Coordinated regulation of autophagy by p38α MAPK through mAtg9 and p38IP

Autophagy, a lysosomal degradation pathway, is essential for homeostasis, development, neurological diseases, and cancer. Regulation of autophagy in human disease is not well understood. Atg9 is a transmembrane protein required for autophagy, and it has been proposed that trafficking of Atg9 may regulate autophagy. Mammalian Atg9 traffics between the TGN and endosomes in basal conditions, and newly formed autophagosomes in response to signals inducing autophagy. We identified p38IP as a new mAtg9 interactor and showed that this interaction is regulated by p38α MAPK. p38IP is required for starvation‐induced mAtg9 trafficking and autophagosome formation. Manipulation of p38IP and p38α alters mAtg9 localization, suggesting p38α regulates, through p38IP, the starvation‐induced mAtg9 trafficking to forming autophagosomes. Furthermore, we show that p38α is a negative regulator of both basal autophagy and starvation‐induced autophagy, and suggest that this regulation may be through a direct competition with mAtg9 for binding to p38IP. Our results provide evidence for a link between the MAPK pathway and the control of autophagy through mAtg9 and p38IP.     

TNF‐α regulates the early development of avascular necrosis of the femoral head by mediating osteoblast autophagy and apoptosis via the p38 MAPK/NF‐κB signaling pathway

Previous studies have shown that the tumor necrosis factor‐α (TNF‐α) levels in serum and bone tissues formed in avascular necrosis of femoral head (ANFH) patients were higher than those of normal individuals, indicating TNF‐α might play a role in the pathogenesis of ANFH. However, the underlying mechanisms remain unclear. Hematoxylin and eosin staining was performed to show the pathological changes of ANFH bone tissues. TNF‐α expression in normal and ANFH tissues was examined by quantitative real‐time polymerase chain reaction and western blot analyses. Osteoblast autophagy and apoptosis, as well as signaling pathways activation, were measured by their corresponding marker proteins. Osteoblast proliferation, autophagy, and apoptosis were evaluated using cell counting kit‐8, transmission electron microscopy, and flow cytometry. The structures of bone tissues of ANFH were obviously damaged. TNF‐α expression was significantly upregulated in ANFH bone tissues compared to normal tissues. Autophagy and apoptosis were remarkably promoted, and p38 mitogen‐activated protein kinase (MAPK)/nuclear factor‐κB (NF‐κB) signaling pathways were markedly activated in ANFH. Suppression of the p38 MAPK/NF‐κB pathway significantly attenuated the TNF‐α‐induced autophagy, however, enhanced the TNF‐α‐induced apoptosis in osteoblasts. Increased TNF‐α in ANFH regulated osteoblast autophagy and apoptosis by p38 MAPK/NF‐κB signaling pathways, blocking the pathway by inhibitors exacerbated TNF‐α‐induced apoptosis through impairing autophagy flux.     

TLR9 deficiency alleviates doxorubicin‐induced cardiotoxicity via the regulation of autophagy

Doxorubicin is a commonly used anthracycline chemotherapeutic drug. Its application for treatment has been impeded by its cardiotoxicity as it is detrimental and fatal. DNA damage, cardiac inflammation, oxidative stress and cell death are the critical links in DOX‐induced myocardial injury. Previous studies found that TLR9‐related signalling pathways are associated with the inflammatory response of cardiac myocytes, mitochondrial dysfunction and cardiomyocyte death, but it remains unclear whether TLR9 could influence DOX‐induced heart injury. Our current data imply that DOX‐induced cardiotoxicity is ameliorated by TLR9 deficiency both in vivo and in vitro, manifested as improved cardiac function and reduced cardiomyocyte apoptosis and oxidative stress. Furthermore, the deletion of TLR9 rescued DOX‐induced abnormal autophagy flux in vivo and in vitro. However, the inhibition of autophagy by 3‐MA abolished the protective effects of TLR9 deletion on DOX‐induced cardiotoxicity. Moreover, TLR9 ablation suppressed the activation of p38 MAPK during DOX administration and may promote autophagy via the TLR9‐p38 MAPK signalling pathway. Our study suggests that the deletion of TLR9 exhibits a protective effect on doxorubicin‐induced cardiotoxicity by enhancing p38‐dependent autophagy. This finding could be used as a basis for the development of a prospective therapy against DOX‐induced cardiotoxicity.     

