Both apoptosis ("self-killing") and autophagy ("self-eating") are evolutionarily conserved processes, and their crosstalk influences anticancer drug sensitivity and cell death. However, the underlying mechanism remains unclear. Here, we demonstrated that HMGB1 (high mobility group box 1), normally a nuclear protein, is a crucial regulator of TNFSF10/TRAIL (tumor necrosis factor [ligand] superfamily, member 10)-induced cancer cell death. Activation of PARP1 (poly [ADP-ribose] polymerase 1) was required for TNFSF10-induced ADP-ribosylation of HMGB1 in cancer cells. Moreover, pharmacological inhibition of PARP1 activity or knockdown of PARP1 gene expression significantly inhibited TNFSF10-induced HMGB1 cytoplasmic translocation and subsequent HMGB1-BECN1 complex formation. Furthermore, suppression of the PARP1-HMGB1 pathway diminished autophagy, increased apoptosis, and enhanced the anticancer activity of TNFSF10 in vitro and in a subcutaneous tumor model. These results indicate that PARP1 acts as a prominent upstream regulator of HMGB1-mediated autophagy and maintains a homeostatic balance between apoptosis and autophagy, which provides new insight into the mechanism of TNFSF10 resistance.
apoptosis; autophagy; HMGB1; PARP-1; TRAIL; ATG, autophagy-related; DISC, death-inducing signaling complex; HMGB1, high mobility group box 1; MAP1LC3A/LC3, microtubule-associated protein 1 light chain 3 α; PARP1, poly (ADP-ribose) polymerase 1; PARylation, poly-ADP-ribosylation; RIPK1/RIP, receptor (TNFRSF)-interacting serine-threonine kinase 1; shRNA, short hairpin RNA; TNFSF10/TRAIL, tumor necrosis factor (ligand) superfamily, member 10; TNF, tumor necrosis factor; TUNEL, TdT-mediated dUTP-X nick end labeling
Complex genetic and physiological variations as well as environmental factors that drive emergence of chromosomal instability, development of unscheduled cell death, skewed differentiation, and altered metabolism are central to the pathogenesis of human diseases and disorders. Understanding the molecular bases for these processes is important for the development of new diagnostic biomarkers, and for identifying new therapeutic targets. In 1973, a group of non-histone nuclear proteins with high electrophoretic mobility was discovered and termed High-Mobility Group (HMG) proteins. The HMG proteins include three superfamilies termed HMGB, HMGN, and HMGA. High-mobility group box 1 (HMGB1), the most abundant and well-studied HMG protein, senses and coordinates the cellular stress response and plays a critical role not only inside of the cell as a DNA chaperone, chromosome guardian, autophagy sustainer, and protector from apoptotic cell death, but also outside the cell as the prototypic damage associated molecular pattern molecule (DAMP). This DAMP, in conjunction with other factors, thus has cytokine, chemokine, and growth factor activity, orchestrating the inflammatory and immune response. All of these characteristics make HMGB1 a critical molecular target in multiple human diseases including infectious diseases, ischemia, immune disorders, neurodegenerative diseases, metabolic disorders, and cancer. Indeed, a number of emergent strategies have been used to inhibit HMGB1 expression, release, and activity in vitro and in vivo. These include antibodies, peptide inhbitiors, RNAi, anti-coagulants, endogenous hormones, various chemical compounds, HMGB1-receptor and signaling pathway inhibition, artificial DNAs, physical strategies including vagus nerve stimulation and other surgical approaches. Future work further investigating the details of HMGB1 localizationtion, structure, post-translational modification, and identifccation of additional partners will undoubtedly uncover additional secrets regarding HMGB1’s multiple functions.
Macroautophagy is an intracellular catabolic process involved in the formation of multiple membrane structures ranging from phagophores to autophagosomes and autolysosomes. Dysfunction of macroautophagy is implicated in both physiological and pathological conditions. To date, 38 autophagy-related (ATG) genes have been identified as controlling these complicated membrane dynamics during macroautophagy in yeast; approximately half of these genes are clearly conserved up to human, and there are additional genes whose products function in autophagy in higher eukaryotes that are not found in yeast. The function of the ATG proteins, in particular their ability to interact with a number of macroautophagic regulators, is modulated by posttranslational modifications (PTMs) such as phosphorylation, glycosylation, ubiquitination, acetylation, lipidation, and proteolysis. In this review, we summarize our current knowledge of the role of ATG protein PTMs and their functional relevance in macroautophagy. Unraveling how these PTMs regulate ATG protein function during macroautophagy will not only reveal fundamental mechanistic insights into the regulatory process, but also provide new therapeutic targets for the treatment of autophagy-associated diseases.
