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1.  Common and divergent functions of Beclin 1 and Beclin 2 
Cell Research  2013;23(12):1341-1342.
In a recent paper published in Cell, He and colleagues reported the identification and functional characterization of Beclin 2, a mammal-specific homolog of the evolutionarily conserved autophagy-regulatory and oncosuppressive factor Beclin 1. In spite of a non-negligible degree of sequence identity, Beclin 1 and Beclin 2 differ from each other in multiple aspects, including their functional profile as well as the genomic organization of the respective loci.
doi:10.1038/cr.2013.129
PMCID: PMC3847569  PMID: 24018378
2.  Mechanisms of apoptotic phosphatidylserine exposure 
Cell Research  2013;23(11):1247-1248.
It has been a long-standing enigma which scramblase causes phosphatidylserine residues to be exposed on the surface of apoptotic cells, thereby facilitating the phagocytic recognition, engulfment and destruction of apoptotic corpses. In a recent paper in Science, Nagata and coworkers reveal that the scramblases Xkr8 and its C. elegans ortholog, CED-8, are activated by caspase cleavage in apoptotic cells.
doi:10.1038/cr.2013.115
PMCID: PMC3817543  PMID: 23979019
3.  ERCC1 function in nuclear excision and interstrand crosslink repair pathways is mediated exclusively by the ERCC1-202 isoform 
Cell Cycle  2013;12(20):3298-3306.
ERCC1 (excision repair cross-complementation group 1) plays essential roles in the removal of DNA intrastrand crosslinks by nucleotide excision repair, and that of DNA interstrand crosslinks by the Fanconi anemia (FA) pathway and homology-directed repair processes (HDR). The function of ERCC1 thus impacts on the DNA damage response (DDR), particularly in anticancer therapy when DNA damaging agents are employed. ERCC1 expression has been proposed as a predictive biomarker of the response to platinum-based therapy. However, the assessment of ERCC1 expression in clinical samples is complicated by the existence of 4 functionally distinct protein isoforms, which differently impact on DDR. Here, we explored the functional competence of each ERCC1 protein isoform and obtained evidence that the 202 isoform is the sole one endowed with ERCC1 activity in DNA repair pathways. The ERCC1 isoform 202 interacts with RPA, XPA, and XPF, and XPF stability requires expression of the ERCC1 202 isoform (but none of the 3 others). ERCC1-deficient non-small cell lung cancer cells show abnormal mitosis, a phenotype reminiscent of the FA phenotype that can be rescued by isoform 202 only. Finally, we could not observe any dominant-negative interaction between ERCC1 isoforms. These data suggest that the selective assessment of the ERCC1 isoform 202 in clinical samples should accurately reflect the DDR-related activity of the gene and hence constitute a useful biomarker for customizing anticancer therapies.
doi:10.4161/cc.26309
PMCID: PMC3885640  PMID: 24036546
DNA repair; ERCC1; NSCLC; interaction; isoform; knockout; mitosis
4.  The mTOR kinase inhibitors, CC214-1 and CC214-2, preferentially block the growth of EGFRvIII-activated glioblastomas 
Purpose
mTOR pathway hyperactivation occurs in nearly 90% of glioblastomas, but the allosteric mTOR inhibitor rapamycin has failed in the clinic. Here we examine the efficacy of the newly discovered ATP-competitive mTOR kinase inhibitors CC214-1 and CC214-2 in glioblastoma, identifying molecular determinants of response and mechanisms of resistance, and develop a pharmacological strategy to overcome it.
Experimental design
We performed in vitro and in vivo studies in glioblastoma cell lines and an intracranial model to: determine the potential efficacy of the recently reported mTOR kinase inhibitors CC214-1 (in vitro use) and CC214-2 (in vivo use) at inhibiting rapamycin resistant signaling and blocking GBM growth and a novel single cell technology, DNA Encoded Antibody Libraries, was used to identify mechanisms of resistance.
