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1.  Infographic 
Autophagy  2012;8(12):1707.
doi:10.4161/auto.22883
PMCID: PMC3541281
2.  Autophagy researchers 
Autophagy  2012;8(12):1708-1711.
doi:10.4161/auto.22305
PMCID: PMC3541282
3.  FOXO3 induces FOXO1-dependent autophagy by activating the AKT1 signaling pathway 
Autophagy  2012;8(12):1712-1723.
Forkhead box O (FOXO) transcriptional protein family members, including FOXO1 and FOXO3, are involved in the modulation of autophagy. However, whether there is redundancy between FOXO1 and FOXO3 in the ability to induce autophagy remains unclear. In this study, we showed that FOXO3 induced a transcription-dependent autophagy, and FOXO1 was required for this process. Overexpression of wild-type FOXO3 (WT) or FOXO3 (3A), which harbors alanine mutations at residues Thr32, Ser253 and Ser315, but not transcription-inactive FOXO3 (∆DB3A), significantly induced autophagy in the human embryonic kidney cell line HEK293T and mouse embryonic fibroblast (MEF) cell lines. Interestingly, depletion of FOXO1 by siRNA attenuated FOXO3-induced autophagy. Our data also showed that FOXO3 overexpression did not increase the expression of FOXO1 at the protein level, although FOXO3 was capable of binding the promoter region of FOXO1 and inducing an increase in the transcription of FOXO1 mRNA. Furthermore, our results showed that FOXO3 promoted the translocation of FOXO1 from the nucleus to the cytoplasm, resulting in an increase in FOXO1-induced autophagy. Moreover, our results supported a mechanism whereby FOXO3 dramatically increased the expression of the class I PtdIns3K catalytic subunit PIK3CA, leading to an increase in AKT1 activity, which resulted in the phosphorylation and nuclear export of FOXO1. To the best of our knowledge, our data are the first to suggest that FOXO1 plays a central role in FOXO3-induced autophagy.
doi:10.4161/auto.21830
PMCID: PMC3541283  PMID: 22931788
FOXO1; FOXO3; autophagy; PIK3CA; AKT1
4.  ATP is released from autophagic vesicles to the extracellular space in a VAMP7-dependent manner 
Autophagy  2012;8(12):1741-1756.
Autophagy is a normal degradative pathway that involves the sequestration of cytoplasmic components and organelles in a vacuole called autophagosome. SNAREs proteins are key molecules of the vesicle fusion machinery. Our results indicate that in a mammalian tumor cell line a subset of VAMP7 (V-SNARE)-positive vacuoles colocalize with LC3 at the cell periphery (focal adhesions) upon starvation. The re-distribution of VAMP7 positive structures is a microtubule-dependent event, with the participation of the motor protein KIF5 and the RAB7 effector RILP. Interestingly, most of the VAMP7-labeled vesicles were loaded with ATP. Moreover, in cells subjected to starvation, these structures fuse with the plasma membrane to release the nucleotide to the extracellular medium. Summarizing, our results show the molecular components involved in the release of ATP to extracellular space, which is recognized as an important autocrine/paracrine signal molecule that participates in the regulation of several cellular functions such as immunogenicity of cancer cell death or inflammation
doi:10.4161/auto.21858
PMCID: PMC3541285  PMID: 22951367
SNAREs; VAMP7; autophagy; autophagosome; LC3; focal adhesions; ATP
5.  Autophagy plays a protective role in endoplasmic reticulum stress-mediated pancreatic β cell death 
Autophagy  2012;8(12):1757-1768.
There is a growing evidence of the role of autophagy in pancreatic β cell homeostasis. During development of type 2 diabetes, β cells are required to supply the increased demand of insulin. In such a stage, β cells have to address high ER stress conditions that could lead to abnormal insulin secretion, and ultimately, β cell death and overt diabetes. In this study, we used insulin secretion-deficient β cells derived from fetal mice. These cells present an increased accumulation of polyubiquitinated protein aggregates and LC3B-positive puncta, when compared with insulinoma-derived β cell lines. We found that insulin secretion deficiency renders these cells hypersensitive to endoplasmic reticulum (ER) stress-mediated cell death. Chemical or shRNA-mediated inhibition of autophagy increased β cell death under ER stress. On the other hand, rapamycin treatment increased both autophagy and cell survival under ER stress. Insulin secretion-deficient β cells showed a marked reduction of the antiapoptotic protein BCL2, together with increased BAX expression and ERN1 hyperactivation upon ER stress induction. These results showed how insulin secretion deficiency in β cells may be contributing to ER stress-mediated cell death, and in this regard, we showed how the autophagic response plays a prosurvival role.
