Do active forms of oxygen interacting with DNA play a regulatory role in the cell?

Paper analyses data on, and reviews mechanisms of, interactions between active oxygen radicals (AOR) and cellular DNA. Some workers suggest that AOR might have positive regulatory role in the cell influencing DNA because synthesis of some cellular proteins is being activated in the presence of AOR. The paper offers explanations to such effects through non-specific damage of proteins-repressors or the latter's active centers at DNA by AOR, suggesting that this is not a regulatory role. Author also assesses the existing cellular antioxidant systems and produces evidences that damaging AOR like hydroxyl, peroxide and superoxide-anions can not be treated as positive regulators of genome functioning. However, certain regulatory functions in the cell can be realized by "heavy" free radicals which appear in the cell as a result of AOR-induced oxidation processes. The paper suggests that this is due to complex macromolecular interactions between DNA and "heavy" free radicals rather than because of the latter" s AOR properties, nature and origin.     

A role for pore-forming proteins in the pathogenesis by parasites?

Over the past decade or so, pore-forming proteins (PFPs) have been isolated from various immune cells and nonpathogenic bacteria. It is now becoming apparent that PFPs may also be produced by a number of parasites. Although far from definitive, the evidence currently available for the role of PFPs in the survival and pathogenesis by parasites in briefly presented by David Ojcius and John Ding-E Young.     

River blindness: a role for parasite retinoid-binding proteins in the generation of pathology?

A new family of fatty acid- and retinoid-binding proteins has recently been identified in nematodes. These are apparently nematode specific and have very different structures and binding characteristics to their mammalian counterparts. Retinoids have important roles in vision, tissue differentiation and repair, and can profoundly affect collagen synthesis. Binding proteins released by a parasite might therefore play a part in the generation of the skin and eye pathology seen in river blindness. They might also be involved in the formation of the subcutaneous nodules induced by this parasite.     

A role for G proteins in plant hormone signalling?

The G protein signalling pathway is one of the most highly conserved mechanisms that enables cells to sense and respond to changes in their environment. Essential components of this are cell surface G protein-coupled receptors (GPCRs) that perceive extracellular ligands, and heterotrimeric G proteins (G proteins) that transduce information from activated GPCRs to down-stream effectors such as enzymes or ion channels. It is now clear from a range of biochemical and molecular studies that some potential G protein signalling components exist in plants. The best examples of these are the seven transmembrane receptor homologue GCR1 and the G_α (GPA1) and G_β (Gβ1) subunit homologues of heterotrimeric G proteins. G protein agonists and antagonists are known to influence a variety of signalling events in plants and have been used to implicate G proteins in a range of signalling pathways that include the plant hormones gibberellin and auxin. Furthermore, antisense suppression of GCR1 expression in Arabidopsis leads to a phenotype that supports a role for this receptor in cytokinin signalling. This review considers the current evidence for and against functional G protein signalling pathways in higher plants and questions whether or not these might be involved in the action of certain plant hormones.     

ATP-mediated cell–cell signaling in the organ of Corti: the role of connexin channels

Connexin 26 (Cx26) and connexin 30 (Cx30) form hemichannels that release ATP from the endolymphatic surface of cochlear supporting and epithelial cells and also form gap junction (GJ) channels that allow the concomitant intercellular diffusion of Ca²⁺ mobilizing second messengers. Released ATP in turn activates G-protein coupled P2Y₂ and P2Y₄ receptors, PLC-dependent generation of IP₃, release of Ca²⁺ from intracellular stores, instigating the regenerative propagation of intercellular Ca²⁺ signals (ICS). The range of ICS propagation is sensitive to the concentration of extracellular divalent cations and activity of ectonucleotidases. Here, the expression patterns of Cx26 and Cx30 were characterized in postnatal cochlear tissues obtained from mice aged between P5 and P6. The expression gradient along the longitudinal axis of the cochlea, decreasing from the basal to the apical cochlear turn (CT), was more pronounced in outer sulcus (OS) cells than in inner sulcus (IS) cells. GJ-mediated dye coupling was maximal in OS cells of the basal CT, inhibited by the nonselective connexin channel blocker carbenoxolone (CBX) and absent in hair cells. Photostimulating OS cells with caged inositol (3,4,5) tri-phosphate (IP₃) resulted in transfer of ICS in the lateral direction, from OS cells to IS cells across the hair cell region (HCR) of medial and basal CTs. ICS transfer in the opposite (medial) direction, from IS cells photostimulated with caged IP₃ to OS cells, occurred mostly in the basal CT. In addition, OS cells displayed impressive rhythmic activity with oscillations of cytosolic free Ca²⁺ concentration ([Ca²⁺]_i) coordinated by the propagation of Ca²⁺ wavefronts sweeping repeatedly through the same tissue area along the coiling axis of the cochlea. Oscillations evoked by uncaging IP₃ or by applying ATP differed greatly, by as much as one order of magnitude, in frequency and waveform rise time. ICS evoked by direct application of ATP propagated along convoluted cellular paths in the OS, which often branched and changed dynamically over time. Potential implications of these findings are discussed in the context of developmental regulation and cochlear pathophysiology.     

