High Conformational Variability in the GluK2 Kainate Receptor Ligand-Binding Domain

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Effect of novel non-peptidic delta opioid receptor antagonists on human T and B cell activation

The effects of the antagonist naltrindole (NTI) on cells of the immune system have been largely studied although the mechanisms of action are still unclear. The aim of this study is to evaluate, in vitro, the immunomodulatory activity of four new delta-selective opioid compounds structurally related to naltrindole. The effects at different concentrations of these opioid antagonists on proliferative response were studied on normal human peripheral blood mononuclear cells (PBMC) stimulated with different stimuli: mitogens, the antigen PPD, the anti-CD3 monoclonal antibodies (mAb), the superantigen Staphylococcus aureus Cowan strain 1 (SAC) and alloantigens in the mixed lymphocyte cultures (MLR). The immunomodulatory capacity of these compounds was evaluated by determining the interleukin-2 (IL-2) release in mitogen activated PBMC. The present study shows that all the new delta opioid antagonists at 10(-5) M concentration are immunosuppressive. The inhibitory action is also evident at lower concentrations when anti-CD3 mAb and SAC were used as stimulators. In addition, the production of IL-2 was inhibited by the opioid treatment, but this might not be the only mechanism of action.     

Recruitment of C-terminal Src kinase by the leukocyte inhibitory receptor CD85j

The CD85j inhibitory receptor (also termed ILT2 or LIR-1) is a type-I transmembrane protein that belongs to the Ig superfamily and is expressed by different leukocyte lineages. The extracellular region of CD85j binds HLA class I molecules and its cytoplasmic domain displays four immunoreceptor tyrosine-based inhibition motifs (ITIM). Upon tyrosine phosphorylation CD85j recruits the SHP-1 tyrosine phosphatase, involved in negative signaling. In order to identify other molecules to which CD85j might interact with in a phosphotyrosine-dependent manner, a cDNA B-cell library was screened in a three-hybrid system in yeast using the CD85j cytoplasmic tail as bait in the presence of the Src-kinase c-fyn420, 531Y-F, 176R-Q mutant. In this system, the C-terminal Src kinase (Csk) was shown to interact with CD85j. Phosphorylation-dependent recruitment of Csk to the CD85j cytoplasmic tail was confirmed in CD85j-transfected mammalian cells by immunoprecipitation and Western blot analysis. Mutational analyses and phospho-peptide mapping suggested that the SH2 domain of Csk may preferentially bind to ITIM Y562 of CD85j; yet, mutation to phenylalanine of Y533, Y614, and Y644 also significantly reduced Csk recruitment by CD85j. Even though CD85j was detected in both anti-SHP1 and CSK immunoprecipitates, these two molecules did not co-precipitate together with CD85j. Our data support the possibility that Csk regulates the function of CD85j.     

GABA(B) receptors in 5-HT transporter- and 5-HT1A receptor-knock-out mice: further evidence of a transduction pathway shared with 5-HT1A receptors

The functional properties of GABA(B) receptors were examined in the dorsal raphe nucleus (DRN) and the hippocampus of knock-out mice devoid of the 5-HT transporter (5-HTT-/-) or the 5-HT(1A) receptor (5-HT(1A)-/-). Electrophysiological recordings in brain slices showed that the GABA(B) receptor agonist baclofen caused a lower hyperpolarization and neuronal firing inhibition of DRN 5-HT cells in 5-HTT-/- versus 5-HTT+/+ mice. In addition, [(35)S]GTP-gamma-S binding induced by GABA(B) receptor stimulation in the DRN was approximately 40% less in these mutants compared with wild-type mice. In contrast, GABA(B) receptors appeared functionally intact in the hippocampus of 5-HTT-/-, and in both this area and the DRN of 5-HT(1A)-knock-out mice. The unique functional changes of DRN GABA(B) receptors closely resembled those of 5-HT(1A) autoreceptors in 5-HTT-/- mice, further supporting the idea that both receptor types are coupled to a common pool of G-proteins in serotoninergic neurons.     

Acetylcholine-induced calcium signalling in adrenaline- and noradrenaline-containing adrenal chromaffin cells

Adrenal chromaffin cells secrete catecholamines in response to cholinergic receptor activation by acetylcholine (ACh). Characteristics of Ca(2+) transients induced by activation of nicotinic (nAChRs) and muscarinic (mAChRs) receptors were analyzed using Fura-2 fluorescent measurements on rat chromaffin cells. We first found two populations of chromaffin cells, which differently responded on AChR stimulation. In the first group (n-cells), consecutive ACh applications evoked persistent Ca(2+) transients, whereas desensitizing transients were observed in the other group (m-cells). The AChR agonists and antagonists precisely imitated or abolished the ACh action on n- and m-type cells, respectively. Cytochemical staining showed that n-cells contained adrenaline, whereas m-cells-noradrenaline. Thus, for the first time we found that nAChRs and mAChRs are differentially expressed in adrenergic and noradrenergic chromaffin cells, respectively. Our data suppose that chromaffin cells can be differentially regulated by incoming ACh signals and in such way release different substances-adrenaline and noradrenaline.     

