(1/30) Caspase-2 induces apoptosis by releasing proapoptotic proteins from mitochondria.

Caspase-2 is one of the earliest identified caspases, but the mechanism of caspase-2-induced apoptosis remains unknown. We show here that caspase-2 engages the mitochondria-dependent apoptotic pathway by inducing the release of cytochrome c (Cyt c) and other mitochondrial apoptogenic factors into the cell cytoplasm. In support of these observations we found that Bcl-2 and Bcl-xL can block caspase-2- and CRADD (caspase and RIP adaptor with death domain)-induced cell death. Unlike caspase-8, which can process all known caspase zymogens directly, caspase-2 is completely inactive toward other caspase zymogens. However, like caspase-8, physiological levels of purified caspase-2 can cleave cytosolic Bid protein, which in turn can trigger the release of Cyt c from isolated mitochondria. Interestingly, caspase-2 can also induce directly the release of Cyt c, AIF (apoptosis-inducing factor), and Smac (second mitochondria-derived activator of caspases protein) from isolated mitochondria independent of Bid or other cytosolic factors. The caspase-2-released Cyt c is sufficient to activate the Apaf-caspase-9 apoptosome in vitro. In combination, our data suggest that caspase-2 is a direct effector of the mitochondrial apoptotic pathway.  (+info)

(2/30) Delineation of RAID1, the RACK1 interaction domain located within the unique N-terminal region of the cAMP-specific phosphodiesterase, PDE4D5.

BACKGROUND: The cyclic AMP specific phosphodiesterase, PDE4D5 interacts with the beta-propeller protein RACK1 to form a signaling scaffold complex in cells. Two-hybrid analysis of truncation and mutant constructs of the unique N-terminal region of the cAMP-specific phosphodiesterase, PDE4D5 were used to define a domain conferring interaction with the signaling scaffold protein, RACK1. RESULTS: Truncation and mutagenesis approaches showed that the RACK1-interacting domain on PDE4D5 comprised a cluster of residues provided by Asn-22/Pro-23/Trp-24/Asn-26 together with a series of hydrophobic amino acids, namely Leu-29, Val-30, Leu-33, Leu-37 and Leu-38 in a 'Leu-Xaa-Xaa-Xaa-Leu' repeat. This was done by 2-hybrid analyses and then confirmed in biochemical pull down analyses using GST-RACK1 and mutant PDE4D5 forms expressed in COS cells. Mutation of Arg-34, to alanine, in PDE4D5 attenuated its interaction with RACK1 both in 2-hybrid screens and in pull down analyses. A 38-mer peptide, whose sequence reflected residues 12 through 49 of PDE4D5, bound to RACK1 with similar affinity to native PDE4D5 itself (Ka circa 6 nM). CONCLUSIONS: The RACK1 Interaction Domain on PDE4D5, that we here call RAID1, is proposed to form an amphipathic helical structure that we suggest may interact with the C-terminal beta-propeller blades of RACK1 in a manner akin to the interaction of the helical G-gamma signal transducing protein with the beta-propeller protein, G-beta.  (+info)

(3/30) RAIDD aggregation facilitates apoptotic death of PC12 cells and sympathetic neurons.

In human cell lines, the caspase 2 adaptor RAIDD interacts selectively with caspase 2 through its caspase recruitment domain (CARD) and leads to caspase 2-dependent death. Whether RAIDD induces such effects in neuronal cells is unknown. We have previously shown that caspase 2 is essential for apoptosis of trophic factor-deprived PC12 cells and rat sympathetic neurons. We report here that rat RAIDD, cloned from PC12 cells, interacts with rat caspase 2 CARD. RAIDD overexpression induced caspase 2 CARD- and caspase 9-dependent apoptosis of PC12 cells and sympathetic neurons. Apoptosis correlated with the formation of discrete perinuclear aggregates. Both death and aggregates required the expression of full-length RAIDD. Such aggregates may enable more effective activation of caspase 2 through close proximity. Following trophic deprivation, RAIDD overexpression increased death and aggregate formation. Therefore, RAIDD aggregation is important for its death-promoting effects and may play a role in trophic factor withdrawal-induced neuronal apoptosis.  (+info)

(4/30) The PIDDosome, a protein complex implicated in activation of caspase-2 in response to genotoxic stress.

Apoptosis is triggered by activation of initiator caspases upon complex-mediated clustering of the inactive zymogen, as occurs in the caspase-9-activating apoptosome complex. Likewise, caspase-2, which is involved in stress-induced apoptosis, is recruited into a large protein complex, the molecular composition of which remains elusive. We show that activation of caspase-2 occurs in a complex that contains the death domain-containing protein PIDD, whose expression is induced by p53, and the adaptor protein RAIDD. Increased PIDD expression resulted in spontaneous activation of caspase-2 and sensitization to apoptosis by genotoxic stimuli. Because PIDD functions in p53-mediated apoptosis, the complex assembled by PIDD and caspase-2 is likely to regulate apoptosis induced by genotoxins.  (+info)

(5/30) Association of caspase-2 with the promyelocytic leukemia protein nuclear bodies.