doi:10.4161/auto.21994
PMCID: PMC3541286  PMID: 22951927
pancreatic beta cells; insulin secretion deficiency; endoplasmic reticulum stress; apoptosis; autophagy; rapamycin
6.  Glutathione participates in the modulation of starvation-induced autophagy in carcinoma cells 
Autophagy  2012;8(12):1769-1781.
Glutathione (γ-L-glutamyl-L-cysteinyl-glycine, GSH) is the most abundant low molecular weight, thiol-containing compound within the cells and has a primary role in the antioxidant defense and intracellular signaling. Here we demonstrated that nutrient deprivation led to a significant decrease of intracellular GSH levels in three different carcinoma cell lines. This phenomenon was dependent on ABCC1-mediated GSH extrusion, along with GCL inhibition and, to a minor extent, the formation of GSH-protein mixed disulfides that synergistically contributed to the modulation of autophagy by shifting the intracellular redox state toward more oxidizing conditions. Modulation of intracellular GSH by inhibiting its de novo synthesis through incubation with buthionine sulfoximine, or by maintaining its levels through GSH ethyl ester, affected the oxidation of protein thiols, such as PRDXs and consequently the kinetics of autophagy activation. We also demonstrated that thiol-oxidizing or -alkylating agents, such as diamide and diethyl maleate activated autophagy, corroborating the evidence that changes in thiol redox state contributed to the occurrence of autophagy.
doi:10.4161/auto.22037
PMCID: PMC3541287  PMID: 22964495
ABCC1; BECN1; diamide; diethylmaleate; glutathione; peroxiredoxins; redox state
7.  Impaired autophagy and delayed autophagic clearance of transforming growth factor β-induced protein (TGFBI) in granular corneal dystrophy type 2 
Autophagy  2012;8(12):1782-1797.
Granular corneal dystrophy type 2 (GCD2) is an autosomal dominant disease characterized by a progressive age-dependent extracellular accumulation of transforming growth factor β-induced protein (TGFBI). Corneal fibroblasts from GCD2 patients also have progressive degenerative features, but the mechanism underlying this degeneration remains unknown. Here we observed that TGFBI was degraded by autophagy, but not by the ubiquitin/proteasome-dependent pathway. We also found that GCD2 homozygous corneal fibroblasts displayed a greater number of fragmented mitochondria. Most notably, mutant TGFBI (mut-TGFBI) extensively colocalized with microtubule-associated protein 1 light chain 3β (MAP1LC3B, hereafter referred to as LC3)-enriched cytosolic vesicles and CTSD in primary cultured GCD2 corneal fibroblasts. Levels of LC3-II, a marker of autophagy activation, were significantly increased in GCD2 corneal fibroblasts. Nevertheless, levels of SQSTM1/p62 and of polyubiquitinated protein were also significantly increased in GCD2 corneal fibroblasts compared with wild-type (WT) cells. However, LC3-II levels did not differ significantly between WT and GCD2 cells, as assessed by the presence of bafilomycin A1, the fusion blocker of autophagosomes and lysosomes. Likewise, bafilomycin A1 caused a similar change in levels of SQSTM1. Thus, the increase in autophagosomes containing mut-TGFBI may be due to inefficient fusion between autophagosomes and lysosomes. Rapamycin, an autophagy activator, decreased mut-TGFBI, whereas inhibition of autophagy increased active caspase-3, poly (ADP-ribose) polymerase 1 (PARP1) and reduced the viability of GCD2 corneal fibroblasts compared with WT controls. These data suggest that defective autophagy may play a critical role in the pathogenesis of GCD2.
doi:10.4161/auto.22067
PMCID: PMC3541288  PMID: 22995918
LC3/MAP1LC3B; SQSTM1/p62; TGFBI; defective autophagy; rapamycin; ubiquitination
8.  Aurora kinase A inhibition-induced autophagy triggers drug resistance in breast cancer cells 
Autophagy  2012;8(12):1798-1810.