Results
Here we demonstrate that CC214-1 and CC214-2 suppress rapamycin-resistant mTORC1 signaling; block mTORC2 signaling and significantly inhibit the growth of glioblastomas in vitro and in vivo. EGFRvIII expression and PTEN loss enhance sensitivity to CC214 compounds, consistent with enhanced efficacy in strongly mTOR-activated tumors. Importantly, CC214 compounds potently induce autophagy, preventing tumor cell death. Genetic or pharmacologic inhibition of autophagy greatly sensitizes GBM cells and orthotopic xenografts to CC214-1 and CC214-2 induced cell death.
Conclusions
These results identify CC214-1 and CC214-2 as potentially efficacious mTOR kinase inhibitors in GBM and suggest a strategy for identifying patients most likely to benefit from mTOR inhibition. This study also demonstrates a central role for autophagy in preventing mTOR-kinase inhibitor-mediated tumor cell death, and suggests a pharmacological strategy for overcoming it.
doi:10.1158/1078-0432.CCR-13-0527
PMCID: PMC3815450  PMID: 24030701
5.  EGFR inhibitors exacerbate differentiation and cell cycle arrest induced by retinoic acid and vitamin D3 in acute myeloid leukemia cells 
Cell Cycle  2013;12(18):2978-2991.
By means of an unbiased, automated fluorescence microscopy-based screen, we identified the epidermal growth factor receptor (EGFR) inhibitors erlotinib and gefitinib as potent enhancers of the differentiation of HL-60 acute myeloid leukemia (AML) cells exposed to suboptimal concentrations of vitamin A (all-trans retinoic acid, ATRA) or vitamin D (1α,25-hydroxycholecalciferol, VD). Erlotinib and gefitinib alone did not promote differentiation, yet stimulated the acquisition of morphological and biochemical maturation markers (including the expression of CD11b and CD14 as well as increased NADPH oxidase activity) when combined with either ATRA or VD. Moreover, the combination of erlotinib and ATRA or VD synergistically induced all the processes that are normally linked to terminal hematopoietic differentiation, namely, a delayed proliferation arrest in the G0/G1 phase of the cell cycle, cellular senescence, and apoptosis. Erlotinib potently inhibited the (auto)phosphorylation of mitogen-activated protein kinase 14 (MAPK14, best known as p38MAPK) and SRC family kinases (SFKs). If combined with the administration of ATRA or VD, the inhibition of p38MAPK or SFKs with specific pharmacological agents mimicked the pro-differentiation activity of erlotinib. These data were obtained with 2 distinct AML cell lines (HL-60 and MOLM-13 cells) and could be confirmed on primary leukemic blasts isolated from the circulation of AML patients. Altogether, these findings point to a new regimen for the treatment of AML, in which naturally occurring pro-differentiation agents (ATRA or VD) may be combined with EGFR inhibitors.
doi:10.4161/cc.26016
PMCID: PMC3875673  PMID: 23974111
BCR-ABL; PML-RARα; cancer; dasatinib; imatinib; monocyte-specific esterase
6.  SnapShot: Macroautophagy 
Cell  2008;132(1):162.e1-162.e3.
doi:10.1016/j.cell.2007.12.026
PMCID: PMC4160893  PMID: 25221369
7.  ATG4B/autophagin-1 regulates intestinal homeostasis and protects mice from experimental colitis 
Autophagy  2013;9(8):1188-1200.
The identification of inflammatory bowel disease (IBD) susceptibility genes by genome-wide association has linked this pathology to autophagy, a lysosomal degradation pathway that is crucial for cell and tissue homeostasis. Here, we describe autophagy-related 4B, cysteine peptidase/autophagin-1 (ATG4B) as an essential protein in the control of inflammatory response during experimental colitis. In this pathological condition, ATG4B protein levels increase in parallel with the induction of autophagy. Moreover, ATG4B expression is significantly reduced in affected areas of the colon from IBD patients. Consistently, atg4b−/− mice present Paneth cell abnormalities, as well as an increased susceptibility to DSS-induced colitis. atg4b-deficient mice exhibit significant alterations in proinflammatory cytokines and mediators of the immune response to bacterial infections, which are reminiscent of those found in patients with Crohn disease or ulcerative colitis. Additionally, antibiotic treatments and bone marrow transplantation from wild-type mice reduced colitis in atg4b−/− mice. Taken together, these results provided additional evidence for the importance of autophagy in intestinal pathologies and describe ATG4B as a novel protective protein in inflammatory colitis. Finally, we propose that atg4b-null mice are a suitable model for in vivo studies aimed at testing new therapeutic strategies for intestinal diseases associated with autophagy deficiency.
doi:10.4161/auto.24797
PMCID: PMC3748191  PMID: 23782979
ATG4B; autophagin-1; autophagy; colitis; inflammation; intestinal homeostasis; cysteine peptidase; Paneth cell
8.  Trial Watch 
Oncoimmunology  2014;3:e29179.
