RESUMO
We show that mitochondrial DNA (mtDNA)-depleted 143B cells are hypersensitive to staurosporine-induced cell death as evidenced by a more pronounced DNA fragmentation, a stronger activation of caspase-3, an enhanced poly(ADP-ribose) polymerase-1 (PARP-1) cleavage, and a more dramatic cytosolic release of cytochrome c. We also show that B-cell CLL/lymphoma-2 (Bcl-2), B-cell lymphoma extra large (Bcl-X(L)), and myeloid cell leukemia-1 (Mcl-1) are constitutively less abundant in mtDNA-depleted cells, that the inhibition of Bcl-2 and Bcl-X(L) can sensitize the parental cell line to staurosporine-induced apoptosis, and that overexpression of Bcl-2 or Bcl-X(L) can prevent the activation of caspase-3 in ρ(0)143B cells treated with staurosporine. Moreover, the inactivation of cathepsin B with CA074-Me significantly reduced cytochrome c release, caspase-3 activation, PARP-1 cleavage, and DNA fragmentation in mtDNA-depleted cells, whereas the pan-caspase inhibitor failed to completely prevent PARP-1 cleavage and DNA fragmentation in these cells, suggesting that caspase-independent mechanisms are responsible for cell death even if caspases are activated. Finally, we show that cathepsin B is released in the cytosol of ρ(0) cells in response to staurosporine, suggesting that the absence of mitochondrial activity leads to a facilitated permeabilization of lysosomal membranes in response to staurosporine.
Assuntos
Apoptose/genética , Catepsina B/metabolismo , DNA Mitocondrial/genética , Regulação para Baixo , Inibidores Enzimáticos/farmacologia , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , Estaurosporina/farmacologia , Caspase 3/metabolismo , Catepsina B/antagonistas & inibidores , Linhagem Celular Tumoral , Citocromos c/metabolismo , Fragmentação do DNA , Dipeptídeos/farmacologia , Humanos , Proteína de Sequência 1 de Leucemia de Células Mieloides , Poli(ADP-Ribose) Polimerase-1 , Poli(ADP-Ribose) Polimerases/metabolismo , Proteínas Proto-Oncogênicas c-bcl-2/genética , Proteína bcl-X/metabolismoRESUMO
RNA-mediated gene silencing (RNA interference) is a powerful way to knock down gene expression and has revolutionized the fields of cellular and molecular biology. Indeed, the transfection of cultured cells with small interfering RNAs (siRNAs) is currently considered to be the best and easiest approach to loss-of-function experiments. However, several recent studies underscore the off-target and potential cytotoxic effects of siRNAs, which can lead to the silencing of unintended mRNAs. In this study, we used a low-density microarray to assess gene expression modifications in response to five different siRNAs in various cell types and transfection conditions. We found major differences in off-target signature according to: (a) siRNA sequence; (b) cell type; (c) duration of transfection; and (d) post-transfection time before analysis. These results contribute to a better understanding of important parameters that could impact on siRNA side effects in knockdown experiments.
Assuntos
Regulação da Expressão Gênica , Inativação Gênica , RNA Interferente Pequeno/metabolismo , Linhagem Celular Tumoral , Perfilação da Expressão Gênica , Técnicas Genéticas , Humanos , Cinética , Análise de Sequência com Séries de Oligonucleotídeos , Interferência de RNA , RNA Mensageiro/metabolismo , Proteína de Ligação a Elemento Regulador de Esterol 1/metabolismo , Fatores de Tempo , TransfecçãoRESUMO
Alterations in mitochondrial activity resulting from defects in mitochondrial DNA (mtDNA) can modulate the biogenesis of mitochondria by mechanisms that are still poorly understood. In order to study mitochondrial biogenesis in cells with impaired mitochondrial activity, we used rho-L929 and rho(0)143 B cells (partially and totally depleted of mtDNA, respectively), that maintain and even up-regulate mitochondrial population, to characterize the activity of major transcriptional regulators (Sp1, YY1, MEF2, PPARgamma, NRF-1, NRF-2, CREB and PGC-1alpha) known to control the expression of numerous nuclear genes encoding mitochondrial proteins. Among these regulators, cyclic AMP-responsive element binding protein (CREB) activity was the only one to be increased in mtDNA-depleted cells. CREB activation mediated by a calcium-dependent pathway in these cells also regulates the expression of cytochrome c and the abundance of mitochondrial population as both are decreased in mtDNA-depleted cells that over-express CREB dominant negative mutants. Mitochondrial biogenesis in mtDNA-depleted cells is also dependent on intracellular calcium as its chelation reduces mitochondrial mass. Despite a slight increase in mitochondrial mass in mtDNA-depleted cells, the mitochondrial protein import activity was reduced as shown by a decrease in the import of radiolabeled matrix-targeted recombinant proteins into isolated mitochondria and by the reduced mitochondrial localization of ectopically expressed HA-apoaequorin targeted to the mitochondria. Decrease in ATP content, in mitochondrial membrane potential as well as reduction in mitochondrial Tim44 abundance could explain the lower mitochondrial protein import in mtDNA-depleted cells. Taken together, these results suggest that mitochondrial biogenesis is stimulated in mtDNA-depleted cells and involves a calcium-CREB signalling pathway but is associated with a reduced mitochondrial import for matrix proteins.