We have previously shown that elevated expression of mitotic kinase aurora kinase A (AURKA) in cancer cells promotes the development of metastatic phenotypes and is associated clinically with adverse prognosis. Here, we first revealed a clinically positive correlation between AURKA and autophagy-associated protein SQSTM1 in breast cancer and further demonstrated that AURKA regulated SQSTM1 through autophagy. Indeed, depletion by siRNA or chemical inhibition of AURKA by the small molecule VX-680 increased both the level of microtubule-associated protein 1 light chain 3-II (LC3-II) and the number of autophagosomes, along with decreased SQSTM1. Conversely, overexpression of AURKA inhibited autophagy, as assessed by decreased LC3-II and increased SQSTM1 either upon nutrient deprivation or normal conditions. In addition, phosphorylated forms of both RPS6KB1 and mechanistic target of rapamycin (MTOR) were elevated by overexpression of AURKA whereas they were suppressed by depletion or inhibition of AURKA. Moreover, inhibition of MTOR by PP242, an inhibitor of MTOR complex1/2, abrogated the changes in both LC3-II and SQSTM1 in AURKA-overexpressing BT-549 cells, suggesting that AURKA-suppressed autophagy might be associated with MTOR activation. Lastly, repression of autophagy by depletion of either LC3 or ATG5, sensitized breast cancer cells to VX-680-induced apoptosis. Similar findings were observed in cells treated with the autophagy inhibitors chloroquine (CQ) and bafilomycin A1 (BAF). Our data thus revealed a novel role of AURKA as a negative regulator of autophagy, showing that AURKA inhibition induced autophagy, which may represent a novel mechanism of drug resistance in apoptosis-aimed therapy for breast cancer.
doi:10.4161/auto.22110
PMCID: PMC3541289  PMID: 23026799
AURKA; SQSTM1; autophagy; breast cancer; MTOR; apoptosis
9.  Attenuation of TNFSF10/TRAIL-induced apoptosis by an autophagic survival pathway involving TRAF2- and RIPK1/RIP1-mediated MAPK8/JNK activation 
Autophagy  2012;8(12):1811-1821.
Although it is known that tumor necrosis factor-related apoptosis-inducing ligand (TNFSF10/TRAIL) induces autophagy, the mechanism by which autophagy is activated by TNFSF10 is still elusive. In this report, we show evidence that TRAF2- and RIPK1-mediated MAPK8/JNK activation is required for TNFSF10-induced cytoprotective autophagy. TNFSF10 activated autophagy rapidly in cancer cell lines derived from lung, bladder and prostate tumors. Blocking autophagy with either pharmacological inhibitors or siRNAs targeting the key autophagy factors BECN1/Beclin 1 or ATG7 effectively increased TNFSF10-induced apoptotic cytotoxicity, substantiating a cytoprotective role for TNFSF10-induced autophagy. Blocking MAPK8 but not NFκB effectively blocked autophagy, suggesting that MAPK8 is the main pathway for TNFSF10-induced autophagy. In addition, blocking MAPK8 effectively inhibited degradation of BCL2L1/Bcl-xL and reduction of the autophagy-suppressing BCL2L1–BECN1complex. Knockdown of TRAF2 or RIPK1 effectively suppressed TNFSF10-induced MAPK8 activation and autophagy. Furthermore, suppressing autophagy inhibited expression of antiapoptosis factors BIRC2/cIAP1, BIRC3/cIAP2, XIAP and CFLAR/c-FLIP and increased the formation of TNFSF10-induced death-inducing signaling complex (DISC). These results reveal a critical role for the MAPK8 activation pathway through TRAF2 and RIPK1 for TNFSF10-induced autophagy that blunts apoptosis in cancer cells. Thus, suppression of MAPK8-mediated autophagy could be utilized for sensitizing cancer cells to therapy with TNFSF10.
doi:10.4161/auto.22145
PMCID: PMC3541290  PMID: 23051914
autophagy; MAPK8/JNK; RIPK1/RIP1; TRAF2; TNFSF10/TRAIL; apoptosis
10.  The DUB-ious lack of ALIS in Salmonella infection 
Autophagy  2012;8(12):1824-1826.
