Cell Biology & Molecular Genetics

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End date: 2009Subject: search.filters.subject.Biology, Molecular

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    CHARACTERIZATION OF THE ROLE OF MAPKS IN LEISHMANIA INFECTED MACROPHAGES.
    (2009) Yang, Ziyan; Mosser, David M.; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In the current study, we examined the role of the Mitogen Activated Protein Kinases (MAPKs) on the biological responses of macrophages infected with Leishmania. The first section examined the role of MAPK/ERK in IL-10 production by Leishmania-infected macrophages. The macrophage-derived IL-10 has been shown to exacerbate Leishmaniasis. However, the molecular mechanisms whereby Leishmaniasis prompts IL-10 induction are poorly understood. A combination of two signals was necessary for IL-10 induction by the Leishmania amastigotes-infected macrophages. The first signal is mediated by TLR ligation whereas the second signal is mediated by FcgammaR ligation, which yields a population of regulatory macrophages that produce high levels of IL-10. Infection of macrophages with L. amazonensis amastigotes from the lesion sites sparked MAPK/ERK activation, which was required, but not sufficient for IL-10 induction. In combination with an inflammatory stimulus, LMW-HA from the extracellular matrix, these parasites triggered the macrophages to highly produce IL-10. MAPK/ERK activation initiated an epigenetic modification of chromatin at the IL-10 locus, which allowed for transcription factor Sp1 binding to drive IL-10 transcription and subsequent production. U0126, an inhibitor of MAPK/ERK activation, decreased lesion progression in Leishmania infected mice. The second section examined the role of MAPK/p38 in cytokine production and vaccination against Leishmaniasis. TLR agonists activate macrophages to produce pro-inflammatory cytokines and reactive oxygen intermediates. Inhibition of MAPK/p38 reciprocally increased IL-12 but decreased TNFa production from LPS-stimulated macrophages, which also occurred following stimulation by a variety of other TLR agonists, and using different APCs. MAPK/p38 inhibition induced IL-12p40 mRNA accumulation mainly due to enhanced mRNA stability, which was independent of IL-10. Similar results were observed by knocking down MAPK/p38 using specific siRNAs or by targeted deletion of MKK3. IL-12 production following the inhibition of MAPK/p38 skewed antigen-specific T cells to produce more IFN-gamma and less IL-4 in vitro. A MAPK/p38 inhibitor was applied as an adjuvant to vaccine mice against L. major, which resulted in smaller lesions with fewer parasites. Our findings reveal an important role of MAPKs in the Leishmania pathogenesis, and suggest that the manipulation of these kinases may provide novel therapeutics for potential clinical applications.
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    CHARACTERIZATION OF TWO HIGHLY CONSERVED POXVIRUS TRANSMEMBRANE PROTEINS OF UNKNOWN FUNCTION
    (2009) Sood, Cindy Leigh; Moss, Bernard; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The vaccinia virus I5L open reading frame encodes a 79-amino-acid protein, with two predicted transmembrane domains, conserved among all sequenced members of the chordopoxvirus subfamily. No nonpoxvirus homologs or functional motifs have been recognized, and the role of the I5 protein remains unknown. I5 synthesis was dependent on viral DNA replication and occurred exclusively at late times, consistent with a consensus late promoter motif adjacent to the start of the open reading frame. I5 was present in preparations of purified virions and could be extracted with nonionic detergent, suggesting membrane insertion. Transmission electron microscopy of immunogold-labeled thawed cryosections of infected cells revealed the association of an epitope-tagged I5 with the membranes of immature and mature virions. Viable I5L deletion and frameshift mutants were constructed and found to replicate like wild-type virus in a variety of cell lines, indicating that the protein was dispensable for in vitro cultivation. However, mouse intranasal challenge experiments indicated that a mutant virus with a frameshift resulting in a stop codon near the N terminus of I5 was attenuated compared to control virus. The attenuation correlated with clearance of mutant viruses from the respiratory tract and with less progression and earlier resolution of pathological changes. We suggest that I5 is involved in an aspect of host defense that is evolutionarily conserved although a role in cell tropism should also be considered. The vaccinia virus A43R open reading frame encodes a 168-amino acid protein with a predicted N-terminal signal sequence and a C-terminal transmembrane domain. Although A43R is conserved in all sequenced members of the orthopoxvirus genus, no non-orthopoxvirus homolog or functional motif was recognized. Biochemical and confocal microscopic studies indicated that A43 is expressed at late times following viral DNA synthesis and is a type-1 membrane protein with two N-linked oligosaccharide chains. Neither mature nor enveloped virions contained appreciable amounts of A43, which was detected in Golgi and plasma membranes. Loss of A43R expression had no discernible effect on plaque size or virus replication in cell culture and little effect on virulence in a mouse intranasal infection model. Although the A43 mutant produced significantly smaller lesions in the skin of mice than the control, the amounts of virus recovered from the lesions were similar.
