The SPRY domain of SSB-2 adopts a novel fold that presents conserved Par-4-binding residues

The four mammalian SPRY domain-containing SOCS box proteins (SSB-1 to SSB-4) are characterized by a C-terminal SOCS box and a central SPRY domain. We have determined the first SPRY-domain structure, as part of SSB-2, by NMR. This domain adopts a novel fold consisting of a beta-sandwich structure formed by two four-stranded antiparallel beta-sheets with a unique topology. We demonstrate that SSB-1, SSB-2 and SSB-4, but not SSB-3, bind prostate apoptosis response protein-4 (Par-4). Mutational analysis of SSB-2 loop regions identified conserved structural determinants for its interaction with Par-4 and the hepatocyte growth factor receptor, c-Met. Mutations in analogous loop regions of pyrin and midline-1 SPRY domains have been shown to cause Mediterranean fever and Opitz syndrome, respectively. Our findings provide a template for SPRY-domain structure and an insight into the mechanism of SPRY-protein interaction.     

The structure of SOCS3 reveals the basis of the extended SH2 domain function and identifies an unstructured insertion that regulates stability

SOCS3 is essential for regulating the extent, duration, and specificity of cellular responses to cytokines such as G-CSF and IL-6. Here we describe the solution structure of SOCS3, the first structure determined for any SOCS protein, in complex with a phosphotyrosine-containing peptide from the IL-6 receptor signaling subunit gp130. The structure of the complex shows that seven peptide residues form a predominantly hydrophobic binding motif. Regions outside the SOCS3 SH2 domain are important for ligand binding, in particular, a single 15 residue alpha helix immediately N-terminal to the SH2 domain makes direct contacts with the phosphotyrosine binding loop and, in part, determines its geometry. The SH2 domain itself is remarkable in that it contains a 35 residue unstructured PEST motif insertion that is not required for STAT inhibition. The PEST motif increases SOCS3 turnover and affects its degradation pathway, implying that it has an important regulatory role inside the cell.     

Suppressor of cytokine signaling-1 has IFN-gamma-independent actions in T cell homeostasis

Suppressor of cytokine signaling (SOCS)-1 is a member of a family of proteins that negatively regulate cytokine signaling pathways. We have previously established that SOCS-1 is a key regulator of IFN-gamma signaling and that IFN-gamma is responsible for the complex inflammatory disease that leads to the death of SOCS-1-deficient mice. In this study, we provide evidence that SOCS-1 is also a critical regulator of IFN-gamma-independent immunoregulatory factors. Mice lacking both SOCS-1 and IFN-gamma, although outwardly healthy, have clear abnormalities in their immune system, including a reduced ratio of CD4:CD8 T cells in lymphoid tissues and increased expression of T cell activation markers. To examine the contribution of TCR Ag specificity to these immune defects, we have generated two lines of SOCS-1-deficient mice expressing a transgenic TCR specific for an exogenous Ag, OVA (OT-I and OT-II). Although TCR transgenic SOCS-1(-/-) mice have a longer lifespan than nontransgenic SOCS-1(-/-) mice, they still die as young adults with inflammatory disease and the TCR transgenic SOCS-1(-/-) T cells appear activated despite the absence of OVA. This suggests that both Ag-dependent and -independent mechanisms contribute to the disease in SOCS-1-deficient mice. Thus, SOCS-1 is a critical regulator of T cell activation and homeostasis, and its influence extends beyond regulating IFN-gamma signaling.     

Reduced inflammation and tissue damage in transgenic rabbits overexpressing 15-lipoxygenase and endogenous anti-inflammatory lipid mediators

PGs and leukotrienes (LTs) mediate cardinal signs of inflammation; hence, their enzymes are targets of current anti-inflammatory therapies. Products of arachidonate 15-lipoxygenases (LO) types I and II display both beneficial roles, such as lipoxins (LXs) that stereoselectively signal counterregulation, as well as potential deleterious actions (i.e., nonspecific phospholipid degradation). In this study, we examined transgenic (TG) rabbits overexpressing 15-LO type I and their response to inflammatory challenge. Skin challenges with either LTB(4) or IL-8 showed that 15-LO TG rabbits give markedly reduced neutrophil (PMN) recruitment and plasma leakage at dermal sites with LTB(4). PMN from TG rabbits also exhibited a dramatic reduction in LTB(4)-stimulated granular mobilization that was not evident with peptide chemoattractants. Leukocytes from 15-LO TG rabbits gave enhanced LX production, underscoring differences in lipid mediator profiles compared with non-TG rabbits. Microbe-associated inflammation and leukocyte-mediated bone destruction were assessed by initiating acute periodontitis. 15-LO TG rabbits exhibited markedly reduced bone loss and local inflammation. Because enhanced LX production was associated with an increased anti-inflammatory status of 15-LO TG rabbits, a stable analog of 5S,6R,15S-trihydroxyeicosa-7E,9E,11Z,13E-tetraenoic acid (LXA(4)) was applied to the gingival crevice subject to periodontitis. Topical application with the 15-epi-16-phenoxy-para-fluoro-LXA(4) stable analog (ATLa) dramatically reduced leukocyte infiltration, ensuing bone loss as well as inflammation. These results indicate that overexpression of 15-LO type I and LXA(4) is associated with dampened PMN-mediated tissue degradation and bone loss, suggesting that enhanced anti-inflammation status is an active process. Moreover, they suggest that LXs can be targets for novel approaches to diseases, e.g., periodontitis and arthritis, where inflammation and bone destruction are features.     

