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

Summary: Galectin-3 is a member of a family of b-galactoside-binding animal lectins and is the only chimera type galectin. Galectin-3 consists of two structural domains: a N-terminal domain that contains a phosphorylation site and a repeated 9 amino acids sequence rich in Pro, Gly, Tyr and Glu; and a C-terminal domain that contains a carbohydrate recognition domain. In human genome galectin-3 is coded by a single gene LGALS3 which is situated on chromosome 14 and composed of six exons and five introns. Galectin-3 is localized in the cytoplasm as well as in the nucleus. Galectin-3 is involved in many biological processes, such as: cell-cell and cell-extracellular matrix adhesion, mRNA splicing, cell growth and differentiation, cell cycle, signaling, apoptosis and angiogenesis. Consequently, galectin-3 is involved in regulation immune reaction, tumor growth and metastasis. Despite of fact that galectin-3 is synthesised by free ribosomes in the cytosol and lacks signal sequence, there are evidence for its extracellular localization. Differential galectin-3 distribution is associated with many functions it performs in the cell.

Summary: Gal-3 shares several significant structural properties with Bcl-2 family. Both proteins contain anti-death motif, critical for their anti-apoptotic function but the mechanism by which gal-3 exhibits anti-apoptotic activity cannot be explained solely on it. Depending on the type, state and condition of the cell as well as depending on the type of stimulus gal-3 can show pro- or anti-apoptotic activity. Cytoplasmic gal-3 expression seems to be strongly implicated in an anti-apoptotic function and drug resistance in cancer cells, suggesting that cytoplasmic gal-3 is a candidate target protein to suppress anticancer drug resistance. Gal-3 previously known as IgE-binding protein is a pro-inflammatory lectin. In response to pro-inflammatory agents some cells produce and release high amount of gal-3. Taking together, gal-3 can provide a new therapeutic target for improving chemotherapy of cancer. In addition the detection of extracellular gal-3 may be of diagnostic value as prognostic cancer marker.

Summary: RNA degradation in yeast and mammalian cells take place in cytoplasm, nucleus and mitochondria. Degradation of transcripts with a premature termination codon or without stop codon results in repression of aberrant protein synthesis. The mRNA decay pathway, which degrades mRNAs containing a stem-loop structure has been discovered and characterized in the yeast Saccharomyces cerevisiae. Eukaryotic transcripts with AU-rich elements in their 3'-untranslated region have a very short half-life. These elements regulate mRNA level in cells. The multi-enzymatic nuclear exosome complex, Rat1p and cap binding complex degrade mRNAs in the yeast nucleus. The mitochondrial degradosome (mtEXO) is an enzymatic complex which has a major function in the mitochondrial genome post-transcription gene expression regulation. RNA interference cleaves mRNA after a previous induction by dsRNA. The 2-5A/RNase L system inhibits replication of viral RNA.

Key words: f mRNA degradation, P bodies, exosome, NMD, NSD, NGD, AMD, DRN, mitochondrial degradosome, RNA interference, 2-5A/RNase L system

