Abstract Caspase-3 (CASP3) and caspase-7 (CASP7) are the two major executioner caspases that are proteolytically activated by upstream initiator caspases. They possess almost indistinguishable activity, which has led to the overall view that these caspases have functionally redundant roles. Here, we generate knock-in mice expressing cleavage-resistant CASP3(D175A) or CASP7(D198A). Our results show that proteolytic activation of CASP3 and CASP7 is decisive for their activity in vivo and controls redundant processes during embryonic development as combined expression of both CASP3(D175A) and CASP7(D198A) causes embryonic lethality. In adult mice, however, activation of CASP3 and CASP7 controls different processes in different tissues, without the involvement of apoptosis. While CASP7 activation is required for male fertility by controlling spermatogenesis, CASP3 activation appears crucial for lymphoid tissue development by regulating interferon signalling. Our findings shed light on emerging roles of caspases in non-apoptotic processes and provide impetus for reconsidering their involvement in physiological and pathological conditions.

Severe defects in human IFNγ immunity predispose individuals to both Bacillus Calmette-Guérin disease and tuberculosis, whereas milder defects predispose only to tuberculosis1. Here we report two adults with recurrent pulmonary tuberculosis who are homozygous for a private loss-of-function TNF variant. Neither has any other clinical phenotype and both mount normal clinical and biological inflammatory responses. Their leukocytes, including monocytes and monocyte-derived macrophages (MDMs) do not produce TNF, even after stimulation with IFNγ. Blood leukocyte subset development is normal in these patients. However, an impairment in the respiratory burst was observed in granulocyte-macrophage colony-stimulating factor (GM-CSF)-matured MDMs and alveolar macrophage-like (AML) cells2 from both patients with TNF deficiency, TNF- or TNFR1-deficient induced pluripotent stem (iPS)-cell-derived GM-CSF-matured macrophages, and healthy control MDMs and AML cells differentiated with TNF blockers in vitro, and in lung macrophages treated with TNF blockers ex vivo. The stimulation of TNF-deficient iPS-cell-derived macrophages with TNF rescued the respiratory burst. These findings contrast with those for patients with inherited complete deficiency of the respiratory burst across all phagocytes, who are prone to multiple infections, including both Bacillus Calmette-Guérin disease and tuberculosis3. Human TNF is required for respiratory-burst-dependent immunity to Mycobacterium tuberculosis in macrophages but is surprisingly redundant otherwise, including for inflammation and immunity to weakly virulent mycobacteria and many other infectious agents.

Biallelic loss-of-function variants in SMPD4 cause a rare and severe neurodevelopmental disorder with progressive congenital microcephaly and early death. SMPD4 encodes a sphingomyelinase that hydrolyses sphingomyelin into ceramide at neutral pH and can thereby affect membrane lipid homeostasis. SMPD4 localizes to the membranes of the endoplasmic reticulum and nuclear envelope and interacts with nuclear pore complexes (NPC). We refine the clinical phenotype of loss-of-function SMPD4 variants by describing five individuals from three unrelated families with longitudinal data due to prolonged survival. All individuals surviving beyond infancy developed insulin-dependent diabetes, besides presenting with a severe neurodevelopmental disorder and microcephaly, making diabetes one of the most frequent age-dependent non-cerebral abnormalities. We studied the function of SMPD4 at the cellular and organ levels. Knock-down of SMPD4 in human neural stem cells causes reduced proliferation rates and prolonged mitosis. Moreover, SMPD4 depletion results in abnormal nuclear envelope breakdown and reassembly during mitosis and decreased post-mitotic NPC insertion. Fibroblasts from affected individuals show deficient SMPD4-specific neutral sphingomyelinase activity, without changing (sub)cellular lipidome fractions, which suggests a local function of SMPD4 on the nuclear envelope. In embryonic mouse brain, knockdown of Smpd4 impairs cortical progenitor proliferation and induces premature differentiation by altering the balance between neurogenic and proliferative progenitor cell divisions. We hypothesize that, in individuals with SMPD4-related disease, nuclear envelope bending, which is needed to insert NPCs in the nuclear envelope, is impaired in the absence of SMPD4 and interferes with cerebral corticogenesis and survival of pancreatic beta cells.

