The Journal of Biological Chemistry

Structural Characterization of HIV gp41 with the Membrane-proximal External Region [Immunology]

Human immunodeficiency virus, type 1 (HIV-1) envelope glycoprotein (gp120/gp41) plays a critical role in virus infection and pathogenesis. Three of the six monoclonal antibodies considered to have broadly neutralizing activities (2F5, 4E10, and Z13e1) bind to the membrane-proximal external region (MPER) of gp41. This makes the MPER a desirable template for developing immunogens that can elicit antibodies with properties similar to these monoclonal antibodies, with a long term goal of developing antigens that could serve as novel HIV vaccines. In order to provide a structural basis for rational antigen design, an MPER construct, HR1-54Q, was generated for x-ray crystallographic and x-ray footprinting studies to provide both high resolution atomic coordinates and verification of the solution state of the antigen, respectively. The crystal structure of HR1-54Q reveals a trimeric, coiled-coil six-helical bundle, which probably represents a postfusion form of gp41. The MPER portion extends from HR2 in continuation of a slightly bent long helix and is relatively flexible. The structures observed for the 2F5 and 4E10 epitopes agree well with existing structural data, and enzyme-linked immunosorbent assays indicate that the antigen binds well to antibodies that recognize the above epitopes. Hydroxyl radical-mediated protein footprinting of the antigen in solution reveals specifically protected and accessible regions consistent with the predictions based on the trimeric structure from the crystallographic data. Overall, the HR1-54Q antigen, as characterized by crystallography and footprinting, represents a postfusion, trimeric form of HIV gp41, and its structure provides a rational basis for gp41 antigen design suitable for HIV vaccine development.

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A Nodule Interaction{diamondsuit}: Interaction of Cytosolic Glutamine Synthetase of Soybean Root Nodules with the C-terminal Domain of the Symbiosome Membrane Nodulin 26 Aquaglyceroporin [Papers Of The Week]

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Respiratory Syncytial Virus Limits {alpha} Subunit of Eukaryotic Translation Initiation Factor 2 (eIF2{alpha}) Phosphorylation to Maintain Translation and Viral Replication [Microbiology]

The impact of respiratory syncytial virus (RSV) on morbidity and mortality is significant in that it causes bronchiolitis in infants, exacerbations in patients with obstructive lung disease, and pneumonia in immunocompromised hosts. RSV activates protein kinase R (PKR), a cellular kinase relevant to limiting viral replication (Groskreutz, D. J., Monick, M. M., Powers, L. S., Yarovinsky, T. O., Look, D. C., and Hunninghake, G. W. (2006) J. Immunol. 176, 1733–1740). It is activated by autophosphorylation, likely triggered by a double-stranded RNA intermediate during replication of the virus. In most instances, ph-PKR targets the subunit of eukaryotic translation initiation factor 2 (eIF2) protein via phosphorylation, leading to an inhibition of translation of cellular and viral protein. However, we found that although ph-PKR increases in RSV infection, significant eIF2 phosphorylation is not observed, and inhibition of protein translation does not occur. RSV infection attenuates eIF2 phosphorylation by favoring phosphatase rather than kinase activity. Although PKR is activated, RSV sequesters PKR away from eIF2 by binding of the kinase to the RSV N protein. This occurs in conjunction with an increase in the association of the phosphatase, PP2A, with eIF2 following PKR activation. The result is limited phosphorylation of eIF2 and continued translation of cellular and viral proteins.

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Functional Disruption of the Moloney Murine Leukemia Virus Preintegration Complex by Vaccinia-related Kinases [Dna and Chromosomes]