autophagy; autophagy-related proteins; posttranslational modification; AMPK, AMP-activated protein kinase; ATG, autophagy-related; MTORC1, mechanistic target of rapamycin complex 1; PE, phosphatidylethanolamine; PTM, posttranslational modification; Ub, ubiquitin; Ubl, ubiquitin like
High mobility group box 1 (HMGB1) is a prototype damage-associated molecular pattern (DAMP) that can induce inflammatory and immune responses alone as well as in combination with other molecules such as DNA. However, the intricate molecular mechanisms underlying HMGB1-DNA complex-mediated innate immune response remains largely elusive. In this study, we demonstrated that HMGB1-DNA complex initially induced absent in melanoma 2 (AIM2)-dependent inflammasome activation, and promoted rapid release of inflammasome-dependent early proinflammatory cytokines such as interleukin 1β (IL-1β). Subsequently, HMGB1-DNA complex stimulated an ATG5-dependent cellular degradation process, autophagy, which was paralleled by a cessation of AIM2 inflammasome activation and IL-1β release. These HMGB1-DNA complex-induced inflammasome activation and autophagy were both dependent on the receptor for advanced glycation endproducts (RAGE) that recognizes a wide array of ligands (including HMGB1 and DNA). Thus, autophagy may function as a negative counter-regulatory mechanism for HMGB1-DNA complex-induced inflammasome activation, and provide a checkpoint to limit the development of inflammation.
inflammasome; autophagy; HMGB1; RAGE; AIM2; DNA
Kushen (Radix Sophorae Flavescentis) has a long history of use for the treatment of tumors, inflammation and other diseases in traditional Chinese medicine. Compound Kushen Injection (CKI) is a mixture of natural compounds extracted from Kushen and Baituling (Rhizoma Smilacis Glabrae). The main principles of CKI are matrine (MT) and oxymatrine (OMT) that exhibit a variety of pharmacological activities, including anti-inflammatory, anti-allergic, anti-viral, anti-fibrotic and cardiovascular protective effects. Recent evidence shows that these compounds also produce anti-cancer actions, such as inhibiting cancer cell proliferation, inducing cell cycle arrest, accelerating apoptosis, restraining angiogenesis, inducing cell differentiation, inhibiting cancer metastasis and invasion, reversing multidrug resistance, and preventing or reducing chemotherapy- and/or radiotherapy-induced toxicity when combined with chemotherapeutic drugs. In this review, we summarize recent progress in studying the anti-cancer activities of MT, OMT and CKI and their potential molecular targets, which provide clues and references for further study.
traditional Chinese medicine; Compound Kushen Injection; matrine; oxymatrine; anti-cancer drug
High mobility group box 1 (HMGB1) is a widely-expressed and highly-abundant protein that acts as an extracellular signal upon active secretion by immune cells or passive release by dead, dying, and injured cells. Both intracellular and extracellular HMGB1 play pivotal roles in regulation of the cellular response to stress. Targeting the translocation, release, and activity of HMGB1 can limit inflammation and reduce tissue damage during infection and sterile inflammation. Although the mechanisms contributing to HMGB1 biology are still under investigation, it appears that oxidative stress is a central regulator of HMGB1's translocation, release, and activity in inflammation and cell death (e.g., necrosis, apoptosis, autophagic cell death, pyroptosis, and NETosis). Thus, targeting HMGB1 with antioxidant compounds may be an attractive therapeutic strategy for inflammation-associated diseases such as sepsis, ischemia and reperfusion injury, arthritis, diabetes, and cancer.
HMGB1; ROS; inflammation; necrosis; apoptosis; autophagy; pyroptosis; NETosis
BACKGROUND & AIMS:
High mobility group box 1 (HMGB1) is an abundant protein that regulates chromosome architecture and also functions as a damage-associated molecular pattern molecule. Little is known about its intracellular roles in response to tissue injury or during subsequent local and systemic inflammatory responses. We investigated the function of Hmgb1 in mice following induction of acute pancreatitis.
