Inhibiting autophagy potentiates the anticancer activity of IFN1@/IFNα in chronic myeloid leukemia cells.

IFN1@ (interferon, type 1, cluster, also called IFNα) has been extensively studied as a treatment for patients with chronic myeloid leukemia (CML). The mechanism of anticancer activity of IFN1@ is complex and not well understood. Here, we demonstrate that autophagy, a mechanism of cellular homeostasis for the removal of dysfunctional organelles and proteins, regulates IFN1@-mediated cell death. IFN1@ activated the cellular autophagic machinery in immortalized or primary CML cells. Activation of JAK1-STAT1 and RELA signaling were required for IFN1@-induced expression of BECN1, a key regulator of autophagy. Moreover, pharmacological and genetic inhibition of autophagy enhanced IFN1@-induced apoptosis by activation of the CASP8-BID pathway. Taken together, these findings provide evidence for an important mechanism that links autophagy to immunotherapy in leukemia.

Direct molecular interactions between HMGB1 and TP53 in colorectal cancer.

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 cross-regulation of apoptosis and autophagy and central to colon cancer biology.

The expression of the receptor for advanced glycation endproducts (RAGE) is permissive for early pancreatic neoplasia.

Pancreatic cancer is an almost uniformly lethal disease, characterized by late diagnosis, early metastasis, resistance to chemotherapy, and early mutation of the Kras oncogene. Here we show that the receptor for advanced glycation endproducts (RAGE) is required for the activation of interleukin 6 (IL-6)-mediated mitochondrial signal transducers and activators of transcription 3 (STAT3) signaling in pancreatic carcinogenesis. RAGE expression correlates with elevated levels of autophagy in pancreatic cancer in vivo and in vitro, and this heightened state of autophagy is required for IL-6-induced STAT3 activation. To further explore the intersection of RAGE, autophagy, and pancreatic carcinogenesis, we created a transgenic murine model, backcrossing RAGE-null mice to a spontaneous mouse model of pancreatic cancer, Pdx1-Cre:Kras(G12D/+) (KC). Targeted ablation of Rage in KC mice delayed neoplasia development, decreased levels of autophagy, and inhibited mitochondrial STAT3 activity and subsequent ATP production. Our results suggest a critical role for RAGE expression in the earliest stages of pancreatic carcinogenesis, potentially acting as the "autophagic switch," regulating mitochondrial STAT3 signaling.

HMGB1 is a therapeutic target for leukemia.

High mobility group box 1 (HMGB1) is a nuclear DNA-binding protein, which functions as Damage Associated Molecular Pattern molecule (DAMP) when released from cells under conditions of stress, such as injury and infection. Recent studies indicate that HMGB1 plays an important role in leukemia pathogenesis and chemotherapy resistance. Serum HMGB1 is increased in childhood acute lymphocytic leukemia as compared to healthy control and complete remission groups. Moreover, HMGB1 is a negative regulator of apoptosis in leukemia cells through regulation of Bcl-2 expression and caspase-3 activity. As a positive regulator of autophagy, intracellular HMGB1 interacts with Beclin 1 in leukemia cells leading to autophagosome formation. Additionally, exogenous HMGB1 directly induces autophagy and cell survival in leukemia cells. Experimental strategies that selectively target HMGB1 effectively reverse and prevent chemotherapy resistance in leukemia cells, suggesting that HMGB1 is a novel therapeutic target in leukemia.

p53/HMGB1 complexes regulate autophagy and apoptosis.

The balance between apoptosis ("programmed cell death") and autophagy ("programmed cell survival") is important in tumor development and response to therapy. Here, we show that high mobility group box 1 (HMGB1) and p53 form a complex that regulates the balance between tumor cell death and survival. We show that knockout of p53 in HCT116 cells increases expression of cytosolic HMGB1 and induces autophagy. Conversely, knockout of HMGB1 in mouse embryonic fibroblasts increases p53 cytosolic localization and decreases autophagy. p53 is thus a negative regulator of the HMGB1/Beclin 1 complex, and HMGB1 promotes autophagy in the setting of diminished p53. HMGB1-mediated autophagy promotes tumor cell survival in the setting of p53-dependent processes. The HMGB1/p53 complex affects the cytoplasmic localization of the reciprocal binding partner, thereby regulating subsequent levels of autophagy and apoptosis. These insights provide a novel link between HMGB1 and p53 in the cross-regulation of apoptosis and autophagy in the setting of cell stress, providing insights into their reciprocal roles in carcinogenesis.

High-mobility group box 1 is essential for mitochondrial quality control.

