Showing papers in "Advances in Experimental Medicine and Biology in 2012"

Molecular Mechanisms of Superoxide Production by the Mitochondrial Respiratory Chain

Abstract: The mitochondrial respiratory chain is a major source of reactive oxygen species (ROS) in eukaryotic cells. Mitochondrial ROS production associated with a dysfunction of respiratory chain complexes has been implicated in a number of degenerative diseases and biological aging. Recent findings suggest that mitochondrial ROS can be integral components of cellular signal transduction as well. Within the respiratory chain, complexes I (NADH:ubiquinone oxidoreductase) and III (ubiquinol:cytochrome c oxidoreductase; cytochrome bc 1 complex) are generally considered as the main producers of superoxide anions that are released into the mitochondrial matrix and the intermembrane space, respectively. The primary function of both respiratory chain complexes is to employ energy supplied by redox reactions to drive the vectorial transfer of protons into the mitochondrial intermembrane space. This process involves a set of distinct electron carriers designed to minimize the unwanted leak of electrons from reduced cofactors onto molecular oxygen and hence ROS generation under normal circumstances. Nevertheless, it seems plausible that superoxide is derived from intermediates of the normal catalytic cycles of complexes I and III. Therefore, a detailed understanding of the molecular mechanisms driving these enzymes is required to understand mitochondrial ROS production during oxidative stress and redox signalling. This review summarizes recent findings on the chemistry and control of the reactions within respiratory complexes I and III that result in increased superoxide generation. Regulatory contributions of other components of the respiratory chain, especially complex II (succinate:ubiquinone oxidoreductase) and the redox state of the ubiquinone pool (Q-pool) will be briefly discussed.

The mitochondrial pathways of apoptosis.

Abstract: Apoptosis is a process of programmed cell death that serves as a major mechanism for the precise regulation of cell numbers, and as a defense mechanism to remove unwanted and potentially dangerous cells. Studies in nematode, Drosophila and mammals have shown that, although regulation of the cell death machinery is somehow different from one species to another, it is controlled by homologous proteins and involves mitochondria. In mammals, activation of caspases (cysteine proteases that are the main executioners of apoptosis) is under the tight control of the Bcl-2 family proteins, named in reference to the first discovered mammalian cell death regulator. These proteins mainly act by regulating the release of caspases activators from mitochondria. Although for a long time the absence of mitochondrial changes was considered as a hallmark of apoptosis, mitochondria appear today as the central executioner of apoptosis. In this chapter, we present the current view on the mitochondrial pathway of apoptosis with a particular attention to new aspects of the regulation of the Bcl-2 proteins family control of mitochondrial membrane permeabilization: the mechanisms implicated in their mitochondrial targeting and activation during apoptosis, the function(s) of the oncosuppressive protein p53 at the mitochondria and the role of the processes of mitochondrial fusion and fission.

Mitochondria and aging.

Abstract: Aging is a degenerative process that is associated with progressive accumulation of deleterious changes with time, reduction of physiological function and increase in the chance of disease and death. Studies in several species reveal a wide spectrum of alterations in mitochondria and mitochondrial DNA (mtDNA) with aging, including (1) increased disorganization of mitochondrial structure, (2) decline in mitochondrial oxidative phosphorylation (OXPHOS) function, (3) accumulation of mtDNA mutation, (4) increased mitochondrial production of reactive oxygen species (ROS) and (5) increased extent of oxidative damage to DNA, proteins, and lipids. In this chapter, we outline the common alterations in mitochondria of the aging tissues and recent advances in understanding the role of mitochondrial H2O2 production and mtDNA mutation in the aging process and lifespan determination. In addition, we discuss the effect of caloric restriction on age-associated mitochondrial changes and its role in longevity. Taking these findings together, we suggest that decline in mitochondrial energy metabolism, enhanced mitochondrial oxidative stress, and accumulation of mtDNA mutations are important contributors to human aging.

