Advances in Cell biology, vol. 32, 2005, issue 1

Summary: The natural polyamines are in multiple ways involved in cell growth and the maintenance of cell viability. In the course of the last 10 years more and more evidence hinted also at their role in gene regulation. It is therefore not surprising that the polyamines are involved in events inherent to genetically programmed cell death. Numerous links have been identified between the polyamines and apoptotic pathways. Aberrant polyamine concentration is most probably not a first cause of programmed cell death but it may promote apoptotic mechanisms if they reach concentration above or below physiological limits. Polyamines can be associated with many molecules by different types of binding. One of these is conjugation to protein via transglutaminases, a family of enzymes that catalyse the covalent binding of substrates with primary amine groups, like polyamines, to the protein. Transglutaminases are one of the relevant factors of programmed cell death in animals; in fact in several animal cell-lines, the presence and the activity of transglutaminases are considered markers of apoptosis. In contrast to the many evidence for involvement of polyamines in the mammalian programmed cell death, almost no information is avail-able regarding these factors during programmed cell death in plants. This review discusses the possible mechanisms of the action of polyamines in physiological processes, including programmed cell death. Natural polyamines can act within cells by: regulation of the expression of growth related genes; binding to anionic sites and forming ion bonds; forming covalent bonds by enzyme-catalysed reactions; acting as scavenging radicals; or producing cytotoxic aldehydes and reactive oxygen species via their oxidative deaminations.

Cumulus Oophorus Expansion: Indispensable Process for Proper Ovulation and Fertilization

Summary: Cumulus oophorus expansion takes place in matured ovarian follicles in response to preovulatory increased concentration of luteinizing hormone (LH) in blood. As a result of intensive extracellular matrix synthesis cumulus granulosa cells expand, the whole structure multiplies its volume and finally separates together with the oocyte from the follicle wall. Because cumulus cells practically do not have LH receptors, expansion inducing signal reach them through the medium of other molecules. These molecules are above all prostaglandin E₂and epidermal growth factors (EGF) secreted by mural granulosa cells as well as transforming growth factor b (TGF-b) superfamily members deriving from the oocyte. Extracellular matrix of fully expanded cumulus oophorus consists of hialuronic acid chains to which other components are bound. These components are synthesized by granulosa cells (versican, TSG-6, pentraxin 3) or derive from serum (heavy chains of inter-alpha-trypsin inhibitors). Creation of mice with knockouts of genes responsible for cumulus expansion allowed to prove that this process is absolutely indispensable for successful ovulation. Moreover, cumulus cells together with reach extracellular matrix surround the oocyte while it pass through the oviduct interacting with oviductal epithelium. They also facilitate fertilization by trapping spermatozoa, guiding them to the oocyte, favoring capacitation and acrosomal reaction.

Key words: cumulus oophorus, granulosa cells, ovulation, fertilization, extracellular matrix

Summary: Glioblastoma multiforme (GBM) is the most frequent malignant tumor derived from glial cells. Median survival with this type of tumor is about 1 year after surgical resection followed by radiotherapy. High invasiveness of GBM is the result of improper signal transduction through the intracellular pathway involving PI3K, Akt/PKB and mTOR, kinases responsible for the regulation of proliferation, differentiation and survival. Mutations in genes encoding mentioned enzymes lead to the increased activity of kinases and to increased cell survival after chemotherapy. In this article, the function of mentioned kinases in GBM cells has been described, as well as specific inhibitors of these enzymes and their potential usefulness in cancer therapy.

Key words: PI3K, Akt/PKB, mTOR, gliomas

The Current Knowledge Of Invertebrate Aquaporin Water Channels with Particular Emphasis on Insect AQPs

Summary: Aquaporins (AQPs) or water channels are some of the most ubiquitous integral membrane proteins that are present in all living organisms. Their presence in the lipid bilayer of cell membranes considerably increases their permeability to water and, in some cases, to other small solutes. All identified AQPs share the same structure, with the presence of six transmembrane segments and two conservative regions forming the pore. Depending on the transported solutes, AQPs can be divided into two classes: 'classical' aquaporins (permeable only to water) and aquaglyceroporins (permeable also to glycerol and/or other solutes). Many subtypes of AQPs coexist in a single organism. Localization of particular subtypes of AQPs is tissue-specific. AQPs have been well characterized in almost all vertebrate classes. However, little is known about their counterparts in invertebrates. Most of the characterised water channels in invertebrates are found in insects. Therefore, the full knowledge of aquaporins in invertebrates is generally nothing but the information concerning water channels in these class of organisms. Insects are characterised by astonishing variety of physiological adaptations, noticeable especially in their feeding strategy or survival strategies in hostile environments. The example of such is feeding on blood or tolerating extreme cold or drought. It seems obvious that many of these adaptation patterns emerged due to the expression and regulation of particular aquaporins. Here we review the current state of knowledge of invertebrate AQPs (insects and nematode AQPs) and compare their structure and function with mammalian water channels.

