Targeting the Hedgehog Pathway in Pediatric Medulloblastoma

Medulloblastoma (MB), a primitive neuroectomal tumor of the cerebellum, is the most common malignant pediatric brain tumor. The cause of MB is largely unknown, but aberrant activation of Hedgehog (Hh) pathway is responsible for ~30% of MB. Despite aggressive treatment with surgical resection, radiation and chemotherapy, 70%-80% of pediatric medulloblastoma cases can be controlled, but most treated patients suffer devastating side effects. Therefore, developing a new effective treatment strategy is urgently needed. Hh signaling controls transcription of target genes by regulating activities of the three Glioma-associated oncogene (Gli1-3) transcription factors. In this review, we will focus on current clinical treatment options of MB and discuss mechanisms of drug resistance. In addition, we will describe current known molecular pathways which crosstalk with the Hedgehog pathway both in the context of medulloblastoma and non-medulloblastoma cancer development. Finally, we will introduce post-translational modifications that modulate Gli1 activity and summarize the positive and negative regulations of the Hh/Gli1 pathway. Towards developing novel combination therapies for medulloblastoma treatment, current information on interacting pathways and direct regulation of Hh signaling should prove critical

AP2IX-4, a cell cycle regulated nuclear factor, modulates gene expression during bradyzoite development in toxoplasma gondii

Indiana University-Purdue University Indianapolis (IUPUI)Toxoplasma gondii is a ubiquitous, protozoan parasite contributing significantly to global human and animal health. In the host, this obligate intracellular parasite converts into a latent tissue cyst form known as the bradyzoite, which is impervious to the immune response. The tissue cysts facilitate wide-spread transmission through the food chain and give rise to chronic toxoplasmosis in immune compromised patients. In addition, they may reactivate into replicating tachyzoites which cause tissue damage and disseminated disease. Current available drugs do not appear to have appreciable activity against latent bradyzoites. Therefore, a better understanding of the molecular mechanisms that drive interconversion between tachyzoite and bradyzoite forms is required to manage transmission and pathogenesis of Toxoplasma. Conversion to the bradyzoite is accompanied by an altered transcriptome, but the molecular players directing this process are largely uncharacterized. Studies of stage-specific promoters revealed that conventional cis-acting mechanisms operate to regulate developmental gene expression during tissue cyst formation. The major class of transcription factor likely to work through these cis-regulatory elements appears to be related to the Apetala-2 (AP2) family in plants. The Toxoplasma genome contains nearly 70 proteins harboring at least one predicted AP2 domain, but to date only three of these T. gondii AP2 proteins have been linked to bradyzoite development. We show that the putative T. gondii transcription factor, AP2IX-4, is localized to the parasite nucleus and exclusively expressed in tachyzoites and bradyzoites undergoing division. Knockout of AP2IX-4 had negligible effect on tachyzoite replication, but resulted in a reduced frequency of bradyzoite cysts in response to alkaline stress induction – a defect that is reversible by complementation. Microarray analyses revealed an enhanced activation of bradyzoite-associated genes in the AP2IX-4 knockout during alkaline conditions. In mice, the loss of AP2IX-4 resulted in a modest virulence defect and reduced brain cyst burden. Complementation of the AP2IX-4 knockout restored cyst counts to wild-type levels. These findings illustrate the complex role of AP2IX-4 in bradyzoite development and that certain transcriptional mechanisms responsible for tissue cyst development operate across parasite division

Medulloblastoma: Clinical Challenges and Emerging Molecular Discoveries

Medulloblastoma is the most common type of malignant brain tumor in children, responsible for 25% of pediatric brain cancers. Conventional treatment methods, which include surgery, radiotherapy, and chemotherapy, have improved overall survival rates for patients with medulloblastoma to over 50%. A majority of survivors, however, suffer serious long-term side effects, including developmental, neurological, and psychosocial deficits. Now entering clinical trials for sonic hedgehog-driven medulloblastomas, Smoothened inhibitors have been FDA approved for the treatment of basal cell carcinomas. However, treatment efficacy endures only for a few months before lesion relapses and drug resistance occurs. Therefore, there is an urgent need for new therapies to reduce the significant problems associated with current drug-resistant treatments. In this chapter, we will illustrate the clinical presentation and current treatment methods for medulloblastoma and detail the molecular pathways within each of the four molecular subgroups of medulloblastoma, with an eye for possible candidates for novel combination therapies

