New Pathophysiological Insights from Serum Proteome Profiling in Equine Atypical Myopathy

Equine atypical myopathy (AM) is a severe environmental intoxication linked to the ingestion of protoxins contained in seeds and seedlings of the sycamore maple (Acer pseudoplatanus) in Europe. The toxic metabolites cause a frequently fatal rhabdomyolysis syndrome in grazing horses. Since these toxic metabolites can also be present in cograzing horses, it is still unclear as to why, in a similar environmental context, some horses show signs of AM, whereas others remain clinically healthy. Label-free proteomic analyses on the serum of 26 diseased AM, 23 cograzers, and 11 control horses were performed to provide insights into biological processes and pathways. A total of 43 and 44 differentially abundant proteins between "AM vs cograzing horses" and "AM vs control horses" were found. Disease-linked changes in the proteome of different groups were found to correlate with detected amounts of toxins, and principal component analyses were performed to identify the 29 proteins representing a robust AM signature. Among the pathway-specific changes, the glycolysis/gluconeogenesis pathway, the coagulation/complement cascade, and the biosynthesis of amino acids were affected. Sycamore maple poisoning results in a combination of inflammation, oxidative stress, and impaired lipid metabolism, which is trying to be counteracted by enhanced glycolysis.

Indacaterol inhibits collective cell migration and IGDQ-mediated single cell migration in metastatic breast cancer MDA-MB-231 cells

Metastasis is the main cause of deaths related to breast cancer. This is particular the case for triple negative breast cancer. No targeted therapies are reported as efficient until now. The extracellular matrix, in particular the fibronectin type I motif IGDQ, plays a major role in regulating cell migration prior metastasis formation. This motif interacts with specific integrins inducing their activation and the migratory signal transduction.Here, we characterized the migratory phenotype of MDA-MB-231 cells, using functionalized IGDQ-exposing surfaces, and compared it to integrin A5 and integrin B3 knock-down cells. A multiomic analysis was developed that highlighted the splicing factor SRSF6 as a putative master regulator of cell migration and of integrin intracellular trafficking. Indacaterol-induced inhibition of SRSF6 provoked: i) the inhibition of collective and IGDQ-mediated cell migration and ii) ITGA5 sequestration into endosomes and lysosomes. Upon further studies, indacaterol may be a potential therapy to prevent cell migration and reduce metastasis formation in breast cancer. Video Abstract.

Senescence Induced by UVB in Keratinocytes Impairs Amino Acids Balance

Skin is one of the most exposed organs to external stress. Namely, UV rays are the most harmful stress that could induce important damage leading to skin aging and cancers. At the cellular level, senescence is observed in several skin cell types and contributes to skin aging. However, the origin of skin senescent cells is still unclear but is probably related to exposure to stresses. In this work, we developed an in vitro model of UVB-induced premature senescence in normal human epidermal keratinocytes. UVB-induced senescent keratinocytes display a common senescent phenotype resulting in an irreversible cell cycle arrest, an increase in the proportion of senescence-associated β-galactosidase‒positive cells, unrepaired DNA damage, and a long-term DNA damage response activation. Moreover, UVB-induced senescent keratinocytes secrete senescence-associated secretory phenotype factors that influence cutaneous squamous cell carcinoma cell migration. Finally, a global transcriptomic study highlighted that senescent keratinocytes present a decrease in the expression of several amino acid transporters, which is associated with reduced intracellular levels of glycine, alanine, and leucine. Interestingly, the chemical inhibition of the glycine transporter SLC6A9/Glyt1 triggers senescence features.