Background Hypobaric hypoxia has been reported to cause endothelial cell and platelet dysfunction implicated in the formation of microvascular lesions, and in its extremes may contribute to vascular leakage in high altitude pulmonary edema or blood brain barrier disruption leading to cerebral micro-hemorrhage (MH). Platelet function in the development of microvascular lesions remained ill defined, and is still incompletely understood. In this study platelet-and endothelial cell-derived extracellular vesicles (PEV and EEV, respectively) and cell adhesion molecules were characterized in plasma samples of members of a high altitude expedition to delineate the contribution of platelets and endothelial cells to hypobaric hypoxiainduced vascular dysfunction. Methods and findings In this observational study, platelet and endothelial cell-derived extracellular vesicles were analysed by flow-cytometry in plasma samples from 39 mountaineers participating in a medical research climbing expedition to Himlung Himal, Nepal, 7,050m asl. Megakaryocyte/platelet-derived AnnexinV(pos), PECAM-1 (CD31) and glycoprotein-1b (GP1b, CD42b) positive extracellular vesicles (PEV) constituted the predominant fraction of EV in plasma samples up to 6,050m asl. Exposure to an altitude of 7,050m led to a marked decline of CD31(pos) CD42(neg) EEV as well as of CD31(pos) CD42b(pos) PEV at the same time giving rise to a quantitatively prevailing CD31(neg) CD42b(low/neg) subpopulation of AnnexinV(pos) EV. An almost hundredfold increase in the numbers of this previously unrecognized population of CD31 neg CD42b(low/neg) EV was observed in all participants reaching 7,050m asl. Conclusions The emergence of CD31(neg) CD42b(low/neg) EV was observed in all participants and thus represents an early hypoxic marker at extreme altitude. Since CD31 and CD42b are required for platelet-endothelial cell interactions, these hypobaric hypoxia-dependent quantitative and phenotypic changes of AnnexinV(pos) EV subpopulations may serve as early and sensitive indicators of compromised vascular homeostasis.

Bacterial infection induces macrophages to produce mitochondrial reactive oxygen species that covalently link NEMO molecules.

The intracellular pathogen Listeria monocytogenes (L.m.) is targeted by the autophagic machinery, but the molecular mechanisms involved and consequences for anti-listerial immunity remain enigmatic. Here, we demonstrate that L.m. infection of macrophages in vivo exclusively evokes LC3-associated phagocytosis (LAP), but not canonical autophagy, and that targeting of L.m. by LAP is required for anti-listerial immunity. The pathway leading to LAP induction in response to L.m. infection emanates from the β2 integrin Mac-1 (CR3, integrin αMβ2), a receptor recognizing diverse microbial ligands. Interaction of L.m. with Mac-1 induces acid sphingomyelinase-mediated changes in membrane lipid composition that facilitate assembly and activation of the phagocyte NAPDH oxidase Nox2. Nox2-derived reactive oxygen species then trigger LC3 recruitment to L.m.-containing phagosomes by LAP. By promoting fusion of L.m.-containing phagosomes with lysosomes, LAP increases exposure of L.m. to bactericidal acid hydrolases, thereby enhancing anti-listerial activity of macrophages and immunity of mice.