Toll-like receptors (TLRs) are an evolutionarily conserved group of enzymatically inactive, single membrane-spanning proteins that recognize a wide panel of exogenous and endogenous danger signals. Besides constituting a crucial component of the innate immune response to bacterial and viral pathogens, TLRs appear to play a major role in anticancer immunosurveillance. In line with this notion, several natural and synthetic TLR ligands have been intensively investigated for their ability to boost tumor-targeting immune responses elicited by a variety of immunotherapeutic and chemotherapeutic interventions. Three of these agents are currently approved by the US Food and Drug Administration (FDA) or equivalent regulatory agencies for use in cancer patients: the so-called bacillus Calmette-Guérin, monophosphoryl lipid A, and imiquimod. However, the number of clinical trials testing the therapeutic potential of both FDA-approved and experimental TLR agonists in cancer patients is stably decreasing, suggesting that drug developers and oncologists are refocusing their interest on alternative immunostimulatory agents. Here, we summarize recent findings on the use of TLR agonists in cancer patients and discuss how the clinical evaluation of FDA-approved and experimental TLR ligands has evolved since the publication of our first Trial Watch dealing with this topic.
doi:10.4161/onci.29179
PMCID: PMC4091055  PMID: 25083332
BCG; CpG-7909; Hiltonol™; damage-associated molecular patterns; polyI:C; resiquimod
9.  Immunogenic cell death inducers as anticancer agents 
Oncotarget  2014;5(14):5190-5191.
PMCID: PMC4170601  PMID: 25114034
10.  The intestinal microbiota modulates the anticancer immune effects of cyclophosphamide 
Science (New York, N.Y.)  2013;342(6161):971-976.
Cyclophosphamide is one of several clinically important cancer drugs whose therapeutic efficacy is due in part to their ability to stimulate anti-tumor immune responses. Studying mouse models, we demonstrate that cyclophosphamide alters the composition of microbiota in the small intestine and induces the translocation of selected species of Gram+ bacteria into secondary lymphoid organs. There, these bacteria stimulate the generation of a specific subset of “pathogenic” T helper 17 (pTh17) cells and memory Th1 immune responses. Tumor-bearing mice that were germ-free or that had been treated with antibiotics to kill Gram+ bacteria showed a reduction in pTh17 responses and their tumors were resistant to cyclophosphamide. Adoptive transfer of pTh17 cells partially restored the anti-tumor efficacy of cyclophosphamide. These results suggest that the gut microbiota help shape the anticancer immune response.
doi:10.1126/science.1240537
PMCID: PMC4048947  PMID: 24264990
11.  Trial watch 
Oncoimmunology  2014;3:e29030.
Tumor-targeting immune responses provide a significant contribution to (when they do not entirely account for) the clinical activity of diverse antineoplastic regimens, encompassing not only a large panel of immunotherapeutic strategies but also conventional cytotoxic molecules, targeted anticancer agents and irradiation. In line with this notion, several approaches have been devised to elicit novel or boost existing anticancer immune responses, including the administration of immunomodulatory cytokines. Such a relatively unspecific intervention suffices to mediate clinical effects in (at least a subset of) patients bearing particularly immunogenic tumors, like melanoma and renal cell carcinoma. More often, however, immunostimulatory cytokines are administered to boost the immunogenic potential of other agents, including (but not limited to) immune checkpoint-blocking antibodies, anticancer vaccines, oncolytic viruses and immunogenic chemotherapeutics. Here, we summarize the latest advances in the clinical development of recombinant cytokines as an immunomodulatory intervention for cancer therapy.
doi:10.4161/onci.29030
PMCID: PMC4091551  PMID: 25083328
GM-CSF; IFN; IL-2; TGFβ1; TNFα; chemokines
12.  Trial Watch: 
Oncoimmunology  2014;3:e28694.