Characterization of the Proteins Secreted by Equine Muscle-Derived Mesenchymal Stem Cells Exposed to Cartilage Explants in Osteoarthritis Model

BACKGROUND

Osteoarthritis (OA) is a highly prevalent joint degenerative disease for which therapeutic treatments are limited or invasive. Cell therapy based on mesenchymal stem/stromal cells (MSCs) is therefore seen as a promising approach for this disease, in both human and horses. As the regenerative potential of MSCs is mainly conferred by paracrine function, the goal of this study was to characterize the secreted proteins of muscle-derived MSCs (mdMSCs) in an in vitro model of OA to evaluate the putative clinical interest of mdMSCs as cell therapy for joint diseases like osteoarthritis.

METHODS

An equine osteoarthritis model composed of cartilage explants exposed to pro-inflammatory cytokines was first developed. Then, the effects of mdMSC co-culture on cartilage explant were studied by measuring the glycosaminoglycan release and the NO₂^- production. To identify the underlying molecular actors, stable isotope-labeling by amino acids in cell culture based secreted protein analyses were conducted, in the presence of serum. The relative abundance of highly sequenced proteins was finally confirmed by western blot.

RESULTS

Co-culture with muscle-derived MSCs decreases the cytokine-induced glycosaminoglycan release by cartilage explants, suggesting a protecting effect of mdMSCs. Among the 52 equine proteins sequenced in the co-culture conditioned medium, the abundance of decorin and matrix metalloproteinase 3 was significantly modified, as confirmed by western blot analyses.

CONCLUSIONS

These results suggest that muscle-derived MSCs could reduce the catabolic effect of TNFα and IL-1β on cartilage explant by decreasing the secretion and activity of matrix metalloproteinase 3 and increasing the decorin secretion. mdMSCs capacity to reduce the catabolic consequences of cartilage exposure to pro-inflammatory cytokines. These effects can be explained by mdMSC-secreted bioactive such as TIMP-1 and decorin, known as an inhibitor of MMP3 and an anti-inflammatory protein, respectively.

The global downregulation of protein synthesis observed during hepatogenic maturation is associated with a decrease in TOP mRNA translation

Translational regulation is of paramount importance for proteome remodeling during stem cell differentiation at both the global and the transcript-specific levels. In this study, we characterized translational remodeling during hepatogenic differentiation of induced pluripotent stem cells (iPSCs) by polysome profiling. We demonstrate that protein synthesis increases during exit from pluripotency and is then globally repressed during later steps of hepatogenic maturation. This global downregulation of translation is accompanied by a decrease in the abundance of protein components of the translation machinery, which involves a global reduction in translational efficiency of terminal oligopyrimidine tract (TOP) mRNA encoding translation-related factors. Despite global translational repression during hepatogenic differentiation, key hepatogenic genes remain efficiently translated, and the translation of several transcripts involved in hepatospecific functions and metabolic maturation is even induced. We conclude that, during hepatogenic differentiation, a global decrease in protein synthesis is accompanied by a specific translational rewiring of hepatospecific transcripts.

DNA repair during nonreductional meiosis in the asexual rotifer Adineta vaga

Rotifers of the class Bdelloidea are microscopic animals notorious for their long-term persistence in the apparent absence of sexual reproduction and meiotic recombination. This evolutionary paradox is often counterbalanced by invoking their ability to repair environmentally induced genome breakage. By studying the dynamics of DNA damage response in the bdelloid species Adineta vaga, we found that it occurs rapidly in the soma, producing a partially reassembled genome. By contrast, germline DNA repair is delayed to a specific time window of oogenesis during which homologous chromosomes adopt a meiotic-like juxtaposed configuration, resulting in accurate reconstitution of the genome in the offspring. Our finding that a noncanonical meiosis is the mechanism of germline DNA repair in bdelloid rotifers gives previously unidentified insights on their enigmatic long-term evolution.

