AMP-Activated Protein Kinase Regulates the Cell Surface Proteome and Integrin Membrane Traffic

O-GlcNAc transferase modulates the cellular endocytosis machinery by controlling the formation of clathrin-coated pits

Clathrin-mediated endocytosis (CME) controls the internalization and function of a wide range of cell surface proteins. CME occurs by the assembly of clathrin and many other proteins on the inner leaflet of the plasma membrane into clathrin-coated pits (CCPs). These structures recruit specific cargo destined for internalization, generate membrane curvature, and in many cases undergo scission from the plasma membrane to yield intracellular vesicles. The diversity of functions of cell surface proteins controlled via internalization by CME may suggest that regulation of CCP formation could be effective to allow cellular adaptation under different contexts. Of interest is how cues derived from cellular metabolism may regulate CME, given the reciprocal role of CME in controlling cellular metabolism. The modification of proteins with O-linked β-GlcNAc (O-GlcNAc) is sensitive to nutrient availability and may allow cellular adaptation to different metabolic conditions. Here, we examined how the modification of proteins with O-GlcNAc may control CCP formation and thus CME. We used perturbation of key enzymes responsible for protein O-GlcNAc modification, as well as specific mutants of the endocytic regulator AAK1 predicted to be impaired for O-GlcNAc modification. We identify that CCP initiation and the assembly of clathrin and other proteins within CCPs are controlled by O-GlcNAc protein modification. This reveals a new dimension of regulation of CME and highlights the important reciprocal regulation of cellular metabolism and endocytosis.

Laminin-α4 Negatively Regulates Adipocyte Beiging Through the Suppression of AMPKα in Male Mice

Laminin-α4 (LAMA4) is an extracellular matrix protein implicated in the regulation of adipocyte differentiation and function. Prior research describes a role for LAMA4 in modulating adipocyte thermogenesis and uncoupling protein-1 (UCP1) expression in white adipose; however, the mechanisms involved are poorly understood. Here, we describe that Lama4 knockout mice (Lama4-/-) exhibit heightened mitochondrial biogenesis and peroxisome proliferator-activated receptor γ coactivator-1 (PGC-1) expression in subcutaneous white adipose tissue (sWAT). Furthermore, the acute silencing of LAMA4 with small interfering RNA in primary murine adipocytes was sufficient to upregulate the expression of thermogenic markers UCP1 and PR domain containing 16 (PRDM16). Silencing also resulted in an upregulation of PGC1-α and adenosine 5'-monophosphate-activated protein kinase (AMPK)-α expression. Subsequently, we show that integrin-linked kinase (ILK) is downregulated in the sWAT of Lama4-/- mice, and its silencing in adipocytes similarly resulted in elevated expression of UCP1 and AMPKα. Last, we demonstrate that treatment of human induced pluripotent stem cell-derived thermogenic adipocytes with LAMA4 (LN411) inhibited the expression of thermogenic markers and AMPKα. Overall, our results indicate that LAMA4 negatively regulates a thermogenic phenotype and pathways involving mitochondrial biogenesis in adipocytes through the suppression of AMPKα.

A paraguayan toad Rhinella schneideri preparation based on Mbya tradition increases mitochondrial bioenergetics with migrastatic effects dependent on AMPK in breast cancer cells

ETHNOPHARMACOLOGICAL RELEVANCE

In Paraguay, healers from the Mbya culture treat cancer with a recipe prepared with the native toad Rhinella schneideri. However, the chemical composition and biological effects of the recipe remain unknown.

AIM OF THE STUDY

The aim is to determine the composition of the traditional preparation made using the toad R. schneideri and to evaluate its effect on human breast cancer (BC) cells.

MATERIALS AND METHODS

The metabolites contained in the preparation were concentrated using XAD-7 resin, and the concentrate was analyzed by HPLC-MS/MS. The effect of the preparation was assessed in normal (MCF10F) and BC cells (MDA-MB-231 and MCF7). The mitochondrial membrane potential (Δψm), reactive oxygen species (ROS) levels, and cell cycle progression were determined by flow cytometry. The oxygen consumption rate (OCR) was measured by Clark electrode, and fibronectin-dependent migration in normoxia and hypoxia-like conditions were evaluated by transwell assay.

