guanosine-triphosphate and Neurodegenerative-Diseases

Innate immunity is regulated by a broad set of evolutionary conserved receptors to finely probe the local environment and maintain host integrity. Besides pathogen recognition through conserved motifs, several of these receptors also sense aberrant or misplaced self-molecules as a sign of perturbed homeostasis. Among them, self-nucleic acid sensing by the cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING) pathway alerts on the presence of both exogenous and endogenous DNA in the cytoplasm. We review recent literature demonstrating that self-nucleic acid detection through the STING pathway is central to numerous processes, from cell physiology to sterile injury, auto-immunity and cancer. We address the role of STING in autoimmune diseases linked to dysfunctional DNAse or related to mutations in DNA sensing pathways. We expose the role of the cGAS/STING pathway in inflammatory diseases, neurodegenerative conditions and cancer. Connections between STING in various cell processes including autophagy and cell death are developed. Finally, we review proposed mechanisms to explain the sources of cytoplasmic DNA.

Topics: Adenosine Triphosphate; Adult; Autoimmune Diseases; Autophagy; Cytokines; Cytoplasm; DNA; Guanosine Triphosphate; Humans; Immunity, Innate; Infant; Inflammation; Interferon Type I; Membrane Proteins; Mitochondria; Neoplasms; Neurodegenerative Diseases; NF-kappa B; Nucleotides, Cyclic; Nucleotidyltransferases; Signal Transduction

Alternative splicing is an important mechanism for modulating gene function that accounts for a considerable proportion of proteomic complexity in higher eukaryotes. Alternative splicing is often tightly regulated in a cell-type- or developmental-stage- specific manner and can cause a single gene to have multiple functions. Human Tissue transglutaminase (TGM2) is a multifunctional enzyme with transglutaminase crosslinking (TGase), G protein signaling and kinase activities that are postulated to play a role in many disease states. TGM2 mRNA is regulated by alternative splicing, producing C-terminal truncated forms of TGM2 that are predicted to have distinct biochemical properties and biological functions. In this review, we will discuss how alternatively spliced forms of TGM2 could modulate its roles in cancer, neurodegeneration, inflammation and wound healing.

Topics: Alternative Splicing; Animals; Autoimmunity; Calcium; Cell Adhesion; Epithelial-Mesenchymal Transition; GTP-Binding Proteins; Guanosine Triphosphate; Humans; Models, Molecular; Neurodegenerative Diseases; Protein Glutamine gamma Glutamyltransferase 2; Transglutaminases; Wound Healing

The small GTPase Rab7 is a key regulator of endosomal maturation in eukaryotic cells. Mutations in rab7 are thought to cause the dominant neuropathy Charcot-Marie-Tooth 2B (CMT2B) by a gain-of-function mechanism. Here we show that loss of rab7, but not overexpression of rab7 CMT2B mutants, causes adult-onset neurodegeneration in a Drosophila model. All CMT2B mutant proteins retain 10-50% function based on quantitative imaging, electrophysiology, and rescue experiments in sensory and motor neurons in vivo. Consequently, expression of CMT2B mutants at levels between 0.5 and 10-fold their endogenous levels fully rescues the neuropathy-like phenotypes of the rab7 mutant. Live imaging reveals that CMT2B proteins are inefficiently recruited to endosomes, but do not impair endosomal maturation. These findings are not consistent with a gain-of-function mechanism. Instead, they indicate a dosage-dependent sensitivity of neurons to rab7-dependent degradation. Our results suggest a therapeutic approach opposite to the currently proposed reduction of mutant protein function. DOI: http://dx.doi.org/10.7554/eLife.01064.001.

Topics: Animals; Base Sequence; Charcot-Marie-Tooth Disease; Disease Models, Animal; Drosophila; Guanosine Diphosphate; Guanosine Triphosphate; Laminopathies; Molecular Sequence Data; Mutation; Neurodegenerative Diseases; rab GTP-Binding Proteins; rab7 GTP-Binding Proteins; Sensory Receptor Cells; Sequence Homology, Nucleic Acid

α-Synuclein is an abundant presynaptic protein and a primary component of Lewy bodies in Parkinson disease. Although its pathogenic role remains unclear, in healthy nerve terminals α-synuclein undergoes a cycle of membrane binding and dissociation. An α-synuclein binding assay was used to screen for vesicle proteins involved in α-synuclein membrane interactions and showed that antibodies directed to the Ras-related GTPase Rab3a and its chaperone RabGDI abrogated α-synuclein membrane binding. Biochemical analyses, including density gradient sedimentation and co-immunoprecipitation, suggested that α-synuclein interacts with membrane-associated GTP-bound Rab3a but not to cytosolic GDP-Rab3a. Accumulation of membrane-bound α-synuclein was induced by the expression of a GTPase-deficient Rab3a mutant, by a dominant-negative GDP dissociation inhibitor mutant unable to recycle Rab3a off membranes, and by Hsp90 inhibitors, radicicol and geldanamycin, which are known to inhibit Rab3a dissociation from membranes. Thus, all treatments that inhibited Rab3a recycling also increased α-synuclein sequestration on intracellular membranes. Our results suggest that membrane-bound GTP-Rab3a stabilizes α-synuclein on synaptic vesicles and that the GDP dissociation inhibitor·Hsp90 complex that controls Rab3a membrane dissociation also regulates α-synuclein dissociation during synaptic activity.

Topics: alpha-Synuclein; Animals; Brain; Cell Line, Tumor; Cell Membrane; Cytosol; Epitopes; Glycerol; Guanosine Triphosphate; HSP90 Heat-Shock Proteins; Humans; Mice; Mice, Transgenic; Models, Biological; Neurodegenerative Diseases; Neurons; rab3A GTP-Binding Protein; Subcellular Fractions; Synapses; Synaptosomes

Human leucine-rich repeat kinase 1 (LRRK1) is a multi-domain protein of unknown function belonging to the ROCO family of complex proteins. Here, we report the molecular characterization of human LRRK1 and show, for the first time, that LRRK1 is both a functional protein kinase and a GDP/GTP-binding protein. Binding of GTP to LRRK1 is specific, requires the GTPase-like Roc domain, and leads to a stimulation of LRRK1 kinase activity. LRRK1 is the first example of a GTP-regulated protein kinase harboring both the kinase effector domain and the GTP-binding regulatory domain. Hence, we propose a model in which LRRK1 cycles between a GTP-bound active and a GDP-bound inactive state. Moreover, we mutated LRRK1 to mimic mutations previously identified in LRRK2/dardarin, the only human paralogue of LRRK1, that have been linked to autosomal-dominant parkinsonism. We demonstrate that three of four mutations analyzed significantly downregulate LRRK1 kinase activity. Ultimately, the results presented for LRRK1 may contribute to the elucidation of LRRK2's role in the pathogenesis of Parkinson's disease.

Topics: Amino Acid Sequence; Enzyme Activation; Guanosine Triphosphate; Humans; Models, Biological; Molecular Sequence Data; Multiprotein Complexes; Mutation; Neurodegenerative Diseases; Protein Binding; Protein Serine-Threonine Kinases; Protein Structure, Tertiary; Sequence Alignment; Signal Transduction; Up-Regulation