Suppressor of cytokine signaling 1 regulates IL-15 receptor signaling in CD8+CD44high memory T lymphocytes

T lymphocyte survival, proliferation, and death in the periphery are dependent on several cytokines. Many of these cytokines induce the expression of suppressor of cytokine signaling-1 (SOCS1), a feedback inhibitor of JAK kinases. However, it is unclear whether the cytokines that regulate T lymphocyte homeostasis are critically regulated by SOCS1 in vivo. Using SOCS1(-/-)IFN-gamma(-/-) mice we show that SOCS1 deficiency causes a lymphoproliferative disorder characterized by decreased CD4/CD8 ratio due to chronic accumulation of CD8+CD44(high) memory phenotype T cells. SOCS1-deficient CD8+ T cells express elevated levels of IL-2Rbeta, show increased proliferative response to IL-15 and IL-2 in vitro, and undergo increased bystander proliferation and vigorous homeostatic expansion in vivo. Sorted CD8+CD44(high) T cells from SOCS1(-/-)IFN-gamma(-/-) mice respond 5 times more strongly than control cells, indicating that SOCS1 is a critical regulator of IL-15R signaling. Consistent with this idea, IL-15 stimulates sustained STAT5 phosphorylation in SOCS1-deficient CD8+ T cells. IL-15 strongly induces TNF-alpha production in SOCS1-deficient CD8+ T cells, indicating that SOCS1 is also a critical regulator of CD8+ T cell activation by IL-15. However, IL-15 and IL-2 induce comparable levels of Bcl-2 and Bcl-x(L) in SOCS1-deficient and SOCS1-sufficient CD8+ T cells, suggesting that cytokine receptor signals required for inducing proliferation and cell survival signals are not identical. These results show that SOCS1 differentially regulates common gamma-chain cytokine signaling in CD8+ T cells and suggest that CD8+ T cell homeostasis is maintained by distinct mechanisms that control cytokine-mediated survival and proliferation signals.     

Plasmodium falciparum merozoite surface protein 1.

In addition to the major carbohydrate moieties of the glycosylphosphatidylinositol (GPI) anchor, we report that Plasmodium falciparum merozoite surface protein 1 (MSP-1) bears O-GlcNAc modifications predominantly in beta-anomeric configuration, in both the C- and N-terminal portions of the protein. Subcellular fractionation of parasitized erythrocytes in the late trophozoite/schizont stage reveals that GPI-anchored C-terminal fragments of MSP-1 are recovered in Triton X-100 resistant, low-density membrane fractions. Our results suggest that O-GlcNAc-modified MSP-1 N-terminal fragments tend to localize within the parasitophorous vacuolar membrane while GPI-anchored MSP-1 C-terminal fragments associate with low-density, Triton X-100 resistant membrane domains (rafts), redistribute in the parasitized erythrocyte and are eventually shed as membrane vesicles that also contain the endogenous, GPI-linked CD59.     

Regulatory role of E-NTPase/E-NTPDase in Ca<Superscript>2+</Superscript>/Mg<Superscript>2+</Superscript> transport via gated channel

Background  

E-NTPase/E-NTPDase is activated by millimolar concentrations of Ca²⁺ or Mg²⁺ with a pH optimum of 7.5 for the hydrolysis of extracellular NTP and NDP. It has been generally accepted that E-NTPase/E-NTPDase plays regulatory role in purinergic signalling, but other functions may yet be discovered.     

Non-anatomical placement adversely affects the functional performance of the meniscal implant: a finite element study

Biomechanics and Modeling in Mechanobiology - Non-anatomical placement may occur during the surgical implantation of the meniscal implant, and its influence on the resulting biomechanics of the...     

Inflammation: a novel mechanism for the transport of extracellular nucleotide-induced arachidonic acid by S100A8/A9 for transcellular metabolism