Summary: The phytohormone abscisic acid (ABA) coordinates plant responses to stressors such as drought, extreme temperature and high salinity, as well regulates non-stress responses including seed formation and maturation, seed and bud dormancy, root growth, leaf senescence, and transition between vegetative and reproductive growth. ABA, similarly like the others plant hormones, functions through a complex network of signaling pathway, where ABA signal perception by ABA receptors is the primary event that triggers downstream signaling cascades to induce the final physiological responses. Since 2006, several proteins have been identified as possible ABA receptors. These are the nuclear flowering-time protein FCA, the plastid-associated Mg-protoporphyrin IX chelatase H subunit (CHLH/GUN5), a membrane-bound GCR2, and two novel G-protein coupled receptors GTG1 and GTG2. However, the results obtained in these studies are contested or questioned by several researchers, and in one case lately retracted. The situation improved with the publication of the recent studies indicating that receptors for this hormone are a group of small soluble proteins referred to as Pyrabactin Resistance 1 (PYR1), or PYR-like (PYL), encoded in Arabidopsis thaliana by fourteen genes. Proteins of this family were found to bind ABA and inhibit the activity of specific protein phosphatase enzymes, the type 2C plant PP2Cs, which were previously implicated in the ABA responses. In the absence of ABA, the PP2Cs act as constitutive negative regulators of a family of protein kinases SnRK2s whose autophosphorylation is required for kinase activity towards downstream targets. When abscisic acid enters a plant cell, PYR1/PYL receptor forms a binary complex with hormone and then immediately binds to, and inhibits the PP2C. The inhibition of the negatively acting PP2Cs leads to the successful activation of SnRK2.2, SnRK2.3 and SnRK2.6, which phosphorylate the basic leucine zipper (bZIP) transcription factors called ABFs/AREBs inducing the expression of ABA-responsive genes. By determining the crystal structures of members of the receptor family, with and without bound abscisic acid and protein phosphatase, high-definition structural images of the receptor complex are now available. In the hormone-free form, the PYR1/PYL protein presents an open and accessible cavity with two flexible surface loops that guard the ABA-binding pocket. Binding of ABA to the receptor-protein initiates an allosteric transition of the gating loops that sequester ABA in the pocked. The protein phosphatase PP2C binds to the hydrophobic site on the gating loops, which interact closely with the active site of the phosphatase, blocking its ability to bind and dephosphorylate its substrate. A conserved tryptophan residue of the phosphatase inserts its side chain to the gating loops. In this respect, PP2C acts as a potent co-receptor to enhance the affinity of the hormone for its receptor.

Key words: abscisic acid, ABA receptors, ABA signaling

Summary: The rotation of earth around its axis leads to environmental changes in light intensity and temperature that predictably define day-night cycle. Most organisms coordinate their life cycle in anticipation of these environmental fluctuations. The measurement of time and synchronization with the environment are achieved by an internal time-keeping mechanism – biological clock. The circadian clock is an endogenous mechanism that generates rhythms with an approximately 24-h period and enables plants to adapt to daily and seasonal changes in their environment. The circadian clock can be considered as a mechanism that translates environmental signals into temporal information in order to rhythmically coordinate metabolism and physiology. Circadian rhythms enable biological processes to occur at the most appropriate times during the day-night cycle, which confers a advantage to organisms. Circadian clock regulates many processes in plants, including leaf and stomatal movements, photosynthesis and growth and contributes to photoperiodism. Circadian rhythms are generated by molecular oscillators that in Arabidopsis thaliana have been shown to consist of network of transcription factors arranged in interlocking negative-feedback loops involving a number of elements. Circadian clock is based on the feedback loop involving the genes TOC1 (TIMING OF CAB EXPRESSION1), CCA1 (CIRCADIAN CLOCK ASSOCIATED1) and LHY (LATE ELONGATED HYPOCOTYL). Protein TOC1 induces the transcription of genes LHY1 and CCA1, which are translated into proteins that repress the expression of TOC1. An important characteristic of circadian oscillators is that they can be entrained by cues from the environment, such as daily changes in light and temperature, transduced via input pathways. The last components of circadian clock model are the output pathways that provide a link between the oscillator and the various biological processes and their rhythms, which are controlled by circadian clock. A unique property of circadian oscillator's mechanism is temperature compensation – the stability of the period of the clock over a wide range of physiological temperatures and the persistence of rhythms in the absence of environmental signals. Bidirectional, mutual regulation is known between plant hormones' (auxin, abscisic acid, cytokinin) signaling pathways and grid of interactions of central oscillator's compounds. Plant hormones and central oscillator together control many physiological processes, and additionally, parallel regulation of common pool of genes was reported. Mechanism of central oscillator is regulated not only during initiation of transcription of genes encoding oscillator's compounds. It was shown that influence on the expression of oscillator's genes encoding transcription factors is exerted at the level of transcript stability, alternative splicing or miRNA as well. Control of degradation of oscillator's proteins, through their phosphorylation as a first step, is yet another level of genes expression regulation. Distinct and still not fully elucidated aspect of expression of central oscillator's genes is its regulation through alterations of chromatin architecture.