Structural and Functional Reorganisation of Podocytes in Idiopathic Nephrotic Syndrome in Children

Key words: adult stem cells, adipose tissue, multipotency, pluripotency, in vitro differentiation, tissue engineering, cell-based therapy

Summary: Nitric oxide (NO) is a reactive gaseous molecule recognized as biological mediator in all leaving organisms. Although there is a lot of evidences on both enzymatic and nonenzymatic synthesis of NO in plant cells, this problem still remains puzzling. NO is generated in different cellular compartments from L-arginine or nitrite ions in reaction catalyzed by nitric oxide synthase or nitrate reductase, respectively. Recent experimental data have shown NO involvement in regulation of many different physiological processes in plants such as seed germination, flowering, root rhizogenesis or senescence. NO acts as signaling molecule in plant reaction to biotic (pathogen attack) and abiotic stresses (heavy metals, salinity, drought, hypoxia). NO itself not only participate in signal transduction but also modifies cellular components, mainly proteins through cysteine S-nitrosylation and probably tyrosine nitration. The involvement of NO into regulation of so many responses implies a severe mechanism of regulation of its concentration in the tissue. A number of reports implicated non-symbiotic hemoglobins as a key system for modulation of NO bioactivity in plants, especially during low oxygen support. Plant hemoglobins with properties distinct from symbiotic hemoglobin are expressed in different organs and tissue and are widespread in the plant kingdom. Hemoglobins are suggested to protect plant cells against nitrosative stress resulting from enhanced reactive nitrogen species production and to modify NO signaling action. The aim of the paper is to explain the main physiological and biochemical functions reported for non-symbiotic hemoglobins in plants and characterize the mechanism by which hemoglobins interact with NO in plants exposed to low oxygen conditions. The function of hemoglobin/nitric oxide cycle is described as the way of restoration redox and energy status of the cells.

Key words: hypoxia, nonsybiotic hemoglobins, nitration, nitrosylation, nitric oxide

Summary: Pollen grain, because of its unique structural organization, is extremely useful experimental model, both in cytological, molecular as well as in genetic studies. Easiness of pollen grains isolation, their sorting as well as simple extraction of their DNA, RNA and proteins, caused that male gametophyte cells of angiosperms are presently one of the most intensively studied among different plant cells. A strong and rapid progress in development of experimental tools dedicated for exploration genome caused significant increase in the number of reports concerning on different aspects of gene expression during microsporogenesis and microgametogenesis in angiosperm plants. In the present review we synthesized the actual knowledge of pollen transcriptome and proteome during different stages of male gametophyte development, specially in Arabidopsis thaliana. Most of results presented here was obtained basing on experiments carried out using microarrays, which were designed basing on known sequence of Arabidopsis genome.

Summary: This review presents the experimental data indicating that complement system plays an important, however, up to now underestimated role in the regulation of hematopoiesis. The cleavage fragments of the third complement component (C3) regulate the response of early hematopoietic cells to an SDF-1 gradient, which is the main chemoattractant for stem cells. Complement system is activated in bone marrow both during myeloablative conditioning for hematopoietic transplantation as well as during pharmacological mobilization of stem cells. Therefore modulation of complement activation may lead to new strategies to accelerate engraftment of stem cells or to increase their mobilization into peripheral blood.

Key words: stromal derived factor-1 (SDF-1), hematopoiesis, CXCR4 receptor, complement system

Summary: The MAP kinases (MAPKs), including ERK, JNK and p38 families consist the part of intracellular signaling network, which is essential for signal transduction from receptors and biological answer to the stimuli. Activity of MAPKs plays a crucial role in normal functioning of the immune system. By taking part in cytokine production upon signaling from activated TLR receptors, MAPKs are involved in initiation of innate immunity and in responses to binding of cytokines by appropriate receptors. MAPKs activity is also important for T and B lymphocyte differentiation, by the ITAM signaling pathway. Moreover, their involvement in apoptosis supports lymphocyte T cytotoxicity and enables to remove damaged, infected or transformed cells. Correct functioning of the MAPK signaling is crucial for effective immune response, and therefore MAPKs inhibitors consist a promising therapeutic goal.

Summary: Immunity can be defined as the ability of each living organism to maintain its own integrity (homeostasis) through recognizing non-self and discriminating it from self. In vertebrates innate and adaptive immunity mechanisms are involved in fighting against pathogens. According to general opinions, filogenetically older invertebrates respond to infection activating only innate immunity reactions. How-ever, a growing line of evidence indicates that the immune system in insects, crustaceans and molluscs can specifically recognize and remember infection with certain pathogens. Involvement of multiple isoforms of pattern recognition receptors containing variable Ig domains, eg. insect Dscam and snail FREPs is implicated in specific recognition of different pathogens and in selection of immune competent fagocytes. There are suggestions that invertebrates possess an alternative type of adaptive immunity functioning through mechanisms which differ from the ones known in vertebrates. The review describes new discoveries in invertebrate immunity, with special focus on insects.

Key words: innate immunity, defense peptides, Drosophila melanogaster, Toll, imd, Dscam