Zebrafish: model for the study of inflammation and the innate immune response to infectious diseases

Abstract: The zebrafish (Danio rerio) has been extensively used in biomedical research as a model to study vertebrate development and hematopoiesis and recently, it has been adopted into varied fields including immunology. After fertilization, larvae survive with only the innate immune responses because adaptive immune system is morphologically and functionally mature only after 4–6 weeks postfertilization. This temporal separation provides a suitable system to study the vertebrate innate immune response in vivo, independently from the adaptive immune response. The transparency of early life stages allows a useful real-time visualization. Adult zebrafish which have complete (innate and adaptative) immune systems offer also advantages over other vertebrate infection models: small size, relatively rapid life cycle, ease of breeding, and a growing list of molecular tools for the study of infectious diseases. In this review, we have tried to give some examples of the potential of zebrafish as a valuable model in innate immunity and inflammation studies.

Synaptic dysfunction in Parkinson's disease.

Abstract: Activity-dependent modifications in synaptic efficacy, such as long-term depression (LTD) and long-term potentiation (LTP), represent key cellular substrates for adaptive motor control and procedural memory. The impairment of these two forms of synaptic plasticity in the nucleus striatum could account for the onset and the progression of motor and cognitive symptoms of Parkinson's disease (PD), characterized by the massive degeneration of dopaminergic neurons. In fact, both LTD and LTP are peculiarly controlled and modulated by dopaminergic transmission coming from nigrostriatal terminals. Changes in corticostriatal and nigrostriatal neuronal excitability may influence profoundly the threshold for the induction of synaptic plasticity, and changes in striatal synaptic transmission efficacy are supposed to play a role in the occurrence of PD symptoms. Understanding of these maladaptive forms of synaptic plasticity has mostly come from the analysis of experimental animal models of PD. A series of cellular and synaptic alterations occur in the striatum of experimental parkinsonism in response to the massive dopaminergic loss. In particular, dysfunctions in trafficking and subunit composition of glutamatergic NMDA receptors on striatal efferent neurons contribute to the clinical features of the experimental parkinsonism. Interestingly, it has become increasingly evident that in striatal spiny neurons, the correct assembly of NMDA receptor complex at the postsynaptic site is a major player in early phases of PD, and it is sensitive to distinct degrees of DA denervation. The molecular defects at the basis of PD progression may be not confined just at the postsynaptic neuron: accumulating evidences have recently shown that the genes linked to PD play a critical role at the presynaptic site. DA release into the synaptic cleft relies on a proper presynaptic vesicular transport; impairment of SV trafficking, modification of DA flow, and altered presynaptic plasticity have been described in several PD animal models. Furthermore, an impaired DA turnover has been described in presymptomatic PD patients. Thus, given the pathological events occurring precociously at the synapses of PD patients, post- and presynaptic sites may represent an adequate target for early therapeutic intervention.

The oxidative phosphorylation system in mammalian mitochondria.

Abstract: The chapter provides a review of the state of art of the oxidative phosphorylation system in mammalian mitochondria. The sections of the paper deal with: (i) the respiratory chain as a whole: redox centers of the chain and protonic coupling in oxidative phosphorylation (ii) atomic structure and functional mechanism of protonmotive complexes I, III, IV and V of the oxidative phosphorylation system (iii) biogenesis of oxidative phosphorylation complexes: mitochondrial import of nuclear encoded subunits, assembly of oxidative phosphorylation complexes, transcriptional factors controlling biogenesis of the complexes.

Galectins as pattern recognition receptors: structure, function, and evolution.

Abstract: Galectins constitute an evolutionary conserved family of s-galactoside-binding proteins, ubiquitous in mammals and other vertebrate taxa, invertebrates, and fungi. Since their discovery in the 1970s, their biological roles, initially understood as limited to recognition of carbohydrate ligands in embryogenesis and development, have expanded in recent years by the discovery of their immunoregulatory activities. A gradual paradigm shift has taken place in the past few years through the recognition that galectins also bind glycans on the surface of potentially pathogenic microbes, and function as recognition and effector factors in innate immunity. Further, an additional level of functional complexity has emerged with the most recent findings that some parasites “subvert” the recognition roles of the vector/host galectins for successful attachment or invasion.

Molecular mechanisms of HIV entry.