Oncolytic viruses are natural or genetically modified viral species that selectively infect and kill neoplastic cells. Such an innate or exogenously conferred specificity has generated considerable interest around the possibility to employ oncolytic viruses as highly targeted agents that would mediate cancer cell-autonomous anticancer effects. Accumulating evidence, however, suggests that the therapeutic potential of oncolytic virotherapy is not a simple consequence of the cytopathic effect, but strongly relies on the induction of an endogenous immune response against transformed cells. In line with this notion, superior anticancer effects are being observed when oncolytic viruses are engineered to express (or co-administered with) immunostimulatory molecules. Although multiple studies have shown that oncolytic viruses are well tolerated by cancer patients, the full-blown therapeutic potential of oncolytic virotherapy, especially when implemented in the absence of immunostimulatory interventions, remains unclear. Here, we cover the latest advances in this active area of translational investigation, summarizing high-impact studies that have been published during the last 12 months and discussing clinical trials that have been initiated in the same period to assess the therapeutic potential of oncolytic virotherapy in oncological indications.
doi:10.4161/onci.28694
PMCID: PMC4091053  PMID: 25097804
adenovirus; ColoAd1; mesenchymal stem cells; MV-NIS; reolysin; talimogene laherparepvec
13.  Lifespan Extension by Methionine Restriction Requires Autophagy-Dependent Vacuolar Acidification 
PLoS Genetics  2014;10(5):e1004347.
Reduced supply of the amino acid methionine increases longevity across species through an as yet elusive mechanism. Here, we report that methionine restriction (MetR) extends yeast chronological lifespan in an autophagy-dependent manner. Single deletion of several genes essential for autophagy (ATG5, ATG7 or ATG8) fully abolished the longevity-enhancing capacity of MetR. While pharmacological or genetic inhibition of TOR1 increased lifespan in methionine-prototroph yeast, TOR1 suppression failed to extend the longevity of methionine-restricted yeast cells. Notably, vacuole-acidity was specifically enhanced by MetR, a phenotype that essentially required autophagy. Overexpression of vacuolar ATPase components (Vma1p or Vph2p) suffices to increase chronological lifespan of methionine-prototrophic yeast. In contrast, lifespan extension upon MetR was prevented by inhibition of vacuolar acidity upon disruption of the vacuolar ATPase. In conclusion, autophagy promotes lifespan extension upon MetR and requires the subsequent stimulation of vacuolar acidification, while it is epistatic to the equally autophagy-dependent anti-aging pathway triggered by TOR1 inhibition or deletion.
Author Summary
Health- or lifespan-prolonging regimes would be beneficial at both the individual and the social level. Nevertheless, up to date only very few experimental settings have been proven to promote longevity in mammals. Among them is the reduction of food intake (caloric restriction) or the pharmacological administration of caloric restriction mimetics like rapamycin. The latter one, however, is accompanied by not yet fully estimated and undesirable side effects. In contrast, the limitation of one specific amino acid, namely methionine, which has also been demonstrated to elongate the lifespan of mammals, has the advantage of being a well applicable regime. Therefore, understanding the underlying mechanism of the anti-aging effects of methionine restriction is of crucial importance. With the help of the model organism yeast, we show that limitation in methionine drastically enhances autophagy, a cellular process of self-digestion that is also switched on during caloric restriction. Moreover, we demonstrate that this occurs in causal conjunction with an efficient pH decrease in the organelle responsible for the digestive capacity of the cell (the vacuole). Finally, we prove that autophagy-dependent vacuolar acidification is necessary for methionine restriction-mediated lifespan extension.