A role for the NF-κB pathway in cell protection from complement-dependent cytotoxicity

Nucleated cells are equipped with several mechanisms that support their resistance to complement-dependent cytotoxicity (CDC). The role of the NF-κB pathway in cell protection from CDC was examined. Elevated sensitivity to CDC was demonstrated in cells lacking the p65 subunit of NF-κB or the IκB kinases IKKα or IKKβ, and in cells treated with p65 small interfering RNA. Pretreatment with the IKK inhibitor PS-1145 also enhanced CDC of wild-type cells (WT) but not of p65(-/-) cells. Furthermore, reconstitution of p65 into p65(-/-) cells and overexpression of p65 in WT cells lowered their sensitivity to CDC. The postulated effect of p65 on the JNK-mediated death-signaling pathway activated by complement was examined. p65 small interfering RNA enhanced CDC in WT cells but not in cells lacking JNK. JNK phosphorylation induced by complement was more pronounced in p65(-/-) cells than in WT cells. The results indicate that the NF-κB pathway mediates cell resistance to CDC, possibly by suppressing JNK-dependent programmed necrotic cell death.     

A role for Wnt/planar cell polarity signaling during lens fiber cell differentiation?

Wnt signaling through frizzled (Fz) receptors plays key roles in just about every developmental system that has been studied. Several Wnt-Fz signaling pathways have been identified including the Wnt/planar cell polarity (PCP) pathway. PCP signaling is crucial for many developmental processes that require major cytoskeletal rearrangements. Downstream of Fz, PCP signaling is thought to involve the GTPases, Rho, Rac and Cdc42 and regulation of the JNK cascade. Here we report on the localization of these GTPases and JNK in the lens and assess their involvement in the cytoskeletal reorganisation that is a key element of FGF-induced lens fiber cell differentiation.     

What is the role of PIWI family proteins in adult pluripotent stem cells? Insights from asexually reproducing animals,planarians

Planarians have a remarkable regenerative ability owing to their adult pluripotent stem cells (aPSCs), which are called “neoblasts.” Planarians maintain a considerable number of neoblasts throughout their adulthood to supply differentiated cells for the maintenance of tissue homeostasis and asexual reproduction (fission followed by regeneration). Thus, planarians serve as a good model to study the regulatory mechanisms of in vivo aPSCs. In asexually reproducing invertebrates, such as sponge, Hydra, and planaria, piwi family genes are the markers most commonly expressed in aPSCs. While piwi family genes are known as guardians against transposable elements in the germline cells of animals that only sexually propagate, their functions in the aPSC system have remained elusive. In this review, we introduce recent knowledge on the PIWI family proteins in the aPSC system in planarians and other organisms and discuss how PIWI family proteins contribute to the regulation of the aPSC system.     

What befalls the proteins and water in a living cell when the cell dies?