Ubiquitinated aggregates are formed in eukaryotic cells in response to several external stimuli, including exposure to bacterial lipopolysaccharide (LPS). Although Salmonella enterica serovar Typhimurium (S. Typhimurium) LPS has been shown to induce aggresome-like induced structures (ALIS) in macrophages, these have not been described in S. Typhimurium-infected macrophages. Given that LPS is present in infection, this suggests that S. Typhimurium might suppress the formation of ALIS. We found that S. Typhimurium induces the formation of ubiquitinated aggregates in epithelial cells and macrophages, but that their presence is masked by the deubiquitinase (DUB) activity of the S. Typhimurium virulence protein, SseL. SseL deubiquitinates SQSTM1/p62-bound proteins found in S. Typhimurium-induced aggregates and ALIS, and reduces the recruitment of autophagic components. While the functions of ALIS and other ubiquitinated aggregates remain unclear, they serve to sequester cytosolic proteins under a variety of stress conditions and are suggested to be involved in host immune defense. During infection, the deubiquitinase activity of SseL reduces autophagic flux in infected cells and favors bacterial replication. This is a new example of how a bacterial pathogen counteracts the autophagy pathway through the action of a translocated virulence protein.
doi:10.4161/auto.21742
PMCID: PMC3541292  PMID: 22931829
S. Typhimurium; ALIS; DUB; Salmonella; aggregate; autophagy; deubiquitinase; ubiquitin
11.  Heat shock 70 kDa protein 5/glucose-regulated protein 78 “AMP”ing up autophagy 
Autophagy  2012;8(12):1827-1829.
Breast cancer is one of the most prevalent cancers in women, with more than 240,000 new cases reported in the United States in 2011. Classification of breast cancer based upon hormone and growth factor receptor profiling shows that approximately 70% of all breast cancers express estrogen receptor-α. Thus, drugs that either block estrogen biosynthesis (aromatase inhibitors like Letrozole), or compete with estrogen for estrogen receptor (ER) binding (selective ER modulators including tamoxifen; TAM) and/or cause ER degradation (selective estrogen receptor downregulators such as fulvestrant), are among the most prescribed targeted therapeutics for breast cancer. However, overall clinical benefit from the use of these drugs is often limited by resistance; ER+ breast cancers either fail to respond to endocrine therapies initially (de novo resistance), or they respond and then lose sensitivity over time (acquired resistance). While several preclinical studies postulate how antiestrogen resistance occurs, for the most part, the molecular mechanism(s) of resistance is unknown.
doi:10.4161/auto.21765
PMCID: PMC3541293  PMID: 22931685
breast cancer; antiestrogen resistance; glucose-regulated protein 78; unfolded protein response; autophagy; AMP-activated protein kinase; MTOR
12.  Deprive to kill 
Autophagy  2012;8(12):1830-1832.
Killing properties of antitumor drugs can be enhanced by strategies targeting biochemical adaptations of cancer cells. Recently, we reported that depriving cancer cells of glutamine is a feasible approach to enhance antitumor effects of the alkylating analog of pyruvic acid, 3-bromopyruvate, which rely on the induction of autophagic cell death by metabolic-oxidative stress. 3-bromopyruvate chemopotentiation is the result of its increased intracellular uptake mediated by the monocarboxylate transporter 1, whose expression is post-transcriptionally increased upon glutamine withdrawal. Overall, our results identified the metabolic condition able to increase the selectivity of 3-bromopyruvate targets in neoplastic tissues, thereby providing a stage for its use in clinical settings for targeting malignancies and represent a proof of principle that modulation of glutamine availability can influence the delivery of monocarboxylic drugs into tumors.
doi:10.4161/auto.21795
PMCID: PMC3541294  PMID: 22932475
glutamine deprivation; metabolic oxidative stress; MCT-1; chemopotentiation; 3-bromopyruvate
13.  Manipulation of autophagy by MIR375 generates antitumor effects in liver cancer 
Autophagy  2012;8(12):1833-1834.