doi:10.1371/journal.pgen.1004347
PMCID: PMC4006742  PMID: 24785424
14.  Self-consumption: the interplay of autophagy and apoptosis 
Autophagy and apoptosis control the turnover of organelles and proteins within cells, and of cells within organisms, respectively, and many stress pathways sequentially elicit autophagy, and apoptosis within the same cell. Generally autophagy blocks the induction of apoptosis, and apoptosis-associated caspase activation shuts off the autophagic process. However, in special cases, autophagy or autophagy-relevant proteins may help to induce apoptosis or necrosis, and autophagy has been shown to degrade the cytoplasm excessively, leading to ‘autophagic cell death’. The dialogue between autophagy and cell death pathways influences the normal clearance of dying cells, as well as immune recognition of dead cell antigens. Therefore, the disruption of the relationship between autophagy and apoptosis has important pathophysiological consequences.
doi:10.1038/nrm3735
PMCID: PMC3970201  PMID: 24401948
15.  Synergistic interaction between cisplatin and PARP inhibitors in non-small cell lung cancer 
Cell Cycle  2013;12(6):877-883.
The antineoplastic agent cis-diammineplatinum(II) dichloride (cisplatin, CDDP) is part of the poorly effective standard treatment of non-small cell lung carcinoma (NSCLC). Here, we report a novel strategy to improve the efficacy of CDDP. In conditions in which CDDP alone or either of two PARP inhibitors, PJ34 hydrochloride hydrate or CEP 8983, used as standalone treatments were inefficient in killing NSCLC cells, the combination of CDDP plus PJ34 or that of CDDP plus CEP 8983 were found to kill a substantial fraction of the cells. This cytotoxic synergy could be recapitulated by combining CDDP and the siRNA-mediated depletion of the principal PARP isoform, PARP1, indicating that it is mediated by on-target effects of PJ34 or CEP 8983. CDDP and PARP inhibitors synergized in inducing DNA damage foci, mitochondrial membrane permeabilization leading to cytochrome c release, and dissipation of the inner transmembrane potential, caspase activation, plasma membrane rupture and loss of clonogenic potential in NSCLC cells. Collectively, our results indicate that CDDP can be advantageously combined with PARP inhibitors to kill several NSCLC cell lines, independently from their p53 status. Combined treatment with CDDP and PARP inhibitors elicits the intrinsic pathway of apoptosis.
doi:10.4161/cc.24034
PMCID: PMC3637345  PMID: 23428903
apoptosis; CEP 8983; DNA damage response; A549 cells; PJ34 hydrochloride; small-interfering RNA
16.  Nucleocytosolic Depletion of the Energy Metabolite Acetyl-Coenzyme A Stimulates Autophagy and Prolongs Lifespan 
Cell Metabolism  2014;19(3):431-444.
Summary
Healthy aging depends on removal of damaged cellular material that is in part mediated by autophagy. The nutritional status of cells affects both aging and autophagy through as-yet-elusive metabolic circuitries. Here, we show that nucleocytosolic acetyl-coenzyme A (AcCoA) production is a metabolic repressor of autophagy during aging in yeast. Blocking the mitochondrial route to AcCoA by deletion of the CoA-transferase ACH1 caused cytosolic accumulation of the AcCoA precursor acetate. This led to hyperactivation of nucleocytosolic AcCoA-synthetase Acs2p, triggering histone acetylation, repression of autophagy genes, and an age-dependent defect in autophagic flux, culminating in a reduced lifespan. Inhibition of nutrient signaling failed to restore, while simultaneous knockdown of ACS2 reinstated, autophagy and survival of ach1 mutant. Brain-specific knockdown of Drosophila AcCoA synthetase was sufficient to enhance autophagic protein clearance and prolong lifespan. Since AcCoA integrates various nutrition pathways, our findings may explain diet-dependent lifespan and autophagy regulation.
Graphical Abstract
Highlights
•Acetyl-CoA (AcCoA) metabolism regulates autophagy during aging•Autophagy regulation by AcCoA metabolism acts downstream of nutrient signaling•Brain-specific knockdown of Drosophila AcCoA synthetase prolongs lifespan•Histone point mutations permanently activate autophagy during aging
Autophagy plays a crucial role in healthy aging. By blocking mitochondrial AcCoA production, Eisenberg et al. show that accumulation of nucleocytosolic AcCoA inhibits autophagy and reduces lifespan through a conserved epigenetic mechanism involving histone acetylation of specific autophagy genes in yeast and flies.
doi:10.1016/j.cmet.2014.02.010
PMCID: PMC3988959  PMID: 24606900
17.  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
18.  Prognostic value of LIPC in non-small cell lung carcinoma 
Cell Cycle  2013;12(4):647-654.