We utilized a Cre/LoxP system to create mice with pancreas-specific disruption in Hmbg1 (Pdx1-Cre; HMGB1flox/flox mice). Acute pancreatitis was induced in these mice (HMGB1flox/flox mice served as controls) following injection of L-arginine or cerulein. Pancreatic tissues and acinar cells were collected and analyzed by histologic, immunoblot, and immunohistochemical analyses.
Following injection of L-arginine or cerulein, Pdx1-Cre; HMGB1flox/flox mice developed acute pancreatitis more rapidly than controls, with increased mortality. Pancreatic tissues of these mice also had higher levels of serum amylase, acinar cell death, leukocyte infiltration, and interstitial edema than controls. Pancreatic tissues and acinar cells collected from the Pdx1-Cre; HMGB1flox/flox mice following L-arginine- or cerulein injection demonstrated nuclear catastrophe with greater nucleosome release when compared with controls, along with increased phosphorylation/activation of RELA Nfκb, degradation of Iκb, and phosphorylation of Mapk. Inhibitors of reactive oxygen species (N-acetyl-L-cysteine) blocked L-arginine–induced DNA damage, necrosis, apoptosis, release of nucleosomes, and activation of Nfκb in pancreatic tissues and acinar cells from Pdx1-Cre; HMGB1flox/flox and control mice. Exogenous genomic DNA and recombinant histone H3 proteins significantly induced release of HMGB1 from mouse macrophages; administration of antibodies against H3 to mice reduced serum levels of HMGB1 and increased survival following L-arginine injection.
In 2 mouse models of acute pancreatitis, intracellular HMGB1 appeared to prevent nuclear catastrophe and release of inflammatory nucleosomes to block inflammation. These findings indicate a role for the innate immune response in tissue damage.
DNA damage; pancreatitis; oxidative stress; Nfκb
MIR34A (microRNA 34a) is a tumor suppressor gene, but how it regulates chemotherapy response and resistance is not completely understood. Here, we show that the microRNA MIR34A-dependent high mobility group box 1 (HMGB1) downregulation inhibits autophagy and enhances chemotherapy-induced apoptosis in the retinoblastoma cell. HMGB1 is a multifaceted protein with a key role in autophagy, a self-degradative, homeostatic process with a context-specific role in cancer. MIR34A inhibits HMGB1 expression through a direct MIR34A-binding site within the HMGB1 3′ untranslated region. MIR34A inhibition of HMGB1 leads to a decrease in autophagy under starvation conditions or chemotherapy treatment. Inhibition of autophagy promotes oxidative injury and DNA damage and increases subsequent CASP3 activity, CASP3 cleavage, and PARP1 [poly (ADP-ribose) polymerase 1] cleavage, which are important to the apoptotic process. Finally, upregulation of MIR34A, knockdown of HMGB1, or inhibition of autophagy (e.g., knockdown of ATG5 and BECN1) restores chemosensitivity and enhances tumor cell death in the retinoblastoma cell. These data provide new insights into the mechanisms governing the regulation of HMGB1 expression by microRNA and their possible contribution to autophagy and drug resistance.
microRNA; Hmbg1; autophagy; apoptosis; chemotherapy
Acute promyelocytic leukemia (APL) results from a blockade of granulocyte differentiation during the promyelocytic stage. As a fusion protein of promyelocytic leukemia (PML) and retinoic acid receptor-α (RARα), PML-RARα oncoprotein is degraded through the differentiation of all-trans retinoic acid (ATRA)-induced cells. Here reactive oxygen species (ROS) and high-mobility group box 1 (HMGB1) were proven essential for the differentiation of APL cells. A down-regulation of ROS by ROS quencher (NAC) blocked the differentiation of APL cell line NB4 while an over-expression of ROS by superoxide dismutase-1 (SOD1) RNA interference (RNAi) increased cell differentiation. HMGB1 was vital for the differentiation of ROS-mediated NB4 cells and its up-regulation promoted ATRA-induced autophagy and the degradation of PML-RARα. Furthermore, ATRA treatment elevated the levels of ROS, enhanced autophagic flux and thereby promoted cytosolic translocation of HMGB1. HMGB1 regulated the interactions between ubiquitin-binding adaptor protein p62/SQSTM and PML-RARα so as to affect the degradation of PML-RARα during ATRA-induced autophagy. Also a depletion of p62/SQSTM1 expression inhibited HMGB1-mediated PML-RARα degradation and cell differentiation. The overall results suggested that HMGB1 is an essential regulator of ROS-induced cell differentiation. And it may become a potential drug target for therapeutic intervention of APL.
