Rewiring the Mitochondrial Electron Transport Chain Enhances Tumor Antigen Presentation and Immunogenicity [bulk RNA-seq]
Ontology highlight
ABSTRACT: Loss of antigen presentation by MHCI is a common mechanism of tumor immune evasion. Mitochondrial oxidative phosphorylation (OXPHOS) capacity influences MHCI expression, but the underlying molecular mechanisms remain unclear. Here, we demonstrate that the relative flow of electrons through complex I or II of the mitochondrial electron transport chain (ETC) regulates MHCI expression and antigen presentation in cancer cells. Specifically, reducing electron flow from complex II increases mitochondrial succinate which activates transcription of MHCI and antigen processing and presentation (APP) genes. These phenotypes are independent of the interferon (IFN) signaling pathway and driven by succinate-mediated enzymatic inhibition of lysine-specific demethylases, KDM5A/B and destabilization of polycomb repressor complex 2 (PRC2). Finally, knockout of the mitochondrial Complex I inhibitor protein, MCJ, preferentially reduces electron flow through Complex II and increases succinate which drives an enhanced antigen-dependent CD8+ T cell response to mouse melanoma tumors in vivo. These findings suggest that the mitochondrial ETC can be manipulated therapeutically to enhance antitumor immune responses independently of IFNγ.
Project description:Although tumor growth requires the mitochondrial electron transport chain (ETC), the relative contribution of Complex I (CI) and II (CII), the gatekeepers for initiating electron flow, remains unclear. Here, we report that loss of CII, but not CI, reduces melanoma tumor growth by increasing antigen presentation and T cell-mediated killing. This is driven by succinate-mediated transcriptional and epigenetic activation of major histocompatibility complex I-antigen processing and presentation (MHC-APP) genes that is independent of interferon signaling. Furthermore, knock-out of MCJ, to promote electron entry preferentially via CI, provides proof-of-concept of ETC rewiring to achieve anti-tumor responses without side effects associated with an overall reduction in mitochondrial respiration in non-cancer cells. Our results hold therapeutic potential for tumors that have reduced MHC-APP expression, a common mechanism of cancer immunoevasion.
Project description:Ciona intestinalis alternative oxidase (AOX) is a mitochondrial respiratory enzyme that acts as an alternative electron sink for ubiquinol (reduced quinone) when the cytochrome bc1 complex (complex III) and/or cytochrome c oxidase (complex IV) are inhibited or impaired (El-Khoury et al., 2014). AOX thus enables electron flux through the mitochondrial electron transport chain (ETC) and thereby prevents reverse electron transport from succinate dehydrogenase (complex II) to NADH:ubiquinone oxidoreductase (complex I) and mitochondrial ROS production, restores redox balance and Krebs cycle activity. As a non-proton-motive enzyme, however, AOX does not directly support ATP production. Previously, a mouse model was generated that despite ubiquitous expression of AOX revealed no deviations from normal physiology and which now is used as model to test mitochondrial disease paradigms (Szibor et al., 2017).
Project description:The NLRP3 inflammasome is linked to sterile and pathogen-dependent inflammation, and its dysregulation underlies many chronic diseases. Mitochondria have been implicated as regulators of NLRP3 inflammasome through multiple mechanisms including generation of mitochondrial ROS. Here we report that mitochondrial electron transport chain (ETC) complexes I, II, III and V inhibitors all prevent NLRP3 inflammasome activation. Ectopic expression of Saccharomyces cerevisiae NADH dehydrogenase (NDI1) or Ciona intestinalis alternative oxidase (AOX), which can respectively complement the functional loss of mitochondrial complex I or III, without generation of ROS, rescued NLRP3 inflammasome activation in the absence of endogenous mitochondrial complex I or complex III function. Metabolomics revealed phosphocreatine (PCr), which can sustain ATP levels, as a common metabolite that is diminished by mitochondrial ETC inhibitors. PCr depletion decreased ATP levels and NLRP3 inflammasome activation. Thus, mitochondrial ETC sustains NLRP3 inflammasome activation through PCr-dependent generation of ATP but a ROS independent mechanism.