Abstract: Human immunodeficiency virus (HIV) entry is a complex and intricate process that facilitates delivery of the viral genome to the host cell. The only viral surface protein, Envelope (Env), is composed of a trimer of gp120 and gp41 heterodimers. It is essentially a fusion machine cloaked in a shroud of carbohydrate structures and variable loops of amino acids that enable it to evade the humoral immune response. For entry to occur gp120 sequentially engages the host protein CD4 and then one of two chemokine coreceptors, either CCR5 or CXCR4. CD4 binding facilitates exposure and formation of the coreceptor-binding site, and coreceptor binding then triggers the membrane fusion machinery in the gp41 subunit. Our understanding of HIV entry has led to the development of successful small molecule inhibitors for the clinical treatment of HIV infection as well as insights into viral tropism and pathogenesis.

Gliotransmission and the Tripartite Synapse

Abstract: In the last years, the classical view of glial cells (in particular of astrocytes) as a simple supportive cell for neurons has been replaced by a new vision in which glial cells are active elements of the brain. Such a new vision is based on the existence of a bidirectional communication between astrocytes and neurons at synaptic level. Indeed, perisynaptic processes of astrocytes express active G-protein-coupled receptors that are able (1) to sense neurotransmitters released from the synapse during synaptic activity, (2) to increase cytosolic levels of calcium, and (3) to stimulate the release of gliotransmitters that in turn can interact with the synaptic elements. The mechanism(s) by which astrocytes can release gliotransmitter has been extensively studied during the last years. Many evidences have suggested that a fraction of astrocytes in situ release neuroactive substances both with calcium-dependent and calcium-independent mechanism(s); whether these mechanisms coexist and under what physiological or pathological conditions they occur, it remains unclear. However, the calcium-dependent exocytotic vesicular release has received considerable attention due to its potential to occur under physiological conditions via a finely regulated way. By releasing gliotransmitters in millisecond time scale with a specific vesicular apparatus, astrocytes can integrate and process synaptic information and control or modulate synaptic transmission and plasticity.

Fuzzy Complexes: A More Stochastic View of Protein Function

Abstract: Intrinsically disordered proteins (IDPs) are widespread in eukaryotic proteomes and challenge the classical structure-function paradigm that equates a folded 3-D structure with protein function. However, IDPs often function by molecular recognition, in which they bind a partner molecule and undergo “induced folding” or “disorder-to-order transition” upon binding, which apparently suggests that in a functional context IDPs become ordered. Whereas this observation would restore the “prestige” of the classical structure-function paradigm, a closer inspection of the complexes of IDPs reveals that they do not always become fully ordered, but preserve functionally significant disorder in the complex with their binding partner(s). This phenomenon, which we termed “fuzziness”, is the ultimate extension of structural disorder to the functional native state of proteins. In this introductory chapter, we outline the most important aspects of fuzziness, such as its structural categories, molecular mechanisms of function it mediates and the biological processes, in which it plays a distinguished role. As confirmed by all the other chapters of the book, we will show that new cases of fuzziness pop up at an accelerating pace, underscoring that this phenomenon presents a widespread novel paradigm of protein structure and function.

Contractile tail machines of bacteriophages

Abstract: Bacteriophages with contractile tails epitomize the concepts of "virus" and "phage" for many because the tails of these phages undergo a large conformational change - resembling the action of a syringe - upon the attachment to the host cell. The contractile tails belong to the recently recognized class of "contractile systems," which includes phage tails, their close relatives R-type pyocins, the bacterial type VI secretion system, and the virulence cassette of Photorhabdus. Their function is to deliver large proteins and/or DNA into the cytoplasm of a bacterial or eukaryotic cell. The structure of the core components of all contractile tail-like systems is conserved, but the corresponding genes have diverged to such a degree that the common ancestry can no longer be easily detected at the level of amino acid sequence. At present, it is unclear, whether the contractile systems originated in bacteria or in phages. This chapter describes the structure and function of phage contractile tails and compares them with other phage tails and with other known contractile systems.

