Caspase-2 Acts Upstream of Mitochondria to Promote Cytochromec Release during Etoposide-induced Apoptosis

Abstract

DNA damage induced by the cancer chemotherapeutic drug etoposide triggers the onset of a series of intracellular events characteristic of apoptosis. Among the early changes observed is the release of cytochrome c from mitochondria, although the mechanism responsible for this effect is unclear. We demonstrate here a role for caspase-2 in etoposide-induced cytochrome c release. In particular, Jurkat T-lymphocytes treated with an irreversible caspase-2 inhibitor, benzyloxycarbonylVal-Asp-Val-Ala-Asp-fluoromethyl ketone (z-VDVADfmk), or stably transfected with pro-caspase-2 antisense (Casp-2/AS) are refractory to cytochrome c release stimulated by etoposide. Experiments performed using a reconstituted cell-free system indicate that etoposide-induced cytochrome c release by way of caspase-2 occurs independently of cytosolic factors, suggesting that the nuclear pool of pro-caspase-2 is critical to this process. Apart from inhibiting cytochrome c release, undermining caspase-2 activity results in an attenuation of downstream events, such as pro-caspase-9 and -3 activation, phosphatidylserine exposure on the plasma membrane, and DNA fragmentation. Taken together, our data indicate that caspase-2 provides an important link between etoposide-induced DNA damage and the engagement of the mitochondrial apoptotic pathway.

Retinoid-related molecules require caspase 9 for the effective release of Smac and the rapid induction of apoptosis

“…The latter is possibly due to the activation of caspase 2, which occurs independently of caspase 9 activity in MX781-treated cells and may provoke the translocation of proapoptotic proteins from the mitochondria. 15,16,64 This assumption is further supported by our observations that Z-VAD-fmk, a poor inhibitor of caspase 2, 65 weakly prevented MX781-mediated release of Smac.…”

“…66 Despite the activation of caspase 2 by MX781 in cells overexpressing Bcl-2 or C9DN, this is not sufficient to cause the rapid induction of DEVDase activity that is observed in control cells, in which the mitochondria-caspase 9 loop is functional. No substrates for caspase 2 have been identified, with the exception of golgin p160 67 and, therefore, the consequences of caspase 2 activity other than targeting mitochondria 15,16,64 are not completely understood. The activation of caspase 2 upstream of caspase 9 is perhaps responsible for the degradation of PARP observed in Jurkat-C9DN cells stimulated with MX781, which occurs in the presence of low levels of DEVDase activity.…”

“…Recent evidence suggests that caspase 2 activation upstream of the mitochondria can provoke the release of mitochondrial proapoptotic factors and is essential for UV-and stress-induced apoptosis. [15][16][17] A second mechanism of apoptosis initiation is triggered by extracellular signals that bind to cell surface death receptors, such as Fas/CD95, TNFR1, or DR-5, which activate the extrinsic pathway. Upon ligand binding, death receptors dimerize and engage in the formation of the deathinducing signaling complex (DISC), which contains at least the receptor, initiator procaspases 8 or 10, and the protein adaptor Fas-associated death domain or TNFR1-associated death domain.…”

Caspase-2 is required for cell death induced by cytoskeletal disruption

“…Previous studies have suggested caspase-2 acts upstream of MOMP (Guo et al, 2002;Kumar and Vaux, 2002;Lassus et al, 2002;Paroni et al, 2002;Robertson et al, 2002;Zhivotovsky and Orrenius, 2005). It has been shown to cause MOMP by activating Bid and Bax (Bonzon et al, 2006).…”

p53-induced protein with a death domain (PIDD) isoforms differentially activate nuclear factor-kappaB and caspase-2 in response to genotoxic stress

“…These include Bad, Bax, PUMA and Noxa (for a recent review, see Roos and Kaina, 2006). Furthermore, caspase-2 has been shown to be activated by PIDD and to act upstream of the mitochondria by promoting mitochondrial membrane permeabilization (Guo et al, 2002;Lassus et al, 2002;Robertson et al, 2002). Caspase-2 can act indirectly on the mitochondria by cleaving and activating Bid (Guo et al, 2002) or by directly targeting the mitochondria, independently of its enzymatic activity (Robertson et al, 2002).…”