IGDQ motogenic peptide gradient induces directional cell migration through integrin (αv)β3 activation in MDA-MB-231 metastatic breast cancer cells

In the context of breast cancer metastasis study, we have shown in an in vitro model of cell migration that IGDQ-exposing (IsoLeu-Gly-Asp-Glutamine type I Fibronectin motif) monolayers (SAMs) on gold sustain the adhesion of breast cancer MDA-MB-231 cells by triggering Focal Adhesion Kinase and integrin activation. Such tunable scaffolds are used to mimic the tumor extracellular environment, inducing and controlling cell migration. The observed migratory behavior induced by the IGDQ-bearing peptide gradient along the surface allows to separate cell subpopulations with a "stationary" or "migratory" phenotype. In this work, we knocked down the integrins α5(β1) and (αv)β since they are already known to be implicated in cell migration. To this aim, a whole proteomic analysis was performed in beta 3 integrin (ITGB3) or alpha 5 integrin (ITGA5) knock-down MDA-MB-231 cells, in order to highlight the pathways implied in the integrin-dependent cell migration. Our results showed that i) ITGB3 depletion influenced ITGA5 mRNA expression, ii) ITGB3 and ITGA5 were both necessary for IGDQ-mediated directional single cell migration and iii) integrin (αv)β3 was activated by IGDQ fibronectin type I motif. Finally, the proteomic analysis suggested that co-regulation of recycling transport of ITGB3 by ITGA5 is potentially necessary for directional IGDQ-mediated cell migration.

Taking Advantage of the Senescence-Promoting Effect of Olaparib after X-ray and Proton Irradiation Using the Senolytic Drug, ABT-263

Radiotherapy (RT) is a key component of cancer treatment. Although improvements have been made over the years, radioresistance remains a challenge. For this reason, a better understanding of cell fates in response to RT could improve therapeutic options to enhance cell death and reduce adverse effects. Here, we showed that combining RT (photons and protons) to noncytotoxic concentration of PARP inhibitor, Olaparib, induced a cell line-dependent senescence-like phenotype. The senescent cells were characterized by morphological changes, an increase in p21 mRNA expression as well as an increase in senescence-associated β-galactosidase activity. We demonstrated that these senescent cells could be specifically targeted by Navitoclax (ABT-263), a Bcl-2 family inhibitor. This senolytic drug led to significant cell death when combined with RT and Olaparib, while limited cytotoxicity was observed when used alone. These results demonstrate that a combination of RT with PARP inhibition and senolytics could be a promising therapeutic approach for cancer patients.

Priming of mesenchymal stem cells with a hydrosoluble form of curcumin allows keeping their mesenchymal properties for cell-based therapy development

Mesenchymal stem cells are increasingly studied for their use as drug‐carrier in addition to their intrinsic potential for regenerative medicine. They could be used to transport molecules with a poor bioavailability such as curcumin in order to improve their clinical usage. This natural polyphenol, well‐known for its antioxidant and anti‐inflammatory properties, has a poor solubility that limits its clinical potential. For this purpose, the use of NDS27, a curcumin salt complexed with hydroxypropyl‐beta‐cyclodextrin (HPβCD), displaying an increased solubility in aqueous solution, is preferred. This study aims to evaluate the uptake of NDS27 into skeletal muscle‐derived mesenchymal stem cells (mdMSCs) and the effects of such uptake onto their mesenchymal properties. It appeared that the uptake of NDS27 into mdMSCs is concentration‐dependent and not time‐dependent. The use of a concentration of 7 µmol/L which does not affect the viability and proliferation also allows preservation of their adhesion, invasion and T cell immunomodulatory abilities.

Optimization of label-free nano LC-MS/MS analysis of the placental proteome

The placenta can be regarded as a mirror of the events to which the fetus is exposed during development. The placental proteome has been studied with several methodologies differing in sample handling, protein extraction, and processing. We optimized a protocol to analyze the placental proteome by means of label-free nano-LC-MS/MS mass spectrometry with regard to sample treatment, protein extraction, and protein digestion, in order to obtain a high protein concentration for identification of a specific protein signature according to the conditions studied. We recommend mechanical tissue disruption, blood removal prior to protein extraction, and FASP-based or in-gel digestion.