Assuntos
Cálcio/metabolismo , DNA Mitocondrial/metabolismo , Mitocôndrias/genética , Mitocôndrias/metabolismo , Proteínas Mitocondriais/metabolismo , Trifosfato de Adenosina/metabolismo , Animais , Biomarcadores , Sinalização do Cálcio , Proteína Quinase Tipo 4 Dependente de Cálcio-Calmodulina , Proteínas Quinases Dependentes de Cálcio-Calmodulina/metabolismo , Linhagem Celular , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/metabolismo , Proteínas de Ligação a DNA/metabolismo , Camundongos , Microscopia Eletrônica , Mitocôndrias/ultraestrutura , Fator 1 Relacionado a NF-E2 , Fator 2 Relacionado a NF-E2 , Fator 1 Nuclear Respiratório , Fatores Nucleares Respiratórios , Transporte Proteico , Transativadores/metabolismoRESUMO
Impairment of mitochondrial activity affects lipid-metabolizing tissues and mild mitochondrial uncoupling has been proposed as a possible strategy to fight obesity and associated diseases. In this report, we characterized the 3T3-L1-adipocyte ;de-differentiation' induced by carbonyl cyanide (p-trifluoromethoxy)-phenylhydrazone (FCCP), a mitochondrial uncoupler. We found a decrease in triglyceride (TG) content in adipocytes incubated with this molecule. We next analyzed the expression of genes encoding adipogenic markers and effectors and compared the differentially expressed genes in adipocytes treated with FCCP or TNFalpha (a cytokine known to induce adipocyte de-differentiation). Furthermore, a significant decrease in the transcriptional activity of PPARgamma and C/EBPalpha transcription factors was found in adipocytes with impaired mitochondrial activity. However, although these modifications were also found in TNFalpha-treated adipocytes, rosiglitazone and 9-cis retinoic acid (PPARgamma and RXR ligands) were unable to prevent triglyceride loss in FCCP-treated cells. Metabolic assays also revealed that TG reduction could be mediated by a downregulation of lipid synthesis rather than an upregulation of fatty acid oxidation. Finally, lipolysis stimulated by the uncoupler also seems to contribute to the TG reduction, a process associated with perilipin A downregulation. These results highlight some new mechanisms that might potentially be involved in adipocyte de-differentiation initiated by a mitochondrial uncoupling.