The exploration into the roles of autophagy in tumorigenesis, either as tumor suppressor or tumor promoter, has led to a great increase in the knowledge of cancer development, progression and treatment. However, there is currently no consensus on how to manipulate autophagy to improve antitumor effects. In this study, we investigated the role of autophagy in established liver cancer cells in response to hypoxia. Hypoxia not only is the most pervasive microenvironmental stress in solid tumors but is also a canonical stimulus for autophagy. The involvement of dysregulated microRNAs in hypoxia-induced autophagy and their therapeutic potential in advanced liver cancer were examined.
doi:10.4161/auto.21796
PMCID: PMC3541295  PMID: 22929050
autophagy; microRNA; hepatocellular carcinoma
14.  The Ume6-Sin3-Rpd3 complex regulates ATG8 transcription to control autophagosome size 
Autophagy  2012;8(12):1835-1836.
The vast majority of studies addressing the induction of autophagy have focused upon cytoplasmic aspects of its regulation. Recently, we have started to expand our knowledge regarding the nuclear events of autophagic induction. Many autophagy-related genes are transcriptionally upregulated upon induction of autophagy, but only in a limited number of cases do we know the pathways leading to this upregulation. Few transcription factors have been implicated in controlling autophagy genes in yeast. However, many of the ATG genes show some level of transcriptional induction upon starvation. Now, we show that transcription of ATG8 is repressed under growing conditions by the Ume6-Sin3-Rpd3 complex.
doi:10.4161/auto.21845
PMCID: PMC3541296  PMID: 22960621
autophagosome; lysosome; phagophore; stress; vacuole
15.  Genetic animal models for evaluating the role of autophagy in etiopathogenesis of Parkinson disease 
Autophagy  2012;8(12):1837-1838.
Parkinson disease (PD) is the most common neurodegenerative movement disorder and is characterized pathologically by the formation of ubiquitin and SNCA/α-synuclein-containing inclusions (Lewy bodies), dystrophic midbrain dopaminergic (DAergic) terminals, and degeneration of midbrain DAergic neurons. The vast majority of PD occurs sporadically, while approximately 5% of all PD cases are inherited. Genetic mutations of a few genes have been identified as causes of familiar PD, i.e., mutations in SNCA, PARK2/parkin, UCHL1, PARK7/DJ1, PINK1 and LRRK2, leading to DAergic cell death, but variable pathological changes. The evidence supports the hypothesis that several pathogenic mechanisms are likely involved at initial stages of the disease, and eventually they merge to cause parkinsonism. The current challenge facing PD research is to unravel the components in these pathways that contribute to the pathogenesis of PD. Accumulating evidence has implicated dysfunctional autophagy, a regulated lysosomal pathway with a capacity for clearing protein aggregates and cellular organelles, as one of the pathogenic systems contributing to the development of idiopathic PD.
doi:10.4161/auto.21859
PMCID: PMC3541297  PMID: 22931754
autophagy; neurodegeneration; Atg7; Parkinson disease; LRRK2; alpha-synuclein; dopamine; motor deficits
16.  PPARGC1A/PGC-1α, TFEB and enhanced proteostasis in Huntington disease 
Autophagy  2012;8(12):1845-1847.
Huntington disease (HD) results from CAG repeats that encode expanded polyglutamine tracts in the HTT/huntingtin protein. HD belongs to a large category of inherited and sporadic neurodegenerative disorders in which production of a misfolded protein initiates the pathogenic cascade. Previous studies have shown that misfolded proteins become resistant to cellular protein turnover pathways by eluding and disabling the ubiquitin-proteasome system (UPS) and autophagy-lysosome pathway. Based upon earlier work implicating impaired PPARGC1A function in HD, we derived inducible PPARGC1A mice and crossed them with HD mice. We found that PPARGC1A overexpression can rescue HD neurological phenotypes and neurodegeneration. An unexpected outcome of the rescue was the virtual elimination of huntingtin aggregates, and we found that PPARGC1A-mediated aggregate elimination required the autophagy pathway. Moreover, we observed decreased expression of transcription factor EB (TFEB), a master regulator of the autophagy-lysosome pathway, in HD cells and mice, and documented PPARGC1A co-activation of TFEB in these model systems, noting that PPARGC1A is upstream of TFEB in promoting proteostasis. These findings underscore the importance of bioenergetics and autophagy in neurodegeneration, and indicate that PPARGC1A promotes mitochondrial quality control to support high-energy production states in cells, such as neurons. As impaired energy production and altered protein–organelle quality control appear inextricably linked in disorders such as HD, Parkinson disease, and Alzheimer disease, efforts directed at enhancing PPARGC1A and TFEB action may represent viable strategies for therapy development in neurodegeneration.