Cycling hypoxia promotes a pro-inflammatory phenotype in macrophages via JNK/p65 signaling pathway

Cycling hypoxia (cyH), also called intermittent hypoxia, occurs in solid tumors and affects different cell types in the tumor microenvironment and in particular the tumor-associated macrophages (TAMs). As cyH and TAMs both favor tumor progression, we investigated whether cyH could drive the pro-tumoral phenotype of macrophages. Here, the effects of cyH on human THP-1 macrophages and murine bone marrow-derived macrophages (BMDM), either unpolarized M0, or polarized in M1 or M2 phenotype were studied. In M0 macrophages, cyH induced a pro-inflammatory phenotype characterized by an increase in TNFα and IL-8/MIP-2 secretion. CyH amplified the pro-inflammatory phenotype of M1 macrophages evidenced by an increased pro-inflammatory cytokine secretion and pro-inflammatory gene expression. Furthermore, cyH increased c-jun activation in human M0 macrophages and highly increased c-jun and NF-κB activation in M1 macrophages. C-jun and p65 are implicated in the effects of cyH on M0 and M1 macrophages since inhibition of their activation prevented the cyH pro-inflammatory effects. In conclusion, we demonstrated that cyH induces or amplifies a pro-inflammatory phenotype in M0 and M1 macrophages by activating JNK/p65 signaling pathway. These results highlight a specific role of cyH in the amplification of tumor-related inflammation by modulating the inflammatory phenotype of macrophages.

Characterization of the role of TMEM45A in cancer cell sensitivity to cisplatin

TMEM45A is a transmembrane protein involved in tumor progression and cancer resistance to chemotherapeutic agents in hypoxic condition. It is correlated to a low breast cancer patient overall survival. However, little is known about this protein, in particular the mechanisms by which TMEM45A modulates cancer cell chemosensitivity. In this work, the messenger RNA expression of TMEM45A was assessed in head and neck squamous cell carcinoma (HNSCC) and renal cell carcinoma (RCC) biopsies. TMEM45A was upregulated in patients diagnosed for head and neck or renal cancer. Then, the implication of this protein in cisplatin sensitivity was explored in SQD9 and RCC4 + pVHL cells. TMEM45A inactivation decreased cell proliferation and modulated cell responses to cisplatin. Indeed, TMEM45A inactivation increased the sensitivity of SQD9 cells to cisplatin, whereas it rendered RCC4 + pVHL cells resistant to this anticancer agent. Through RNA-sequencing analysis, we identified several deregulated pathways that indicated that the impact on cisplatin sensitivity may be associated to the inhibition of DNA damage repair and to UPR pathway activation. This study demonstrated, for the first time, an anti or a pro-apoptotic role of this protein depending on the cancer type and highlighted the role of TMEM45A in modulating patient responses to treatment.

Proteomic Study of SUMOylation During Solanum tuberosum-Phytophthora infestans Interactions

Invasive plant pathogens have developed the ability to modify the metabolism of their host, promoting metabolic processes that facilitate the growth of the pathogen at the general expense of the host. The particular enzymatic process SUMOylation, which performs posttranslational modification of target proteins, leading to changes in many aspects of protein activity and, hence, metabolism, has been demonstrated to be active in many eukaryotic organisms, both animals and plants. Here, we provide experimental evidence that indicates that, in leaves of Solanum tuberosum that have been infected by Phytophthora infestans, the SUMO (small ubiquitin-like modifier) pathway enzymes of the host are partially under transcriptional control exerted by the oomycete. Using a recently developed approach that employs three-dimensional gels, we show that, during the infection process, the abundances of most of the known SUMO conjugates of S. tuberosum change significantly, some decreasing, but many increasing in abundance. The new proteomic approach has the potential to greatly facilitate investigation of the molecular events that take place during the invasion by a pathogen of its host plant.