Mycobacterial lipoprotein activates autophagy via TLR2/1/CD14 and a functional vitamin D receptor signalling

In human monocytes, Toll‐like receptor (TLR) 2/1 activation leads to vitamin D3‐dependent antimycobacterial activities, but the molecular mechanisms by which TLR2/1 stimulation induces antimicrobial activities against mycobacteria remain unclear. Here we show that TLR2/1/CD14 stimulation by mycobacterial lipoprotein LpqH can robustly activate antibacterial autophagy through vitamin D receptor signalling activation and cathelicidin induction. We found that CCAAT/enhancer‐binding protein (C/EBP)‐β‐dependent induction of 25‐hydroxycholecalciferol‐1α‐hydroxylase (Cyp27b1) hydroxylase was critical for LpqH‐induced cathelicidin expression and autophagy. In addition, increases in intracellular calcium following AMP‐activated protein kinase (AMPK) activation played a crucial role in LpqH‐induced autophagy. Moreover, AMPK‐dependent p38 mitogen‐activated protein kinase (MAPK) activation was required for LpqH‐induced Cyp27b1 expression and autophagy activation. Collectively, these data suggest that TLR2/1/CD14‐Ca²⁺‐AMPK‐p38 MAPK pathways contribute to C/EBP‐β‐dependent expression of Cyp27b1 and cathelicidin, which played an essential role in LpqH‐induced autophagy. Furthermore, these results establish a previously uncharacterized signalling pathway of antimycobacterial host defence through a functional link of TLR2/1/CD14‐dependent sensing to the induction of autophagy.     

Mevalonate cascade regulation of airway mesenchymal cell autophagy and apoptosis: a dual role for p53

Statins inhibit the proximal steps of cholesterol biosynthesis, and are linked to health benefits in various conditions, including cancer and lung disease. We have previously investigated apoptotic pathways triggered by statins in airway mesenchymal cells, and identified reduced prenylation of small GTPases as a primary effector mechanism leading to p53-mediated cell death. Here, we extend our studies of statin-induced cell death by assessing endpoints of both apoptosis and autophagy, and investigating their interplay and coincident regulation. Using primary cultured human airway smooth muscle (HASM) and human airway fibroblasts (HAF), autophagy, and autophagosome formation and flux were assessed by transmission electron microscopy, cytochemistry (lysosome number and co-localization with LC3) and immunoblotting (LC3 lipidation and Atg12-5 complex formation). Chemical inhibition of autophagy increased simvastatin-induced caspase activation and cell death. Similarly, Atg5 silencing with shRNA, thus preventing Atg5-12 complex formation, increased pro-apoptotic effects of simvastatin. Simvastatin concomitantly increased p53-dependent expression of p53 up-regulated modulator of apoptosis (PUMA), NOXA, and damage-regulated autophagy modulator (DRAM). Notably both mevalonate cascade inhibition-induced autophagy and apoptosis were p53 dependent: simvastatin increased nuclear p53 accumulation, and both cyclic pifithrin-α and p53 shRNAi partially inhibited NOXA, PUMA expression and caspase-3/7 cleavage (apoptosis) and DRAM expression, Atg5-12 complex formation, LC3 lipidation, and autophagosome formation (autophagy). Furthermore, the autophagy response is induced rapidly, significantly delaying apoptosis, suggesting the existence of a temporally coordinated p53 regulation network. These findings are relevant for the development of statin-based therapeutic approaches in obstructive airway disease.     