Mitochondria and reactive oxygen species. Which role in physiology and pathology

Abstract: Oxidative stress is among the major causes of toxicity due to interaction of Reactive Oxygen Species (ROS) with cellular macromolecules and structures and interference with signal transduction pathways. The mitochondrial respiratory chain, specially from Complexes I and III, is considered the main origin of ROS particularly under conditions of high membrane potential, but several other sources may be important for ROS generation, such as mitochondrial p66Shc, monoamine oxidase, α-ketoglutarate dehydogenase, besides redox cycling of redox-active molecules. ROS are able to oxidatively modify lipids, proteins, carbohydrates and nucleic acids in mitochondria and to activate/inactivate signalling pathways by oxidative modification of redox-active factors. Cells are endowed with several defence mechanisms including repair or removal of damaged molecules, and antioxidant systems, either enzymatic or non-enzymatic. Oxidative stress is at the basis of ageing and many pathological disorders, such as ischemic diseases, neurodegenerative diseases, diabetes, and cancer, although the underlying mechanisms are not always completely understood.

Mitochondria in Neurodegeneration

Abstract: Many neurodegenerative diseases demonstrate abnormal mitochondrial morphology and biochemical dysfunction. Alterations are often systemic rather than brain-limited. Mitochondrial dysfunction may arise as a consequence of abnormal mitochondrial DNA, mutated nuclear proteins that interact directly or indirectly with mitochondria, or through unknown causes. In most cases it is unclear where mitochondria sit in relation to the overall disease cascades that ultimately causes neuronal dysfunction and death, and there is still controversy regarding the question of whether mitochondrial dysfunction is a necessary step in neurodegeneration. In this chapter we highlight and catalogue mitochondrial perturbations in some of the major neurodegenerative diseases including Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington’s disease (HD). We consider data that suggest mitochondria may be critically involved in neurodegenerative disease neurodegeneration cascades.

CAVEOLIN-1: Role in Cell Signaling

Abstract: Caveolins (Cavs) are integrated plasma membrane proteins that are complex signaling regulators with numerous partners and whose activity is highly dependent on cellular context. Cavs are both positive and negative regulators of cell signaling in and/or out of caveolae, invaginated lipid raft domains whose formation is caveolin expression dependent. Caveolins and rafts have been implicated in membrane compartmentalization; proteins and lipids accumulate in these membrane microdomains where they transmit fast, amplified and specific signaling cascades. The concept of plasma membrane organization within functional rafts is still in exploration and sometimes questioned. In this chapter, we discuss the opposing functions of caveolin in cell signaling regulation focusing on the role of caveolin both as a promoter and inhibitor of different signaling pathways and on the impact of membrane domain localization on caveolin functionality in cell proliferation, survival, apoptosis and migration.

Notch inhibition as a promising new approach to cancer therapy.

Abstract: The Notch pathway powerfully influences stem cell maintenance, development and cell fate and is increasingly recognized for the key roles it plays in cancer. Notch promotes cell survival, angiogenesis and treatment resistance in numerous cancers, making it a promising target for cancer therapy. It also crosstalks with other critical oncogenes, providing a means to affect numerous signaling pathways with one intervention. While the gamma-secretase inhibitors are the only form of Notch inhibitors in clinical trials, other forms of Notch inhibition have been developed or are theoretically feasible. In this chapter we review the rationales for Notch inhibition in cancer and then discuss in detail the various modalities for Notch inhibition, both current and speculative.

Calcium binding proteins.

Abstract: The role of Ca2+ as a key and pivotal second messenger in cells depends largely on a wide number of heterogeneous so-called calcium binding proteins (CBP), which have the ability to bind this ion in specific domains. CBP contribute to the control of Ca2+ concentration in the cytosol and participate in numerous cellular functions by acting as Ca2+ transporters across cell membranes or as Ca2+-modulated sensors, i.e., decoding Ca2+ signals. In this chapter we review the main Ca2+-modulated CBP, starting with those intracellular CBP that contain the structural EF-hand domain: parvalbumin, calmodulin, S100 proteins and calcineurin. Then, we address intracellular CBP lacking the EF-hand domain: CBP within intracellular Ca2+ stores (paying special attention to calreticulin and calsequestrin), annexins and proteins that contain a C2 domain, such as protein kinase C (PKC) or sinaptotagmin. Finally, extracellular CBP have been classified in six groups, according to their Ca2+ binding structures: (i) EF-hand domains; (ii) EGF-like domains; (iii) γ-carboxyl glutamic acid (GLA)-rich domains; (iv) cadherin domains; (v) Ca2+-dependent (C)-type lectin-like domains; (vi) Ca2+-binding pockets of family C G-protein-coupled receptors. For all proteins, we briefly review their structure, location and function and additionally their potential as pharmacological targets in several human diseases.

