Insulin-dependent signaling regulates azurophil granule-selective macroautophagy in human myeloblastic cells

[Transcriptomics and proteomics in studies of induced differentiation of leukemia cells]

Induced differentiation of leukemia cells is in the focus of basic and applied biomedical studies medicine and biology for more than 30 years. During this period specific regulatory molecules involved in the maturation process have been identified by biochemical and molecular biological methods. Recent developments of high-throughput transcriptomic and proteomic techniques made it possible to analyze large sets of mRNA and proteins; this resulted in identification of functionally important signal transduction pathways and networks of molecular interactions, and thus extent existing knowledge on the molecular mechanisms of induced differentiation. Despite significant advances in mechanisms of induced differentiation, many problems related to the molecular mechanism of cell maturation, a phenomenon of therapeutic resistance of leukemic cells need better understanding and thus require further detailed study. Transcriptomics and proteomics methods provide a suitable methodological platform for the implementation of such studies. This review highlights the use of transcriptomic and proteomic methods in studies aimed at various aspects of the induced differentiation. Special attention is paid to the employment of the systems approach for investigation of various aspects of cell maturation. The use of the systems approach in studies of induced differentiation is an important step for the transition from the formal data accumulation on expression of mRNA and proteins towards creating models of biological processes in silico.

Induction of an incomplete autophagic response by cancer-preventive geranylgeranoic acid (GGA) in a human hepatoma-derived cell line

GGA (geranylgeranoic acid) is a natural polyprenoic acid, derivatives of which has been shown to prevent second primary hepatoma. GGA induces mitochondria-mediated PCD (programmed cell death), which may be relevant to cancer prevention. To gain further insights into GGA-induced PCD, autophagy processes were examined in human hepatoma-derived HuH-7 cells. Treatment of HuH-7/GFP (green fluorescent protein)–LC3 cells with GGA induced green fluorescent puncta in the cytoplasm within 30 min and their massive accumulation at 24 h. After 15 min of GGA treatment, a burst of mitochondrial superoxide production occurred and LC3β-I was appreciably converted into LC3β-II. GGA-induced early stages of autophagy were unequivocally confirmed by electron-microscopic observation of early/initial autophagic vacuoles. On the other hand, LC3β-II as well as p62/SQSTM1 (sequestosome 1) continuously accumulated and co-localized in the cytoplasmic puncta after GGA treatment. Furthermore, GGA treatment of HuH-7/mRFP (monomeric red fluorescent protein)–GFP–LC3 cells showed yellow fluorescent puncta, whereas glucose deprivation of the cells gave red fluorescent puncta. These results strongly suggest that GGA induces the initial phase of autophagy, but blocks the maturation process of autolysosomes or late stages of autophagy, insomuch that GGA provides substantial accumulation of autophagosomes under serum-starvation conditions in human hepatoma cells.

High-efficiency production of subculturable vascular endothelial cells from feeder-free human embryonic stem cells without cell-sorting technique

We previously reported a feeder-free culture method for pure production of subculturable vascular endothelial cells (VECs) from cynomolgus monkey embryonic stem cells (cmESCs) without as using cell-sorting technique. By this method, canonical vascular endothelial (VE)-cadherin/platelet-endothelial cell adhesion molecule 1 (PECAM1)-positive VECs (c-VECs) and atypical VE-cadherin/PECAM1-negative VECs (a-VECs) were generated without a contamination by pericytes, lymphatic endothelial cells, or immature ES cells. More recently, we established a unique culture technique to maintain human ESCs (hESCs) under a feeder-free and recombinant cytokine-free condition. Combining these two systems, we have successfully generated pure VECs from two lines of hESCs, khES-1 and khES-3, under a completely feeder-free condition. Our method is very simple: spheres generated from hESCs by floating culture using differentiation media supplemented with vascular endothelial growth factor, bone morphogenetic protein 4, stem cell factor, FMS-related tyrosine kinase-3 ligand, and interleukin 3 (IL3) and IL6 were cultured on gelatin-coated plates. Cell passage was performed by an ordinary enzymatic treatment. The hESC-derived differentiated cells demosntrated cord-forming activities and acetylated low-density lipoprotein-uptaking capacities. Moreover, they exclusively expressed von Willebrand factor and endothelial nitric oxide synthase. Flow cytometric analyses indicate that khES-3 generated both c-VECs and a-VECs as in the case of cmESCs. By contrast, khES-1 produced only a-VECs, which nonetheless demonstrated effective recruitment into neovascularity in vivo. Interestingly, a-VECs turned to express PECAM1 after transplantation into immunodeficient mice. The hESC-derived VECs were subculturable at least up to 10 passages without functional depression. Our method does not require a presorting processes to enrich progenitor fractions such as CD34-positive or kinase insert domain receptor (KDR)-positive cells, providing the most efficient and easiest technique for VEC production from hESCs.