Retroviral integration is executed by the preintegration complex (PIC), which contains viral DNA together with a number of proteins. Barrier-to-autointegration factor (BAF), a cellular component of Moloney murine leukemia virus (MMLV) PICs, has been demonstrated to protect viral DNA from autointegration and stimulate the intermolecular integration activity of the PIC by its DNA binding activity. Recent studies reveal that the functions of BAF are regulated by phosphorylation via a family of cellular serine/threonine kinases called vaccinia-related kinases (VRK), and VRK-mediated phosphorylation causes a loss of the DNA binding activity of BAF. These results raise the possibility that BAF phosphorylation may influence the integration activities of the PIC through removal of BAF from viral DNA. In the present study, we report that VRK1 was able to abolish the intermolecular integration activity of MMLV PICs in vitro. This was accompanied by an enhancement of autointegration activity and dissociation of BAF from the PICs. In addition, in vitro phosphorylation of BAF by VRK1 abrogated the activity of BAF in PIC function. Among the VRK family members, VRK1 as well as VRK2, which catalyze hyperphosphorylation of BAF, could abolish PIC function. We also found that treatment of PICs with certain nucleotides such as ATP resulted in the inhibition of the intermolecular integration activity of PICs through the dissociation of BAF. More importantly, the ATP-induced disruption was not observed with the PICs from VRK1 knockdown cells. Our in vitro results therefore suggest the presence of cellular kinases including VRKs that can inactivate the retroviral integration complex via BAF phosphorylation.

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Regulation of Intracellular pH by p90Rsk-dependent Activation of an Na+/H+ Exchanger in Starfish Oocytes [Signal Transduction]

Starfish oocytes arrest at metaphase of the first meiotic division (MI arrest) in the ovary and resume meiosis after spawning into seawater. MI arrest is maintained by lower intracellular pH (pHi) and release from arrest by cellular alkalization. To elucidate pHi regulation in oocytes, we cloned the starfish (Asterina pectinifera) Na+/H+ exchanger 3 (ApNHE3) expressed in the plasma membrane of oocytes. The cytoplasmic domain of ApNHE3 contains p90 ribosomal S6 kinase (p90Rsk) phosphorylation sites, and injection of a constitutively active p90Rsk and the upstream regulator Mos to immature oocytes, stimulated an increase in pHi. This increase was blocked by 5-(N-ethyl-N-isopropyl)-amiloride, a NHE inhibitor, and SL0101, a specific Rsk inhibitor. The MAPK kinase (MEK) inhibitor U0126 blocked the Mos-induced, but not the p90Rsk-induced, pHi increase, suggesting that the Mos-MEK-MAPK-p90Rsk pathway promotes ApNHE3 activation. In a cell-free extract, the Mos-MEK-MAPK-p90Rsk pathway phosphorylates ApNHE3 at Ser-590, -606, and -673. When p90Rsk-dependent ApNHE3 phosphorylation was blocked by a dominant-negative C-terminal fragment, or neutralizing antibody, the p90Rsk-induced pHi increase was suppressed in immature oocytes. However, ApNHE3 is up-regulated via the upstream phosphatidylinositol 3-kinase pathway before MAPK activation and the active state is maintained until spawning, suggesting that the p90Rsk-dependent ApNHE3 phosphorylation is unlikely to be the primary regulatory mechanism involved in MI arrest exit. After meiosis is completed, unfertilized eggs maintain their elevated pHi (~7.4) until the onset of apoptosis. We suggest that the p90Rsk/ApNHE3-dependent elevation of pHi increases fertilization success by delaying apoptosis initiation.

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Insertion of Epicatechin Gallate into the Cytoplasmic Membrane of Methicillin-resistant Staphylococcus aureus Disrupts Penicillin-binding Protein (PBP) 2a-mediated {beta}-Lactam Resistance by Delocalizing PBP2 [Membrane Biology]

Epicatechin gallate (ECg) sensitizes methicillin-resistant Staphylococcus aureus (MRSA) to oxacillin and other β-lactam agents; it also reduces the secretion of virulence-associated proteins, prevents biofilm formation, and induces gross morphological changes in MRSA cells without compromising the growth rate. MRSA is resistant to oxacillin because of the presence of penicillin-binding protein 2a (PBP2a), which allows peptidoglycan synthesis to continue after oxacillin-mediated acylation of native PBPs. We show that ECg binds predominantly to the cytoplasmic membrane (CM), initially decreasing the fluidity of the bilayer, and induces changes in gene expression indicative of an attempt to preserve and repair a compromised cell wall. On further incubation, the CM is reorganized; the amount of lysylphosphatidylglycerol is markedly reduced, with a concomitant increase in phosphatidylglycerol, and the proportion of branched chain fatty acids increases, resulting in a more fluid structure. We found no evidence that ECg modulates the enzymatic activity of PBP2a through direct binding to the protein but determined that PBP2 is delocalized from the FtsZ-anchored cell wall biosynthetic machinery at the septal division site following intercalation into the CM. We argue that many features of the ECg-induced phenotype can be explained by changes in the fluid dynamics of the CM.