Algoriphagus machipongonensis sp. nov., co-isolated with a colonial choanoflagellate

A Gram-negative, non-motile, non-spore-forming bacterial strain, PR1[superscript T], was isolated from a mud core sample containing colonial choanoflagellates near Hog Island, Virginia, USA. Strain PR1[superscript T] grew optimally at 30 °C and with 3 % (w/v) NaCl. Strain PR1[superscript T] contained MK-7 as the major menaquinone as well as carotenoids but lacked pigments of the flexirubin-type. The predominant fatty acids were iso-C15 : 0 (29.4 %), iso-C17 : 1ω9c (18.5 %) and summed feature 3 (C16 : 1ω6c and/or C16 : 1ω7c; 11.3 %). The major polar lipids detected in strain PR1[superscript T] were phosphatidylethanolamine, an unknown phospholipid, an aminophospholipid, an aminolipid and two lipids of unknown character. The DNA G+C content was 38.7 mol%. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain PR1[superscript T] fell within the cluster comprising the genus Algoriphagus and was most closely related to Algoriphagus halophilus JC 2051[superscript T] (95.4 % sequence similarity) and Algoriphagus lutimaris S1-3[superscript T] (95.3 % sequence similarity). The 16S rRNA gene sequence similarity between strain PR1[superscript T] and the type strains of other species of the genus Algoriphagus were in the range 91–95 %. Differential phenotypic properties and phylogenetic and genetic distinctiveness of strain PR1[superscript T] demonstrated that this strain was distinct from other members of the genus Algoriphagus, including its closest relative, A. halophilus. Based on phenotypic, chemotaxonomic, phylogenetic and genomic data, strain PR1[superscript T] should be placed in the genus Algoriphagus as a representative of a novel species, for which the name Algoriphagus machipongonensis sp. nov. is proposed. The type strain is PR1[superscript T] ( = ATCC BAA-2233[superscript T]  = DSM 24695[superscript T]).Gordon and Betty Moore Foundation (Investigator Award (581))National Institutes of Health (U.S.) (NIH National Research Service Award and Fellowship grant (5F32GM086054))United States. National Aeronautics and Space Administration (NASA Astrobiology Institute (NNA08CN84A

Fibroblastic niches prime T cell alloimmunity through Delta-like Notch ligands

Alloimmune T cell responses induce graft-versus-host disease (GVHD), a serious complication of allogeneic bone marrow transplantation (allo-BMT). Although Notch signaling mediated by Delta-like 1/4 (DLL1/4) Notch ligands has emerged as a major regulator of GVHD pathogenesis, little is known about the timing of essential Notch signals and the cellular source of Notch ligands after allo-BMT. Here, we have shown that critical DLL1/4-mediated Notch signals are delivered to donor T cells during a short 48-hour window after transplantation in a mouse allo-BMT model. Stromal, but not hematopoietic, cells were the essential source of Notch ligands during in vivo priming of alloreactive T cells. GVHD could be prevented by selective inactivation of Dll1 and Dll4 in subsets of fibroblastic stromal cells that were derived from chemokine Ccl19-expressing host cells, including fibroblastic reticular cells and follicular dendritic cells. However, neither T cell recruitment into secondary lymphoid organs nor initial T cell activation was affected by Dll1/4 loss. Thus, we have uncovered a pathogenic function for fibroblastic stromal cells in alloimmune reactivity that can be dissociated from their homeostatic functions. Our results reveal what we believe to be a previously unrecognized Notch-mediated immunopathogenic role for stromal cell niches in secondary lymphoid organs after allo-BMT and define a framework of early cellular and molecular interactions that regulate T cell alloimmunity