doi:10.4161/auto.21862
PMCID: PMC3541300  PMID: 22932698
PGC-1-alpha; TFEB; autophagy; Huntington disease; mitochondria; neurodegeneration; oxidative stress; transcription; aggregate
17.  Bacterial autophagy 
Autophagy  2012;8(12):1848-1850.
Autophagy is a vital process through which cellular material and dysfunctional organelles are degraded and recycled, and it is inhibited by the metabolic checkpoint kinase MTOR. Autophagy also targets intracellular bacteria (a process termed xenophagy) for lysosomal degradation, thereby playing a key role in innate immunity. In the past few years, the identification of molecules, such as CALCOCO2/NDP52, SQSTM1/p62 and ubiquitin, implicated in the specific targeting of intracellular bacteria, received considerable attention. However, it remains unclear how xenophagy is initiated, since this process commonly occurs in metabolically replete cells. In a recent study, we demonstrated that infection with Shigella and Salmonella triggered an early state of intracellular amino acid (AA) starvation causing MTOR dissociation from endomembranes, downregulation of MTOR activity and activation of the EIF2AK4/GCN2-EIF2S1/eIF2α/ATF3 signaling axis. We also observed that AA starvation was caused by host membrane damage, which appeared to be transient in the case of Salmonella and sustained in Shigella-infected cells, thus highlighting the existence of key timing disparities in xenophagy triggering, depending on the bacterial pathogen. Together, our findings demonstrate that xenophagy is only one arm of a more general metabolic switch geared toward AA starvation in bacteria-infected cells.
doi:10.4161/auto.21863
PMCID: PMC3541301  PMID: 22932645
amino acid starvation; mTOR; Salmonella; Shigella; bacteria
18.  How Atg18 and the WIPIs sense phosphatidylinositol 3-phosphate 
Autophagy  2012;8(12):1851-1852.
The key autophagic lipid sensors are Atg18 in yeast and the WIPI proteins in mammals. Atg18 and the WIPIs belong to the PROPPIN family of proteins. PROPPINs are seven- bladed β-propellers that bind to phosphatidylinositol 3-phosphate (PtdIns3P) and phosphatidylinositol 3,5-bisphosphate [PtdIns(3,5)P2]. In order to understand how PROPPINs bind phosphoinositides, we have determined the crystal structure of a representative, biochemically tractable PROPPIN, Hsv2 of Kluveromyces lactis. The structure revealed that PROPPINs contain two phosphoinositide binding sites which cooperate with a hydrophobic anchoring loop in membrane binding. These three binding elements cooperate in function, as demonstrated by the incremental loss of function in Atg18 mutants impaired in combinations of the two phosphoinositide binding sites and the hydrophobic loop.
doi:10.4161/auto.22077
PMCID: PMC3541302  PMID: 22996041
Atg18; Atg21; WIPI; autophagy; membrane binding
19.  The roles of BECN1 and autophagy in cancer are context dependent 
Autophagy  2012;8(12):1853-1855.
Malignant tissue contains a rare population of multi-potent cells known as cancer stem-like cells (CSCs). Autophagy is an important mechanism in cancer cell survival and tumor growth; it can both suppress malignant transformation and promote the growth of established cancers. However, the molecular mechanisms underlying the tumor-promoting and tumor-suppressing functions of autophagy in CSCs are not understood. Our work demonstrates that a prosurvival autophagic pathway is critical for breast CSC maintenance. Notably, we provide new evidence for the existence of two separate, context-dependent, autophagic programs that are regulated in opposite ways by BECN1.
doi:10.4161/auto.21996
PMCID: PMC3541303  PMID: 22960473
breast cancer; autophagy; cancer stem-like/progenitor cell; Beclin 1
20.  Protective autophagy induced by RBX1/ROC1 knockdown or CRL inactivation via modulating the DEPTOR-MTOR axis 
Autophagy  2012;8(12):1856-1858.
