Refine
Document Type
- Article (2)
Language
- English (2)
Has Fulltext
- yes (2)
Is part of the Bibliography
- no (2)
Institute
- Biochemie und Chemie (1)
- Medizin (1)
Ubiquitination now ranks with phosphorylation as one of the best-studied post-translational modifications of proteins with broad regulatory roles across all of biology. Ubiquitination usually involves the addition of ubiquitin chains to target protein molecules, and these may be of eight different types, seven of which involve the linkage of one of the seven internal lysine (K) residues in one ubiquitin molecule to the carboxy-terminal diglycine of the next. In the eighth, the so-called linear ubiquitin chains, the linkage is between the amino-terminal amino group of methionine on a ubiquitin that is conjugated with a target protein and the carboxy-terminal carboxy group of the incoming ubiquitin. Physiological roles are well established for K48-linked chains, which are essential for signaling proteasomal degradation of proteins, and for K63-linked chains, which play a part in recruitment of DNA repair enzymes, cell signaling and endocytosis. We focus here on linear ubiquitin chains, how they are assembled, and how three different avenues of research have indicated physiological roles for linear ubiquitination in innate and adaptive immunity and suppression of inflammation.
CD95 co-stimulation blocks activation of naive T cells by inhibiting T cell receptor signaling
(2009)
CD95 is a multifunctional receptor that induces cell death or proliferation depending on the signal, cell type, and cellular context. Here, we describe a thus far unknown function of CD95 as a silencer of T cell activation. Naive human T cells triggered by antigen-presenting cells expressing a membrane-bound form of CD95 ligand (CD95L) or stimulated by anti-CD3 and -CD28 antibodies in the presence of recombinant CD95L had reduced activation and proliferation, whereas preactivated, CD95-sensitive T cells underwent apoptosis. Triggering of CD95 during T cell priming interfered with proximal T cell receptor signaling by inhibiting the recruitment of ζ-chain–associated protein of 70 kD, phospholipase-γ, and protein kinase C-θ into lipid rafts, thereby preventing their mutual tyrosine protein phosphorylation. Subsequently, Ca2+ mobilization and nuclear translocation of transcription factors NFAT, AP1, and NF-κB were strongly reduced, leading to impaired cytokine secretion. CD95-mediated inhibition of proliferation in naive T cells could not be reverted by the addition of exogenous interleukin-2 and T cells primed by CD95 co-stimulation remained partially unresponsive upon secondary T cell stimulation. HIV infection induced CD95L expression in primary human antigeen-presenting cells, and thereby suppressed T cell activation, suggesting that CD95/CD95L-mediated silencing of T cell activation represents a novel mechanism of immune evasion.
