Autophagy is essential to suppress cell stress and to allow BCR-Abl-mediated leukemogenesis

Hydroquinone-selected chronic myelogenous leukemia cells are sensitive to chloroquine-induced cytotoxicity via MCL1 suppression and glycolysis inhibition

Previous studies have provided evidence that repeated exposure to the benzene metabolite hydroquinone (HQ) induces malignant transformation and increases basal autophagy in the chronic myeloid leukemia (CML) cell line K562. This study explored the cytotoxicity of the autophagy inhibitor chloroquine (CQ) on parental and HQ-selected K562 (K562/HQ) cells. CQ triggered apoptosis in these cells independently of inhibiting autophagic flux; however, in K562/HQ cells, CQ-induced cytotoxicity was higher than in K562 cells. Mechanistically, CQ-induced NOXA upregulation led to MCL1 downregulation and mitochondrial depolarization in K562/HQ cells. MCL1 overexpression or NOXA silencing attenuated CQ-mediated cytotoxicity in K562/HQ cells. CQ triggered ERK inactivation to increase Sp1, NFκB, and p300 expression, and co-assembly of Sp1, NFκB, and p300 in the miR-29a promoter region coordinately upregulated miR-29a transcription. CQ-induced miR-29a expression destabilized tristetraprolin (TTP) mRNA, which in turn reduced TTP-mediated NOXA mRNA decay, thereby increasing NOXA protein expression. A similar mechanism explained the CQ-induced downregulation of MCL1 in K562 cells. K562/HQ cells relied more on glycolysis for ATP production than K562 cells, whereas inhibition of glycolysis by CQ was greater in K562/HQ cells than in K562 cells. Likewise, CQ-induced MCL1 suppression and glycolysis inhibition resulted in higher cytotoxicity in CML KU812/HQ cells than in KU812 cells. Taken together, our data confirm that CQ inhibits MCL1 expression through the ERK/miR-29a/TTP/NOXA pathway, and that inhibition of glycolysis is positively correlated to higher cytotoxicity of CQ on HQ-selected CML cells.

Targeting PP2A-dependent autophagy enhances sensitivity to ruxolitinib in JAK2V617F myeloproliferative neoplasms

The Janus kinase 2 (JAK2)-driven myeloproliferative neoplasms (MPNs) are chronic malignancies associated with high-risk complications and suboptimal responses to JAK inhibitors such as ruxolitinib. A better understanding of cellular changes induced by ruxolitinib is required to develop new combinatory therapies to improve treatment efficacy. Here, we demonstrate that ruxolitinib induced autophagy in JAK2^V617F cell lines and primary MPN patient cells through the activation of protein phosphatase 2A (PP2A). Inhibition of autophagy or PP2A activity along with ruxolitinib treatment reduced proliferation and increased the death of JAK2^V617F cells. Accordingly, proliferation and clonogenic potential of JAK2^V617F-driven primary MPN patient cells, but not of normal hematopoietic cells, were markedly impaired by ruxolitinib treatment with autophagy or PP2A inhibitor. Finally, preventing ruxolitinib-induced autophagy with a novel potent autophagy inhibitor Lys05 improved leukemia burden reduction and significantly prolonged the mice's overall survival compared with ruxolitinib alone. This study demonstrates that PP2A-dependent autophagy mediated by JAK2 activity inhibition contributes to resistance to ruxolitinib. Altogether, our data support that targeting autophagy or its identified regulator PP2A could enhance sensitivity to ruxolitinib of JAK2^V617F MPN cells and improve MPN patient care.

Japanese Flounder pol-miR-155 Is Involved in Edwardsiella tarda Infection via ATG3

MicroRNAs (miRNAs) are small RNA molecules that function in the post-transcriptionally regulation of the expression of diverse genes, including those involved in immune defense. Edwardsiella tarda can infect a broad range of hosts and cause severe disease in aquatic species, including Japanese flounder (Paralichthys olivaceus). In this study, we examined the regulation mechanism of a flounder miRNA, pol-miR-155, during the infection of E. tarda. Pol-miR-155 was identified to target flounder ATG3. Overexpression of pol-miR-155 or knockdown of ATG3 expression suppressed autophagy and promoted the intracellular replication of E. tarda in flounder cells. Overexpression of pol-miR-155 activated the NF-κB signaling pathway and further promoted the expression of downstream immune related genes of interleukin (IL)-6 and IL-8. These results unraveled the regulatory effect of pol-miR-155 in autophagy and in E. tarda infection.

Identification and validation of a novel CD8+ T cell-associated prognostic model based on ferroptosis in acute myeloid leukemia

Acute myeloid leukemia (AML) is a highly aggressive cancer with great heterogeneity and variability in prognosis. Though European Leukemia Net (ELN) 2017 risk classification has been widely used, nearly half of patients were stratified to "intermediate" risk and requires more accurate classification via excavating biological features. As new evidence showed that CD8+ T cell can kill cancer cells through ferroptosis pathway. We firstly use CIBERSORT algorithm to divide AMLs into CD8+ ^high and CD8+ ^low T cell groups, then 2789 differentially expressed genes (DEGs) between groups were identified, of which 46 ferroptosis-related genes associated with CD8+ T cell were sorted out. GO, KEGG analysis and PPI network were conducted based on these 46 DEGs. By jointly using LASSO algorithm and Cox univariate regression, we generated a 6-gene prognostic signature comprising VEGFA, KLHL24, ATG3, EIF2AK4, IDH1 and HSPB1. Low-risk group shows a longer overall survival. We then validated the prognostic value of this 6-gene signature using two independent external datasets and patient sample collection dataset. We also proved that incorporation of the 6-gene signature obviously enhanced the accuracy of ELN risk classification. Finally, gene mutation analysis, drug sensitive prediction, GSEA and GSVA analysis were conducted between high-risk and low-risk AML patients. Collectively, our findings suggested that the prognostic signature based on CD8+ T cell-related ferroptosis genes can optimize the risk stratification and prognostic prediction of AML patients.

Role of autophagy in aging: The good, the bad, and the ugly

Autophagy (self-eating) is a conserved catabolic homeostatic process required for cellular metabolic demands by removal of the damaged molecules and organelles and for alleviation of stress initiated by pathology and infection. By such actions, autophagy is essential for the prevention of aging, disease, and cancer. Genetic defects of autophagy genes lead to a host of developmental, metabolic, and pathological aberrations. Similarly, the age-induced decline in autophagy leads to the loss of cellular homeostatic control. Paradoxically, such a valuable mechanism is hijacked by diseases, during tumor progression and by senescence, presumably due to high levels of metabolic demand. Here, we review both the role of autophagy in preventing cellular decline in aging by fulfillment of cellular bioenergetic demands and its contribution to the maintenance of the senescent state and SASP by acting on energy and nutritional sensors and diverse signaling pathways.

Autophagy in Hematological Malignancies

Simple Summary

Autophagy is a dynamic and tightly regulated process that seems to have dual effects in cancer. In some contexts, it can induce carcinogenesis and promote cancer cell survival, whereas in others, it acts preventing tumor cell growth and tumor progression. Thus, autophagy functions seem to strictly depend on cancer ontogenesis, progression, and type. Here, we will dive into the current knowledge of autophagy in hematological malignancies and will highlight the main genetic components involved in each cancer type.