Mitochondria are organelles centrally important for bioenergetics as well as regulation of apoptotic death in eukaryotic cells. High-mobility group box 1 (HMGB1), an evolutionarily conserved chromatin-associated protein which maintains nuclear homeostasis, is also a critical regulator of mitochondrial function and morphology. We show that heat shock protein beta-1 (HSPB1 or HSP27) is the downstream mediator of this effect. Disruption of the HSPB1 gene in embryonic fibroblasts with wild-type HMGB1 recapitulates the mitochondrial fragmentation, deficits in mitochondrial respiration, and adenosine triphosphate (ATP) synthesis observed with targeted deletion of HMGB1. Forced expression of HSPB1 reverses this phenotype in HMGB1 knockout cells. Mitochondrial effects mediated by HMGB1 regulation of HSPB1 expression serve as a defense against mitochondrial abnormality, enabling clearance and autophagy in the setting of cellular stress. Our findings reveal an essential role for HMGB1 in autophagic surveillance with important effects on mitochondrial quality control.

Metabolic regulation by HMGB1-mediated autophagy and mitophagy.

Autophagy is a dynamic process for degradation of cytosolic components such as dysfunctional organelles and proteins and a means for generating metabolic substrates during periods of starvation. Mitochondrial autophagy ("mitophagy") is a selective form of autophagy, which is important in maintaining mitochondrial homeostasis. High mobility group box 1 (HMGB1) plays important intranuclear, cytosolic and extracellular roles in the regulation of autophagy. Cytoplasmic HMGB1 is a novel Beclin 1-binding protein active in autophagy. Extracellular HMGB1 induces autophagy, and this role is dependent on its redox state and receptor (Receptor for Advanced Glycation End products, RAGE) expression. Nuclear HMGB1 modulates the expression of heat shock protein ß-1 (HSPB1/HSP27). As a cytoskeleton regulator, HSPB1 is critical for dynamic intracellular trafficking during autophagy and mitophagy. Loss of either HMGB1 or HSPB1 results in a phenotypically similar deficiency in mitophagy typified by mitochondrial fragmentation with decreased aerobic respiration and adenosine triphosphate (ATP) production. These findings reveal a novel pathway coupling autophagy and cellular energy metabolism.

A critical role for UVRAG in apoptosis.

Autophagy and apoptosis are tightly regulated biological processes that are crucial for cell growth, development and tissue homeostasis. UVRAG (UV radiation resistance-associated gene), a mammalian homolog of yeast Vps38, activates the Beclin 1/PtdIns3KC3 (class III phosphatidylinositol-3-kinase) complex, which promotes autophagosome formation. Moreover, UVRAG promotes autophagosome maturation by recruiting class C Vps complexes (HOPS complexes) and Rab7 of the late endosome. We found that UVRAG has anti-apoptotic activity during tumor therapy through interactions with Bax. UVRAG inhibits Bax translocation from the cytosol to mitochondria during chemotherapy- or UV irradiation-induced apoptosis of human tumor cells. Moreover, deletion of the UVRAG C2 domain abolishes Bax binding and anti-apoptotic activity. These results suggest that, in addition to its previously recognized pro-autophagy activity in response to starvation, UVRAG has cytoprotective functions in the cytosol that control the localization of Bax in tumor cells exposed to apoptotic stimuli.

UV irradiation resistance-associated gene suppresses apoptosis by interfering with BAX activation.

Ultraviolet irradiation resistance-associated gene (UVRAG) is a well-known regulator of autophagy by promoting autophagosome formation and maturation. However, little is known about the non-autophagic functions of UVRAG. Here, we present evidence that UVRAG functions as an unusual BCL2-associated X protein (Bax) suppressor to regulate apoptosis. Chemotherapy and radiation induces UVRAG expression and subsequently upregulates autophagy and apoptosis in tumour cells. Depletion of UVRAG expression by RNA interference renders tumour cells more sensitive to chemotherapy- and radiation-induced apoptosis in vitro and in vivo. Moreover, UVRAG interacts with Bax, which inhibits apoptotic stimuli-induced mitochondrial translocation of Bax, reduction of mitochondrial membrane potential, cytochrome c release and activation of caspase-9 and -3. Our findings show that UVRAG has an essential role in the intrinsic mitochondrial pathway of apoptosis by regulating the localization of Bax. This pathway represents a target for clinical intervention against tumours.

HMGB1 as an autophagy sensor in oxidative stress.

High mobility group box 1 (HMGB1) is a DNA-binding nuclear protein, actively released following cytokine stimulation as well as passively during cell injury and death. Autophagy is a tightly regulated cellular stress pathway involving the lysosomal degradation of cytoplasmic organelles or proteins. Organisms respond to oxidative injury by orchestrating stress responses such as autophagy to prevent further damage. Recently, we reported that HMGB1 is an autophagy sensor in the presence of oxidative stress. Hydrogen peroxide (H 2O 2) and loss of superoxide dismutase 1 (SOD1)-mediated oxidative stress promotes cytosolic HMGB1 expression and extracellular release. Inhibition of HMGB1 release or loss of HMGB1 decreases the number of autolysosomes and autophagic flux in human and mouse cell lines under conditions of oxidative stress. These findings provide insight into how HMGB1, a damage associated molecular pattern (DAMP), triggers autophagy as defense mechanism under conditions of cellular stress.

