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1.  Direct interaction between STAT3 and EIF2AK2 controls fatty acid-induced autophagy 
Autophagy  2013;9(3):415-417.
A chemical screen designed to identify novel inducers of autophagy led to the discovery that signal transducer and activator of transcription 3 (STAT3) inhibitors can potently stimulate the autophagic flux. Although STAT3 is best known as a pro-inflammatory and oncogenic transcription factor, mechanistic analyses revealed that autophagy is regulated by the cytoplasmic, not nuclear, pool of STAT3. Cytoplasmic STAT3 normally interacts with the eukaryotic translation initiation factor 2, subunit 1α, 35kDa (EIF2S1/eIF2α) kinase 2/protein kinase, RNA-activated (EIF2AK2/PKR), a sensor of double-stranded RNA. This interaction, which could be recapitulated using recombinant proteins in pull-down experiments, involves the catalytic domain of EIF2AK2 as well as the SH2 domain of STAT3, which can adopt a fold similar to that of EIF2S1. Thus, STAT3 may act as a competitive inhibitor of EIF2AK2. Indeed, pharmacological or genetic inhibition of STAT3 stimulates EIF2AK2-dependent EIF2S1 phosphorylation and autophagy. Conversely, the overexpression of wild-type STAT3 as well as of STAT3 mutants that cannot be phosphorylated by JAK2 or are excluded from the nucleus inhibits autophagy. However, STAT3 mutants that fail to interact with EIF2AK2 are unable to suppress autophagy. Both STAT3-targeting agents (i.e., Stattic, JSI-124 and WP1066) and EIF2AK2 activators (such as the double-strand RNA mimetic polyinosinic:polycytidylic acid) are capable of disrupting the inhibitory interaction between STAT3 and EIF2AK2 in cellula, yet only the latter does so in cell-free systems in vitro. A further screen designed to identify EIF2AK2-dependent autophagy inducers revealed that several fatty acids including palmitate trigger autophagy via a pathway that involves the disruption of the STAT3-EIF2AK2 complex as well as the phosphorylation of mitogen-activated protein kinase 8/c-Jun N-terminal kinase 1 (MAPK8/JNK1) and EIF2S1. These results reveal an unsuspected crosstalk between cellular metabolism (fatty acids), pro-inflammatory signaling (STAT3), innate immunity (EIF2AK2), and translational control (EIF2S1) that regulates autophagy.
doi:10.4161/auto.22910
PMCID: PMC3590262  PMID: 23221979
EIF2S1S51A; endoplasmic reticulum; IRS1; palmitate; polyI:C; STAT3Y705F
2.  Pro-autophagic polyphenols reduce the acetylation of cytoplasmic proteins 
Cell Cycle  2012;11(20):3851-3860.
Resveratrol is a polyphenol contained in red wine that has been amply investigated for its beneficial effects on organismal metabolism, in particular in the context of the so-called “French paradox,” i.e., the relatively low incidence of coronary heart disease exhibited by a population with a high dietary intake of cholesterol and saturated fats. At least part of the beneficial effect of resveratrol on human health stems from its capacity to promote autophagy by activating the NAD-dependent deacetylase sirtuin 1. However, the concentration of resveratrol found in red wine is excessively low to account alone for the French paradox. Here, we investigated the possibility that other mono- and polyphenols contained in red wine might induce autophagy while affecting the acetylation levels of cellular proteins. Phenolic compounds found in red wine, including anthocyanins (oenin), stilbenoids (piceatannol), monophenols (caffeic acid, gallic acid) glucosides (delphinidin, kuronamin, peonidin) and flavonoids (catechin, epicatechin, quercetin, myricetin), were all capable of stimulating autophagy, although with dissimilar potencies. Importantly, a robust negative correlation could be established between autophagy induction and the acetylation levels of cytoplasmic proteins, as determined by a novel immunofluorescence staining protocol that allows for the exclusion of nuclear components from the analysis. Inhibition of sirtuin 1 by both pharmacological and genetic means abolished protein deacetylation and autophagy as stimulated by resveratrol, but not by piceatannol, indicating that these compounds act through distinct molecular pathways. In support of this notion, resveratrol and piceatannol synergized in inducing autophagy as well as in promoting cytoplasmic protein deacetylation. Our results highlight a cause-effect relationship between the deacetylation of cytoplasmic proteins and autophagy induction by red wine components.
doi:10.4161/cc.22027
PMCID: PMC3495827  PMID: 23070521
Beclin 1; LC3; longevity; p62/SQSTM1; trichostatin A; U2OS
4.  Selective killing of p53-deficient cancer cells by SP600125 
EMBO Molecular Medicine  2012;4(6):500-514.