RESULTS

From the Amberlite-retained extract from the preparation, 24 compounds were identified, including alkaloids, amino acids, bufadienolides, and flavonoids, among others. The crude extract (CE) did not affect cell cycle progression and viability of BC cell lines. Moreover, it did not make cancer cells more sensitive to the cytotoxic effect of the chemotherapeutics doxorubicin and teniposide. On the other hand, the CE reduced the menadione-induced ROS production and increased NADH, Δψm, and the OCR. Respiratory complexes I and III as well as ATP synthase levels were increased in an AMPK-dependent manner. Moreover, the CE inhibited the migration of BC cells in normoxia and a hypoxia-like condition using CoCl₂ as a HIF1α-stabilizing agent. This latter effect involved an AMPK-dependent reduction of HIF1α levels.

CONCLUSIONS

The Paraguayan toad recipe contains metabolites from the toad ingredient, including alkaloids and bufadienolide derivatives. The CE lacks cytotoxic effects alone or in combination with chemotherapeutics. However, it increases mitochondrial bioenergetics and inhibits the cancer cell migration in an AMPK-dependent manner in BC cells. This is the first report of the in vitro anticancer effect of a traditional Rhinella sp. toad preparation based on Mbya tradition.

Mitochondrial complex I as a therapeutic target for Alzheimer's disease

Alzheimer's disease (AD), the most prominent form of dementia in the elderly, has no cure. Strategies focused on the reduction of amyloid beta or hyperphosphorylated Tau protein have largely failed in clinical trials. Novel therapeutic targets and strategies are urgently needed. Emerging data suggest that in response to environmental stress, mitochondria initiate an integrated stress response (ISR) shown to be beneficial for healthy aging and neuroprotection. Here, we review data that implicate mitochondrial electron transport complexes involved in oxidative phosphorylation as a hub for small molecule-targeted therapeutics that could induce beneficial mitochondrial ISR. Specifically, partial inhibition of mitochondrial complex I has been exploited as a novel strategy for multiple human conditions, including AD, with several small molecules being tested in clinical trials. We discuss current understanding of the molecular mechanisms involved in this counterintuitive approach. Since this strategy has also been shown to enhance health and life span, the development of safe and efficacious complex I inhibitors could promote healthy aging, delaying the onset of age-related neurodegenerative diseases.

Rapid Enzyme-Mediated Biotinylation for Cell Surface Proteome Profiling

Cell surface is the primary site for sensing extracellular stimuli. The knowledge of the transient changes on the surfaceome upon a perturbation is very important as the initial changed proteins could be driving molecules for some phenotype. In this study, we report a fast cell surface labeling strategy based on peroxidase-mediated oxidative tyrosine coupling strategy, enabling efficient and selective cell surface labeling within seconds. With a labeling time of 1 min, 2684 proteins, including 1370 (51%) cell surface-annotated proteins (cell surface/plasma membrane/extracellular), 732 transmembrane proteins, and 81 cluster of differentiation antigens, were identified from HeLa cells. By comparison with the negative control experiment using quantitative proteomics, 500 (68%) out of the 731 significantly enriched proteins (p-value < 0.05, ≥2-fold) in positive experimental samples were cell surface-annotated proteins. Finally, this technology was applied to track the dynamic changes of the surfaceome upon insulin stimulation at two time points (5 min and 2 h) in HepG2 cells. Thirty-two proteins, including INSR, CTNNB1, TFRC, IGF2R, and SORT1, were found to be significantly regulated (p-value < 0.01, ≥1.5-fold) after insulin exposure by different mechanisms. We envision that this technique could be a powerful tool to analyze the transient changes of the surfaceome with a good time resolution and to delineate the temporal and spatial regulation of cellular signaling.

