Project description:Reactive oxygen species (ROS) production is a conserved immune response, primarily mediated in Arabidopsis by the respiratory burst oxidase homolog D (RBOHD), a nicotinamide adenine dinucleotide phosphate (NADPH) oxidase associated with the plasma membrane. A rapid increase in NADPH is necessary to fuel RBOHD proteins and hence maintain ROS production. However, the molecular mechanism underlying the NADPH generation for fueling RBOHD remains unclear. In this study, we isolated a new mutant allele of flagellin-insensitive 4 (FIN4), encoding the first enzyme in de novo NAD biosynthesis. fin4 mutants show reduced NADPH levels and impaired ROS production. However, FIN4 and other genes involved in the NAD- and NADPH-generating pathways are not highly upregulated upon elicitor treatment. Therefore, we hypothesized that a cytosolic NADP-linked dehydrogenase might be post-transcriptionally activated to keep the NADPH supply close to RBOHD. RPM1-INDUCED PROTEIN KINASE (RIPK), a receptor-like cytoplasmic kinase, regulates broad-spectrum ROS signaling in plant immunity. We then isolated the proteins associated with RIPK and identified NADP-malic enzyme 2 (NADP-ME2), an NADPH-generating enzyme. Compared with wild-type plants, nadp-me2 mutants display decreased NADP-ME activity, lower NADPH levels, as well as reduced ROS production in response to immune elicitors. Furthermore, we found that RIPK can directly phosphorylate NADP-ME2 and enhance its activity in vitro. The phosphorylation of NADP-ME2 S371 residue contributes to ROS production upon immune elicitor treatment and the susceptibility to the necrotrophic bacterium, Pectobacterium carotovorum. Overall, our study suggests that RIPK activates NADP-ME2 to rapidly increase cytosolic NADPH, hence fueling RBOHD to sustain ROS production in plant immunity.
Project description:we report that U251 glioblastoma tumor spheres exhibit low cytosolic folate cycle and a reprogrammmed mitochondrial folate cycle that is presumably oriented towards oxidizing the formyl group to CO2 with the production of TetraHydroFolate and release of NADPH instead of synthesizing formate
Project description:Defects in mitochondrial metabolism have been increasingly linked with age-onset protein misfolding diseases such as Alzheimerâs, Parkinsonâs, and Huntingtonâs. In response to protein folding stress, compartment-specific unfolded protein responses (UPRs) within the endoplasmic reticulum, mitochondria, and cytosol work in parallel to ensure cellular protein homeostasis. While perturbation of individual compartments can make other compartments more susceptible to protein stress, the cellular conditions that trigger cross-communication between the individual UPRs remain poorly understood. We have uncovered a conserved, robust mechanism linking mitochondrial protein homeostasis and the cytosolic folding environment through changes in lipid homeostasis. Metabolic restructuring caused by mitochondrial stress or small molecule activators trigger changes in gene expression coordinated uniquely by both the mitochondrial and cytosolic UPRs, protecting the cell from disease-associated proteins. Our data suggest an intricate and unique system of communication between UPRs in response to metabolic changes that could unveil new targets for diseases of protein misfolding. Because the induction of the MCSR due to hsp-6 RNAi required both hsf-1 and dve-1, key transcription factors required for the HSR and UPRmt, respectively, we asked which gene sets are coordinately regulated by both factors. We performed microarray analyses to determine which genes have their expression altered by hsp-6 RNAi and whether these genes are regulated either by hsf-1, dve-1 or both
Project description:Mitochondrial biogenesis relies on both the nuclear and mitochondrial genomes, and imbalance in their expression can lead to inborn errors of metabolism, inflammation, and aging. Here, we investigate N6AMT1, a nucleo-cytosolic methyltransferase that exhibits genetic codependency with mitochondria. We determine transcriptional and translational profiles of N6AMT1 and report that it is required for the cytosolic translation of TRMT10C (MRPP1) and PRORP (MRPP3), two subunits of the mitochondrial RNAse P enzyme. In the absence of N6AMT1, or when its catalytic activity is abolished, RNA processing within mitochondria is impaired, leading to the accumulation of unprocessed and double-stranded RNA, thus preventing mitochondrial protein synthesis and oxidative phosphorylation, and leading to an immune response. Our work sheds light on the function of N6AMT1 in protein synthesis and highlights a cytosolic program required for proper mitochondrial biogenesis.
