Showing papers by "Jeffrey M. Beekman published in 2008"

The ins and outs of syntenin, a multifunctional intracellular adaptor protein

Abstract: One of the most challenging issues currently facing cell biologists is how signal specificity and compartmentalization is achieved, allowing extracellular stimulation to result in a unique and pre-defined intracellular outcome. For this to occur, intracellular components must be correctly positioned in both space and time. Adaptor molecules, which contain protein-interaction domains, are often involved in the assembly of multimeric complexes that organize intracellular signal-transduction pathways. One such protein is syntenin, a PDZ-domain-containing molecule that has a surprising variety and diversity of interaction partners. Here we assimilate and discuss current data that support a role for syntenin in regulating transmembrane-receptor trafficking, tumour-cell metastasis and neuronal-synapse function.

Filamin A stabilizes Fc gamma RI surface expression and prevents its lysosomal routing.

Abstract: Filamin A, or actin-binding protein 280, is a ubiquitously expressed cytosolic protein that interacts with intracellular domains of multiple receptors to control their subcellular distribution, and signaling capacity. In this study, we document interaction between FcγRI, a high-affinity IgG receptor, and filamin A by yeast two-hybrid techniques and coimmunoprecipitation. Both proteins colocalized at the plasma membrane in monocytes, but dissociated upon FcγRI triggering. The filamin-deficient cell line M2 and a filamin-reconstituted M2 subclone (A7), were used to further study FcγRI-filamin interactions. FcγRI transfection in A7 cells with filamin resulted in high plasma membrane expression levels. In filamin-deficient M2 cells and in filamin RNA-interference studies, FcγRI surface expression was consistently reduced. FcγRI localized to LAMP-1-positive vesicles in the absence of filamin as shown by confocal microscopy indicative for lysosomal localization. Mouse IgG2a capture experiments suggested a transient membrane expression of FcγRI before being transported to the lysosomes. These data support a pivotal role for filamin in FcγRI surface expression via retention of FcγRI from a default lysosomal pathway.

4.5 Defective phosphorylation of the interleukin 18 receptor beta-chain causes impaired NK cell function in systemic onset Juvenile Idiopathic Arthritis

Abstract: Systemic onset Juvenile Idiopathic Arthritis (SoJIA) is an autoimmune disease characterised by arthritis and systemic features. Cytokines like IL1, IL6 and IL18 are thought to be responsible for clinical symptoms. IL18 can drive NK cell function. Recently we showed high IL18 levels in plasma correlate with disease activity in SoJIA [1]. Since SoJIA patients have diminished NK cell function we investigated the functionality of these cells in relation to IL18. All cell culture experiments were performed with IL18 in the presence or absence of IL12. SoJIA patients (n = 15) show significant lower NK cells present in peripheral blood and a differential NK cell receptor phenotype is present compared with pJIA patients (n = 15) and healthy controls (n = 10). No difference in IL18 receptor expression was observed. Furthermore IL18 in plasma of SoJIA patients is able to drive NK cell function of healthy controls and is able to bind the IL18 receptor. However, SoJIA patients fail to upregulate cell mediated killing molecules, such as perforin and IFNγ after IL18 stimulation, nor does IL18 induce phosphorylation of several MAP kinases (ERK1/2 and JNK). Both pJIA patients and healthy controls show phosphorylation of MAP kinases which results in upregulation of cell mediated killing molecules such as IFNg and perforin after stimulation with IL18. We were able to pinpoint the mechanism of the impaired NK cell – IL18 axis to an IL18 receptor defect. This important observation has major implications for understanding the immunepathogenesis of SoJIA.