Polar Auxin Transport – Hipotheses and Discoveries

Summary: Polar auxin transport (PAT) is a process, which controls many stages of plant growth and development. According to the chemiosmotic hypothesis auxins move in the polar manner through the influx (AUX) and the efflux (PIN) carriers connected with the plasma membrane. Recent molecular studies have identified gene families encoding these carriers. It has been established that auxin efflux carrier is a protein complex. Its putative components and factors influencing this carrier localisation in plasma membrane have been partially identified. Nevertheless, any of processes, which are controlled by auxin has been explained yet. However, recent molecular studies supplied new data, demanding verification of the present view on the polar auxin transport. The known basipetal PAT in xylem parenchyma and cambium appears to be not sole conduit for long distance auxin transport from the stem to the root. The similar transport has been discovered in the phloem. This requires the presence of auxin influx carrier. It is likely, that in a plant many auxin transport ways are present and act simultaneously, and each of these may be connected with the control of different process. The important discovery was, that auxin influx carriers could change their location in plasma membrane. Thus the direction of auxin transport could also be altered, theoretically into anyone, depending on the site, in which the carriers are located at a given moment.

Key words: polar auxin transport (PAT), auxin influx carrier,  AUX, auxin efflux carrier, PIN, Arabidopsis.

Sieve Tubes – Phenomenon of Functionality

Summary: The anatomy of sieve tubes has been known for a long time. Only recently however, new discoveries led to understand how sieve tube ultrastructure fit to its functions: fast flow of phloem sap and extreme resistance to injuries as well as pathogen attack. Phloem sap contains not only sugars and ions, but also of hormones, proteins and RNA. These molecules are involved in signalization as well as in systemic response of plants against viruses. It is now apparent, that sieve tubes being cell continuum play the role analogical to distinct animal systems: alimentary, circulatory, lymphatic, or even nervous.

Key words: phloem, transport, ultrastructure.

Genetic Instability in Cancer II. Microsatellite Instability and Loss of Heterozygosity

Summary: Genomic instability is one of the main feature of cancer cells. It is expressed by the accumulation of chromosomal aberrations and mutations in cancer cell, but also by microsatellite instability (MSI) and loss of heterozygosity (LOH). MSI means a change in the length (size) of one out of two allels in a given loci, caused by an increase or decrease in the number of microsatellite repeats. MSI results in mutator phenotype and is observed in both, sporadic and familial cancers, however with the variable frequency. LOH is caused by a deletion of one of the gene alleles, and leads to hemizygosity. MSI and LOH are observed in early as well as in late stages of the process of neoplastic transformation. The implications of MSI and LOH for the carcinogenesis as well as methods of their diagnosis are presented in the review.

Key words: genomic instability, microsatellite instability (MSI), loss of heterozygosity (LOH), cancer.

Molecular Responses of Plant to Phosphate Starvation

Summary: The deficiency of available for plants inorganic phosphate (Pi) in the environment is a common phenomenon. Plants adapt to such stress conditions by developing a number of mechanisms, e.g. increasing Pi uptake from soil and/or Pi mobilization from intercellular pools. Plant roots can secrete organic acids, acid phosphatase and, if necessary, also ribonucleases to the ground with simultaneous induction of Pi transporters and numerous phosphatases in cells. These changes are usually preceded or accompanied by activation or repression of specific genes. Under phosphate starvation conditions the induction of genes encoding Pi transporters,  acid phosphatases, ribonucleases, ?-glucosidase and others was observed in roots. To react fast and adequately to the variety of environmental changes plants require efficient signal perception and transduction systems. Little is known about mechanisms of Pi signaling, however this problem is recently under extensive study. Studies on the function of hormones, phosphonate, Pi transporters and other factors in signal transduction are currently underway. In addition, selection and characterization of various phosphate mutants (with decresed or increased Pi level and acid phosphatases activity) – may provide information that help in elucidating Pi signaling pathway(s) and mechanisms of plant responses to Pi starvation.

Key words: gene expression, metabolism regulation, pho, phosphate deficiency, Pi signaling.

The Role of Nuclear Xenobiotic Receptors in Cytochrome P450 Induction

Summary: Heterodimeric nuclear receptors, constitutive androstane receptor  (CAR), pregnane X receptor and steroid  and xenobiotic receptor (PXR/SXR) bind unspecific ligands, such as toxic endogenous metabolites and exogenous xenobiotics. Activated by ligands, receptors  are able to induce and stimulate expression of cytochrome P450 genes. Specific responsive elements in DNA, recognised and bound by pregnane X receptor and steroid and xenobiotic receptor is located mainly in the promoter of CYP3A genes and that of costitutive androstane receptor – in CYP2B genes. Both CYP families play central role in xenobiotic metabolism and processes of detoxication. Both receptors are colacalized with CYP2B and CYP3A in liver and intestine, where main detoxication reactions take place. Ligand and species specifity of receptors and their crosstalk is described.

Key words: CAR, cytochromes P450, CYP3A, CYP2B, PXR, SXR, xenobiotics.

Molecular Aspects of Helicobacter Pylori Infection

Summary: H. pylori is a causative agent of chronic gastritis, peptic ulcer diseases and has a significant impact on gastric carcinogenesis. Gastrointestinal disorders associated with H. pylori infection are predominantly results of the immune responses of gastric epithelial cells and adaptation of bacteria to stomach environment determined by chemical structure and biological specificity of bacterial adhesins, activity of H. pylori urease and motility/chemotaxis of the bacterium. In this paper the overview of structural and functional differentiation of H. pylori genome and the mechanism for its colonizing the gastric mucus is presented.