HMGB1; ROS; cell differentiation; autophagy
Increasing evidence suggests the important role of metabolic reprogramming in the regulation of the innate inflammatory response, but the underlying mechanism remains unclear. Here, we provide evidence to support a novel role for the pyruvate kinase M2 (PKM2)-mediated Warburg effect, namely aerobic glycolysis, in the regulation of high mobility group box 1 (HMGB1) release. PKM2 interacts with hypoxia-inducible factor 1α (HIF1α) and activates the HIF-1α-dependent transcription of enzymes necessary for aerobic glycolysis in macrophages. Knockdown of PKM2, HIF1α, and glycolysis-related genes uniformly decreases lactate production and HMGB1 release. Similarly, a potential PKM2 inhibitor, shikonin, reduces serum lactate and HMGB1 levels and protects mice from lethal endotoxemia and sepsis. Collectively, these findings shed light on a novel mechanism for metabolic control of inflammation by regulating HMGB1 release and highlight the importance of targeting aerobic glycolysis in the treatment of sepsis and other inflammatory diseases.
System restoration from cascading failures is an integral part of the overall defense against catastrophic breakdown in networked critical infrastructures. From the outbreak of cascading failures to the system complete breakdown, actions can be taken to prevent failure propagation through the entire network. While most analysis efforts have been carried out before or after cascading failures, restoration during cascading failures has been rarely studied. In this paper, we present a modeling framework to investigate the effects of in-process restoration, which depends strongly on the timing and strength of the restoration actions. Furthermore, in the model we also consider additional disturbances to the system due to restoration actions themselves. We demonstrate that the effect of restoration is also influenced by the combination of system loading level and restoration disturbance. Our modeling framework will help to provide insights on practical restoration from cascading failures and guide improvements of reliability and resilience of actual network systems.
Cell death and inflammation are key pathologic responses of acute pancreatitis (AP), the leading cause of hospital admissions for gastrointestinal disorders. It is becoming increasingly clear that damage-associated molecular pattern molecules (DAMPs) play an important role in the pathogenesis of AP by linking local tissue damage to systemic inflammation syndrome. Endogenous DAMPs released from dead, dying or injured cells initiate and extend sterile inflammation via specific pattern recognition receptors. Inhibition of the release and activity of DAMPs (for example, high mobility group box 1, DNA, histones and adenosine triphosphate) provides significant protection against experimental AP. Moreover, increased serum levels of DAMPs in patients with AP correlate with disease severity. These findings provide novel insight into the mechanism, diagnosis and management of AP. DAMPs might be an attractive therapeutic target in AP.
High mobility group box 1 (HMGB1) is an evolutionarily ancient protein that is present in one form or another in all eukaryotes. It fundamentally resides in the nucleus but translocates to the cytosol with stress and is subsequently released into the extracellular space. HMGB1 global knockout mice exhibit lethal hypoglycemia, whereas tissues and cells from conditional knockout or knock-in mice are born alive without apparent significant functional deficit. An aberrant response to targeted stress in the liver, pancreas, heart or myeloid cells is consistent with a protective role for HMGB1 in sustaining nuclear homeostasis and enabling other stress responses, including autophagy. Under some conditions, HMGB1 is not required for liver and heart function. Many challenges remain with respect to understanding the multiple roles of HMGB1 in health and disease.
Sepsis is caused by an overwhelming immune response to bacterial infection. The discovery of high mobility group box 1 (HMGB1) as a late mediator of lethal sepsis has prompted investigation into the development of new therapeutics which specifically target this protein. Here, we show that chloroquine, an anti-malarial drug, prevents lethality in mice with established endotoxemia or sepsis. This effect is still observed even if administration of chloroquine is delayed. The protective effects of chloroquine were mediated through inhibition of HMGB1 release in macrophages, monocytes, and endothelial cells, thereby preventing its cytokine-like activities. As an inhibitor of autophagy, chloroquine specifically inhibited HMGB1-induced Iκ-B degradation and NF-κB activation. These findings define a novel mechanism for the anti-inflammatory effects of chloroquine and also suggest a new potential clinical use for this drug in the setting of sepsis.
