Shedding light on the immunomodulatory properties of galectins: novel regulators of innate and adaptive immune responses

Galectins are a large family of structurally related beta-galactoside-binding proteins that play a pivotal role in the control of cell differentiation, proliferation, activation and apoptosis of many different cell types including immune cells. By crosslinking specific glycoconjugates, different members of the galectin family behave as pro-inflammatory or anti-inflammatory "cytokine-like" mediators, acting at different levels of innate and adaptive immune responses. Here we will review recent advances on the role of galectins in key events of the immune and inflammatory response, such as tolerance induction, cell cycle progression, cell adhesion, chemotaxis, antigen presentation and apoptosis. In particular we will examine the influence of individual members of the galectin family in the physiology of different immune cell types involved in innate and adaptive immune responses. Moreover, we will discuss the importance of these sugar-binding proteins as therapeutic targets in Th1- and Th2-mediated immune disorders, an exciting area for future research.     

Pancreatic polypeptide inhibits somatostatin secretion

Pancreatic polypeptide (PP) is a major agonist for neuropeptide Y4 receptors (NPY4R). While NPY4R has been identified in various tissues, the cells on which it is expressed and its function in those cells has not been clearly delineated. Here we report that NPY4R is present in all somatostatin-containing cells of tissues that we tested, including pancreatic islets, duodenum, hippocampus, and hypothalamus. Its agonism by PP decreases somatostatin secretion from human islets. Mouse embryonic hippocampal (mHippo E18) cells expressed NPY4Rs and their activation by PP consistently decreased somatostatin secretion. Furthermore, central injection of PP in mice induced c-Fos immunoreactivity in somatostatin-containing cells in the hippocampus compared with PBS-injected mice. In sum, our results identify PP as a pivotal modulator of somatostatin secretion.     

The Neural/Immune Gene Ontology: clipping the Gene Ontology for neurological and immunological systems

Background  

The Gene Ontology (GO) is used to describe genes and gene products from many organisms. When used for functional annotation of microarray data, GO is often slimmed by editing so that only higher level terms remain. This practice is designed to improve the summarizing of experimental results by grouping high level terms and the statistical power of GO term enrichment analysis.     

Isolation and Characterization of a Cellobiose Dehydrogenase Formed by a Nonsporulating Mycelial Fungus INBI 2-26(-)

A nonsporulating fungus isolated from dioxin-containing tropical soils forms cellobiose dehydrogenase when grown in media supplemented by a source of cellulose. The enzyme purified to homogeneity by SDS-PAGE (yield, 43%) had an M_r of 95 kDa; its pH optimum was in the range 5.5–7.0; more than 50% activity was retained at pH 4.0–8.0 (citrate–phosphate buffer). The absorption spectrum of the enzyme in the visible range had the characteristic appearance of flavocytochrome proteins. Cellobiose dehydrogenase oxidized cellobiose and lactose (the respective K _M values at pH 6.0 equaled 4.5 ± 1.5 and 56 M) in the presence of dichlorophenolindophenol (K _M,_app = 15 ± 3 M at pH 6.0) taken as an electron acceptor. Other sugars were barely if at all oxidized by the enzyme. Neither ethyl--D-cellobioside, heptobiose, nor chitotriose inhibited the enzymatic oxidation of lactose, even under the conditions of 100-fold molar excess. The enzyme was weakly inhibited by sodium azide dichlorophenolindophenol reduction and exhibited an affinity for amorphous cellulose. At 55°C and pH 6.0 (optimum stability), time to half-maximum inactivation equaled 99 min. The enzyme reduced by cellobiose was more stable than the nonreduced form. Conversely, the presence of an oxidizer (dichlorophenolindophenol) decreased the stability eight times at pH 6.0. In addition, the enzyme acted as a potent reducer of the one-electron acceptor cytochrome c ³⁺ (K _{M app} = 15 M at pH 6.0).     

Membrane topology of the multidrug transporter MdfA: complementary gene fusion studies reveal a nonessential C-terminal domain

The hydrophobicity profile and sequence alignment of the Escherichia coli multidrug transporter MdfA indicate that it belongs to the 12-transmembrane-domain family of transporters. According to this prediction, MdfA contains a single membrane-embedded charged residue (Glu26), which was shown to play an important role in substrate recognition. To test the predicted secondary structure of MdfA, we analyzed complementary pairs of hybrids of MdfA-PhoA (alkaline phosphatase, functional in the periplasm) and MdfA-Cat (chloramphenicol acetyltransferase, functional in the cytoplasm), generated in all the putative cytoplasmic and periplasmic loops of MdfA. Our results support the 12-transmembrane topology model and the suggestion that except for Glu26, no other charged residues are present in the membrane domain of MdfA. Surprisingly, by testing the ability of the truncated MdfA-Cat and MdfA-PhoA hybrids to confer multidrug resistance, we demonstrate that the entire C-terminal transmembrane domain and the cytoplasmic C terminus are not essential for MdfA-mediated drug resistance and transport.     