Non-small cell lung carcinoma (NSCLC) is the most common form of lung cancer and is associated with a high mortality rate worldwide. The majority of individuals bearing NSCLC are treated with surgery plus adjuvant cisplatin, an initially effective therapeutic regimen that, however, is unable to prevent relapse within 5 years after tumor resection in an elevated proportion of patients. The factors that predict the clinical course of NSCLC and its sensitivity to therapy remain largely obscure. One notable exception is provided by pyridoxal kinase (PDXK), the enzyme that generates the bioactive form of vitamin B6. PDXK has recently been shown to be required for optimal cisplatin responses in vitro and in vivo and to constitute a bona fide prognostic marker in the NSCLC setting. Together with PDXK, 84 additional factors were identified that influence the response of NSCLC cells to cisplatin, in vitro including the hepatic lipase LIPC. Here, we report that the intratumoral levels of LIPC, as assessed by immunohistochemistry in two independent cohorts of NSCLC patients, positively correlate with disease outcome. In one out of two cohorts studied, the overall survival of NSCLC patients bearing LIPChigh lesions was unaffected, if not slightly worsened, by cisplatin-based adjuvant therapy. Conversely, the overall survival of patients with LIPClow lesions was prolonged by post-operative cisplatin. Pending validation in appropriate clinical series, these results suggest that LIPClow NSCLC patients would be those who mainly benefit from adjuvant cisplatin therapy. Thus, the expression levels of LIPC appear to have an independent prognostic value (and perhaps a predictive potential) in the setting of NSCLC. If these findings were confirmed by additional studies, LIPC expression levels might allow not only for NSCLC patient stratification, but also for the implementation of personalized therapeutic approaches.
doi:10.4161/cc.23517
PMCID: PMC3594265  PMID: 23343765
anaplastic lymphoma kinase; apoptosis; BCL-XL; PDXP; personalized medicine; pyridoxine
19.  Role of the c subunit of the FO ATP synthase in mitochondrial permeability transition 
Cell Cycle  2013;12(4):674-683.
The term “mitochondrial permeability transition” (MPT) refers to an abrupt increase in the permeability of the inner mitochondrial membrane to low molecular weight solutes. Due to osmotic forces, MPT is paralleled by a massive influx of water into the mitochondrial matrix, eventually leading to the structural collapse of the organelle. Thus, MPT can initiate mitochondrial outer membrane permeabilization (MOMP), promoting the activation of the apoptotic caspase cascade as well as of caspase-independent cell death mechanisms. MPT appears to be mediated by the opening of the so-called “permeability transition pore complex” (PTPC), a poorly characterized and versatile supramolecular entity assembled at the junctions between the inner and outer mitochondrial membranes. In spite of considerable experimental efforts, the precise molecular composition of the PTPC remains obscure and only one of its constituents, cyclophilin D (CYPD), has been ascribed with a crucial role in the regulation of cell death. Conversely, the results of genetic experiments indicate that other major components of the PTPC, such as voltage-dependent anion channel (VDAC) and adenine nucleotide translocase (ANT), are dispensable for MPT-driven MOMP. Here, we demonstrate that the c subunit of the FO ATP synthase is required for MPT, mitochondrial fragmentation and cell death as induced by cytosolic calcium overload and oxidative stress in both glycolytic and respiratory cell models. Our results strongly suggest that, similar to CYPD, the c subunit of the FO ATP synthase constitutes a critical component of the PTPC.
doi:10.4161/cc.23599
PMCID: PMC3594268  PMID: 23343770
ATP5G1; apoptosis; caspases; cytochrome c; mitochondrial respiratory chain; p53; permeability transition pore (PTP)
20.  Vitamin B6 metabolism influences the intracellular accumulation of cisplatin 
Cell Cycle  2013;12(3):417-421.