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The Multifunctional Protein in Peroxisomal {beta}-Oxidation: STRUCTURE AND SUBSTRATE SPECIFICITY OF THE ARABIDOPSIS THALIANA PROTEIN MFP2 [Enzymology]

Plant fatty acids can be completely degraded within the peroxisomes. Fatty acid degradation plays a role in several plant processes including plant hormone synthesis and seed germination. Two multifunctional peroxisomal isozymes, MFP2 and AIM1, both with 2-trans-enoyl-CoA hydratase and l-3-hydroxyacyl-CoA dehydrogenase activities, function in mouse ear cress (Arabidopsis thaliana) peroxisomal β-oxidation, where fatty acids are degraded by the sequential removal of two carbon units. A deficiency in either of the two isozymes gives rise to a different phenotype; the biochemical and molecular background for these differences is not known. Structure determination of Arabidopsis MFP2 revealed that plant peroxisomal MFPs can be grouped into two families, as defined by a specific pattern of amino acid residues in the flexible loop of the acyl-binding pocket of the 2-trans-enoyl-CoA hydratase domain. This could explain the differences in substrate preferences and specific biological functions of the two isozymes. The in vitro substrate preference profiles illustrate that the Arabidopsis AIM1 hydratase has a preference for short chain acyl-CoAs compared with the Arabidopsis MFP2 hydratase. Remarkably, neither of the two was able to catabolize enoyl-CoA substrates longer than 14 carbon atoms efficiently, suggesting the existence of an uncharacterized long chain enoyl-CoA hydratase in Arabidopsis peroxisomes.

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Peroxisomal Plant 3-Ketoacyl-CoA Thiolase Structure and Activity Are Regulated by a Sensitive Redox Switch [Enzymology]

The breakdown of fatty acids, performed by the β-oxidation cycle, is crucial for plant germination and sustainability. β-Oxidation involves four enzymatic reactions. The final step, in which a two-carbon unit is cleaved from the fatty acid, is performed by a 3-ketoacyl-CoA thiolase (KAT). The shortened fatty acid may then pass through the cycle again (until reaching acetoacetyl-CoA) or be directed to a different cellular function. Crystal structures of KAT from Arabidopsis thaliana and Helianthus annuus have been solved to 1.5 and 1.8 Å resolution, respectively. Their dimeric structures are very similar and exhibit a typical thiolase-like fold; dimer formation and active site conformation appear in an open, active, reduced state. Using an interdisciplinary approach, we confirmed the potential of plant KATs to be regulated by the redox environment in the peroxisome within a physiological range. In addition, co-immunoprecipitation studies suggest an interaction between KAT and the multifunctional protein that is responsible for the preceding two steps in β-oxidation, which would allow a route for substrate channeling. We suggest a model for this complex based on the bacterial system.

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Crystal Structure of Liganded Rat Peroxisomal Multifunctional Enzyme Type 1: A FLEXIBLE MOLECULE WITH TWO INTERCONNECTED ACTIVE SITES [Protein Structure and Folding]

The crystal structure of the full-length rat peroxisomal multifunctional enzyme, type 1 (rpMFE1), has been determined at 2.8 Å resolution. This enzyme has three catalytic activities and two active sites. The N-terminal part has the crotonase fold, which builds the active site for the 3,2-enoyl-CoA isomerase and the 2-enoyl-CoA hydratase-1 catalytic activities, and the C-terminal part has the (3S)-hydroxyacyl-CoA dehydrogenase fold and makes the (3S)-hydroxyacyl-CoA dehydrogenase active site. rpMFE1 is a multidomain protein having five domains (A–E). The crystal structure of full-length rpMFE1 shows a flexible arrangement of the A-domain with respect to the B–E-domains. Because of a hinge region near the end of the A-domain, two different positions of the A-domain were observed for the two protein molecules (A and B) of the asymmetric unit. In the most closed conformation, the mode of binding of CoA is stabilized by domains A and B (helix-10), as seen in other crotonase fold members. Domain B, although functionally belonging to the N-terminal part, is found tightly associated with the C-terminal part, i.e. fixed to the E-domain. The two active sites of rpMFE1 are ~40 Å apart, separated by a tunnel, characterized by an excess of positively charged side chains. Comparison of the structures of rpMFE1 with the monofunctional crotonase and (3S)-hydroxyacyl-CoA dehydrogenase superfamily enzymes, as well as with the bacterial 2β2-fatty acid oxidation multienzyme complex, reveals that this tunnel could be important for substrate channeling, as observed earlier on the basis of the kinetics of rpMFE1 purified from rat liver.

