Fas death receptor signalling: roles of Bid and XIAP

Fas (also called CD95 or APO-1), a member of a subgroup of the tumour necrosis factor receptor superfamily that contain an intracellular death domain, can initiate apoptosis signalling and has a critical role in the regulation of the immune system. Fas-induced apoptosis requires recruitment and activation of the initiator caspase, caspase-8 (in humans also caspase-10), within the death-inducing signalling complex. In so-called type 1 cells, proteolytic activation of effector caspases (-3 and -7) by caspase-8 suffices for efficient apoptosis induction. In so-called type 2 cells, however, killing requires amplification of the caspase cascade. This can be achieved through caspase-8-mediated proteolytic activation of the pro-apoptotic Bcl-2 homology domain (BH)3-only protein BH3-interacting domain death agonist (Bid), which then causes mitochondrial outer membrane permeabilisation. This in turn leads to mitochondrial release of apoptogenic proteins, such as cytochrome c and, pertinent for Fas death receptor (DR)-induced apoptosis, Smac/DIABLO (second mitochondria-derived activator of caspase/direct IAP binding protein with low Pi), an antagonist of X-linked inhibitor of apoptosis (XIAP), which imposes a brake on effector caspases. In this review, written in honour of Juerg Tschopp who contributed so much to research on cell death and immunology, we discuss the functions of Bid and XIAP in the control of Fas DR-induced apoptosis signalling, and we speculate on how this knowledge could be exploited to develop novel regimes for treatment of cancer.

XIAP discriminates between type I and type II FAS-induced apoptosis

FAS (also called APO-1 and CD95) and its physiological ligand, FASL, regulate apoptosis of unwanted or dangerous cells, functioning as a guardian against autoimmunity and cancer development. Distinct cell types differ in the mechanisms by which the 'death receptor' FAS triggers their apoptosis. In type I cells, such as lymphocytes, activation of 'effector caspases' by FAS-induced activation of caspase-8 suffices for cell killing, whereas in type II cells, including hepatocytes and pancreatic beta-cells, caspase cascade amplification through caspase-8-mediated activation of the pro-apoptotic BCL-2 family member BID (BH3 interacting domain death agonist) is essential. Here we show that loss of XIAP (X-chromosome linked inhibitor of apoptosis protein) function by gene targeting or treatment with a second mitochondria-derived activator of caspases (SMAC, also called DIABLO; direct IAP-binding protein with low pI) mimetic drug in mice rendered hepatocytes and beta-cells independent of BID for FAS-induced apoptosis. These results show that XIAP is the critical discriminator between type I and type II apoptosis signalling and suggest that IAP inhibitors should be used with caution in cancer patients with underlying liver conditions.

Epigallocatechin-3-gallate induces cell death in acute myeloid leukaemia cells and supports all-trans retinoic acid-induced neutrophil differentiation via death-associated protein kinase 2

Acute promyelocytic leukaemia (APL) patients are successfully treated with all-trans retinoic acid (ATRA). However, concurrent chemotherapy is still necessary and less toxic therapeutic approaches are needed. Earlier studies suggested that in haematopoietic neoplasms, the green tea polyphenol epigallocatechin-3-gallate (EGCG) induces cell death without adversely affecting healthy cells. We aimed at deciphering the molecular mechanism of EGCG-induced cell death in acute myeloid leukaemia (AML). A significant increase of death-associated protein kinase 2 (DAPK2) levels was found in AML cells upon EGCG treatment paralleled by increased cell death that was significantly reduced upon silencing of DAPK2. Moreover, combined ATRA and EGCG treatment resulted in cooperative DAPK2 induction and potentiated differentiation. EGCG toxicity of primary AML blasts correlated with 67 kDa laminin receptor (67LR) expression. Pretreatment of AML cells with ATRA, causing downregulation of 67LR, rendered these cells resistant to EGCG-mediated cell death. In summary, it was found that (i) DAPK2 is essential for EGCG-induced cell death in AML cells, (ii) ATRA and EGCG cotreatment significantly boosted neutrophil differentiation, and 67LR expression correlates with susceptibility of AML cells to EGCG. We thus suggest that EGCG, by selectively targeting leukaemic cells, may improve differentiation therapies for APL and chemotherapy for other AML subtypes.