Vitamin B6 metabolism influences the adaptive response of non-small lung carcinoma (NSCLC) cells to distinct, potentially lethal perturbations in homeostasis, encompassing nutrient deprivation, hyperthermia, hypoxia, irradiation as well as the exposure to cytotoxic chemicals, including the DNA-damaging agent cisplatin (CDDP). Thus, the siRNA-mediated downregulation of pyridoxal kinase (PDXK), the enzyme that generates the bioactive form of vitamin B6, protects NSCLC cells (as well as a large collection of human and murine malignant cells of distinct histological derivation) from the cytotoxic effects of CDDP. Accordingly, the administration of pyridoxine, one of the inactive precursors of vitamin B6, exacerbates cisplatin-induced cell death, in vitro and in vivo, but only when PDXK is expressed. Conversely, antioxidants such as non-oxidized glutathione (GSH) are known to protect cancer cells from CDDP toxicity. Pyridoxine increases the amount of CDDP-DNA adducts formed upon the exposure of NSCLC cells to CDDP and aggravates the consequent DNA damage response. On the contrary, in the presence of GSH, NSCLC cells exhibit near-to-undetectable levels of CDDP-DNA adducts and a small fraction of the cell population activates the DNA damage response. We therefore wondered whether vitamin B6 metabolism and GSH might interact with CDDP in a pharmacokinetic fashion. In this short communication, we demonstrate that GSH inhibits the intracellular accumulation of CDDP, while pyridoxine potentiates it in a PDXK-dependent fashion. Importantly, such pharmacokinetic effects do not involve plasma membrane transporters that mediate a prominent fraction of CDDP influx, i.e., solute carrier family 31, member 1 (SLC31A1, best known as copper transporter 1, CTR1) and efflux, i.e., ATPase, Cu2+ transporting, β polypeptide (ATP7B).
doi:10.4161/cc.23275
PMCID: PMC3587442  PMID: 23287530
A549; apoptosis; N-acetyl-cysteine; PDXP; reactive oxygen species; Wilson disease
21.  Immunosurveillance against tetraploidization-induced colon tumorigenesis 
Cell Cycle  2013;12(3):473-479.
Circumstantial evidence suggests that colon carcinogenesis can ensue the transient tetraploidization of (pre-)malignant cells. In line with this notion, the tumor suppressors APC and TP53, both of which are frequently inactivated in colon cancer, inhibit tetraploidization in vitro and in vivo. Here, we show that—contrarily to their wild-type counterparts—Tp53−/− colonocytes are susceptible to drug-induced or spontaneous tetraploidization in vitro. Colon organoids generated from tetraploid Tp53−/− cells exhibit a close-to-normal morphology as compared to their diploid Tp53−/− counterparts, yet the colonocytes constituting these organoids are characterized by an increased cell size and an elevated expression of the immunostimulatory protein calreticulin on the cell surface. The subcutaneous injection of tetraploid Tp53−/− colon organoids led to the generation of proliferating tumors in immunodeficient, but not immunocompetent, mice. Thus, tetraploid Tp53−/− colonocytes fail to survive in immunocompetent mice and develop neoplastic lesions in immunocompromised settings only. These results suggest that tetraploidy is particularly oncogenic in the context of deficient immunosurveillance.
doi:10.4161/cc.23369
PMCID: PMC3587448  PMID: 23324343
apoptosis; cell cycle; cytochalasin D; mitotic catastrophe; nocodazole; p53
22.  Trial Watch 
Oncoimmunology  2014;3:e27297.
Immunostimulatory monoclonal antibodies (mAbs) exert antineoplastic effects by eliciting a novel or reinstating a pre-existing antitumor immune response. Most often, immunostimulatory mAbs activate T lymphocytes or natural killer (NK) cells by inhibiting immunosuppressive receptors, such as cytotoxic T lymphocyte-associated protein 4 (CTLA4) or programmed cell death 1 (PDCD1, best known as PD-1), or by engaging co-stimulatory receptors, like CD40, tumor necrosis factor receptor superfamily, member 4 (TNFRSF4, best known as OX40) or TNFRSF18 (best known as GITR). The CTLA4-targeting mAb ipilimumab has been approved by the US Food and Drug Administration for use in patients with unresectable or metastatic melanoma in 2011. The therapeutic profile of ipilimumab other CTLA4-blocking mAbs, such as tremelimumab, is currently being assessed in subjects affected by a large panel of solid neoplasms. In the last few years, promising clinical results have also been obtained with nivolumab, a PD-1-targeting mAb formerly known as BMS-936558. Accordingly, the safety and efficacy of nivolumab and other PD-1-blocking molecules are being actively investigated. Finally, various clinical trials are underway to test the therapeutic potential of OX40- and GITR-activating mAbs. Here, we summarize recent findings on the therapeutic profile of immunostimulatory mAbs and discuss clinical trials that have been launched in the last 14 months to assess the therapeutic profile of these immunotherapeutic agents.