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Crystal Structure of CCM3, a Cerebral Cavernous Malformation Protein Critical for Vascular Integrity [Molecular Bases Of Disease]

CCM3 mutations are associated with cerebral cavernous malformation (CCM), a disease affecting 0.1–0.5% of the human population. CCM3 (PDCD10, TFAR15) is thought to form a CCM complex with CCM1 and CCM2; however, the molecular basis for these interactions is not known. We have determined the 2.5 Å crystal structure of CCM3. This structure shows an all -helical protein containing two domains, an N-terminal dimerization domain with a fold not previously observed, and a C-terminal focal adhesion targeting (FAT)-homology domain. We show that CCM3 binds CCM2 via this FAT-homology domain and that mutation of a highly conserved FAK-like hydrophobic pocket (HP1) abrogates CCM3-CCM2 interaction. This CCM3 FAT-homology domain also interacts with paxillin LD motifs using the same surface, and partial CCM3 co-localization with paxillin in cells is lost on HP1 mutation. Disease-related CCM3 truncations affect the FAT-homology domain suggesting a role for the FAT-homology domain in the etiology of CCM.

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Ubiquitin Regulates GGA3-mediated Degradation of BACE1 [Cell Biology]

BACE1 (β-site amyloid precursor protein-cleaving enzyme 1) is a membrane-tethered member of the aspartyl proteases, essential for the production of β-amyloid, a toxic peptide that accumulates in the brain of subjects affected by Alzheimer disease. The BACE1 C-terminal fragment contains a DXXLL motif that has been shown to bind the VHS (VPS27, Hrs, and STAM) domain of GGA1–3 (Golgi-localized -ear-containing ARF-binding proteins). GGAs are trafficking molecules involved in the transport of proteins containing the DXXLL signal from the Golgi complex to endosomes. Moreover, GGAs bind ubiquitin and traffic synthetic and endosomal ubiquitinated cargoes to lysosomes. We have previously shown that depletion of GGA3 results in increased BACE1 levels and activity because of impaired lysosomal degradation. Here, we report that the accumulation of BACE1 is rescued by the ectopic expression of GGA3 in H4 neuroglioma cells depleted of GGA3. Accordingly, the overexpression of GGA3 reduces the levels of BACE1 and β-amyloid. We then established that mutations in the GGA3 VPS27, Hrs, and STAM domain (N91A) or in BACE1 di-leucine motif (L499A/L500A), able to abrogate their binding, did not affect the ability of ectopically expressed GGA3 to rescue BACE1 accumulation in cells depleted of GGA3. Instead, we found that BACE1 is ubiquitinated at lysine 501 and is mainly monoubiquitinated and Lys-63-linked polyubiquitinated. Finally, a GGA3 mutant with reduced ability to bind ubiquitin (GGA3L276A) was unable to regulate BACE1 levels both in rescue and overexpression experiments. These findings indicate that levels of GGA3 tightly and inversely regulate BACE1 levels via interaction with ubiquitin sorting machinery.

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Complete Functional Segregation of Planarian {beta}-Catenin-1 and -2 in Mediating Wnt Signaling and Cell Adhesion [Cell Biology]

β-Catenin is a bifunctional protein participating in both cell adhesion and canonical Wnt signaling. In cell adhesion, it bridges the transmembrane cadherin and the actin-binding protein -catenin and is essential for adherens junction formation, whereas in canonical Wnt signaling, it shuttles between the cytosol and nucleus and functions as an essential transcriptional activator. Schmidtea mediterranea β-catenin-1 was identified as a determinant of antero-posterior polarity during body regeneration by mediating Wnt signaling. Here we show that S. mediterranea β-catenin-2 is specifically expressed in epithelial cells in the gut and pharynx, where it has a putative role in mediating cell adhesion. We show evidence that planarian β-catenin-1 and -2 have distinct biochemical properties. β-Catenin-1 can interact with the components of the canonical Wnt signaling pathway but not with -catenin, whereas β-catenin-2 interacts with cell adhesion molecules, including E-cadherin and -catenin, but not with Wnt signaling components. Consistent with their specific function, β-catenin-1 is a potent transcriptional activator, whereas β-catenin-2 has no transcriptional activity. Protein sequence alignment also indicates that the planarian β-catenin-1 and -2 retain distinct critical residues and motifs, which are in agreement with the differences in their biochemical properties. At last, phylogenetic analysis reveals a probable Platyhelminthes- specific structural and functional segregation from which the monofunctional β-catenins evolved. Our results thus identify the first two monofunctional β-catenins in metazoans.