Project description:The metabolic principles underlying the differences between follicular and marginal zone B cells (FoB and MZB, respectively) are not well understood. Here we show, by studying mice with B cell-specific ablation of the catalytic subunit of glutamate cysteine ligase (Gclc), that glutathione synthesis affects homeostasis and differentiation of MZB to a larger extent than FoB, while glutathione-dependent redox control contributes to the metabolic dependencies of FoB. Specifically, Gclc ablation in FoB induces metabolic features of wild-type MZB such as increased ATP levels, glucose metabolism, mTOR activation and protein synthesis. Furthermore, Gclc-deficient FoB have a block in the mitochondrial electron transport chain (ETC) due to diminished complex I and II activity and thereby accumulate the tricarboxylic acid cycle metabolite succinate. Finally, Gclc deficiency hampers FoB activation and antibody responses in vitro and in vivo, and induces susceptibility to viral infections. In summary, Gclc is required to ensure the development of MZB, the integrity of the mitochondrial ETC in FoB and it is crucial for antibody-mediated immunity.
Project description:We have developed a tet-inducible SV-40 large T antigen-expressing lentivirus-immortalized mouse embryonic fibroblast (iMEF) cell culture model of mitochondrial electron transport chain (ETC) dysfunction involving complex II (succinate dehydrogenase; SDH) in which silencing gene rearrangement of the Sdhc floxed allele is driven by doxycycline-dependent expression of cre-recombinase from a tet-inducible promoter (R26M2rtTA/+;TetOcre;Sdhcfl/fl). Following doxycycline induction, dilutional subcloning was employed to obtain stable Sdhc -/- (SDHC KO) cell lines. Sdhc gene rearrangement status for each clonally-derived cell line was confirmed by PCR. Cell lines were grown in standard DMEM containing penicillin/streptomycin antibiotics (0.5 mg/mL), non-essential amino acids (100 micromolar each of glycine, alanine, asparagine, aspartic acid, glutamic acid, proline, and serine), sodium pyruvate (1 mM), and HEPES buffer (10 mM) at 21% O2 and 5% CO2. Following cell line derivation and verification of Sdhc genetic status, cells were treated with histone acetyltransferase inhibitors C646 (10 µM) and MB-3 (100 µM) or vehicle for 3 days. Accessible chromatin regions were subsequently interrogated by ATAC-seq.
Project description:Mitochondrial function is an important control variable in the progression of metabolic dysfunction associated fatty liver disease (MAFLD). We hypothesize that organization and function of mitochondrial electron transport chain (ETC) in this pathologic condition is a consequence of shifted substrate availability. Paradoxically, in MAFLD increased de novo lipogenesis (DNL) occurs despite hepatic insulin resistance. Therefore, we addressed this question using our animal model alb-SREBP-1c, which exhibits increased DNL by constitutively active SREBP-1c. Using an omics approach, we show that the abundance of ETC complex subunits and metabolic pathways are altered in liver of these animals. Analyses of cellular metabolic status by functional assays revealed that SREBP-1c-forced DNL induces a limitation of substrates for oxidative phosphorylation that is rescued by enhanced complex II activity. Furthermore, energy metabolism associated gene regulation indicates the counteracting to increase expression of mitochondrial genes and features cell communication by miRNA and exosomal RNA transfer. In conclusion, substrate availability fuels mainly complex II electron flows as a consequence of activated DNL with impact on whole body by liver-specific exosomal RNAs in early stages of MAFLD.