Extracellular nucleotides cause neutrophil degranulation by activating the purinergic receptor subtype P2Y. However, the molecular mechanism involved in the signal pathway remains unknown. A hypothetical scheme suggesting that leukotriene(s) and leukotriene receptor(s) activation is required for extracellular nucleotide-mediated neutrophil degranulation is presented here. Subsequent to the extracellular nucleotide binding to its receptors, intracellular arachidonic acid (AA) levels are elevated. Although AA is a known substrate of the lipoxygenase pathway mediated by 5-lipoxygenase, excess AA could form a complex with S100A8/A9 for transport to the extracellular milieu. Extracellular availability of the S100A8/A9+AA complex could potentially be used for transcellular metabolism by resting and/or activated leukocytes (PMN, MN), vascular endothelium and smooth muscle cells at the inflammatory foci. Once imported into the resting and/or activated leukocytes, AA derived from the S100A8/A9+AA complex could serve as a substrate in the 5-lipoxygenase-mediated leukotriene pathway. Essentially, in addition to extracellular nucleotide-induced leukotrienes, AA derived from the S100A8/A9+AA complex could also be utilized for the synthesis of inflammatory mediators such as leukotriene B(4)(LTB(4)), which in turn could trigger leukocyte degranulation, as well as cellular damage to vascular endothelium and smooth muscle cells, thereby exacerbating inflammation.     

Immunolocalization of the sarcolemmal Ca2+/Mg2+ ecto-ATPase (myoglein) in rat myocardium

Cardiac plasma membrane Ca²⁺/Mg²⁺ ecto-ATPase (myoglein) requires millimolar concentrations of either Ca²⁺ or Mg²⁺ for maximal activity. In this paper, we report its localization by employing an antiserum raised against the purified rat cardiac Ca²⁺/Mg²⁺ ATPase. As assessed by Western blot analysis, the antiserum and the purified immunoglobulin were specific for Ca²⁺/Mg²⁺ ecto-ATPase; no cross reaction was observed towards other membrane bound enzymes such as cardiac sarcoplasmic reticulum Ca²⁺-pump ATPase or sarcolemmal Ca²⁺-pump ATPase. On the other hand, the cardiac Ca²⁺/Mg²⁺ ecto-ATPase was not recognized by antibodies specific for either cardiac sarcoplasmic reticulum Ca²⁺-pump ATPase or plasma membrane Ca²⁺-pump ATPase. Furthermore, the immune serum inhibited the Ca²⁺/Mg²⁺ ecto-ATPase activity of the purified enzyme preparation. Immunofluorescence of cardiac tissue sections and neonatal cultured cardiomyocytes with the Ca²⁺/Mg²⁺ ecto-ATPase antibodies indicated the localization of Ca²⁺/Mg²⁺ ecto-ATPase in association with the plasma membrane of myocytes, in areas of cell-matrix or cell-cell contact. Staining for the Ca²⁺/Mg²⁺ ecto-ATPase was not cardiac specific since the antibodies detected the presence of membrane proteins in sections from skeletal muscle, brain, liver and kidney. The results indicate that Ca²⁺/Mg²⁺ ecto-ATPase is localized to the plasma membranes of cardiomyocytes as well as other tissues such as brain, liver, kidney and skeletal muscle.     

Biophysical characterization of rat cardiac Ca2+/Mg2+ ecto-ATPase (Myoglein)

Sarcolemmal Ca²⁺/Mg²⁺ ecto-ATPase (Myoglein; MW 180 kD) is a membrane bound enzyme which requires a millimolar concentration of either Ca²⁺ or Mg²⁺ for maximal hydrolysis of ATP. The isoelectric point (pI) of the cardiac ecto-ATPase was 5.7. The purified Ca²⁺/Mg²⁺ ecto-ATPase from the rat heart sarcolemmal appeared as a single band with MW 90 kD in the SDS-PAGE. In order to understand the nature of this enzyme, the 90 kD band in the SDS-PAGE was electroeluted; the analysis of the eluate showed 2 prominent bands with MW 90 and 85 kD. The presence of 2 bands was further confirmed by gradient gel (10-20%) electrophoresis in 0.375 M Tris-HCl buffer, pH 8.8. Analysis of the purified Ca²⁺/Mg²⁺ ecto-ATPase as well as the electroeluted protein in a non-equilibrium linear two dimensional electrophoresis (Ampholyte pI 3.0-10.0) also showed two distinct bands. Mass spectroscopic analysis of the enzyme using different matrix combinations revealed the presence of multi-components indicating microheterogeneity in the protein structure. Treatment of the ecto-ATPase with DL-dithiothreitol did not alter the pattern of mass spectroscopic analysis and this indicated that the microheterogeneity may be due to some posttranslational modifications. It is concluded that rat cardiac Ca²⁺/Mg²⁺ ecto-ATPase is an acidic protein having two subunits. Furthermore, the enzyme shows microheterogeneity in its molecular structure.