Lactate limits CNS autoimmunity by stabilizing HIF-1α in dendritic cells

Dendritic cells (DCs) have a role in the development and activation of self-reactive pathogenic T cells1,2. Genetic variants that are associated with the function of DCs have been linked to autoimmune disorders3,4, and DCs are therefore attractive therapeutic targets for such diseases. However, developing DC-targeted therapies for autoimmunity requires identification of the mechanisms that regulate DC function. Here, using single-cell and bulk transcriptional and metabolic analyses in combination with cell-specific gene perturbation studies, we identify a regulatory loop of negative feedback that operates in DCs to limit immunopathology. Specifically, we find that lactate, produced by activated DCs and other immune cells, boosts the expression of NDUFA4L2 through a mechanism mediated by hypoxia-inducible factor 1α (HIF-1α). NDUFA4L2 limits the production of mitochondrial reactive oxygen species that activate XBP1-driven transcriptional modules in DCs that are involved in the control of pathogenic autoimmune T cells. We also engineer a probiotic that produces lactate and suppresses T cell autoimmunity through the activation of HIF-1α-NDUFA4L2 signalling in DCs. In summary, we identify an immunometabolic pathway that regulates DC function, and develop a synthetic probiotic for its therapeutic activation.

Engineered probiotics limit CNS autoimmunity by stabilizing HIF-1α in dendritic cells

Dendritic cells (DCs) control the generation of self-reactive pathogenic T cells. Thus, DCs are considered attractive therapeutic targets for autoimmune diseases. Using single-cell and bulk transcriptional and metabolic analyses in combination with cell-specific gene perturbation studies we identified a negative feedback regulatory pathway that operates in DCs to limit immunopathology. Specifically, we found that lactate, produced by activated DCs and other immune cells, boosts NDUFA4L2 expression through a mechanism mediated by HIF-1α. NDUFA4L2 limits the production of mitochondrial reactive oxygen species that activate XBP1-driven transcriptional modules in DCs involved in the control of pathogenic autoimmune T cells. Moreover, we engineered a probiotic that produces lactate and suppresses T-cell autoimmunity in the central nervous system via the activation of HIF-1α/NDUFA4L2 signaling in DCs. In summary, we identified an immunometabolic pathway that regulates DC function, and developed a synthetic probiotic for its therapeutic activation.

Metabolic modulation of tumours with engineered bacteria for immunotherapy

The availability of L-arginine in tumours is a key determinant of an efficient anti-tumour T cell response^1-4. Consequently, increases of typically low L-arginine concentrations within the tumour may greatly potentiate the anti-tumour responses of immune checkpoint inhibitors, such as programmed death-ligand 1 (PD-L1)-blocking antibodies⁵. However, currently no means are available to locally increase intratumoural L-arginine levels. Here we used a synthetic biology approach to develop an engineered probiotic Escherichia coli Nissle 1917 strain that colonizes tumours and continuously converts ammonia, a metabolic waste product that accumulates in tumours⁶, to L-arginine. Colonization of tumours with these bacteria increased intratumoural L-arginine concentrations, increased the number of tumour-infiltrating T cells and had marked synergistic effects with PD-L1 blocking antibodies in the clearance of tumours. The anti-tumour effect of these bacteria was mediated by L-arginine and was dependent on T cells. These results show that engineered microbial therapies enable metabolic modulation of the tumour microenvironment leading to enhanced efficacy of immunotherapies.

Abstract 2920: Metabolic modulation of the tumor microenvironment using Synthetic Biotic™ Medicines

Background: The immunosuppressive milieu found within the tumor microenvironment (TME) has long been understood to be a key driver of tumor initiation and progression. More recently it has been appreciated that metabolites derived from biosynthetic pathways are major components in forming this immune-privileged niche. For example, the conversion of tryptophan into kynurenine by indoleamine 2,3 dioxygenase (IDO) or the reduction of adenosine triphosphate to adenosine by the ectoenzymes CD39 and CD73 leads to T cell dysfunction and exhaustion, and a significantly blunted antitumor immune response. At Synlogic we are using synthetic biology in combination with natural probiotics to develop engineered bacteria or “Synthetic Biotic Medicines,” which are programmed with precision to correct disease-causing and -promoting metabolic defects. Here we present results showing the development of two engineered bacterial strains that have been designed to consume either kynurenine or adenosine, two molecules known to play central roles in promoting tumor immune tolerance, with the goal of relieving TME-associated immunosuppression and promoting antitumor immunity.