Project description:We have developed a tet-inducible SV-40 large T antigen-expressing lentivirus-immortalized mouse embryonic fibroblast (iMEF) cell culture model of mitochondrial electron transport chain (ETC) dysfunction involving complex II (succinate dehydrogenase; SDH) in which silencing gene rearrangement of the Sdhc floxed allele is driven by doxycycline-dependent expression of cre-recombinase from a tet-inducible promoter (R26M2rtTA/+;TetOcre;Sdhcfl/fl). For comparison, we include an isogenic Sdhc wt control line (R26M2rtTA/+;TetOcre;Sdhcfl/wt) that retains one intact copy of Sdhc upon doxycycline exposure. Following doxycycline induction of both cell lines, dilutional subcloning was employed to obtain stable Sdhc -/- (SDHC KO) and Sdhc +/- (Control) cell lines. Sdhc gene rearrangement status for each clonally-derived cell line was confirmed by PCR. Cell lines were grown in standard DMEM containing penicillin/streptomycin antibiotics (0.5 mg/mL), non-essential amino acids (100 micromolar each of glycine, alanine, asparagine, aspartic acid, glutamic acid, proline, and serine), sodium pyruvate (1 mM), and HEPES buffer (10 mM) at 21% O2 and 5% CO2. Following cell line derivation and verification of Sdhc genetic status, long-range genomic contacts were profiled using eHi-C.
Project description:We have developed a tet-inducible SV-40 large T antigen-expressing lentivirus-immortalized mouse embryonic fibroblast (iMEF) cell culture model of mitochondrial electron transport chain (ETC) dysfunction involving complex II (succinate dehydrogenase; SDH) in which silencing gene rearrangement of the Sdhc floxed allele is driven by doxycycline-dependent expression of cre-recombinase from a tet-inducible promoter (R26M2rtTA/+;TetOcre;Sdhcfl/fl). For comparison, we include an isogenic Sdhc wt control line (R26M2rtTA/+;TetOcre;Sdhcfl/wt) that retains one intact copy of Sdhc upon doxycycline exposure. Following doxycycline induction of both cell lines, dilutional subcloning was employed to obtain stable Sdhc -/- (SDHC KO) and Sdhc +/- (Control) cell lines. Sdhc gene rearrangement status for each clonally-derived cell line was confirmed by PCR. Cell lines were grown in standard DMEM containing penicillin/streptomycin antibiotics (0.5 mg/mL), non-essential amino acids (100 micromolar each of glycine, alanine, asparagine, aspartic acid, glutamic acid, proline, and serine), sodium pyruvate (1 mM), and HEPES buffer (10 mM) at 21% O2 and 5% CO2. Following cell line derivation and verification of Sdhc genetic status, chromatin epigenomic marks including H3K4me3, H3K27me2, H3K27ac, CTCF, acetyllysine, propionyllysine, and butyryllysine were characterized by CUT&RUN.
Project description:We have developed a tet-inducible SV-40 large T antigen-expressing lentivirus-immortalized mouse embryonic fibroblast (iMEF) cell culture model of mitochondrial electron transport chain (ETC) dysfunction involving complex II (succinate dehydrogenase; SDH) in which silencing gene rearrangement of the Sdhc floxed allele is driven by doxycycline-dependent expression of cre-recombinase from a tet-inducible promoter (R26M2rtTA/+;TetOcre;Sdhcfl/fl). For comparison, we include an isogenic Sdhc wt control line (R26M2rtTA/+;TetOcre;Sdhcfl/wt) that retains one intact copy of Sdhc upon doxycycline exposure. Following doxycycline induction of both cell lines, dilutional subcloning was employed to obtain stable Sdhc -/- (SDHC KO) and Sdhc +/- (Control) cell lines. Sdhc gene rearrangement status for each clonally-derived cell line was confirmed by PCR. Cell lines were grown in standard DMEM containing penicillin/streptomycin antibiotics (0.5 mg/mL), non-essential amino acids (100 micromolar each of glycine, alanine, asparagine, aspartic acid, glutamic acid, proline, and serine), sodium pyruvate (1 mM), and HEPES buffer (10 mM) at 21% O2 and 5% CO2. Following cell line derivation and verification of Sdhc genetic status, accessible chromatin regions in each cell line were interrogated by ATAC-seq.