Abstract

Autophagy is a highly conserved metabolic pathway via which unwanted intracellular materials, such as unfolded proteins or damaged organelles, are digested. It is activated in response to conditions of oxidative stress or starvation, and is essential for the maintenance of cellular homeostasis and other vital functions, such as differentiation, cell death, and the cell cycle. Therefore, autophagy plays an important role in the initiation and progression of tumors, including hematological malignancies, where damaged autophagy during hematopoiesis can cause malignant transformation and increase cell proliferation. Over the last decade, the importance of autophagy in response to standard pharmacological treatment of hematological tumors has been observed, revealing completely opposite roles depending on the tumor type and stage. Thus, autophagy can promote tumor survival by attenuating the cellular damage caused by drugs and/or stabilizing oncogenic proteins, but can also have an antitumoral effect due to autophagic cell death. Therefore, autophagy-based strategies must depend on the context to create specific and safe combination therapies that could contribute to improved clinical outcomes. In this review, we describe the process of autophagy and its role on hematopoiesis, and we highlight recent research investigating its role as a potential therapeutic target in hematological malignancies. The findings suggest that genetic variants within autophagy-related genes modulate the risk of developing hemopathies, as well as patient survival.

Chemotherapy Resistance: Role of Mitochondrial and Autophagic Components

Simple Summary

Chemotherapy resistance is a common occurrence during cancer treatment that cancer researchers are attempting to understand and overcome. Mitochondria are a crucial intracellular signaling core that are becoming important determinants of numerous aspects of cancer genesis and progression, such as metabolic reprogramming, metastatic capability, and chemotherapeutic resistance. Mitophagy, or selective autophagy of mitochondria, can influence both the efficacy of tumor chemotherapy and the degree of drug resistance. Regardless of the fact that mitochondria are well-known for coordinating ATP synthesis from cellular respiration in cellular bioenergetics, little is known its mitophagy regulation in chemoresistance. Recent advancements in mitochondrial research, mitophagy regulatory mechanisms, and their implications for our understanding of chemotherapy resistance are discussed in this review.

Abstract

Cancer chemotherapy resistance is one of the most critical obstacles in cancer therapy. One of the well-known mechanisms of chemotherapy resistance is the change in the mitochondrial death pathways which occur when cells are under stressful situations, such as chemotherapy. Mitophagy, or mitochondrial selective autophagy, is critical for cell quality control because it can efficiently break down, remove, and recycle defective or damaged mitochondria. As cancer cells use mitophagy to rapidly sweep away damaged mitochondria in order to mediate their own drug resistance, it influences the efficacy of tumor chemotherapy as well as the degree of drug resistance. Yet despite the importance of mitochondria and mitophagy in chemotherapy resistance, little is known about the precise mechanisms involved. As a consequence, identifying potential therapeutic targets by analyzing the signal pathways that govern mitophagy has become a vital research goal. In this paper, we review recent advances in mitochondrial research, mitophagy control mechanisms, and their implications for our understanding of chemotherapy resistance.

NEAT1 Confers Radioresistance to Hepatocellular Carcinoma Cells by Inducing Autophagy through GABARAP

A long noncoding RNA (lncRNA), nuclear enriched abundant transcript 1 (NEAT1) variant 1 (NEAT1v1), is involved in the maintenance of cancer stem cells (CSCs) in hepatocellular carcinoma (HCC). CSCs are suggested to play important roles in therapeutic resistance. Therefore, we investigated whether NEAT1v1 is involved in the sensitivity to radiation therapy in HCC. Gene knockdown was performed using short hairpin RNAs, and NEAT1v1-overexpressing HCC cell lines were generated by stable transfection with a NEAT1v1-expressing plasmid DNA. Cells were irradiated using an X-ray generator. We found that NEAT1 knockdown enhanced the radiosensitivity of HCC cell lines and concomitantly inhibited autophagy. NEAT1v1 overexpression enhanced autophagy in the irradiated cells and conferred radioresistance. Gamma-aminobutyric acid receptor-associated protein (GABARAP) expression was downregulated by NEAT1 knockdown, whereas it was upregulated in NEAT1v1-overexpressing cells. Moreover, GABARAP was required for NEAT1v1-induced autophagy and radioresistance as its knockdown significantly inhibited autophagy and sensitized the cells to radiation. Since GABARAP is a crucial protein for the autophagosome-lysosome fusion, our results suggest that NEAT1v1 confers radioresistance to HCC by promoting autophagy through GABARAP.

Autophagy in Cancer: A Metabolic Perspective

Autophagy is an intracellular catabolic degradative process in which damaged cellular organelles, unwanted proteins and different cytoplasmic components get recycled to maintain cellular homeostasis or metabolic balance. During autophagy, a double membrane vesicle is formed to engulf these cytosolic materials and fuse to lysosomes wherein the entire cargo degrades to be used again. Because of this unique recycling ability of cells, autophagy is a universal stress response mechanism. Dysregulation of autophagy leads to several diseases, including cancer, neurodegeneration and microbial infection. Thus, autophagy machineries have become targets for therapeutics. This chapter provides an overview of the paradoxical role of autophagy in tumorigenesis in the perspective of metabolism.

Metabolic Rewiring Is Essential for AML Cell Survival to Overcome Autophagy Inhibition by Loss of ATG3

Simple Summary

The importance of autophagy in leukemia progression and survival has been studied previously. However, little is known about the development of resistance mechanisms to autophagy inhibition in leukemia. Here, we present data on the mechanisms by which leukemia cells maintain their cell survival after inhibition of autophagy by the loss of ATG3. After the loss of ATG3, leukemia cells upregulated their energy metabolism by increasing glycolysis and mitochondrial metabolism, in particular oxidative phosphorylation, which resulted in higher ATP levels. Moreover, inhibition of mitochondrial function strongly impaired cell survival in ATG3 deficiency, thus demonstrating the importance of ATG3 in the regulation of metabolism and survival of leukemic cells. Therefore, our data provide a rationale for combining autophagy inhibitors with inhibitors targeting mitochondrial metabolism for the development of leukemia therapy to overcome the potential obstacle of emerging resistance to autophagy inhibition.

Abstract

Autophagy is an important survival mechanism that allows recycling of nutrients and removal of damaged organelles and has been shown to contribute to the proliferation of acute myeloid leukemia (AML) cells. However, little is known about the mechanism by which autophagy- dependent AML cells can overcome dysfunctional autophagy. In our study we identified autophagy related protein 3 (ATG3) as a crucial autophagy gene for AML cell proliferation by conducting a CRISPR/Cas9 dropout screen with a library targeting around 200 autophagy-related genes. shRNA-mediated loss of ATG3 impaired autophagy function in AML cells and increased their mitochondrial activity and energy metabolism, as shown by elevated mitochondrial ROS generation and mitochondrial respiration. Using tracer-based NMR metabolomics analysis we further demonstrate that the loss of ATG3 resulted in an upregulation of glycolysis, lactate production, and oxidative phosphorylation. Additionally, loss of ATG3 strongly sensitized AML cells to the inhibition of mitochondrial metabolism. These findings highlight the metabolic vulnerabilities that AML cells acquire from autophagy inhibition and support further exploration of combination therapies targeting autophagy and mitochondrial metabolism in AML.

