Autophagy Inhibition Dysregulates TBK1 Signaling and Promotes Pancreatic Inflammation

Integrating bioengineering, super-resolution microscopy and mechanobiology in autophagy research: addendum to the guidelines (4th edition)

Recent key technological developments, such as super-resolution microscopy and microfabrication, enabled investigation of biological processes, including macroautophagy/autophagy, with unprecedented spatiotemporal resolution and control over experimental conditions. Such disruptive innovations deepened our capability to provide mechanistic understandings of the autophagic process and its causes. This addendum aims to expand the guidelines on autophagy in three key directions: optical methods enabling visualization of autophagic machinery beyond the diffraction-limited resolution; bioengineering enabling accurate designs and control over experimental conditions; and theoretical advances in mechanobiology connecting autophagy and mechanical processes of the cell. Abbreviation: 3D: three-dimensional; SIM: structured illumination microscopy; STORM: stochastic optical reconstruction microscopy.

Unveiling the physiological impact of ESCRT-dependent autophagosome closure by targeting the VPS37A ubiquitin E2 variant-like domain

Macroautophagy (autophagy) involves the formation of phagophores that mature into autophagosomes. The impact of inhibiting autophagosome closure remains unclear. Here, we report the generation and analysis of mice with impaired autophagosome closure by targeting the ubiquitin E2 variant-like (UEVL) β strands of the endosomal sorting complex required for transport (ESCRT) I subunit VPS37A. The VPS37A UEVL mutation (Δ43-139) impairs bulk autophagic flux without disrupting ESCRT-I complex assembly and endosomal function. Homozygous mutant mice exhibit signs of autophagy impairment, including p62/SQSTM1 and ubiquitinated protein accumulation, neuronal dysfunction, growth retardation, antioxidant gene upregulation, and tissue abnormalities. However, about half of the mutant neonates survive to adulthood without severe liver injury. LC3 proximity proteomics reveals that the VPS37A UEVL mutation leads to active TANK-binding kinase 1 (TBK1) accumulation on phagophores, resulting in increased p62 phosphorylation and inclusion formation. These findings reveal a previously unappreciated role of LC3-conjugated phagophores in facilitating protein aggregation and sequestration, potentially alleviating proteotoxicity.

Mechanism of TBK1 activation in cancer cells

TANK-binding kinase 1 (TBK1) is a serine/threonine kinase with well-established roles as a central player in innate immune signaling. Dysregulation of TBK1 activity has been implicated in a variety of pathophysiologic conditions, including cancer. Generally, TBK1 acts as an oncogene and increased TBK1 activity, indicated by increased phosphorylation at the Ser172 residue, can be observed in multiple human cancers. TBK1 can be activated either by autophosphorylation of Ser172 or transphosphorylation at this site by upstream kinases. Serving as a hub for integrating numerous extracellular and intracellular signals, TBK1 can be activated through multiple signaling pathways. However, the direct upstream kinase responsible for TBK1 activation remains elusive, which limits our comprehensive understanding of its activation mechanism and potential therapeutic application targeting TBK1-related signaling especially in cancer. In this review, we summarize the findings on mechanisms of TBK1 activation in cancer cells and recent discoveries that shed light on the direct upstream kinases promoting TBK1 activation.

Tumour-associated neutrophils: Potential therapeutic targets in pancreatic cancer immunotherapy

Pancreatic cancer (PC) is a highly malignant tumour of the digestive system with poor therapeutic response and low survival rates. Immunotherapy has rapidly developed in recent years and has achieved significant outcomes in numerous malignant neoplasms. However, responses to immunotherapy in PC are rare, and the immunosuppressive and desmoplastic tumour microenvironment (TME) significantly hinders their efficacy in PC. Tumour-associated neutrophils (TANs) play a crucial role in the PC microenvironment and exert a profound influence on PC immunotherapy by establishing a robust stromal shelter and restraining immune cells to assist PC cells in immune escape, which may subvert the current status of PC immunotherapy. The present review aims to offer a comprehensive summary of the latest progress in understanding the involvement of TANs in PC desmoplastic and immunosuppressive functions and to emphasise the potential therapeutic implications of focusing on TANs in the immunotherapy of this deleterious disease. Finally, we provide an outlook for the future use of TANs in PC immunotherapy.

Fundamental insights and molecular interactions in pancreatic cancer: Pathways to therapeutic approaches

The gastrointestinal tract can be affected by a number of diseases that pancreatic cancer (PC) is a malignant manifestation of them. The prognosis of PC patients is unfavorable and because of their diagnosis at advanced stage, the treatment of this tumor is problematic. Owing to low survival rate, there is much interest towards understanding the molecular profile of PC in an attempt in developing more effective therapeutics. The conventional therapeutics for PC include surgery, chemotherapy and radiotherapy as well as emerging immunotherapy. However, PC is still incurable and more effort should be performed. The molecular landscape of PC is an underlying factor involved in increase in progression of tumor cells. In the presence review, the newest advances in understanding the molecular and biological events in PC are discussed. The dysregulation of molecular pathways including AMPK, MAPK, STAT3, Wnt/β-catenin and non-coding RNA transcripts has been suggested as a factor in development of tumorigenesis in PC. Moreover, cell death mechanisms such as apoptosis, autophagy, ferroptosis and necroptosis demonstrate abnormal levels. The EMT and glycolysis in PC cells enhance to ensure their metastasis and proliferation. Furthermore, such abnormal changes have been used to develop corresponding pharmacological and nanotechnological therapeutics for PC.

Activin A signaling stimulates neutrophil activation and macrophage migration in pancreatitis

Acute Pancreatitis (AP) is associated with high mortality and current treatment options are limited to supportive care. We found that blockade of activin A (activin) in mice improves outcomes in two murine models of AP. To test the hypothesis that activin is produced early in response to pancreatitis and is maintained throughout disease progression to stimulate immune cells, we first performed digital spatial profiling (DSP) of human chronic pancreatitis (CP) patient tissue. Then, transwell migration assays using RAW264.7 mouse macrophages and qPCR analysis of "neutrophil-like" HL-60 cells were used for functional correlation. Immunofluorescence and western blots on cerulein-induced pancreatitis samples from pancreatic acinar cell-specific Kras knock-in (Ptf1aCreER™; LSL-KrasG12D) and functional WT Ptf1aCreER™ mouse lines mimicking AP and CP to allow for in vivo confirmation. Our data suggest activin promotes neutrophil and macrophage activation both in situ and in vitro, while pancreatic activin production is increased as early as 1 h in response to pancreatitis and is maintained throughout CP in vivo. Taken together, activin is produced early in response to pancreatitis and is maintained throughout disease progression to promote neutrophil and macrophage activation.

The Pathogenesis of Pancreatitis and the Role of Autophagy

The pathogenesis of acute and chronic pancreatitis has recently evolved as new findings demonstrate a complex mechanism operating through various pathways. In this review, the current evidence indicating that several mechanisms act in concert to induce and perpetuate pancreatitis were presented. As autophagy is now considered a fundamental mechanism in the pathophysiology of both acute and chronic pancreatitis, the fundamentals of the autophagy pathway were discussed to allow for a better understanding of the pathophysiological mechanisms of pancreatitis. The various aspects of pathogenesis, including trypsinogen activation, ER stress and mitochondrial dysfunction, the implications of inflammation, and macrophage involvement in innate immunity, as well as the significance of pancreatic stellate cells in the development of fibrosis, were also analyzed. Recent findings on exosomes and the miRNA regulatory role were also presented. Finally, the role of autophagy in the protection and aggravation of pancreatitis and possible therapeutic implications were reviewed.