Insulin-like growth factor-I prevents the accumulation of autophagic vesicles and cell death in Purkinje neurons by increasing the rate of autophagosome-to-lysosome fusion and degradation

Continuous macroautophagic activity is critical for the maintenance of neuronal homeostasis; however, unchecked or dysregulated autophagy can lead to cell death. Cultured Purkinje neurons die by an autophagy-associated cell death mechanism when deprived of trophic support. Here, we report that insulin-like growth factor-I (IGF-I) completely blocked the autophagy-associated cell death of Purkinje neurons. To examine the mechanism by which IGF-I influences autophagy, neurons were infected with adeno-RFP-LC3 and subjected to trophic factor withdrawal, and the size and number of autophagosomes were analyzed by live-cell fluorescence imaging. In control neurons, autophagy occurred at a constitutive low level with most autophagosomes measuring less than 0.75 microm. Trophic factor withdrawal increased the number and size of autophagosomes with most autophagosomes ranging between 0.75 and 1.5 microm and some reaching 1.5-2.25 microm. IGF-I added at the time of trophic factor withdrawal prevented the accumulation of the larger autophagosomes; however, it had no effect on the conversion of LC3, an indicator of autophagy induction. Instead, the rate of autophagosome-to-lysosome fusion measured by colocalization of RFP-LC3 and LysoSensor Green was accelerated by IGF-I. Treating the neurons with bafilomycin A(1) in the presence of IGF-I led to the accumulation of autophagosomes even larger than those induced by trophic factor withdrawal alone, indicating that IGF-I regulates autophagic vesicle turnover. Finally, the effect of IGF-I on autophagy was mediated by an Akt/mTOR-de pend ent and an ERK-independent pathway. These data suggest a novel role for IGF-I in protecting Purkinje neurons from autophagy-associated cell death by increasing autophagy efficiency downstream of autophagy induction.

Highly efficient and feeder-free production of subculturable vascular endothelial cells from primate embryonic stem cells

The vascular endothelial cell (VEC) differentiation from primate embryonic stem (ES) cells has critical problems: low differentiation efficiencies (<2%) and/or subculture incapability. We report a novel feeder-free culture method for high efficiency production of subculturable VECs from cynomolgus monkey ES cells. Spheres, which were generated from ES cells in the presence of cytokine cocktail, were cultured on gelatin-coated plates. Cobblestone-shaped cells spread out after a few days, which were followed by an emergence of a sac-like structure containing hematopoietic cells. All adherent cells including sac walls cells and surrounding cobblestone cells expressed vascular endothelial cadherin (VE-cadherin) at intercellular junctions. Subculture of these cells resulted in a generation of homogeneous spindle-shaped population bearing cord-forming activities and a uniform acetylated low density lipoprotein-uptaking capacity with von Willbrand factor and endothelial nitric oxide synthetase expressions. They were freeze-thaw-tolerable and subculturable up to eight passages. Co-existence of pericytes or immature ES cells was ruled out. When introduced in a collagen sponge plug implanted intraperitoneally in mice, ES-derived cells recruited into neovascularity. Although percentages of surface VE-cadherin-positive population varied from 20% to 80% as assessed by flow cytometry, the surface VE-cadherin-negative population showed intracellular VE-cadherin expression and mature functions, as we call it as atypical VECs. When sorted, the surface VE-cadherin-positive population expanded as almost pure (>90%) VE-cadherin/PECAM-1-positive VECs by 160-fold after five passages. Thus, our system provides pure production of functional, subculturable and freeze-thaw-tolerable VECs, including atypical VECs, from primate ES cells.