Key words: gly circadian rhythm, circadian clock, central oscillator, feedback mechanism, transcription factors

Summary: In the paper the current state-of-the-art of the preclinical and clinical trials concerning GM-CSF-secreting tumor cell vaccines was presented. Cytokine gene-modified cancer vaccines are experimental immunotherapeutics applied as adjuvants or as main medications in the treatment of metastatic neoplasms. The principle of their action consists in the delivery of cancer antigens in association with GM-CSF to the patient's organism. The cytokine improves recruitment and activation of dendritic cells, leading to more efficient antigens' presentation. Retroviruses and adenoviruses are the most widely applied vectors for cytokine gene transfer because of the high efficiency. Effectiveness of the vaccine therapy in the preclinical studies, usually in the models of murine melanoma, was high in the prophylactic as well as in the therapeutic model. Phase I clinical trials, carried out in the patients with metastatic melanoma, lung cancer and prostate cancer, confirmed safety of the therapy, indicated augmented immune response in most of the patients, but only some of them experienced prolonged survival in comparison to the prognosis. Phase II and III studies did not reveal the superiority of vaccination over standard therapy so far. The research carried on at the moment are aimed at finding the reasons for limited clinical efficiency of GM-CSF-secreting tumor cell vaccines. Methods of augmenting its effectiveness contain the following main targets: suppressor CD4 CD25 Foxp3 T-cells, MFG-E8 protein and co-stimulatory molecule CTLA-4.

Summary: The rapidly developing regenerative medicine searches for pluripotential stem cell that will be able to differentiate into stem cells from all three germ layers. In this review we will focus on germ line stem cells that have been recently purified from adult ovaries, testes and other extragonadal tissues. We will discuss their potential clinical application and their relationship of these cells to so called very small embryonic-like stem cells (VSELs), a population of epiblast/germ line pluripotent stem cells identified recently by our team in adult tissues.

Summary: The skin is a complex organ of human body, which plays an essential role, providing physical barrier against mechanical, chemical and biological factors and, through its pigments produced in melanocytes, provides defense system against UV radiation, and reduces the risk of UV-induced DNA damage in human epidermis. The skin is composed of three layers: epidermis and its derivatives, dermis, and hypodermis. The function of the skin, especially hair growth and activity of sebaceous glands, is regulated by sex steroids, and skin is the target organ for these hormones. All enzymes of steroidogenesis are present in the skin, which is also capable of de novo synthesis of androgens. Due to the activity of 5a-reductase and cytochrome P450 aromatase, testosterone can be metabolized into the dihydrotestosterone (DHT) and 17b-estradiol (E2), respectively. Therefore, mammalian skin can be regarded as peripheral endocrine organ.

Summary: The skin constitutes the metabolically active biological barrier separating the internal milieu of mammalian organism and the external environment. The skin is continuously exposed to hostile environmental factors, therefore the anatomic localization determines its many functions. Both, the central endocrine system and the cutaneous endocrine system control and integrate the functions. All factors controlling the activity of the hypothalamus-pituitary-target organ axis are expressed in the skin. The skin cells produce locally hormones, neuropeptides, neurotransmitters and together with the nerve endings form the cutaneous neuroendocrine system. Cutaneous neuroendocrine elements are organized in epidermal and dermal units, including epidermal and dermal cells. The system preserves and maintains the skin local and systemic homeostasis, independently of the central regulation.