Deciphering JAK/STAT signaling pathway: A multifaceted approach to tumorigenesis, progression and therapeutic interventions

The Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway, essential for cellular communication, orchestrates a myriad of physiological and pathological processes. Recently, the intricate association between the pathway's dysregulation and the progression of malignant tumors has garnered increasing attention. Nevertheless, there is no systematic summary detailing the anticancer effects of molecules targeting the JAK/STAT pathway in the context of tumor progression. This review offers a comprehensive overview of pharmaceutical agents targeting the JAK/STAT pathway, encompassing phytochemicals, synthetic drugs, and biomolecules. These agents can manifest their anticancer effects through various mechanisms, including inhibiting proliferation, inducing apoptosis, suppressing tumor metastasis, and angiogenesis. Notably, we emphasize the clinical challenges of drug resistance while spotlighting the potential of integrating JAK/STAT inhibitors with other therapies as a transformative approach in cancer treatment. Moreover, this review delves into the avant-garde strategy of employing nanocarriers to enhance the solubility and bioavailability of anticancer drugs, significantly amplifying their therapeutic prowess. Through this academic exploration of the multifaceted roles of the JAK/STAT pathway in the cancer milieu, we aim to sketch a visionary trajectory for future oncological interventions.

TRPM2-dependent autophagy inhibition exacerbates oxidative stress-induced CXCL16 secretion by keratinocytes in vitiligo

Vitiligo is a depigmented skin disease due to the destruction of melanocytes. Under oxidative stress, keratinocyte-derived chemokine C-X-C motif ligand 16 (CXCL16) plays a critical role in recruiting CD8+ T cells, which kill melanocytes. Autophagy serves as a protective cell survival mechanism and impairment of autophagy has been linked to increased secretion of the proinflammatory cytokines. However, the role of autophagy in the secretion of CXCL16 under oxidative stress has not been investigated. Herein, we initially found that autophagy was suppressed in both keratinocytes of vitiligo lesions and keratinocytes exposed to oxidative stress in vitro. Autophagy inhibition also promoted CXCL16 secretion. Furthermore, upregulated transient receptor potential cation channel subfamily M member 2 (TRPM2) functioned as an upstream oxidative stress sensor to inhibit autophagy. Moreover, TRPM2-mediated Ca2+ influx activated calpain to shear autophagy related 5 (Atg5) and Atg12-Atg5 conjugate formation was blocked to inhibit autophagy under oxidative stress. More importantly, Atg5 downregulation enhanced the binding of interferon regulatory factor 3 (IRF3) to the CXCL16 promoter region by activating Tank-binding kinase 1 (TBK1), thus promoting CXCL16 secretion. These findings suggested that TRPM2-restrained autophagy promotes CXCL16 secretion via the Atg5-TBK1-IRF3 signaling pathway under oxidative stress. Inhibition of TRPM2 may serve as a potential target for the treatment of vitiligo. © 2024 The Pathological Society of Great Britain and Ireland.

Immune checkpoints between epithelial-mesenchymal transition and autophagy: A conflicting triangle

Inhibitory immune checkpoint (ICP) molecules are pivotal in inhibiting innate and acquired antitumor immune responses, a mechanism frequently exploited by cancer cells to evade host immunity. These evasion strategies contribute to the complexity of cancer progression and therapeutic resistance. For this reason, ICP molecules have become targets for antitumor drugs, particularly monoclonal antibodies, collectively referred to as immune checkpoint inhibitors (ICI), that counteract such cancer-associated immune suppression and restore antitumor immune responses. Over the last decade, however, it has become clear that tumor cell-associated ICPs can also induce tumor cell-intrinsic effects, in particular epithelial-mesenchymal transition (EMT) and macroautophagy (hereafter autophagy). Both of these processes have profound implications for cancer metastasis and drug responsiveness. This article reviews the positive or negative cross-talk that tumor cell-associated ICPs undergo with autophagy and EMT. We discuss that tumor cell-associated ICPs are upregulated in response to the same stimuli that induce EMT. Moreover, ICPs themselves, when overexpressed, become an EMT-inducing stimulus. As regards the cross-talk with autophagy, ICPs have been shown to either stimulate or inhibit autophagy, while autophagy itself can either up- or downregulate the expression of ICPs. This dynamic equilibrium also extends to the autophagy-apoptosis axis, further emphasizing the complexities of cellular responses. Eventually, we delve into the intricate balance between autophagy and apoptosis, elucidating its role in the broader interplay of cellular dynamics influenced by ICPs. In the final part of this article, we speculate about the driving forces underlying the contradictory outcomes of the reciprocal, inhibitory, or stimulatory effects between ICPs, EMT, and autophagy. A conclusive identification of these driving forces may allow to achieve improved antitumor effects when using combinations of ICIs and compounds acting on EMT and/or autophagy. Prospectively, this may translate into increased and/or broadened therapeutic efficacy compared to what is currently achieved with ICI-based clinical protocols.

Exploiting autophagy balance in T and NK cells as a new strategy to implement adoptive cell therapies

Autophagy is an essential cellular homeostasis pathway initiated by multiple stimuli ranging from nutrient deprivation to viral infection, playing a key role in human health and disease. At present, a growing number of evidence suggests a role of autophagy as a primitive innate immune form of defense for eukaryotic cells, interacting with components of innate immune signaling pathways and regulating thymic selection, antigen presentation, cytokine production and T/NK cell homeostasis. In cancer, autophagy is intimately involved in the immunological control of tumor progression and response to therapy. However, very little is known about the role and impact of autophagy in T and NK cells, the main players in the active fight against infections and tumors. Important questions are emerging: what role does autophagy play on T/NK cells? Could its modulation lead to any advantages? Could specific targeting of autophagy on tumor cells (blocking) and T/NK cells (activation) be a new intervention strategy? In this review, we debate preclinical studies that have identified autophagy as a key regulator of immune responses by modulating the functions of different immune cells and discuss the redundancy or diversity among the subpopulations of both T and NK cells in physiologic context and in cancer.

The Distinct Properties of Polysaccharide Nanoparticles Tune Immune Responses against mRNA Antigen via Stimulator of Interferon Genes-Mediated Autophagy and Inflammasome

mRNA antigens require powerful nanocarriers for efficient delivery, as well as immunomodulators for controlling their excessive immunogenicity. While lipid nanoparticles (LNPs) used in mRNA vaccines exhibited systemic toxicity, there is an urgent need for developing potential nanoparticles with strong immunoenhancing effects for mRNA antigens. Although natural polysaccharides as adjuvants assisted various types of antigens in triggering potent immune responses, they have been rarely investigated in mRNA vaccines. Here, we constructed four polysaccharide nanoparticles with different molecular weights (MWs) to deliver and protect mRNA antigens, and boosted antigen cross-presentation, DC maturation, CD4+/CD8+T cell responses and humoral immune responses. Importantly, the immunoenhancing capacities of polysaccharide nanoparticles were highly dependent on their MW properties. CS NPs with high MW initiated stimulator of interferon genes (STING)-mediated autophagy and NOD-like receptor thermal protein domain associated protein 3 (NLRP3) inflammasome signaling, consequently possessing superior mRNA antigen-specific immune responses in vitro and in vivo. In contrast, CS NPs with low MWs induced NLRP3 signaling without STING or autophagy activation, which failed to induce robust immune responses. Therefore, it uncovered the MW-dependent immunoenhancing effects and mechanism of polysaccharide nanoparticles, providing a platform for designing potential nanosized polysaccharide immunomodulators for mRNA vaccines.