Effects of a Sublethal and Transient Stress of the Endoplasmic Reticulum on the Mitochondrial Population

Endoplasmic reticulum (ER) and mitochondria are not discrete intracellular organelles but establish close physical and functional interactions involved in several biological processes including mitochondrial bioenergetics, calcium homeostasis, lipid synthesis, and the regulation of apoptotic cell death pathways. As many cell types might face a transient and sublethal ER stress during their lifetime, it is thus likely that the adaptive UPR response might affect the mitochondrial population. The aim of this work was to study the putative effects of a non-lethal and transient endoplasmic reticulum stress on the mitochondrial population in HepG2 cells. The results show that thapsigargin and brefeldin A, used to induce a transient and sublethal ER stress, rapidly lead to the fragmentation of the mitochondrial network associated with a decrease in mitochondrial membrane potential, O2 (•-) production and less efficient respiration. These changes in mitochondrial function are transient and preceded by the phosphorylation of JNK. Inhibition of JNK activation by SP600125 prevents the decrease in O2 (•-) production and the mitochondrial network fragmentation observed in cells exposed to the ER stress but has no impact on the reduction of the mitochondrial membrane potential. In conclusion, our data show that a non-lethal and transient ER stress triggers a rapid activation of JNK without inducing apoptosis, leading to the fragmentation of the mitochondrial network and a reduction of O2 (•-) production. J. Cell. Physiol. 231: 1913-1931, 2016. © 2015 Wiley Periodicals, Inc.

Copper(II) oxide nanoparticles penetrate into HepG2 cells, exert cytotoxicity via oxidative stress and induce pro-inflammatory response

The potential toxic effects of two types of copper(II) oxide (CuO) nanoparticles (NPs) with different specific surface areas, different shapes (rod or spheric), different sizes as raw materials and similar hydrodynamic diameter in suspension were studied on human hepatocarcinoma HepG2 cells. Both CuO NPs were shown to be able to enter into HepG2 cells and induce cellular toxicity by generating reactive oxygen species. CuO NPs increased the abundance of several transcripts coding for pro-inflammatory interleukins and chemokines. Transcriptomic data, siRNA knockdown and DNA binding activities suggested that Nrf2, NF-κB and AP-1 were implicated in the response of HepG2 cells to CuO NPs. CuO NP incubation also induced activation of MAPK pathways, ERKs and JNK/SAPK, playing a major role in the activation of AP-1. In addition, cytotoxicity, inflammatory and antioxidative responses and activation of intracellular transduction pathways induced by rod-shaped CuO NPs were more important than spherical CuO NPs. Measurement of Cu(2+) released in cell culture medium suggested that Cu(2+) cations released from CuO NPs were involved only to a small extent in the toxicity induced by these NPs on HepG2 cells.

Hypersensitivity of mtDNA-depleted cells to staurosporine-induced apoptosis: roles of Bcl-2 downregulation and cathepsin B

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.

Proteomic profiling of human keratinocytes undergoing UVB-induced alternative differentiation reveals TRIpartite Motif Protein 29 as a survival factor

Background

Repeated exposures to UVB of human keratinocytes lacking functional p16^INK-4a and able to differentiate induce an alternative state of differentiation rather than stress-induced premature senescence.

Methodology/Principal Findings

A 2D-DIGE proteomic profiling of this alternative state of differentiation was performed herein at various times after the exposures to UVB. Sixty-nine differentially abundant protein species were identified by mass spectrometry, many of which are involved in keratinocyte differentiation and survival. Among these protein species was TRIpartite Motif Protein 29 (TRIM29). Increased abundance of TRIM29 following UVB exposures was validated by Western blot using specific antibody and was also further analysed by immunochemistry and by RT-PCR. TRIM29 was found very abundant in keratinocytes and reconstructed epidermis. Knocking down the expression of TRIM29 by short-hairpin RNA interference decreased the viability of keratinocytes after UVB exposure. The abundance of involucrin mRNA, a marker of late differentiation, increased concomitantly. In TRIM29-knocked down reconstructed epidermis, the presence of picnotic cells revealed cell injury. Increased abundance of TRIM29 was also observed upon exposure to DNA damaging agents and PKC activation. The UVB-induced increase of TRIM29 abundance was dependent on a PKC signaling pathway, likely PKCδ.