Autophagy and apoptosis act as partners to induce germ cell death after heat stress in mice

Testicular heating suppresses spermatogenesis which is marked by germ cell loss via apoptotic pathways. Recently, it is reported that autophagy also can be induced by heat treatment in somatic cells. In this study, the status of autophagy in germ cells after heat treatment, as well as the partnership between autophagy and apoptosis in these cells was investigated. The results demonstrated that besides initiating apoptotic pathways, heat also induced autophagic pathways in germ cells. Exposure of germ cells to hyperthermia resulted in several specific features of the autophagic process, including autophagosome formation and the conversion of LC3-I to LC3-II. Furthermore, the ubiquitin-like protein conjugation system was implicated as being likely responsible for heat-induced autophagy in germ cells since all genes involving this system were found to be expressed in the testes. In addition, the upstream protein in this system, Atg7 (Autophagy-related gene 7), was found to be expressed in all types of spermatogenic cells, and its expression level was positively correlated with the level of autophagy in germ cells. As a result, Atg7 was selected as the investigative target to further analyze the role of autophagy in heat-induced germ cell death. It was shown that down expression of Atg7 protein resulted in the notable decrease in the level of autophagy in heat-treated germ cells, and this down-regulation of autophagy caused by Atg7 knockdown further reduced the apoptotic rate of germ cells. These results suggest that autophagy plays a positive role in the process of germ cell apoptosis after heat treatment. In conclusion, this study demonstrates that heat triggers autophagy and apoptosis in germ cells. These two mechanisms might act as partners, not antagonist, to induce cell death and lead to eventual destruction of spermatogenesis.     

Oxyresveratrol activates parallel apoptotic and autophagic cell death pathways in neuroblastoma cells

BackgroundDrug resistance from apoptosis is a challenging issue with different cancer types, and there is an interest in identifying other means of inducing cytotoxicity. Here, treatment of neuroblastoma cells with oxyresveratrol (OXYRES), a natural antioxidant, led to dose-dependent cell death and increased autophagic flux along with activation of caspase-dependent apoptosis.MethodsFor cell viability, we performed the CCK-8 assay. Protein expression changes were with Western blot and immunocytochemistry. Silencing of proteins was with siRNA. The readouts for cell cycle, mitochondria membrane potential, caspase-3, autophagy and apoptosis were performed with flow cytometry.ResultsPhosphorylation of p38 MAPK increased with OXYRES treatment and inhibition of p38 reduced autophagy and cell death from OXYRES. In contrast, PI3K/AKT/mTOR signaling decreased in the target cells with OXYRES and inhibition of PI3K or mTOR enhanced OXYRES-mediated cytotoxicity with increased levels of autophagy. Modulation of either of the apoptosis and autophagy flux pathways affected the extent of cell death by OXYRES, but did not affect the indicators of these pathways with respect to each other. Both pathways were independent of ROS generation or p53 activation.ConclusionOXYRES led to cell death from autophagy, which was independent of apoptosis induction. The OXYRES effects were due to changes in the activity levels of p38 MAPK and PI3K/AKT/mTOR.General significanceWith two independent and parallel pathways for cytotoxicity induction in target cells, this study puts forward a potential utility for OXYRES or the pathways it represents as novel means of inducing cell death in neuroblastoma cells.     

Defective autophagy in vascular smooth muscle cells enhances cell death and atherosclerosis

Macroautophagy/autophagy is considered as an evolutionarily conserved cellular catabolic process. In this study, we aimed to elucidate the role of autophagy in vascular smooth muscle cells (SMCs) on atherosclerosis. SMCs cultured from mice with SMC-specific deletion of the essential autophagy gene atg7 (Atg7cKO) showed reduced serum-induced cell growth, increased cell death, and decreased cell proliferation rate. Furthermore, 7-ketocholestrerol enhanced apoptosis and the expression of CCL2 (chemokine [C-C motif] ligand 2) with the activation of TRP53, the mouse ortholog of human and rat TP53, in SMCs from Atg7cKO mice. In addition, Atg7cKO mice crossed with Apoe (apolipoprotein E)-deficient mice (apoeKO; Atg7cKO:apoeKO) showed reduced medial cellularity and increased TUNEL-positive cells in the descending aorta at 10 weeks of age. Intriguingly, Atg7cKO: apoeKO mice fed a Western diet containing 1.25% cholesterol for 14 weeks showed a reduced survival rate. Autopsy of the mice demonstrated the presence of aortic rupture. Analysis of the descending aorta in Atg7cKO:apoeKO mice showed increased plaque area, increased TUNEL-positive area, decreased SMC-positive area, accumulation of macrophages in the media, and adventitia and perivascular tissue, increased CCL2 expression in SMCs in the vascular wall, medial disruption, and aneurysm formation. In conclusion, our data suggest that defective autophagy in SMCs enhances atherosclerotic changes with outward arterial remodeling.     