The genetic or functional inactivation of p53 is highly prevalent in human cancers. Using high-content videomicroscopy based on fluorescent TP53+/+ and TP53−/− human colon carcinoma cells, we discovered that SP600125, a broad-spectrum serine/threonine kinase inhibitor, kills p53-deficient cells more efficiently than their p53-proficient counterparts, in vitro. Similar observations were obtained in vivo, in mice carrying p53-deficient and -proficient human xenografts. Such a preferential cytotoxicity could be attributed to the failure of p53-deficient cells to undergo cell cycle arrest in response to SP600125. TP53−/− (but not TP53+/+) cells treated with SP600125 became polyploid upon mitotic abortion and progressively succumbed to mitochondrial apoptosis. The expression of an SP600125-resistant variant of the mitotic kinase MPS1 in TP53−/− cells reduced SP600125-induced polyploidization. Thus, by targeting MPS1, SP600125 triggers a polyploidization program that cannot be sustained by TP53−/− cells, resulting in the activation of mitotic catastrophe, an oncosuppressive mechanism for the eradication of mitosis-incompetent cells.
doi:10.1002/emmm.201200228
PMCID: PMC3443949  PMID: 22438244
caspases; HCT 116; high-throughput screening; mitochondrial outer membrane permeabilization; MPS1
5.  Cacospongionolide and Scalaradial, Two Marine Sesterterpenoids as Potent Apoptosis-Inducing Factors in Human Carcinoma Cell Lines 
PLoS ONE  2012;7(4):e33031.
Apoptosis, a form of programmed cell death, is a critical defence mechanism against the formation and progression of cancer and acts by eliminating potentially deleterious cells without causing such adverse effects, as inflammatory response and ensuing scar formation. Therefore, targeting apoptotic pathways becomes an intriguing strategy for the development of chemotherapeutic agents. In last decades, marine natural products, such as sesterterpenoids, have played an important role in the discovery and development of new drugs. Interestingly, many of these compounds have a strong potential as anticancer drugs by inhibiting cell proliferation and/or inducing cell death. In the present study, we investigated the effects of scalaradial and cacospongionolide, two sesterterpenoids from Cacospongia scalaris and Fasciospongia cavernosa marine sponges, on the apoptotic signalling pathway in three different human tumoral cells. Results were obtained by using DNA fragmentation, comet and viability assays, quantification of the mitochondrial transmembrane potential and Western blot. The T47D (human breast carcinoma), A431 (human epidermoid carcinoma), HeLa (human cervix carcinoma) and HCT116 (human colon carcinoma) cells were incubated for 24 h with scalaradial or cacospongionolide. Treatment of T47D cells with scalaradial or cacospongionolide for 24 h brought about a significant increase in DNA migration as well as fragmentation. Moreover, incubation of HCT116 and HeLa cells with scalaradial or cacospongionolide for 24 h caused an increased expression of pro-apoptotic proteins. Furthermore, scalaradial or cacospongionolide, added to HCT116 and HeLa cells overnight, induced a significant and concentration-dependent loss of mitochondrial transmembrane potential, an early apoptosis signalling event. These effects paralleled with those achieved with p50 and p65, NF-κB subunits, nuclear level. In conclusion, scalaradial and cacospongionolide, by determining human cancer cell apoptosis, may represent new promising compounds to inhibit cancer cell proliferation.
doi:10.1371/journal.pone.0033031
PMCID: PMC3317917  PMID: 22509253
6.  Spermidine and resveratrol induce autophagy by distinct pathways converging on the acetylproteome 
The Journal of Cell Biology  2011;192(4):615-629.
The acetylase inhibitor spermidine and the sirtuin-1 activator resveratrol disrupt the antagonistic network of acetylases and deacetylases that regulate autophagy.
Autophagy protects organelles, cells, and organisms against several stress conditions. Induction of autophagy by resveratrol requires the nicotinamide adenine dinucleotide–dependent deacetylase sirtuin 1 (SIRT1). In this paper, we show that the acetylase inhibitor spermidine stimulates autophagy independent of SIRT1 in human and yeast cells as well as in nematodes. Although resveratrol and spermidine ignite autophagy through distinct mechanisms, these compounds stimulate convergent pathways that culminate in concordant modifications of the acetylproteome. Both agents favor convergent deacetylation and acetylation reactions in the cytosol and in the nucleus, respectively. Both resveratrol and spermidine were able to induce autophagy in cytoplasts (enucleated cells). Moreover, a cytoplasm-restricted mutant of SIRT1 could stimulate autophagy, suggesting that cytoplasmic deacetylation reactions dictate the autophagic cascade. At doses at which neither resveratrol nor spermidine stimulated autophagy alone, these agents synergistically induced autophagy. Altogether, these data underscore the importance of an autophagy regulatory network of antagonistic deacetylases and acetylases that can be pharmacologically manipulated.
doi:10.1083/jcb.201008167
PMCID: PMC3044119  PMID: 21339330

Results 1-6 (6)