Key words: H. pylori infection, colonization, bacterial adhesins, H. pylori urease, ureotaxis.

Metaloproteinases ADAM – The Role in Cell Fusion and Proteolisis

Summary: Proteolysis on the cell surface and in the extracellular matrix is a very important process in normal cellular functions. Metalloproteinases ADAM are transmembrane proteins, which combine features of adhesion molecules and proteases. They participate in: adhesion, fusion, release ectodomains of membrane proteins, signal transduction. ADAMs play a key role in: fertilization, myoblasts fusion, neurogenesis, and other processes. A particularly interesting is: participation of ADAM 17 in TNFa releasing, role of ADAM 10 in Notch-mediated signaling, function of fertilin in fertilization and meltrin a in myoblast fusion.

Key words: ADAM, fertilin, fusion, Kuzbanian, meltrin, metaloproteinases, proteolysis, TACE.
 

Cerebellin – Synthesis, Localization and Role

Summary: Cerebellin represents a rather new and poorly recognised neuropeptide, consisting of 16 amino acids. At present, four precursors of the peptide are known, termed precerebellins. Within a single species genes for individual precerebellins are located on different chromosomes and in each case such a gene includes three exons. Comparison of individual precerebellins between various species demonstrates their very high homology. Using RIA presence of immunoreactive cerebellin has been demonstrated in cerebellum and in other parts of the brain, in alimentary tract, kidney, suprarenal glands and in their tumours. Activity of cerebellin has not been fully elucidatred yet. Among other, the peptide stimulates secretion of aldosteron, cortisol/corticosterone by adrenal cortex and directly stimulates release of catecholamines from adrenal medulla. Available dates suggest inhibitory effect of cerebellin on thyroid gland function.

Keywords: cerebellin (CR), precerebellin (Cbln), neuropeptides, evolution, gene, brain, adrenal cortex, thyroid.

Metalloproteinases in Physiology and Pathology of The Central Nervous System

Summary: The matrix metalloproteinases (MMPs) constitute a group of at least 25 Zn2+-depending egzopeptidases, which modulates the extracellular milieu primary through cleavage of extracellular matrix (ECM) proteins, membrane receptors and cytokines. These proteins are synthesised in cells, and secreted to the extracellular space as inactive enzymes, where they are activated by the cleavage in the propeptide region. MMPs are tightly regulated at the transcriptional and post-transcriptional levels and via their endogenous inhibitors (TIMPs) to avoid unwanted proteolysis. Proteolytic remodelling of the extracellular matrix occurs normally during development. Extracellular proteolysis by MMPs is associated with tissue destruction in many pathological settings including ischemia, multiple sclerosis and cancer. An understanding of these processes would provide new insight for therapy in diseases of central nervous system (CNS).

Key words: metalloproteinases, gelatinases, central nervous system, extracellular matrix.

Signal Transduction by Bone Morphogenetic Proteins Receptors

Summary: The : Bone Morphogenetic Proteins are pleiotropic cytokines belonging to Transforming Growth Factor b superfamily. They bind to two different types of serin-threonine kinase receptors. Smad proteins are secondary mediators of intracellular signaling. Phosphorylation of R-Smad leads to formation of complex with Co-Smad, which then translocates to the nucleus and regulates expression of target genes. Signaling pathway from BMPs receptors is modulated by different biological factors.

Key words: Bone Morphogenetic Proteins, Transforming Growth Factor type b superfamily, Smad proteins.

Phosducin and its isoforms - regulators of G-protein functions

Summary: Phosducin (Phd) and its isoforms, phosducin-like proteins (PhdLPs) and recently discovered phosducin-like orphan proteins (PhdLOPs), represent superfamily of proteins, that are established as important cytoplasmic regulators of heterotrimeric G-protein functions. Phosducin is abundantly expressed in retinal photoreceptor cells and in lower contents in cells of many other tissues and some lower eukaryotic organisms. This phosphoprotein can be phosphorylated during darkness by protein kinase A, Ca2+/calmodulin-dependent kinase II and G-protein-coupled receptor kinase. In the light, the dephosphorylated form of phosducin favors the binding of bg-subunits of G-protein (Gbg), prevents interaction of  bg-subunits with a-subunit of G-protein (Ga) to form heterotrimer, thus it can function as negative regulator of cGMP cascade in visual system. In general, similar down-regulation mechanisms have been ascribed for Phd isoform, like PhdLPs. These observations suggest that phosducin might be involved in photoreceptor cell processes for light and dark adaptation mechanism. Phd and its isomers may serve, as it has been reported recently, as protective factors for Gbg degradation in proteasomes or potentially may act also as transcriptional regulators.

Key words: phosducin, phosducin-like proteins, phosducin-like orphan proteins, bg-subunits of G-protein, phosphorylation, transcriptional factor CRX.
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Mechanism of Prolactin Action in Reproductive Tract of Sows

Summary: Prolactin (PRL) is one of the factors involved in controlling luteal and follicular steroidogenesis in sows. PRL stimulates progesterone production by luteal cells during the early luteal phase of the estrous cycle and by theca cells form large follicles. PRL affects also follicular production of estrogens. Prolactin receptors are present in both luteal and theca cells of porcine ovaries. Available data suggest that prolactin signaling in ovarian steroidogenic cells in pigs involves more than one intracellular pathway. Transduction of PRL signal in porcine luteal and theca cells includes protein kinase C and nonreceptor tyrosine kinases pathways. It appears that protein phosphatases are also involved in PRL signaling in steroidogenic cells of porcine ovaries.

Key words: prolactin, sow, corpus luteum, follicle, steroidogenesis, protein kinase C, tyrosine kinases, phosphatases, signal transduction.