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Audrey Minden - One of the best experts on this subject based on the ideXlab platform.
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Death receptor-induced activation of Initiator Caspase 8 is antagonized by serine/threonine kinase PAK4.
Molecular and cellular biology, 2003Co-Authors: Nerina Gnesutta, Audrey MindenAbstract:Normal cell growth requires a precisely controlled balance between cell death and survival. This involves activation of different types of intracellular signaling cascades within the cell. While some types of signaling proteins regulate apoptosis, or programmed cell death, other proteins within the cell can promote survival. The serine/threonine kinase PAK4 can protect cells from apoptosis in response to several different types of stimuli. As is the case for other members of the p21-activated kinase (PAK) family, one way that PAK4 may promote cell survival is by phosphorylating and thereby inhibiting the proapoptotic protein Bad. This leads in turn to the inhibition of effector Caspases such as Caspase 3. Here we show that in response to cytokines which activate death domain-containing receptors, such as the tumor necrosis factor and Fas receptors, PAK4 can inhibit the death signal by a different mechanism. Under these conditions, PAK4 inhibits apoptosis early in the Caspase cascade, antagonizing the activation of Initiator Caspase 8. This inhibition, which does not require PAK4's kinase activity, may involve inhibition of Caspase 8 recruitment to the death domain receptors. This role in regulating Initiator Caspases is an entirely novel role for the PAK proteins and suggests a new mechanism by which these proteins promote cell survival.
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death receptor induced activation of Initiator Caspase 8 is antagonized by serine threonine kinase pak4
Molecular and Cellular Biology, 2003Co-Authors: Nerina Gnesutta, Audrey MindenAbstract:Normal cell growth requires a precisely controlled balance between cell death and survival. This involves activation of different types of intracellular signaling cascades within the cell. While some types of signaling proteins regulate apoptosis, or programmed cell death, other proteins within the cell can promote survival. The serine/threonine kinase PAK4 can protect cells from apoptosis in response to several different types of stimuli. As is the case for other members of the p21-activated kinase (PAK) family, one way that PAK4 may promote cell survival is by phosphorylating and thereby inhibiting the proapoptotic protein Bad. This leads in turn to the inhibition of effector Caspases such as Caspase 3. Here we show that in response to cytokines which activate death domain-containing receptors, such as the tumor necrosis factor and Fas receptors, PAK4 can inhibit the death signal by a different mechanism. Under these conditions, PAK4 inhibits apoptosis early in the Caspase cascade, antagonizing the activation of Initiator Caspase 8. This inhibition, which does not require PAK4's kinase activity, may involve inhibition of Caspase 8 recruitment to the death domain receptors. This role in regulating Initiator Caspases is an entirely novel role for the PAK proteins and suggests a new mechanism by which these proteins promote cell survival.
Nerina Gnesutta - One of the best experts on this subject based on the ideXlab platform.
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Death receptor-induced activation of Initiator Caspase 8 is antagonized by serine/threonine kinase PAK4.
Molecular and cellular biology, 2003Co-Authors: Nerina Gnesutta, Audrey MindenAbstract:Normal cell growth requires a precisely controlled balance between cell death and survival. This involves activation of different types of intracellular signaling cascades within the cell. While some types of signaling proteins regulate apoptosis, or programmed cell death, other proteins within the cell can promote survival. The serine/threonine kinase PAK4 can protect cells from apoptosis in response to several different types of stimuli. As is the case for other members of the p21-activated kinase (PAK) family, one way that PAK4 may promote cell survival is by phosphorylating and thereby inhibiting the proapoptotic protein Bad. This leads in turn to the inhibition of effector Caspases such as Caspase 3. Here we show that in response to cytokines which activate death domain-containing receptors, such as the tumor necrosis factor and Fas receptors, PAK4 can inhibit the death signal by a different mechanism. Under these conditions, PAK4 inhibits apoptosis early in the Caspase cascade, antagonizing the activation of Initiator Caspase 8. This inhibition, which does not require PAK4's kinase activity, may involve inhibition of Caspase 8 recruitment to the death domain receptors. This role in regulating Initiator Caspases is an entirely novel role for the PAK proteins and suggests a new mechanism by which these proteins promote cell survival.
