Structure of an extracellular gp130 cytokine receptor signaling complex.

The activation of gp130, a shared signal-transducing receptor for a family of cytokines, is initiated by recognition of ligand followed by oligomerization into a higher order signaling complex. Kaposi's sarcoma-associated herpesvirus encodes a functional homolog of human interleukin-6 (IL-6) that activates human gp130. In the 2.4 angstrom crystal structure of the extracellular signaling assembly between viral IL-6 and human gp130, two complexes are cross-linked into a tetramer through direct interactions between the immunoglobulin domain of gp130 and site III of viral IL-6, which is necessary for receptor activation. Unlike human IL-6 (which uses many hydrophilic residues), the viral cytokine largely uses hydrophobic amino acids to contact gp130, which enhances the complementarity of the viral IL-6-gp130 binding interfaces. The cross-reactivity of gp130 is apparently due to a chemical plasticity evident in the amphipathic gp130 cytokine-binding sites.

EBV B lymphoma cell lines from patients with post-transplant lymphoproliferative disease are resistant to TRAIL-induced apoptosis.

Lymphomas associated with post-transplant lymphoproliferative disease (PTLD) represent a significant complication of immunosuppression in transplant recipients. In immunocompetent individuals, EBV-specific cytotoxic T lymphocytes (CTL) prevent the outgrowth of activated B lymphoblasts through apoptosis induction. Soluble versions of TNF-related apoptosis-inducing ligand/Apo2 ligand (TRAIL) can induce apoptosis in numerous tumor cell types. Given the therapeutic potential of TRAIL, we examined the sensitivity of EBV+ spontaneous lymphoblastoid cell lines (SLCL) derived from patients with PTLD to treatment with soluble TRAIL. Despite abundant expression of TRAIL receptors (TRAIL-R), resistance to TRAIL-induced apoptosis was observed in all SLCL examined. This resistance could not be overcome by concomitant treatment with several pharmacological agents. Unlike BJAB positive control cells, for each SLCL tested, cleavage and activation of caspase 8 was inhibited due to failed recruitment of FADD and caspase 8 to TRAIL receptors upon stimulation. Further indicative of a proximal defect, TRAIL receptor aggregation could not be detected on the cell surface of SLCL following ligand engagement. These results suggest that the use of TRAIL for eliminating PTLD-associated tumors may be of limited clinical utility, and illustrate another mechanism by which EBV+ B lymphoma cells can evade tumor surveillance at the level of death receptor signaling.

Utilization of emergency center services by older adults with a psychiatric diagnosis.

Information regarding older adult emergency center (EC) patient characteristics remains limited, despite its increasing importance in health care delivery systems. This retrospective study encompasses all EC visits over an eight-year period (n = 825,682) to a large urban county hospital. Only participants with a primary psychiatric diagnosis were examined, and included a total of 53,894 adults, 18-64 years old and 1,478 adults, > or =65 years old. Despite an increasing aging population, EC visits for older adults with psychiatric disorders did not increase over time. Within the older adult sample, cognitive, psychotic, and bipolar disorders were associated with higher rates of admission to the hospital, while substance use, depressive, and anxiety disorders were associated with lower numbers of inpatient admissions. African-Americans were over-represented in the EC and admitted to the hospital at higher rates, compared to other ethnic groups. Caucasian patients were the group most frequently diagnosed with a substance use disorder. In conclusion, differences in race, and diagnosis support the idea that such variables directly relate to utilization rates, presentation, and disposition within the EC.

FRIP, a hematopoietic cell-specific rasGAP-interacting protein phosphorylated in response to cytokine stimulation.

The human IL-4 receptor contains a sequence (the 14R motif) centered on Y497 that, when phosphorylated, interacts with phosphotyrosine-binding (PTB) domain proteins. Here, we describe a PTB domain protein, FRIP, that is phosphorylated in response to cytokine stimulation. FRIP is related to the rasGAP-associated protein p62dok and is bound by the N-terminal SH2 domain of rasGAP. The frip gene maps to the hairless (hr) locus on mouse chromosome 14. hr/hr mice exhibit lymphadenopathy, and their lymph node T cells proliferate more vigorously to anti-CD3 with IL-4 or IL-2 stimulation than +/hr T cells. FRIP expression is significantly reduced in T cells from hr/hr mice. FRIP may negatively regulate proliferation by acting as an adapter molecule between rasGAP and receptor complexes.

Resistance to Fas-mediated apoptosis in EBV-infected B cell lymphomas is due to defects in the proximal Fas signaling pathway.

Post-transplant lymphoproliferative disorder is characterized by the outgrowth of EBV-infected B cell lymphomas in immunosuppressed transplant recipients. Using a panel of EBV-infected spontaneous lymphoblastoid cell lines (SLCL) derived from post-transplant lymphoproliferative disorder patients, we assessed the sensitivity of such lymphomas to Fas-mediated cell death. Treatment with either an agonist anti-Fas mAb or Fas ligand-expressing cells identifies two subsets of SLCL based on their sensitivity or resistance to Fas-driven apoptosis. Fas resistance in these cells cannot be attributed to reduced Fas expression or to mutations in the Fas molecule itself. In addition, all SLCL are sensitive to staurosporine-induced cell death, indicating that there is no global defect in apoptosis. Although all SLCL express comparable levels of Fas signaling molecules including Fas-associated death domain protein, caspase 8, and caspase 3, Fas-resistant SLCL exhibit a block in Fas-signaling before caspase 3 activation. In two SLCL, this block results in impaired assembly of the death-inducing signaling complex, resulting in reduced caspase 8 activation. In a third Fas-resistant SLCL, caspase 3 activation is hindered despite intact death-inducing signaling complex formation and caspase 8 activation. Whereas multiple mechanisms exist by which tumor cells can evade Fas-mediated apoptosis, these studies suggest that the proximal Fas-signaling pathway is impeded in Fas-resistant post-transplant lymphoproliferative disorder-associated EBV(+) B cell lymphomas.