Assembly and Architecture of HIV

Abstract: HIV forms spherical, membrane-enveloped, pleomorphic virions, 1,000–1,500 A in diameter, which contain two copies of its single-stranded, positive-sense RNA genome. Virus particles initially bud from host cells in a noninfectious or immature form, in which the genome is further encapsulated inside a spherical protein shell composed of around 2,500 copies of the virally encoded Gag polyprotein. The Gag molecules are radially arranged, adherent to the inner leaflet of the viral membrane, and closely associated as a hexagonal, paracrystalline lattice. Gag comprises three major structural domains called MA, CA, and NC. For immature virions to become infectious, they must undergo a maturation process that is initiated by proteolytic processing of Gag by the viral protease. The new Gag-derived proteins undergo dramatic rearrangements to form the mature virus. The mature MA protein forms a “matrix” layer and remains attached to the viral envelope, NC condenses with the genome, and approximately 1,500 copies of CA assemble into a new cone-shaped protein shell, called the mature capsid, which surrounds the genomic ribonucleoprotein complex. The HIV capsid conforms to the mathematical principles of a fullerene shell, in which the CA subunits form about 250 CA hexamers arrayed on a variably curved hexagonal lattice, which is closed by incorporation of exactly 12 pentamers, seven pentamers at the wide end and five at the narrow end of the cone. This chapter describes our current understanding of HIV’s virion architecture and its dynamic transformations: the process of virion assembly as orchestrated by Gag, the architecture of the immature virion, the virus maturation process, and the structure of the mature capsid.

Principles of Virus Structural Organization

Abstract: Viruses, the molecular nanomachines infecting hosts ranging from prokaryotes to eukaryotes, come in different sizes, shapes, and symmetries. Questions such as what principles govern their structural organization, what factors guide their assembly, how these viruses integrate multifarious functions into one unique structure have enamored researchers for years. In the last five decades, following Caspar and Klug’s elegant conceptualization of how viruses are constructed, high-resolution structural studies using X-ray crystallography and more recently cryo-EM techniques have provided a wealth of information on structures of a variety of viruses. These studies have significantly ­furthered our understanding of the principles that underlie structural organization in viruses. Such an understanding has practical impact in providing a rational basis for the design and development of antiviral strategies. In this chapter, we review principles underlying capsid formation in a variety of viruses, emphasizing the recent developments along with some historical perspective.

Assembly factors of human mitochondrial respiratory chain complexes: physiology and pathophysiology.

Abstract: Mitochondrial disorders are clinical syndromes associated with -abnormalities of the oxidative phosphorylation (OXPHOS) system, the main responsible for the production of energy in the cell. OXPHOS is carried out in the inner mitochondrial membrane by the five enzymatic complexes of the mitochondrial respiratory chain (MRC). The subunits constituting these multimeric complexes have a dual genetic origin, mitochondrial or nuclear. Hence, mitochondrial syndromes can be due to mutations of mitochondrial DNA or to abnormalities in nuclear genes. The biogenesis of the MRC complexes is an intricate and finely tuned process. The recent discovery of several OXPHOS-related human genes, mutated in different clinical syndromes, indicates that the majority of the inherited mitochondrial disorders are due to nuclear genes, and many of them encode proteins necessary for the proper assembly/stability of the MRC complexes. The detailed mechanisms of these processes are not fully understood and the exact function of many such factors remains obscure.We present an overview on the hypothesized assembly processes of the different MRC complexes, focusing on known assembly factors and their clinical importance.