Retroviral transfer of antisense sequences results in reduction of c-Abl and induction of apoptosis in hemopoietic cells

The c-abl proto-oncogene is ubiquitously expressed during mammalian development. Activated forms of c-Abl proteins are oncogenic and have been shown to suppress apoptosis. The biological role of normal c-Abl protein is unknown. In this study, we have introduced c-abl antisense sequences into various hemopoietic cells by retroviral gene transfer. Introduction and expression of the antisense sequence effectively reduced the amount of c-Abl protein in a number of transduced hemopoietic cells, that consequently underwent apoptosis. When factor-dependent cell lines were examined, we observed that the addition of sufficient amounts of growth factors could suppress apoptosis in myeloid but not in lymphoid lines. The ability of myeloid cells to be rescued by growth factors correlated with upregulation of mRNA level of IL-3 receptor subunits. Our data suggest that c-Abl provides an anti-apoptotic signal during mammalian cell growth, and that myeloid and lymphoid cells are different in their resistance to apoptosis.     

Synthesis and biological activity of a novel class nicotinic acetylcholine receptors (nAChRs) ligands structurally related to anatoxin-a

The introduction of the isoxazole ring as bioisosteric replacement of the acetyl group of anatoxin-a led to a new series of derivatives binding to nicotinic acetylcholine receptors. Bulkier substitutions than methyl at the 3 position of isoxazole were shown to be detrimental for the activity. The binding potency of the most interesting compounds with α1, α7 and α3β4 receptor subtypes, was, anyway, only at micromolar level. Moreover, differently from known derivatives with pyridine, isoxazole condensed to azabicyclo ring led to no activity.     

Sphingosine 1-phosphate receptors modulate intracellular Ca2+ homeostasis

Ligation of sphingosine 1-phosphate (S1P) to a set of specific receptors named S1P receptors (S1PRs) regulates important biological processes. Although the ability of S1P to increase cytosolic Ca2+ in various cell types is well known, the role of the individual S1PRs has not been fully characterized. Here, we provide a complete analysis of S1P-dependent intracellular Ca2+ homeostasis in HeLa cells. Overexpression of S1P2, or S1P3, but not S1P1, leads to a significant increase in cytosolic and mitochondrial [Ca2+] in response to S1P challenge. Moreover, cells ectopically expressing S1P2, or S1P3 exhibited an appreciable decrease of the free Ca2+ concentration in the endoplasmic reticulum, dependent on stimulation of receptors by S1P endogenously present in the culture medium which was accompanied by a reduced susceptibility to C2-ceramide-induced cell death. These results demonstrate a differential contribution of individual S1PRs to Ca2+ homeostasis and its possible implication in the regulation of cell survival.     

Photoresponse in the heterotrophic marine dinoflagellate Oxyrrhis marina

Expressed rhodopsins were detected by proteomic analysis in an investigation of potential signal receptors in the cell membrane of the marine heterotrophic dinoflagellate Oxyrrhis marina (CCMP604). We inferred these to be sensory rhodopsins, a type of G-protein-coupled receptor trans-membrane signaling molecule. Because phototactic behavior based on sensory rhodopsins has been reported in other protists, we investigated the photosensory response of O. marina. This dinoflagellate exhibited strongest positive phototaxis at low levels (2-3 μE/m(2)/s) of white light when the cells were previously light adapted and well fed. Positive phototaxis was also found for blue (450 nm), green (525 nm), and red (680 nm) wavelengths. In a further test, O. marina showed significantly greater phototaxis toward concentrated algal food illuminated by blue light to stimulate red chlorophyll-a autofluorescence in the prey, compared with using bleached algae as prey. Concentration of a cytoplasmic downstream messenger molecule, cyclic adenosine monophosphate, a component of the signaling pathway of G-protein-coupled receptor molecules, rapidly increased in O. marina cells after exposure to white light. In addition, treatment with hydroxylamine, a rhodopsin signaling inhibitor, significantly decreased their phototactic response. Our results demonstrate that a heterotrophic marine dinoflagellate can orient to light based on rhodopsins present in the outer cell membrane and may be able to use photosensory response to detect algal prey based on chlorophyll autofluorescence.