Regulation of biochemical and morphological features of chemical- and receptor-mediated apoptosis in Jurkat T cells
2014-12-15T10:32:00Z (GMT) by
Evidence suggests that the signalling events which occur after apoptotic stimulation, define two basic mechanisms for the induction of apoptosis. The first is dependent on signalling via the mitochondria and the second is dependent upon signalling directly from the death receptors. After induction of apoptosis, there is a convergence in signalling at the level of caspase activation and subsequent biochemical and morphological changes. Therefore the efficacy of various inhibitors of apoptosis is dependent upon the initiating signal. In order to understand the apoptotic pathway, the mechanisms by which these inhibitors regulate chemical- and receptor-mediated apoptosis must be understood. The anti-apoptotic oncoprotein, Bcl-2, was shown to inhibit both staurosporine and Fas-mediated apoptosis in a manner which was partially dependent upon the level of Bcl-2 protein expressed. During both staurosporine and Fas-induced apoptosis Bcl-2 acted downstream of caspase-8 activation. High levels of Bcl-2 expression did not effectively inhibit apoptosis induced by anti-Fas but inhibited AICD by inhibiting the secretion of sFasL at a level above caspase-8 activation. The peptide based caspase inhibitor z-VAD-FMK resulted in a novel nuclear morphological change, characterized by partially condensed nuclear morphology and could be dissociated from the externalisation of PS, HMW DNA fragmentation and preceded the appearance of a condensed nuclear morphology during staurosporine-induced apoptosis. Furthermore, the appearance of the partially condensed nuclear morphology was independent of effector caspases. The nuclear morphological change occurred downstream of cytochrome c release, disruption of mitochondrial membrane potential and could be inhibited by Bcl-2. Finally the role of caspase-3 and DFF40/45 were examined in staurosporine- and Fas-mediated apoptosis. Using the MCF-7 cell line, it was found that caspase-3 and DFF40/45 were dispensable for the formation of HMW DNA fragments. Furthermore, the serine protease inhibitor, TPCK which has been previously shown to inhibit oligonucleosomal-length DNA fragmentation, was found to exert this effect by acting downstream of DFF40 activation.