Antitumor mechanism of Saikosaponin A in the Xiaoying Sanjie Decoction for treatment of anaplastic thyroid cancer by network pharmacology analysis and experiments in vitro and in vivo

Effective therapies for anaplastic thyroid cancer (ATC) are still limited due to its dedifferentiated phenotype and high invasiveness. Xiaoying Sanjie Decoction (XYSJD), a clinically empirical Chinese medicine compound, has shown positive effects for ATC treatment and recovery. However, the pharmacological mechanisms of effective active compound in XYSJD remain unclear. In this study, we aimed at elucidating the antitumor mechanism of the active compound and identifying the kernel molecular mechanisms of XYSJD against ATC. Firstly, the main chemical constituents of XYSJD were identified by ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS). Then we used network pharmacology and ClusterONE algorithm to analyze the possible targets and pathways of the prescription and active compound Saikosaponin A (SSA). Seven core targets, including P2RY12, PDK1, PPP1CC, PPP2CA, TBK1, ITGB1 and ITGB6, which may be involved in the anti-tumor activity of XYSJD were screened. Finally, using cell biology, molecular biology and experimental zoology techniques, we investigated the mechanism of active compound SSA in the treatment of ATC. The results of qRT-PCR indicated that these seven nuclear targets might play an important role in SSA, the active compound of XYSJD. The combined data provide preliminary study of the pharmacological mechanisms of SSA in XYSJD. SSA may be a promising potential therapeutic and chemopreventive candidate for ATC.

RAS signaling and immune cells: a sinister crosstalk in the tumor microenvironment

The rat sarcoma virus (RAS) gene is the most commonly mutated oncogene in cancer, with about 19% of cancer patients carrying RAS mutations. Studies on the interaction between RAS mutation and tumor immune microenvironment (TIM) have been flourishing in recent years. More and more evidence has proved that RAS signals regulate immune cells' recruitment, activation, and differentiation while assisting tumor cells to evade immune surveillance. This review concluded the direct and indirect treatment strategies for RAS mutations. In addition, we updated the underlying mechanisms by which RAS signaling modulated immune infiltration and immune escape. Finally, we discussed advances in RAS-targeted immunotherapies, including cancer vaccines and adoptive cell therapies, with a particular focus on combination strategies with personalized therapy and great potential to achieve lasting clinical benefits.

Constitutively active autophagy in macrophages dampens inflammation through metabolic and post-transcriptional regulation of cytokine production

Autophagy is an essential cellular process that is deeply integrated with innate immune signaling; however, studies that examine the impact of autophagic modulation in the context of inflammatory conditions are lacking. Here, using mice with a constitutively active variant of the autophagy gene Beclin1, we show that increased autophagy dampens cytokine production during a model of macrophage activation syndrome and in adherent-invasive Escherichia coli (AIEC) infection. Moreover, loss of functional autophagy through conditional deletion of Beclin1 in myeloid cells significantly enhances innate immunity in these contexts. We further analyzed primary macrophages from these animals with a combination of transcriptomics and proteomics to identify mechanistic targets downstream of autophagy. Our study reveals glutamine/glutathione metabolism and the RNF128/TBK1 axis as independent regulators of inflammation. Altogether, our work highlights increased autophagic flux as a potential approach to reduce inflammation and defines independent mechanistic cascades involved in this control.

Emerging applications of cancer bacteriotherapy towards treatment of pancreatic cancer

Pancreatic cancer is a highly aggressive form of cancer with a five-year survival rate of only ten percent. Pancreatic ductal adenocarcinoma (PDAC) accounts for ninety percent of those cases. PDAC is associated with a dense stroma that confers resistance to current treatment modalities. Increasing resistance to cancer treatments poses a challenge and a need for alternative therapies. Bacterial mediated cancer therapies were proposed in the late 1800s by Dr. William Coley when he injected osteosarcoma patients with live streptococci or a fabrication of heat-killed Streptococcus pyogenes and Serratia marcescens known as Coley's toxin. Since then, several bacteria have gained recognition for possible roles in potentiating treatment response, enhancing anti-tumor immunity, and alleviating adverse effects to standard treatment options. This review highlights key bacterial mechanisms and structures that promote anti-tumor immunity, challenges and risks associated with bacterial mediated cancer therapies, and applications and opportunities for use in PDAC management.

Association between autophagy and acute pancreatitis

Autophagy pathway involves maintaining intracellular homeostasis by regulating the degradation of cytoplasmic components. Disfunction of autophagic process has been confirmed to be critical mechanism in many diseases, including cancer, inflammation, infection, degeneration and metabolic disorders. Recent studies have shown that autophagy is one of the early events in acute pancreatitis. Impaired autophagy promotes the abnormal activation of zymogen granules and results in apoptosis and necrosis of exocrine pancreas. Furthermore, multiple signal paths involve progression of acute pancreatitis by regulating autophagy pathway. This article provides a comprehensive review of the recent advances in epigenetic regulation of autophagy and the role of autophagy in acute pancreatitis.

Identification of Small GTPases That Phosphorylate IRF3 through TBK1 Activation Using an Active Mutant Library Screen

Interferon regulatory factor 3 (IRF3) integrates both immunological and non-immunological inputs to control cell survival and death. Small GTPases are versatile functional switches that lie on the very upstream in signal transduction pathways, of which duration of activation is very transient. The large number of homologous proteins and the requirement for site-directed mutagenesis have hindered attempts to investigate the link between small GTPases and IRF3. Here, we constructed a constitutively active mutant expression library for small GTPase expression using Gibson assembly cloning. Small-scale screening identified multiple GTPases capable of promoting IRF3 phosphorylation. Intriguingly, 27 of 152 GTPases, including ARF1, RHEB, RHEBL1, and RAN, were found to increase IRF3 phosphorylation. Unbiased screening enabled us to investigate the sequence-activity relationship between the GTPases and IRF3. We found that the regulation of IRF3 by small GTPases was dependent on TBK1. Our work reveals the significant contribution of GTPases in IRF3 signaling and the potential role of IRF3 in GTPase function, providing a novel therapeutic approach against diseases with GTPase overexpression or active mutations, such as cancer.

Autophagy in Cancer Immunotherapy

Autophagy is a stress-induced process that eliminates damaged organelles and dysfunctional cargos in cytoplasm, including unfolded proteins. Autophagy is involved in constructing the immunosuppressive microenvironment during tumor initiation and progression. It appears to be one of the most common processes involved in cancer immunotherapy, playing bidirectional roles in immunotherapy. Accumulating evidence suggests that inducing or inhibiting autophagy contributes to immunotherapy efficacy. Hence, exploring autophagy targets and their modifiers to control autophagy in the tumor microenvironment is an emerging strategy to facilitate cancer immunotherapy. This review summarizes recent studies on the role of autophagy in cancer immunotherapy, as well as the molecular targets of autophagy that could wake up the immune response in the tumor microenvironment, aiming to shed light on its immense potential as a therapeutic target to improve immunotherapy.