Clostridium difficile toxin B induces autophagic cell death in colonocytes

Toxin B (TcdB) is a major pathogenic factor of Clostridum difficile. However, the mechanism by which TcdB exerts its cytotoxic action in host cells is still not completely known. Herein, we report for the first time that TcdB induced autophagic cell death in cultured human colonocytes. The induction of autophagy was demonstrated by the increased levels of LC3‐II, formation of LC3⁺ autophagosomes, accumulation of acidic vesicular organelles and reduced levels of the autophagic substrate p62/SQSTM1. TcdB‐induced autophagy was also accompanied by the repression of phosphoinositide 3‐kinase (PI3K)/Akt/mechanistic target of rapamycin (mTOR) complex 1 activity. Functionally, pharmacological inhibition of autophagy by wortmannin or chloroquine or knockdown of autophagy‐related genes Beclin 1, Atg5 and Atg7 attenuated TcdB‐induced cell death in colonocytes. Genetic ablation of Atg5, a gene required for autophagosome formation, also mitigated the cytotoxic effect of TcdB. In conclusion, our study demonstrated that autophagy serves as a pro‐death mechanism mediating the cytotoxic action of TcdB in colonocytes. This discovery suggested that blockade of autophagy might be a novel therapeutic strategy for C. difficile infection.     

Regulatory T cells protected against abdominal aortic aneurysm by suppression of the COX‐2 expression

CD4⁺CD25⁺ regulatory T cells (Tregs) have been shown to protect against the development of abdominal aortic aneurysm (AAA). Cyclooxygenase‐2 (COX‐2), a pro‐inflammatory protein, can convert arachidonic acid into prostaglandins (PGs). The present study was aimed to investigate the effect of Tregs on COX‐2 expression in angiotension II (Ang II)‐induced AAA in ApoE^?/? mice. Tregs were injected via tail vein in every 2 weeks. Ang II was continuously infused by a micropump for 28 days to induce AAA. In vivo, compared with the control group, adoptive transfer of Tregs significantly reduced the incidence of AAA, maximal diameter, and the mRNA and protein expression of COX‐2 in mice. Immunofluorescence showed that Tregs treatment reduced COX‐2 expression both in smooth muscle cells (SMCs) and macrophages in AAA. In vitro, the Western blot analysis showed that Tregs reduced Ang II‐induced COX‐2 expression in macrophages and SMCs. Meanwhile, ELISA showed that Tregs reduced Ang II‐induced prostaglandin E₂ (PGE₂) secretion. Moreover, Tregs increased SMC viability and induced transition of macrophages phenotype from M1 to M2. In conclusion, Tregs treatment dramatically decreased the expression of COX‐2 in vivo and in vitro, suggesting that Tregs could protect against AAA through inhibition of COX‐2. The study may shed light on the immune treatment of AAA.     