Conclusions/Significance

These findings suggest that TRIM29 allows keratinocytes to enter a protective alternative differentiation process rather than die massively after stress.

Dual effect of echinomycin on hypoxia-inducible factor-1 activity under normoxic and hypoxic conditions

Hypoxia-inducible factor-1 (HIF-1) is now recognized as a possible target for cancer treatment. This transcription factor is responsible for the overexpression of several genes favouring cancer cell survival and inducing neo-angiogenesis. Echinomycin has recently been described to inhibit HIF-1 DNA binding and transcriptional activity. In this work, it is shown that echinomycin strongly inhibits the activity of HIF-1 under hypoxic conditions, and also interferes with the activity of other transcription factors. These results demonstrate the lack of specificity of this molecule. Moreover, it is demonstrated that echinomycin induces an increase in HIF-1 activity under normoxic conditions, parallel to an increase in the expression of HIF-1 target genes. This effect is caused by an increase in HIF-1alpha protein level, resulting from an increase in the transcription of the HIF-1A gene in the presence of a low concentration of echinomycin. Transfection experiments with HIF-1alpha promoter constructs revealed the presence of an Sp1 binding element responsive to echinomycin. Furthermore, echinomycin enhanced Sp1 activity, as measured by the use of a specific reporter system. These findings show, for the first time, that echinomycin has a dual effect on HIF-1 activity under normoxic and hypoxic conditions, demonstrating that this molecule cannot be used in cancer treatment.

CREB activation induced by mitochondrial dysfunction triggers triglyceride accumulation in 3T3-L1 preadipocytes

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.

Accumulation of the pro-apoptotic factor Bak is controlled by antagonist factor Mcl-1 availability

Apoptosis has become recognized as a crucial mechanism involved in a wide range of physiological and pathological processes. Following an initial pro-apoptotic signal, controlling phases allow the cell to reinforce or downgrade signals leading to the irrevocable entry into apoptosis. Bak (Bcl-2-antagonist killer) is a mitochondrial pore-forming pro-apoptotic effector inhibited through titration by the anti-apoptotic protein Mcl-1 (Myeloid cell leukemia-1). Viruses have taken advantage of proteasome-dependent degradation of Bak as a mechanism to prevent apoptosis in infected cells. It is not clear however whether regulation of Bak protein level is involved in other physiological processes. In this report, we show that Mcl-1 level is paralleled by Bak while a Mcl-1 non-interacting mutant of Bak does not accumulate in cells. This mechanism is proteasome independent. Following serum withdrawal, Bak accumulation becomes independent of Mcl-1 level and cells are sensitized to pro-apoptotic stimuli. Based on these results, we propose that regulation of Mcl-1-Bak steochiometry is a control mechanism used as a checkpoint to prevent or allow entry into apoptosis.