Methods and Results: Synthetic biologic techniques were employed to generate the adenosine-consuming strain (SYN-Ade) or the kynurenine-consuming strain (SYN-Kyn) by introduction of genetic elements that were highly efficient in the metabolism of adenosine or kynurenine, respectively. In in vitro biochemical assays, SYN-Ade and SYN-Kyn were able to deplete test media containing levels of adenosine and kynurenine that are ~100-fold and 20-fold higher than the adenosine or kynurenine levels found in the tumors of cancer patients, (180uM of adenosine or 80uM of kynurenine, respectively) to undetectable levels within 2 hours. For the kynurenine-consuming strain, this in vitro kynurenine consumption translated to robust in vivo pharmacodynamic activity. In mice bearing subcutaneous CT26 tumors, the administration of SYN-Kyn by intratumoral (IT) injection led to significant decreases in tumor kynurenine levels, which was equivalent to small-molecule inhibition of the IDO enzyme. Importantly, the combination of SYN-Kyn with an anti-CTLA4 antibody in the CT26 tumor model or the combination of SYN-Kyn or SYN-Ade with a cocktail of anti-PD1/CTLA4 antibodies in MC38 tumor-bearing mice led to significant antitumor effects over those observed with the antibodies alone.

Conclusions: Taken together, these results demonstrate that the application of synthetic biology to engineer nonpathogenic bacteria is a viable approach to deliver profound efficacy in experimental models of cancer, and support the further development of these Synthetic Biotic medicines as potential immuno-oncology therapies.

Citation Format: Kip A. West, Adam Fisher, Dan Leventhal, Anna Sokolovska, Ning Li, Chris Plescia, Mary Castillo, Vincent Isabella, Starsha Kolodziej, Paul Miller, Jose M. Lora. Metabolic modulation of the tumor microenvironment using Synthetic Biotic™ Medicines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2920.

Antiinflammatory effects of bromodomain and extraterminal domain inhibition in cystic fibrosis lung inflammation

Significant morbidity in cystic fibrosis (CF) results from chronic lung inflammation, most commonly due to Pseudomonas aeruginosa infection. Recent data suggest that IL-17 contributes to pathological inflammation in the setting of abnormal mucosal immunity, and type 17 immunity-driven inflammatory responses may represent a target to block aberrant inflammation in CF. Indeed, transcriptomic analysis of the airway epithelium from CF patients undergoing clinical bronchoscopy revealed upregulation of IL-17 downstream signature genes, implicating a substantial contribution of IL-17-mediated immunity in CF lungs. Bromodomain and extraterminal domain (BET) chromatin modulators can regulate T cell responses, specifically Th17-mediated inflammation, by mechanisms that include bromodomain-dependent inhibition of acetylated histones at the IL17 locus. Here, we show that, in vitro, BET inhibition potently suppressed Th17 cell responses in explanted CF tissue and inhibited IL-17-driven chemokine production in human bronchial epithelial cells. In an acute P. aeruginosa lung infection murine model, BET inhibition decreased inflammation, without exacerbating infection, suggesting that BET inhibition may be a potential therapeutic target in patients with CF.

Regulatory T Cell Modulation by CBP/EP300 Bromodomain Inhibition

Covalent modification of histones is a fundamental mechanism of regulated gene expression in eukaryotes, and interpretation of histone modifications is an essential feature of epigenetic control. Bromodomains are specialized binding modules that interact with acetylated histones, linking chromatin recognition to gene transcription. Because of their ability to function in a domain-specific fashion, selective disruption of bromodomain:acetylated histone interactions with chemical probes serves as a powerful means for understanding biological processes regulated by these chromatin adaptors. Here we describe the discovery and characterization of potent and selective small molecule inhibitors for the bromodomains of CREBBP/EP300 that engage their target in cellular assays. We use these tools to demonstrate a critical role for CREBBP/EP300 bromodomains in regulatory T cell biology. Because regulatory T cell recruitment to tumors is a major mechanism of immune evasion by cancer cells, our data highlight the importance of CREBBP/EP300 bromodomain inhibition as a novel, small molecule-based approach for cancer immunotherapy.

Discovery of Benzotriazolo[4,3-d][1,4]diazepines as Orally Active Inhibitors of BET Bromodomains

Inhibition of the bromodomains of the BET family, of which BRD4 is a member, has been shown to decrease myc and interleukin (IL) 6 in vivo, markers that are of therapeutic relevance to cancer and inflammatory disease, respectively. Herein we report substituted benzo[b]isoxazolo[4,5-d]azepines and benzotriazolo[4,3-d][1,4]diazepines as fragment-derived novel inhibitors of the bromodomain of BRD4. Compounds from these series were potent and selective in cells, and subsequent optimization of microsomal stability yielded representatives that demonstrated dose- and time-dependent reduction of plasma IL-6 in mice.

BET bromodomain inhibition suppresses TH17-mediated pathology

Interleukin (IL) 17-producing T helper (T(H)17) cells have been selected through evolution for their ability to control fungal and bacterial infections. It is also firmly established that their aberrant generation and activation results in autoimmune conditions. Using a characterized potent and selective small molecule inhibitor, we show that the bromodomain and extra-terminal domain (BET) family of chromatin adaptors plays fundamental and selective roles in human and murine T(H)17 differentiation from naive CD4(+) T cells, as well as in the activation of previously differentiated T(H)17 cells. We provide evidence that BET controls T(H)17 differentiation in a bromodomain-dependent manner through a mechanism that includes the direct regulation of multiple effector T(H)17-associated cytokines, including IL17, IL21, and GMCSF. We also demonstrate that BET family members Brd2 and Brd4 associate with the Il17 locus in T(H)17 cells, and that this association requires bromodomains. We recapitulate the critical role of BET bromodomains in T(H)17 differentiation in vivo and show that therapeutic dosing of the BET inhibitor is efficacious in mouse models of autoimmunity. Our results identify the BET family of proteins as a fundamental link between chromatin signaling and T(H)17 biology, and support the notion of BET inhibition as a point of therapeutic intervention in autoimmune conditions.

