Satellites of the largest Kuiper Belt objects

We have searched the four brightest objects in the Kuiper Belt for the presence of satellites using the newly commissioned Keck Observatory Laser Guide Star Adaptive Optics system. Satellites are seen around three of the four objects: Pluto (whose satellite Charon is well-known and whose recently discovered smaller satellites are too faint to be detected), 2003 EL61 (where a second satellite is seen in addition to the previously known satellite), and 2003 UB313 (where a satellite is seen for the first time). The object 2005 FY9, the brightest Kuiper Belt object (KBO) after Pluto, does not have a satellite detectable within 0".4 with a brightness of more than 1% of the primary. The presence of satellites around three of the four brightest KBOs is inconsistent with the fraction of satellites in the Kuiper Belt at large at the 99.2% confidence level, suggesting a different formation mechanism for these largest KBO satellites. The two satellites of 2003 EL61, and the one satellite of 2003 UB313, with fractional brightnesses of 5% and 1.5%, and 2%, of their primaries, respectively, are significantly fainter relative to their primaries than other known KBO satellites, again pointing to possible differences in their origin

Cytokine receptor signaling activates an IKK-dependent phosphorylation of PUMA to prevent cell death

P53-upregulated modifier of apoptosis (PUMA), a pro-apoptotic member of the Bcl-2 family, is transcriptionally activated by p53 and is a key effector of p53-dependent apoptosis. We show that PUMA protein is subject to rapid post-translational regulation by phosphorylation at a conserved residue, serine 10, following serum or interleukin-3 (IL-3) stimulation. Serine 10 is not within the Bcl-2 homology (BH3) domain, and PUMA phosphorylated at serine 10 retained the ability to co-immunoprecipitate with antiapoptotic Bcl-2 family members. However, phosphorylated PUMA was targeted for proteasomal degradation indicating that it is less stable than unphosphorylated PUMA. Importantly, we identified IKK1/IKK2/Nemo as the kinase complex that interacts with and phosphorylates PUMA, thereby also demonstrating that IL-3 activates NFκB signaling. The identification and characterization of this novel survival pathway has important implications for IL-3 signaling and hematopoietic cell development.JJ Sandow, AM Jabbour, MR Condina, CP Daunt, FC Stomski, BD Green, CD Riffkin, P Hoffmann, MA Guthridge, J Silke, AF Lopez and PG Eker

Cytokine receptors

Cytokine receptors initiate intracellular signalling that regulate a diverse range of biological and medically important functions including metabolism control, neural stem cell activation, inflammatory responses, bone development, as well as blood cell and immune cell development and growth. The unifying feature of these receptors is their ability to activate the JAK-STAT pathway, however they are grouped into two structurally related classes, known as class I and class II. Class I cytokine receptors has over 30 members including receptors for erythropoietin (EPO), prolactin (PRL), growth hormone (GH), thrombopoietin (TPO), leptin, (LEP), granulocyte-macrophage colony-stimulating factor (GM-CSF), leukaemia inhibitory factor (LIF), interleukin-3 (IL-3), IL-5, IL-6, and IL-7. The Class I cytokine receptor family includes the interferon receptors, IL-10 receptor, and number of more recently discovered cytokine receptors for IL-19, IL-20, IL-22, IL-24, IL-26, and IL-29. This chapter will review the structure, activation mechanism, and signalling of cytokine receptors