Lysosomes in glioblastoma: pump up the volume

Lysosomes are acidic, dynamic organelles that supervise catabolism, integrate signaling cascades, and tune cellular trafficking. Moreover, the loss of their integrity may jeopardize cell viability. In cancer cells, lysosomes are qualitatively and quantitatively modified for the tumor's own benefit. For all these reasons, these organelles emerge as appealing intracellular targets to manipulate non-oncogene addiction. This is of particular interest for brain diseases, including neurodegenerative disorders and cancer, in which stem cells are exhausted and transformed, respectively. Recent publications had demonstrated that stem cells displayed disarmed lysosomes in terms of number and functions during aging and oncogenic progression. Likewise, our laboratory identified that the arginine protease MALT1, normally dedicated to the assembly of proper NF-kB activation and processing a number of substrates, arbitrates lysosome biogenesis and mTOR signaling in glioblastoma stem-like cells. Indeed, blocking either the expression or the activity of this enzyme leads to an aberrant increase of lysosomes, alongside of the down-regulation of the mTOR signaling. This surge of lysosomes eradicates glioblastoma stem-like cells. Targeting lysosomes might thus inspire the design of new strategies to face this devastating human cancer. Here, we provide an overview of the functions of the lysosome as well as its role as a cell death initiator, to highlight the potential of lysosomal drugs for glioblastoma therapy.

Irisin induces trophoblast differentiation via AMPK activation in the human placenta

Irisin, an adipokine, regulates differentiation and phenotype in various cell types including myocytes, adipocytes, and osteoblasts. Circulating irisin concentration increases throughout human pregnancy. In pregnancy disorders such as preeclampsia and gestational diabetes mellitus, circulating irisin levels are reduced compared to healthy controls. To date, there are no data on the role and molecular function of irisin in the human placenta or its contribution to pathophysiology. Aberrant trophoblast differentiation is involved in the pathophysiology of preeclampsia. The current study aimed to assess the molecular effects of irisin on trophoblast differentiation and function. First-trimester placental explants were cultured and treated with low (10 nM) and high (50 nM) physiological doses of irisin. Treatment with irisin dose-dependently increased both in vitro placental outgrowth (on Matrigel™) and trophoblast cell-cell fusion. Adenosine monophosphate-activated protein kinase (AMPK) signaling, an important regulator of cellular energy homeostasis that is involved in trophoblast differentiation and pathology, was subsequently investigated. Here, irisin exposure induced placental AMPK activation. To determine the effects of irisin on trophoblast differentiation, two trophoblast-like cell lines, HTR-8/SVneo and BeWo, were treated with irisin and/or a specific AMPK inhibitor (Compound C). Irisin-induced AMPK phosphorylation in HTR-8/SVneo cells. Additionally, as part of the differentiation process, integrin switching from α6 to α1 occurred as well as increased invasiveness. Overall, irisin promoted differentiation in villous and extravillous cell-based models via AMPK pathway activation. These findings provide evidence that exposure to irisin promotes differentiation and improves trophoblast functions in the human placenta that are affected in abnormal placentation.

Fluid flow-induced activation of subcellular AMPK and its interaction with FAK and Src

AMP-activated protein kinase (AMPK) is a metabolic energy sensor that plays a critical role in cancer cell survival and growth. While the physical microenvironment is believed to influence tumor growth and progression, its role in AMPK regulation remains largely unknown. In the present study, we evaluated AMPK response to mechanical forces and its interaction with other mechano-responsive signaling proteins, FAK and Src. Using genetically encoded biosensors that can detect AMPK activities at different subcellular locations (cytosol, plasma membrane, nucleus, mitochondria, and Golgi apparatus), we observed that AMPK responds to shear stress in a subcellular location-dependent manner in breast cancer cells (MDA-MB-231). While normal epithelial cells (MCF-10A) also similarly responded to shear stress, they are less sensitive to shear stress compared to MDA-MB-231 cells. Inhibition of FAK and Src significantly decreased the basal activity level of AMPK at all five subcellular locations in MDA-MB-231 cells and selectively blocked shear stress-induced AMPK activation. Moreover, testing with cytoskeletal drugs revealed that myosin II might be the critical mediator of shear stress-induced AMPK activation in MDA-MB-231 cells. These findings suggest that breast cancer cells and normal epithelial cells may have different mechanosensitivity in AMPK signaling and that FAK and Src as well as the myosin II-dependent signaling pathway are involved in subcellular AMPK mechanotransduction in breast cancer cells.

