Regulation of STIM1 and SOCE by the Ubiquitin-Proteasome System (UPS)

The ubiquitin proteasome system (UPS) mediates the majority of protein degradation in eukaryotic cells. The UPS has recently emerged as a key degradation pathway involved in synapse development and function. In order to better understand the function of the UPS at synapses we utilized a genetic and proteomic approach to isolate and identify novel candidate UPS substrates from biochemically purified synaptic membrane preparations. Using these methods, we have identified Stromal interacting molecule 1 (STIM1). STIM1 is as an endoplasmic reticulum (ER) calcium sensor that has been shown to regulate store-operated Ca2+ entry (SOCE). We have characterized STIM1 in neurons, finding STIM1 is expressed throughout development with stable, high expression in mature neurons. As in non-excitable cells, STIM1 is distributed in a membranous and punctate fashion in hippocampal neurons. In addition, a population of STIM1 was found to exist at synapses. Furthermore, using surface biotinylation and live-cell labeling methods, we detect a subpopulation of STIM1 on the surface of hippocampal neurons. The role of STIM1 as a regulator of SOCE has typically been examined in non-excitable cell types. Therefore, we examined the role of the UPS in STIM1 and SOCE function in HEK293 cells. While we find that STIM1 is ubiquitinated, its stability is not altered by proteasome inhibitors in cells under basal conditions or conditions that activate SOCE. However, we find that surface STIM1 levels and thapsigargin (TG)-induced SOCE are significantly increased in cells treated with proteasome inhibitors. Additionally, we find that the overexpression of POSH (Plenty of SH3′s), an E3 ubiquitin ligase recently shown to be involved in the regulation of Ca2+ homeostasis, leads to decreased STIM1 surface levels. Together, these results provide evidence for previously undescribed roles of the UPS in the regulation of STIM1 and SOCE function

Type I Interferons and Interferon Regulatory Factors Regulate TNF-Related Apoptosis-Inducing Ligand (TRAIL) in HIV-1-Infected Macrophages

TNF-related apoptosis-inducing ligand (TRAIL) is a member of the TNF family that participates in HIV-1 pathogenesis through the depletion of CD4+ T cells. TRAIL is expressed on the cell membrane of peripheral immune cells and can be cleaved into a soluble, secreted form. The regulation of TRAIL in macrophages during HIV-1 infection is not completely understood. In this study, we investigated the mechanism(s) of TRAIL expression in HIV-1-infected macrophages, an important cell type in HIV-1 pathogenesis. A human monocyte-derived macrophage (MDM) culture system was infected with macrophage-tropic HIV-1ADA, HIV-1JR-FL, or HIV-1BAL strains. TRAIL, predominantly the membrane-bound form, increased following HIV-1 infection. We found that HIV-1 infection also induced interferon regulatory factor (IRF)-1, IRF-7 gene expression and signal transducers and activators of transcription 1 (STAT1) activation. Small interfering RNA knockdown of IRF-1 or IRF-7, but not IRF-3, reduced STAT1 activation and TRAIL expression. Furthermore, the upregulation of IRF-1, IRF-7, TRAIL, and the activation of STAT1 by HIV-1 infection was reduced by the treatment of type I interferon (IFN)-neutralizing antibodies. In addition, inhibition of STAT1 by fludarabine abolished IRF-1, IRF-7, and TRAIL upregulation. We conclude that IRF-1, IRF-7, type I IFNs, and STAT1 form a signaling feedback loop that is critical in regulating TRAIL expression in HIV-1-infected macrophages

Selective blockade of interferon-α and -β reveals their non-redundant functions in a mouse model of West Nile virus infection

Although type I interferons (IFNs) were first described almost 60 years ago, the ability to monitor and modulate the functional activities of the individual IFN subtypes that comprise this family has been hindered by a lack of reagents. The major type I IFNs, IFN-β and the multiple subtypes of IFN-α, are expressed widely and induce their effects on cells by interacting with a shared heterodimeric receptor (IFNAR). In the mouse, the physiologic actions of IFN-α and IFN-β have been defined using polyclonal anti-type I IFN sera, by targeting IFNAR using monoclonal antibodies or knockout mice, or using Ifnb-/- mice. However, the corresponding analysis of IFN-α has been difficult because of its polygenic nature. Herein, we describe two monoclonal antibodies (mAbs) that differentially neutralize murine IFN-β or multiple subtypes of murine IFN-α. Using these mAbs, we distinguish specific contributions of IFN-β versus IFN-α in restricting viral pathogenesis and identify IFN-α as the key mediator of the antiviral response in mice infected with West Nile virus. This study thus suggests the utility of these new reagents in dissecting the antiviral and immunomodulatory roles of IFN-β versus IFN-α in murine models of infection, immunity, and autoimmunity