RBX1/ROC1 is an essential subunit of the largest multiunit Cullin-RING E3 ligase (CRL), which controls the degradation of diverse substrates, thereby regulating numerous cellular processes. Recently, we reported that RBX1 is overexpressed in hepatocellular carcinomas (HCC) and its expression is negatively correlated with patient survival. Moreover, siRNA silencing of RBX1 inhibits the proliferation of liver cancer cells both in vitro and in vivo by inducing CDKN1A/p21-dependent cell senescence. Interestingly, independent of senescence, RBX1 knockdown also triggers an autophagy response, due, at least in part, to the accumulation of the MTOR-inhibitory protein DEPTOR, a recently identified CRL substrate. Biologically, blockage of autophagy significantly enhances the growth-suppressive effect of RBX1 knockdown by triggering massive apoptosis, indicating that the autophagy response upon RBX1 knockdown serves as a survival signal in liver cells. Similar observations were also made in many types of human cancer cells upon inhibition of CRL by MLN4924. These findings suggest that RBX1-CRL is a promising anti-cancer drug target and provide proof-of-concept evidence for a novel drug combination of RBX1-CRL inhibitor and autophagy inhibitor for effective treatment of human cancer.
doi:10.4161/auto.22024
PMCID: PMC3541304  PMID: 22965024
ROC1; RBX1; Cullin-RING E3 ligase; autophagy; senescence; DEPTOR; MTOR; neddylation; MLN4924
21.  Autophagic flux, supported by toll-like receptor 2 activity, defends against the carcinogenesis of hepatocellular carcinoma 
Autophagy  2012;8(12):1859-1861.
Hepatocellular carcinoma (HCC), the most common primary malignant liver tumor, is the third leading cause of cancer deaths. The pathogenesis of HCC is closely associated with chronic liver inflammation fired by a variety of stimulates such as virus infection and metabolic stress. Recent work indicates that autophagy, a homeostatic self-degradation process, which decides cell survival or death upon stress, acts as an effector machinery of immune systems in defending microbial invasion and carcinogenesis. SQSTM1 is a selective target and receptor of autophagy, and the protein content of SQSTM1 reflects the level of autophagic flux in cells. Through degrading SQSTM1, decreasing SQSTM1 aggregates, and therefore interrupting the positive feedback between SQSTM1 aggregates and ROS production, autophagy plays a protective role against hepatocellular carcinoma. Indeed, our studies indicate that toll-like receptor 2 (TLR2)-mediated immune activities in the genotoxic carcinogen diethylnitrosamine (DEN)-injured liver tissue provide essential nutrient stimulates to induce intracellular senescence, which can ensure the activation and maturation of autophagy in liver cells. Loss of TLR2-mediated immune activity and senescence leads to the attenuation of autophagic flux, which cannot eliminate SQSTM1 aggregates, ROS accumulation, and DNA damage, and facilitates the development and progression of HCC.
doi:10.4161/auto.22094
PMCID: PMC3541305  PMID: 22996042
DEN; SQSTM1; autophagic flux; hepatocellular carcinoma; immune network; senescence; toll-like receptor 2
22.  Glutamine metabolism links growth factor signaling to the regulation of autophagy 
Autophagy  2012;8(12):1862-1864.
Activation of the PI3K-AKT1-FOXO module by growth factors increases survival and stress resistance. We identified the gene encoding glutamine synthetase (GLUL, glutamate-ammonia ligase) as a novel transcriptional target of this signaling cascade. Growth factor removal increases glutamine synthetase expression and activity through activation of FOXO transcription factors. Surprisingly, increased levels of glutamine synthetase inhibit MTOR signaling by blocking its lysosomal translocation. Furthermore, FOXO activation induces autophagosome formation and autophagic flux in a glutamine synthetase-dependent manner. This may be important for maintaining cell survival during conditions of growth factor and nutrient deprivation since inhibition of autophagy induces cell death. These studies reveal that glutamine metabolism can play an important regulatory role in the regulation of autophagy by growth factor signaling. In addition, the induction of autophagy by FOXO-mediated glutamine synthetase expression might contribute to the tumor suppressive function of FOXOs.
doi:10.4161/auto.22152
PMCID: PMC3541306  PMID: 22996802
FOXO; MTOR; PI3K; autophagy; glutamine metabolism
23.  Staphylococcus aureus promotes autophagy by decreasing intracellular cAMP levels 
Autophagy  2012;8(12):1865-1867.
