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p53-dependent impairment of T-cell proliferation in FADD dominant-negative transgenic mice
1Imperial Cancer Research Fund, 44 Lincoln's Inn Fields, London, WC2A 3PX, UK.
Abstract:
Members of the tumour necrosis factor (TNF) receptor family exert pleiotropic effects and can trigger both apoptosis and proliferation [1]. In their cytoplasmic region, some of these receptors share a conserved sequence motif - the 'death domain' - which is required for transduction of the apoptotic signal by recruiting other death-domain-containing adaptor molecules like the Fas-associated protein FADD/MORT1 or the TNF receptor-associated protein TRADD [2-4]. FADD links the receptor signal to the activation of the caspase family of cysteine proteases [5,6]. Functional inactivation of individual receptor family members often fails to exhibit a distinctive phenotype, probably because of redundancy [7-9]. To circumvent this problem, we used a dominant-negative mutant of FADD (FADD-DN) which should block all TNF receptor family members that use FADD as an adaptor. We established transgenic mice expressing FADD-DN under the influence of the lck promoter and investigated the consequences of its expression in T cells. As expected, FADD-DN thymocytes were protected from death induced by CD95 (Fas/Apo1), whereas apoptosis induced by ultraviolet (UV) irradiation, anti-CD3 antibody treatment or dexamethasone was unaffected, as was spontaneous cell death. Surprisingly, however, we also observed profound inhibition of thymocyte proliferation in vivo and of activation-induced proliferation of thymocytes and mature T cells in vitro. This inhibition of proliferation was not due to increased cell death and appeared to be p53 dependent.
Insights
Dominant-negative FADD (FADD-DN) blocked TNF receptor family-induced apoptosis in T cells. Unexpectedly, FADD-DN also profoundly inhibited T cell proliferation, a process dependent on p53.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- Tumor necrosis factor (TNF) receptor family members mediate diverse cellular processes, including apoptosis and proliferation.
- Some TNF receptors utilize a conserved 'death domain' for signal transduction, recruiting adaptor proteins like Fas-associated protein FADD/MORT1.
- Redundancy among TNF receptor family members often complicates phenotype analysis upon individual gene inactivation.
Purpose of the Study:
- To investigate the role of FADD in TNF receptor signaling and T cell function.
- To circumvent redundancy by using a dominant-negative FADD mutant (FADD-DN) to block multiple TNF receptor family members.
- To assess the impact of FADD-DN expression on T cell apoptosis and proliferation in transgenic mice.
Main Methods:
- Generation of transgenic mice expressing a dominant-negative mutant of FADD (FADD-DN) under the lck promoter.
- Analysis of thymocyte apoptosis induced by various stimuli (CD95, UV irradiation, anti-CD3 antibody, dexamethasone) and spontaneous cell death.
- Assessment of T cell proliferation in vivo and in vitro following activation.
Main Results:
- FADD-DN expression protected thymocytes from CD95-mediated apoptosis.
- Apoptosis induced by UV irradiation, anti-CD3, dexamethasone, and spontaneous cell death remained unaffected.
- Profound inhibition of thymocyte and T cell proliferation was observed, independent of increased cell death and dependent on p53.
Conclusions:
- FADD plays a critical role in TNF receptor family-mediated apoptosis in T cells.
- FADD signaling is unexpectedly involved in regulating T cell proliferation.
- The inhibitory effect of FADD-DN on proliferation is p53-dependent, suggesting a novel link between death domain signaling and cell cycle control.