Autophagy blockade potentiates cancer-associated immunosuppression through programmed death ligand-1 upregulation in bladder cancer

A high basal level of autophagic flux in bladder cancer (BC) cells prevents cell death and weakens chemotherapy efficacy. However, how autophagy influences cancer-associated immunosuppression in BC remains undetermined. In this study, we observed a negative correlation between the autophagy-related markers LC3-II and programmed death ligand-1 (PD-L1) in BC cells. The autophagy inhibitors chloroquine (CQ) and bafilomycin A1 (Baf-A1) increased PD-L1 expression in BC cells through the ERK-JNK-c-Jun signal-transduction pathway. Moreover, the treatment of BC cells with CQ and Baf-A1 inhibited hsa-microRNA-34a (miR-34a) expression and miR-34a overexpression in BC cells prevented the autophagy blockade-induced PD-L1 expression; a negative correlation between miR-34a and PD-L1 expression was observed during treatment with autophagy inhibitors. Furthermore, miR-34a overexpression induced the cytotoxic activity of natural killer cells against BC cells. Our results provide evidence that autophagy blockade and its regulatory pathway affect cancer-associated immunosuppression through PD-L1 elevation. Thus, the coadministration of autophagy inhibitors and a PD-L1 immune checkpoint blockade provides a potential therapeutic approach for treating BC.

TBK1 is part of a galectin 8 dependent membrane damage recognition complex and drives autophagy upon Adenovirus endosomal escape

Intracellular pathogens cause membrane distortion and damage as they enter host cells. Cells perceive these membrane alterations as danger signals and respond by activating autophagy. This response has primarily been studied during bacterial invasion, and only rarely in viral infections. Here, we investigate the cellular response to membrane damage during adenoviral entry. Adenoviruses and their vector derivatives, that are an important vaccine platform against SARS-CoV-2, enter the host cell by endocytosis followed by lysis of the endosomal membrane. We previously showed that cells mount a locally confined autophagy response at the site of endosomal membrane lysis. Here we describe the mechanism of autophagy induction: endosomal membrane damage activates the kinase TBK1 that accumulates in its phosphorylated form at the penetration site. Activation and recruitment of TBK1 require detection of membrane damage by galectin 8 but occur independently of classical autophagy receptors or functional autophagy. Instead, TBK1 itself promotes subsequent autophagy that adenoviruses need to take control of. Deletion of TBK1 reduces LC3 lipidation during adenovirus infection and restores the infectivity of an adenovirus mutant that is restricted by autophagy. By comparing adenovirus-induced membrane damage to sterile lysosomal damage, we implicate TBK1 in the response to a broader range of types of membrane damage. Our study thus highlights an important role for TBK1 in the cellular response to adenoviral endosome penetration and places TBK1 early in the pathway leading to autophagy in response to membrane damage.

Rapid detection of invading pathogens is crucial for cell survival. Membrane alterations in this process are detected by cells but are rarely studied in the context of viral infections. TBK1 is an important kinase driving innate immunity and autophagy in response to pathogen invasion. Here we report that TBK1 promotes autophagy in response to membrane penetration by adenoviruses. We demonstrate that TBK1 is rapidly activated and recruited to virus membrane penetration sites, and promotes autophagy through its kinase activity. We show that TBK1 recruitment depends on membrane damage recognition via galectin 8 but occurs independently of classical autophagy receptors or functional autophagy. Moreover, we demonstrate that TBK1 activation is part of a wider cellular response to endo-lysosomal damage. Our work highlights a prominent role for TBK1 in the swift cellular response to membrane damage and the downstream activation of autophagy.

Novel Effects of Statins on Cancer via Autophagy

Cancer is one of the main causes of death globally. Most of the molecular mechanisms underlying cancer are marked by complex aberrations that activate the critical cell-signaling pathways that play a pivotal role in cell metabolism, tumor development, cytoskeletal reorganization, and metastasis. The phosphatidylinositol 3-kinase/protein kinase-B/mammalian target of the rapamycin (PI3K/AKT/mTOR) pathway is one of the main signaling pathways involved in carcinogenesis and metastasis. Autophagy, a cellular pathway that delivers cytoplasmic components to lysosomes for degradation, plays a dual role in cancer, as either a tumor promoter or a tumor suppressor, depending on the stage of the carcinogenesis. Statins are the group of drugs of choice to lower the level of low-density lipoprotein (LDL) cholesterol in the blood. Experimental and clinical data suggest the potential of statins in the treatment of cancer. In vitro and in vivo studies have demonstrated the molecular mechanisms through which statins inhibit the proliferation and metastasis of cancer cells in different types of cancer. The anticancer properties of statins have been shown to result in the suppression of tumor growth, the induction of apoptosis, and autophagy. This literature review shows the dual role of the autophagic process in cancer and the latest scientific evidence related to the inducing effect exerted by statins on autophagy, which could explain their anticancer potential.

Identification of 1H-pyrazolo[3,4-b]pyridine derivatives as novel and potent TBK1 inhibitors: design, synthesis, biological evaluation, and molecular docking study

TANK-binding kinase 1 (TBK1), a noncanonical member of the inhibitor-kappaB kinases (IKKs) family, plays a vital role in coordinating the signalling pathways of innate immunity, involving in the process of neuroinflammation, autophagy, and oncogenesis. In current study, based on rational drug design strategy, we discovered a series of 1H-pyrazolo[3,4-b]pyridine derivatives as potent TBK1 inhibitors and dissected the structure–activity relationships (SARs). Through the several rounds of optimisation, compound 15y stood out as a potent inhibitor on TBK1 with an IC₅₀ value of 0.2 nM and also displayed good selectivity. The mRNA detection of TBK1 downstream genes showed that compound 15y effectively inhibited TBK1 downstream IFN signalling in stimulated THP-1 and RAW264.7 cells. Meanwhile, compound 15y exhibited a micromolar antiproliferation effect on A172, U87MG, A375, A2058, and Panc0504 cell lines. Together, current results provided a promising TBK1 inhibitor 15y as lead compound for immune- and cancer-related drug discovery.

Therapeutic targeting of TANK-binding kinase signaling towards anticancer drug development: Challenges and opportunities

TANK-binding kinase 1 (TBK1) plays a fundamental role in regulating the cellular responses and controlling several signaling cascades. It regulates inflammatory, interferon, NF-κB, autophagy, and Akt pathways. Post-translational modifications (PTM) of TBK1 control its action and subsequent cellular signaling. The dysregulation of the TBK1 pathway is correlated to many pathophysiological conditions, including cancer, that implicates the promising therapeutic advantage for targeting TBK1. The present study summarizes current updates on the molecular mechanisms and cancer-inducing roles of TBK1. Designed inhibitors of TBK1 are considered a potential therapeutic agent for several diseases, including cancer. Data from pre-clinical tumor models recommend that the targeting of TBK1 could be an attractive strategy for anti-tumor therapy. This review further highlighted the therapeutic potential of potent and selective TBK1 inhibitors, including Amlexanox, Compound II, BX795, MRT67307, SR8185 AZ13102909, CYT387, GSK8612, BAY985, and Domainex. These inhibitors may be implicated to facilitate therapeutic management of cancer and TBK1-associated diseases in the future.