High mobility group box 1 (HMGB1) activates an autophagic response to oxidative stress.

AIMS: Autophagy, the process by which cells break down spent biochemical and damaged components, plays an important role in cell survival following stress. High mobility group box 1 (HMGB1) regulates autophagy in response to oxidative stress. RESULTS: Exogenous hydrogen peroxide (H(2)O(2)) treatment or knockdown of the major superoxide scavenger enzyme, superoxide dismutase 1 (SOD1), by small interfering RNA (siRNA) increases autophagy in mouse and human cell lines. Addition of either SOD1 siRNA or H(2)O(2) promotes cytosolic HMGB1 expression and extracellular release. Importantly, inhibition of HMGB1 release or loss of HMGB1 decreases the number of autophagolysosomes and autophagic flux under oxidative stress in vivo and in vitro. INNOVATION: HMGB1 release may be a common mediator of response to oxidative stress. CONCLUSION: HMGB1 is important for oxidative stress-mediated autophagy and serves as a new target for the treatment of stress-associated disorders.

DAMP-mediated autophagy contributes to drug resistance.

Damage-associated molecular pattern molecules (DAMPs) are cellularly derived molecules that can initiate and perpetuate immune responses following trauma, ischemia and other types of tissue damage in the absence of pathogenic infection. High mobility group box 1 (HMGB1) is a prototypical DAMP and is associated with the hallmarks of cancer. Recently we found that HMGB1 release after chemotherapy treatment is a critical regulator of autophagy and a potential drug target for therapeutic interventions in leukemia. Overexpression of HMGB1 by gene transfection rendered leukemia cells resistant to cell death; whereas depletion or inhibition of HMGB1 and autophagy by RNA interference or pharmacological inhibitors increased the sensitivity of leukemia cells to chemotherapeutic drugs. HMGB1 release sustains autophagy as assessed by microtubule-associated protein 1 light chain 3 (LC3) lipidation, redistribution of LC3 into cytoplasmic puncta, degradation of p62 and accumulation of autophagosomes and autolysosomes. Moreover, these data suggest a role for HMGB1 in the regulation of autophagy through the PI3KC3-MEKERK: pathway, supporting the notion that HMGB1-induced autophagy promotes tumor resistance to chemotherapy.

Autophagy regulates myeloid cell differentiation by p62/SQSTM1-mediated degradation of PML-RARα oncoprotein.

PML-RARα oncoprotein is a fusion protein of promyelocytic leukemia (PML) and the retinoic acid receptor-α (RARα) and causes acute promyelocytic leukemias (APL). A hallmark of all-trans retinoic acid (ATRA) responses in APL is PML-RARα degradation which promotes cell differentiation. Here, we demonstrated that autophagy is a crucial regulator of PML-RARα degradation. Inhibition of autophagy by short hairpin (sh) RNA that target essential autophagy genes such as Atg1, Atg5 and PI3KC3 and by autophagy inhibitors (e.g. 3-methyladenine), blocked PML-RARα degradation and subsequently granulocytic differentiation of human myeloid leukemic cells. In contrast, rapamycin, the mTOR kinase inhibitor, enhanced autophagy and promoted ATRA-induced PML-RARα degradation and myeloid cell differentiation. Moreover, PML-RARα co-immunoprecipitated with ubiquitin-binding adaptor protein p62/SQSTM1, which is degraded through autophagy. Furthermore, knockdown of p62/SQSTM1 inhibited ATRA-induced PML-RARα degradation and myeloid cell differentiation. The identification of PML-RARα as a target of autophagy provides new insight into the mechanism of action of ATRA and its specificity for APL.

The Receptor for Advanced Glycation End-products (RAGE) protects pancreatic tumor cells against oxidative injury.

Reactive oxygen species, including hydrogen peroxide (H(2)O(2)), can cause toxicity and act as signaling molecules in various pathways regulating both cell survival and cell death. However, the sequence of events between the oxidative insult and cell damage remains unclear. In the current study, we investigated the effect of oxidative stress on activation of the Receptor for Advanced Glycation End-products (RAGE) and subsequent protection against H(2)O(2)-induced pancreatic tumor cell damage. We found that exposure of pancreatic tumor cells to H(2)O(2) provoked a nuclear factor kappa B (NF-κB)-dependent increase in RAGE expression. Further, suppression of RAGE expression by RNA interference increased the sensitivity of pancreatic tumor cells to oxidative injury. Furthermore, targeted knockdown of RAGE led to increased cell death by apoptosis and diminished cell survival by autophagy during H(2)O(2)-induced oxidative injury. Moreover, we demonstrate that RAGE is a positive feedback regulator for NF-κB as knockdown of RAGE decreased H(2)O(2)-induced activity of NF-κB. Taken together, these results suggest that RAGE is an important regulator of oxidative injury.