Project description:Mitochondrial biogenesis relies on both the nuclear and mitochondrial genomes, and imbalance in their expression can lead to inborn errors of metabolism, inflammation, and aging. Here, we investigate N6AMT1, a nucleo-cytosolic methyltransferase that exhibits genetic codependency with mitochondria. We determine transcriptional and translational profiles of N6AMT1 and report that it is required for the cytosolic translation of TRMT10C (MRPP1) and PRORP (MRPP3), two subunits of the mitochondrial RNAse P enzyme. In the absence of N6AMT1, or when its catalytic activity is abolished, RNA processing within mitochondria is impaired, leading to the accumulation of unprocessed and double-stranded RNA, thus preventing mitochondrial protein synthesis and oxidative phosphorylation, and leading to an immune response. Our work sheds light on the function of N6AMT1 in protein synthesis and highlights a cytosolic program required for proper mitochondrial biogenesis.
Project description:Calcium acts as a universal second messenger to regulate gene expression in both developmental processes and responses to environmental stresses. Previous studies showed that a number of stimuli can induce calcium increases in the cytoplasm and nucleus, independently. However, the gene expression network deciphering [Ca2+]cyt and/or [Ca2+]nuc signaling pathway remain obscure. Using transgenic Arabidopsis containing a fusion protein, comprising rat parvalbumin (PV) with either a nuclear export sequence (PV-NES) or a nuclear localization sequence (NLS-PV), to selectively buffer the cytosolic or nucleosolic calcium, we identified the [Ca2+]cyt- or /and [Ca2+]nuc-regulated ABA- and MeJA-responsible genes with the Arabidopsis Genome Oligo array.
Project description:Small nucleolar RNAs (snoRNAs) guide nucleotide modifications of cellular RNAs in the nucleus. We have previously shown that box C/D snoRNAs from the Rpl13a locus are unexpected mediators of physiologic oxidative stress, independent of their predicted ribosomal RNA modifications. Here, we demonstrate that oxidative stress induced by doxorubicin causes rapid cytoplasmic accumulation of the Rpl13a snoRNAs through a mechanism that requires superoxide and a nuclear splice variant of NADPH oxidase. RNA-sequencing analysis reveals that box C/D snoRNAs as a class are present in the cytoplasm, where their levels are dynamically regulated by NADPH oxidase. These findings suggest that snoRNAs may orchestrate the response to environmental stress through molecular interactions outside of the nucleus.
Project description:Defects in mitochondrial metabolism have been increasingly linked with age-onset protein misfolding diseases such as Alzheimer’s, Parkinson’s, and Huntington’s. In response to protein folding stress, compartment-specific unfolded protein responses (UPRs) within the endoplasmic reticulum, mitochondria, and cytosol work in parallel to ensure cellular protein homeostasis. While perturbation of individual compartments can make other compartments more susceptible to protein stress, the cellular conditions that trigger cross-communication between the individual UPRs remain poorly understood. We have uncovered a conserved, robust mechanism linking mitochondrial protein homeostasis and the cytosolic folding environment through changes in lipid homeostasis. Metabolic restructuring caused by mitochondrial stress or small molecule activators trigger changes in gene expression coordinated uniquely by both the mitochondrial and cytosolic UPRs, protecting the cell from disease-associated proteins. Our data suggest an intricate and unique system of communication between UPRs in response to metabolic changes that could unveil new targets for diseases of protein misfolding.
Project description:Nitric oxide acts substantially in cellular signal transduction through stimulus-coupled S-nitrosylation of cysteine residues. The mechanisms that might subserve protein denitrosylation in cellular signaling remain uncharacterized. Our search for denitrosylase activities focused on caspase-3, an exemplar of stimulus-dependent denitrosylation, and identified thioredoxin and thioredoxin reductase in a biochemical screen. In resting human lymphocytes, thioredoxin-1 actively denitrosylated cytosolic caspase-3 and thereby maintained a low steady-state amount of S-nitrosylation. Upon stimulation of Fas, thioredoxin-2 mediated denitrosylation of mitochondria-associated caspase-3, a process required for caspase-3 activation, and promoted apoptosis. Inhibition of thioredoxin-thioredoxin reductases enabled identification of additional substrates subject to endogenous S-nitrosylation. Thus, specific enzymatic mechanisms may regulate basal and stimulus-induced denitrosylation in mammalian cells.