The death-associated protein kinase 2 is up-regulated during normal myeloid differentiation and enhances neutrophil maturation in myeloid leukemic cells

The death-associated protein kinase 2 (DAPK2) belongs to a family of Ca(2+)/calmodulin-regulated serine/threonine kinases involved in apoptosis. During investigation of candidate genes operative in granulopoiesis, we identified DAPK2 as highly expressed. Subsequent investigations demonstrated particularly high DAPK2 expression in normal granulocytes compared with monocytes/macrophages and CD34(+) progenitor cells. Moreover, significantly increased DAPK2 mRNA levels were seen when cord blood CD34(+) cells were induced to differentiate toward neutrophils in tissue culture. In addition, all-trans retinoic acid (ATRA)-induced neutrophil differentiation of two leukemic cell lines, NB4 and U937, revealed significantly higher DAPK2 mRNA expression paralleled by protein induction. In contrast, during differentiation of CD34(+) and U937 cells toward monocytes/macrophages, DAPK2 mRNA levels remained low. In primary leukemia, low expression of DAPK2 was seen in acute myeloid leukemia samples, whereas chronic myeloid leukemia samples in chronic phase showed intermediate expression levels. Lentiviral vector-mediated expression of DAPK2 in NB4 cells enhanced, whereas small interfering RNA-mediated DAPK2 knockdown reduced ATRA-induced granulocytic differentiation, as evidenced by morphology and neutrophil stage-specific maturation genes, such as CD11b, G-CSF receptor, C/EBPepsilon, and lactoferrin. In summary, our findings implicate a role for DAPK2 in granulocyte maturation.

Structural rearrangements of the central region of the morbillivirus attachment protein stalk domain trigger F protein refolding for membrane fusion

It is unknown how receptor binding by the paramyxovirus attachment proteins (HN, H, or G) triggers the fusion (F) protein to fuse with the plasma membrane for cell entry. H-proteins of the morbillivirus genus consist of a stalk ectodomain supporting a cuboidal head; physiological oligomers consist of non-covalent dimer-of-dimers. We report here the successful engineering of intermolecular disulfide bonds within the central region (residues 91-115) of the morbillivirus H-stalk; a sub-domain that also encompasses the putative F-contacting section (residues 111-118). Remarkably, several intersubunit crosslinks abrogated membrane fusion, but bioactivity was restored under reducing conditions. This phenotype extended equally to H proteins derived from virulent and attenuated morbillivirus strains and was independent of the nature of the contacted receptor. Our data reveal that the morbillivirus H-stalk domain is composed of four tightly-packed subunits. Upon receptor binding, these subunits structurally rearrange, possibly inducing conformational changes within the central region of the stalk, which, in turn, promote fusion. Given that the fundamental architecture appears conserved among paramyxovirus attachment protein stalk domains, we predict that these motions may act as a universal paramyxovirus F-triggering mechanism.

Identification of Novel Death-Associated Protein Kinase 2 Interaction Partners by Proteomic Screening Coupled with Bimolecular Fluorescence Complementation.

Death-associated protein kinase 2 (DAPK2) is a Ca(2+)/calmodulin-dependent Ser/Thr kinase that possesses tumor-suppressive functions and regulates programmed cell death, autophagy, oxidative stress, hematopoiesis, and motility. As only few binding partners of DAPK2 have been determined, the molecular mechanisms governing these biological functions are largely unknown. We report the identification of 180 potential DAPK2 interaction partners by affinity purification-coupled mass spectrometry, 12 of which are known DAPK binding proteins. A small subset of established and potential binding proteins detected in this screen was further investigated by bimolecular fluorescence complementation (BiFC) assays, a method to visualize protein interactions in living cells. These experiments revealed that α-actinin-1 and 14-3-3-β are novel DAPK2 binding partners. The interaction of DAPK2 with α-actinin-1 was localized at the plasma membrane, resulting in massive membrane blebbing and reduced cellular motility, whereas the interaction of DAPK2 with 14-3-3-β was localized to the cytoplasm, with no impact on blebbing, motility, or viability. Our results therefore suggest that DAPK2 effector functions are influenced by the protein's subcellular localization and highlight the utility of combining mass spectrometry screening with bimolecular fluorescence complementation to identify and characterize novel protein-protein interactions.