Quantitation of autophagy by luciferase release assay

Autophagy is a cellular process that has been defined and analyzed almost entirely by qualitative measures. In no small part, this is attributable to the absence of robust quantitative assays that can easily and reliably permit the progress of key steps in autophagy to be assessed. We have recently developed a cell-based assay that specifically measures proteolytic cleavage of a tripartite sensor protein by the autophagy protease ATG4B. Activation of ATG4B results in release of Gaussia luciferase from cells that can be non-invasively harvested from cellular supernatants. Here, we compare this technique to existing methods and propose that this type of assay will be suitable for genome-wide functional screens and in vivo analysis of autophagy.

Efficient and repetitive production of hematopoietic and endothelial cells from feeder-free monolayer culture system of primate embryonic stem cells

We have established an innovative culture system for the efficient differentiation of hematopoietic and endothelial cells from primate embryonic stem (ES) cells without feeder cells, embryoid bodies, or cell-sorting processes. After several days' culture in murine stromal OP9-conditioned medium supplemented with a cytokine cocktail on collagen-coated dishes, ES cells differentiated into a very unique population of cells with a finger-like appearance. These finger-like cells were positive for mesodermal and/or hemangioblastic markers of kinase insert domain receptor (KDR) and T-cell acute lymphocytic leukemia 1 (TAL1), and produced large amounts of protein tyrosine phosphatase, receptor type, C-positive hematopoietic cells. These hematopoietic cells showed the morphology of immature hematopoietic cells, formed blast cell colonies with high efficiency, and were positive for CD34 antigen, KDR, TAL1, and GATA binding protein 1, suggesting that these blast cells are equivalent to the multipotent hematopoietic progenitor cells. Moreover, they produced functional macrophages in murine stromal MS-5-conditioned medium and primitive erythroblasts in the presence of erythropoietin. The finger-like cells, putative mesodermal progenitors and/or hemangioblasts, actively proliferated and repetitively produced hematopoietic cells as long as they were maintained on the original dish. By contrast, the majority of the finger-like cells differentiated into endothelial cells with specific markers and specific functions after transfer to fresh dishes, indicating that conditions established in the original dish supported the proliferation and hematopoietic differentiation of the finger-like cells. Our method provides a highly controllable culture protocol for repetitive production of hematopoietic and endothelial cells from feeder-free monolayer cultivation of primate ES cells.

Proteomic analysis on insulin signaling in human hematopoietic cells: identification of CLIC1 and SRp20 as novel downstream effectors of insulin

Insulin/IGF-I-dependent signals play important roles for the regulation of proliferation, differentiation, metabolism, and autophagy in various cells, including hematopoietic cells. Although the early protein kinase activation cascade has been intensively studied, the whole picture of intracellular signaling events has not yet been clarified. To identify novel downstream effectors of insulin-dependent signals in relatively early phases, we performed high-resolution two-dimensional electrophoresis (2-DE)-based proteomic analysis using human hematopoietic cells 1 h after insulin stimulation. We identified SRp20, a splicing factor, and CLIC1, an intracellular chloride ion channel, as novel downstream effectors besides previously reported effectors of Rho-guanine nucleotide dissociation inhibitor 2 and glutathione S-transferase-pi. Reduction in SRp20 was confirmed by one-dimensional Western blotting. Moreover, MG-132, a proteasome inhibitor, prevented this reduction. By contrast, upregulation of CLIC1 was not observed in one-dimensional Western blotting, unlike the 2-DE results. As hydrophilic proteins were predominantly recovered in 2-DE, the discrepancy between the 1-DE and 2-DE results may indicate a certain qualitative change of the protein. Indeed, the nuclear localization pattern of CLIC1 was remarkably changed by insulin stimulation. Thus insulin induces the proteasome-dependent degradation of SRp20 as well as the subnuclear relocalization of CLIC1.