Autophagy in cancer cell remodeling and quality control

As one of the two highly conserved cellular degradation systems, autophagy plays a critical role in regulation of protein, lipid, and organelle quality control and cellular homeostasis. This evolutionarily conserved pathway singles out intracellular substrates for elimination via encapsulation within a double-membrane vesicle and delivery to the lysosome for degradation. Multiple cancers disrupt normal regulation of autophagy and hijack its degradative ability to remodel their proteome, reprogram their metabolism, and adapt to environmental challenges, making the autophagy-lysosome system a prime target for anti-cancer interventions. Here, we discuss the roles of autophagy in tumor progression, including cancer-specific mechanisms of autophagy regulation and the contribution of tumor and host autophagy in metabolic regulation, immune evasion, and malignancy. We further discuss emerging proteomics-based approaches for systematic profiling of autophagosome-lysosome composition and contents. Together, these approaches are uncovering new features and functions of autophagy, leading to more effective strategies for targeting this pathway in cancer.

The role of TBK1 in cancer pathogenesis and anticancer immunity

The TANK-binding kinase 1 (TBK1) is a serine/threonine kinase belonging to the non-canonical inhibitor of nuclear factor-κB (IκB) kinase (IKK) family. TBK1 can be activated by pathogen-associated molecular patterns (PAMPs), inflammatory cytokines, and oncogenic kinases, including activated K-RAS/N-RAS mutants. TBK1 primarily mediates IRF3/7 activation and NF-κB signaling to regulate inflammatory cytokine production and the activation of innate immunity. TBK1 is also involved in the regulation of several other cellular activities, including autophagy, mitochondrial metabolism, and cellular proliferation. Although TBK1 mutations have not been reported in human cancers, aberrant TBK1 activation has been implicated in the oncogenesis of several types of cancer, including leukemia and solid tumors with KRAS-activating mutations. As such, TBK1 has been proposed to be a feasible target for pharmacological treatment of these types of cancer. Studies suggest that TBK1 inhibition suppresses cancer development not only by directly suppressing the proliferation and survival of cancer cells but also by activating antitumor T-cell immunity. Several small molecule inhibitors of TBK1 have been identified and interrogated. However, to this point, only momelotinib (MMB)/CYT387 has been evaluated as a cancer therapy in clinical trials, while amlexanox (AMX) has been evaluated clinically for treatment of type II diabetes, nonalcoholic fatty liver disease, and obesity. In this review, we summarize advances in research into TBK1 signaling pathways and regulation, as well as recent studies on TBK1 in cancer pathogenesis. We also discuss the potential molecular mechanisms of targeting TBK1 for cancer treatment. We hope that our effort can help to stimulate the development of novel strategies for targeting TBK1 signaling in future approaches to cancer therapy.

Regulation of Intrinsic Functions of PD-L1 by Post-Translational Modification in Tumors

Tumor cells are eliminated by the immune system, including T lymphocytes and natural killer cells; however, many types of tumor cells acquire the immune tolerance by inhibiting T-cell activation and functions via immune checkpoint molecules. Immunotherapy targeting immune checkpoint molecules such as Programmed death receptor 1 (PD-1)/Programmed death ligand 1 (PD-L1) and cytotoxic T lymphocyte associated protein 4 (CTLA-4) have shown successful outcomes for multiple cancer treatments, however some patients show the lack of durable responses. Thus, discovering the chemical compounds or drugs manipulating the expression or function of immune checkpoint molecules are anticipated to overcome the drug resistance of immune checkpoint inhibitors. Function of inhibitory immune checkpoint molecules is often dysregulated by the transcriptional and post-translational levels in tumors. Here, this review focuses on the post-translational modification of intrinsic PD-L1 functions and regulators for PD-L1 transcription.

The Role of Decorin Proteoglycan in Mitophagy

Proteoglycans are emerging as critical regulators of intracellular catabolism. This rise in prominence has transformed our basic understanding and alerted us to the existence of non-canonical pathways, independent of nutrient deprivation, that potently control the autophagy downstream of a cell surface receptor. As a member of the small leucine-rich proteoglycan gene family, decorin has single-handedly pioneered the connection between extracellular matrix signaling and autophagy regulation. Soluble decorin evokes protracted endothelial cell autophagy via Peg3 and breast carcinoma cell mitophagy via mitostatin by interacting with VEGFR2 or the MET receptor tyrosine kinase, respectively. In this paper, we give a mechanistic perspective of the vital factors underlying the nutrient-independent, SLRP-dependent programs utilized for autophagic and/or mitophagic progression in breast cancer. Future protein therapies based on decorin (or fellow proteoglycan members) will represent a quantum leap forward in transforming autophagic progression into a powerful tool to control intracellular cell catabolism from the outside.

Prkci Regulates Autophagy and Pancreatic Tumorigenesis in Mice

Protein kinase C iota (PKCι) functions as a bonafide human oncogene in lung and ovarian cancer and is required for KrasG12D-mediated lung cancer initiation and progression. PKCι expression is required for pancreatic cancer cell growth and maintenance of the transformed phenotype; however, nothing is known about the role of PKCι in pancreas development or pancreatic tumorigenesis. In this study, we investigated the effect of pancreas-specific ablation of PKCι expression on pancreatic cellular homeostasis, susceptibility to pancreatitis, and KrasG12D-mediated pancreatic cancer development. Knockout of pancreatic Prkci significantly increased pancreatic immune cell infiltration, acinar cell DNA damage, and apoptosis, but reduced sensitivity to caerulein-induced pancreatitis. Prkci-ablated pancreatic acinar cells exhibited P62 aggregation and a loss of autophagic vesicles. Loss of pancreatic Prkci promoted KrasG12D-mediated pancreatic intraepithelial neoplasia formation but blocked progression to adenocarcinoma, consistent with disruption of autophagy. Our results reveal a novel promotive role for PKCι in pancreatic epithelial cell autophagy and pancreatic cancer progression.

Regulation and function of autophagy in pancreatic cancer

Oncogenic KRAS mutation-driven pancreatic ductal adenocarcinoma is currently the fourth-leading cause of cancer-related deaths in the United States. Macroautophagy (hereafter "autophagy") is one of the lysosome-dependent degradation systems that can remove abnormal proteins, damaged organelles, or invading pathogens by activating dynamic membrane structures (e.g., phagophores, autophagosomes, and autolysosomes). Impaired autophagy (including excessive activation and defects) is a pathological feature of human diseases, including pancreatic cancer. However, dysfunctional autophagy has many types and plays a complex role in pancreatic tumor biology, depending on various factors, such as tumor stage, microenvironment, immunometabolic state, and death signals. As a modulator connecting various cellular events, pharmacological targeting of nonselective autophagy may lead to both good and bad therapeutic effects. In contrast, targeting selective autophagy could reduce potential side effects of the drugs used. In this review, we describe the advances and challenges of autophagy in the development and therapy of pancreatic cancer.Abbreviations: AMPK: AMP-activated protein kinase; CQ: chloroquine; csc: cancer stem cells; DAMP: danger/damage-associated molecular pattern; EMT: epithelial-mesenchymal transition; lncRNA: long noncoding RNA; MIR: microRNA; PanIN: pancreatic intraepithelial neoplasia; PDAC: pancreatic ductal adenocarcinoma; PtdIns3K: phosphatidylinositol 3-kinase; SNARE: soluble NSF attachment protein receptor; UPS: ubiquitin-proteasome system.