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death receptor induced activation of Initiator Caspase 8 is antagonized by serine threonine kinase pak4
Molecular and Cellular Biology, 2003Co-Authors: Nerina Gnesutta, Audrey MindenAbstract:Normal cell growth requires a precisely controlled balance between cell death and survival. This involves activation of different types of intracellular signaling cascades within the cell. While some types of signaling proteins regulate apoptosis, or programmed cell death, other proteins within the cell can promote survival. The serine/threonine kinase PAK4 can protect cells from apoptosis in response to several different types of stimuli. As is the case for other members of the p21-activated kinase (PAK) family, one way that PAK4 may promote cell survival is by phosphorylating and thereby inhibiting the proapoptotic protein Bad. This leads in turn to the inhibition of effector Caspases such as Caspase 3. Here we show that in response to cytokines which activate death domain-containing receptors, such as the tumor necrosis factor and Fas receptors, PAK4 can inhibit the death signal by a different mechanism. Under these conditions, PAK4 inhibits apoptosis early in the Caspase cascade, antagonizing the activation of Initiator Caspase 8. This inhibition, which does not require PAK4's kinase activity, may involve inhibition of Caspase 8 recruitment to the death domain receptors. This role in regulating Initiator Caspases is an entirely novel role for the PAK proteins and suggests a new mechanism by which these proteins promote cell survival.
Andreas Bergmann - One of the best experts on this subject based on the ideXlab platform.
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Non-apoptotic enteroblast-specific role of the Initiator Caspase Dronc for development and homeostasis of the Drosophila intestine.
Scientific reports, 2021Co-Authors: Jillian L. Lindblad, Meghana Tare, Alla Amcheslavsky, Alicia Shields, Andreas BergmannAbstract:The Initiator Caspase Dronc is the only CARD-domain containing Caspase in Drosophila and is essential for apoptosis. Here, we report that homozygous dronc mutant adult animals are short-lived due to the presence of a poorly developed, defective and leaky intestine. Interestingly, this mutant phenotype can be significantly rescued by enteroblast-specific expression of dronc+ in dronc mutant animals, suggesting that proper Dronc function specifically in enteroblasts, one of four cell types in the intestine, is critical for normal development of the intestine. Furthermore, enteroblast-specific knockdown of dronc in adult intestines triggers hyperplasia and differentiation defects. These enteroblast-specific functions of Dronc do not require the apoptotic pathway and thus occur in a non-apoptotic manner. In summary, we demonstrate that an apoptotic Initiator Caspase has a very critical non-apoptotic function for normal development and for the control of the cell lineage in the adult midgut and therefore for proper physiology and homeostasis.
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Non-apoptotic enteroblast-specific role of the Initiator Caspase Dronc for development and homeostasis of the Drosophila intestine
2020Co-Authors: Jillian L. Lindblad, Meghana Tare, Alla Amcheslavsky, Alicia Shields, Andreas BergmannAbstract:The Initiator Caspase Dronc is the only CARD-domain containing Caspase in Drosophila and is essential for apoptosis. Here, we report that homozygous dronc mutant adult animals are short-lived due to the presence of a poorly developed, defective and leaky intestine. Interestingly, this mutant phenotype can be significantly rescued by enteroblast-specific expression of dronc+ in dronc mutant animals, suggesting that proper Drone function specifically in enteroblasts, one of four cell types in the intestine, is critical for normal development of the intestine. Furthermore, enteroblast-specific knockdown of dronc in adult intestines triggers hyperplasia and differentiation defects. These enteroblast-specific functions of Drone do not require the apoptotic pathway and thus occur in a non-apoptotic manner. In summary, we demonstrate that an apoptotic Initiator Caspase has a very critical non-apoptotic function for normal development and for the control of the cell lineage in the adult midgut and therefore for proper physiology and homeostasis. HighlightsO_LIdronc mutants die from a fragile and leaky intestine C_LIO_LIdronc has a critical function in enteroblasts of the intestine C_LIO_LIdronc controls proliferation and differentiation in the intestine C_LIO_LIdronc performs these functions in an apoptosis-independent (non-apoptotic) manner C_LI
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An inhibitory mono-ubiquitylation of the Drosophila Initiator Caspase Dronc functions in both apoptotic and non-apoptotic pathways.