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    Resistance to Ionizing Radiation and Oxidative Stress in Halobacterium salinarum NRC-1
    (2009) Robinson, Courtney Kathryn; Dinman, Jonathan; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Oxidative stress results from environmental challenges that cause unchecked production of reactive oxygen species (ROS). We analyzed the cellular damage and stress response of the extremophile Halobacterium salinarum NRC-1 exposed to chemical oxidants and to ionizing radiation (IR). In contrast to IR, cellular damage from H2O2 and superoxide suggested that cell death resulted from interference with major metabolic pathways rather than generalized oxidative lesions. We found that essential ROS scavenging enzymes were not necessary for H. salinarum NRC-1 survival to IR. Protection assays using enzyme-free cellular extracts from H. salinarum NRC-1 demonstrated high level of protection for protein activity but not for DNA integrity against IR. Biochemical analysis of the extracts underlined an essential role in ROS scavenging for specific nucleosides and MnPO4 complexes. These studies contributed novel findings on the critical role played by non-enzymatic systems in IR resistance in H. salinarum NRC-1.
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    Molecular Mechanisms of the Inhibition of Apoptosis by Mycobacterium tuberculosis
    (2009) Miller, Jessica Lynn; Briken, Volker; Molecular and Cell Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The capacity of infected cells to undergo apoptosis upon insult with a pathogen is an ancient innate immune defense mechanism. Consequently, the ability of persistent intracellular pathogens, such as the human pathogen Mycobacterium tuberculosis (Mtb), to inhibit infection-induced apoptosis of macrophages is important for virulence and to achieve persistence in the host. The nuoG gene of Mtb, which encodes the NuoG subunit of the type I NADH dehydrogenase NDH-1, is important in Mtb-mediated inhibition of host macrophage apoptosis. Here I determine the molecular mechanisms of this host-pathogen interaction. Apoptosis induced by the nuoG deletion mutant (nuoG ) is caspase-8 and TNF-α dependent. This cell death was also reduced in the presence of neutralizers and inhibitors of reactive oxygen species (ROS) and in macrophages derived from NOX2 deficient mice, suggesting that DnuoG induced death is dependent upon NOX2 derived ROS. Correlatively, nuoG infected macrophages also produced more phagosomal ROS than those infected with Mtb, or cells derived from NOX2 deficient mice. NuoG also inhibited apoptosis in human alveolar macrophages in a NOX2 dependant manner. These data suggest that reduction of phagosomal ROS is important for inhibition of apoptosis. Consistent with this hypothesis, Mtb deficient in the ROS neutralizing catalase, KatG, also accumulated ROS in the phagosome and was pro-apoptotic in macrophages. The specific mechanism by which NuoG reduces phagosomal ROS is still unknown. We could not detect secretion of NuoG, so direct neutralization of ROS is unlikely. Interestingly, preliminary data suggests that  nuoG may be defective in secretion of SodA and KatG, enzymes known to be important for neutralizing ROS. In conclusion, these studies revealed that Mtb inhibits macrophage apoptosis by neutralizing phagosomal ROS via the NuoG dependent secretion of SodA and KatG. Furthermore, this research suggests a novel function for NOX2 activity in innate immunity, which is the sensing of persisting intracellular pathogens and subsequent induction of host cell apoptosis as a second line of defense for pathogens resistant to the respiratory burst.