The antimetastatic effect of a single low dose of cyclophosphamide involves modulation of galectin-1 and Bcl-2 expression

We have demonstrated that a single low dose of cyclophosphamide has an antimetastatic effect on lymphoma (L-TACB)-bearing rats by modulating the host immune response. Galectin-1, a member of the galectin family with specificity for beta-galactosides, has potent immunomodulatory properties by regulating cell-matrix interactions and T-cell apoptosis. Since galectin-1 is expressed by highly metastatic tumors, in the present study we investigated the participation of this beta-galactoside-binding protein in cyclophosphamide-induced immunomodulation. Inbred " e" rats were s.c. challenged with L-TACB. After 14 days, half of the animals received an i.p. injection of cyclophosphamide (10 mg/kg), and on day 21 tumors and spleens were excised. Cell extracts were prepared and galectin-1 expression was determined by Western blot analysis and correlated with Bcl-2 expression levels and the DNA fragmentation profile. Expression of galectin-1 was significantly decreased in tumors from cyclophosphamide-treated rats compared to non-treated rats. The same effect was observed regarding expression of Bcl-2 by tumors. In contrast, expression of Bcl-2 was significantly higher in spleens from treated animals than in non-treated rats. This effect correlated with a decreased intensity in the pattern of DNA fragmentation of spleen cells from cyclophosphamide-treated animals. Our results suggest that a single low dose of cyclophosphamide modulates the expression of galectin-1 and Bcl-2 by tumors, which could in turn influence the apoptotic threshold of spleen mononuclear cells. This mechanism could explain, at least in part, the antimetastatic effect evidenced in our tumor experimental model.     

Topology selection by chaotic neurons of a pyloric central pattern generator

The pyloric Central Pattern Generator (CPG) in the lobster has an architecture in which every neuron receives at least one connection from another member of the CPG. We call this a "non-open" network topology. An "open" topology, where at least one neuron does not receive synapses from any other CPG member, is found neither in the pyloric nor in the gastric mill CPG. Here we investigate a possible reason for this topological structure using the ability to perform a biologically functional task as a measure of the efficacy of the network. When the CPG is composed of model neurons that exhibit regular membrane voltage oscillations, open topologies are as able to maximize this functionality as non-open topologies. When we replace these models by neurons which exhibit chaotic membrane voltage oscillations, the functional criterion selects non-open topologies. As isolated neurons from invertebrate CPGs are known in some cases to undergo chaotic oscillations, this suggests that there is a biological basis for the class of non-open network topologies that we observe.     

Stress renders T cell blasts sensitive to killing by activated syngeneic NK cells

Exposure of primary T cell blasts to stress in the forms of heat, hydrogen peroxide, or high-density growth conditions resulted in a state of enhanced susceptibility to killing by syngeneic IL-2-activated NK cells or lymphokine-activated killer cells, but not to killing by CTL. Cytotoxicity was perforin mediated and was not due to decreased target expression of total MHC class I. The levels of stress used had little effect on cell viability. For thermal stress, sensitization increased with temperature, required a minimum exposure time, and disappeared when cells were given a long enough recovery time. Our data support a model that predicts that activated NK cells play a role in the immunosurveillance of nontransformed stressed cells in normal animals.     

A computer investigation of intramolecular bond ordering: unsaturated chains of natural lipids

Computer simulations (by the Monte Carlo method) of unperturbed linear hydrocarbon chains of 18-22 carbon atoms with methylene-interrupted cis-double bonds (18:0, 20:0, 22:0, 18:1delta11cis, 18:2delta9, 12cis, 18:3delta9, 12, 15cis, 20:3delta5, 8, 11cis, 20:4delta5, 8, 11, 14cis, 20:5delta5, 8, 11, 14, 17cis, 22:6delta4, 7, 10, 13, 16, 19cis), typical components of natural lipids, at a temperature of 298 K have been carried out. The conformations generated with continuous variation of all single C-C bond rotation angles within the (0, 360 degrees) range have been considered. The energy of nonbonded interactions and torsion and electrostatic terms have been taken into account. The intramolecular bond order parameters S(CC) and S(CH) about the axes along inertia tensor eigenvectors and bond orientation distributions rho(theta) with respect to the maximum molecule span axis (theta is the angle between the bond and the axis) have been calculated. The relation of the bond orientation distributions rho(theta) to the order parameters S are analyzed in terms of angles thetamax (a "geometric" factor, rho(thetamax) = max) and widths deltatheta of the distributions (factor of "fluctuations"). The results indicate that fluctuation factors depend on both the segment chemical structure and location in the chain; fluctuations increase from the centre of the chain towards the terminals, all things being equal. The two deltatheta values of C-H bonds flanking the cis-double bond are smaller than that obtained for adjacent CH2 groups by a factor of 1.5-2. Defining these properties is a necessary step to gaining a more complete understanding of polyunsaturated lipid hydrocarbon chains significance. The mean molecule magnitudes of ?S(CH)? decrease when unsaturation increases. The cis-double bond parameters S(CC) are found to be higher than those of adjacent single C-C bonds: the parameter S(CC) odd-even effect in the polyunsaturated molecules of such structure changes the "sign" between double bonds. The order parameter profiles -S(CH) of cis-18:1 and cis-18:2 obtained from the simulations (at the portion which corresponds to the double bonds location) are in qualitative agreement with experimental data on bilayers in the liquid-crystal phase. This has made possible the quantitative prognosis of the ordering properties of experimentally uninvestigated unsaturated lipids.