Although numerous pathogenic changes within the mitochondrial respiratory chain (RC) have been associated with an elevated occurrence of apoptosis within the affected tissues, the mechanistic insight into how mitochondrial dysfunction initiates apoptotic cell death is still unknown. In this study, we show that the specific alteration of the cytochrome c oxidase (COX), representing a common defect found in mitochondrial diseases, facilitates mitochondrial apoptosis in response to oxidative stress. Our data identified an increased ceramide synthase 6 (CerS6) activity as an important pro-apoptotic response to COX dysfunction induced either by chemical or genetic approaches. The elevated CerS6 activity resulted in accumulation of the pro-apoptotic C 16 : 0 ceramide, which facilitates the mitochondrial apoptosis in response to oxidative stress. Accordingly, inhibition of CerS6 or its specific knockdown diminished the increased susceptibility of COX-deficient cells to oxidative stress. Our results provide new insights into how mitochondrial RC dysfunction mechanistically interferes with the apoptotic machinery. On the basis of its pivotal role in regulating cell death upon COX dysfunction, CerS6 might potentially represent a novel target for therapeutic intervention in mitochondrial diseases caused by COX dysfunction.

The X-linked inhibitor of apoptosis protein (XIAP) is a potent caspase inhibitor, best known for its anti-apoptotic function in cancer. During apoptosis, XIAP is antagonized by SMAC, which is released from the mitochondria upon caspase-mediated activation of BID. Recent studies suggest that XIAP is involved in immune signaling. Here, we explore XIAP as an important mediator of an immune response against the enteroinvasive bacterium Shigella flexneri, both in vitro and in vivo. Our data demonstrate for the first time that Shigella evades the XIAP-mediated immune response by inducing the BID-dependent release of SMAC from the mitochondria. Unlike apoptotic stimuli, Shigella activates the calpain-dependent cleavage of BID to trigger the release of SMAC, which antagonizes the inflammatory action of XIAP without inducing apoptosis. Our results demonstrate how the cellular death machinery can be subverted by an invasive pathogen to ensure bacterial colonization.

Riboflavin, also known as vitamin B 2 , is converted by riboflavin kinase (RFK) into flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), which are essential cofactors of dehydrogenases, reductases, and oxidases including the phagocytic NADPH oxidase 2 (Nox2). Riboflavin deficiency is common in young adults and elderly individuals, who are at the coincidental risk for listeriosis. To address the impact of acute riboflavin deficiency on host defense against Listeria monocytogenes (L.m.), we generated conditional RFK knockout (KO) strains of mice. Phagocyte‐specific RFK KO impaired the capability of phagocytes to control intracellular L.m., which corresponded to a greater susceptibility of mice to in vivo challenge with L.m. The oxidative burst of RFK‐deficient phagocytes in response to L.m. infection was significantly reduced. Mechanistically, TNF‐induced priming of Nox2, which is needed for oxidative burst, was defective in RFK‐deficient phagocytes. Lack of riboflavin in wild‐type macrophages for only 6 h shut down TNF‐induced, RFK‐mediated de novo FMN/FAD generation, which was accompanied by diminished ROS production and impaired anti‐listerial activity. Vice versa, ROS production by riboflavin‐deprived macrophages was rapidly restored by riboflavin supplementation. Our results suggest that acute riboflavin deficiency immediately impairs priming of Nox2, which is of crucial relevance for an effective phagocytic immune response in vivo.

Combinations with proteasome inhibitors are currently being investigated to improve the therapy of hematological malignancies. We previously found that proteasome inhibition by bortezomib failed to sensitize anti-CD30 antibody (Ab)-based lymphoma cell killing. In this study, we demonstrate in L540 Hodgkin's lymphoma cells that proteasome inhibition not only communicates apoptosis but also more rapidly causes a loss of CD30 antigen from cell membrane and a simultaneous release of soluble CD30, a targeting competitor. This shedding was catalyzed by the tumor necrosis factor (TNF)-α-converting enzyme (TACE, ADAM17) and blocked by the ADAM17-selective inhibitor, Ro32-7315. In parallel with CD30 shedding, bortezomib caused the generation of reactive oxygen species (ROS). As apoptosis and shedding were inhibited by the radical scavenger, N -acetyl- L -cysteine, ROS might have a pivotal function in both effects. In contrast, the pan-caspase inhibitor, zVAD- fmk , blocked bortezomib-induced apoptosis but not CD30 shedding, and Ro32-7315 blocked shedding but allowed apoptosis. This suggests independent terminal signaling pathways that are conflicting in Ab-based immunotherapy. Consequently, shedding inhibition substantially improved the synergistic antitumor efficacy of the human anti-CD30 Ab, MDX-060, and bortezomib. As proteasome inhibition also stimulated loss of TNF receptors, interleukin-6 receptor and syndecan-1 in different leukemia and lymphoma cell lines, we concluded that proteasome inhibition might impede targeted therapy against antigens susceptible to shedding.