The Lysosome Signaling Platform: Adapting With the Times

Lysosomes are the terminal degradative compartment of autophagy, endocytosis and phagocytosis. What once was viewed as a simple acidic organelle in charge of macromolecular digestion has emerged as a dynamic organelle capable of integrating cellular signals and producing signal outputs. In this review, we focus on the concept that the lysosome surface serves as a platform to assemble major signaling hubs like mTORC1, AMPK, GSK3 and the inflammasome. These molecular assemblies integrate and facilitate cross-talk between signals such as amino acid and energy levels, membrane damage and infection, and ultimately enable responses such as autophagy, cell growth, membrane repair and microbe clearance. In particular, we review how molecular machinery like the vacuolar-ATPase proton pump, sestrins, the GATOR complexes, and the Ragulator, modulate mTORC1, AMPK, GSK3 and inflammation. We then elaborate how these signals control autophagy initiation and resolution, TFEB-mediated lysosome adaptation, lysosome remodeling, antigen presentation, inflammation, membrane damage repair and clearance. Overall, by being at the cross-roads for several membrane pathways, lysosomes have emerged as the ideal surveillance compartment to sense, integrate and elicit cellular behavior and adaptation in response to changing environmental and cellular conditions.

Signal transduction via integrin adhesion complexes

Integrin adhesion complexes (IACs) have evolved over millions of years to integrate metazoan cells physically with their microenvironment. It is presumed that the simultaneous interaction of thousands of integrin receptors to binding sites in anisotropic extracellular matrix (ECM) networks enables cells to assemble a topological description of the chemical and mechanical properties of their surroundings. This information is then converted into intracellular signals that influence cell positioning, differentiation and growth, but may also influence other fundamental processes, such as protein synthesis and energy regulation. In this way, changes in the microenvironment can influence all aspects of cell phenotype. Current concepts envisage cell fate decisions being controlled by the integrated signalling output of myriad receptor clusters, but the mechanisms are not understood. Analyses of the adhesome, the complement of proteins attracted to the vicinity of IACs, are now providing insights into some of the primordial links connecting these processes. This article reviews recent advances in our understanding of the composition of IACs, the mechanisms used to transduce signals through these junctions, and the links between IACs and cell phenotype.

Nutrient scavenging in cancer

While cancer cell proliferation depends on access to extracellular nutrients, inadequate tumour perfusion means that glucose, amino acids and lipids are often in short supply. To overcome this obstacle to growth, cancer cells utilize multiple scavenging strategies, obtaining macromolecules from the microenvironment and breaking them down in the lysosome to produce substrates for ATP generation and anabolism. Recent studies have revealed four scavenging pathways that support cancer cell proliferation in low-nutrient environments: scavenging of extracellular matrix proteins via integrins, receptor-mediated albumin uptake and catabolism, macropinocytic consumption of multiple components of the tumour microenvironment and the engulfment and degradation of entire live cells via entosis. New evidence suggests that blocking these pathways alone or in combination could provide substantial benefits to patients with incurable solid tumours. Both US Food and Drug Administration (FDA)-approved drugs and several agents in preclinical or clinical development shut down individual or multiple scavenging pathways. These therapies may increase the extent and durability of tumour growth inhibition and/or prevent the development of resistance when used in combination with existing treatments. This Review summarizes the evidence suggesting that scavenging pathways drive tumour growth, highlights recent advances that define the oncogenic signal transduction pathways that regulate scavenging and considers the benefits and detriments of therapeutic strategies targeting scavenging that are currently under development.

