Biomedical subjects

Andreas Krueger

Publications and source records attributed to Andreas Krueger.

25 records · Page 2Linked to original sources

PubMed2003

An IL-2-dependent switch between CD95 signaling pathways sensitizes primary human T cells toward CD95-mediated activation-induced cell death.

The CD95 (APO-1/Fas) system plays a critical role in activation-induced cell death (AICD) of T cells. We previously described two distinct CD95 (APO-1/Fas) signaling pathways: 1) type I cells show strong death-inducing signaling complex (DISC) formation and mitochondria-independent apoptosis and 2) DISC formation is reduced in type II cells, leading to mitochondria-dependent apoptosis. To investigate the relevance of these pathways, we set up an in vitro model that mimics the initiation and the down phase of an immune response, respectively. Freshly activated human T cells (initiation) are resistant toward CD95-mediated AICD despite high expression of CD95. We previously reported that these T cells show reduced DISC formation. In this study, we show that freshly activated T cells are CD95-type II cells that show high expression levels of Bcl-x(L) and display a block in the mitochondrial apoptosis pathway. Furthermore, we show that, upon prolonged culture (down phase), human T cells undergo a switch from type II to type I cells that renders T cells sensitive to CD95-mediated AICD. Finally, we demonstrate that this switch is dependent on the presence of IL-2. Our observations reveal for the first time that the existence of coexisting CD95 signaling pathways is of physiological relevance.

Apoptosis↗

PubMed2003

An unexpected role for FosB in activation-induced cell death of T cells.

The CD95 (APO-1/Fas) system plays a major role in induction of apoptosis in lymphoid and nonlymphoid tissues. The CD95 (APO-1/Fas) ligand (CD95L) is induced in response to a variety of signals including TCR/CD3 stimulation or application of chemotherapeutic drugs. Here we report that an AP-1 site located in the 5' untranslated region of the CD95L gene is required for TCR/CD3-mediated induction of the human CD95L promoter. Electrophoretic mobility shift assays using nuclear extracts of Jurkat T cells as well as TCR/CD3-restimulated primary human T cells demonstrated specific binding of AP-1, predominantly composed of c-Jun and FosB, to this sequence. Ectopic expression of transdominant negative Jun mutants strongly reduced CD95L promoter activity and activation-induced cell death (AICD), confirming the functional significance of FosB/c-Jun binding. Thus, our results demonstrate an important novel function for FosB dimerized with c-Jun in TCR/CD3-mediated AICD in human T cells.

5' Untranslated Regions↗

PubMed2003

The role of CD95 in the regulation of peripheral T-cell apoptosis.

Apoptosis of activated peripheral T cells during the termination phase of an immune response is critical to maintain T-cell homeostasis. Activated T cells can be removed by two mechanisms: activation-induced cell death (AICD) and death by neglect. AICD is triggered by death receptors, whereas death by neglect is induced by cytokine withdrawal. CD95 (APO-1/Fas) belongs to the subfamily of death receptors and plays a major role in AICD. In this review, we focus on the molecular mechanisms of AICD, in particular those involving the CD95 system. Moreover, we discuss the relative contribution of AICD and death by neglect to terminate a T-cell immune response. In order to become fully activated, T cells require a second signal provided by antigen-presenting cells. We discuss how these costimulatory signals counteract pro-apoptotic signals and, finally, which signals might protect T cells from death to generate a pool of memory T cells.

Apoptosis↗

PubMed2002

Specificity of anti-human CD95 (APO-1/Fas) antibodies.

The CD95 (APO-1/Fas) death receptor plays an important role in many physiological and pathophysiological systems. Thus, the CD95 system contributes to activation-induced cell death. Therefore, reliable antibodies recognizing human CD95 are of great interest. Detection of CD95 expression often relies on antibodies, e.g., suitable for Western blotting. To detect CD95, we compared the specificity of nine different anti-human CD95 antibodies recognizing different epitopes by using postnuclear supernatants of four different cell lines. Only two of the antibodies tested, both directed against intracellular epitopes of human CD95, detected endogenous human CD95 by Western blotting. Therefore, we conclude that results obtained with other anti-CD95 antibodies should be treated with caution.

Animals↗

PubMed2002

Viral IFN-regulatory factors inhibit activation-induced cell death via two positive regulatory IFN-regulatory factor 1-dependent domains in the CD95 ligand promoter.

The CD95 (also called APO-1/Fas) system plays a major role in the induction of apoptosis in lymphoid and nonlymphoid tissues. The CD95 ligand (CD95L) is induced in response to a variety of signals, including IFN-gamma and TCR/CD3 stimulation. Here we report the identification of two positive regulatory IFN-regulatory factor-dependent domains (PRIDDs) in the CD95L promoter and its 5' untranslated region, respectively. EMSAs demonstrate specific binding of IFN-gamma-induced IFN-regulatory factor 1 (IRF-1) to the PRIDD sequences. Ectopic IRF-1 expression induces CD95L promoter activity. Furthermore, we demonstrate that PRIDDs play an important role in TCR/CD3-mediated CD95L induction. Most interestingly, viral IRFs of human herpes virus 8 (HHV8) totally abolish IRF-1-mediated and strongly reduce TCR/CD3-mediated CD95L induction. We demonstrate here for the first time that viral IRFs inhibit activation-induced cell death. Thus, these results demonstrate an important mechanism of HHV8 to modulate the immune response by down-regulation of CD95L expression. Inhibition of CD95-dependent T cell function might contribute to the immune escape of HHV8.

Apoptosis↗

PubMed2002

Regulation of T cell apoptosis during the immune response.

Apoptosis of T-lymphocytes is a fundamental process regulating antigen receptor repertoire selection during T cell maturation and homeostasis of the immune system. It also plays a key role in elimination of autoreactive lymphocytes. Resting mature T cells are activated by antigen to elicit an appropriate immune response. In contrast, preactivated T cells undergo activation-induced cell death (AICD) in response to TCR triggering alone. Thus, death by apoptosis is essential for function, growth and differentiation of T-lymphocytes. This review focuses on apoptosis mechanisms involved in T cell development and during the course of an immune response.

Animals↗

PubMed2001

Glutathione dependence of caspase-8 activation at the death-inducing signaling complex.

Apoptosis triggered by the death receptor CD95 (APO-1 or Fas) is pivotal for the homeostasis of the immune system. We investigated differential effects of glutathione depletion on CD95-triggered apoptosis in T and B cell lines as well as the glutathione dependence of caspase-8 activation. In B lymphoblastoid SKW6.4 cells, CD95-mediated apoptosis was prevented upstream of caspase-8 activation and caspase-3-like activity after acute glutathione depletion by diethyl maleate or cis-chloro-dinitrobenzene. Immunoprecipitation of the death-inducing signaling complex (DISC) revealed that the DISC was still formed in the glutathione-depleted state. The first cleavage step of procaspase-8 activation at the DISC, however, was inhibited. Accordingly, under cell-free conditions, radiolabeled procaspase-8 was processed at the immunoprecipitated DISC only after the addition of exogenous dithiothreitol or reduced glutathione. We also observed suppression of CD95-mediated apoptosis in glutathione-depleted CEM and H9 cells. Notably, Jurkat cells still died upon CD95 engagement under this condition, displaying incomplete nuclear fragmentation and a partial switch to necrosis; this may be explained by reduced cytochrome c/dATP-mediated caspase activation observed in cytosol from glutathione-depleted Jurkat cytosol. Our data indicate that the activation of caspase-8 at the DISC and hence CD95-mediated apoptosis induction shows a cell-specific requirement for intracellular glutathione.

Apoptosis↗