrate that elevated nutrient levels can drive resistance to targeted cancer treatments and nominate mTORC2 as a central node for integrating growth factor signaling with nutrient availability in GBM.

mTOR Complexes as a Nutrient Sensor for Driving Cancer Progression.

Recent advancement in the field of molecular cancer research has clearly revealed that abnormality of oncogenes or tumor suppressor genes causes tumor progression thorough the promotion of intracellular metabolism. Metabolic reprogramming is one of the strategies for cancer cells to ensure their survival by enabling cancer cells to obtain the macromolecular precursors and energy needed for the rapid growth. However, an orchestration of appropriate metabolic reactions for the cancer cell survival requires the precise mechanism to sense and harness the nutrient in the microenvironment. Mammalian/mechanistic target of rapamycin (mTOR) complexes are known downstream effectors of many cancer-causing mutations, which are thought to regulate cancer cell survival and growth. Recent studies demonstrate the intriguing role of mTOR to achieve the feat through metabolic reprogramming in cancer. Importantly, not only mTORC1, a well-known regulator of metabolism both in normal and cancer cell, but mTORC2, an essential partner of mTORC1 downstream of growth factor receptor signaling, controls cooperatively specific metabolism, which nominates them as an essential regulator of cancer metabolism as well as a promising candidate to garner and convey the nutrient information from the surrounding environment. In this article, we depict the recent findings on the role of mTOR complexes in cancer as a master regulator of cancer metabolism and a potential sensor of nutrients, especially focusing on glucose and amino acid sensing in cancer. Novel and detailed molecular mechanisms that amino acids activate mTOR complexes signaling have been identified. We would also like to mention the intricate crosstalk between glucose and amino acid metabolism that ensures the survival of cancer cells, but at the same time it could be exploitable for the novel intervention to target the metabolic vulnerabilities of cancer cells.