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: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 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:S-adenosylmethionine (SAM) is the principle biological methyl group donor for a diverse range of substrates. It is synthesised in the cytosolic methionine cycle and shuttled throughout the cell. The mitochondrial SAM (mitoSAM) pool depends on import through the inner-membrane SAMC and supports the maturation of metabolites and mitochondrial RNAs. Mutations in SAMC in patients cause a severe metabolic crisis, however, the organellar regulation of mitoSAM and the protein methylation landscape within mitochondria are largely unknown. We mapped mitochondrial protein methylation sites in Drosphila and, in a targeted screen, we find that methylated residues are highly conserved between fly, mouse and human. Unexpectedly, many methylation events occur outside of mitochondria, independent of the mitoSAM pool. Our results define the critical role of cytoplasmic SAM production for mitochondrial methylation events and highlight the indirect effect of one-carbon metabolism on cellular bioenergetics.
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:What is known is that methionine-dependency is a feature of some cancers. So far, it was attributed to mutations in genes involved in the methionine de novo or salvage pathways. What is new is that in this work we propose that methionine dependency stems from an altered cellular metabolism. We provide evidence that in U251 glioblastoma cell line, only cancer stem cells -isolated as tumor spheres in non adherent conditions- are methionine dependent and not monolayer cells grown in adherent conditions. Transcriptome wide-sequencing reveals that several genes involved in cytosolic folate cycle are downregulated whereas some transcripts of genes involved in mitochondrial folate cycle are upregulated. Genome wide DNA methylation does not account for these changes in gene expression. Mass spectrometry measurements confirm that tumor spheres display low cytosolic folate cycle unable to produce enough 5-methyltetrahydrofolate to remethylate homocystein to methionine. This decreased 5-methyltetrahydrofolate bioavailability is presumably due to a reprogrammed mitochondrial folate cycle which instead of synthesizing formate, intended to fuel the cytosolic folate cycle, oxidizes the formyl group to CO2 with the attendant reduction of NADP+ to NADPH and release of tetrahydrofolate. The originality of this work resides in that it replaces methionine deprivation as a useful nutritional strategy in cancer growth control since cancer stem cells are much more tumoregenic than their non stem-like counterparts. Second, it reveals that the primary default responsible of the reprogrammation of folate metabolism originates in the mitochondria. Thus, mitochondrial enzymes could be novel and more promising anticancer targets than dihydrofolate reductase (DHFR), the current target of drug therapy linked with folate metabolism.
Project description:MicroRNAs (miRNAs) are small non-coding RNAs that associate with Argonaute 2 protein to regulate gene expression at the post-transcriptional level in the cytoplasm. However, recent studies have reported that some miRNAs localize to and function in other cellular compartments. Mitochondria harbour their own genetic system that may be a potential site for miRNA-mediated post-transcriptional regulation. We aimed at investigating whether nuclear-encoded miRNAs can localize to and function in human mitochondria. To enable identification of mitochondrial-enriched miRNAs, we profiled the mitochondrial and cytosolic RNA fractions from the same HeLa cells by miRNA microarray analysis. Mitochondria were purified using a combination of cell fractionation and immunoisolation, and assessed for the lack of protein and RNA contaminants. We found 57 miRNAs differentially expressed in HeLa mitochondria and cytosol. Of these 57, a signature of 13 nuclear-encoded miRNAs was reproducibly enriched in mitochondrial RNA and validated by RT-PCR for hsa-miR-494, hsa-miR-1275 and hsa-miR-1974. This study provides the first comprehensive view of the localization of RNA interference components to the mitochondria. Our data outline the molecular bases for a novel layer of crosstalk between nucleus and mitochondria through a specific subset of human miRNAs that we termed ‘mitomiRs’. To assess whether nuclear-encoded miRNA are detectable in human mitochondria, we performed the following four steps approach. First, cultured HeLa cells were allowed to reach 80-100% confluence and subjected to fractionation in order to isolate the cytosolic fraction. From the same HeLa cells, mitochondria were isolated by immunomagnetic Anti-TOM22 MicroBeads from the Mitochondria Isolation Kit (Miltenyi Biotec). In total, six mitochondria preparations were perfromed, three of these were additionally treated with RNase A. Second, total RNA was extracted from the mitochondrial and cytosolic fractions. Third, mitochondrial and cytosolic RNA were respectively profiled by microRNA microarray analysis. Last, data were analyzed and normalized.Three independent assays were performed.