The SOCS box: a tale of destruction and degradation

Although initially identified in the suppressor of cytokine signaling (SOCS) family of proteins, the C-terminal SOCS box has now been identified in more than 40 proteins in nine different families. Growing evidence suggests that the SOCS box, similar to the F-box, acts as a bridge between specific substrate-binding domains and the more generic proteins that comprise a large family of E3 ubiquitin protein ligases. In this way, SOCS proteins regulate protein turnover by targeting proteins for polyubiquitination and, therefore, for proteasome-mediated degradation.     

Docosahexaenoic acid-derived neuroprotectin D1 induces neuronal survival via secretase- and PPARγ-mediated mechanisms in Alzheimer's disease models

Neuroprotectin D1 (NPD1) is a stereoselective mediator derived from the omega-3 essential fatty acid docosahexaenoic acid (DHA) with potent inflammatory resolving and neuroprotective bioactivity. NPD1 reduces Aβ42 peptide release from aging human brain cells and is severely depleted in Alzheimer's disease (AD) brain. Here we further characterize the mechanism of NPD1's neurogenic actions using 3xTg-AD mouse models and human neuronal-glial (HNG) cells in primary culture, either challenged with Aβ42 oligomeric peptide, or transfected with beta amyloid precursor protein (βAPP)(sw) (Swedish double mutation APP695(sw), K595N-M596L). We also show that NPD1 downregulates Aβ42-triggered expression of the pro-inflammatory enzyme cyclooxygenase-2 (COX-2) and of B-94 (a TNF-α-inducible pro-inflammatory element) and apoptosis in HNG cells. Moreover, NPD1 suppresses Aβ42 peptide shedding by down-regulating β-secretase-1 (BACE1) while activating the α-secretase ADAM10 and up-regulating sAPPα, thus shifting the cleavage of βAPP holoenzyme from an amyloidogenic into the non-amyloidogenic pathway. Use of the thiazolidinedione peroxisome proliferator-activated receptor gamma (PPARγ) agonist rosiglitazone, the irreversible PPARγ antagonist GW9662, and overexpressing PPARγ suggests that the NPD1-mediated down-regulation of BACE1 and Aβ42 peptide release is PPARγ-dependent. In conclusion, NPD1 bioactivity potently down regulates inflammatory signaling, amyloidogenic APP cleavage and apoptosis, underscoring the potential of this lipid mediator to rescue human brain cells in early stages of neurodegenerations.     

SOCS-6 binds to insulin receptor substrate 4, and mice lacking the SOCS-6 gene exhibit mild growth retardation

SOCS-6 is a member of the suppressor of cytokine signaling (SOCS) family of proteins (SOCS-1 to SOCS-7 and CIS) which each contain a central SH2 domain and a carboxyl-terminal SOCS box. SOCS-1, SOCS-2, SOCS-3, and CIS act to negatively regulate cytokine-induced signaling pathways; however, the actions of SOCS-4, SOCS-5, SOCS-6, and SOCS-7 remain less clear. Here we have used both biochemical and genetic approaches to examine the action of SOCS-6. We found that SOCS-6 and SOCS-7 are expressed ubiquitously in murine tissues. Like other SOCS family members, SOCS-6 binds to elongins B and C through its SOCS box, suggesting that it might act as an E3 ubiquitin ligase that targets proteins bound to its SH2 domain for ubiquitination and proteasomal degradation. We investigated the binding specificity of the SOCS-6 and SOCS-7 SH2 domains and found that they preferentially bound to phosphopeptides containing a valine in the phosphotyrosine (pY) +1 position and a hydrophobic residue in the pY +2 and pY +3 positions. In addition, these SH2 domains interacted with a protein complex consisting of insulin receptor substrate 4 (IRS-4), IRS-2, and the p85 regulatory subunit of phosphatidylinositol 3-kinase. To investigate the physiological role of SOCS-6, we generated mice lacking the SOCS-6 gene. SOCS-6(-/-) mice were born in a normal Mendelian ratio, were fertile, developed normally, and did not exhibit defects in hematopoiesis or glucose homeostasis. However, both male and female SOCS-6(-/-) mice weighed approximately 10% less than wild-type littermates.     