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Target of Rapamycin (TOR)-like 1 Kinase Is Involved in the Control of Polyphosphate Levels and Acidocalcisome Maintenance in Trypanosoma brucei [Microbiology]

Target of rapamycin (TOR) kinases are highly conserved protein kinases that integrate signals from nutrients and growth factors to coordinate cell growth and cell cycle progression. It has been previously described that two TOR kinases control cell growth in the protozoan parasite Trypanosoma brucei, the causative agent of African trypanosomiasis. Here we studied an unusual TOR-like protein named TbTOR-like 1 containing a PDZ domain and found exclusively in kinetoplastids. TbTOR-like 1 localizes to unique cytosolic granules. After hyperosmotic stress, the localization of the protein shifts to the cell periphery, different from other organelle markers. Ablation of TbTOR-like 1 causes a progressive inhibition of cell proliferation, producing parasites accumulating in the S/G2 phase of the cell cycle. TbTOR-like 1 knocked down cells have an increased area occupied by acidic vacuoles, known as acidocalcisomes, and are enriched in polyphosphate and pyrophosphate. These results suggest that TbTOR-like 1 might be involved in the control of acidocalcisome and polyphosphate metabolism in T. brucei.

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Reactive Oxygen Species, Ki-Ras, and Mitochondrial Superoxide Dismutase Cooperate in Nerve Growth Factor-induced Differentiation of PC12 Cells [Signal Transduction]

Nerve growth factor (NGF) induces terminal differentiation in PC12, a pheochromocytoma-derived cell line. NGF binds a specific receptor on the membrane and triggers the ERK1/2 cascade, which stimulates the transcription of neural genes. We report that NGF significantly affects mitochondrial metabolism by reducing mitochondrial-produced reactive oxygen species and stabilizing the electrochemical gradient. This is accomplished by stimulation of mitochondrial manganese superoxide dismutase (MnSOD) both transcriptionally and post-transcriptionally via Ki-Ras and ERK1/2. Activation of MnSOD is essential for completion of neuronal differentiation because 1) expression of MnSOD induces the transcription of a neuronal specific promoter and neurite outgrowth, 2) silencing of endogenous MnSOD by small interfering RNA significantly reduces transcription induced by NGF, and 3) a Ki-Ras mutant in the polylysine stretch at the COOH terminus, unable to stimulate MnSOD, fails to induce complete differentiation. Overexpression of MnSOD restores differentiation in cells expressing this mutant. ERK1/2 is also downstream of MnSOD, as a SOD mimetic drug stimulates ERK1/2 with the same kinetics of NGF and silencing of MnSOD reduces NGF-induced late ERK1/2. Long term activation of ERK1/2 by NGF requires SOD activation, low levels of hydrogen peroxide, and the integrity of the microtubular cytoskeleton. Confocal immunofluorescence shows that NGF stimulates the formation of a complex containing membrane-bound Ki-Ras, microtubules, and mitochondria. We propose that active NGF receptor induces association of mitochondria with plasma membrane. Local activation of ERK1/2 by Ki-Ras stimulates mitochondrial SOD, which reduces reactive oxygen species and produces H2O2. Low and spatially restricted levels of H2O2 induce and maintain long term ERK1/2 activity and ultimately differentiation of PC12 cells.