A perspective on the role of autophagy in cancer

Autophagy refers to a ubiquitous set of catabolic pathways required to achieve proper cellular homeostasis. Aberrant autophagy has been implicated in a multitude of diseases including cancer. In this review, we highlight pioneering and groundbreaking research that centers on delineating the role of autophagy in cancer initiation, proliferation and metastasis. First, we discuss the autophagy-related (ATG) proteins and their respective roles in the de novo formation of autophagosomes and the subsequent delivery of cargo to the lysosome for recycling. Next, we touch upon the history of cancer research that centers upon ATG proteins and regulatory mechanisms that control an appropriate autophagic response and how these are altered in the diseased state. Then, we discuss the various discoveries that led to the idea of autophagy as a double-edged sword when it comes to cancer therapy. This review also briefly narrates how different types of autophagy-selective macroautophagy and chaperone-mediated autophagy, have been linked to different cancers. Overall, these studies build upon a steadfast trajectory that aims to solve the monumentally daunting challenge of finding a cure for many types of cancer by modulating autophagy either through inhibition or induction.

Folic Acid-Appended Hydroxypropyl-β-Cyclodextrin Exhibits Potent Antitumor Activity in Chronic Myeloid Leukemia Cells via Autophagic Cell Death

Simple Summary

2-Hydroxypropyl-β-cyclodextrin (HP-β-CyD) is a cyclic oligosaccharide widely used as an excipient in pharmaceutical preparations, in addition to also being used as a cholesterol regulator. HP-β-CyD was used in clinical trials for patients with Niemann-Pick Type C disease to remove accumulated intracellular lipid. HP-β-CyD has anti-leukemia activity by inducing apoptosis and cell-cycle arrest; however, the antitumor activity of HP-β-CyD lacks tumor cell-selectivity. Taking advantage of the fact that folate receptors are highly expressed in many cancer cells, we synthesized folate-appended HP-β-CyD (FA-HP-β-CyD) to confer tumor cell-selectivity to HP-β-CyD. FA-HP-β-CyD inhibited the proliferation of chronic myeloid leukemia (CML) cells and the mechanism underlying the effect of FA-HP-β-CyD in inducing cell death may involve autophagy. The combination of FA-HP-β-CyD and ABL tyrosine kinase inhibitors (imatinib and ponatinib) had a synergistic inhibitory effect on CML cells. In a mouse model of BCR-ABL-induced leukemia, FA-HP-β-CyD had a stronger inhibitory effect on leukemia progression than HP-β-CyD or imatinib.

Abstract

2-Hydroxypropyl-β-cyclodextrin (HP-β-CyD) is widely used as an enabling excipient in pharmaceutical formulations. We previously demonstrated that HP-β-CyD disrupted cholesterol homeostasis, and inhibited the proliferation of leukemia cells by inducing apoptosis and cell-cycle arrest. Recently developed drug delivery systems using folic acid (FA) and folic acid receptors (FR) are currently being used in cancer treatment. To confer tumor cell-selectivity to HP-β-CyD, we synthesized folate-appended HP-β-CyD (FA-HP-β-CyD) and evaluated the potential of FA-HP-β-CyD as an anticancer agent using chronic myeloid leukemia (CML) cells in vitro and in vivo. FA-HP-β-CyD inhibited the growth of FR-expressing cells but not that of FR-negative cells. FA-HP-β-CyD had stronger anti-leukemia and cell-binding activities than HP-β-CyD in CML cells. Unlike HP-β-CyD, FA-HP-β-CyD entered CML cells through endocytosis and induced both apoptosis and autophagy via mitophagy. FA-HP-β-CyD increased the inhibitory effects of the ABL tyrosine kinase inhibitors imatinib mesylate and ponatinib, which are commonly used in CML. In vivo experiments in a BCR-ABL leukemia mouse model showed that FA-HP-β-CyD was more effective than HP-β-CyD at a ten-fold lower dose. These results indicate that FA-HP-β-CyD may be a novel tumor-targeting agent for the treatment of leukemia.

Autophagy and Metabolism in Normal and Malignant Hematopoiesis

The hematopoietic system relies on regulation of both metabolism and autophagy to maintain its homeostasis, ensuring the self-renewal and multipotent differentiation potential of hematopoietic stem cells (HSCs). HSCs display a distinct metabolic profile from that of their differentiated progeny, while metabolic rewiring from glycolysis to oxidative phosphorylation (OXPHOS) has been shown to be crucial for effective hematopoietic differentiation. Autophagy-mediated regulation of metabolism modulates the distinct characteristics of quiescent and differentiating hematopoietic cells. In particular, mitophagy determines the cellular mitochondrial content, thus modifying the level of OXPHOS at the different differentiation stages of hematopoietic cells, while, at the same time, it ensures the building blocks and energy for differentiation. Aberrations in both the metabolic status and regulation of the autophagic machinery are implicated in the development of hematologic malignancies, especially in leukemogenesis. In this review, we aim to investigate the role of metabolism and autophagy, as well as their interconnections, in normal and malignant hematopoiesis.

Binding Features and Functions of ATG3

Autophagy is an evolutionarily conserved catabolic process that is essential for maintaining cellular, tissue, and organismal homeostasis. Autophagy-related (ATG) genes are indispensable for autophagosome formation. ATG3 is one of the key genes involved in autophagy, and its homologs are common in eukaryotes. During autophagy, ATG3 acts as an E2 ubiquitin-like conjugating enzyme in the ATG8 conjugation system, contributing to phagophore elongation. ATG3 has also been found to participate in many physiological and pathological processes in an autophagy-dependent manner, such as tumor occurrence and progression, ischemia-reperfusion injury, clearance of pathogens, and maintenance of organelle homeostasis. Intriguingly, a few studies have recently discovered the autophagy-independent functions of ATG3, including cell differentiation and mitosis. Here, we summarize the current knowledge of ATG3 in autophagosome formation, highlight its binding partners and binding sites, review its autophagy-dependent functions, and provide a brief introduction into its autophagy-independent functions.

Recent advances in understanding chronic myeloid leukemia: where do we stand?

While the need for complete eradication of leukemic stem cells (LSCs) in chronic myeloid leukemia may be controversial, it is agreed that remaining LSCs are the cause of relapse and disease progression. Current efforts are focused on the understanding of the persistence of immunophenotypically defined LSCs, which feature abnormalities in signaling pathways relating to autophagy, metabolism, epigenetics, and others and are influenced by leukemia cell-extrinsic factors such as the immune and bone marrow microenvironments. In sum, these elements modulate response and resistance to therapies and the clinical condition of treatment-free remission (TFR), the newly established goal in CML treatment, once the patient has achieved a durable molecular remission after treatment with tyrosine kinase inhibitors. Novel combination therapies based on these identified vulnerabilities of LSCs, aimed at the induction or maintenance of TFR, are being developed, while other research is directed at the elucidation of factors mediating progression to blast crisis.

Autophagy and senescence: Insights from normal and cancer stem cells

Autophagy is a fundamental cellular process, which allows cells to adapt to metabolic stress through the degradation and recycling of intracellular components to generate macromolecular precursors and produce energy. Autophagy is also critical in maintaining cellular/tissue homeostasis, as well preserving immunity and preventing human disease. Deregulation of autophagic processes is associated with cancer, neurodegeneration, muscle and heart disease, infectious diseases and aging. Research on a variety of stem cell types establish that autophagy plays critical roles in normal and cancer stem cell quiescence, activation, differentiation, and self-renewal. Considering its critical function in regulating the metabolic state of stem cells, autophagy plays a dual role in the regulation of normal and cancer stem cell senescence, and cellular responses to various therapeutic strategies. The relationships between autophagy, senescence, dormancy and apoptosis frequently focus on responses to various forms of stress. These are interrelated processes that profoundly affect normal and abnormal human physiology that require further elucidation in cancer stem cells. This review provides a current perspective on autophagy and senescence in both normal and cancer stem cells.