Apoptotic cell death is executed by a family of cysteine proteases known as caspases. Synthesized as inactive precursors, caspases become activated sequentially in cascades. Activation of apical or initiator caspases in these cascades occurs in macromolecular complexes located in various compartments. One such complex is the plasma membrane-bound death-inducing signaling complex (DISC), formed upon engagement of death receptors, which recruits and activates caspase-8 and -10. Another complex is the cytosolic apoptosome, assembled in response to the release of mitochondrial cytochrome c, which recruits caspase-9. The other major human initiator caspase is caspase-2, which is activated in response to various lethal stimuli and has recently been shown to be required for DNA damage-induced apoptosis. The regulation of caspase-2 is not well understood. Here we present evidence that caspase-2 is localized to the promyelocytic leukemia protein nuclear bodies (PML-NBs), nuclear macro-molecular complexes that are involved in many scenarios of apoptosis including DNA damage. The localization of caspase-2 requires both the prodomain and protease domain but appears to be independent of its adaptor protein, CRADD/RAIDD. These data suggest the existence of a nuclear apoptosis pathway that involves both caspase-2 and the PML-NBs.  (+info)

(6/30) RAIDD is required for apoptosis of PC12 cells and sympathetic neurons induced by trophic factor withdrawal.

Caspase 2 has been implicated in trophic deprivation-induced neuronal death. We have shown that overexpression of the caspase 2-binding protein RAIDD induces neuronal apoptosis, acting synergistically with trophic deprivation. Currently, we examine the role of endogenous RAIDD in apoptosis of PC12 cells and sympathetic neurons. Expression of a truncated caspase recruitment domain-only form of caspase 2, which presumably disrupts the RAIDD interaction with endogenous caspase 2, attenuated trophic deprivation-induced apoptosis. Furthermore, downregulation of RAIDD by small interfering RNA led to inhibition of trophic deprivation-induced death, whereas death induced by DNA damage, which is not caspase 2-mediated, was not inhibited. Therefore, RAIDD, likely through interaction with caspase 2, is involved in trophic deprivation-induced neuronal apoptosis. This is the first demonstration of the involvement of RAIDD in apoptosis, and provides further support for the idea that apoptotic pathways in the same system may differ depending on the initiating stimulus.  (+info)

(7/30) Apoptosis caused by p53-induced protein with death domain (PIDD) depends on the death adapter protein RAIDD.

The p53 tumor suppressor promotes cell cycle arrest or apoptosis in response to diverse stress stimuli. p53-mediated cell death depends in large part on transcriptional up-regulation of target genes. One of these targets, P53-induced protein with a death domain (PIDD), was shown to function as a mediator of p53-dependent apoptosis. Here we show that PIDD is a cytoplasmic protein, and that PIDD-induced apoptosis and growth suppression in embryonic fibroblasts depend on the adaptor protein receptor-interacting protein (RIP)-associated ICH-1/CED-3 homologous protein with a death domain (RAIDD). We provide evidence that PIDD-induced cell death is associated with the early activation of caspase-2 and later activation of caspase-3 and -7. Our results also show that caspase-2(-/-), in contrast to RAIDD(-/-), mouse embryonic fibroblasts, are only partially resistant to PIDD. Our findings suggest that caspase-2 contributes to PIDD-mediated cell death, but that it is not the sole effector of this pathway.  (+info)

(8/30) PIDD mediates NF-kappaB activation in response to DNA damage.

Activation of NF-kappaB following genotoxic stress allows time for DNA-damage repair and ensures cell survival accounting for acquired chemoresistance, an impediment to effective cancer therapy. Despite this clinical relevance, little is known about pathways that enable genotoxic-stress-induced NF-kappaB induction. Previously, we reported a role for the p53-inducible death-domain-containing protein, PIDD, in caspase-2 activation and apoptosis in response to DNA damage. We now demonstrate that PIDD plays a critical role in DNA-damage-induced NF-kappaB activation. Upon genotoxic stress, a complex between PIDD, the kinase RIP1, and a component of the NF-kappaB-activating kinase complex, NEMO, is formed. PIDD expression enhances genotoxic-stress-induced NF-kappaB activation through augmented sumoylation and ubiquitination of NEMO. Depletion of PIDD and RIP1, but not caspase-2, abrogates DNA-damage-induced NEMO modification and NF-kappaB activation. We propose that PIDD acts as a molecular switch, controlling the balance between life and death upon DNA damage.  (+info)