NF-κB and Pancreatic Cancer; Chapter and Verse

Pancreatic Ductal Adenocarcinoma (PDAC) is one of the world's most lethal cancers. An increase in occurrence, coupled with, presently limited treatment options, necessitates the pursuit of new therapeutic approaches. Many human cancers, including PDAC are initiated by unresolved inflammation. The transcription factor NF-κB coordinates many signals that drive cellular activation and proliferation during immunity but also those involved in inflammation and autophagy which may instigate tumorigenesis. It is not surprising therefore, that activation of canonical and non-canonical NF-κB pathways is increasingly recognized as an important driver of pancreatic injury, progression to tumorigenesis and drug resistance. Paradoxically, NF-κB dysregulation has also been shown to inhibit pancreatic inflammation and pancreatic cancer, depending on the context. A pro-oncogenic or pro-suppressive role for individual components of the NF-κB pathway appears to be cell type, microenvironment and even stage dependent. This review provides an outline of NF-κB signaling, focusing on the role of the various NF-κB family members in the evolving inflammatory PDAC microenvironment. Finally, we discuss pharmacological control of NF-κB to curb inflammation, focussing on novel anti-cancer agents which reinstate the process of cancer cell death, the Smac mimetics and their pre-clinical and early clinical trials.

Metabolic networks in mutant KRAS-driven tumours: tissue specificities and the microenvironment

Oncogenic mutations in KRAS drive common metabolic programmes that facilitate tumour survival, growth and immune evasion in colorectal carcinoma, non-small-cell lung cancer and pancreatic ductal adenocarcinoma. However, the impacts of mutant KRAS signalling on malignant cell programmes and tumour properties are also dictated by tumour suppressor losses and physiological features specific to the cell and tissue of origin. Here we review convergent and disparate metabolic networks regulated by oncogenic mutant KRAS in colon, lung and pancreas tumours, with an emphasis on co-occurring mutations and the role of the tumour microenvironment. Furthermore, we explore how these networks can be exploited for therapeutic gain.

Impact of single amino acid substitution on the structure and function of TANK-binding kinase-1

Tank-binding kinase 1 (TBK1) is a serine/threonine protein kinase involved in various signaling pathways and subsequently regulates cell proliferation, apoptosis, autophagy, antiviral and antitumor immunity. Dysfunction of TBK1 can cause many complex diseases, including autoimmunity, neurodegeneration, and cancer. This dysfunction of TBK1 may result from single amino acid substitutions and subsequent structural alterations. This study analyzed the effect of substituting amino acids on TBK1 structure, function, and subsequent disease using advanced computational methods and various tools. In the initial assessment, a total of 467 mutations were found to be deleterious. After that, in detailed structural and sequential analyses, 13 mutations were found to be pathogenic. Finally, based on the functional importance, two variants (K38D and S172A) of the TBK1 kinase domain were selected and studied in detail by utilizing all-atom molecular dynamics (MD) simulation for 200 ns. MD simulation, including correlation matrix and principal component analysis, helps to get deeper insights into the TBK1 structure at the atomic level. We observed a substantial change in variants' conformation, which may be possible for structural alteration and subsequent TBK1 dysfunction. However, substitution S172A shows a significant conformational change in TBK1 structure as compared to K38D. Thus, this study provides a structural basis to understand the effect of mutations on the kinase domain of TBK1 and its function associated with disease progression.

FIP200 controls the TBK1 activation threshold at SQSTM1/p62-positive condensates

The protein kinase TBK1 is a central regulator of innate immune responses and autophagy, and ablation of either function has been linked to neuroinflammatory or degenerative diseases. Autophagy is an intracellular process that recycles old or damaged proteins and organelles. In recent years, the TBK1-dependent regulation of autophagy pathways has been characterized. However, the autophagy-dependent regulation of TBK1 activity awaits further clarification. Here, we observed that TBK1 is recruited to SQSTM1/p62-containing aggregates via the selective autophagy receptor TAX1BP1. In these aggregates, TBK1 phosphorylates SQSTM1/p62 at serine 403 and thus presumably regulates the efficient engulfment and clearance of these structures. We found that TBK1 activation is strongly increased if FIP200, a component of the autophagy-inducing ULK1 complex, is not present or cannot bind to TAX1BP1. Given our collective findings, we hypothesize that FIP200 ensures the inducible activation of TBK1 at SQSTM1/p62 condensates.

A review on the role of TANK-binding kinase 1 signaling in cancer

TANK-binding kinase 1 (TBK1) regulates various biological processes including, NF-κB signaling, immune response, autophagy, cell division, Ras-mediated oncogenesis, and AKT pro-survival signaling. Enhanced TBK1 activity is associated with autoimmune diseases and cancer, suggesting its role in therapeutic targeting of interferonopathies. In addition, dysregulation of TBK1 activity promotes several inflammatory disorders and oncogenesis. Structural and biochemical study reports provide the molecular process of TBK1 activation and recap the substrate selection about TBK1. This review summarizes recent findings on the molecular mechanisms by which TBK1 is involved in cancer signaling. The IKK-ε and TBK1 are together associated with inflammatory diseases by inducing type I IFNs. Furthermore, TBK1 signaling regulates radiation-induced epithelial-mesenchymal transition by controlling phosphorylation of GSK-3β and expression of Zinc finger E-box-binding homeobox 1, suggesting, TBK1 could be targeted for radiotherapy-induced metastasis therapy. Despite a considerable increase in the list of TBK1 inhibitors, only a few has potential to control cancer. Among them, a compound BX795 is considered a potent and selective inhibitor of TBK1. We discussed the therapeutic potential of small-molecule inhibitors of TBK1, particularly those with high selectivity, which will enable further exploration in the therapeutic management of cancer and inflammatory diseases.

Selective inhibition of soluble TNF using XPro1595 relieves pain and attenuates cerulein-induced pathology in mice

Background

Symptoms associated with acute pancreatitis can be debilitating, and treatment remains a challenge. This study aimed to investigate the efficacy of selectively inhibiting the soluble form of TNF (solTNF) using the biologic XPro1595 in a mouse model of acute pancreatitis.

Methods

Acute pancreatitis was induced in adult male C57Bl/6J mice by administering cerulein (8 injections of 50 µg/kg I.P., spaced an hour apart), with XPro1595 (10 mg/kg, S.C.) or vehicle being administered approximately 18 h after the last injection. Serum was collected 6 or 18 h after the last cerulein injection, pancreatic tissue was collected 2 and 7 days post-induction, and brain hippocampal tissue was collected at 7 days post-induction. The animal’s pain level was assessed 3, 5 and 7 days post-induction.

Results

The induction of acute pancreatitis promoted a strong increase in serum amylase levels, which had receded back to baseline levels by the next morning. XPro1595 treatment began after amylase levels had subsided at 18 h, and prevented pancreatic immune cell infiltration, that subsequently prevented tissue disruption and acinar cell death. These improvements in pathology were associated with a significant reduction in mechanical hypersensitivity (neuropathic pain). XPro1595 treatment also prevented an increase in hippocampal astrocyte reactivity, that may be associated with the prevention of neuropathic pain in this mouse model.

Conclusion

Overall, we observed that selectively inhibiting solTNF using XPro1595 improved the pathophysiological and neurological sequelae of cerulein-induced pancreatitis in mice, which provides support of its use in patients with pancreatitis.