FR58P1a; a new uncoupler of OXPHOS that inhibits migration in triple-negative breast cancer cells via Sirt1/AMPK/β1-integrin pathway

Highly malignant triple-negative breast cancer (TNBC) cells rely mostly on glycolysis to maintain cellular homeostasis; however, mitochondria are still required for migration and metastasis. Taking advantage of the metabolic flexibility of TNBC MDA-MB-231 cells to generate subpopulations with glycolytic or oxidative phenotypes, we screened phenolic compounds containing an ortho-carbonyl group with mitochondrial activity and identified a bromoalkyl-ester of hydroquinone named FR58P1a, as a mitochondrial metabolism-affecting compound that uncouples OXPHOS through a protonophoric mechanism. In contrast to well-known protonophore uncoupler FCCP, FR58P1a does not depolarize the plasma membrane and its effect on the mitochondrial membrane potential and bioenergetics is moderate suggesting a mild uncoupling of OXPHOS. FR58P1a activates AMPK in a Sirt1-dependent fashion. Although the activation of Sirt1/AMPK axis by FR58P1a has a cyto-protective role, selectively inhibits fibronectin-dependent adhesion and migration in TNBC cells but not in non-tumoral MCF10A cells by decreasing β1-integrin at the cell surface. Prolonged exposure to FR58P1a triggers a metabolic reprograming in TNBC cells characterized by down-regulation of OXPHOS-related genes that promote cell survival but comprise their ability to migrate. Taken together, our results show that TNBC cell migration is susceptible to mitochondrial alterations induced by small molecules as FR58P1a, which may have therapeutic implications.

mTOR complex 1 controls the nuclear localization and function of glycogen synthase kinase 3β

Glycogen synthase kinase 3β (GSK3β) phosphorylates and thereby regulates a wide range of protein substrates involved in diverse cellular functions. Some GSK3β substrates, such as c-Myc and Snail, are nuclear transcription factors, suggesting the possibility that GSK3β function is controlled through its nuclear localization. Here, using ARPE-19 and MDA-MB-231 human cell lines, we found that inhibition of mTOR complex 1 (mTORC1) leads to partial redistribution of GSK3β from the cytosol to the nucleus and to a GSK3β-dependent reduction of the levels of both c-Myc and Snail. mTORC1 is known to be controlled by metabolic cues, such as by AMP-activated protein kinase (AMPK) or amino acid abundance, and we observed here that AMPK activation or amino acid deprivation promotes GSK3β nuclear localization in an mTORC1-dependent manner. GSK3β was detected on several distinct endomembrane compartments, including lysosomes. Consistently, disruption of late endosomes/lysosomes through a perturbation of RAS oncogene family member 7 (Rab7) resulted in loss of GSK3β from lysosomes and in enhanced GSK3β nuclear localization as well as GSK3β-dependent reduction of c-Myc levels. These findings indicate that the nuclear localization and function of GSK3β is suppressed by mTORC1 and suggest a link between metabolic conditions sensed by mTORC1 and GSK3β-dependent regulation of transcriptional networks controlling cellular biomass production.

Embigin Promotes Prostate Cancer Progression by S100A4-Dependent and-Independent Mechanisms

Embigin, a transmembrane glycoprotein belonging to the immunoglobulin superfamily, is involved in prostate and mammary gland development. As embigin’s roles in cancer remain elusive, we studied its biological functions and interaction with extracellular S100A4 in prostate cancer progression. We found by a pull-down assay that embigin is a novel receptor for S100A4, which is one of the vital cancer microenvironment milleu. Binding of extracellular S100A4 to embigin mediates prostate cancer progression by inhibition of AMPK activity, activation of NF-κB, MMP9 and mTORC1 signaling, and inhibition of autophagy, which increase prostate cancer cell motility. We also found that embigin promotes prostate cancer growth, spheroid- and colony-forming ability, and survival upon chemotherapy independently of S100A4. An in vivo growth mouse model confirmed the importance of embigin and its cytoplasmic tail in mediating prostate tumor growth. Moreover, embigin and p21^WAF1 can be used to predict survival of prostate cancer patients. Our results demonstrated for the first time that the S100A4-embigin/AMPK/mTORC1/p21^WAF1 and NF-κB/MMP9 axis is a vital oncogenic molecular cascade for prostate cancer progression. We proposed that embigin and p21^WAF1 could be used as prognostic biomarkers and a strategy to inhibit S100A4-embigin binding could be a therapeutic approach for prostate cancer patients.