The solvency of solutes of varying molecular size in the intracellular water of freshly-killed Ehrlich carcinoma cells fits the same theoretical curve that describes the solvency of similar solutes in a 36% solution of native bovine hemoglobin--a protein found only in red blood cells and making up 97.3% of the red cell's total intracellular proteins. The merging of the two sets of data confirms the prediction of the AI Hypothesis that key intracellular protein(s) in dying cells undergo(es) a transition from: (1) one in which the polypeptide NHCO groups assume a fully-extended conformation with relatively strong power of polarizing and orienting the bulk-phase water in multilayers; to (2) one in which most of the polypeptide NHCO groups are engaged in alpha-helical and other "introvert" conformations (see below for definition) with much weaker power in polarizing-orienting multilayers of bulk-phase water. This concordance of the two sets of data also shows that what we now call native hemoglobin--supposedly denoting hemoglobin found in its natural state in living red blood cells--, in fact, more closely resembles the water-polarizing, and -orienting intracellular proteins in dead cells. Although in the dead Ehrlich carcinoma cells as well as in the 36% solution of native hemoglobin, much of the protein's polypeptide NHCO groups are engaged in alpha-helical and other "introvert" conformation (Perutz 1969; Weissbluth 1974), both systems produce a weak but nonetheless pervasive and "long-range" water polarization and orientation. It is suggested that in both the dead Ehrlich carcinoma ascites cells and in the 36% native bovine hemoglobin solution, enough polypeptide NHCO groups assume the fully-extended conformation to produce the weak but far-reaching multilayer water polarization and orientation observed.     

Regulating RISK: a role for JAK-STAT signaling in postconditioning?

Postconditioning (POC), a novel strategy of cardioprotection against ischemia-reperfusion injury, is clinically attractive because of its therapeutic application at the predictable onset of reperfusion. POC activates several intracellular kinase signaling pathways, including phosphatidylinositol 3-kinase (PI3K)-Akt (RISK). The regulation of POC-induced survival kinase signaling, however, has not been fully characterized. JAK-STAT activation is integral to cardiac ischemic tolerance and may provide upstream regulation of RISK. We hypothesized that POC requires the activation of both JAK-STAT and RISK signaling. Langendorff-perfused mouse hearts were subjected to 30 min of global ischemia and 40 min of reperfusion, with or without POC immediately after ischemia. A separate group of POC hearts was treated with AG 490, a JAK2 inhibitor, Stattic, a specific STAT3 inhibitor, or LY-294002, a PI3K inhibitor, at the onset of reperfusion. Cardiomyocyte-specific STAT3 knockout (KO) hearts were also subjected to non-POC or POC protocols. Myocardial performance (+dP/dt(max), mmHg/s) was assessed throughout each perfusion protocol. Phosphorylated (p-) STAT3 and Akt expression was analyzed by Western immunoblotting. POC enhanced myocardial functional recovery and increased expression of p-STAT3 and p-Akt. JAK-STAT inhibition abrogated POC-induced functional protection. STAT3 inhibition decreased expression of both p-STAT3 and p-Akt. PI3K inhibition also attenuated POC-induced cardioprotection and reduced p-Akt expression but had no effect on STAT3 phosphorylation. Interestingly, STAT3 KO hearts undergoing POC exhibited improved ischemic tolerance compared with KO non-POC hearts. POC induces myocardial functional protection by activating the RISK pathway. JAK-STAT signaling, however, is insufficient for effective POC without PI3K-Akt activation.     

The role of β-adrenergic receptor signaling in the proliferation of hemangioma-derived endothelial cells

Background

Infantile hemangioma (IH) is a benign vascular neoplasm that arises from the abnormal proliferation of endothelial cells and enhanced angiogenesis. Recently, propranolol has been found to be effective in the management of IH, suggesting that β-adrenergic receptors (β-ARs) may play an important role in the pathogenesis of IH.

Results

In the present study, we investigated the β-adrenergic signaling that is associated with hemangioma-derived endothelial cell (HemEC) proliferation. The results showed that both β₁- and β₂-ARs were expressed in HemECs. Stimulation of the β-ARs by isoprenaline induced cell proliferation and elevation of second messenger cAMP levels. The proliferation-promoting action of isoprenaline was abolished by a β₁-selective antagonist and was more effectively abolished by a β₂-selective antagonist; the mechanism for the action of the antagonists was a G₀/G₁ phase cell cycle arrest which was associated with decreased cyclin D1, CDK-4, CDK-6 and phospho-Rb expression. Pre-treatment of the cells with VEGFR-2 or ERK inhibitors also prevented the isoprenaline-mediated proliferation of cells. In agreement with the involvement of β-ARs and VEGFR-2 in the HemEC response, β-AR antagonists and the VEGFR-2 inhibitor significantly attenuated isoprenaline-induced ERK phosphorylation. Moreover, treating the cells with isoprenaline markedly increased VEGF-A expression and VEGFR-2 activity in a β₂-AR-dependent manner.