TANK-binding kinase 1 (TBK1): An emerging therapeutic target for drug discovery

Dysregulation of TANK-binding kinase 1 (TBK1) homeostasis leads to the occurrence and progression of many diseases, such as inflammation, autoimmune diseases, metabolic diseases, and cancer. Therefore, there is a need to develop TBK1 inhibitors as therapeutic agents. In this review, we highlight the diverse biological functions of TBK1 and summarize the promising small-molecule inhibitors of TBK1 that have the potential to be developed as therapeutic candidates.

Analysis of Autophagy-Related Signatures Identified Two Distinct Subtypes for Evaluating the Tumor Immune Microenvironment and Predicting Prognosis in Ovarian Cancer

Ovarian cancer (OC) is one of the most lethal gynecologic malignant tumors. The interaction between autophagy and the tumor immune microenvironment has clinical importance. Hence, it is necessary to explore reliable biomarkers associated with autophagy-related genes (ARGs) for risk stratification in OC. Here, we obtained ARGs from the MSigDB database and downloaded the expression profile of OC from TCGA database. The k-means unsupervised clustering method was used for clustering, and two subclasses of OC (cluster A and cluster B) were identified. SsGSEA method was used to quantify the levels of infiltration of 24 subtypes of immune cells. Metascape and GSEA were performed to reveal the differential gene enrichment in signaling pathways and cellular processes of the subtypes. We found that patients in cluster A were significantly associated with higher immune infiltration and immune-associated signaling pathways. Then, we established a risk model by LASSO Cox regression. ROC analysis and Kaplan-Meier analysis were applied for evaluating the efficiency of the risk signature, patients with low-risk got better outcomes than those with high-risk in overall survival. Finally, ULK2 and GABARAPL1 expression was further validated in clinical samples. In conclusion, Our study constructed an autophagy-related prognostic indicator, and identified two promising targets in OC.

TBK1/IKKε Negatively Regulate LPS-Induced Neutrophil Necroptosis and Lung Inflammation

ABSTRACT

Cell necroptosis, a form of regulated inflammatory cell death, is one of the mechanisms that controls cell release of inflammatory mediators from innate immune cells, such as polymorphonuclear neutrophils (PMNs), and critically regulates the progress of inflammation. Cell necroptosis features receptor-interacting protein (RIPK) 1 activation and necroptosome formation. This leads to loss of plasma membrane integrity, the release of cell contents into the extracellular space, and subsequent increased inflammation. Here, we report an intra-PMN mechanism of negative regulation of necroptosis mediated through TBK1/IKKε. Using an in vivo mouse model of intratracheal injection (i.t.) of LPS and in vitro LPS stimulation of mouse PMN, we found that LPS-TLR4 signaling in PMNs activates and phosphorylates TBK1 and IKKε, which in turn suppress LPS-induced formation of the RIPK1-RIPK3-MLKL (necrosome) complex. TBK1 dysfunction by knockdown or inhibitor significantly increases the phosphorylation of RIPK1 (∼67%), RIPK3 (∼68%), and MLKL (∼50%) and promotes RIPK1-RIPK3 and RIPK3-MLKL interactions and increases PMN necroptosis (∼83%) in response to LPS, with subsequent augmented lung inflammation. These findings suggest that the LPS-TLR4-TBK1 axis serves as a negative regulator for PMN necroptosis and might be a therapeutic target for modulating PMN death and inflammation.

Mitophagy in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC), one of the most aggressive solid malignancies, is characterized by the presence of oncogenic KRAS mutations, poor response to current therapies, prone to metastasis, and a low 5-year overall survival rate. Macroautophagy (herein referred to as autophagy) is a lysosome-dependent degradation system that forms a series of dynamic membrane structures to engulf, degrade, and recycle various cargoes, such as unused proteins, damaged organelles, and invading pathogens. Autophagy is usually upregulated in established cancers, but it plays a dual role in the regulation of the initiation and progression of PDAC. As a type of selective autophagy, mitophagy is a mitochondrial quality control mechanism that uses ubiquitin-dependent (e.g., the PINK1-PRKN pathway) and -independent (e.g., BNIP3L/NIX, FUNDC1, and BNIP3) pathways to regulate mitochondrial turnover and participate in the modulation of metabolism and cell death. Genetically engineered mouse models indicate that the loss of PINK1 or PRKN promotes, whereas the depletion of BNIP3L inhibits oncogenic KRAS-driven pancreatic tumorigenesis. Mitophagy also play a dual role in the regulation of the anticancer activity of certain cytotoxic agents (e.g., rocaglamide A, dichloroacetate, fisetin, and P. suffruticosa extracts) in PDAC cells or xenograft models. In this min-review, we summarize the latest advances in understanding the complex role of mitophagy in the occurrence and treatment of PDAC.

Forkhead box O1-mediated ubiquitination suppresses RIG-I-mediated antiviral immune responses

RNA virus infection activates the RIG-I-like Receptor (RLR) signaling pathway to produce type I interferons (IFNs), the key components of the antiviral immune response. Forkhead box O1 (FoxO1) is a host transcription factor that participates in multiple biological processes. In this study, FoxO1 was identified as a critical negative regulator of RIG-I-triggered signaling. FoxO1 promoted Sendai virus (SeV) replication and downregulated type I IFN production. Upon SeV infection, FoxO1 suppressed K63-linked ubiquitination of TRAF3 and the interaction between TRAF3 and TBK1, after which the production of type I IFNs via the interferon regulatory transcription factor 3 (IRF3) pathways was reduced. In addition, FoxO1 destabilized IRF3 by facilitating E3 ligase TRIM22- or TRIM21-mediated K48-linked ubiquitination of IRF3. Moreover, the inhibitory effect of FoxO1 was found to depend on its DNA binding domain (DBD). Thus, our findings highlight novel important roles of FoxO1 in controlling RLR-mediated antiviral innate immunity.

Experimental Acute Pancreatitis Models: History, Current Status, and Role in Translational Research

Acute pancreatitis is a potentially severe inflammatory disease that may be associated with a substantial morbidity and mortality. Currently there is no specific treatment for the disease, which indicates an ongoing demand for research into its pathogenesis and development of new therapeutic strategies. Due to the unpredictable course of acute pancreatitis and relatively concealed anatomical site in the retro-peritoneum, research on the human pancreas remains challenging. As a result, for over the last 100 years studies on the pathogenesis of this disease have heavily relied on animal models. This review aims to summarize different animal models of acute pancreatitis from the past to present and discuss their main characteristics and applications. It identifies key studies that have enhanced our current understanding of the pathogenesis of acute pancreatitis and highlights the instrumental role of animal models in translational research for developing novel therapies.

Proteoglycan-driven Autophagy: A Nutrient-independent Mechanism to Control Intracellular Catabolism

Proteoglycans are rapidly emerging as versatile regulators of intracellular catabolic pathways. This is predominantly achieved via the non-canonical induction of autophagy, a fundamentally and evolutionarily conserved eukaryotic pathway necessary for maintaining organismal homeostasis. Autophagy facilitated by either decorin, a small leucine-rich proteoglycan, or perlecan, a basement membrane heparan sulfate proteoglycan, proceeds independently of ambient nutrient conditions. We found that soluble decorin evokes endothelial cell autophagy and breast carcinoma cell mitophagy by directly interacting with vascular endothelial growth factor receptor 2 (VEGFR2) or the Met receptor tyrosine kinase, respectively. Endorepellin, a soluble, proteolytic fragment of perlecan, induces autophagy and endoplasmic reticulum stress within the vasculature, downstream of VEGFR2. These potent matrix-derived cues transduce key biological information via receptor binding to converge upon a newly discovered nexus of core autophagic machinery comprised of Peg3 (paternally expressed gene 3) for autophagy or mitostatin for mitophagy. Here, we give a mechanistic overview of the nutrient-independent, proteoglycan-driven programs utilized for autophagic or mitophagic progression. We propose that catabolic control of cell behavior is an underlying basis for proteoglycan versatility and may provide novel therapeutic targets for the treatment of human disease.