doi:10.4161/onci.27297
PMCID: PMC3961485  PMID: 24701370
CD137; checkpoint blockade; immunogenic chemotherapy; immunosuppression; lirilumab; IPH2101; PD-L1
23.  Chemokines and chemokine receptors required for optimal responses to anticancer chemotherapy 
Oncoimmunology  2014;3:e27663.
Depending on tumor type, stage and immunological contexture, the inhibition of chemokines or their receptors may yield positive or deleterious effects on disease progression. We have recently demonstrated in several murine models of anthracycline-based chemotherapy that the inhibition of chemokine (C-C motif) ligand 2 (CCL2) or chemokine (C-C motif) receptor 2 (CCR2) may impair the elicitation of anticancer immune responses that contribute to therapeutic success.
doi:10.4161/onci.27663
PMCID: PMC4008453  PMID: 24800170
ATP; autophagy; cancer stem cells; immunogenic cell death; immunosurveillance; γδ T lymphocytes
24.  Trial Watch 
Oncoimmunology  2014;3:e27048.
In 1997, for the first time in history, a monoclonal antibody (mAb), i.e., the chimeric anti-CD20 molecule rituximab, was approved by the US Food and Drug Administration for use in cancer patients. Since then, the panel of mAbs that are approved by international regulatory agencies for the treatment of hematopoietic and solid malignancies has not stopped to expand, nowadays encompassing a stunning amount of 15 distinct molecules. This therapeutic armamentarium includes mAbs that target tumor-associated antigens, as well as molecules that interfere with tumor-stroma interactions or exert direct immunostimulatory effects. These three classes of mAbs exert antineoplastic activity via distinct mechanisms, which may or may not involve immune effectors other than the mAbs themselves. In previous issues of OncoImmunology, we provided a brief scientific background to the use of mAbs, all types confounded, in cancer therapy, and discussed the results of recent clinical trials investigating the safety and efficacy of this approach. Here, we focus on mAbs that primarily target malignant cells or their interactions with stromal components, as opposed to mAbs that mediate antineoplastic effects by activating the immune system. In particular, we discuss relevant clinical findings that have been published during the last 13 months as well as clinical trials that have been launched in the same period to investigate the therapeutic profile of hitherto investigational tumor-targeting mAbs.
doi:10.4161/onci.27048
PMCID: PMC3937194  PMID: 24605265
bevacizumab; brentuximab vedotin; cetuximab; nimotuzumab; trastuzumab; tumor-associated antigen
25.  The Hallmarks of Aging 
Cell  2013;153(6):1194-1217.
Aging is characterized by a progressive loss of physiological integrity, leading to impaired function and increased vulnerability to death. This deterioration is the primary risk factor for major human pathologies including cancer, diabetes, cardiovascular disorders, and neurodegenerative diseases. Aging research has experienced an unprecedented advance over recent years, particularly with the discovery that the rate of aging is controlled, at least to some extent, by genetic pathways and biochemical processes conserved in evolution. This review enumerates nine tentative hallmarks that represent common denominators of aging in different organisms, with special emphasis on mammalian aging. These hallmarks are: genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient-sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication. A major challenge is to dissect the interconnectedness between the candidate hallmarks and their relative contribution to aging, with the final goal of identifying pharmaceutical targets to improve human health during aging with minimal side-effects.
doi:10.1016/j.cell.2013.05.039
PMCID: PMC3836174  PMID: 23746838
aging; cancer; DNA damage; epigenetic; healthspan; lifespan; longevity; metabolism; mitochondria; nutrient-signaling pathways; senescence; stem cells; telomeres

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