PLoS genetics, 2017Co-Authors: Hatem Elif Kamber Kaya, Pascal Meier, Mark Ditzel, Andreas BergmannAbstract:Apoptosis is an evolutionary conserved cell death mechanism, which requires activation of Initiator and effector Caspases. The Drosophila Initiator Caspase Dronc, the ortholog of mammalian Caspase-2 and Caspase-9, has an N-terminal CARD domain that recruits Dronc into the apoptosome for activation. In addition to its role in apoptosis, Dronc also has non-apoptotic functions such as compensatory proliferation. One mechanism to control the activation of Dronc is ubiquitylation. However, the mechanistic details of ubiquitylation of Dronc are less clear. For example, monomeric inactive Dronc is subject to non-degradative ubiquitylation in living cells, while ubiquitylation of active apoptosome-bound Dronc triggers its proteolytic degradation in apoptotic cells. Here, we examined the role of non-degradative ubiquitylation of Dronc in living cells in vivo, i.e. in the context of a multi-cellular organism. Our in vivo data suggest that in living cells Dronc is mono-ubiquitylated on Lys78 (K78) in its CARD domain. This ubiquitylation prevents activation of Dronc in the apoptosome and protects cells from apoptosis. Furthermore, K78 ubiquitylation plays an inhibitory role for non-apoptotic functions of Dronc. We provide evidence that not all of the non-apoptotic functions of Dronc require its catalytic activity. In conclusion, we demonstrate a mechanism whereby Dronc’s apoptotic and non-apoptotic activities can be kept silenced in a non-degradative manner through a single ubiquitylation event in living cells.
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The Initiator Caspase Dronc is subject of enhanced autophagy upon proteasome impairment in Drosophila.
Cell death and differentiation, 2016Co-Authors: Tom V. Lee, H. E. Kamber Kaya, Rachel T. Simin, Eric H. Baehrecke, Andreas BergmannAbstract:A major function of ubiquitylation is to deliver target proteins to the proteasome for degradation. In the apoptotic pathway in Drosophila, the inhibitor of apoptosis protein 1 (Diap1) regulates the activity of the Initiator Caspase Dronc (death regulator Nedd2-like Caspase; Caspase-9 ortholog) by ubiquitylation, supposedly targeting Dronc for degradation by the proteasome. Using a genetic approach, we show that Dronc protein fails to accumulate in epithelial cells with impaired proteasome function suggesting that it is not degraded by the proteasome, contrary to the expectation. Similarly, decreased autophagy, an alternative catabolic pathway, does not result in increased Dronc protein levels. However, combined impairment of the proteasome and autophagy triggers accumulation of Dronc protein levels suggesting that autophagy compensates for the loss of the proteasome with respect to Dronc turnover. Consistently, we show that loss of the proteasome enhances endogenous autophagy in epithelial cells. We propose that enhanced autophagy degrades Dronc if proteasome function is impaired.
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Drosophila IAP1-Mediated Ubiquitylation Controls Activation of the Initiator Caspase DRONC Independent of Protein Degradation
PLoS genetics, 2011Co-Authors: Tom V. Lee, Meike Broemer, Yun Fan, Shiuan Wang, Mayank Srivastava, Pascal Meier, Andreas BergmannAbstract:Ubiquitylation targets proteins for proteasome-mediated degradation and plays important roles in many biological processes including apoptosis. However, non-proteolytic functions of ubiquitylation are also known. In Drosophila, the inhibitor of apoptosis protein 1 (DIAP1) is known to ubiquitylate the Initiator Caspase DRONC in vitro. Because DRONC protein accumulates in diap1 mutant cells that are kept alive by Caspase inhibition (“undead” cells), it is thought that DIAP1-mediated ubiquitylation causes proteasomal degradation of DRONC, protecting cells from apoptosis. However, contrary to this model, we show here that DIAP1-mediated ubiquitylation does not trigger proteasomal degradation of full-length DRONC, but serves a non-proteolytic function. Our data suggest that DIAP1-mediated ubiquitylation blocks processing and activation of DRONC. Interestingly, while full-length DRONC is not subject to DIAP1-induced degradation, once it is processed and activated it has reduced protein stability. Finally, we show that DRONC protein accumulates in “undead” cells due to increased transcription of dronc in these cells. These data refine current models of Caspase regulation by IAPs.
Yigong Shi - One of the best experts on this subject based on the ideXlab platform.