With about 350 million virus carriers, hepatitis B virus (HBV) infection remains a major health problem. HBV is a noncytopathic virus causing persistent infection, but it is still unknown whether host recognition of HBV may activate an innate immune response. We describe that upon infection of primary human liver cells, HBV is recognized by nonparenchymal cells of the liver, mainly by liver macrophages (Kupffer cells), although they are not infected. Within 3 hours, this recognition leads to the activation of nuclear factor kappa B (NF-kappa B) and subsequently to the release of interleukin-6 (IL-6) and other proinflammatory cytokines (IL-8, TNF-alpha, IL-1 beta), but does not induce an interferon response. The activation of proinflammatory cytokines, however, is transient, and even inhibits responsiveness toward a subsequent challenge. IL-6 released by Kupffer cells after activation of NF-kappa B controls HBV gene expression and replication in hepatocytes at the level of transcription shortly after infection. Upon binding to its receptor complex, IL-6 activates the mitogen-activated protein kinases exogenous signal-regulated kinase 1/2, and c-jun N-terminal kinase, which inhibit expression of hepatocyte nuclear factor (HNF) 1 alpha and HNF 4 alpha, two transcription factors essential for HBV gene expression and replication. Conclusion: Our results demonstrate recognition of HBV patterns by nonparenchymal liver cells, which results in IL6-mediated control of HBV infection at the transcriptional level. Thus, IL-6 ensures early control of the virus, limiting activation of the adaptive immune response and preventing death of the HBV-infected hepatocyte. This pattern recognition may be essential for a virus, which infects a new host with only a few virions. Our data also indicate that therapeutic neutralization of IL-6 for treatment of certain diseases may represent a risk if the patient is HBV-infected. (HEPATOLOGY 2009;50:1773-1782.)

Riboflavin kinase: linking TNF receptor to NAPDH oxidation Riboflavin kinase has been identified as a novel interacting partner for the death domain of receptor-1 for tumour necrosis factor (TNF-R1). It is required to recruit to and functionally couple p22 phox to TNF-R1. As p22 phox is the catalytic subunit of NADPH oxidases Nox1–4, this has general implications for TNF-induced NADPH oxidase activation and reactive oxygen species (ROS) production by many cell types and tissues. These findings may also be of relevance to the role of ROS in host defence and in the pathogenesis of many diseases including inflammation or atherosclerosis.

Granules containing perforin and granzymes are secreted from cytotoxic T lymphocytes. Krönke and co-workers find that acid sphingomyelase is needed for granule shrinkage just before exocytosis in this process.