Conclusions

We have demonstrated that the activation of the β-ARs in the ERK pathway may be important mechanisms in promoting HemEC growth. Furthermore, stimulation of the β-AR may transactivate VEGFR-2 signaling and further increase HemEC proliferation.     

Are RB proteins a potential substrate of Pin1 in the regulation of the cell cycle?

RB family members are post-transductionally regulated proteins and phosphorylation at Ser/Thr residues leads to their gradual inactivation. Cyclin/cdk complexes are mainly responsible for the regulation of these pocket proteins, which is crucial for release of E2F factor. Despite the fact that E2F release is a phosphorylation-dependent process, it is still not evident how phosphorylation physically determines the shift from the active to the inactive feature of RB molecules. We would like to put forward the hypothesis that Pin1 is involved in RB proteins phosphorylation and E2F release, suggesting an additional post-translational level of control on this family of molecules.     

Chaperoning stem cells: a role for heat shock proteins in the modulation of stem cell self‐renewal and differentiation?

Self‐renewal and differentiation of stem cells are tightly regulated processes subject to intrinsic and extrinsic signals. Molecular chaperones and co‐chaperones, especially heat shock proteins (Hsp), are ubiquitous molecules involved in the modulation of protein conformational and complexation states. The function of Hsp, which are typically associated with stress response and tolerance, is well characterized in differentiated cells, while their role in stem cells remains unclear. It appears that embryonic stem cells exhibit increased stress tolerance and concomitant high levels of chaperone expression. This review critically evaluates stem cell research from a molecular chaperone perspective. Furthermore, we propose a model of chaperone‐modulated self‐renewal in mouse embryonic stem cells.     

Is there a role for glucocorticoid receptor beta in asthma?

Glucocorticoids (GCs) are routinely used as anti-inflammatory drugs in the treatment of asthma. They act through binding to glucocorticoid receptor α (GRα), which represses numerous genes encoding pro-inflammatory mediators. A hormone binding deficient GR isoform named GRβ has been isolated in humans. When overexpressed by transfection, GRβ may function as a dominant negative modulator of GRα. However, to act as such, GRβ has to be more abundant than GRα, and conflicting data have been obtained concerning the relative levels of the two isoforms in cell lines and freshly isolated cells. Moreover, the dominant negative effect was not confirmed by independent laboratories. In GC-resistant asthmatics, GRβ was expressed by an increased number of peripheral blood mononuclear cells (PBMCs), airway T cells, and cells found in skin biopsies of tuberculin responses. However, the relative amounts of GRα and GRβ in these cells were not determined. In GC-dependent asthmatics, PBMCs expressed GRα predominantly. No cells containing higher levels of GRβ than GRα have yet been reported in asthmatics. Even if the existence of such cells is demonstrated, the role of GRβ in asthma will remain a matter of controversy because functional studies have given discrepant data.     

What is the role of SNARE proteins in membrane fusion?

Soluble N-ethylmaleimide-sensitive factor activating protein receptor (SNARE) proteins have been at the fore-front of research on biological membrane fusion for some time. The subcellular localization of SNAREs and their ability to form the so-called SNARE complex may be integral to determining the specificity of intracellular fusion (the SNARE hypothesis) and/or serving as the minimal fusion machinery. Both the SNARE hypothesis and the idea of the minimal fusion machinery have been challenged by a number of experimental observations in various model systems, suggesting that SNAREs may have other functions. Considering recent advances in the SNARE literature, it appears that SNAREs may actually function as part of a complex fusion "machine." Their role in the machinery could be any one or a combination of roles, including establishing tight membrane contact, formation of a scaffolding on which to build the machine, binding of lipid surfaces, and many others. It is also possible that complexations other than the classic SNARE complex participate in membrane fusion.