The discovery of the TRAIL protein and its death receptors DR4/5 changed the horizon of cancer research because TRAIL specifically kills cancer cells. However, the validity of TRAIL-based cancer ...therapies has yet to be established, as most cancer cells are TRAIL-resistant. In this report, we demonstrate that TRAIL-resistance of many cancer cell lines can be overcome after siRNA- or rocaglamide-mediated downregulation of c-FLIP expression and simultaneous inhibition of IAPs activity using AT406, a pan-antagonist of IAPs. Combined triple actions of the TRAIL, the IAPs inhibitor, AT406, and the c-FLIP expression inhibitor, rocaglamide (ART), markedly improve TRAIL-induced apoptotic effects in most solid cancer cell lines through the activation of an extrinsic apoptosis pathway. Furthermore, this ART combination does not harm normal cells. Among the 18 TRAIL-resistant cancer cell lines used, 15 cell lines become sensitive or highly sensitive to ART, and two out of three glioma cell lines exhibit high resistance to ART treatment due to very low levels of procaspase-8. This study provides a rationale for the development of TRAIL-induced apoptosis-based cancer therapies.
A better understanding of the mechanisms through which anticancer drugs exert their effects is essential to improve combination therapies. While studying how genotoxic stress kills cancer cells, we ...discovered a large ∼2MDa cell death-inducing platform, referred to as “Ripoptosome.” It contains the core components RIP1, FADD, and caspase-8, and assembles in response to genotoxic stress-induced depletion of XIAP, cIAP1 and cIAP2. Importantly, it forms independently of TNF, CD95L/FASL, TRAIL, death-receptors, and mitochondrial pathways. It also forms upon Smac-mimetic (SM) treatment without involvement of autocrine TNF. Ripoptosome assembly requires RIP1's kinase activity and can stimulate caspase-8-mediated apoptosis as well as caspase-independent necrosis. It is negatively regulated by FLIP, cIAP1, cIAP2, and XIAP. Mechanistically, IAPs target components of this complex for ubiquitylation and inactivation. Moreover, we find that etoposide-stimulated Ripoptosome formation converts proinflammatory cytokines into prodeath signals. Together, our observations shed new light on fundamental mechanisms by which chemotherapeutics may kill cancer cells.
Display omitted
► Genotoxic stress and depletion of IAPs triggers the formation of the Ripoptosome ► The Ripoptosome can stimulate apoptosis as well as necrosis in cancer cells ► It can form independently of mitochondrial and death-receptor pathways ► cFLIP and IAPs negatively regulate Ripoptosome-mediated apoptosis and necrosis
Tumor necrosis-factor related apoptosis-inducing ligand, also known as TRAIL or APO2L (Apo-2 ligand), is a cytokine of the TNF superfamily acknowledged for its ability to trigger selective apoptosis ...in tumor cells while being relatively safe towards normal cells. Its binding to its cognate agonist receptors, namely death receptor 4 (DR4) and/or DR5, can induce the formation of a membrane-bound macromolecular complex, coined DISC (death-signaling inducing complex), necessary and sufficient to engage the apoptotic machinery. At the very proximal level, TRAIL DISC formation and activation of apoptosis is regulated both by antagonist receptors and by glycosylation. Remarkably, though, despite the fact that all membrane-bound TRAIL receptors harbor putative glycosylation sites, only pro-apoptotic signaling through DR4 and DR5 has, so far, been found to be regulated by
- and
-glycosylation, respectively. Because putative
-glycosylation sequons and
-glycosylation sites are also found and conserved in all these receptors throughout all animal species (in which these receptors have been identified), glycosylation is likely to play a more prominent role than anticipated in regulating receptor/receptor interactions or trafficking, ultimately defining cell fate through TRAIL stimulation. This review aims to present and discuss these emerging concepts, the comprehension of which is likely to lead to innovative anticancer therapies.
A time to kill: targeting apoptosis in cancer Koff, Jean L; Ramachandiran, Sampath; Bernal-Mizrachi, Leon
International journal of molecular sciences,
01/2015, Letnik:
16, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The process of apoptosis is essential for maintaining the physiologic balance between cell death and cell growth. This complex process is executed by two major pathways that participate in activating ...an executioner mechanism leading to chromatin disintegration and nuclear fragmentation. Dysregulation of these pathways often contributes to cancer development and resistance to cancer therapy. Here, we review the most recent discoveries in apoptosis regulation and possible mechanisms for resensitizing tumor cells to therapy.
Interleukin-1β (IL-1β) is a potent inflammatory cytokine that is usually cleaved and activated by inflammasome-associated caspase-1. To determine whether IL-1β activation is regulated by inhibitor of ...apoptosis (IAP) proteins, we treated macrophages with an IAP-antagonist “Smac mimetic” compound or genetically deleted the genes that encode the three IAP family members cIAP1, cIAP2, and XIAP. After Toll-like receptor priming, IAP inhibition triggered cleavage of IL-1β that was mediated not only by the NLRP3-caspase-1 inflammasome, but also by caspase-8 in a caspase-1-independent manner. In the absence of IAPs, rapid and full generation of active IL-1β by the NLRP3-caspase-1 inflammasome, or by caspase-8, required the kinase RIP3 and reactive oxygen species production. These results demonstrate that activation of the cell death-inducing ripoptosome platform and RIP3 can generate bioactive IL-1β and implicate them as additional targets for the treatment of pathological IL-1-driven inflammatory responses.
