RESUMO
Fas-associated death domain (FADD) and caspase-8 are key signal transducers for death receptor-induced apoptosis, whereas cellular FLICE-inhibitory protein (cFLIP) antagonizes this process. Interestingly, FADD and caspase-8 also play a role in T cell development and T cell receptor (TCR)-mediated proliferative responses. To investigate the underlying mechanism, we generated cFLIP-deficient T cells by reconstituting Rag-/- blastocysts with cFLIP-deficient embryonic stem cells. These Rag chimeric mutant mice (rcFLIP-/-) had severely reduced numbers of T cells in the thymus, lymph nodes, and spleen, although mature T lymphocytes did develop. Similar to FADD- or caspase-8-deficient cells, rcFLIP-/- T cells were impaired in proliferation in response to TCR stimulation. Further investigation revealed that cFLIP is required for T cell survival, as well as T cell cycling in response to TCR stimulation. Interestingly, some signaling pathways from the TCR complex appeared competent, as CD3 plus CD28 cross-linking was capable of activating the ERK pathway in rcFLIP-/- T cells. We demonstrate an essential role for cFLIP in T cell function.
Assuntos
Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Sistema de Sinalização das MAP Quinases/fisiologia , Linfócitos T/fisiologia , Proteínas Adaptadoras de Transdução de Sinal , Animais , Proteína Reguladora de Apoptosis Semelhante a CASP8 e FADD , Antígenos CD28/metabolismo , Complexo CD3/metabolismo , Caspase 8 , Caspases/metabolismo , Proliferação de Células , Sobrevivência Celular/genética , Sobrevivência Celular/fisiologia , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Proteína de Domínio de Morte Associada a Fas , Peptídeos e Proteínas de Sinalização Intracelular/genética , Sistema de Sinalização das MAP Quinases/genética , Camundongos , Camundongos Knockout , Receptores de Antígenos de Linfócitos T/metabolismoRESUMO
The p53-induced protein with a death domain, PIDD, was identified as a p53 target gene whose main role is to execute apoptosis in a p53-dependent manner. To investigate the physiological role of PIDD in apoptosis, we generated PIDD-deficient mice. Here, we report that, although PIDD expression is inducible upon DNA damage, PIDD-deficient mice undergo apoptosis normally not only in response to DNA damage, but also in response to various p53-independent stress signals and to death receptor (DR) engagement. This indicates that PIDD is not required for DNA damage-, stress-, and DR-induced apoptosis. Also, in the absence of PIDD, both caspase-2 processing and activation occur in response to DNA damage. Our findings demonstrate that PIDD does not play an essential role for all p53-mediated or p53-independent apoptotic pathways.
Assuntos
Apoptose , Proteínas de Transporte/metabolismo , Dano ao DNA , Estresse Fisiológico , Animais , Caspase 2/metabolismo , Proteínas Adaptadoras de Sinalização de Receptores de Domínio de Morte , Marcação de Genes , Marcação In Situ das Extremidades Cortadas , Camundongos , Processamento de Proteína Pós-Traducional , Transdução de Sinais , Proteína Supressora de Tumor p53/metabolismo , Irradiação Corporal TotalRESUMO
Protein kinase B (PKBalpha/Akt1) a PI3K-dependent serine-threonine kinase, promotes T cell viability in response to many stimuli and regulates homeostasis and autoimmune disease in vivo. To dissect the mechanisms by which PKB inhibits apoptosis, we have examined the pathways downstream of PKB that promote survival after cytokine withdrawal vs Fas-mediated death. Our studies show that PKB-mediated survival after cytokine withdrawal is independent of protein synthesis and the induction of NF-kappaB. In contrast, PKB requires de novo gene transcription by NF-kappaB to block apoptosis triggered by the Fas death receptor. Using gene-deficient and transgenic mouse models, we establish that NF-kappaB1, and not c-Rel, is the critical signaling molecule downstream of the PI3K-PTEN-PKB signaling axis that regulates lymphocyte homeostasis.