Suppressor of cytokine signaling-1 regulates signaling in response to interleukin-2 and other gamma c-dependent cytokines in peripheral T cells

Suppressor of cytokine signaling-1 (SOCS-1) is an essential regulator of cytokine signaling. SOCS-1-/- mice die before weaning with a complex disease characterized by fatty degeneration and necrosis of the liver. This disease is mediated by interferon (IFN) gamma as neonatal mortality fails to occur in SOCS-1-/-IFNgamma-/- mice. However, the immune system of healthy SOCS-1-/-IFNgamma-/- mice is dysregulated with a reduced ratio of CD4:CD8 T cells and increases in some aspects of T cell activation. SOCS-1-/-IFNgamma-/- mice also die before their wild type and IFNgamma-/- counterparts with a range of inflammatory conditions including pneumonia, gut infiltration, and skin ulceration, suggesting that SOCS-1 controls not only IFNgamma signaling, but also other immunoregulatory factors. This study shows that T cells from SOCS-1-deficient mice display hypersensitivity to cytokines that act through the gammac receptor. SOCS-1 expression is induced by interleukin (IL) 2, IL-4, IL-7, and IL-15, and SOCS-1-deficient T cells show increased proliferation and prolonged survival in response to IL-2 and IL-4. Furthermore, IL-2 induced increased STAT5 phosphorylation and CD44 expression in SOCS-1-deficient T cells compared with controls. Hypersensitivity to gammac-dependent cytokines may contribute to abnormal T cell function, as well as the pathology observed in mice lacking SOCS-1.     

No difference in pubertal growth and final height between treated hypogonadal and non-hypogonadal thalassemic patients

BACKGROUND: Many factors can negatively affect growth in thalassemic patients, and hypogonadism has been considered as the main factor responsible for their pubertal growth failure. OBJECTIVE: To evaluate the influence of hypogonadism and its treatment on pubertal growth and final height in thalassemic patients. METHODS: We compared the growth of 28 hypogonadal thalassemic patients in whom puberty was induced to that of 25 patients in whom puberty occurred spontaneously. RESULTS: In both groups of patients we observed reduced peak height velocity (induced puberty: females 4.9 +/- 2.1, males 6.0 +/- 1.8 cm/year; spontaneous puberty: females 6.1 +/- 1.5, males 7.3 +/- 2.1 cm/year) and pubertal height gain (induced puberty: females 11.3 +/- 4.0, males 18.0 +/- 4.5 cm/year; spontaneous puberty: females 15.8 +/- 2.7, males 18.1 +/- 5.3 cm/year) and a short final height (induced puberty: females -1.8 +/- 0.7, males -2.1 +/- 1.0 SDS; spontaneous puberty: females -2.3 +/- 1.0, males -1.9 +/- 1.0 SDS). CONCLUSIONS: Poor pubertal growth is present in thalassemic patients regardless of hypogonadism. Other factors are responsible for the reduced growth spurt and the final short stature observed in these patients.     

HIV-1, lipid rafts,and antibodies to liposomes: implications for anti-viral-neutralizing antibodies (Review)

The human immunodeficiency virus type 1 (HIV-1) is an enveloped virus with a lipid bilayer that contains several glycoproteins that are anchored in, or closely associated with, the membrane surface. The envelope proteins have complex interactions with the lipids both on the host cells and on the target cells. The processes of budding from host cells and entry into target cells occur at sites on the plasma membrane, known as lipid rafts, that represent specialized regions that are rich in cholesterol and sphingolipids. Although the envelope glycoproteins are antigenic molecules that potentially might be used for development of broadly neutralizing antibodies in a vaccine to HIV-1, the development of such antibodies that have broad specificities against primary field isolates of virus has been largely thwarted to date by the ability of the envelope proteins to evade the immune system through various mechanisms. In this review, the interactions of HIV-1 with membrane lipids are summarized. Liposomes are commonly used as models for understanding interactions of proteins with membrane lipids; and liposomes have also been used both as carriers for vaccines, and as antigens for induction of antibodies to liposomal lipids. The possibility is proposed that liposomal lipids, or liposome-protein combinations, could be useful as antigens for inducing broadly neutralizing antibodies to HIV-1.