Vaccinium angustifolium (lowbush blueberry) leaf extract increases extravillous trophoblast cell migration and invasion in vitro

Perturbations to extravillous trophoblast (EVT) cell migration and invasion are associated with the development of placenta-mediated diseases. Phytochemicals found in the lowbush blueberry plant (Vaccinium angustifolium) have been shown to influence cell migration and invasion in models of tumorigenesis and noncancerous, healthy cells, however never in EVT cells. We hypothesized that the phenolic compounds present in V. angustifolium leaf extract promote trophoblast migration and invasion. Using the HTR-8/SVneo human EVT cell line and Boyden chamber assays, the influence of V. angustifolium leaf extract (0 to 2 × 10⁴  ng/ml) on trophoblast cell migration (n = 4) and invasion (n = 4) was determined. Cellular proliferation and viability were assessed using immunoreactivity to Ki67 (n = 3) and trypan blue exclusion assays (n = 3), respectively. At 20 ng/ml, V. angustifolium leaf extract increased HTR-8/SVneo cell migration and invasion (p < .01) and did not affect cell proliferation or viability. Chlorogenic acid was identified as a major phenolic compound of the leaf extract and the most active compound. Evidence from Western blot analysis (n = 3) suggests that the effects of the leaf extract and chlorogenic acid on trophoblast migration and invasion are mediated through an adenosine monophosphate-activated protein (AMP) kinase-dependent mechanism. Further investigations examining the potential therapeutic applications of this natural health product extract and its major chemical compounds in the context of placenta-mediated diseases are warranted.

Selective regulation of clathrin-mediated epidermal growth factor receptor signaling and endocytosis by phospholipase C and calcium

Clathrin-mediated endocytosis is a major regulator of cell-surface protein internalization. Clathrin and other proteins assemble into small invaginating structures at the plasma membrane termed clathrin-coated pits (CCPs) that mediate vesicle formation. In addition, epidermal growth factor receptor (EGFR) signaling is regulated by its accumulation within CCPs. Given the diversity of proteins regulated by clathrin-mediated endocytosis, how this process may distinctly regulate specific receptors is a key question. We examined the selective regulation of clathrin-dependent EGFR signaling and endocytosis. We find that perturbations of phospholipase Cγ1 (PLCγ1), Ca²⁺, or protein kinase C (PKC) impair clathrin-mediated endocytosis of EGFR, the formation of CCPs harboring EGFR, and EGFR signaling. Each of these manipulations was without effect on the clathrin-mediated endocytosis of transferrin receptor (TfR). EGFR and TfR were recruited to largely distinct clathrin structures. In addition to control of initiation and assembly of CCPs, EGF stimulation also elicited a Ca²⁺- and PKC-dependent reduction in synaptojanin1 recruitment to clathrin structures, indicating broad control of CCP assembly by Ca²⁺ signals. Hence EGFR elicits PLCγ1-calcium signals to facilitate formation of a subset of CCPs, thus modulating its own signaling and endocytosis. This provides evidence for the versatility of CCPs to control diverse cellular processes.