Role for casein kinase 2 in the regulation of HIF-1 activity

Hypoxia-inducible factor-1 (HIF-1) is a heterodimeric transcription factor that plays a major role in cellular adaptation to hypoxia. The mechanisms regulating HIF-1 activity occurs at multiple levels in vivo. The HIF-1alpha subunit is highly sensible to oxygen and is rapidly degraded by the proteasome 26S in normoxia. Activation in hypoxia occurs through a multistep process including inhibition of HIF-1alpha degradation, but also increase in the transactivation activity of HIF-1. Several data indicate that phosphorylation could play a role in this regulation. In this report, we investigated the role of casein kinase 2 (CK2), an ubiquitous serine/threonine kinase, in the regulation of HIF-1 activity. Hypoxia was capable of increasing the expression of the beta subunit of CK2, of inducing a relocalization of this subunit at the plasma membrane, of inducing nuclear translocation of the alpha subunit and of increasing CK2 activity. Three inhibitors of this kinase, DRB (5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole), TBB (4,5,6,7-tetrabromotriazole) and apigenin, as well as overexpression of a partial dominant negative mutant of CK2alpha, were shown to inhibit HIF-1 activity as measured by a reporter assay and through hypoxia-induced VEGF and aldolase expression. This does not occur at the stabilization process since they did not affect HIF-1alpha protein level. DNA-binding activity was also not inhibited. We conclude that CK2 is an important regulator of HIF-1 transcriptional activity but the mechanism of this regulation remains to be determined. Since HIF-1 plays a major role in tumor angiogenesis and since CK2 has been described to be overexpressed in tumor cells, this new pathway of regulation can be one more way for tumor cells to survive.

Mitochondrial biogenesis in mtDNA-depleted cells involves a Ca2+-dependent pathway and a reduced mitochondrial protein import

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.

Mitochondrial dysfunction induces triglyceride accumulation in 3T3-L1 cells: role of fatty acid beta-oxidation and glucose

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.

mtCLIC is up-regulated and maintains a mitochondrial membrane potential in mtDNA-depleted L929 cells

To explain why mitochondrial DNA (mtDNA)-depleted or rho0 cells still keep a mitochondrial membrane potential (Delta(psi)m) in the absence of respiration, several hypotheses have been proposed. The principal and well accepted one involves a reverse of action for ANT combined to F1-ATPase activity. However, the existence of other putative electrogenic channels has been speculated. Here, using mRNA differential display reverse transcriptase-polymerase chain reaction on L929 mtDNA-depleted cells, we identified mtCLIC as a differentially expressed gene in cells deprived from mitochondrial ATP production. Mitochondrial chloride intracellular channel (mtCLIC), a member of a recently discovered and expanding family of chloride intracellular channels, is up-regulated in mtDNA-depleted and rho0 cells. We showed that its expression is dependent on CREB and p53 and is sensitive to calcium and tumor necrosis factor alpha. Interestingly, up- or down-regulation of mtCLIC protein expression changes Delta(psi)m whereas the chloride channel inhibitor NPPB reduces the Delta(psi)m in mtDNA-depleted L929 cells, measured with the fluorescent probe rhodamine 123. Finally, we demonstrated that purified mitochondria from mtDNA-depleted cells incorporate, in a NPPB-sensitive manner, more 36chloride than parental mitochondria. These findings suggest that mtCLIC could be involved in mitochondrial membrane potential generation in mtDNA-depleted cells, a feature required to prevent apoptosis and to drive continuous protein import into mitochondria.

Regulation of hypoxia-inducible factor-1alpha protein level during hypoxic conditions by the phosphatidylinositol 3-kinase/Akt/glycogen synthase kinase 3beta pathway in HepG2 cells