The acid sphingomyelinase (ASMase) hydrolyses the membrane lipid sphingomyelin into ceramide and phosporylcholine. ASMase localises to phagosomes, endosomes, lysosomes and the plasma membrane, i.e. those subcellular sites which are at the crossroads of many immunological processes. One of these is granule-mediated cytotoxicity as the major effector mechanism of CD8+ cytotoxic T lymphocytes (CTL). Cytotoxic granules have been characterized previously as secretory lysosomes. This raised the question, whether ASMase contributes to granule-mediated cytotoxicity of CD8+ T cells. In my diploma project, I have already shown that ASMase is required for the effective control of the acute infection with the Lymphocytic Choriomeningitis Virus (LCMV) in mice. More specifically, ASMase-deficient (ASMase-/-) CTL were shown to be severely impaired in their virus-specific cytotoxicity. This project aimed at elucidating the ASMase-dependent mechanism contributing to effective cytotoxicity of CD8+ CTL. Analysis of ASMase-/- CD8+ T cells revealed that the transcription, translation, intracellular storage and processing of cytotoxic effector molecules proceed without defects. Moreover, in ASMase-/- CD8+ T cells no hints for the accumulation of sphingomyelin were detected. These findings excluded excessive sphingomyelin as the cause for impaired cytotoxicity. The specificity of the ASMase-dependent mechanism was shown by a strongly reduced T cell receptor-triggered release of cytotoxic effector molecules while secretion of the chemokine RANTES was not impaired in ASMase-/- CTL. In ASMase-/- T cells, cytotoxic granules were shown to fuse properly with the plasma membrane at the immunological synapse. The very last step of granule exocytosis, i.e. the extrusion of granular contents, is impaired by deficiency in ASMase. Even in CTL unable to generate high molecular weight granule matrix, the secretion of low molecular weight granule contents was strongly impaired by ASMase-deficiency. Biomorphometry revealed that cytotoxic granules are of identical size in wt and ASMase-/- CTL prior to fusion with the plasma membrane. However, after fusion with the plasma membrane, in ASMase-/- CD8+ T cells the granules remain significantly larger than in wt cells. This phenomenon can be explained by the biophysical consequences of ASMase activity: Generation of ceramide in wt cells increases the surface tension within the inner leaflet of cytotoxic granules. According to Laplace�s law this facilitates the collapse of the fused granule, thus leading to effective extrusion of the granules contents.

The WD-repeat protein factor associated with nSMase activity (FAN) is a member of the family of TNF receptor adaptor proteins that are coupled to specific signaling cascades. However, the precise functional involvement of FAN in specific cellular TNF responses remain unclear. Here, we report the involvement of FAN in TNF-induced actin reorganization and filopodia formation mediated by activation of Cdc42. The pleckstrin-homology (PH) domain of FAN specifically binds to phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P), which targets FAN to the plasma membrane. Site-specific mutagenesis revealed that the ability of FAN to mediate filopodia formation was blunted either by the destruction of the PtdIns(4,5)P binding motif, or by the disruption of intramolecular interactions between the PH domain and the adjacent beige and Chediak-Higashi (BEACH) domain. Furthermore, FAN was shown to interact with the actin cytoskeleton in TNF-stimulated cells via direct filamentous actin (F-actin) binding. The results of this study suggest that PH-mediated plasma membrane targeting of FAN is critically involved in TNF-induced Cdc42 activation and cytoskeleton reorganization.

The proteasome inhibitor bortezomib has been shown to possess promising antitumor activity and significant efficacy against a variety of malignancies. Different studies demonstrated that bortezomib breaks the chemoresistance in different tumor cells basically by altering nuclear factor-kappaB (NF-kappaB) activity. NF-kappaB has been shown to be constitutively active in most primary Hodgkin-Reed-Sternberg (H-RS) cells in lymph node sections and in Hodgkin lymphoma (HL) cell lines and was suggested to be a central molecular switch in apoptosis resistance in HL. Here we report a bimodal effect of bortezomib in HL cells. Whereas high-dose bortezomib induced direct cytotoxicity that correlated with decreased NF-kappaB activity, low-dose bortezomib sensitized HL cells against a variety of cytotoxic drugs without altering NF-kappaB action. Strikingly, bortezomib induced marked XIAP down-regulation at the posttranslational level that was independent of the NF-kappaB status. Similarly, RNA interference (RNAi)-mediated XIAP down-regulation generated susceptibility to cytostatic agents. The results identify XIAP as an NF-kappaB-independent target of bortezomib action that controls the chemoresistant phenotype of HL cells.