HMGB1; chloroquine; sepsis; autophagy; NF-κB; Beclin 1
Forty years ago, high mobility group box 1 (HMGB1) was discovered in calf thymus and named according to its electrophoretic mobility in polyacrylamide gels. Now, we know that HMGB1 performs dual functions. Inside the cell, HMGB1 is a highly conserved chromosomal protein acting as a DNA chaperone. Outside of the cell, HMGB1 is a prototypical damage-associated molecular pattern, acting with cytokine, chemokine, and growth factor. During tumor development and in cancer therapy, HMGB1 has been reported to play paradoxical roles in promoting both cell survival and death by regulating multiple signaling pathways, including inflammation, immunity, genome stability, proliferation, metastasis, metabolism, apoptosis, and autophagy. Here, we review the current knowledge of both HMGB1’s oncogenic and tumor suppressive roles and the potential strategies that target HMGB1 for the prevention and treatment of cancer.
Pancreatic ductal adenocarcinoma (PDA) has an aggressive natural history and is resistant to therapy. The receptor for advanced glycation end-products (RAGE) is a pattern recognition receptor for many damage associated molecular pattern (DAMP) molecules. RAGE is overexpressed in both human and murine models of PDA as well as most advanced epithelial neoplasms. The immunosuppressive nature of the PDA micro-environment is facilitated, in part, by the accumulation of regulatory immune cell infiltrates such as myeloid-derived suppressor cells (MDSCs). To study the role of RAGE expression in the setting of mutant Ras-promoted pancreatic carcinogenesis (KC), a triple transgenic model of spontaneous murine PDA in a RAGE-null background (KCR) was generated. KCR mice had markedly delayed pancreatic carcinogenesis and a significant diminution of MDSCs compared to KC mice at comparable time points post weaning. While RAGE was not required for the development or suppressor activity of MDSCs, its absence was associated with temporally limited pancreatic neoplasia and altered phenotype and function of the myeloid cells. In lieu of MDSCs, KCR animals at comparable time points exhibited mature CD11b+Gr1−F4/80+ cells which were not immunosuppressive in vitro. KCR mice also maintained a significantly less suppressive milieu evidenced by marked decreases in CCL22 in relation to CXCL10 and diminished serum levels of IL-6.
Rodent; Monocytes/Macrophages; Inflammation; Tolerance/Suppression/Anergy; Tumor Immunity; Transgenic/Knockout Mice
Autophagy is a double-edged sword in tumorigenesis and plays an important role in the resistance of cancer cells to chemotherapy. S100A8 is a member of the S100 calcium-binding protein family and plays an important role in the drug resistance of leukemia cells, with the mechanisms largely unknown. Here we report that S100A8 contributes to drug resistance in leukemia by promoting autophagy. S100A8 level was elevated in drug resistance leukemia cell lines relative to the nondrug resistant cell lines. Adriamycin and vincristine increased S100A8 in human leukemia cells, accompanied with upregulation of autophagy. RNA interference-mediated knockdown of S100A8 restored the chemosensitivity of leukemia cells, while overexpression of S100A8 enhanced drug resistance and increased autophagy. S100A8 physically interacted with the autophagy regulator BECN1 and was required for the formation of the BECN1-PI3KC3 complex. In addition, interaction between S100A8 and BECN1 relied upon the autophagic complex ULK1-mAtg13. Furthermore, we discovered that exogenous S100A8 induced autophagy, and RAGE was involved in exogenous S100A8-regulated autophagy. Our data demonstrated that S100A8 is involved in the development of chemoresistance in leukemia cells by regulating autophagy, and suggest that S100A8 may be a novel target for improving leukemia therapy.