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Nitric Oxide Mediates the Glutamate-dependent Pathway for Neurotransmission in Sepia officinalis Chromatophore Organs [Signal Transduction]

Chromatophore organs are complex and unique structures responsible for the variety of body coloration patterns used by cephalopods to communicate and camouflage. They are formed by a pigment-containing cytoelastic sacculus, surrounded by muscle fibers directly innervated from the brain. Muscle contraction and relaxation are responsible for expansion and retraction of the pigment-containing cell. Their functioning depends on glutamate and Phe-Met-Arg-Phe-NH2-related peptides, which induce fast and slow cell expansion, respectively, and 5-hydroxytryptamine, which induces retraction. Apart from these three substances and acetylcholine, which acts presynaptically, no other neuroactive compounds have so far been found to be involved in the neuroregulation of chromatophore physiology, and the detailed signaling mechanisms are still little understood. Herein, we disclose the role of nitric oxide (NO) as mediator in one of the signaling pathways by which glutamate activates body patterning. NO and nitric-oxide synthase have been detected in pigment and muscle fibers of embryo, juvenile, and adult chromatophore organs from Sepia officinalis. NO-mediated Sepia chromatophore expansion operates at slower rate than glutamate and involves cGMP, cyclic ADP-ribose, and ryanodine receptor activation. These results demonstrate for the first time that NO is an important messenger in the long term maintenance of the body coloration patterns in Sepia.

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Inhibitor of DNA Binding 4 (ID4) Regulation of Adipocyte Differentiation and Adipose Tissue Formation in Mice [Lipids]

Inhibitor of DNA binding 4 (ID4) is a helix-loop-helix protein that heterodimerizes with basic helix-loop-helix transcription factors inhibiting their function. ID4 expression is important for adipogenic differentiation of the 3T3-L1 cell line, and inhibition of ID4 is associated with a concomitant decrease in CCAAT/enhancer-binding protein and peroxisome proliferator-activated receptor mRNA and protein expression. Mice with a homozygous deletion of Id4 (Id4–/–) have reduced body fat and gain much less weight compared with wild-type littermates when placed on diets with high fat content. Mouse embryonic fibroblasts (MEFs) isolated from Id4–/– mice have reduced adipogenic potential when compared with wild-type MEFs. In agreement with changes in morphological differentiation, the levels of CCAAT/enhancer-binding protein and peroxisome proliferator-activated receptor were also reduced in MEFs from Id4–/– mice. Our results demonstrate the importance of ID4 in adipocyte differentiation and the implications of this regulation for adipose tissue formation.

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The Number of Vitamin D Receptor Binding Sites Defines the Different Vitamin D Responsiveness of the CYP24 Gene in Malignant and Normal Mammary Cells [Gene Regulation]

Primary 1,25-dihydroxyvitamin D3 (1,25(OH)2D3)-responding genes are controlled by the vitamin D receptor (VDR) binding to specific sites (VDREs) that are located within the regulatory regions of these genes. According to previous studies, the gene encoding 25-dihydroxyvitamin D3 24-hydroxylase, CYP24, which is the strongest known 1,25(OH)2D3-responsive gene, has multiple VDREs that locate within the proximal and the distal promoter. However, it has remained unclear, what is the biological role of these regions and how they participate in the regulation of transcription. In this study, we found a different CYP24 expression profile in normal (MCF-10A) and malignant (MCF-7) human mammary cells. Moreover, CYP24 mRNA showed to be three times more stable in MCF-7 cells than in MCF-10A cells. We studied the mechanism of this difference using expression profiling, quantitative chromatin immunoprecipitation and chromosome conformation capture assays. Interestingly, the number of functional VDREs was higher in MCF-7 cells than in MCF-10A cells. Three functional VDREs in MCF-7 cells are connected to linear mRNA accumulation, whereas only one VDRE seems to lead to stepwise CYP24 mRNA accumulation in MCF-10A cells. The distal VDREs were involved in transcriptional regulation via ligand-dependent, dynamic chromatin looping, which brings cyclically the distal elements together either individually or simultaneously next to the transcription start site. In conclusion, our data suggest that in comparison to normal cells, clearing of 1,25(OH)2D3 is enhanced in malignant cells due to differences in transcriptional regulation of CYP24 and metabolism of CYP24 mRNA.