Enhanced Sensitivity to NVP-BEZ235 by Inhibition of p62/SQSTM1 in Human Bladder Cancer KoTCC-1 Cells Both In Vitro and In Vivo

BACKGROUND/AIM

The prognosis of patients with invasive bladder cancer remains poor. The objective of this study was to evaluate the efficacy of NVP-BEZ235 (NVP), a dual PI3K/mTOR inhibitor, combined with the inactivation of p62/SQSTM1 (p62) in a human bladder cancer KoTCC-1 model.

MATERIALS AND METHODS

An expression plasmid with short hairpin RNA targeted against p62 was transfected into KoTCC-1 cells (KoTCC-1/sh-p62). The antitumor effects of NVP on KoTCC-1/sh-p62 were investigated in comparison with those on KoTCC-1 transfected with a control plasmid alone (KoTCC-1/C).

RESULTS

KoTCC-1/sh-p62 showed significantly higher sensitivity to NVP than KoTCC-1/C. Treatment of both cell lines with NVP markedly inactivated the PI3K/Akt/mTOR signaling pathway. However, NVP treatment stimulated the autophagic pathway in KoTCC-1/C, but not in KoTCC-1/sh-p62. Furthermore, compared with KoTCC-1/C, NVP treatment induced apoptosis of KoTCC-1/sh-p62 cells, which was accompanied by significant downregulation of c-IAP-1 and XIAP as well as upregulation of Bax. Moreover, the in vivo growth of KoTCC-1/sh-p62 tumors was significantly suppressed by treatment with NVP compared to KoTCC-1/C tumors.

CONCLUSION

Inhibition of p62 expression combined with NVP may represent an effective therapeutic approach for patients with invasive bladder cancer.

The Dual Role of Autophagy in Cancer Development and a Therapeutic Strategy for Cancer by Targeting Autophagy

Autophagy is a delicate intracellular degradation process that occurs due to diverse stressful conditions, including the accumulation of damaged proteins and organelles as well as nutrient deprivation. The mechanism of autophagy is initiated by the creation of autophagosomes, which capture and encapsulate abnormal components. Afterward, autophagosomes assemble with lysosomes to recycle or remove degradative cargo. The regulation of autophagy has bipolar roles in cancer suppression and promotion in diverse cancers. Furthermore, autophagy modulates the features of tumorigenesis, cancer metastasis, cancer stem cells, and drug resistance against anticancer agents. Some autophagy regulators are used to modulate autophagy for anticancer therapy but the dual roles of autophagy limit their application in anticancer therapy, and present as the main reason for therapy failure. In this review, we summarize the mechanisms of autophagy, tumorigenesis, metastasis, cancer stem cells, and resistance against anticancer agents. Finally, we discuss whether targeting autophagy is a promising and effective therapeutic strategy in anticancer therapy.

Regulation of Beclin 1-Mediated Autophagy by Oncogenic Tyrosine Kinases

Beclin 1 is a major regulator of autophagy, and it is a core component of the class III PI3K complexes. Beclin 1 is a highly conserved protein and its function is regulated in a number of ways, including post-translational modifications. Several studies indicate that receptor and non-receptor tyrosine kinases regulate autophagy activity in cancer, and some suggest the importance of Beclin 1 tyrosine phosphorylation in this process. Here we summarize the current knowledge of the mechanism whereby some oncogenic tyrosine kinases regulate autophagy through Beclin 1.

Recent developments in autophagy-targeted therapies in cancer

Autophagy plays a crucial role in cellular development and differentiation as well as in the maintenance of homeostasis in healthy cells. Autophagy is well documented in neurodegenerative disorders, aging, and infectious diseases. However, recognizing its significance in cancer has always been challenging due to its tumor-promoting and suppressive attributes. Various modulators targeting key components of autophagy machinery directly or indirectly have been developed over the years, and have shown promising results in preclinical models. Some of these compounds are even being tested in clinical trials for safety and efficacy. A detailed review of strategies used to target autophagy in cancer is presented including our opinion on developing better therapies and outstanding issues.

Various Aspects of Calcium Signaling in the Regulation of Apoptosis, Autophagy, Cell Proliferation, and Cancer

Calcium (Ca²⁺) is a major second messenger in cells and is essential for the fate and survival of all higher organisms. Different Ca²⁺ channels, pumps, or exchangers regulate variations in the duration and levels of intracellular Ca²⁺, which may be transient or sustained. These changes are then decoded by an elaborate toolkit of Ca²⁺-sensors, which translate Ca²⁺ signal to intracellular operational cell machinery, thereby regulating numerous Ca²⁺-dependent physiological processes. Alterations to Ca²⁺ homoeostasis and signaling are often deleterious and are associated with certain pathological states, including cancer. Altered Ca²⁺ transmission has been implicated in a variety of processes fundamental for the uncontrolled proliferation and invasiveness of tumor cells and other processes important for cancer progression, such as the development of resistance to cancer therapies. Here, we review what is known about Ca²⁺ signaling and how this fundamental second messenger regulates life and death decisions in the context of cancer, with particular attention directed to cell proliferation, apoptosis, and autophagy. We also explore the intersections of Ca²⁺ and the therapeutic targeting of cancer cells, summarizing the therapeutic opportunities for Ca²⁺ signal modulators to improve the effectiveness of current anticancer therapies.

The Role of Metabolic Enzymes in the Regulation of Inflammation

Immune cells undergo dramatic metabolic reprogramming in response to external stimuli. These metabolic pathways, long considered as simple housekeeping functions, are increasingly understood to critically regulate the immune response, determining the activation, differentiation, and downstream effector functions of both lymphoid and myeloid cells. Within the complex metabolic networks associated with immune activation, several enzymes play key roles in regulating inflammation and represent potential therapeutic targets in human disease. In some cases, these enzymes control flux through pathways required to meet specific energetic or metabolic demands of the immune response. In other cases, key enzymes control the concentrations of immunoactive metabolites with direct roles in signaling. Finally, and perhaps most interestingly, several metabolic enzymes have evolved moonlighting functions, with roles in the immune response that are entirely independent of their conventional enzyme activities. Here, we review key metabolic enzymes that critically regulate inflammation, highlighting mechanistic insights and opportunities for clinical intervention.

Discovery of Berberine that Targetedly Induces Autophagic Degradation of both BCR-ABL and BCR-ABL T315I through Recruiting LRSAM1 for Overcoming Imatinib Resistance

PURPOSE

Imatinib, the breakpoint cluster region protein (BCR)/Abelson murine leukemia viral oncogene homolog (ABL) inhibitor, is widely used to treat chronic myeloid leukemia (CML). However, imatinib resistance develops in many patients. Therefore, new drugs with improved therapeutic effects are urgently needed. Berberine (BBR) is a potent BCR-ABL inhibitor for imatinib-sensitive and -resistant CML.

EXPERIMENTAL DESIGN

Protein structure analysis and virtual screening were used to identify BBR targets in CML. Molecular docking analysis, surface plasmon resonance imaging, nuclear magnetic resonance assays, and thermoshift assays were performed to confirm the BBR target. The change in BCR-ABL protein expression after BBR treatment was assessed by Western blotting. The effects of BBR were assessed in vitro in cell lines, in vivo in mice, and in human CML bone marrow cells as a potential strategy to overcome imatinib resistance.