Hypoxia initiates an intracellular signaling pathway leading to the activation of the transcription factor hypoxia-inducible factor-1 (HIF-1). HIF-1 activity is regulated through different mechanisms involving stabilization of HIF-1alpha, phosphorylations, modifications of redox conditions, and interactions with coactivators. However, it appears that some of these steps can be cell type-specific. Among them, the involvement of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway in the regulation of HIF-1 by hypoxia remains controversial. Here, we investigated the activation state of PI3K/Akt/glycogen synthase kinase 3beta (GSK3beta) in HepG2 cells. Increasing incubation times in hypoxia dramatically decreased both the phosphorylation of Akt and the inhibiting phosphorylation of GSK3beta. The PI3K/Akt pathway was necessary for HIF-1alpha stabilization early during hypoxia. Indeed, its inhibition was sufficient to decrease HIF-1alpha protein level after 5-h incubation in hypoxia. However, longer exposure (16 h) in hypoxia resulted in a decreased HIF-1alpha protein level compared with early exposure (5 h). At that time, Akt was no longer present or active, which resulted in a decrease in the inhibiting phosphorylation of GSK3beta on Ser-9 and hence in an increased GSK3beta activity. GSK3 inhibition reverted the effect of prolonged hypoxia on HIF-1alpha protein level; more stabilized HIF-1alpha was observed as well as increased HIF-1 transcriptional activity. Thus, a prolonged hypoxia activates GSK3beta, which results in decreased HIF-1alpha accumulation. In conclusion, hypoxia induced a biphasic effect on HIF-1alpha stabilization with accumulation in early hypoxia, which depends on an active PI3K/Akt pathway and an inactive GSK3beta, whereas prolonged hypoxia results in the inactivation of Akt and activation of GSK3beta, which then down-regulates the HIF-1 activity through down-regulation of HIF-1alpha accumulation.

CREB activation induced by mitochondrial dysfunction is a new signaling pathway that impairs cell proliferation

We characterized a new signaling pathway leading to the activation of cAMP-responsive element-binding protein (CREB) in several cell lines affected by mitochondrial dysfunction. In vitro kinase assays, inhibitors of several kinase pathways and overexpression of a dominant-negative mutant for calcium/calmodulin kinase IV (CaMKIV), which blocks the activation of CREB, showed that CaMKIV is activated by a mitochondrial activity impairment. A high calcium concentration leading to the disruption of the protein interaction with protein phosphatase 2A explains CaMKIV activation in these conditions. Transcrip tionally active phosphorylated CREB was also found in a rho0 143B human osteosarcoma cell line and in a MERRF cybrid cell line mutated for tRNA(Lys) (A8344G). We also showed that phosphorylated CREB is involved in the proliferation defect induced by a mitochondrial dysfunction. Indeed, cell proliferation inhibition can be prevented by CaMKIV inhibition and CREB dominant-negative mutants. Finally, our data suggest that phosphorylated CREB recruits p53 tumor suppressor protein, modifies its transcriptional activity and increases the expression of p21(Waf1/Cip1), a p53-regulated cyclin-dependent kinase inhibitor.

Synthesis and structural analysis of the copper(II) complexes of N2-(2-pyridylmethyl)-2-pyridinecarboxamide

Previous investigations of the potential of metal-organic compounds as inhibitors of human immunodeficiency virus type I protease (HIV-1 PR) showed that the copper(II) complex diaqua [bis(2-pyridylcarbonyl)amido] copper(II) nitrate dihydrate and the complex bis[N2-(2,3,6-trimethoxybenzyl)-4-2-pyridinecarboxamide] copper(II) behaved as inhibitors of HIV-1 PR. In a search for similar readily accessible ligands, we synthesised and studied the structural properties of N2-(2-pyridylmethyl)-2-pyridinecarboxamide (L) copper(II) complexes. Three different crystal structures were obtained. Two were found to contain ligand L simultaneously in a tridentate and bidentate conformation [Cu(L(tri)L(bi))]. The other contained two symmetry-related ligands, coordinated through the pyridine nitrogen and the amide oxygen atoms [Cu(L(bi))(2)]. A search of the Cambridge Structural Database indicated that L(tri) resulting from nitrogen bound amide hydrogen metal substitution is favoured over chelation through the amide oxygen atom. In our case, we calculated that the conformation of L(tri) is 11 kcal/mol more favourable than that of L(bi). ESI-MS experiments showed that the Cu(L(bi))(2) structure could not be observed in solution, while Cu(L(tri)L(bi))-related complexes were indeed present. The lack of protease inhibition of the pyridine carboxamide copper(II) complexes was explained by the fact that the Cu(L(bi)L(tri)) complex could not fit into the HIV-1 active site.