Assuntos
Células 3T3-L1/metabolismo , Desdiferenciação Celular/fisiologia , Mitocôndrias , PPAR gama/metabolismo , Fator de Necrose Tumoral alfa/metabolismo , Desacopladores/farmacologia , Animais , Biomarcadores/metabolismo , Carbonil Cianeto p-Trifluormetoxifenil Hidrazona/farmacologia , Perfilação da Expressão Gênica , Metabolismo dos Lipídeos , Camundongos , Mitocôndrias/efeitos dos fármacos , Mitocôndrias/metabolismo , Receptores X de Retinoides/metabolismoRESUMO
Several mitochondrial pathologies are characterized by lipid redistribution and microvesicular cell phenotypes resulting from triglyceride accumulation in lipid-metabolizing tissues. However, the molecular mechanisms underlying abnormal fat distribution induced by mitochondrial dysfunction remain poorly understood. In this study, we show that inhibition of respiratory complex III by antimycin A as well as inhibition of mitochondrial protein synthesis trigger the accumulation of triglyceride vesicles in 3T3-L1 fibroblasts. We also show that treatment with antimycin A triggers CREB activation in these cells. To better delineate how mitochondrial dysfunction induces triglyceride accumulation in preadipocytes, we developed a low-density DNA microarray containing 89 probes, which allows gene expression analysis for major effectors and/or markers of adipogenesis. We thus determined gene expression profiles in 3T3-L1 cells incubated with antimycin A and compared the patterns obtained with differentially expressed genes during the course of in vitro adipogenesis induced by a standard pro-adipogenic cocktail. After an 8-day treatment, a set of 39 genes was found to be differentially expressed in cells treated with antimycin A, among them CCAAT/enhancer-binding protein alpha (C/EBPalpha), C/EBP homologous protein-10 (CHOP-10), mitochondrial glycerol-3-phosphate dehydrogenase (GPDmit), and stearoyl-CoA desaturase 1 (SCD1). We also demonstrate that overexpression of two dominant negative mutants of the cAMP-response element-binding protein CREB (K-CREB and M1-CREB) and siRNA transfection, which disrupt the factor activity and expression, respectively, inhibit antimycin-A-induced triglyceride accumulation. Furthermore, CREB knockdown with siRNA also downregulates the expression of several genes that contain cAMP-response element (CRE) sites in their promoter, among them one that is potentially involved in synthesis of triglycerides such as SCD1. These results highlight a new role for CREB in the control of triglyceride metabolism during the adaptative response of preadipocytes to mitochondrial dysfunction.
Assuntos
Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/metabolismo , Mitocôndrias/patologia , Triglicerídeos/biossíntese , Células 3T3-L1 , Adipócitos/citologia , Animais , Antimicina A/farmacologia , Western Blotting , Diferenciação Celular , Cloranfenicol/farmacologia , DNA/análise , DNA/genética , DNA Complementar/genética , Ensaio de Imunoadsorção Enzimática , Fluoresceínas , Técnica Indireta de Fluorescência para Anticorpo , Corantes Fluorescentes , Perfilação da Expressão Gênica , Inativação Gênica , Genes Reporter , Hibridização In Situ , Metabolismo dos Lipídeos , Luciferases/análise , Luciferases/metabolismo , Camundongos , Mitocôndrias/metabolismo , Análise de Sequência com Séries de Oligonucleotídeos , Ligação Proteica , RNA Interferente Pequeno/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
Mitochondrial cytopathy has been associated with modifications of lipid metabolism in various situations, such as the acquisition of an abnormal adipocyte phenotype observed in multiple symmetrical lipomatosis or triglyceride (TG) accumulation in muscles associated with the myoclonic epilepsy with ragged red fibers syndrome. However, the molecular signaling leading to fat metabolism dysregulation in cells with impaired mitochondrial activity is still poorly understood. Here, we found that preadipocytes incubated with inhibitors of mitochondrial respiration such as antimycin A (AA) accumulate TG vesicles but do not acquire specific markers of adipocytes. Although the uptake of TG precursors is not stimulated in 3T3-L1 cells with impaired mitochondrial activity, we found a strong stimulation of glucose uptake in AA-treated cells mediated by calcium and phosphatidylinositol 3-kinase/Akt1/glycogen synthase kinase 3beta, a pathway known to trigger the translocation of glucose transporter 4 to the plasma membrane in response to insulin. TG accumulation in AA-treated cells is mediated by a reduced peroxisome proliferator-activated receptor gamma activity that downregulates muscle carnitine palmitoyl transferase-1 expression and fatty acid beta-oxidation, and by a direct conversion of glucose into TGs accompanied by the activation of carbohydrate-responsive element binding protein, a lipogenic transcription factor. Taken together, these results could explain how mitochondrial impairment leads to the multivesicular phenotype found in some mitochondria-originating diseases associated with a dysfunction in fat metabolism.