Specificity and mechanism of the histone methyltransferase Pr-Set7

Methylation of lysine residues of histones is an important epigenetic mark that correlates with functionally distinct regions of chromatin. We present here the crystal structure of a ternary complex of the enzyme Pr-Set7 (also known as Set8) that methylates Lys 20 of histone H4 (H4-K20). We show that the enzyme is exclusively a mono-methylase and is therefore responsible for a signaling role quite distinct from that established by other enzymes that target this histone residue. We provide evidence from NMR for the C-flanking domains of SET proteins becoming ordered upon addition of AdoMet cofactor and develop a model for the catalytic cycle of these enzymes. The crystal structure reveals the basis of the specificity of the enzyme for H4-K20 because a histidine residue within the substrate, close to the target lysine, is required for completion of the active site. We also show how a highly variable component of the SET domain is responsible for many of the enzymes' interactions with its target histone peptide and probably also how this part of the structure ensures that Pr-Set7 is nucleosome specific.     

Effect of reduced temperature on glycoprotein (Ig, HLA) processing and transport in lymphoid cells

Secretion of Igs and surface expression of HLA antigens was examined in lymphoid cells as a function of temp. Upon reducing the temp from 37 to 20 degrees C a progressive decrease in the secretion of Ig and surface expression of HLA antigens was noted. When the status of the oligosaccharides present on these glycoproteins was examined, conversion of high-mannose [endo-beta-N-acetylglucosaminidase-(Endo H) sensitive] to complex-type (Endo H resistant) oligosaccharides diminished with decreasing temp. At no time was an accumulation of Endo H resistant glycoproteins seen intracellularly. These results show that the phenomenon observed for synthesis and intracellular transport of viral glycoproteins in epithelial cells at reduced temp, namely intracellular accumulation of viral glycoproteins carrying complex sugar moieties, does not necessarily apply to glycoprotein transport in lymphoid cells. A difference in subcellular organization of epithelial and lymphoid cells may be responsible for this discrepancy.     

Study of the HLA system in Burkitt's lymphoma

Seventy-eight patients with Burkitt's lymphoma and seventy controls from Ghana were typed for HLA-A, B, C and DR antigens, to determine whether there is an association between the HLA system and Burkitt's lymphoma. Increased relative risk was observed in Burkitt's lymphoma patients with DR7, HLA-A1 and B12 (BW44).     

Chronic Cocaine Injections Attenuate Behavioral Response of κ-Opioid Receptors to U-50,488H Agonist

Chronic injections of cocaine (20 mg/kg daily for 10 days) increase activity and decrease anxiety in male C57Bl/6j mice in comparison with animals chronically injected with normal saline. U-50,488H (κ-opioid receptor agonist; 2.5 mg/kg) produced an anxiolytic effect in animals preinjected with normal saline and had no effect in animals chronically injected with cocaine. Presumably, chronic activation of dopaminergic systems caused by cocaine injections is paralleled by desensitization of k-opioid receptor system. __________ Translated from Byulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 140, No. 9, pp. 305–307, September, 2005     

Amiloride enhances the secretion but not the synthesis of renin in renal juxtaglomerular cells

In this study we have examined a potential role of the sodium/proton exchange system in the regulation of renin secretion. We found that the inhibitors of the Na⁺/H⁺ antiport, amiloride (1 mM) and ethylisopro-pylamiloride (EIPA, 50 M), led to a 125% increase of renin secretion from cultured mouse juxtaglomerular cells. The stimulatory effect of EIPA on renin secretion was dependent on the extracellular concentrations of sodium and hydrogen ions. While lowering the extracellular pH from 7.3 to 7.0, and lowering [Na⁺]_e from 130 mM to 5 mM had no effect on basal renin release, it markedly attenuated or even blunted the effect of EIPA on renin secretion. The stimulatory effect of forskolin on renin secretion, however, was not altered by decreases of extracellular pH and of sodium. Inhibition of basal renin release was achieved with angiotensin II (1 M). In the presence of EIPA the inhibitory effect angiotensin II was markedly attenuated. Although effective on renin secretion, neither amiloride nor EIPA exerted a significant effect on the de novo synthesis of renin in cultured mouse JG cells. These findings are compatible with the idea that an amiloride-sensitive transport process, presumably the Na⁺/H⁺ exchanger, acts indirectly as an inhibitory signal transduction system for renin secretion from renal juxtaglomerular cells.     

Longer term progesterone treatment induces changes of GABAA receptor levels in forebrain sites in the female hamster: quantitative autoradiography study

Summary Quantitative receptor autoradiography was applied to evaluate the effects of one and three injections of 1 mg progesterone (P) on ³H muscimol binding levels in the different forebrain areas of the female hamster. The overall effect of P resulted in substantial increases in ³H muscimol binding in brain areas containing gonadal steroid receptors: medial preoptic area and ventromedial hypothalamic nucleus as well as in bed nucleus stria terminalis and subiculum. Similarly, the caudate putamen, a region where gonadal steroid receptors are not abundant, also showed substantial increases of ³H muscimol binding receptor levels. Moreover, female hamsters treated with P for 3 days presented altered ³H muscimol binding levels in the amygdala and thalamic nucleus that were, in some cases, not produced by one dose of P. P treatment also decreased GABA_A binding in two areas of the thalamus. These results are consistent with the proposal that P may alter GABAergic inhibitory activity via changes in the levels of GABA_A receptors in certain forebrain areas in the female hamster, changes which may be linked to the mediation of anxiolytic effects and to the inhibition of aggressive behavior. These data also suggest that P treatment increases the binding of high affinity GABA receptors in some forebrain sites and may be responsible for maintenance of the anxiolytic effects.     

Human serum IgE-mediated mast cell degranulation shows poor correlation to allergen-specific IgE content

BACKGROUND: Although allergen-specific IgE content in serum can be determined immunochemically, little is known about the relationship between this parameter and the strength of the degranulation response upon allergen triggering. OBJECTIVES: Analyse the degranulation capacity of immunochemically defined purified and serum IgE after challenge with anti-IgE or allergen using a rat mast cell line (RBL) transfected with the alpha-chain of the human high-affinity IgE receptor (FcepsilonRI). METHODS: Purified IgE specific for 4-hydroxy-3nitrophenylacetyl, purified IgE of unknown specificity, and sera from allergic patients sensitive to Dermatophagoides pteronyssinus and Dactylis glomerata were assessed. Degranulation was measured by a beta-hexosaminidase release assay after anti-IgE or allergen-specific challenge. RESULTS: For purified monoclonal IgE a significant correlation (r = 0.97) was found between the proportion of bound allergen-specific IgE and the strength of the degranulation response. In contrast, no correlation (r = 0.27) was detected after sensitization with serum IgE. CONCLUSION: Our studies demonstrate that mast cell activation mediated through IgE from allergic patients is a result of complex relationships that are not only dependent on allergen-specific IgE content but also relate to the capacity to efficiently sensitize and trigger the signalling responses that lead to degranulation.     

Mucosal bromodomain-containing protein 4 mediates aeroallergen-induced inflammation and remodeling

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