Protein overexpression following lentiviral infection of primary mature neutrophils is due to pseudotransduction

Neutrophils are terminally differentiated cells with a short life-span due to constitutive apoptosis. Because of these characteristics, genetic manipulation of neutrophils has been difficult, although it is highly desired given the importance of neutrophils in the immune system. Here we demonstrate that transduction of primary human mature neutrophils with enhanced green fluorescent protein (eGFP)-encoding lentiviral particles results in GFP-containing cells as previously reported. Yet, our data further show that GFP expression in neutrophils upon transduction is largely due to protein transfer, a process called lentiviral pseudotransduction, and not due to bona fide transduction. Thus, inhibition of viral genome integration by the reverse transcriptase inhibitor 3'-azido-3'-deoxythymidine (AZT) or of protein biosynthesis by cycloheximide (CHX) did not abolish GFP levels in transduced neutrophils. Importantly, lentiviral pseudotransduction of the enzyme death-associated protein kinase 2 (DAPK2) into primary human mature neutrophils resulted in increased protein levels, but not enzymatic functionality. Based on our data and previous reports of unspecific viral effects on immune cells following lentiviral transduction, we discourage scientists to use lentiviral transduction methods to manipulate primary mature neutrophils.

Targeted disruption of the intracellular domain of receptor FgfrL1 in mice.

FgfrL1 is the fifth member of the fibroblast growth factor receptor (Fgfr) family. Studies with FgfrL1 deficient mice have demonstrated that the gene plays an important role during embryonic development. FgfrL1 knock-out mice die at birth as they have a malformed diaphragm and lack metanephric kidneys. Similar to the classical Fgfrs, the FgfrL1 protein contains an extracellular part composed of three Ig-like domains that interact with Fgf ligands and heparin. However, the intracellular part of FgfrL1 is not related to the classical receptors and does not possess any tyrosine kinase activity. Curiously enough, the amino acid sequence of this domain is barely conserved among different species, with the exception of three motifs, namely a dileucine peptide, a tandem tyrosine-based motif YXXΦ and a histidine-rich sequence. To investigate the function of the intracellular domain of FgfrL1, we have prepared genetically modified mice that lack the three conserved sequence motifs, but instead contain a GFP cassette (FgfrL1ΔC-GFP). To our surprise, homozygous FgfrL1ΔC-GFP knock-in mice are viable, fertile and phenotypically normal. They do not exhibit any alterations in the diaphragm or the kidney, except for a slight reduction in the number of glomeruli that does not appear to affect life expectancy. In addition, the pancreas of both FgfrL1ΔC-GFP knock-in and FgfrL1 knock-out mice do not show any disturbances in the production of insulin, in contrast to what has been suggested by recent studies. Thus, the conserved motifs of the intracellular FgfrL1 domain are dispensable for organogenesis and normal life. We conclude that the extracellular domain of the protein must conduct the vital functions of FgfrL1.

Evidence for direct squalene and 2,3-oxidosqualene binding by supernatant protein factor

We present the crystal structures of the SEC14-like domain of supernatant protein factor (SPF) in complex with squalene and 2,3-oxidosqualene. The structures were resolved at 1.75 Å (complex with squalene) and 1.6 Å resolution (complex with 2,3-oxidosqualene), leading in both cases to clear images of the protein/ substrate interactions. Ligand binding is facilitated by removal of the Golgi-dynamics (GOLD) C-terminal domain of SPF, which, as shown in previous structures of the apo-protein, blocked the opening of the binding pocket to the exterior. Both substrates bind into a large hydrophobic cavity, typical of such lipid-transporter family. Our structures report no specific recognition mode for the epoxide group. In fact, for both molecules, ligand affinity is dominated by hydrophobic interactions, and independent investigations by computational models or differential scanning micro-calorimetry reveal similar binding affinities for both ligands. Our findings elucidate the molecular bases of the role of SPF in sterol endo-synthesis, supporting the original hypothesis that SPF is a facilitator of substrate flow within the sterol synthetic pathway. Moreover, our results suggest that the GOLD domain acts as a regulator, as its conformational displacement must occur to favor ligand binding and release during the different synthetic steps.