Autophagy is a lysosome-mediated catabolic process involving the degradation of intracellular contents (e.g., proteins and organelles) as well as invading microbes (e.g., parasites, bacteria and viruses). Multiple forms of cellular stress can stimulate this pathway, including nutritional imbalances, oxygen deprivation, immunological response, genetic defects, chromosomal anomalies and cytotoxic stress. Damage-associated molecular pattern molecules (DAMPs) are released by stressed cells undergoing autophagy or injury, and act as endogenous danger signals to regulate the subsequent inflammatory and immune response. A complex relationship exists between DAMPs and autophagy in cellular adaption to injury and unscheduled cell death. Since both autophagy and DAMPs are important for pathogenesis of human disease, it is crucial to understand how they interplay to sustain homeostasis in stressful or dangerous environments.
autophagy; DAMP; stress; HMGB1; ATP; IL1B; injury
Colorectal cancer (CRC) remains a major worldwide cause of cancer-related morbidity and mortality largely due to the insidious onset of the disease. The current clinical procedures utilized for disease diagnosis are invasive, unpleasant, and inconvenient. Hence, the need for simple blood tests that could be used for the early detection is crucial for its ultimate control and prevention.
The present work is a case–control study focused on proteomic analysis of serum of healthy volunteers and CRC patients by the ClinProt profiling technology based on mass spectrometry. This approach allowed to identifying a pattern of proteins/peptides able to differentiate the studied populations. Moreover, some of peptides differentially expressed in the serum of patients as compared to healthy volunteers were identified by LTQ Orbitrap XL.
A Quick Classifier Algorithm was used to construct the peptidome patterns (m/z 1208, 1467, 1505, 1618, 1656 and 4215) for the identification of CRC from healthy volunteers with accuracy close to 100% (>CEA, P < 0.05). Peaks at m/z 1505 and 1618 were identified as alpha-2-HS-glycoprotein precursor and tubulin beta chain, respectively.
Alpha-2-HS-glycoprotein precursor and tubulin beta chain could be involved in the pathogenesis of CRC and perform as potential serology diagnosis biomarker.
The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/4796578761089186.
Colorectal neoplasms; Diagnosis; Biological markers; Proteomics; Alpha-2-HS-glycoprotein; Tubulin beta chain
Autophagy is an evolutionarily conserved pathway responsible for delivery of cytoplasmic material into the lysosomal degradation pathway to enable vesicular exocytosis. Interleukin (IL)-2 is produced by T-cells and its activity is important for immunoregulation. Fibroblasts are an immune competent cell type, playing a critical role in wound healing, chronic inflammation, and tumor development. Although autophagy plays an important role in each of these processes, whether it regulates IL-2 activity in fibroblasts is unknown. Here, we show that autophagy is required for IL-2-induced cell growth in fibroblasts. IL-2 significantly induced autophagy in mouse embryonic fibroblasts (MEFs) and primary lung fibroblasts. Autophagy inhibitors (e.g., 3-methylamphetamine and bafilomycin A1) or knockdown of ATG5 and beclin 1 blocked clinical grade IL-2-induced autophagy. Moreover, IL-2 induced HMGB1 cytoplasmic translocation in MEFs and promoted interaction between HMGB1 and beclin1, which is required for autophagy induction. Pharmacological and genetic inhibition of autophagy inhibited IL-2-induced cell proliferation and enhanced IL-2-induced apoptosis. These findings suggest that autophagy is an important pro-survival regulator for IL-2-induced cell growth in fibroblasts.
IL-2; Autophagy; Apoptosis; Immunotherapy; HMGB1
Damage-associated molecular pattern (DAMP) molecules are essential for the initiation of innate inflammatory responses to infection and injury. The prototypic DAMP molecule, high-mobility group box 1 (HMGB1), is an abundant architectural chromosomal protein that has location-specific biological functions: within the nucleus as a DNA chaperone, within the cytosol to sustain autophagy and outside the cell as a DAMP molecule. Recent research indicates that aberrant activation of HMGB1 signaling can promote the onset of inflammatory and autoimmune diseases, raising interest in the development of therapeutic strategies to control their function. The importance of HMGB1 activation in various forms of liver disease in relation to liver damage, steatosis, inflammation, fibrosis, tumorigenesis and regeneration is discussed in this review.
Pathogen-associated molecular pattern molecules (PAMPs) are derived from microorganisms and recognized by pattern recognition receptor (PRR)-bearing cells of the innate immune system as well as many epithelial cells. In contrast, damage-associated molecular pattern molecules (DAMPs) are cell-derived and initiate and perpetuate immunity in response to trauma, ischemia, and tissue damage, either in the absence or presence of pathogenic infection. Most PAMPs and DAMPs serve as so-called ‘Signal 0s’ that bind specific receptors [Toll-like receptors, NOD-like receptors, RIG-I-like receptors, AIM2-like receptors, and the receptor for advanced glycation end products (RAGE)] to promote autophagy. Autophagy, a conserved lysosomal degradation pathway, is a cell survival mechanism invoked in response to environmental and cellular stress. Autophagy is inferred to have been present in the last common eukaryotic ancestor and only to have been lost by some obligatory intracellular parasites. As such, autophagy represents a unifying biology, subserving survival and the earliest host defense strategies, predating apoptosis, within eukaryotes. Here, we review recent advances in our understanding of autophagic molecular mechanisms and functions in emergent immunity.
