RESUMO
Stimulation of CD95 (APO-1/Fas) by its natural ligand CD95L (APO-1L/FasL) leads to the formation of the death-inducing signaling complex. Here we report that upon CD95 stimulation in several T and B cell lines, a novel signaling complex is formed, which we term complex II. Complex II is composed of the death effector domain proteins as follows: procaspase-8a/b, three isoforms of c-FLIP (c-FLIP(L), c-FLIP(S), c-FLIP(R)), and FADD. Notably, complex II does not contain CD95. Based on our findings we suggest that CD95 signaling includes two steps. The first step involves formation of the death-inducing signaling complex at the cell membrane. The second step involves formation of the cytosolic death effector domain protein-containing complex that may play an important role in amplification of caspase activation.
Assuntos
Linfócitos B/metabolismo , Proteína Ligante Fas/metabolismo , Complexos Multiproteicos/metabolismo , Transdução de Sinais/fisiologia , Linfócitos T/metabolismo , Receptor fas/metabolismo , Animais , Proteína Reguladora de Apoptosis Semelhante a CASP8 e FADD/metabolismo , Caspase 8/metabolismo , Membrana Celular/metabolismo , Proteína Ligante Fas/farmacologia , Proteína de Domínio de Morte Associada a Fas/metabolismo , Humanos , Células Jurkat , Camundongos , Isoformas de Proteínas/metabolismo , Estrutura Terciária de Proteína/fisiologia , Transdução de Sinais/efeitos dos fármacos , Receptor fas/agonistasRESUMO
Caspase-2 was reported to be involved in a number of apoptotic pathways triggered by various stimuli. However, the molecular mechanism of procaspase-2 activation in the course of apoptosis remains poorly defined. In this report, we demonstrate that procaspase-2 is recruited to the CD95 (Fas/APO-1) death-inducing signaling complex (DISC) in human T- and B-cell lines. We show that procaspase-2 is activated at the DISC on CD95 stimulation. Despite its presence at the DISC, caspase-2 does not initiate apoptosis on CD95 stimulation in caspase-8-deficient cell lines. Taken together, our data reveal that caspase-2 is activated at the DISC but does not play an initiating role in the CD95-induced apoptosis.