Key words: skin, neuroendocrine system, neurohormones, neuropeptides, neurotransmitters, hypothalamic-pituitary-target organ axis

Summary: Since kisspeptin appeared on the stage of endocrinology of reproduction in 2003, its role as a key trigger of the complex aspects of reproduction and especially of the stimulation of gonadotrophin releasing hormone/luteinising hormone in females, was progressively explored and documented. The family of peptides called kisspeptins are products of KiSS-1 gene and are able to bind and activate GRR54 receptor. The role of KiSS-1/GPR54 ligand-receptor system working generally in the hypothalamus, was described in many species of both sexes including humans. In presented review, the key role of this system in the activation of the hypothalamo-pituitary-gonadal (HPG) axis in females from puberty to ovulation was characterized. It is believed, that KiSS-1 system plays an essential role in the timing of puberty onset, what is additionally related to the modulatory action of metabolic and environmental factors. The effect of kisspeptin on dynamic changes in the HPG axis in mature females during the oestrous cycle and its participation in the negative and positive feedback effects of sex hormones on gonadotrophin secretion was also discussed. Finally, investigations concerning the localization and morpho-physiological activity of kisspeptin neurons in the the hypothalamus of mammals and their contacts with GnRH neurons were presented.

Key words: KiSS-1, kisspeptin, GPR54, puberty, oestrous cycle, GnRH-neurons.

Chromosomal mosaicism as a reason of developmental disorders in human. Part I. Mechanisms of formation

Summary: The chromosomal mosaicism connected with unbalanced karyotype due to numeric and structural chromosome aberrations may be a reason of the developmental disorders or by the presence of chromosome instability manifesting in some monogenic disorders in human. The mechanisms of formation the mosaicism like the postzygotic nondisjunction, anaphase lagging, postzygotic duplication, disturbances of protein function of genes responsible for repair of double-strand DNA breaks and control cell divisions, the genes controlling the separation of sisters chromatid or telomere length have been presented. In addition the hot spots – LCR (low copy repeats) as the predisposing factor of illegitimate somatic recombination responsible for chromosome breakage and chromosomal rearrangements were also considered. The specific form of mosaicism leading to developmental disturbances due to genomic imprinting of some genes being in disomy state of entire or segments of chromosomes were taken also into consideration.

Key words: anaphase lagging, chromosomal instability, developmental disorders, mosaicism, nondisjunction, postzygotic duplication

Summary: Arginine vasopressin (AVP) related water resorption in the collecting duct acts through aqua-porins 2 – specific water channels. AQP2 are small integral tetrameric plasma membrane proteins. Each of four subunits is selectively permeable to water. In mammals lack of vasopressin stimulation causes AQP2 storage in intracellular vesicles of the principal cells of the renal distal tubule and collecting duct. AVP acts through specific V₂ receptors. Arginine vasopressin receptor binding increases intracellular production of cAMP and increases protein kinase A (PKA) activity. Ser256, Ser261, Ser264 and Ser269 are phosphorylated in the cytoplasmic C-terminal region of AQP2 by active PKA. Phosphorylation of at least three AQP2 monomers in each tetramer is required to start AQP2 translocation from intracellular vesicles and to cause their fusion with the apical membrane. Kidneys of animals and human neonates show a lot of morphological and functional differences. Adaptation, growth and maturation processes may be accompanied by escalation of diseases. Especially water-electrolyte imbalance can occur as a result of renal and extrarenal loss of water and electrolytes. Kidney immaturity after birth (renal narrow functional reserve and limited ability to excrete concentrated urine) favors this kind of disorders. Reduced ability to form osmotic gradient in kidney medulla as well as less efficient kidney response to vasopressin with AQP2 may cause lower capacity to save water in neonate kidneys. Role of this aquaporin in water tubular resorption in neonate is not explained but it may play the key role in this process. The renal tubular AQP2 expression in neonates is about 50% lower than in adults. In addition lower expression of V₂ receptors in newborn kidneys causes reduced response to AVP. Higher levels of PGE₂, lesser levels of cAMP and restricted PKAaproduction are also observed in neonates. Moreover in neonates in comparison to adults renal AQP2 excretion do not correlate strictly with AVP concentration.