Human immunodeficiency virus type I-encoded Tat protein is a transactivating factor essentially required for viral replication. Tat binds specifically to the transactivation response RNA stem loop, which is formed at the 5' end of all viral transcripts. The TAR binding motif of Tat also contains a protein transduction domain, PTD that mediates not only nuclear localization of Tat but is also capable of transducing cargo across cellular membranes. In order to target a Tat antagonist directly to the TAR binding site in the nucleus, we engineered a chimeric protein consisting of the Tat-derived PTD fused to the anti-Tat single chain antibody scFvtat1 that binds intracellularly to Tat. Recombinant scFvtat1-PTDTAT fusion antibody retained both, anti-Tat specificity and PTDTAT-mediated transduction-competence leading to its nuclear accumulation within living cells. Incubation of Jurkat T cells with scFvtat1-PTDTAT suppressed Tat-dependent transcription of a HIV-1 reporter gene by > 80%. Transfection of a scFvtat1-PTDTAT expression plasmid in HEK293 cells resulted in diffuse cytoplasmic and nuclear expression. ScFvtat1-PTDTAT did not inhibit HIV-1 Tat translocation to the nucleus, yet showed increased inhibition of 78%, indicating a nuclear site of scFvtat1-PTDTAT action. Strikingly, the PTDTAT. alone showed 55% inhibition in the HIV-1 luciferase reporter assay, indicating competition with HIV-1 Tat binding to the TAR element. The results of this study suggest that Tat traffic can only marginally be affected by anti-Tat antibodies and that effective inhibition of Tat function requires both competition with HIV Tat for TAR binding mediated by PTDTAT and steric hindrance mediated by the scFvtat1 moiety. (c) 2006 Elsevier Ltd. All rights reserved.

Two genes encoding neutral sphingomyelinases- 1 and - 2 ( sphingomyelin phosphodiesterases- 2 and - 3) have been recently identified that hydrolyze sphingomyelin to phosphorylcholine and ceramide. Data bank searches using a peptide sequence derived from a previously purified bovine neutral sphingomyelinase ( nSMase) allowed us to identify a cDNA encoding a novel human sphingomyelinase, nSMase3, that shows only a little homology to nSMase1 and - 2. nSMase3 was biochemically characterized by overexpression in a yeast strain, JK9 - 3d Delta Isc1p, lacking endogenous SMase activity. Similar to nSMase2, nSMase3 is Mg2+- dependent and shows optimal activity at pH7, which is enhanced in the presence of phosphatidylserine and inhibited by scyphostatin. nSMase3 is ubiquitously expressed as a 4.6- kb mRNA species. nSMase3 lacks an N- terminal signal peptide, yet contains a 23- amino- acid transmembrane domain close to the C terminus, which is indicative for the family of C- tail- anchored integral membrane proteins. Cellular localization studies with hemagglutinin- tagged nSMase3 demonstrated colocal-ization with markers of the endoplasmic reticulum as well as with Golgi markers. Tumor necrosis factor stimulates rapid activation of nSMase3 in MCF7 cells with peak activity at 1.5 min, which was impaired by expression of dominant negative FAN.

Ultraviolet light-induced apoptosis can be caused by DNA damage but also involves immediate-early cell death cascades characteristic of death receptor signaling. Here we show that the UV light-induced apoptotic signaling pathway is unique, targeting Bax activation at the mitochondrial membrane independent of caspase-8 or cathepsin D activity. Cells deficient in acid sphingomyelinase (ASMase) do not show UV light-induced Bax activation, cytochrome c release, or apoptosis. In ASMase-deficient cells, the apoptotic UV light response is restored by stable or transient expression of human ASMase. Bax conformational change in ASMase(-/-) cells is also caused by synthetic C-16-ceramide acting on intact cells or isolated mitochondria. The results suggest that UV light-triggered ASMase activation is essentially required for Bax conformational change leading to mitochondrial release of pro-apoptotic factors like cytochrome c and Smac.