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Structure of the apoptosome: mechanistic insights into activation of an Initiator Caspase from Drosophila
Genes & development, 2015Co-Authors: Yuxuan Pang, Chuangye Yan, Xiao Chen Bai, Qi Hao, Zheqin Chen, Jiawei Wang, Sjors H.w. Scheres, Yigong ShiAbstract:Apoptosis is executed by a cascade of Caspase activation. The autocatalytic activation of an Initiator Caspase, exemplified by Caspase-9 in mammals or its ortholog, Dronc, in fruit flies, is facilitated by a multimeric adaptor complex known as the apoptosome. The underlying mechanism by which Caspase-9 or Dronc is activated by the apoptosome remains unknown. Here we report the electron cryomicroscopic (cryo-EM) structure of the intact apoptosome from Drosophila melanogaster at 4.0 A resolution. Analysis of the Drosophila apoptosome, which comprises 16 molecules of the Dark protein (Apaf-1 ortholog), reveals molecular determinants that support the assembly of the 2.5-MDa complex. In the absence of dATP or ATP, Dronc zymogen potently induces formation of the Dark apoptosome, within which Dronc is efficiently activated. At 4.1 A resolution, the cryo-EM structure of the Dark apoptosome bound to the Caspase recruitment domain (CARD) of Dronc (Dronc-CARD) reveals two stacked rings of Dronc-CARD that are sandwiched between two octameric rings of the Dark protein. The specific interactions between Dronc-CARD and both the CARD and the WD40 repeats of a nearby Dark protomer are indispensable for Dronc activation. These findings reveal important mechanistic insights into the activation of Initiator Caspase by the apoptosome.
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Molecular determinants of Caspase-9 activation by the Apaf-1 apoptosome
Proceedings of the National Academy of Sciences of the United States of America, 2014Co-Authors: Wen Chen, Zhen Yan, Chuangye Yan, Qionglin Liang, Yigong ShiAbstract:Autocatalytic activation of an Initiator Caspase triggers the onset of apoptosis. In dying cells, Caspase-9 activation is mediated by a multimeric adaptor complex known as the Apaf-1 apoptosome. The molecular mechanism by which Caspase-9 is activated by the Apaf-1 apoptosome remains largely unknown. Here we demonstrate that the previously reported 1:1 interaction between Apaf-1 Caspase recruitment domain (CARD) and Caspase-9 CARD is insufficient for the activation of Caspase-9. Rather, formation of a multimeric CARD:CARD assembly between Apaf-1 and Caspase-9, which requires three types of distinct interfaces, underlies Caspase-9 activation. Importantly, an additional surface area on the multimeric CARD assembly is essential for Caspase-9 activation. Together, these findings reveal mechanistic insights into the activation of Caspase-9 by the Apaf-1 apoptosome and support the induced conformation model for Initiator Caspase activation by adaptor complexes.
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Structure and activation mechanism of the Drosophila Initiator Caspase Dronc.
The Journal of biological chemistry, 2006Co-Authors: Nieng Yan, Jun R. Huh, Virgil Schirf, Borries Demeler, Bruce A. Hay, Yigong ShiAbstract:Activation of an Initiator Caspase is essential to the execution of apoptosis. The molecular mechanisms by which Initiator Caspases are activated remain poorly understood. Here we demonstrate that the autocatalytic cleavage of Dronc, an important Initiator Caspase in Drosophila, results in a drastic enhancement of its catalytic activity in vitro. The autocleaved Dronc forms a homodimer, whereas the uncleaved Dronc zymogen exists exclusively as a monomer. Thus the autocatalytic cleavage in Dronc induces its stable dimerization, which presumably allows the two adjacent monomers to mutually stabilize their active sites, leading to activation. Crystal structure of a prodomain-deleted Dronc zymogen, determined at 2.5 A resolution, reveals an unproductive conformation at the active site, which is consistent with the observation that the zymogen remains catalytically inactive. This study revealed insights into mechanism of Dronc activation, and in conjunction with other observations, suggests diverse mechanisms for the activation of Initiator Caspases.
