Project description:Exposure to hypoxia requires adaptive mechanisms for survival. During acute hypoxia, Na,K-ATPase endocytosis in alveolar epithelial cells (AEC) occurs via protein kinase C zeta (PKCζ) phosphorylation of α1- Na,K-ATPase independently of the hypoxia inducible factor (HIF). However, exaggerated Na,K-ATPase down-regulation leads to cell death. Here we report that during prolonged hypoxia plasma membrane Na,K-ATPase levels were maintained at ~50% of normoxic values due to HIF mediated regulation of HOIL-1L which targets PKCζ for degradation. Silencing HOIL-1L in the lung epithelium prevented PKCζ degradation causing Na,K-ATPase downregulation. Accordingly, HIF regulation of HOIL-1L targets the phosphorylated PKCζ for degradation and serves as an hypoxia-adaptive mechanism to stabilize the Na,K-ATPase avoiding significant lung injury.
Project description:HOIL-1L is an essential member of the linear ubiquitin assembly complex (LUBAC), which targets Nemo for linear ubiquitination during NF-kB activation in response to a variety of simuli, including LPS and TNFa treatment. HOIL-1L has also been suggested to function as a transcription factor. Here we analyzed changes in the global transcriptional profiles of primary bone marrow derived macrophage (BMDMs) from WT and HOIL-1L-/- mice upon treatment with NF-kB activating simuli.
Project description:The linear ubiquitin chain assembly complex (LUBAC) is the only known ubiquitin ligase that generates linear/Met1-linked ubiquitin chains. One of the LUBAC components, HOIL-1L, was recently shown to catalyse oxyester bond formation between the C-terminus of ubiquitin and some substrates. However, oxyester bond formation in the context of LUBAC has not been directly observed. We present the first 3D reconstruction of LUBAC obtained by electron microscopy and report its generation of heterotypic ubiquitin chains containing linear linkages with oxyester-linked branches. We found that addition of the oxyester-bound branches depends on HOIL-1L catalytic activity. We suggest a coordinated ubiquitin relay mechanism between the HOIP and HOIL-1L ligases supported by cross-linking mass spectrometry data, which show proximity between the catalytic RBR domains. Mutations in the linear ubiquitin chain-binding NZF domain of HOIL-1L reduces chain branching confirming its role in the process. In cells, these heterotypic chains were induced by TNF. In conclusion, we demonstrate that LUBAC assembles heterotypic ubiquitin chains with linear and oxyester-linked branches by the concerted action of HOIP and HOIL-1L.
Project description:HOIL-1L is an essential member of the linear ubiquitin assembly complex (LUBAC), which targets Nemo for linear ubiquitination during NF-kB activation in response to a variety of simuli, including LPS and TNFa treatment. HOIL-1L has also been suggested to function as a transcription factor. Here we analyzed changes in the global transcriptional profiles of primary bone marrow derived macrophage (BMDMs) from WT and HOIL-1L-/- mice upon treatment with NF-kB activating simuli. BMDMs were differentiated for 1 week and then treated with mock (untreated), 10ng/ml LPS, or 1ng/ml TNFa for 4 hours. RNA was immediately collected and analyzed in biological duplicates by the Agilent 8x60 mouse array.
Project description:Electrochemical gradients of monovalent cations across the plasma membrane (high intracellular potassium, [K+]i vs low intracellular sodium, [Na+]i) are created by the Na+,K+-pump and determine a large variety of physiologically important processes. We hypothesized that transcriptomics changes triggered by hypoxia are at least partially caused by Na+i/K+i-mediated excitation-transcription coupling . We used microarrays for identification and functional characterization of [Na+]i/]K+]i-sensitive transcriptome in RASMC
Project description:Hypoxia is the most prominent feature in human solid tumors and induces activation of hypoxia-inducible factors and their downstream genes to promote cancer progression. However, whether and how hypoxia regulates overall mRNA homeostasis is unclear. Here we show that hypoxia inhibits global-mRNA decay in cancer cells. Mechanistically, hypoxia induces the interaction of AGO2 with HOIL-1L/HOIP, two crucial components of a linear ubiquitin chain assembly complex, which co-localizes with miRNA-induced silencing complex and in turn catalyzes AGO2 occurring Met1-linked linear ubiquitination (M1-Ubi). A series of biochemical experiments reveal that M1-Ubi of AGO2 restrains miRNA-mediated gene silencing. Moreover, combination analyses of the AGO2-associated mRNA transcriptome by RIP-Seq and the mRNA transcriptome by RNA-Seq confirm that AGO2 M1-Ubi interferes miRNA-targeted mRNA recruiting to AGO2, and thereby facilitates accumulation of global mRNAs. By this mechanism, short-term hypoxia may protect overall mRNAs and enhances stress tolerance, whereas long-term hypoxia in tumor cells results in serious changing the entire gene expression profile, which is a driving force in the dynamic process of cell malignant evolution.