Genetic and functional characterization of the NanA sialidase from Clostridium chauvoei

ABSTRACT: Clostridium chauvoei is the causative agent of blackleg, a wide spread serious infection of cattle and sheep with high mortality. In this study we have analyzed the sialidase activity of the NanA protein of C. chauvoei and cloned the sialidase gene nanA. Sialidase is encoded as a precursor protein of 722 amino acids with a 26 amino acid signal peptide. The mature sialidase has a calculated molecular mass of 81 kDa and contains the carbohydrate binding module 32 (CBM32, or F5/8 type C domain), the sialic acid binding module CBM40 and the enzymatically active sialidase domain found in all pro- and eukaryotic sialidases. Sialidase activity does not require the CBM32 domain. The NanA protein is secreted by C. chauvoei as a dimer. The nanA gene was found to be conserved and sialidase activity was found in C. chauvoei strains isolated over a period of 50 years from various geographical locations. Antiserum directed against a recombinant 40 kDa peptide containing CBM40 and part of the enzymatically active domain of NanA neutralized the secreted sialidase activity of all C. chauvoei strains tested.

The bovine aristaless-like homeobox 4 (ALX4) as a candidate gene for syndactyly

The ALX4 (aristaless-like homeobox 4) gene encodes a paired-type homeodomain transcriptional activator and plays a major role in anterior-posterior pattern formation during limb development. Here, the cloning, genomic structure and expression of the bovine ortholog of the ALX4 gene are reported. The bovine ALX4 gene consists of four exons and is located on BTA15q28-->q29 in a region syntenic to HSA11p11.2. The transcribed ALX4 mRNA encodes a 397-amino-acid protein showing a paired-type homeodomain and a C-terminal stretch of amino acids known as the OAR- or aristaless domain. The predicted protein shares 92.5% identity to human and mouse ALX4 proteins and all three species share almost complete identity in the conserved domains. ALX4 expression was detected by reverse transcriptase polymerase chain reaction in bovine fetal limb bones. The ALX4 gene was evaluated as a candidate gene for bovine syndactyly which has been mapped on the telomeric region of cattle chromosome 15. Sequencing of the four exons with flanking sequences of the bovine ALX4 gene from a panel of 14 affected animals belonging to German Holstein, German Fleckvieh and crossbreds, and 27 unaffected individuals from German Holstein revealed five silent SNPs within the coding region out of eleven SNPs in total. Four SNPs were polymorphic in the affected animals, but in comparison to the genotyped unaffected individuals the genotype distribution showed no evidence for an association to the phenotype. Therefore our data indicate that the ALX4 gene can probably be excluded as candidate gene for bovine syndactyly in the examined animals.

DAPK2 is a novel E2F1/KLF6 target gene involved in their proapoptotic function

Death-associated protein kinase 2 (DAPK2) belongs to a family of proapoptotic Ca(2+)/calmodulin-regulated serine/threonine kinases. We recently identified DAPK2 as an enhancing factor during granulocytic differentiation. To identify transcriptional DAPK2 regulators, we cloned 2.7 kb of the 5'-flanking region of the DAPK2 gene. We found that E2F1 and Krüppel-like factor 6 (KLF6) strongly activate the DAPK2 promoter. We mapped the E2F1 and KLF6 responsive elements to a GC-rich region 5' of exon 1 containing several binding sites for KLF6 and Sp1 but not for E2F. Moreover, we showed that transcriptional activation of DAPK2 by E2F1 and KLF6 is dependent on Sp1 using Sp1/KLF6-deficient insect cells, mithramycin A treatment to block Sp1-binding or Sp1 knockdown cells. Chromatin immunoprecipitation revealed recruitment of Sp1 and to lesser extent that of E2F1 and KLF6 to the DAPK2 promoter. Activation of E2F1 in osteosarcoma cells led to an increase of endogenous DAPK2 paralleled by cell death. Inhibition of DAPK2 expression resulted in significantly reduced cell death upon E2F1 activation. Similarly, KLF6 expression in H1299 cells increased DAPK2 levels accompanied by cell death that is markedly decreased upon DAPK2 knockdown. Moreover, E2F1 and KLF6 show cooperation in activating the DAPK2 promoter. In summary, our findings establish DAPK2 as a novel Sp1-dependent target gene for E2F1 and KLF6 in cell death response.