RESULTS

We discovered that BBR bound to the protein tyrosine kinase domain of BCR-ABL. BBR inhibited the activity of BCR-ABL and BCR-ABL with the T315I mutation, and it also degraded these proteins via the autophagic lysosome pathway by recruiting E3 ubiquitin-protein ligase LRSAM1. BBR inhibited the cell viability and colony formation of CML cells and prolonged survival in CML mouse models with imatinib sensitivity and resistance.

CONCLUSIONS

The results show that BBR directly binds to and degrades BCR-ABL and BCR-ABL T315I via the autophagic lysosome pathway by recruiting LRSAM1. The use of BBR is a new strategy to improve the treatment of patients with CML with imatinib sensitivity or resistance.See related commentary by Elf, p. 3899.

A randomised phase II trial of hydroxychloroquine and imatinib versus imatinib alone for patients with chronic myeloid leukaemia in major cytogenetic response with residual disease

In chronic-phase chronic myeloid leukaemia (CP-CML), residual BCR-ABL1+ leukaemia stem cells are responsible for disease persistence despite TKI. Based on in vitro data, CHOICES (CHlorOquine and Imatinib Combination to Eliminate Stem cells) was an international, randomised phase II trial designed to study the safety and efficacy of imatinib (IM) and hydroxychloroquine (HCQ) compared with IM alone in CP-CML patients in major cytogenetic remission with residual disease detectable by qPCR. Sixty-two patients were randomly assigned to either arm. Treatment 'successes' was the primary end point, defined as ≥0.5 log reduction in 12-month qPCR level from trial entry. Selected secondary study end points were 24-month treatment 'successes', molecular response and progression at 12 and 24 months, comparison of IM levels, and achievement of blood HCQ levels >2000 ng/ml. At 12 months, there was no difference in 'success' rate (p = 0.58); MMR was achieved in 80% (IM) vs 92% (IM/HCQ) (p = 0.21). At 24 months, the 'success' rate was 20.8% higher with IM/HCQ (p = 0.059). No patients progressed. Seventeen serious adverse events, including four serious adverse reactions, were reported; diarrhoea occurred more frequently with combination. IM/HCQ is tolerable in CP-CML, with modest improvement in qPCR levels at 12 and 24 months, suggesting autophagy inhibition maybe of clinical value in CP-CML.

Unfolded Protein Response in Leukemia: From Basic Understanding to Therapeutic Opportunities

Understanding genetic and epigenetic changes that underlie abnormal proliferation of hematopoietic stem and progenitor cells is critical for development of new approaches to monitor and treat leukemia. The unfolded protein response (UPR) is a conserved adaptive signaling pathway that governs protein folding, secretion, and energy production and serves to maintain protein homeostasis in various cellular compartments. Deregulated UPR signaling, which often occurs in hematopoietic stem cells and leukemia, defines the degree of cellular toxicity and perturbs protein homeostasis, and at the same time, offers a novel therapeutic target. Here, we review current knowledge related to altered UPR signaling in leukemia and highlight possible strategies for exploiting the UPR as treatment for this disease.

Phosphorylation of BECLIN-1 by BCR-ABL suppresses autophagy in chronic myeloid leukemia

Autophagy is a genetically regulated process of adaptation to metabolic stress and was recently shown to be involved in the treatment response of chronic myeloid leukemia (CML). However, in vivo data are limited and the molecular mechanism of autophagy regulators in the process of leukemogenesis is not completely understood. Here we show that Beclin-1 knockdown, but not Atg5 deletion in a murine CML model leads to a reduced leukemic burden and results in a significantly prolonged median survival of targeted mice. Further analyses of murine cell lines and primary patient material indicate that active BCR-ABL directly interacts with BECLIN-1 and phosphorylates its tyrosine residues 233 and 352, resulting in autophagy suppression. By using phosphorylation-deficient and phosphorylation-mimic mutants, we identify BCR-ABL induced BECLIN-1 phosphorylation as a crucial mechanism for BECLIN-1 complex formation: interaction analyses exhibit diminished binding of the positive autophagy regulators UVRAG, VPS15, ATG14 and VPS34 and enhanced binding of the negative regulator Rubicon to BCR-ABL-phosphorylated BECLIN-1. Taken together, our findings show interaction of BCR-ABL and BECLIN-1 thereby highlighting the importance of BECLIN-1-mediated autophagy in BCR-ABL⁺ cells.

Exploiting metabolic vulnerabilities for personalized therapy in acute myeloid leukemia

Changes in cell metabolism and metabolic adaptation are hallmark features of many cancers, including leukemia, that support biological processes involved into tumor initiation, growth, and response to therapeutics. The discovery of mutations in key metabolic enzymes has highlighted the importance of metabolism in cancer biology and how these changes might constitute an Achilles heel for cancer treatment. In this Review, we discuss the role of metabolic and mitochondrial pathways dysregulated in acute myeloid leukemia, and the potential of therapeutic intervention targeting these metabolic dependencies on the proliferation, differentiation, stem cell function and cell survival to improve patient stratification and outcomes.

Oncogenic KIT mutations induce STAT3-dependent autophagy to support cell proliferation in acute myeloid leukemia

Autophagy is associated with both survival and cell death in myeloid malignancies. Therefore, deciphering its role in different genetically defined subtypes of acute myeloid leukemia (AML) is critical. Activating mutations of the KIT receptor tyrosine kinase are frequently detected in core-binding factor AML and are associated with a greater risk of relapse. Herein, we report that basal autophagy was significantly increased by the KIT^D816V mutation in AML cells and contributed to support their cell proliferation and survival. Invalidation of the key autophagy protein Atg12 strongly reduced tumor burden and improved survival of immunocompromised NSG mice engrafted with KIT^D816V TF-1 cells. Downstream of KIT^D816V, STAT3, but not AKT or ERK pathways, was identified as a major regulator of autophagy. Accordingly, STAT3 pharmacological inhibition or downregulation inhibited autophagy and reduced tumor growth both in vitro and in vivo. Taken together, our results support the notion that targeting autophagy or STAT3 opens up an exploratory pathway for finding new therapeutic opportunities for patients with CBF-AML or others malignancies with KIT^D816V mutations.

[Clinical importance of microtubule-associated protein 1 light chain 3 and mammalian target of rapamycin expression in oral leukoplakia and oral squamous cell carcinoma]

OBJECTIVE

This study aimed to investigate the expression and relationship of microtubule-associated protein 1 light chain 3 (LC3) and mammalian target of rapamycin (mTOR) in normal oral mucosa, oral leukoplakia (OLK), and oral squamous cell carcinoma (OSCC). This work also analyzed the relationship between expression levels and clinical factors. This study evaluated the clinical value of LC3B and mTOR as indices to determine the carcinogenic potential of OLK.

METHODS

Immunohistochemistry was used to detect the expression of LC3B and mTOR in 20 cases of normal oral mucosa, 120 cases of OLK, and 30 cases of OSCC. The clinical data of 120 patients with OLK were analyzed. The relationships between expression levels and clinical factors were investigated.

RESULTS

In normal oral mucosa, OLK and OSCC, the positive rates of LC3B expression were 85.0%, 65.8% and 33.3% (P<0.05), whereas the positive rates of mTOR expression were 20.0%, 48.3% and 76.7% (P<0.05). The expression levels of LC3B and mTOR were correlated and related to clinical typing of OLK (P<0.05).

CONCLUSIONS

LC3B and mTOR can be used as molecular biomarkers for early detection of OLK.