Project description:Alternative RNA splicing analysis in Hep3B cell cultured under 21% (N1,3,5) or 1.2% (H2,4,6) oxygen Hypoxia is a common characteristic of many solid tumors. The hypoxic microenvironment stabilizes hypoxia-inducible transcription factor 1? (HIF1?) and 2? (HIF2?) to activate gene transcription, which promotes tumor cell survival. 95% of human genes are alternatively spliced, producing RNA isoforms that code functionally distinct proteins. Thus, effective hypoxia response requires increased HIF target gene transcription as well as proper RNA splicing of these HIF target genes. However, it is unclear if and how hypoxia regulates RNA splicing of HIF target genes. This study determined the effects of hypoxia on alternative splicing (AS) of HIF and non-HIF target genes in Hep3B cells and characterized the role of HIF in regulating AS of HIF induced genes. The results indicated that hypoxia generally promotes exon inclusion for hypoxia-induced, but reduces exon inclusion for hypoxia reduced genes. Mechanistically, HIF activity, but not hypoxia per se is found to be necessary and sufficient to increase exon inclusion of several HIF target genes including pyruvate dehydrogenase kinase 1 (PDK1). PDK1 splicing reporters confirmed that transcriptional activation by HIF is sufficient to increase exon inclusion of PDK1 splicing reporter. In contrast, transcriptional activation of the PDK1 minigene by other transcription factor in the absence of endogenous HIF target gene activation fails to alter PDK1 RNA splicing, demonstrating a novel role of HIF target gene(s) in regulating RNA splicing of HIF target genes. Implications:This study demonstrates a novel function of HIF in regulating RNA splicing of HIF target genes. We analyzed total RNA from Hep3B cells cultured under 21% (N1,3,5) or 1.2% (H2,4,6) oxygen using the Affymetrix Human Exon 1.0 ST platform. Array data was processed by Altanalyze software version 2.0.7. Techinical replicates were performed for Nx and Hx treated Hep3B cells
Project description:The resistance of hypoxic cells to radiotherapy and chemotherapy is a major problem in the treatment of cancer. Recently, an additional level of Hypoxia Inducible Factor (HIF) dependent transcriptional regulation has emerged involving modulation of a specific set of miRNAs including miR-210. We have recently shown that HIF-1 induction of miR-210 also stabilizes HIF-1 through a positive regulatory loop. We therefore hypothesized that by stabilizing HIF-1 in normoxia, miR-210 may protect cancer cells from radiation. We developed Non-Small Cell Lung Cancer (NSCLC)-derived cell lines (A549 and H1975) stably expressing miR-210 (pmiR-210) or a control miRNA (pmiR-Ctl). MiR-210 expressing cells showed a significant stabilization of HIF-1 associated with mitochondrial defects and a glycolytic phenotype. The cells were subjected to radiation levels ranging from 0 to 10Gy in normoxia and hypoxia. Cells expressing miR-210 in normoxia had the same level of resistance than control cells in hypoxia. pmiR-210 cells under hypoxia showed a low mortality rate due to a decrease in apoptosis and an ability to grow even at 10Gy. We have established that radioresistance was independent of p53 and cell cycle status. In addition, we show here that genomic double strand breaks (DSB) foci disappeared faster in pmiR-210 than in pmiR-Ctl cells, suggesting that miR-210 expression promotes a more efficient DSB repair. Finally, HIF-1 invalidation in pmiR-210 cells (pmiR-210/HIF-1-) abolished radioresistance of cells showing that this mechanism was dependent upon HIF-1. In conclusion, miR-210 appears to be a major component in the radioresistance of hypoxic cancer cells. Given the high stability of most miRNAs, this advantage could even be used by tumor cells in conditions where hypoxia may not be present anymore and strongly suggests that strategies targeting miR-210 would enhance tumor radiosensitization. To identify the set of transcripts targeted by miR-210, we overexpressed has-miR-210 or a control miRNA (ce-miR-67) in human lung adenocarcinoma A549 cells by transduction using lentivirus. The resulting pmiR-67 and pmiR-210 that stably overexpress miR-210 were selected by puromycin. RNA samples were harvested at 2 different times following cell plating (24 hours or 48 hours). Experiments were performed in dye-swap.