Tetraspanin CD9 regulates osteoclastogenesis via regulation of p44/42 MAPK activity

Tetraspanin CD9 has been shown to regulate cell-cell fusion in sperm-egg fusion and myotube formation. However, the role of CD9 in osteoclast, another multinucleated cell type, is not still clear. Therefore, we investigated the role of CD9 in osteoclast differentiation. CD9 was expressed in osteoclast lineage cells and its expression level increased during the progression of RANKL-induced osteoclastogenesis. KMC8, a neutralizing antibody specific to CD9, significantly suppressed RANKL-induced multinucleated osteoclast formation and the mRNA expression of osteoclast differentiation marker genes. To define CD9-regulated osteoclastogenic signaling pathway, MAPK pathways were examined. KMC8 induced long-term phosphorylation of p44/42 MAPK, but not of p38 MAPK. Constitutive activation of p44/42 MAPK by overexpressing constitutive-active mutant of MEK1 almost completely blocked osteoclast differentiation. Taken together, these results suggest that CD9 expressed on osteoclast lineage cells might positively regulate osteoclastogenesis via the regulation of p44/42 MAPK activity.     

Protective effect of Homer 1a on tumor necrosis factor-α with cycloheximide-induced apoptosis is mediated by mitogen-activated protein kinase pathways

Although Homer 1, of the postsynaptic density, regulates apoptosis, the signaling mechanisms are not fully elucidated. In this study, we found that tumor necrosis factor-α (TNF-α)/cycloheximide (CHX) treatment transiently increased Homer 1a (the short variant of Homer 1), but did not affect Homer 1b/c (the long variant of Homer 1). Overexpression of Homer 1a blocked TNF-α/CHX-induced apoptotic cell death, whereas inhibition of Homer 1a induction enhanced the pro-apoptotic effect of TNF-α/CHX treatment. Moreover, brain-derived neurotrophic factor, as a potential activator of endogenous Homer 1a, inhibited apoptotic cell death after TNF-α/CHX treatment through induction of Homer 1a. Since three major mitogen-activated protein kinase (MAPK) pathways have important roles in apoptosis, we examined if Homer 1a is involved in the effects of MAPK pathways on apoptosis. It was shown that inhibition of the ERK1/2 pathway increased the expression and the protective effect of Homer 1a, but inhibition of the p38 pathway produced the opposite effect. Cross-talk among MAPK pathways was also associated with the regulation of Homer 1a during apoptotic cell death. Blocking the p38 pathway increased the activity in the ERK1/2 pathway, while inhibition of ERK1/2 pathway abolished the effect of p38 inhibitor on Homer 1a. Furthermore, Homer 1a reversely affected the activation of MAPK pathways. These findings suggest that Homer 1a plays an important role in the prevention of apoptotic cell death and contributes to distinct regulatory effects of MAPK pathways on apoptotic cell death.     

Primary granule release from human neutrophils is potentiated by soluble fibrinogen through a mechanism depending on multiple intracellular signaling pathways

N-Formyl-methionyl-leucyl-phenylalanine (fMLP) is a potent activator of neutrophil degranulation. The intracellular signaling mechanisms involved in the potentiating effect of fibrinogen on fMLP-induced primary granule release from human neutrophils were investigated. Fibrinogen caused a significant leftward shift of the concentration-response curve of fMLP-induced elastase release. An antibody against Mac-1 (CD11b/CD18) prevented the potentiating effect of fibrinogen, suggesting that soluble fibrinogen potentiates fMLP-induced degranulating effect by a mechanism mediated by the integrin Mac-1. Fibrinogen enhanced fMLP-induced tyrosine phosphorylation in human neutrophils and markedly enhanced the phosphorylation of mitogen-activated protein kinases (MAPK) caused by fMLP. However, U0126, an inhibitor of p44/42 MAPK activation, or SB-203580, an inhibitor of p38 MAPK, did not alter the effect of fibrinogen on fMLP-induced elastase release. Wortmannin, a phosphatidylinositol 3-kinase (PI3K) kinase inhibitor, and genistein, a nonspecific tyrosine kinase inhibitor, strongly inhibited fMLP-induced elastase release both in the presence and in the absence of fibrinogen. An Akt/PKB inhibitor failed to alter the potentiating effect of fibrinogen, suggesting that the effect of fibrinogen is mediated by Akt-independent pathways. Go6976, an inhibitor of classical PKC isoforms, caused a significant inhibition of fMLP-induced elastase release in the presence or absence of fibrinogen, while nonselective inhibitors of PKC, Ro 31-8220, GF-109203X, and staurosporine, caused potentiation of fMLP-induced elastase release. We conclude that fibrinogen potentiation of primary granule release induced by fMLP is mediated by the integrin CD11b/CD18 through pathways dependent on PI3K and tyrosine kinases, but other regulatory mechanisms may be also involved.     

