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
Tyrosine kinase growth factor receptor signaling influences proliferation, survival, and apoptosis. Hair follicles undergo cycles of proliferation and apoptotic regression, offering an excellent paradigm to study how this transition is governed. Several factors are known to affect the hair cycle, but it remains a mystery whether Akt kinases that are downstream of growth factor signaling impact this equilibrium. We now show that an Akt relative, Sgk (serum and glucocorticoid responsive kinase) 3, plays a critical role in this process. Hair follicles of mice lacking Sgk3 fail to mature normally. Proliferation is reduced, apoptosis is increased, and follicles prematurely regress. Maintenance of the pool of transiently amplifying matrix cells is impaired. Intriguingly, loss of Sgk3 resembles the gain of function of epidermal growth factor signaling. Using cultured primary keratinocytes, we find that Sgk3 functions by negatively regulating phosphatidylinositol 3 kinase signaling. Our results reveal a novel and important function for Sgk3 in controlling life and death in the hair follicle.
Assuntos
Folículo Piloso/citologia , Folículo Piloso/enzimologia , Peptídeos e Proteínas de Sinalização Intercelular/metabolismo , Proteínas Serina-Treonina Quinases/metabolismo , Transdução de Sinais , Células-Tronco/citologia , Animais , Apoptose/efeitos dos fármacos , Bromodesoxiuridina , Contagem de Células , Diferenciação Celular/efeitos dos fármacos , Proliferação de Células/efeitos dos fármacos , DNA/biossíntese , Fertilidade/efeitos dos fármacos , Marcação de Genes , Folículo Piloso/anormalidades , Folículo Piloso/ultraestrutura , Fator de Crescimento Insulin-Like I/farmacologia , Queratinócitos/efeitos dos fármacos , Queratinócitos/metabolismo , Camundongos , Morfogênese/efeitos dos fármacos , Proteínas Serina-Treonina Quinases/deficiência , Recombinação Genética/efeitos dos fármacos , Regeneração/efeitos dos fármacos , Fase S/efeitos dos fármacos , Transdução de Sinais/efeitos dos fármacos , Células-Tronco/efeitos dos fármacosRESUMO
FKHRL1 (FOXO3a) and p53 are two potent stress-response regulators. Here we show that these two transcription factors exhibit "crosstalk" in vivo. In response to DNA damage, p53 activation led to FKHRL1 phosphorylation and subcellular localization change, which resulted in inhibition of FKHRL1 transcription activity. AKT was dispensable for p53-dependent suppression of FKHRL1. By contrast, serum- and glucocorticoid-inducible kinase 1 (SGK1) was significantly induced in a p53-dependent manner after DNA damage, and this induction was through extracellular signal-regulated kinase 1/2-mediated posttranslational regulation. Furthermore, inhibition of SGK1 expression by a small interfering RNA knockdown experiment significantly decreased FKHRL1 phosphorylation in response to DNA damage. Taken together, our observations reveal previously unrecognized crosstalk between p53 and FKHRL1. Moreover, our findings suggest a new pathway for understanding aging and the age dependency of human diseases governed by these two transcription factors.