Role of C3, C5 and anaphylatoxin receptors in acute lung injury and in sepsis.

Abstract: The complement system plays a major role in innate immune defenses against infectious agents, but exaggerated activation of complement can lead to severe tissue injury. Systemic (intravascular) activation of complement can, via C5a, lead to neutrophil (PMN) activation, sequestration and adhesion to the pulmonary capillary endothelium, resulting in damage and necrosis of vascular endothelial cells and acute lung injury (ALI). Intrapulmonary (intraalveolar) activation of complement can cause ALI that is complement and PMN-dependent, resulting in a cytokine/chemokine storm that leads to intense ALI. Surprisingly, C3−/− mice develop the full intensity of ALI in a C5a-dependent manner due to the action of thrombin that generates C5a directly from C5. There is conflicting evidence on the role of the second C5a receptor, C5L2 in development of ALI. There is accumulating evidence that C5a may suppress inflammatory responses or divert them from Th1 to Th2 responses, impacting the innate immune system. Finally, in experimental polymicrobial sepsis, there is evidence that many of the adverse outcomes can be linked to the roles of C5a and engagement of its two receptors, C5aR and C5L2. These observations underscore the diversity of effects of C5a in a variety of inflammatory settings.

Mitochondria and cancer: a growing role in apoptosis, cancer cell metabolism and dedifferentiation

Abstract: At the beginning of the twentieth century, Otto Warburg demonstrated that cancer cells have a peculiar metabolism. These cells preferentially utilise glycolysis for energetic and anabolic purposes, producing large quantities of lactic acid. He defined this unusual metabolism “aerobic glycolysis”. At the same time, Warburg hypothesised that a disruption of mitochondrial activities played a precise pathogenic role in cancer. Because of this so-called “Warburg effect”, mitochondrial physiology and cellular respiration in particular have been overlooked in pathophysiological studies of cancer. Over time, however, many studies have shown that mitochondria play a fundamental role in cell death by apoptosis or necrosis. Moreover, metabolic enzymes of the Krebs cycle have also recently been recognised as oncosuppressors. Recently, a series of studies were undertaken to re-evaluate the role of oxidative mitochondrial metabolism in cancer cell growth and progression. Some of these data indicate that modulation of mitochondrial respiration may induce an arrest of cancer cell proliferation and differentiation (pseudodifferentiation) and/or or death, suggesting that iatrogenic manipulation of some mitochondrial activities may induce anticancer effects. Moreover, studying the role of mitochondria in cancer cell dedifferentiation/differentiation processes may allow further insight into the pathophysiology and therapy of so-called cancer stem cells.

Influenza Virus Entry

Abstract: As all the enveloped viruses, the entry of influenza viruses includes a number of steps in host cell infection. This chapter summarizes the current knowledge of the entry pathway and the role of the fusion protein of influenza virus, hemagglutinin, in this process. Hemagglutinin (HA) is a trimeric glycoprotein that is present in multiple copies in the membrane envelope of influenza virus. HA contains a fusion peptide, a receptor binding site, a metastable structural motif, and the transmembrane domain. The first step of influenza virus entry is the recognition of the host cell receptor molecule, terminal α-sialic acid, by HA. This multivalent attachment by multiple copies of trimetric HA triggers endocytosis of influenza virus that is contained in the endosome. The endosome-trapped virus traffics via a unidirectional pathway to near the nucleus. At this location, the interior pH of the endosome becomes acidic that induces a dramatic conformational change in HA to insert the fusion peptide into the host membrane, induce juxtaposition of the two membranes, and form a fusion pore that allows the release of the genome segments of influenza virus. HA plays a key role in the entire entry pathway. Inhibitors of virus entry are potentially effective antiviral drugs of influenza viruses.

Short noncontractile tail machines: adsorption and DNA delivery by podoviruses.