Staphylococcus aureus is an intracellular bacterium responsible for serious infectious processes. This pathogen escapes from the phagolysosomal pathway into the cytoplasm, a strategy that allows intracellular bacterial replication and survival with the consequent killing of the eukaryotic host cell and spreading of the infection. S. aureus is able to secrete several virulence factors such as enzymes and toxins. Our recent findings indicate that the main virulence factor of S. aureus, the pore-forming toxin α-hemolysin (Hla), is the secreted factor responsible for the activation of an alternative autophagic pathway. We have demonstrated that this noncanonical autophagic response is inhibited by artificially elevating the intracellular levels of cAMP. This effect is mediated by RAPGEF3/EPAC (Rap guanine nucleotide exchange factor (GEF)3/exchange protein activated by cAMP), a cAMP downstream effector that functions as a GEF for the small GTPase Rap. We have presented evidence that RAPGEF3 and RAP2B, through calpain activation, are the proteins involved in the regulation of Hla and S. aureus-induced autophagy. In addition, we have found that both, RAPGEF3 and RAP2B, are recruited to the S. aureus–containing phagosome. Of note, adding purified α-toxin or infecting the cells with S. aureus leads to a decrease in intracellular cAMP levels, which promotes autophagy induction, a response that favors pathogen intracellular survival, as previously demonstrated. We have identified some key signaling molecules involved in the autophagic response upon infection with a bacterial pathogen, which have important implications in understanding innate immune defense mechanisms.
doi:10.4161/auto.22161
PMCID: PMC3541307  PMID: 23047465
Staphylococcus aureus; LC3; RAP2B; RAPGEF3; autophagy; cAMP; α-hemolysin
24.  Understanding phosphatidylinositol-3-phosphate dynamics during autophagosome biogenesis 
Autophagy  2012;8(12):1868-1870.
Autophagosomes, the hallmark of autophagy, are double-membrane vesicles sequestering cytoplasmic components. They are generated at the phagophore assembly site (PAS), the phagophore being the precursor structure of these carriers. According to the current model, autophagosomes result from the elongation and reorganization of membranes at the PAS/phagophore driven by the concerted action of the autophagy-related (Atg) proteins. Once an autophagosome is completed, the Atg proteins that were associated with the expanding phagophore are released in the cytoplasm and reused for the biogenesis of new vesicles. One molecular event required for autophagosome formation is the generation of phosphatidylinositol 3-phosphate (PtdIns3P) at the PAS. Our data indicate that in addition to the synthesis of this lipid, the dephosphorylation of PtdIns3P is also crucial for autophagy progression. In the absence of Ymr1, a specific PtdIns3P phosphatase and the only yeast member of the myotubularin protein family, Atg proteins remain associated with complete autophagosomes, which are thus unable to fuse with the vacuole.
doi:10.4161/auto.22162
PMCID: PMC3541308  PMID: 22992453
PAS; Ymr1; autophagosome; autophagy; phagophore; phosphatidylinositol-3-phosphate; phosphoinositide phosphatases
25.  Autophagy in astrocytes 
Autophagy  2012;8(12):1871-1872.
Neurodegeneration is a prominent feature of lysosomal storage disorders (LSDs). Emerging data identify autophagy dysfunction in neurons as a major component of the phenotype. However, the autophagy pathway in the CNS has been studied predominantly in neurons, whereas in other cell types it has been largely unexplored. We studied the lysosome-autophagic pathway in astrocytes from a murine model of multiple sulfatase deficiency (MSD), a severe form of LSD. Similar to what was observed in neurons, we found that lysosomal storage in astrocytes impairs autophagosome maturation and this, in turn, has an impact upon the survival of cortical neurons and accounts for some of the neurological features found in MSD. Thus, our data indicate that lysosomal/autophagic dysfunction in astrocytes is an important component of neurodegeneration in LSDs.
doi:10.4161/auto.22184
PMCID: PMC3541309  PMID: 23047468
autophagy; neurodegeneration; lysosome; astrocyte; lysosomal storage disorders

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