Involvement of X-box binding protein 1 and reactive oxygen species pathways in the pathogenesis of tumour necrosis factor receptor-associated periodic syndrome.

OBJECTIVES: To investigate convergence of endoplasmic reticulum stress pathways and enhanced reactive oxygen species (ROS) production, due to intracellular retention of mutant tumour necrosis factor receptor 1 (TNFR1), as a disease mechanism in TNFR-associated periodic syndrome (TRAPS). METHODS: Peripheral blood mononuclear cells from patients with TRAPS (n=16) and healthy controls (HC) (n=22) were studied alongside HEK293T cells expressing wild type-TNFR1 or TRAPS-associated mutations. Unfolded protein response (UPR)-associated proteins (protein kinase-like endoplasmic reticulum kinase, PERK), phosphorylated-PERK (p-PERK), phosphorylated inositol-requiring enzyme 1α (p-IRE1α) and spliced X-box binding protein 1 (sXBP1)) were measured by flow cytometry. XBP1 splicing and UPR-associated transcript expression were assessed by reverse transcription PCR/quantitative real-time PCR. ROS levels were measured using CM-H(2)DCFDA and MitoSOX Red in patients' monocytes or HEK293T cells by flow cytometry. RESULTS: Mutant TNFR1-expressing HEK293T cells had increased TNFR1 expression associated with intracellular aggregation. TRAPS patients had increased sXBP1 transcripts (p<0.01) compared with HC. Raised p-PERK protein was seen, indicative of an UPR, but other UPR-associated transcripts were normal. Increased ROS levels were observed in TRAPS monocytes compared with HCs (p<0.02); these increased further upon IL-6 stimulation (p<0.01). Lipopolysaccharide-stimulated peripheral blood mononuclear cells of patients with TRAPS, but not HCs, demonstrated increased sXBP1 levels (p<0.01), which were reduced by antioxidant treatment (p<0.05). CONCLUSIONS: Patients with TRAPS have evidence of increased sXBP1 and PERK expression but without other signs of classical UPR, and also with high ROS generation that may contribute to the pro-inflammatory state associated with TRAPS. The authors propose a non-traditional XBP1 pathway with enhanced sXBP1 as a novel disease-contributing mechanism in TRAPS.

T-cell receptor early signalling complex activation in response to interferon-alpha receptor stimulation.

Signalling through the IFNalphaR (interferon-alpha receptor) and TCR (T-cell receptor) in Jurkat T lymphocytes results in distinct immune responses. Despite this both receptors elicit ERK (extracellular-signal-regulated kinase)/MAPK (mitogen-activated protein kinase) phosphorylation. Vav and Slp76 are shown to be required for IFNalpha (interferon-alpha)-stimulated ERK activity. These form a subset of proteins which behave identically on stimulation of both receptors. TCR deletion abrogates IFNalphaR-stimulated MAPK activity, whereas the canonical JAK/STAT (Janus kinase/signal transducer and activator of transcription) pathway is unaffected. Thus recruitment of the intact TCR ESC (early signalling complex) is necessary for this downstream MAPK response. Despite using a common ESC, stimulation of the IFNalphaR does not produce the transcriptional response associated with TCR. Up-regulation of the MAPK pathway by IFNalphaR might be important to ensure that the cell responds to only one stimulant.

Negative regulation of immunoreceptor signaling by protein adapters: Shc proteins join the club.

Protein adapters couple surface receptors to multiple intracellular signaling modules by acting as scaffolds for the assembly of multimolecular complexes responsible for the coordination and amplification of signals. Through the spatiotemporally controlled recruitment of mediators with opposite activities (e.g. protein tyrosine kinases and phosphatases), adapters are implicated not only in signal initiation and propagation, but also in feedback loops for signal extinction. Moreover, adaptors specialized in preventing or dampening signaling have been more recently discovered. Here we shall present of brief overview of the principal adaptors which act as negative regulators of TCR and BCR signaling, with a focus of the mechanisms underlying this function. We shall then discuss our recent findings implicating p66Shc and Rai, two members of the Shc family of cytosolic protein adapters, in the negative control of antigen receptor signaling, and their role as gatekeepers of autoimmunity and leukemia.