Key words: neonates, kidneys, vasopressin, V2 receptors, aquaporin 2

Summary: It is known that environmental stresses can have devastating effects on plants and represent the most limiting factors for productivity. Apart from biotic stress caused by plant pathogens, there are a number of abiotic stresses such as extremes in temperature, drought, salinity, heavy metals, radiation and mechanical wounding which have detrimental effects on plant growth and development. Certain plant species have developed various mechanisms to defence or adapt to such stress conditions. Mechanisms of signal perception and subsequent responses to stress are complex and consist of cascades of multiple reactions. For a couple of years these signaling cascades and metabolic responses are of great interest to plant biologists. A better understanding of plant stress responses can lead to improved plant breeding strategies resulting in better plant growth and increased crop yields under disadvantageous conditions. However, as we learn more about the signaling pathways leading to these responses, it is becoming clear that they constitute a network that is interconnected at many levels. Stress signal is first perceived by the receptors, then transduced downstream resulting in the activation of various stress responsive genes, transport across membrane and cytoskeleton reorganization. During the last couple of decades a number of second messengers such as calcium ions, cyclic nucleotides, polyphosphoinositides, that are altered in response to abiotic stressors, have been identified. They act on downstream effectors (decoding elements) that ultimately initiate a multitude of cellular responses. Primary targets of second messengers are calcium-dependent protein kinase, calmodulin, calmodulin-like proteins, SOS proteins in case of Ca²⁺, cyclic nucleotide gated cation channels for cNMP and calcium channels and various enzymes for phos-phoinositides. The knowledge concerning the role of above proteins in stress is far from comprehensive. The usage of mutants, introduction of transgenes that reverse the effect of gene knock-out, blocking of genes by antisens mRNA or point mutations aim in better understanding the mechanisms of adaptation to stress. In this review, we summarize recent progress in abiotic stress studies concerning the participation of second messengers and their effectors in plant adaptation to various abiotic stress factors.

Key words: Ca²⁺, cyclic nucleotides, phosphoinositides, abiotic stress

Biological Properties of the Metallothioneins and their Participation in The Processes of Oxidaction-Reduction in Cells, with the Particular Emphasis on the Human Central Nervous System

Summary: Metallothioneins (MTs), as the low molecular weight proteins rich in the active thiol groups, whose synthesis and half-life are closely connected with the activity of zinc ions inside the cell, exert a significant influence on the antioxidant capacity of the environment within and outside the cell. MTs influence the trace elements homeostasis, contribute to the gene expression process and demonstrate the anti-apoptotic properties. They have the ability to bind and neutralize exogenous electrophilic compounds. The antioxidant property of these proteins deserve a special attention, because the MTs synthesis, during the oxidative stress – in contrast to the activity of GSH and the basic antioxidant enzymes – undergo a durable intensification. The human central nervous system (CNS) is particularly exposed to high concentrations of reactive oxygen species (ROS), since it consumes up to 20% of the pool of oxygen absorbed by the body. It was found that the dimension of the harmful effects of oxidative stress in the brain is inversely proportional to the MTs quantity. MTs in the human brain occur in three main isoforms: MT-1, MT-2 and MT-3. MT-1/-2 are synthesized abundantly in astrocytes. Isoform MT-3 which is characteristic for nerve cells, takes an important part in the zinc ions activity regulation, especially in the neocortical and rhinencephalic neurons. Zinc is necessary for development and the proper functioning of the human CNS. It is a potent stimulator of the MTs synthesis, and participates in the oxidation-reduction processes. MTs are also assignated to take a negative part in the malignancy process of tumors. It is assumed that the intense MTs synthesis in the neoplastic cells is a response to the persistent oxidative stress rolling within these cells and should be placed into the main mechanisms for neutralizing pro-apoptotic properties of ROS.

Key words: metallothioneins, antioxidant potential, zinc, brain, reactive oxygen species