STAP-2 interacts with and modulates BCR-ABL-mediated tumorigenesis

In chronic myeloid leukemia (CML), the BCR-ABL fusion oncoprotein activates multiple pathways involved in cell survival, growth promotion and disease progression. In this report, we show that the signal transducing adaptor protein-2 (STAP-2) is involved in BCR-ABL activity. We demonstrate that STAP-2 bound to BCR-ABL, and BCR and ABL proteins, depending on the STAP-2 Src homology 2-like domain. BCR-ABL phosphorylates STAP-2 Tyr250 and the phosphorylated STAP-2 in turn up-regulated BCR-ABL phosphorylation, leading to enhanced activation of downstream signaling molecules including ERK, STAT5, BCL-xL and BCL-2. In addition, STAP-2 interacts with BCR-ABL to alter chemokine receptor expression leading to downregulation of CXCR4 and upregulation of CCR7. The interaction between STAP-2 and BCR-ABL plays a crucial role in conferring a growth advantage and resistance to imatinib, a BCR-ABL inhibitor, as well as tumor progression. Notably, mice injected with BCR-ABL/STAP-2-expressing Ba/F3 cells developed lymph node enlargement and hepatosplenomegaly. Moreover, suppression of STAP-2 in K562 CML cells resulted in no tumor formation in mice. Our results demonstrate a critical contribution of STAP-2 in BCR-ABL activity, and suggest that STAP-2 might be an important candidate for drug development for patients with CML. Further, the expression of STAP-2 provides useful information for estimating the characteristics of individual CML clones

Physical and functional interactions between Daxx and STAT3.

Signal transducer and activator of transcription 3 (STAT3) play key roles in the intracellular signaling pathways of the interleukin (IL)-6 family of cytokines, which exhibit a diverse set of cellular responses, including cell proliferation and differentiation. Dysregulated IL-6/STAT3 signaling is involved in the pathogenesis of several diseases, for example autoimmune diseases and tumors. Type I interferon (IFN) induces the expression of proapoptotic genes and has been used in the clinical treatment of several tumors. In the present study, we found that type I IFN suppressed IL-6/STAT3-mediated transcription and gene expression. Furthermore, a type I IFN-induced protein, Daxx, also suppressed STAT3-mediated transcriptional activation, while overexpression of Daxx inhibited IL-6/STAT3-mediated gene expression. Importantly, small-interfering RNA-mediated reduction of Daxx expression enhanced IL-6/leukemia inhibitory factor (LIF)-induced STAT3-dependent transcription. Co-immunoprecipitation studies revealed a physical interaction between Daxx and STAT3 in transiently transfected 293T cells. We further found that Daxx and STAT3 were co-localized in the nucleus. These results indicate that Daxx may serve as a transcriptional regulator of type I IFN-mediated suppression of the IL-6/STAT3 signaling pathway

Tyk2 deficiency protects joints against destruction in anti-type II collagen antibody-induced arthritis in mice

Tyrosine kinase-2 (Tyk2) participates in the signaling pathways of multiple cytokines in innate and acquired immunity. In the present study, we investigated in the in vivo involvement of Tyk2 in anti-type II collagen antibody-induced arthritis (CAIA) using Tyk2-deficient mice. Hind paws of wild-type mice showed massive swelling and erythema by arthritogenic antibody injection, while Tyk2 deficient mice did not show any signs of arthritis. Indeed, neither the infiltration of inflammatory cells nor the fibrillation of articular cartilages was observed in Tyk2-deficient mice. Tyk2 deficiency also reduced the production of Th1/Th17-related cytokines, the other pro-inflammatory cytokines and matrix metalloproteases, which are induced in the CAIA paw. Our results demonstrate a critical contribution of Tyk2 in the development of arthritis, and we propose that Tyk2 might be an important candidate for drug development.2012年7月(出版12ヶ月後)公