Inhibition of Akt signaling and enhanced ERK1/2 activity are involved in induction of macroautophagy by triterpenoid B-group soyasaponins in colon cancer cells

Triterpenoid B-group soyasaponins have been found to induce macroautophagy in human colon cancer cells at concentrations obtainable through consumption of legume foodstuffs. In the present studies the mechanism(s) for this autophagy-inducing action of soyasaponins was evaluated by measuring changes in signal transduction pathways associated with autophagy. Specifically, inhibition of the Akt signaling pathway and enhanced activity of ERK1/2 have previously been implicated in controlling induction of macroautophagy in mammalian cancer cells. Here we show that these pathways are also involved in B-group soyasaponin-induced macroautophagy, as changes in enzyme activities preceded significant increases in autophagic activity. The autophagic capacity of HCT-15 cells was significantly increased by 6 h post-saponin exposure, which led us to measure alterations in signaling events that preceded this time point. We determined that exposure to B-group soyasaponins suppressed Akt activity maximally by 50%, which was associated with a reduction in the activating phosphorylation of the Akt-serine473 residue. In addition, ERK1/2 activity was significantly increased by 60%, and was determined to be necessary for B-group soyasaponin-induced autophagy. The raf-1 kinase has been identified as a potential point of cross-talk between the Akt and ERK1/2 signaling cascades. Following B-group soyasaponin treatment activity of raf-1 was significantly increased by a maximal 200%, suggesting that this enzyme in part modulates the enhanced ERK1/2 activity. These results provide new insights into the signaling events that control induction of autophagy by B-group soyasaponins in human colon cancer cells and suggest that soyasaponins warrant further study as potential colon cancer chemopreventive agents.

Akt Activation Is Necessary for Growth Factor–Induced Trafficking of Functional KCaChannels in Developing Parasympathetic Neurons

The protein kinase Akt is a crucial regulator of neuronal survival and apoptosis. Here we show that Akt activation is necessary for mobilization of large-conductance KCachannels in ciliary ganglion (CG) neurons evoked by β-neuregulin-1 (NRG1) and transforming growth factor-β1 (TGFβ1). Application of NRG1 to embryonic day 9 (E9) CG neurons increased Akt phosphorylation, as observed previously for TGFβ1. NRG1- and TGFβ1-evoked stimulation of KCais blocked by inhibitors of PI3K by overexpression of a dominant-negative form of Akt, by overexpression of CTMP, an endogenous negative regulator of Akt, and by application of the Akt inhibitor 1L-6-hydroxymethyl-chiro-inositol 2-( R)-2- O-methyl-3- O-octadecylcarbonate (HIMO). Conversely, overexpression of a constitutively-active form of Akt was sufficient by itself to increase mobilization of functional KCachannels. NRG1 and TGFβ1 evoked an Akt-dependent increase in cell-surface SLO α-subunits. These procedures have no effect on voltage-activated Ca2+currents. Thus Akt plays an essential role in the developmental regulation of excitability in CG neurons.

Autophagy Is a Defense Mechanism Inhibiting BCG and Mycobacterium tuberculosis Survival in Infected Macrophages

Mycobacterium tuberculosis is an intracellular pathogen persisting within phagosomes through interference with phagolysosome biogenesis. Here we show that stimulation of autophagic pathways in macrophages causes mycobacterial phagosomes to mature into phagolysosomes. Physiological induction of autophagy or its pharmacological stimulation by rapamycin resulted in mycobacterial phagosome colocalization with the autophagy effector LC3, an elongation factor in autophagosome formation. Autophagy stimulation increased phagosomal colocalization with Beclin-1, a subunit of the phosphatidylinositol 3-kinase hVPS34, necessary for autophagy and a target for mycobacterial phagosome maturation arrest. Induction of autophagy suppressed intracellular survival of mycobacteria. IFN-gamma induced autophagy in macrophages, and so did transfection with LRG-47, an effector of IFN-gamma required for antimycobacterial action. These findings demonstrate that autophagic pathways can overcome the trafficking block imposed by M. tuberculosis. Autophagy, which is a hormonally, developmentally, and, as shown here, immunologically regulated process, represents an underappreciated innate defense mechanism for control of intracellular pathogens.

Autophagy: a regulated bulk degradation process inside cells

Autophagy is a major intracellular degradation/recycling system ubiquitous in eukaryotic cells. It contributes to the turnover of cellular components by delivering portions of the cytoplasm and organelles to lysosomes, where they are digested. Autophagy is mediated by membrane trafficking of unique double-membrane structures, the so-called autophagosomes, which are formed transiently. Moreover, autophagy is dramatically induced under starvation conditions to maintain an amino acid pool so that essential proteins may be synthesized. Recent studies have revealed insights into the molecular basis of membrane dynamics and the regulation of autophagy, which had remained cryptic for a long time.