Berberine induces autophagic cell death and mitochondrial apoptosis in liver cancer cells: The cellular mechanism

Extensive studies have revealed that berberine, a small molecule derived from Coptidis rhizoma (Huanglian in Chinese) and many other plants, has strong anti‐tumor properties. To better understand berberine‐induced cell death and its underlying mechanisms in cancer, we examined autophagy and apoptosis in the human hepatic carcinoma cell lines HepG2 and MHCC97‐L. The results of this study indicate that berberine can induce both autophagy and apoptosis in hepatocellular carcinoma cells. Berberine‐induced cell death in human hepatic carcinoma cells was diminished in the presence of the cell death inhibitor 3‐methyladenine, or following interference with the essential autophagy gene Atg5. Mechanistic studies showed that berberine may activate mitochondrial apoptosis in HepG2 and MHCC97‐L cells by increasing Bax expression, the formation of permeable transition pores, cytochrome C release to cytosol, and subsequent activation of the caspases 3 and 9 execution pathway. Berberine may also induce autophagic cell death in HepG2 and MHCC97‐L cells through activation of Beclin‐1 and inhibition of the mTOR‐signaling pathway by suppressing the activity of Akt and up‐regulating P38 MAPK signaling. This is the first study to describe the role of Beclin‐1 activation and mTOR inhibition in berberine‐induced autophagic cell death. These results further demonstrate the potential of berberine as a therapeutic agent in the emerging list of cancer therapies with novel mechanisms. J. Cell. Biochem. 111: 1426–1436, 2010. © 2010 Wiley‐Liss, Inc.     

cFLIP-L inhibits p38 MAPK activation: an additional anti-apoptotic mechanism in bile acid-mediated apoptosis

In cholestasis, toxic bile acids accumulate within the liver inducing hepatocyte apoptosis, which exacerbates liver injury. Although bile acids activate both death receptors and mitogen-activated kinase (MAPK) pathways, the mechanistic link between death receptor signaling and MAPK activation in bile acid apoptosis remains unclear. The aim of this study was to ascertain if MAPKs contribute to bile acid cytotoxicity. Although deoxycholate induced apoptosis and activated all three classic mediators of the MAPK pathways including JNK 1/2, p38, and p42/44, only p38 MAPK inhibition attenuated apoptosis. Suppressing FADD expression with siRNA or employing a caspase inhibitor, zVAD-fmk, did not block p38 MAPK activation suggesting its activation was not death receptor-dependent. Unexpectedly, expression of cFLIP-L in a stably transfected cell line blocked apoptosis and p38 MAPK phosphorylation. Based on these data we postulated a direct effect of cFLIP on p38 MAPK activation. The nonphosphorylated but not the phosphorylated/active form of p38 MAPK co-immunoprecipitated with cFLIP-L. In reverse immunoprecipitation experiments, cFLIP-L long but not cFLIP-S co-immunoprecipitate with p38 MAPK. In conclusion, these data suggest that cFLIP-L exerts its anti-apoptotic activity, in part, by inhibiting p38 MAPK activation, an additional anti-apoptotic effect for this protein.     

New insights into the function of Atg9

Autophagy is a lysosomal degradation pathway that is essential for cellular homeostasis. Identification of more than 30 autophagy related proteins including a multi-spanning membrane protein, Atg9, has increased our understanding of the molecular mechanisms involved in autophagy. Atg9 is required for autophagy in several eukaryotic organisms although its function is unknown. Recently, we identified a novel interacting partner of mAtg9, p38 MAPK interacting protein, p38IP. We summarise recent data on the role of Atg9 trafficking in yeast and mammalian autophagy and discuss the role of p38IP and p38 MAPK in regulation of mAtg9 trafficking and autophagy.