[Osteoporosis diet]

Bone requires a wide variety of nutrients to develop normally and to maintain itself after growth. Most important--in the sense that bony abnormalities are associated with their deficiencies--are protein, calcium, phosphorus, vitamin D, C and K, zinc, manganese and copper. The nutrients most likely to be deficient in citizens of industrialized countries are calcium and vitamin D. In this review of the current literature about nutritional aspects of osteoporosis, we have focused on factors influencing calcium requirement: the principal interacting nutrients are sodium, protein, caffeine, fiber, oxalate, phytate, and the acid/alkaline ash character of the overall diet. Fiber and caffeine decrease calcium absorption from the gut and typically exert relatively minor effects, while sodium, protein and the acid/alkaline balance of the diet increase urinary excretion of calcium and are of much greater significance for the calcium homeostasis. Alkali buffers, whether vegetables or fruits reverse this urinary calcium loss. As long as accompanied by adequate calcium intake, protein-rich diet is not deleterious to bone: a calcium-to-protein ratio of 20:1 (mg calcium/g protein) is recommended. Whether a nutrition-based therapeutic approach to osteoporosis is feasible in the near future is yet unclear: at least there are some recent promising data from in-vitro as well as from rat studies showing that extracts taken from various vegetables, mainly from the onion family inhibit bone resorption in a dose-dependent manner.

The additional facet of immunoscore: immunoprofiling as a possible predictive tool for cancer treatment

Recent investigations of the tumor microenvironment have shown that many tumors are infiltrated by inflammatory and lymphocytic cells. Increasing evidence suggests that the number, type and location of these tumor-infiltrating lymphocytes in primary tumors has prognostic value, and this has led to the development of an 'immunoscore. As well as providing useful prognostic information, the immunoscore concept also has the potential to help predict response to treatment, thereby improving decision- making with regard to choice of therapy. This predictive aspect of the tumor microenvironment forms the basis for the concept of immunoprofiling, which can be described as 'using an individual's immune system signature (or profile) to predict that patient's response to therapy' The immunoprofile of an individual can be genetically determined or tumor-induced (and therefore dynamic). Ipilimumab is the first in a series of immunomodulating antibodies and has been shown to be associated with improved overall survival in patients with advanced melanoma. Other immunotherapies in development include anti-programmed death 1 protein (nivolumab), anti-PD-ligand 1, anti-CD137 (urelumab), and anti-OX40. Biomarkers that can be used as predictive factors for these treatments have not yet been clinically validated. However, there is already evidence that the tumor microenvironment can have a predictive role, with clinical activity of ipilimumab related to high baseline expression of the immune-related genes FoxP3 and indoleamine 2,3-dioxygenase and an increase in tumor-infiltrating lymphocytes. These biomarkers could represent the first potential proposal for an immunoprofiling panel in patients for whom anti-CTLA-4 therapy is being considered, although prospective data are required. In conclusion, the evaluation of systemic and local immunological biomarkers could offer useful prognostic information and facilitate clinical decision making. The challenge will be to identify the individual immunoprofile of each patient and the consequent choice of optimal therapy or combination of therapies to be used.

Scp160p is required for translational efficiency of codon-optimized mRNAs in yeast

The budding yeast multi-K homology domain RNA-binding protein Scp160p binds to > 1000 messenger RNAs (mRNAs) and polyribosomes, and its mammalian homolog vigilin binds transfer RNAs (tRNAs) and translation elongation factor EF1alpha. Despite its implication in translation, studies on Scp160p's molecular function are lacking to date. We applied translational profiling approaches and demonstrate that the association of a specific subset of mRNAs with ribosomes or heavy polysomes depends on Scp160p. Interaction of Scp160p with these mRNAs requires the conserved K homology domains 13 and 14. Transfer RNA pairing index analysis of Scp160p target mRNAs indicates a high degree of consecutive use of iso-decoding codons. As shown for one target mRNA encoding the glycoprotein Pry3p, Scp160p depletion results in translational downregulation but increased association with polysomes, suggesting that it is required for efficient translation elongation. Depletion of Scp160p also decreased the relative abundance of ribosome-associated tRNAs whose codons show low potential for autocorrelation on mRNAs. Conversely, tRNAs with highly autocorrelated codons in mRNAs are less impaired. Our data indicate that Scp160p might increase the efficiency of tRNA recharge, or prevent diffusion of discharged tRNAs, both of which were also proposed to be the likely basis for the translational fitness effect of tRNA pairing.