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    Investigation of Ethylene Signal Transduction Mechanisms: Characterizing the Novel Gene AWE1 and Testing Hypothesis of Raf-like CTR1's Function In Vivo
    (2009) Kendrick, Mandy Danielle; Chang, Caren; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Ethylene is a gaseous plant hormone affecting multiple plant processes. Sixteen years ago the first components of the ethylene signaling pathway, the receptor ETR1 and Raf-like kinase CTR1, were identified. Since then many additional components of the pathway have been elucidated through genetic screens. Recent discoveries suggest ethylene signaling, once thought to be a linear pathway from ethylene perception at the endoplasmic reticulum to transcriptional activation at the nucleus, is more complex with multiple auto-feedback loops and potential parallel kinase cascades downstream of the receptors. Although the genetic backbone of the pathway is well established, the signaling mechanisms of the components remain unclear. ETR1 displays histidine kinase activity in vitro and physically interacts with the next-known downstream component of the pathway, CTR1. However the histidine kinase activity of ETR1 is mostly dispensable for signaling to CTR1. How then is CTR1 activated? I proposed that additional proteins, like AWE1, play a role in ETR1 to CTR1 signaling, and that the non-catalytic, amino-terminal region of CTR1 is required both for activation through direct interaction with the ETR1 receptor complex and for auto-inhibition of CTR1 kinase activity. ASSOCIATES-WITH-ETR1 (AWE1) was isolated in a yeast-two-hybrid screen for ETR1-interacting proteins and was of specific interest because the AWE1 clone also interacted with a portion of CTR1. Protein-protein interaction studies and genetic analysis of an awe1 mutant support a role of AWE1 in repressing ethylene responses. However double mutant analysis, over-expression analysis, and protein sub-cellular localization studies suggest that AWE1's function in hypocotyl elongation and cell expansion is more general. AWE1's function may require ETR1 for proper regulation but is likely to lie outside of the direct step from ETR1 to CTR1. To investigate a role of the CTR1 amino-terminal region in CTR1 regulation, I constructed transgenes consisting of truncated ETR1 receptors fused to truncated or full length CTR1 and examined how those transgenes carrying the truncated CTR1 (kinase domain only) affected Arabidopsis seedling growth compared to those transgenes expressing full length CTR1. I concluded that the CTR1 amino-terminal region may have a role in autoregulation, but additional components are required for regulation of CTR1 signaling.
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    EXPLORING THE ROLE OF NFκB HOMOLOGS IN AUTOPHAGIC CELL DEATH IN THE DROSOPHILA SALIVARY GLAND
    (2009) Ivory, Adrienne; Wu, Louisa P; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The innate immune response is an ancient, highly conserved means of defense against pathogens. An important mediator of innate immunity is the NF-κB (Nuclear Factor-Kappa B) family of transcription factors. Activation of immune-signaling pathways leads to the nuclear translocation of NFκB proteins which initiate the transcription of antimicrobial peptides (AMPs) that circulate and destroy microbes. In Drosophila, these AMPs are up-regulated during the destruction of larval salivary glands. Salivary gland cells are destroyed via autophagy during metamorphosis. This project sought to determine what, if any, role the NFκB transcription factors have in autophagic cell death. Using the Drosophila model, it was determined that a loss of AMP activity during metamorphosis results in a failure to completely degrade larval salivary glands, and this defect appears to be due to an inability to remove autophagic vacuoles. It is suggested that AMPs may serve to degrade the membranes of autophagic vacuoles.
