Charakterisierung der molekularen Rolle von Caspasen bei der Proliferation von Fibroblasten und T-Lymphozyten
(Keine Zusammenfassung in deutscher Sprache hinterlegt.)
Recently the proapoptotic caspase family has been described to be involved also in proliferative processes. Initially, in this work, the relevance of the FADD/Caspase signaling pathway for cell growth was investigated using murine fibroblasts. Expression of a dominant-negative FADD mutant caused a reduced growth rate of these cells compared to the wildtype. Subsequently the molecular contribution of caspases during mitogen-induced proliferation of human T lymphocytes was characterized. Experiments using human T cells showed an impaired proliferative response of mitogen-activated T cells, when caspase activity was blocked by pharmacological inhibitors. Moreover, caspase inhibition led to a G1-cell cycle arrest of cells and caused inappropriate regulation of cell cycle-associated proteins. Proliferation assays implicated a positive contribution of caspases to the autocrine IL-2/IL-2R system, since exogeneous IL-2 could partially revert the proliferative defects mediated by caspase inhibitors. Along those lines, caspase inhibition caused a strong reduction in the activation-induced IL-2 secretion of primary T cells. Jurkat T cells lacking functional caspase-8 also exhibited a disability to produce physiological amounts of IL-2. This inhibition occurred at the transcriptional level as shown by quantitative RT-PCR. Luciferase-reporter assays using the human T cell line Jurkat revealed an impaired transcriptional activity of NFkB and the composite RE/AP element within the IL-2 promoter. Finally, caspases might be involved in activation-induced cytokine production of human monocytes, since caspase inhibition led to a reduced TNF secretion after stimulation with bacterial antigens.