The AMP-Related Kinase (AMPK) Induces Ca 2+ -Independent Dilation of Resistance Arteries by Interfering With Actin Filament Formation

Rationale:

Decreasing Ca 2+ sensitivity of vascular smooth muscle (VSM) allows for vasodilation without lowering of cytosolic Ca 2+ . This may be particularly important in states requiring maintained dilation, such as hypoxia. AMP-related kinase (AMPK) is an important cellular energy sensor in VSM. Regulation of Ca 2+ sensitivity usually is attributed to myosin light chain phosphatase activity, but findings in non-VSM identified changes in the actin cytoskeleton. The potential role of AMPK in this setting is widely unknown.

Objective:

To assess the influence of AMPK on the actin cytoskeleton in VSM of resistance arteries with regard to potential Ca 2+ desensitization of VSM contractile apparatus.

Methods and Results:

AMPK induced a slowly developing dilation at unchanged cytosolic Ca 2+ levels in potassium chloride–constricted intact arteries isolated from mouse mesenteric tissue. This dilation was not associated with changes in phosphorylation of myosin light chain or of myosin light chain phosphatase regulatory subunit. Using ultracentrifugation and confocal microscopy, we found that AMPK induced depolymerization of F-actin (filamentous actin). Imaging of arteries from LifeAct mice showed F-actin rarefaction in the midcellular portion of VSM. Immunoblotting revealed that this was associated with activation of the actin severing factor cofilin. Coimmunoprecipitation experiments indicated that AMPK leads to the liberation of cofilin from 14-3-3 protein.

Conclusions:

AMPK induces actin depolymerization, which reduces vascular tone and the response to vasoconstrictors. Our findings demonstrate a new role of AMPK in the control of actin cytoskeletal dynamics, potentially allowing for long-term dilation of microvessels without substantial changes in cytosolic Ca 2+ .

Isoflurane promotes phagocytosis of apoptotic neutrophils through AMPK-mediated ADAM17/Mer signaling

A patient’s recovery from lung inflammatory injury or development of multi-system organ failure is determined by the host’s ability to resolve inflammation and repair tissue damage, both of which require the clearance of apoptotic neutrophils by macrophages (efferocytosis). Here, we investigated the effects of isoflurane on macrophage efferocytosis and resolution of lung inflammatory injury. Treatment of murine bone marrow-derived macrophages (BMDMs) or alveolar macrophages with isoflurane dramatically enhanced phagocytosis of apoptotic neutrophils. Isoflurane significantly increased the surface expression of the receptor tyrosine kinase Mer in macrophages, but markedly decreased the levels of a soluble form of Mer protein in the medium. Isoflurane treatment also caused a decrease in a disintegrin and metalloproteinase 17 (ADAM17) on the cell surface and a concomitant increase in its cytoplasmic fraction. These responses induced by isoflurane were completely reversed by a pharmacological inhibitor or genetic deletion of AMP-activated protein kinase (AMPK). In a mouse model of lipopolysaccharide-induced lung injury, isoflurane accelerated the recovery of lung inflammation and injury that was coupled with an increase in the number of alveolar macrophages containing apoptotic bodies. In alveolar macrophage-depleted mice, administration of isoflurane-pretreated BMDMs facilitated resolution of lung inflammation following lipopolysaccharide challenge. Thus, isoflurane promoted resolution of lipopolysaccharide-induced lung inflammatory injury via enhancement of macrophage efferocytosis. Increased macrophage efferocytosis following isoflurane treatment correlates with upregulation of Mer surface expression through AMPK-mediated blockade of ADAM17 trafficking to the cell membrane.

Combined treatment with Metformin and 2-deoxy glucose induces detachment of viable MDA-MB-231 breast cancer cells in vitro