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    THE ROLE OF SPERMIDINE IN THE REGULATION OF DEVELOPMENT AND DIFFERENTIATION IN SPERMATIDS OF MARSILEA VESTITA
    (2009) Deeb, Faten; Wolniak, Stephen M; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Spermiogenesis in the microspore of the water fern, Marsilea vestita, is a rapid process where a dry microspore containing a single cell undergoes nine successive mitotic divisions to produce 32 spermatids and seven sterile cells. Immediately after the dry microspore is placed into water, cytoplasmic movements precede the first mitotic division; a number of proteins and mRNAs aggregate into zones that later become the spermatogenous initials of the gametophyte. Development is driven by the regulated translation of stored mRNA with little or no new transcription (Hart and Wolniak, 1999). The pattern of translation in the gametophyte is ordered precisely spatially and temporally, which indicates that certain proteins are required in specific locations at specific stages of development. Spermatid differentiation involves the de novo synthesis of 140 basal bodies, the remodeling and condensation of nuclear chromatin and then, nuclear elongation. A complex cytoskeletal structure, the multilayered structure (MLS), is formed at the anterior end of the cell and extends the length of the elongated gamete, and apparently functions in cell and nuclear elongation. This document focuses on the role of kinesin motor proteins and spermidine in the regulation of gametophyte development and spermatid differentiation. Blocking the translation of various kinesin isoforms with RNA interference (RNAi) resulted in arrested development at distinct time points. Centrin and tubulin immunolabeling showed different defects in basal body and microtubule ribbon formation, respectively, with the silencing of specific kinesins. The reduction of spermidine levels in the gametophytes by silencing proteins responsible for its synthesis and transport reveals the involvement of the polyamine in gametophyte cell cycle regulation and in spermatid maturation. In addition, drug inhibition of spermidine synthesis later in development highlighted the importance of its involvement in chromatin remodeling and nuclear elongation. Immunolabeling of spermidine and in situ hybridization assays for its synthesizing enzyme, spermidine synthase, indicated that spermidine levels are controlled in gametophytes by the regulated translation of spermidine synthase. The regulated levels of spermidine in the gametophyte is key to its function as a developmental regulator; spermidine appears to participate in multiple cellular processes in a concentration dependent manner.
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    THE RELATIONSHIP BETWEEN AUTOPHAGY, CELL SURVIVAL AND CELL DEATH IN A MODEL OF NEURODEGENERATION AND DEVELOPMENT.
    (2009) Batlevi, Yakup; Pick, Leslie; Baehrecke, Eric H; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The catabolic degradation of proteins is vital for the proper function and homeostasis of all cells. Autophagy is one of the major catabolic systems, and it is involved in processes that are as diverse as cell survival, cell death, immune reaction, cancer and neurodegeneration. Neurodegenerative diseases often have the pathology of protein accumulation in inclusions, but it is unclear whether these inclusions cause cell toxicity. Here I show that autophagy has protective functions in a model of a polyglutamine neurodegenerative disease in Drosophila. Inhibition of autophagy in this model enhances polyglutmine-induced degeneration, while activation of autophagy suppresses degeneration. Moreover, I observed similar protein aggregates in the larval salivary glands of a Drosophila dynein light chain mutant. This dynein light chain mutant is defective in autophagy, and their salivary glands fail to execute developmentally regulated programmed cell death. Ectopic activation of autophagy is sufficient to suppress the protein accumulation in dynein light chain mutant salivary glands. Both neurons and salivary glands are long-lived post-mitotic cells, and these cells are likely to have unique catabolic needs. Our data indicate that defects in catabolism are responsible for the neurodegenerative and salivary gland cell death defects that I observed, and could explain the association of autophagy with neurodegenerative diseases.
