Medulloblastoma is the most common brain tumour in children; using exome sequencing of tumour samples the authors show that these cancers have low mutation rates and identify 12 significantly mutated genes, among them the gene encoding RNA helicase DDX3X. Medulloblastoma is the most common malignant brain tumour in children. Four papers published in the 2 August 2012 issue of Nature use whole-genome and other sequencing techniques to produce a detailed picture of the genetics and genomics of this condition. Notable findings include the identification of recurrent mutations in genes not previously implicated in medulloblastoma, with significant genetic differences associated with the four biologically distinct subgroups and clinical outcomes in each. Potential avenues for therapy are suggested by the identification of targetable somatic copy-number alterations, including recurrent events targeting TGFβ signalling in Group 3, and NF-κB signalling in Group 4 medulloblastomas. Medulloblastomas are the most common malignant brain tumours in children1. Identifying and understanding the genetic events that drive these tumours is critical for the development of more effective diagnostic, prognostic and therapeutic strategies. Recently, our group and others described distinct molecular subtypes of medulloblastoma on the basis of transcriptional and copy number profiles2,3,4,5. Here we use whole-exome hybrid capture and deep sequencing to identify somatic mutations across the coding regions of 92 primary medulloblastoma/normal pairs. Overall, medulloblastomas have low mutation rates consistent with other paediatric tumours, with a median of 0.35 non-silent mutations per megabase. We identified twelve genes mutated at statistically significant frequencies, including previously known mutated genes in medulloblastoma such as CTNNB1, PTCH1, MLL2, SMARCA4 and TP53. Recurrent somatic mutations were newly identified in an RNA helicase gene, DDX3X, often concurrent with CTNNB1 mutations, and in the nuclear co-repressor (N-CoR) complex genes GPS2, BCOR and LDB1. We show that mutant DDX3X potentiates transactivation of a TCF promoter and enhances cell viability in combination with mutant, but not wild-type, β-catenin. Together, our study reveals the alteration of WNT, hedgehog, histone methyltransferase and now N-CoR pathways across medulloblastomas and within specific subtypes of this disease, and nominates the RNA helicase DDX3X as a component of pathogenic β-catenin signalling in medulloblastoma.

Human cytomegalovirus (HCMV) encodes several genes that disrupt the major histocompatibility complex (MHC) class I antigen presentation pathway. We recently described the HCMV‐encoded US6 gene product, a 23 kDa endoplasmic reticulum (ER)‐resident type I integral membrane protein that binds to the transporter associated with antigen processing (TAP), inhibits peptide translocation and prevents MHC class I assembly. The functional consequence of this inhibition is to prevent the cell surface expression of class I bound viral peptides and their recognition by HCMV‐specific cytotoxic T cells. Here we describe a novel mechanism of action for US6. We demonstrate that US6 inhibits the binding of ATP by TAP1. This is a conformational effect, as the ER lumenal domain of US6 is sufficient to inhibit ATP binding by the cytosolic nucleotide binding domain of TAP1. US6 also stabilizes TAP at 37°C and prevents conformational rearrangements induced by peptide binding. Our findings suggest that the association of US6 with TAP stabilizes a conformation in TAP1 that prevents ATP binding and subsequent peptide translocation.

The antiarrhythmic drug amiodarone was recently demonstrated to have novel broad range fungicidal activity. We provide evidence that amiodarone toxicity is mediated by disruption of Ca²⁺ homeostasis in Saccharomyces cerevisiae. In mutants lacking calcineurin and various Ca²⁺ transporters, including pumps (Pmr1 and Pmc1), channels (Cch1/Mid1 and Yvc1), and exchangers (Vcx1), amiodarone sensitivity correlates with cytoplasmic calcium overload. Measurements of cytosolic Ca²⁺ by aequorin luminescence demonstrate a biphasic response to amiodarone. An immediate and extensive calcium influx was observed that was dose-dependent and correlated with drug sensitivity. The second phase consisted of a sustained release of calcium from the vacuole via the calcium channel Yvc1 and was independent of extracellular Ca²⁺ entry. To uncover additional cellular pathways involved in amiodarone sensitivity, we conducted a genome-wide screen of nearly 5000 single-gene yeast deletion mutants. 36 yeast strains with amiodarone hypersensitivity were identified, including mutants in transporters (pmr1, pdr5, and vacuolar H⁺-ATPase), ergosterol biosynthesis (erg3, erg6, and erg24), intracellular trafficking (vps45 and rcy1), and signaling (ypk1 and ptc1). Of three mutants examined (vps45, vma3, and rcy1), all were found to have defective calcium homeostasis, supporting a correlation with amiodarone hypersensitivity. We show that low doses of amiodarone and an azole (miconazole, fluconazole) are strongly synergistic and exhibit potent fungicidal effects in combination. Our findings point to the potentially effective application of amiodarone as a novel antimycotic, particularly in combination with conventional antifungals.

Patients diagnosed with neurofibromatosis type 2 (NF2) are extremely likely to develop meningiomas, in addition to vestibular schwannomas. Meningiomas are a common primary brain tumor; many NF2 patients suffer from multiple meningiomas. In NF2, patients have mutations in the NF2 gene, specifically with loss of function in a tumor-suppressor protein that has a number of synonymous names, including: Merlin, Neurofibromin 2, and schwannomin. Merlin is a 70 kDa protein that has 10 different isoforms. The Hippo Tumor Suppressor pathway is regulated upstream by Merlin. This pathway is critical in regulating cell proliferation and apoptosis, characteristics that are important for tumor progression. Mutations of the NF2 gene are strongly associated with NF2 diagnosis, leading to benign proliferative conditions such as vestibular schwannomas and meningiomas. Unfortunately, even though these tumors are benign, they are associated with significant morbidity and the potential for early mortality. In this review, we aim to encompass meningiomas and vestibular schwannomas as they pertain to NF2 by assessing molecular genetics, common tumor types, and tumor pathogenesis.

RNA-based therapies offer unique advantages for treating brain tumors. However, tumor penetrance and uptake are hampered by RNA therapeutic size, charge, and need to be “packaged” in large carriers to improve bioavailability. Here, we have examined delivery of siRNA, packaged in 50-nm cationic lipid-polymer hybrid nanoparticles (LPHs:siRNA), combined with microbubble-enhanced focused ultrasound (MB-FUS) in pediatric and adult preclinical brain tumor models. Using single-cell image analysis, we show that MB-FUS in combination with LPHs:siRNA leads to more than 10-fold improvement in siRNA delivery into brain tumor microenvironments of the two models. MB-FUS delivery of Smoothened (SMO) targeting siRNAs reduces SMO protein production and markedly increases tumor cell death in the SMO-activated medulloblastoma model. Moreover, our analysis reveals that MB-FUS and nanoparticle properties can be optimized to maximize delivery in the brain tumor microenvironment, thereby serving as a platform for developing next-generation tunable delivery systems for RNA-based therapy in brain tumors.