The MitoNEET Ligand NL-1 Mediates Antileukemic Activity in Drug-Resistant B-Cell Acute Lymphoblastic Leukemia

Disease relapse in B-cell acute lymphoblastic leukemia (ALL), either due to development of acquired resistance after therapy or because of de novo resistance, remains a therapeutic challenge. In the present study, we have developed a cytarabine (Ara-C)-resistant REH cell line (REH/Ara-C) as a chemoresistance model. REH/Ara-C 1) was not crossresistant to vincristine or methotrexate; 2) showed a similar proliferation rate and cell surface marker expression as parental REH; 3) demonstrated decreased chemotaxis toward bone marrow stromal cells; and 4) expressed higher transcript levels of cytidine deaminase (CDA) and mitoNEET (CISD1) than the parental REH cell line. Based on these findings, we tested NL-1, a mitoNEET inhibitor, which induced a concentration-dependent decrease in cell viability with a comparable IC₅₀ value in REH and REH/Ara-C. Furthermore, NL-1 decreased cell viability in six different ALL cell lines and showed inhibitory activity in a hemosphere assay. NL-1 also impaired the migratory ability of leukemic cells, irrespective of the chemoattractant used, in a chemotaxis assay. More importantly, NL-1 showed specific activity in inducing death in a drug-resistant population of leukemic cells within a coculture model that mimicked the acquired resistance and de novo resistance observed in the bone marrow of relapsed patients. Subsequent studies indicated that NL-1 mediates autophagy, and inhibition of autophagy partially decreased NL-1-induced tumor cell death. Finally, NL-1 showed antileukemic activity in an in vivo mouse ALL model. Taken together, our study demonstrates that mitoNEET has potential as a novel antileukemic drug target in treatment refractory or relapsed ALL.

A novel role for a glycolytic pathway kinase in regulating autophagy has implications in cancer therapy

When it comes to cancer initiation and progression, macroautophagy/autophagy seemingly acts in a contradictory fashion, serving either as a suppressive factor that functions to protect against tumor formation or as a support mechanism that sustains the disease itself through its cytoprotective functions. In tumor suppression, autophagy assists by restricting oxidative stress and curbing genomic instability that could possibly cause oncogenic mutations. However, in certain circumstances, autophagy can also promote cancer by providing nourishment and by limiting stress-response pathways, leading to cancer cell survival and rapid proliferation. Thus, autophagy's role in oncogenesis is highly context-dependent and varies from one cancer type to another. As a consequence, identifying the mechanisms that alter and rewire autophagic regulation and flux is extremely crucial to target autophagy as a possible avenue for anticancer treatment. In a recent study, Qian et al. endeavored to identify one such key regulatory pathway in hypoxia- and glutamine deprivation-induced autophagy in tumorigenic cells. In this pathway, phosphatidylinositol 3-phosphate (PtdIns3P) production by the class III phosphatidylinositol 3-kinase (PtdIns3K) complex is greatly improved through a cascade of posttranslational modifications that culminates in the phosphorylation of the scaffolding protein BECN1 by the glycolytic pathway kinase PGK1.

Autophagy and cancer stem cells: molecular mechanisms and therapeutic applications

Autophagy and mitophagy act in cancer as bimodal processes, whose differential functions strictly depend on cancer ontogenesis, progression, and type. For instance, they can act to promote cancer progression by helping cancer cells survive stress or, instead, when mutated or abnormal, to induce carcinogenesis by influencing cell signaling or promoting intracellular toxicity. For this reason, the study of autophagy in cancer is the main focus of many researchers and several clinical trials are already ongoing to manipulate autophagy and by this way determine the outcome of disease therapy. Since the establishment of the cancer stem cell (CSC) theory and the discovery of CSCs in individual cancer types, autophagy and mitophagy have been proposed as key mechanisms in their homeostasis, dismissal or spread, even though we still miss a comprehensive view of how and by which regulatory molecules these two processes drive cell fate. In this review, we will dive into the deep water of autophagy, mitophagy, and CSCs and offer novel viewpoints on possible therapeutic strategies, based on the modulation of these degradative systems.

The Interplay Between Pattern Recognition Receptors and Autophagy in Inflammation

Pattern recognition receptors (PRRs) are sensors of exogenous and endogenous "danger" signals from pathogen-associated molecular patterns (PAMPs), and damage associated molecular patterns (DAMPs), while autophagy can respond to these signals to control homeostasis. Almost all PRRs can induce autophagy directly or indirectly. Toll-like receptors (TLRs), Nod-like receptors (NLRs), retinoic acid-inducible gene-I-like receptors (RLRs), and cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)-stimulator of interferon genes (STING) pathway can induce autophagy directly through Beclin-1 or LC3-dependent pathway, while the interactions with the receptor for advanced glycation end products (RAGE)/high mobility group box 1 (HMGB1), CD91/Calreticulin, and TLRs/HSPs are achieved by protein, Ca2⁺, and mitochondrial homeostasis. Autophagy presents antigens to PRRs and helps to clean the pathogens. In addition, the induced autophagy can form a negative feedback regulation of PRRs-mediated inflammation in cell/disease-specific manner to maintain homeostasis and prevent excessive inflammation. Understanding the interaction between PRRs and autophagy in a specific disease will promote drug development for immunotherapy. Here, we focus on the interactions between PRRs and autophagy and how they affect the inflammatory response.

Loss of the selective autophagy receptor p62 impairs murine myeloid leukemia progression and mitophagy

Autophagy maintains hematopoietic stem cell integrity and prevents malignant transformation. In addition to bulk degradation, selective autophagy serves as an intracellular quality control mechanism and requires autophagy receptors, such as p62 (SQSTM1), to specifically bridge the ubiquitinated cargos into autophagosomes. Here, we investigated the function of p62 in acute myeloid leukemia (AML) in vitro and in murine in vivo models of AML. Loss of p62 impaired expansion and colony-forming ability of leukemia cells and prolonged latency of leukemia development in mice. High p62 expression was associated with poor prognosis in human AML. Using quantitative mass spectrometry, we identified enrichment of mitochondrial proteins upon immunoprecipitation of p62. Loss of p62 significantly delayed removal of dysfunctional mitochondria, increased mitochondrial superoxide levels, and impaired mitochondrial respiration. Moreover, we demonstrated that the autophagy-dependent function of p62 is essential for cell growth and effective mitochondrial degradation by mitophagy. Our results highlight the prominent role of selective autophagy in leukemia progression, and specifically, the importance of mitophagy to maintain mitochondrial integrity.

The multifaceted role of autophagy in cancer and the microenvironment

Autophagy is a crucial recycling process that is increasingly being recognized as an important factor in cancer initiation, cancer (stem) cell maintenance as well as the development of resistance to cancer therapy in both solid and hematological malignancies. Furthermore, it is being recognized that autophagy also plays a crucial and sometimes opposing role in the complex cancer microenvironment. For instance, autophagy in stromal cells such as fibroblasts contributes to tumorigenesis by generating and supplying nutrients to cancerous cells. Reversely, autophagy in immune cells appears to contribute to tumor‐localized immune responses and among others regulates antigen presentation to and by immune cells. Autophagy also directly regulates T and natural killer cell activity and is required for mounting T‐cell memory responses. Thus, within the tumor microenvironment autophagy has a multifaceted role that, depending on the context, may help drive tumorigenesis or may help to support anticancer immune responses. This multifaceted role should be taken into account when designing autophagy‐based cancer therapeutics. In this review, we provide an overview of the diverse facets of autophagy in cancer cells and nonmalignant cells in the cancer microenvironment. Second, we will attempt to integrate and provide a unified view of how these various aspects can be therapeutically exploited for cancer therapy.