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    Binding Interactions in the Bacterial Chemotaxis Signal Transduction Pathway
    (2008-12-08) Eaton, Anna Kolesar; Stewart, Richard C; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The investigation of signal transduction pathways is critical to the basic understanding of cellular processes as these pathways function to regulate diverse processes in both eukaryotes and prokaryotes. This dissertation focuses on understanding some of the biochemical events that take place in the chemotaxis signal transduction pathway of bacteria. In this system, cell-surface receptor proteins regulate a histidine protein kinase, CheA, that autophosphorylates and then transfers its phosphate to an effector protein, CheY. Phospho-CheY, in turn, influences the direction of flagellar rotation. This sequence of biochemical events establishes a chain of communication that ultimately allows the chemotaxis receptor proteins to regulate the swimming pattern of the bacterial cell when it encounters gradients of attractant and repellent chemicals in its environment. The three projects presented in this dissertation sought to fill basic gaps in our current understanding of CheA and CheY function. In the first project, I examined the nucleotide binding reaction of CheA using the fluorescent nucleotide analogue, TNP-ATP [2'(3')-O-(2,4,6-trinitrophenyl)adenosine 5'-triphosphate]. TNP-ATP is an effective inhibitor for CheA. By monitoring the fluorescence of TNP-ATP when it bound to CheA, I examined the affinity of the binding interaction and discovered that the two ATP binding sites of each CheA dimer exhibited negative cooperativity in their interactions with TNP-ATP. This is the first evidence of cooperativity in the histidine protein kinase superfamily. In the second project, I focused on elucidating the binding mechanism that underlies formation of the CheA:TNP-ATP complex. My results indicated a three-step mechanism, including rapid formation of a low-affinity complex, followed by two steps during which conformational changes give rise to the final high-affinity complex. This same basic mechanism applied to CheA from Escherichia coli and from Thermotoga maritima. In the third project, I turned my attention to studying the CheY phosphorylation and binding reactions using fluorescently labeled versions of CheY. The results of this final study indicated that CheY proteins labeled with the fluorophore Badan [6-bromoacetyl-2-(dimethylamino)naphthalene] could be useful tools for investigating CheY biochemistry. However my results also brought to light some of the limitations and difficulties of this approach.
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    Identification and Characterization of HRG-1 heme transporters in eukaryotes
    (2008-11-21) Rajagopal, Abbhirami; Hamza, Iqbal; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Heme is a prosthetic group in proteins that perform diverse biological functions including respiration, gas sensing, xenobiotic detoxification, cell differentiation, circadian clock control and micro RNA processing. In most eukaryotes, heme is synthesized through a multi-step pathway with defined intermediates that are highly conserved through evolution. Despite our extensive knowledge about heme biosynthesis and degradation, the molecules and pathways involved in intracellular heme trafficking are unknown, primarily due to the inability to dissociate the tightly regulated processes of heme biosynthesis and degradation from intracellular trafficking events. Caenorhabditis elegans and related helminths are natural heme auxotrophs that rely solely on exogenous heme for normal development and reproduction. We performed a genome-wide microarray analysis and identified 288 genes that are regulated by heme at the transcriptional level in C. elegans. Here, we characterize two heme-responsive genes, hrg-1 and its paralog hrg-4, that are highly upregulated at low heme concentrations and demonstrate that HRG-1 and HRG-4 are heme transporters. Depletion of hrg-1 and hrg-4 in worms by RNAi results in the disruption of organismal heme homeostasis and abnormal response to heme analogs. HRG-4 traffics to the plasma membrane, and HRG-1 localizes to endo-lysosomal compartments. While hrg-4 appears to be specific to worms, hrg-1 has homologs in vertebrates. Knock-down of hrg-1 in zebrafish results in severe anemia and profound developmental defects, which are fully rescued by worm hrg-1. Human and worm HRG-1 proteins localize together. CeHRG-1, hHRG1 and CeHRG-4 all bind and transport heme. To further understand the in vivo functions of hrg-1 and hrg-4, we characterize the genetic deletions of these genes in C. elegans. Preliminary experiments suggest that the deletion mutants respond abnormally to heme analogs, although these results do not phenocopy the RNAi knock-down studies. We speculate that the deletion strains may have developed compensatory mechanisms in response to the genetic lesions in hrg-1 and hrg-4. Taken together, the studies described herein lay the foundation for identifying the molecular mechanisms for heme transport by the HRG-1 proteins in metazoans and delineating the heme trafficking pathways in C. elegans.