Enhancement of stress-induced apoptosis in B-lineage cells by caspase-9 inhibitor

Abstract

IntroductionNormal lymphoid cell development in the bone marrow and thymus is autonomously regulated by transcription factors that modify patterns of gene expression 1 and externally regulated by the extracellular matrix, stromal cells, and cytokines/chemokines/colony-stimulating factors. 2,3 The fate of developing lymphoid cells is further influenced by the functional balance of proapoptotic and antiapoptotic proteins expressed at specific points in development and the survival signals that are transduced by external cues such as cytokines. 4,5 Induction of apoptosis proceeds through 2 main pathways. The first initiates at cell surface death receptors such as CD95/Fas or the tumor necrosis receptor (the extrinsic pathway). 6,7 The second is triggered by stress, genotoxic agents, or cytokine deprivation (the intrinsic or mitochondrial pathway). 8,9 The biochemical coupling of proapoptotic molecules of the Bcl-2 homology region 3 (BH3) death domain and B-cell lymphoma 2 (Bcl-2) family members to caspase activation and downstream dismantling of cellular structure has been extensively studied in all metazoans. However, caspase activation by itself does not guarantee that apoptotic signals proceed unchecked. Members of the inhibitor of apoptosis (IAP) family of proteins can suppress or delay apoptosis by inhibiting the enzymatic activity of initiator and executioner caspases. 10,11 Whereas activation of initiator (eg, caspases-8, -9, and -10) and executioner (eg, caspases-3, -6, and -7) caspases generally occur by oligomerization of monomeric zymogens and caspase-mediated cleavage, respectively, 12-14 the consequences of inhibition of activated caspases are not completely understood. Although activation of executioner caspases leads to irreversible commitment to death when IAP function is neutralized by second mitochondria-derived activator of caspase (SMAC)/direct IAP binding protein with low PI (DIABLO), loss of mitochondrial function does not. Outer mitochondrial membrane permeabilization (and concomitant translocation of cytochrome C) is not an irreversible event, since caspase inhibition at this juncture can lead to restoration of mitochondrial transmembrane potential (⌬m). 15 This result might be explained by the recent finding that caspase translocation into the mitochondria leads to cleavage of electron transport complexes I and II and further dissolution of mitochondrial integrity. 16 Mammalian B-cell development is an excellent model to study cell fate decisions that culminate in survival or death, since functional immunoglobulin gene rearrangement and appropriate cues from the bone marrow (BM) microenvironment are essential for survival and differentiation. 17 Perturbations in the balance between proapoptotic and antiapoptotic signals can contribute to development of lymphohematopoietic malignancies. 18 During the course of characterizing the role of the mitochondrial pathway in the demise of bone marrow stromal cell-dependent B-lineage acute lymphoblastic leukemia (ALL), we made the unexpected observatio...

Suppression of Alveolar Macrophage Apoptosis Prolongs Survival of Rats and Mice withPneumocystisPneumonia

“…Results shown are representative of 12-15 rats from each condition. Scale bar, 100 m. also has been shown to increase apoptosis of B-lineage cells in response to stress (54). These results indicate that in-depth studies of the effects of caspase inhibition are needed to discern whether unforeseen responses may accompany the inhibition of this enzyme in patients with Pcp.…”

Novel IL-21 signaling pathway up-regulates c-Myc and induces apoptosis of diffuse large B-cell lymphomas

“…Furthermore, the selective caspase-9 inhibitor Z-LEHD-FMK also prevented IL-21-induced apoptosis in both cell lines, although this inhibitor exhibited some inherent toxicity to RC-K8 cells, as previously reported in some lymphoma cells. 21 In contrast, the selective caspase-8 inhibitor Z-IETD-FMK did not prevent IL-21-induced apoptosis. Because caspase-9 activation can lead to downstream caspase-8 activation, 22 these overall observations suggest that IL-21 induced apoptosis of DLBCL cells by activating the intrinsic apoptotic pathway.…”

Dual Mechanisms of sHA 14-1 in Inducing Cell Death through Endoplasmic Reticulum and Mitochondria

“…molpharm.aspetjournals.org accomplished using the Innocyte Flow Cytometric Cytochrome c Release Kit (Calbiochem, San Diego, CA) according to the manufacturer's instructions. All procedures were conducted as described previously (Shah et al, 2004).…”

“…Western blotting was conducted using standard chemiluminescent techniques as described previously (Shah et al, 2004). After a 2-to 4-h incubation in primary antibody at room temperature, the blot was washed, and secondary staining was accomplished using the corresponding IgG conjugated to horseradish perioxidase.…”