Autophagy and mitochondrial metabolism: insights into their role and therapeutic potential in chronic myeloid leukaemia

Despite the development of selective BCR-ABL-targeting tyrosine kinase inhibitors (TKIs) transforming the management of chronic myeloid leukaemia (CML), therapy-resistant leukaemic stem cells (LSCs) persist after TKI treatment and present an obstacle to a CML cure. Recently, we and others have made significant contributions to the field by unravelling survival dependencies in LSCs to work towards the goal of eradicating LSCs in CML patients. In this review, we describe these findings focusing on autophagy and mitochondrial metabolism, which have recently been uncovered as two essential processes for LSCs quiescence and survival respectively. In addition, we discuss the therapeutic potential of autophagy and mitochondrial metabolism inhibition as a strategy to eliminate CML cells in patients where the resistance to TKI is driven by BCR-ABL-independent mechanism(s).

Nrf2 signaling and autophagy are complementary in protecting breast cancer cells during glucose deprivation

Autophagy can serve as a mechanism for survival of cells during nutrient deprivation by recycling cellular macromolecules and organelles transiently to provide essential metabolic substrates. However, autophagy itself causes metabolic stress to cells, and other cellular protective mechanisms likely cooperate with autophagy to promote cell survival during nutrient deprivation. In this study, we explored protective mechanisms in breast cancer cells in the setting of glucose deprivation. While breast cancer cells (MCF7 and T47D) survive in glucose-free medium for three days or more, autophagy is induced in this setting. Blocking autophagy pharmacologically with chloroquine or by knock-out of an essential autophagy gene, such as Beclin 1 or ATG7, markedly reduces the ability of cells to survive during glucose deprivation. Autophagy previously was shown to degrade p62, a protein that sequesters KEAP1, and KEAP1 in turn sequesters Nrf2, a master regulator of the antioxidant response. Hence, we investigated how the Nrf2 signaling pathway might be affected by glucose deprivation and autophagy. We found that while glucose deprivation does cause decreased cellular levels of p62, Nrf2 protein levels and activity unexpectedly increase in this setting. Moreover, this increase in Nrf2 activity provides important protection to breast cancer cells during glucose deprivation, since siRNA knockdown of Nrf2 markedly impairs survival during glucose deprivation. Antioxidants, N-acetyl cysteine and glutathione also protect these cells during glucose deprivation, leading us to conclude that Nrf2 signaling via its antioxidant activity has a critical and previously undescribed role of protecting cells during glucose deprivation-induced autophagy.

Different BCR/Abl protein suppression patterns as a converging trait of chronic myeloid leukemia cell adaptation to energy restriction

BCR/Abl protein drives the onset and progression of Chronic Myeloid Leukemia (CML). We previously showed that BCR/Abl protein is suppressed in low oxygen, where viable cells retain stem cell potential. This study addressed the regulation of BCR/Abl protein expression under oxygen or glucose shortage, characteristic of the in vivo environment where cells resistant to tyrosine kinase inhibitors (TKi) persist. We investigated, at transcriptional, translational and post-translational level, the mechanisms involved in BCR/Abl suppression in K562 and KCL22 CML cells. BCR/abl mRNA steady-state analysis and ChIP-qPCR on BCR promoter revealed that BCR/abl transcriptional activity is reduced in K562 cells under oxygen shortage. The SUnSET assay showed an overall reduction of protein synthesis under oxygen/glucose shortage in both cell lines. However, only low oxygen decreased polysome-associated BCR/abl mRNA significantly in KCL22 cells, suggesting a decreased BCR/Abl translation. The proteasome inhibitor MG132 or the pan-caspase inhibitor z-VAD-fmk extended BCR/Abl expression under oxygen/glucose shortage in K562 cells. Glucose shortage induced autophagy-dependent BCR/Abl protein degradation in KCL22 cells. Overall, our results showed that energy restriction induces different cell-specific BCR/Abl protein suppression patterns, which represent a converging route to TKi-resistance of CML cells. Thus, the interference with BCR/Abl expression in environment-adapted CML cells may become a useful implement to current therapy.

Synergistic effects of selective inhibitors targeting the PI3K/AKT/mTOR pathway or NUP214-ABL1 fusion protein in human Acute Lymphoblastic Leukemia

Philadelphia chromosome-positive (Ph+) Acute Lymphoblastic Leukemia (ALL) accounts for 25–30% of adult ALL and its incidence increases with age in adults >40 years old. Irrespective of age, the ABL1 fusion genes are markers of poor prognosis and amplification of the NUP214-ABL1 oncogene can be detected mainly in patients with T-ALL. T cell malignancies harboring the ABL1 fusion genes are sensitive to many cytotoxic agents, but up to date complete remissions have not been achieved. The PI3K/Akt/mTOR signaling pathway is often activated in leukemias and plays a crucial role in leukemogenesis.

We analyzed the effects of three BCR-ABL1 tyrosine kinase inhibitors (TKIs), alone and in combination with a panel of selective PI3K/Akt/mTOR inhibitors, on three NUP214-ABL1 positive T-ALL cell lines that also displayed PI3K/Akt/mTOR activation. Cells were sensitive to anti BCR-ABL1 TKIs Imatinib, Nilotinib and GZD824, that specifically targeted the ABL1 fusion protein, but not the PI3K/Akt/mTOR axis. Four drugs against the PI3K/Akt/mTOR cascade, GSK690693, NVP-BGT226, ZSTK474 and Torin-2, showed marked cytotoxic effects on T-leukemic cells, without affecting the NUP214-ABL1 kinase and related pathway. Dephosphorylation of pAkt and pS6 showed the cytotoxicity of these compounds. Either single or combined administration of drugs against the different targets displayed inhibition of cellular viability associated with a concentration-dependent induction of apoptosis, cell cycle arrest in G0/G1 phase and autophagy, having the combined treatments a significant synergistic cytotoxic effect. Co-targeting NUP214-ABL1 fusion gene and PI3K/Akt/mTOR signaling pathway could represent a new and effective pharmacological strategy to improve the outcome in NUP214-ABL1 positive T-ALL.

Chibby 1: a new component of β-catenin-signaling in chronic myeloid leukemia

Chibby 1 (CBY1) is a small and evolutionarily conserved protein, which act as β-catenin antagonist. CBY1 is encoded by C22orf2 (22q13.1) Its antagonistic function on β-catenin involves the direct interaction with:

The C-terminal activation domain of β-catenin, which hinders β-catenin binding with Tcf/Lef transcription factors hence repressing β-catenin transcriptional activation.

14-3-3 scaffolding proteins (σ or ξ), which drive CBY1 nuclear export into a stable tripartite complex with β-catenin.

The relative proximity of C22orf2 gene encoding for CBY1 to the BCR breakpoint on chromosome 22q11, whose translocation and rearrangement with the c-ABL is the causative event of chronic myeloid leukemia (CML), suggested that gene haploinsufficiency may play a role in the disease pathogenesis and progression. We found CBY1 down-modulation associated with the BCR-ABL1, promoted by transcriptional mechanisms (promoter hyper-methylation) and post-transcriptional events, addressing the protein towards proteasome-dependent degradation through SUMOylation. CBY1 reduced expression in clonal progenitors and, more importantly, in leukemic stem cells (LSC), is contingent upon the tyrosine kinase (TK) activity of BCR-ABL1 fusion protein. Accordingly, its induction by Imatinib (IM) and second generation TK inhibitors contributes to β-catenin inactivation through multiple events encompassing the activation of endoplasmic reticulum (ER) stress-associated unfolded protein response (UPR) and autophagy, eventually leading to apoptotic death. These findings support the advantage of combined regimens including drugs targeting DNA epigenetics and/or proteasome to eradicate the BCR-ABL1+ hematopoiesis.