Abstract: Tailed dsDNA bacteriophage virions bind to susceptible cells with the tips of their tails and then deliver their DNA through the tail into the cells to initiate infection This chapter discusses what is known about this process in the short-tailed phages (Podoviridae) Their short tails require that many of these virions adsorb to the outer layers of the cell and work their way down to the outer membrane surface before releasing their DNA Interestingly, the receptor-binding protein of many short-tailed phages (and some with long tails) has an enzymatic activity that cleaves their polysaccharide receptors Reversible adsorption and irreversible adsorption to primary and secondary receptors are discussed, including how sequence divergence in tail fiber and tailspike proteins leads to different host specificities Upon reaching the outer membrane of Gram-negative cells, some podoviral tail machines release virion proteins into the cell that help the DNA efficiently traverse the outer layers of the cell and/or prepare the cell cytoplasm for phage genome arrival Podoviruses utilize several rather different variations on this theme The virion DNA is then released into the cell; the energetics of this process is discussed Phages like T7 and N4 deliver their DNA relatively slowly, using enzymes to pull the genome into the cell At least in part this mechanism ensures that genes in late-entering DNA are not expressed at early times On the other hand, phages like P22 probably deliver their DNA more rapidly so that it can be circularized before the cascade of gene expression begins

The brain's extracellular matrix and its role in synaptic plasticity

Abstract: The extracellular matrix (ECM) of the brain has important roles in regulating synaptic function and plasticity. A juvenile ECM supports the wiring of neuronal networks, synaptogenesis, and synaptic maturation. The closure of critical periods for experience-dependent shaping of neuronal circuits coincides with the implementation of a mature form of ECM that is characterized by highly elaborate hyaluronan-based structures, the perineuronal nets (PNN), and PNN-like perisynaptic ECM specializations. In this chapter, we will focus on some recently reported aspects of ECM functions in brain plasticity. These include (a) the discovery that the ECM can act as a passive diffusion barrier for cell surface molecules including neurotransmitter receptors and in this way compartmentalize cell surfaces, (b) the specific functions of ECM components in actively regulating synaptic plasticity and homeostasis, and (c) the shaping processes of the ECM by extracellular proteases and in turn the activation particular signaling pathways.

Notch signaling pathway and cancer metastasis.

Abstract: Cancer metastasis is the leading cause of cancer-related deaths all over the world at present. Accumulated researches have demonstrated that cancer metastasis is composed of a series of successive incidents, mainly including epithelial-mesenchymal transition (EMT), malignant cell migration, resistance to anoikis, and angiogenesis and lymphangiogenesis processes. However, the complicated cellular and molecular mechanisms underlying and modulating these processes have not been well elucidated. Thus, studies on cancer metastasis mechanism may propose possibilities to therapeutically interfere with signaling pathways required for each step of cancer metastasis, therefore inhibiting the outgrowth of distant metastasis of tumors. Recent insights have linked the Notch signaling pathway, a critical pathways governing embryonic development and maintaining tumor stemness, to cancer metastasis. This chapter highlights the current evidence for aberration of the Notch signaling in metastasis of tumors such as osteosarcoma, breast cancer, prostate cancer, and melanoma. In these studies, Notch activity seems to participate in cancer metastasis by modulating the EMT, tumor angiogenesis processes, and the anoikis-resistance of tumor cells. Therefore, manipulating Notch signaling may represent a promising alternative/ complement therapeutic strategy targeting cancer metastasis besides cancer stemness.

The bacteriophage DNA packaging machine.

Abstract: Large dsDNA bacteriophages and herpesviruses encode a powerful ATP-driven DNA-translocating machine that encapsidates a viral genome into a preformed capsid shell or prohead. The key components of the packaging machine are the packaging enzyme (terminase, motor) and the portal protein that forms the unique DNA entrance vertex of prohead. The terminase complex, comprised of a recognition subunit (small terminase) and an endonuclease/translocase subunit (large terminase), cuts viral genome concatemers. The terminase–viral DNA complex docks on the portal vertex, assembling a motor complex containing five large terminase subunits. The pentameric motor processively translocates DNA until the head shell is full with one viral genome. The motor cuts the DNA again and dissociates from the full head, allowing head-finishing proteins to assemble on the portal, sealing the portal, and constructing a platform for tail attachment. A body of evidence from molecular genetics and biochemical, structural, and biophysical approaches suggests that ATP hydrolysis–driven conformational changes in the packaging motor (large terminase) power DNA motion. Various parts of the motor subunit, such as the ATPase, arginine finger, transmission domain, hinge, and DNA groove, work in concert to translocate about 2 bp of DNA per ATP hydrolyzed. Powerful single-molecule approaches are providing precise delineation of steps during each translocation event in a motor that has a speed as high as a millisecond/step. The phage packaging machine has emerged as an excellent model for understanding the molecular machines, given the mechanistic parallels between terminases, helicases, and numerous motor proteins.