PAMPs; DAMPs; autophagy; apoptosis; danger signals; inflammation; programmed cell death
Pancreatic ductal adenocarcinoma (PDA), the fourth leading cause of cancer death in the United States, is a complex disease that arises in the setting of genetic alterations (KRAS, BRCA1, SMAD4, CDKN2A/p16INK4a and TP53), epigenetic perturbations (MIR155, acetylation and methylation) and epicellular events (diabetes and inflammation). We have demonstrated that the advanced glycation end product-specific receptor (AGER, also called RAGE) contributes to pancreatic tumorigenesis. Targeted ablation of AGER diminishes the amount of autophagic flux and attenuates the development of early pancreatic intraepithelial neoplasia (PanIN) lesions in a murine model of KRAS-drivien carcinogenesis. Autophagy (programmed cell survival), a metabolic process of lysosome-mediated self-digestion, promotes pancreatic cancer growth. In pancreatic tumor cell lines, AGER-mediated autophagy promotes interleukin-6 (IL6)-induced phosphorylation of signal transducer and activator of transcription 3 (pSTAT3) and mitochondrial localization of pSTAT3. Enhanced mitochondrial pSTAT3 increases the pool of available ATP and increases cellular proliferation. Moreover, we observed a positive feedback loop between activation of autophagy and the IL6-pSTAT3 pathway, perhaps different from the role of cytosolic nonphosphorylated STAT3, which has been reported to inhibit autophagy. These AGER-dependent changes were found during the earliest stages of pancreatic cancer development. These observations of inflammation and altered metabolism in PDA provide a pathological link to early precursor lesion development. Thus, AGER is an important inflammatory mediator that modulates crosstalk between prosurvival pathways, IL6-pSTAT3 and autophagy, in PDA tumor cells, and contributes to early PanIN formation.
RAGE; autophagy; oncogene; KRAS; IL6; STAT3
Double-stranded RNA–dependent protein kinase (PKR) is implicated in inflammation and immune dysfunction through its regulation of mitogen-activated protein kinases, interferon regulatory factor 3, nuclear factorκB, apoptosis, and autophagy pathways. A study shows that PKR is also required for the activation of inflammasomes and the subsequent release of high-mobility group box 1 (HMGB1) protein, a proinflammatory cytokine. Thus, the cell stress kinase PKR has multifaceted roles in the regulation of inflammatory immune responses, and PKR and HMGB1 are attractive targets for inflammasome-associated diseases.
Tumorigenesis and the efficacy of cancer therapeutics are both defined by the balance between autophagy and apoptosis. High-mobility group box 1 (HMGB1) is a DNA chaperone and extracellular damage-associated molecular pattern molecule (DAMP) with pro-autophagic activity. TP53/p53 plays a transcription-dependent and -independent role in the regulation of apoptosis, autophagy, metabolism, cell cycle progression, and many other processes. Both HMGB1 and TP53 are tightly linked with the development of cancer, associated with many of the hallmarks defining the altered biology of cancer. We have demonstrated that TP53-HMGB1 complexes regulate the balance between apoptosis and autophagy through regulation of the cytosolic localization of the reciprocal binding partner, whereby increased cytosolic HMGB1 enhances autophagy and increased cytosolic TP53 enhances apoptosis in colon cancer cells. We found that HMGB1-mediated autophagy promotes cell survival in TP53-dependent processes, and that TP53 inhibits autophagy through negative regulation of HMGB1-BECN1 complexes. Nuclear localization of TP53 and HMGB1 in tumors from patients with colon adenocarcinoma had a positive trend with survival time from diagnosis. Thus, HMGB1 and TP53 are critical in the crossregulation of apoptosis and autophagy and central to colon cancer biology.
Apoptosis; autophagy; colorectal cancer; HMGB1; TP53