HMGB1: a novel Beclin 1-binding protein active in autophagy.

The autophagosome delivers damaged cytoplasmic constituents and proteins to the lysosome or to the extracellular space. Beclin 1, an essential: autophagic protein, is a BH3-only protein that binds Bcl-2 anti-apoptotic family members and has a critical role in the initiation of autophagy. How the Beclin 1 complex specifically promotes autophagy remains largely unknown. We have found that high mobility group box 1 (HMGB1), a chromatin-associated nuclear protein and extracellular damage associated molecular pattern molecule (DAMP), is a novel Beclin 1-binding protein important in sustaining autophagy. HMGB1 shares considerable sequence homology with Beclin 1 in yeast, mice and human, representing an evolutionarily conserved regulatory step in early autophagosome formation. Endogenous HMGB1 competes with Bcl-2 for interaction with Beclin 1, and orients Beclin 1 to autophagosomes. Moreover, the intramolecular disulfide bridge (C23/45) of HMGB1 is required for binding to Beclin 1 and sustaining autophagy. Taken together, these findings indicate that endogenous HMGB1 functions as an autophagy effector by regulation of autophagosome formation.

Endogenous HMGB1 regulates autophagy.

Autophagy clears long-lived proteins and dysfunctional organelles and generates substrates for adenosine triphosphate production during periods of starvation and other types of cellular stress. Here we show that high mobility group box 1 (HMGB1), a chromatin-associated nuclear protein and extracellular damage-associated molecular pattern molecule, is a critical regulator of autophagy. Stimuli that enhance reactive oxygen species promote cytosolic translocation of HMGB1 and thereby enhance autophagic flux. HMGB1 directly interacts with the autophagy protein Beclin1 displacing Bcl-2. Mutation of cysteine 106 (C106), but not the vicinal C23 and C45, of HMGB1 promotes cytosolic localization and sustained autophagy. Pharmacological inhibition of HMGB1 cytoplasmic translocation by agents such as ethyl pyruvate limits starvation-induced autophagy. Moreover, the intramolecular disulfide bridge (C23/45) of HMGB1 is required for binding to Beclin1 and sustaining autophagy. Thus, endogenous HMGB1 is a critical pro-autophagic protein that enhances cell survival and limits programmed apoptotic cell death.

Autophagy inhibition in combination cancer treatment.

The effective elimination of cancer cells is compromised by mechanisms of resistance. Such mechanisms have been variably ascribed to drug export transporters, more effective DNA repair mechanisms compared with healthy cells, singularly resistant stem cells, resistance to apoptosis, self-sufficiency for growth factor signaling and an angiogenic switch, as well as immunological pathways associated with T-regulatory cells, myeloid-derived suppressor cells or plasmacytoid dendritic cells. In this review, the critically important process of autophagy, which is a mechanism of cell survival in the presence of genomic injury, endoplasmic reticulum stress, oxidant stress, nutrient insufficiency and viral/bacterial infection, is explored in the setting of cancer treatment. Autophagy has recently been demonstrated as important for conferring resistance to chemotherapy, radiation therapy and immunotherapy. Compounds are now available that can reverse autophagy, including the antimalarial compounds chloroquine and hydroxychloroquine, as well as the antidepressant agent clomipramine. Other strategies for the reversal of autophagy are based on the recent observation that the cytosolic location of the chromatin-binding protein HMGB1 (high-mobility group box-1) is associated with sustained autophagy. Targeting HMGB1 using platinum-containing compounds, ethyl pyruvate or glycyrrhizin has also been used to limit autophagy. Screening for new agents is ongoing, which, coupled with conventional chemotherapeutic compounds, may usher in a new generation of autophagy-inhibiting agents.

The spectrum of Trp- mutants isolated as 5-fluoroanthranilate-resistant clones in Saccharomyces bayanus, S. mikatae and S. paradoxus.

5-Fluoroanthranilic acid (FAA)-resistant mutants were selected in homothallic diploids of three Saccharomyces species, taking care to isolate mutants of independent origin. Mutations were assigned to complementation groups by interspecific complementation with S. cerevisiae tester strains. In all three species, trp3, trp4 and trp5 mutants were recovered. trp1 mutants were also recovered if the selection was imposed on a haploid strain. Thus, FAA selection may be more generally applicable than was previously described.