Targeting TANK-binding kinase 1 (TBK1) in cancer

INTRODUCTION

TANK-binding kinase 1 (TBK1) is a Ser/Thr kinase with a central role in coordinating the cellular response to invading pathogens and regulating key inflammatory signaling cascades. While intact TBK1 signaling is required for successful anti-viral signaling, dysregulated TBK1 signaling has been linked to a variety of pathophysiologic conditions, including cancer. Several lines of evidence support a role for TBK1 in cancer pathogenesis, but the specific roles and regulation of TBK1 remain incompletely understood. A key challenge is the diversity of cellular processes that are regulated by TBK1, including inflammation, cell cycle, autophagy, energy homeostasis, and cell death. Nevertheless, evidence from pre-clinical cancer models suggests that targeting TBK1 may be an effective strategy for anti-cancer therapy in specific settings.

AREAS COVERED

This review provides an overview of the roles and regulation of TBK1 with a focus on cancer pathogenesis and drug targeting of TBK1 as an anti-cancer strategy. Relevant literature was derived from a PubMed search encompassing studies from 1999 to 2020.

EXPERT OPINION

TBK1 is emerging as a potential target for anti-cancer therapy. Inhibition of TBK1 alone may be insufficient to restrain the growth of most cancers; hence, combination strategies will likely be necessary. Improved understanding of tumor-intrinsic and tumor-extrinsic TBK1 signaling will inform novel therapeutic strategies.

Roles of Specialized Pro-Resolving Lipid Mediators in Autophagy and Inflammation

Autophagy is a catabolic pathway that accounts for degradation and recycling of cellular components to extend cell survival under stress conditions. In addition to this prominent role, recent evidence indicates that autophagy is crucially involved in the regulation of the inflammatory response, a tightly controlled process aimed at clearing the inflammatory stimulus and restoring tissue homeostasis. To be efficient and beneficial to the host, inflammation should be controlled by a resolution program, since uncontrolled inflammation is the underlying cause of many pathologies. Resolution of inflammation is an active process mediated by a variety of mediators, including the so-called specialized pro-resolving lipid mediators (SPMs), a family of endogenous lipid autacoids known to regulate leukocyte infiltration and activities, and counterbalance cytokine production. Recently, regulation of autophagic mechanisms by these mediators has emerged, uncovering unappreciated connections between inflammation resolution and autophagy. Here, we summarize mechanisms of autophagy and resolution, focusing on the contribution of autophagy in sustaining paradigmatic examples of chronic inflammatory disorders. Then, we discuss the evidence that SPMs can restore dysregulated autophagy, hypothesizing that resolution of inflammation could represent an innovative approach to modulate autophagy and its impact on the inflammatory response.

Anti-tumor immunity influences cancer cell reliance upon ATG7

Macroautophagy (autophagy) is an essential cellular catabolic process required for survival under conditions of starvation. The role of autophagy in cancer is complex, context-dependent and at times contradictory, as it has been shown to inhibit, promote or be dispensable for tumor progression. In this study, we evaluated the contribution of the immune system to the reliance of tumors on autophagy by depleting autophagy-related 7 (ATG7) in murine tumor cells and grafting into immunocompetent versus immunodeficient hosts. Although loss of ATG7 did not affect tumor growth in vitro or in immunodeficient mice, our studies revealed that cancer cell reliance on autophagy was influenced by anti-tumor immune responses, including those mediated by CD8+ T cells. Furthermore, we provide insights into possible mechanisms by which autophagy disruption can enhance anti-tumor immune responses and suggest that autophagy disruption may further benefit patients with immunoreactive tumors.

A Novel Molecular Mechanism of IKKε-Mediated Akt/mTOR Inhibition in the Cardiomyocyte Autophagy after Myocardial Infarction

Autophagy of cardiomyocytes after myocardial infarction (MI) is an important factor affecting the prognosis of MI. Excessive autophagy can lead to massive death of cardiomyocytes, which will seriously affect cardiac function. IKKε plays a crucial role in the occurrence of autophagy, but the functional role in MI remains largely unknown. To evaluate the impact of IKKε on the autophagy of cardiomyocytes after MI, MI was induced by surgical left anterior descending coronary artery ligation in IKKε knockout (KO) mice and wild-type (WT) mice. Starvation of H9c2 cells with IKKε siRNA and rescued with IKKε overexpressed afterwards to test the mechanism of IKKε in autophagy in vitro. Our results demonstrated that the expression of IKKε was upregulated in mice myocardial tissues which were consistent with cardiomyocyte autophagy after MI. Significantly, the IKKε KO mice showed increased infarct size, decreased viable cardiomyocytes, and exacerbated cardiac dysfunction when compared with the wild-type mice. Western blot and electron micrography analysis also revealed that loss of IKKε induces excessive cardiomyocyte autophagy and reduced the expression of p-Akt and p-mTOR. Similar results were observed in IKKε siRNA H9c2 cells in vitro which were under starvation injury. Notably, the levels of p-Akt and p-mTOR can restore in IKKε rescued cells. In conclusion, our results indicated that IKKε protects cardiomyocyte survival by reduced autophagy following MI via regulation of the Akt/mTOR signaling pathway. Thus, our study suggests that IKKε might represent a potential therapeutic target for the treatment of MI.

The Specific IKKε/TBK1 Inhibitor Amlexanox Suppresses Human Melanoma by the Inhibition of Autophagy, NF-κB and MAP Kinase Pathways

Inhibitor-kappaB kinase epsilon (IKKε) and TANK-binding kinase 1 (TBK1) are non-canonical IκB kinases, both described as contributors to tumor growth and metastasis in different cancer types. Several hints indicate that they are also involved in the pathogenesis of melanoma; however, the impact of their inhibition as a potential therapeutic measure in this "difficult-to-treat" cancer type has not been investigated so far. We assessed IKKε and TBK1 expression in human malignant melanoma cells, primary tumors and the metastasis of melanoma patients. Both kinases were expressed in the primary tumor and in metastasis and showed a significant overexpression in tumor cells in comparison to melanocytes. The pharmacological inhibition of IKKε/TBK1 by the approved drug amlexanox reduced cell proliferation, migration and invasion. Amlexanox did not affect the cell cycle progression nor apoptosis induction but significantly suppressed autophagy in melanoma cells. The analysis of potential functional downstream targets revealed that NF-кB and ERK pathways might be involved in kinase-mediated effects. In an in vivo xenograft model in nude mice, amlexanox treatment significantly reduced tumor growth. In conclusion, amlexanox was able to suppress tumor progression potentially by the inhibition of autophagy as well as NF-кB and MAP kinase pathways and might therefore constitute a promising candidate for melanoma therapy.