Assessing Autophagic Flux by Measuring LC3, p62, and LAMP1 Co-localization Using Multispectral Imaging Flow Cytometry

Autophagy is a catabolic pathway in which normal or dysfunctional cellular components that accumulate during growth and differentiation are degraded via the lysosome and are recycled. During autophagy, cytoplasmic LC3 protein is lipidated and recruited to the autophagosomal membranes. The autophagosome then fuses with the lysosome to form the autolysosome, where the breakdown of the autophagosome vesicle and its contents occurs. The ubiquitin-associated protein p62, which binds to LC3, is also used to monitor autophagic flux. Cells undergoing autophagy should demonstrate the co-localization of p62, LC3, and lysosomal markers. Immunofluorescence microscopy has been used to visually identify LC3 puncta, p62, and/or lysosomes on a per-cell basis. However, an objective and statistically rigorous assessment can be difficult to obtain. To overcome these problems, multispectral imaging flow cytometry was used along with an analytical feature that compares the bright detail images from three autophagy markers (LC3, p62 and lysosomal LAMP1) and quantifies their co-localization, in combination with LC3 spot counting to measure autophagy in an objective, quantitative, and statistically robust manner.

Hydroxychloroquine sensitizes chronic myeloid leukemia cells to Vγ9Vδ2 T cell-mediated lysis independent of autophagy

Hydroxychloroquine (HCQ) is the only autophagy inhibitor in clinical use and it has shown great potential in treating chronic myeloid leukemia (CML). By inhibiting autophagy, HCQ enhances the anti-CML efficiency of chemotherapy. In the present study, we demonstrated that HCQ sensitized CML cells to Vγ9Vδ2 T cell-mediated lysis. HCQ inhibited autophagy in CML cells, but the sensitizing effects of HCQ were autophagy-independent. Since the sensitization was not mimicked by ATG7 knockdown and even occurred in the absence of ATG7. We revealed that in a time-dependent manner HCQ induced the expression of NKG2D ligand ULBP4 on the surface of CML cells. This marks the leukemia cell for recognition by Vγ9Vδ2 T cells. Blocking the interaction of NKG2D with its ligands deleted the sensitizing effects of HCQ. In addition, we showed that HCQ did not affect the synthesis or degradation of ULBP4, but induced the translocation of ULBP4 from the cytoplasm to the cell membrane. Our results uncovered a previously unknown mechanism for HCQ in CML treatment that underlines the ability of HCQ to modulate the immune visibility of CML cells, and pave the way to the development of new combination treatments with HCQ and Vγ9Vδ2 T cells.

A novel AHI-1-BCR-ABL-DNM2 complex regulates leukemic properties of primitive CML cells through enhanced cellular endocytosis and ROS-mediated autophagy

Tyrosine kinase inhibitor (TKI) therapies induce clinical remission with remarkable effects on chronic myeloid leukemia (CML). However, very few TKIs completely eradicate the leukemic clone and persistence of leukemic stem cells (LSCs) remains challenging, warranting new, distinct targets for improved treatments. We demonstrated that the scaffold protein AHI-1 is highly deregulated in LSCs and interacts with multiple proteins, including Dynamin-2 (DNM2), to mediate TKI-resistance of LSCs. We have now demonstrated that the SH3 domain of AHI-1 and the proline rich domain of DNM2 are mainly responsible for this interaction. DNM2 expression was significantly increased in CML stem/progenitor cells; knockdown of DNM2 greatly impaired their survival and sensitized them to TKI treatments. Importantly, a new AHI-1-BCR-ABL-DNM2 protein complex was uncovered, which regulates leukemic properties of these cells through a unique mechanism of cellular endocytosis and ROS-mediated autophagy. Thus, targeting this complex may facilitate eradication of LSCs for curative therapies.

The autophagy interaction network of the aging model Podospora anserina

BACKGROUND

Autophagy is a conserved molecular pathway involved in the degradation and recycling of cellular components. It is active either as response to starvation or molecular damage. Evidence is emerging that autophagy plays a key role in the degradation of damaged cellular components and thereby affects aging and lifespan control. In earlier studies, it was found that autophagy in the aging model Podospora anserina acts as a longevity assurance mechanism. However, only little is known about the individual components controlling autophagy in this aging model. Here, we report a biochemical and bioinformatics study to detect the protein-protein interaction (PPI) network of P. anserina combining experimental and theoretical methods.

RESULTS

We constructed the PPI network of autophagy in P. anserina based on the corresponding networks of yeast and human. We integrated PaATG8 interaction partners identified in an own yeast two-hybrid analysis using ATG8 of P. anserina as bait. Additionally, we included age-dependent transcriptome data. The resulting network consists of 89 proteins involved in 186 interactions. We applied bioinformatics approaches to analyze the network topology and to prove that the network is not random, but exhibits biologically meaningful properties. We identified hub proteins which play an essential role in the network as well as seven putative sub-pathways, and interactions which are likely to be evolutionary conserved amongst species. We confirmed that autophagy-associated genes are significantly often up-regulated and co-expressed during aging of P. anserina.

CONCLUSIONS

With the present study, we provide a comprehensive biological network of the autophagy pathway in P. anserina comprising PPI and gene expression data. It is based on computational prediction as well as experimental data. We identified sub-pathways, important hub proteins, and evolutionary conserved interactions. The network clearly illustrates the relation of autophagy to aging processes and enables further specific studies to understand autophagy and aging in P. anserina as well as in other systems.

Autophagy is dispensable for Kmt2a/Mll-Mllt3/Af9 AML maintenance and anti-leukemic effect of chloroquine

Recently, macroautophagy/autophagy has emerged as a promising target in various types of solid tumor treatment. However, the impact of autophagy on acute myeloid leukemia (AML) maintenance and the validity of autophagy as a viable target in AML therapy remain unclear. Here we show that Kmt2a/Mll-Mllt3/Af9 AML (MA9-AML) cells have high autophagy flux compared with normal bone marrow cells, but autophagy-specific targeting, either through Rb1cc1-disruption to abolish autophagy initiation, or via Atg5-disruption to prevent phagophore (the autophagosome precursor) membrane elongation, does not affect the growth or survival of MA9-AML cells, either in vitro or in vivo. Mechanistically, neither Atg5 nor Rb1cc1 disruption impairs endolysosome formation or survival signaling pathways. The autophagy inhibitor chloroquine shows autophagy-independent anti-leukemic effects in vitro but has no efficacy in vivo likely due to limited achievable drug efficacy in blood. Further, vesicular exocytosis appears to mediate chloroquine resistance in AML cells, and exocytotic inhibition significantly enhances the anti-leukemic effect of chloroquine. Thus, chloroquine can induce leukemia cell death in vitro in an autophagy-independent manner but with inadequate efficacy in vivo, and vesicular exocytosis is a possible mechanism of chloroquine resistance in MA9-AML. This study also reveals that autophagy-specific targeting is unlikely to benefit MA9-AML therapy.