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Human soluble Fas ligand (sFasL) has an apoptotic activity in contrast to murine sFasL. The physiological function of human sFasL is not known, while the pathological consequence of sFasL overproduction has been reported. To understand the physiological function of (human) sFasL, murine and human lymphocytes were treated with sFasL. sFasL treatment significantly decreased CD45RB lo "memory" CD4+ lymphocyte fraction and increased propidium iodide (PI)+ apoptotic CD45RB lo CD4+ lymphocytes among murine peripheral lymphocytes. However, sFasL treatment neither decreased CD45RO+ "memory" CD4+ lymphocyte fraction nor increased PI+ CD45RO+CD4+ lymphocytes among human peripheral lymphocytes, suggesting that the deletion of memory cells by sFasL had already occurred in vivo . Patients with systemic lupus erythematosus had sFasL-susceptible "memory" cell fraction suggesting an incomplete deletion of such "memory" cells. These results suggest that the physiological function of human sFasL is to delete the potentially auto-reactive "memory" lymphocytes, which complements membrance FasL (mFasL)-mediated deletion of auto-reactive cells in human beings but not in mice. [ABSTRACT FROM AUTHOR]

Calcineurin is a widely expressed and highly conserved Ser/Thr phosphatase. Calcineurin is inhibited by the immunosuppressant drug cyclosporine A (CsA) or tacrolimus (FK506). The critical role of CsA/FK506 as an immunosuppressant following transplantation surgery provides a strong incentive to understand the phosphatase calcineurin. Here we uncover a novel regulatory pathway for cyclic AMP (cAMP) signaling by the phosphatase calcineurin which is also evolutionarily conserved in Caenorhabditis elegans. We found that calcineurin binds directly to and inhibits the proteosomal degradation of cAMP-hydrolyzing phosphodiesterase 4D (PDE4D). We show that ubiquitin conjugation and proteosomal degradation of PDE4D are controlled by a cullin 1-containing E3 ubiquitin ligase complex upon dual phosphorylation by casein kinase 1 (CK1) and glycogen synthase kinase 3β (GSK3β) in a phosphodegron motif. Our findings identify a novel signaling process governing G-protein-coupled cAMP signal transduction--opposing actions of the phosphatase calcineurin and the CK1/GSK3β protein kinases on the phosphodegron-dependent degradation of PDE4D. This novel signaling system also provides unique functional insights into the complications elicited by CsA in transplant patients. [ABSTRACT FROM AUTHOR]

Adiponectin is a secretory protein abundantly secreted from adipocytes. It assembles into a number of different higher-order complexes. Adipocytes maintain tight control over circulating plasma levels, suggesting the existence of a complex, highly regulated biosynthetic pathway. However, the critical mediators of adiponectin maturation within the secretory pathway have not been elucidated. Previously, we found that a significant portion of de novo-synthesized adiponectin is not secreted and retained in adipocytes. Here, we show that there is an abundant pool of properly folded adiponectin in the secretory pathway that is retained through thiol-mediated retention, as judged by the release of adiponectin in response to treatment of adipocytes with reducing agents. Adiponectin is covalently bound to the ER chaperone ERp44. An adiponectin mutant lacking cysteine 39 fails to stably interact with ERp44, demonstrating that this residue is the primary site mediating the covalent interaction. Another ER chaperone, Ero1-Lα, plays a critical role in the release of adiponectin from ERp44. Levels of both of these proteins are highly regulated in adipocytes and are influenced by the metabolic state of the cell. While less critical for the secretion of trimers, these chaperones play a major role in the assembly of higher-order adiponectin complexes. Our data highlight the importance of posttranslational events controlling adiponectin levels and the release of adiponectin from adipocytes. One mechanism for increasing circulating levels of specific adiponectin complexes by peroxisome proliferator-activated receptor gamma agonists may be selective upregulation of rate-limiting chaperones. [ABSTRACT FROM AUTHOR]

Compromised immunoregulation contributes to obesity and complications in metabolic pathogenesis. Here, we demonstrate that the nuclear factor of activated T cell (NFAT) group of transcription factors contributes to glucose and insulin homeostasis. Expression of two members of the NFAT family (NFATc2 and NFATc4) is induced upon adipogenesis and in obese mice. Mice with the Nfatc2-/- Nfatc4-/- compound disruption exhibit defects in fat accumulation and are lean. Nfatc2-/- Nfatc4-/- mice are also protected from diet-induced obesity. Ablation of NFATc2 and NFATc4 increases insulin sensitivity, in part, by sustained activation of the insulin signaling pathway. Nfatc2-/- Nfatc4-/- mice also exhibit an altered adipokine profile, with reduced resistin and leptin levels. Mechanistically, NFAT is recruited to the transcription loci and regulates resistin gene expression upon insulin stimulation. Together, these results establish a role for NFAT in glucose/insulin homeostasis and expand the repertoire of NFAT function to metabolic pathogenesis and adipokine gene transcription. [ABSTRACT FROM AUTHOR]