TRIM proteins in cancer.

Abstract: Some members of the tripartite motif (TRIM/RBCC) protein family are thought to be important regulators of carcinogenesis. This is not surprising as the TRIM proteins are involved in several biological processes, such as cell growth, development and cellular differentiation and alteration of these proteins can affect transcriptional regulation, cell proliferation and apoptosis. In particular, four TRIM family genes are frequently translocated to other genes, generating fusion proteins implicated in cancer initiation and progression. Among these the most famous is the promy elocytic leukaemia gene PML, which encodes the protein TRIM19. PML is involved in the t(15;17) translocation that specifically occurs in Acute Promyelocytic Leukaemia (APL), resulting in a PML-retinoic acid receptor-a (PML-RARα) fusion protein.

Secreted Klotho and Chronic Kidney Disease

Abstract: Soluble Klotho (sKl) in the circulation can be generated directly by alterative splicing of the Klotho transcript or the extracellular domain of membrane Klotho can be released from membrane-anchored Klotho on the cell surface. Unlike membrane Klotho which functions as a coreceptor for fibroblast growth factor-23 (FGF23), sKl, acts as hormonal factor and plays important roles in anti-aging, anti-oxidation, modulation of ion transport, and Wnt signaling. Emerging evidence reveals that Klotho deficiency is an early biomarker for chronic kidney diseases as well as a pathogenic factor. Klotho deficiency is associated with progression and chronic complications in chronic kidney disease including vascular calcification, cardiac hypertrophy, and secondary hyperparathyroidism. In multiple experimental models, replacement of sKl, or manipulated up-regulation of endogenous Klotho protect the kidney from renal insults, preserve kidney function, and suppress renal fibrosis, in chronic kidney disease. Klotho is a highly promising candidate on the horizon as an early biomarker, and as a novel therapeutic agent for chronic kidney disease.

Stem cells and calcium signaling.

Abstract: The increasing interest in stem cell research is linked to the promise of developing treatments for many lifethreatening, debilitating diseases, and for cell replacement therapies. However, performing these therapeutic innovations with safety will only be possible when an accurate knowledge about the molecular signals that promote the desired cell fate is reached. Among these signals are transient changes in intracellular Ca2+ concentration [Ca2+]i. Acting as an intracellular messenger, Ca2+ has a key role in cell signaling pathways in various differentiation stages of stem cells. The aim of this chapter is to present a broad overview of various moments in which Ca2+-mediated signaling is essential for the maintenance of stem cells and for promoting their development and differentiation, also focusing on their therapeutic potential.

Notch signaling in cancer stem cells.

Abstract: Subpopulations of cancer cells with stem cell-like characteristics, termed cancer stem cells, have been identified in a wide range of human cancers. Cancer stem cells are defined by their ability to self-renew as well as recapitulate the original heterogeneity of cancer cells in culture and in serial xenotransplants. Not only are cancer stem cells highly tumorigenic, but these cells are implicated in tumor resistance to conventional chemotherapy and radiotherapy, thus highlighting their significance as therapeutic targets. Considerable similarities have been found between cancer stem cells and normal stem cells on their dependence on certain signaling pathways. More specifically, the core stem cell signaling pathways, such as the Wnt, Notch and Hedgehog pathways, also critically regulate the self-renewal and survival of cancer stem cells. While the oncogenic functions of Notch pathway have been well documented, its role in cancer stem cells is just emerging. In this chapter, we will discuss recent advances in cancer stem cell research and highlight the therapeutic potential of targeting Notch in cancer stem cells.