Project description:The resistance of hypoxic cells to radiotherapy and chemotherapy is a major problem in the treatment of cancer. Recently, an additional level of Hypoxia Inducible Factor (HIF) dependent transcriptional regulation has emerged involving modulation of a specific set of miRNAs including miR-210. We have recently shown that HIF-1 induction of miR-210 also stabilizes HIF-1 through a positive regulatory loop. We therefore hypothesized that by stabilizing HIF-1 in normoxia, miR-210 may protect cancer cells from radiation. We developed Non-Small Cell Lung Cancer (NSCLC)-derived cell lines (A549 and H1975) stably expressing miR-210 (pmiR-210) or a control miRNA (pmiR-Ctl). MiR-210 expressing cells showed a significant stabilization of HIF-1 associated with mitochondrial defects and a glycolytic phenotype. The cells were subjected to radiation levels ranging from 0 to 10Gy in normoxia and hypoxia. Cells expressing miR-210 in normoxia had the same level of resistance than control cells in hypoxia. pmiR-210 cells under hypoxia showed a low mortality rate due to a decrease in apoptosis and an ability to grow even at 10Gy. We have established that radioresistance was independent of p53 and cell cycle status. In addition, we show here that genomic double strand breaks (DSB) foci disappeared faster in pmiR-210 than in pmiR-Ctl cells, suggesting that miR-210 expression promotes a more efficient DSB repair. Finally, HIF-1 invalidation in pmiR-210 cells (pmiR-210/HIF-1-) abolished radioresistance of cells showing that this mechanism was dependent upon HIF-1. In conclusion, miR-210 appears to be a major component in the radioresistance of hypoxic cancer cells. Given the high stability of most miRNAs, this advantage could even be used by tumor cells in conditions where hypoxia may not be present anymore and strongly suggests that strategies targeting miR-210 would enhance tumor radiosensitization.
Project description:Alternative RNA splicing analysis in Hep3B cell cultured under 21% (N1,3,5) or 1.2% (H2,4,6) oxygen Hypoxia is a common characteristic of many solid tumors. The hypoxic microenvironment stabilizes hypoxia-inducible transcription factor 1α (HIF1α) and 2α (HIF2α) to activate gene transcription, which promotes tumor cell survival. 95% of human genes are alternatively spliced, producing RNA isoforms that code functionally distinct proteins. Thus, effective hypoxia response requires increased HIF target gene transcription as well as proper RNA splicing of these HIF target genes. However, it is unclear if and how hypoxia regulates RNA splicing of HIF target genes. This study determined the effects of hypoxia on alternative splicing (AS) of HIF and non-HIF target genes in Hep3B cells and characterized the role of HIF in regulating AS of HIF induced genes. The results indicated that hypoxia generally promotes exon inclusion for hypoxia-induced, but reduces exon inclusion for hypoxia reduced genes. Mechanistically, HIF activity, but not hypoxia per se is found to be necessary and sufficient to increase exon inclusion of several HIF target genes including pyruvate dehydrogenase kinase 1 (PDK1). PDK1 splicing reporters confirmed that transcriptional activation by HIF is sufficient to increase exon inclusion of PDK1 splicing reporter. In contrast, transcriptional activation of the PDK1 minigene by other transcription factor in the absence of endogenous HIF target gene activation fails to alter PDK1 RNA splicing, demonstrating a novel role of HIF target gene(s) in regulating RNA splicing of HIF target genes. Implications:This study demonstrates a novel function of HIF in regulating RNA splicing of HIF target genes.