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Starvation-induced Hyperacetylation of Tubulin Is Required for the Stimulation of Autophagy by Nutrient Deprivation [Signal Transduction]

The molecular mechanisms underlying microtubule participation in autophagy are not known. In this study, we show that starvation-induced autophagosome formation requires the most dynamic microtubule subset. Upon nutrient deprivation, labile microtubules specifically recruit markers of autophagosome formation like class III-phosphatidylinositol kinase, WIPI-1, the Atg12-Atg5 conjugate, and LC3-I, whereas mature autophagosomes may bind to stable microtubules. We further found that upon nutrient deprivation, tubulin acetylation increases both in labile and stable microtubules and is required to allow autophagy stimulation. Tubulin hyperacetylation on lysine 40 enhances kinesin-1 and JIP-1 recruitment on microtubules and allows JNK phosphorylation and activation. JNK, in turn, triggers the release of Beclin 1 from Bcl-2-Beclin 1 complexes and its recruitment on microtubules where it may initiate autophagosome formation. Finally, although kinesin-1 functions to carry autophagosomes in basal conditions, it is not involved in motoring autophagosomes after nutrient deprivation. Our results show that the dynamics of microtubules and tubulin post-translational modifications play a major role in the regulation of starvation-induced autophagy.

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Protein Radical Formation Resulting from Eosinophil Peroxidase-catalyzed Oxidation of Sulfite [Immunology]

Eosinophil peroxidase (EPO) is an abundant heme protein in eosinophils that catalyzes the formation of cytotoxic oxidants implicated in asthma, allergic inflammatory disorders, and cancer. It is known that some proteins with peroxidase activity (horseradish peroxidase and prostaglandin hydroperoxidase) can catalyze oxidation of bisulfite (hydrated sulfur dioxide), leading to the formation of sulfur trioxide anion radical (·SO3–). This free radical further reacts with oxygen to form peroxymonosulfate anion radical (–O3SOO·) and the very reactive sulfate anion radical (SO4macr;), which is nearly as strong an oxidant as the hydroxyl radical. However, the ability of EPO to generate reactive sulfur radicals has not yet been reported. Here we demonstrate that eosinophil peroxidase/H2O2 is able to oxidize bisulfite, ultimately forming the sulfate anion radical (SO4macr;), and that these reactive intermediates can oxidize target proteins to protein radicals, thereby initiating protein oxidation. We used immuno-spin trapping and confocal microscopy to study protein oxidation by EPO/H2O2 in the presence of bisulfite in a pure enzymatic system and in human promyelocytic leukemia HL-60 clone 15 cells, maturated to eosinophils. Polyclonal antiserum raised against the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) detected the presence of DMPO covalently attached to the proteins resulting from the DMPO trapping of protein free radicals. We found that sulfite oxidation mediated by EPO/H2O2 induced the formation of radical-derived DMPO spin-trapped human serum albumin and, to a lesser extent, of DMPO-EPO. These studies suggest that EPO-dependent oxidative damage may play a role in tissue injury in bisulfite-exacerbated eosinophilic inflammatory disorders.

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Dynamic Repositioning of Dorsal to Two Different {kappa}B Motifs Controls Its Autoregulation during Immune Response in Drosophila [Immunology]

Autoregulation is one of the mechanisms of imparting feedback control on gene expression. Positive autoregulatory feedback results in induction of a gene, and negative feedback leads to its suppression. Here, we report an interesting mechanism of autoregulation operating on Drosophila Rel gene dorsal that can activate as well as repress its expression. Using biochemical and genetic approaches, we show that upon immune challenge Dorsal regulates its activation as well as repression by dynamically binding to two different B motifs, BI (intronic B) and BP (promoter B), present in the dorsal gene. Although the BI motif functions as an enhancer, the BP motif acts as a transcriptional repressor. Interestingly, Dorsal binding to these two motifs is dynamic; immediately upon immune challenge, Dorsal binds to the BI leading to auto-activation, whereas at the terminal phase of the immune response, it is removed from the BI and repositioned at the BP, resulting in its repression. Furthermore, we show that repression of Dorsal as well as its binding to the BP depends on the transcription factor AP1. Depletion of AP1 by RNA interference resulted in constitutive expression of Dorsal. In conclusion, this study suggests that during acute phase response dorsal is regulated by following two subcircuits: (i) Dl-BI for activation and (ii) Dl-AP1-BP for repression. These two subcircuits are temporally delineated and bring about overall regulation of dorsal during immune response. These results suggest the presence of a previously unknown mechanism of Dorsal autoregulation in immune-challenged Drosophila.

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