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Engineering a Dimeric Caspase-9: A Re-evaluation of the Induced Proximity Model for Caspase Activation
PLoS biology, 2005Co-Authors: Yang Chao, Srinivasa M Srinivasula, Eric N. Shiozaki, Daniel J. Rigotti, Robert Fairman, Yigong ShiAbstract:Caspases are responsible for the execution of programmed cell death (apoptosis) and must undergo proteolytic activation, in response to apoptotic stimuli, to function. The mechanism of Initiator Caspase activation has been generalized by the induced proximity model, which is thought to drive dimerization-mediated activation of Caspases. The Initiator Caspase, Caspase-9, exists predominantly as a monomer in solution. To examine the induced proximity model, we engineered a constitutively dimeric Caspase-9 by relieving steric hindrance at the dimer interface. Crystal structure of the engineered Caspase-9 closely resembles that of the wild-type (WT) Caspase-9, including all relevant structural details and the asymmetric nature of two monomers. Compared to the WT Caspase-9, this engineered dimer exhibits a higher level of catalytic activity in vitro and induces more efficient cell death when expressed. However, the catalytic activity of the dimeric Caspase-9 is only a small fraction of that for the Apaf-1-activated Caspase-9. Furthermore, in contrast to the WT Caspase-9, the activity of the dimeric Caspase-9 can no longer be significantly enhanced in an Apaf-1-dependent manner. These findings suggest that dimerization of Caspase-9 may be qualitatively different from its activation by Apaf-1, and in conjunction with other evidence, posit an induced conformation model for the activation of Initiator Caspases.
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Caspase Activation: Revisiting the Induced Proximity Model
Cell, 2004Co-Authors: Yigong ShiAbstract:Caspases execute cell death. The mechanism of effector Caspase activation primarily involves reorganization of active site loops following the activation cleavage. The Induced Proximity hypothesis, originally proposed to explain the activation of Initiator Caspases, has recently been reinterpreted to be proximity-driven dimerization of Initiator Caspases, and consequently their activation. The evidence supporting these models is critically evaluated and other possible mechanisms for Initiator Caspase activation are discussed.
Olivier Micheau - One of the best experts on this subject based on the ideXlab platform.
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Marine actinomycete crude extracts with potent TRAIL-resistance overcoming activity against breast cancer cells.
Oncology Reports, 2017Co-Authors: Mohammed I Y Elmallah, Olivier Micheau, Mennat Allah G Eid, Ali M S Hebishy, Mohamed S AbdelfattahAbstract:Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising anticancer agent, as it can kill tumor cells selectively. In our search of bioactive natural products to overcome TRAIL-resistance, we isolated 47 actinomycete strains from different sediments and seawater samples collected from the Red Sea coast in Egypt and found four crude extracts (EGY1, EGY3, EGY24 and EGY34) displaying TRAIL sensitizing activity in the resistant breast cancer cell line MDA-MB-231. None of these crude extracts exhibited cytotoxic effect on normal mouse embryonic fibroblasts (MEF), with the exception of EGY34. Analysis of the signaling pathways underlying the sensitization of MDA-MB-231 cells to TRAIL-induced apoptosis, by western blotting, revealed that all crude extracts facilitated Initiator Caspase‑8/-10 activation upon TRAIL stimulation, but that in addition, EGY3 and EGY34, alone, induced strong ER-stress activation, with the appearance of BiP in the cytosolic extracts. Our results pave the way to the discovery and the development of marine-derived drugs for cancer therapy.
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Differential inhibition of TRAIL-mediated DR5-DISC formation by decoy receptors 1 and 2.
Molecular and Cellular Biology, 2006Co-Authors: Delphine Mérino, Najoua Lalaoui, Alexandre Morizot, Pascal Schneider, Eric Solary, Olivier MicheauAbstract:Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF family that induces cancer cell death by apoptosis with some selectivity. TRAIL-induced apoptosis is mediated by the transmembrane receptors death receptor 4 (DR4) (also known as TRAIL-R1) and DR5 (TRAIL-R2). TRAIL can also bind decoy receptor 1 (DcR1) (TRAIL-R3) and DcR2 (TRAIL-R4) that fail to induce apoptosis since they lack and have a truncated cytoplasmic death domain, respectively. In addition, DcR1 and DcR2 inhibit DR4- and DR5-mediated, TRAIL-induced apoptosis and we demonstrate here that this occurs through distinct mechanisms. While DcR1 prevents the assembly of the death-inducing signaling complex (DISC) by titrating TRAIL within lipid rafts, DcR2 is corecruited with DR5 within the DISC, where it inhibits Initiator Caspase activation. In addition, DcR2 prevents DR4 recruitment within the DR5 DISC. The specificity of DcR1- and DcR2-mediated TRAIL inhibition reveals an additional level of complexity for the regulation of TRAIL signaling.