Display omitted
► IAP inhibition induces NLRP3 inflammasome-dependent and -independent IL-1 activation ► Genetic deletion of the three IAPs (cIAP1, cIAP2, XIAP) activates IL-1 ► Inflammasome-independent IL-1 maturation is mediated by caspase-8 cleavage ► RIP3 signaling, and not cell death, activates IL-1
Inflammatory caspases (caspase-1, -4, -5 and -11) are critical for innate defences. Caspase-1 is activated by ligands of various canonical inflammasomes, and caspase-4, -5 and -11 directly recognize ...bacterial lipopolysaccharide, both of which trigger pyroptosis. Despite the crucial role in immunity and endotoxic shock, the mechanism for pyroptosis induction by inflammatory caspases is unknown. Here we identify gasdermin D (Gsdmd) by genome-wide clustered regularly interspaced palindromic repeat (CRISPR)-Cas9 nuclease screens of caspase-11- and caspase-1-mediated pyroptosis in mouse bone marrow macrophages. GSDMD-deficient cells resisted the induction of pyroptosis by cytosolic lipopolysaccharide and known canonical inflammasome ligands. Interleukin-1β release was also diminished in Gsdmd(-/-) cells, despite intact processing by caspase-1. Caspase-1 and caspase-4/5/11 specifically cleaved the linker between the amino-terminal gasdermin-N and carboxy-terminal gasdermin-C domains in GSDMD, which was required and sufficient for pyroptosis. The cleavage released the intramolecular inhibition on the gasdermin-N domain that showed intrinsic pyroptosis-inducing activity. Other gasdermin family members were not cleaved by inflammatory caspases but shared the autoinhibition; gain-of-function mutations in Gsdma3 that cause alopecia and skin defects disrupted the autoinhibition, allowing its gasdermin-N domain to trigger pyroptosis. These findings offer insight into inflammasome-mediated immunity/diseases and also change our understanding of pyroptosis and programmed necrosis.
Apoptosis is the programmed cell death which maintains the healthy survival/death balance in metazoan cells. Defect in apoptosis can cause cancer or autoimmunity, while enhanced apoptosis may cause ...degenerative diseases. The apoptotic signals contribute into safeguarding the genomic integrity while defective apoptosis may promote carcinogenesis. The apoptotic signals are complicated and they are regulated at several levels. The signals of carcinogenesis modulate the central control points of the apoptotic pathways, including inhibitor of apoptosis (IAP) proteins and FLICE-inhibitory protein (c-FLIP). The tumor cells may use some of several molecular mechanisms to suppress apoptosis and acquire resistance to apoptotic agents, for example, by the expression of antiapoptotic proteins such as Bcl-2 or by the downregulation or mutation of proapoptotic proteins such as BAX. In this review, we provide the main regulatory molecules that govern the main basic mechanisms, extrinsic and intrinsic, of apoptosis in normal cells. We discuss how carcinogenesis could be developed via defective apoptotic pathways or their convergence. We listed some molecules which could be targeted to stimulate apoptosis in different cancers. Together, we briefly discuss the development of some promising cancer treatment strategies which target apoptotic inhibitors including Bcl-2 family proteins, IAPs, and c-FLIP for apoptosis induction.
Robust innate immune detection of rapidly evolving pathogens is critical for host defense. Nucleotide-binding domain leucine-rich repeat (NLR) proteins function as cytosolic innate immune sensors in ...plants and animals. However, the structural basis for ligand-induced NLR activation has so far remained unknown. NAIP5 (NLR family, apoptosis inhibitory protein 5) binds the bacterial protein flagellin and assembles with NLRC4 to form amultiprotein complex called an inflammasome. Here we report the cryo–electron microscopy structure of the assembled ~1.4-megadalton flagellin-NAIP5-NLRC4 inflammasome, revealing how a ligand activates an NLR. Six distinct NAIP5 domains contact multiple conserved regions of flagellin, prying NAIP5 into an open and active conformation. We show that innate immune recognition of multiple ligand surfaces is a generalizable strategy that limits pathogen evolution and immune escape.
Objective The purpose of this study is to investigate apoptosis of hippocampal neurons and the expression of glial cell line ⁃derived neurotrophic factor (GDNF) and brain⁃derived neurotrophic factor ...(BDNF) in neonatal pups with EDNRB gene deficiency. Methods The infant rats (2-3 d after birth) with EDNRB gene defect caused by congenital base deletion were divided into wild (+/+), heterozygous (+/sl) and homozygous (sl/sl), 6-8 rats were included in each group. Apoptosis of hippocampal nerve cells was detected by TUNEL staining. The number of apoptotosic cells was calculated by confocal fluorescence microscopy, and the levels of GDNF and BDNF in hippocampus was determined by enzyme⁃linked immunsorbent assay (ELISA). Results The number of apoptotic cells in hippocampus of the three genotypes was significantly different (F=24.315, P=0.000), the number of apoptotic cells in sl/sl was higher than that in +/+ (t=⁃6.780, P=0.000) and +/sl (t=4.801, P=0.000). The number of apoptotic cells was the highest in hippocamp
PDF