Triple naegative breast cancer has an increased rate of distant metastasis and consequently poor prognosis. To metastasize, breast cancer cells must detach from the main tumour mass and resist anoikis, a programmed cell death induced by lack of cell-extracellular matrix communication. Although cancer cells must detach to metastasize in vivo, the viability of floating cancer cells in vitro is rarely investigated. Here we show that co-treatment of anoikis-resistant MDA-MB-231 cells with metformin and 2-deoxy-D-glucose (2-DG) increased the percentage of floating cells, of which about 95% were viable. Floating cells resumed their proliferation once they were reseeded in the pharmacological compound-free medium. Similar effects on detachment were observed on anoikis-prone MCF-7 cells. Co-treatment of MDA-MB-231 cells with metformin and 2-DG induced a strong activation of AMP-activated protein kinase (AMPK), which was reduced by AMPK inhibitor compound C that prevented detachment of MDA-MB-231 cells. However, direct AMPK activators A-769662 and AICAR did not have any major effect on the percentage of floating MDA-MB-231 cells, indicating that AMPK activation is necessary but not sufficient for triggering detachment of cancer cells. Our results demonstrate that separate analysis of floating and attached cancer cells might be important for evaluation of anti-cancer agents.

Integrins and Cell Metabolism: An Intimate Relationship Impacting Cancer

Integrins are important regulators of cell survival, proliferation, adhesion and migration. Once activated, integrins establish a regulated link between the extracellular matrix and the cytoskeleton. Integrins have well-established functions in cancer, such as in controlling cell survival by engagement of many specific intracellular signaling pathways and in facilitating metastasis. Integrins and associated proteins are regulated by control of transcription, membrane traffic, and degradation, as well as by a number of post-translational modifications including glycosylation, allowing integrin function to be modulated to conform to various cellular needs and environmental conditions. In this review, we examine the control of integrin function by cell metabolism, and the impact of this regulation in cancer. Within this context, nutrient sufficiency or deprivation is sensed by a number of metabolic signaling pathways such as AMP-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR) and hypoxia-inducible factor (HIF) 1, which collectively control integrin function by a number of mechanisms. Moreover, metabolic flux through specific pathways also controls integrins, such as by control of integrin glycosylation, thus impacting integrin-dependent cell adhesion and migration. Integrins also control various metabolic signals and pathways, establishing the reciprocity of this regulation. As cancer cells exhibit substantial changes in metabolism, such as a shift to aerobic glycolysis, enhanced glucose utilization and a heightened dependence on specific amino acids, the reciprocal regulation of integrins and metabolism may provide important clues for more effective treatment of various cancers.

Ultrasound Microbubble Treatment Enhances Clathrin-Mediated Endocytosis and Fluid-Phase Uptake through Distinct Mechanisms

Drug delivery to tumors is limited by several factors, including drug permeability of the target cell plasma membrane. Ultrasound in combination with microbubbles (USMB) is a promising strategy to overcome these limitations. USMB treatment elicits enhanced cellular uptake of materials such as drugs, in part as a result of sheer stress and formation of transient membrane pores. Pores formed upon USMB treatment are rapidly resealed, suggesting that other processes such as enhanced endocytosis may contribute to the enhanced material uptake by cells upon USMB treatment. How USMB regulates endocytic processes remains incompletely understood. Cells constitutively utilize several distinct mechanisms of endocytosis, including clathrin-mediated endocytosis (CME) for the internalization of receptor-bound macromolecules such as Transferrin Receptor (TfR), and distinct mechanism(s) that mediate the majority of fluid-phase endocytosis. Tracking the abundance of TfR on the cell surface and the internalization of its ligand transferrin revealed that USMB acutely enhances the rate of CME. Total internal reflection fluorescence microscopy experiments revealed that USMB treatment altered the assembly of clathrin-coated pits, the basic structural units of CME. In addition, the rate of fluid-phase endocytosis was enhanced, but with delayed onset upon USMB treatment relative to the enhancement of CME, suggesting that the two processes are distinctly regulated by USMB. Indeed, vacuolin-1 or desipramine treatment prevented the enhancement of CME but not of fluid phase endocytosis upon USMB, suggesting that lysosome exocytosis and acid sphingomyelinase, respectively, are required for the regulation of CME but not fluid phase endocytosis upon USMB treatment. These results indicate that USMB enhances both CME and fluid phase endocytosis through distinct signaling mechanisms, and suggest that strategies for potentiating the enhancement of endocytosis upon USMB treatment may improve targeted drug delivery.