Suppression of inflammation by a synthetic histone mimic

Interaction of pathogens with cells of the immune system results in activation of inflammatory gene expression. This response, although vital for immune defence, is frequently deleterious to the host due to the exaggerated production of inflammatory proteins. The scope of inflammatory responses reflects the activation state of signalling proteins upstream of inflammatory genes as well as signal-induced assembly of nuclear chromatin complexes that support mRNA expression. Recognition of post-translationally modified histones by nuclear proteins that initiate mRNA transcription and support mRNA elongation is a critical step in the regulation of gene expression. Here we present a novel pharmacological approach that targets inflammatory gene expression by interfering with the recognition of acetylated histones by the bromodomain and extra terminal domain (BET) family of proteins. We describe a synthetic compound (I-BET) that by 'mimicking' acetylated histones disrupts chromatin complexes responsible for the expression of key inflammatory genes in activated macrophages, and confers protection against lipopolysaccharide-induced endotoxic shock and bacteria-induced sepsis. Our findings suggest that synthetic compounds specifically targeting proteins that recognize post-translationally modified histones can serve as a new generation of immunomodulatory drugs.

Effects of LTB4 receptor antagonism on pulmonary inflammation in rodents and non-human primates

Asthma, chronic obstructive pulmonary disease (COPD) and acute lung injury/acute respiratory distress syndrome (ALI/ARDS) are characterized by neutrophilic inflammation and elevated levels of leukotriene B4 (LTB4). However, the exact role of LTB4 pathways in mediating pulmonary neutrophilia and the potential therapeutic application of LTB4 receptor antagonists in these diseases remains controversial. Here we show that a novel dual BLT1 and BLT2 receptor antagonist, RO5101576, potently inhibited LTB4-evoked calcium mobilization in HL-60 cells and chemotaxis of human neutrophils. RO5101576 significantly attenuated LTB4-evoked pulmonary eosinophilia in guinea pigs. In non-human primates, RO5101576 inhibited allergen and ozone-evoked pulmonary neutrophilia, with comparable efficacy to budesonide (allergic responses). RO5101576 had no effects on LPS-evoked neutrophilia in guinea pigs and cigarette smoke-evoked neutrophilia in mice and rats. In toxicology studies RO5101576 was well-tolerated. Theses studies show differential effects of LTB4 receptor antagonism on neutrophil responses in vivo and suggest RO5101576 may represent a potential new treatment for pulmonary neutrophilia in asthma.

Apolipoprotein D is involved in the mechanisms regulating protection from oxidative stress

Many nervous system pathologies are associated with increased levels of apolipoprotein D (ApoD), a lipocalin also expressed during normal development and aging. An ApoD homologous gene in Drosophila, Glial Lazarillo, regulates resistance to stress, and neurodegeneration in the aging brain. Here we study for the first time the protective potential of ApoD in a vertebrate model organism. Loss of mouse ApoD function increases the sensitivity to oxidative stress and the levels of brain lipid peroxidation, and impairs locomotor and learning abilities. Human ApoD overexpression in the mouse brain produces opposite effects, increasing survival and preventing the raise of brain lipid peroxides after oxidant treatment. These observations, together with its transcriptional up-regulation in the brain upon oxidative insult, identify ApoD as an acute response protein with a protective and therefore beneficial function mediated by the control of peroxidated lipids.

Inhibition of NF-kappaB activation reduces the tissue effects of transgenic IL-13

IL-13 is a major Th2 cytokine that is capable of inducing inflammation, excessive mucus production, airway hyperresponsiveness, alveolar remodeling, and fibrosis in the murine lung. Although IL-13 through its binding to IL-4Ralpha/IL-13Ralpha1 uses the canonical STAT6-signaling pathway to mediate these tissue responses, recent studies have demonstrated that other signaling pathways may also be involved. Previous studies from our laboratory demonstrated that IL-13 mediates its tissue effects by inducing a wide variety of downstream genes many of which are known to be regulated by NF-kappaB. As a result, we hypothesized that NF-kappaB activation plays a critical role in the pathogenesis of IL-13-induced tissue alterations. To test this hypothesis, we compared the effects of transgenic IL-13 in mice with normal and diminished levels of NF-kappaB activity. Three pharmacologic approaches were used to inhibit NF-kappaB including 1) PS1145, a small molecule inhibitor of IkappaBalpha kinase (IKK2), 2) antennapedia-linked NF-kappaB essential modulator-binding domain (NBD) peptide (wild-type NBD), and 3) an adenoviral construct expressing a dominant-negative version of IKK2. We also crossed IL-13-transgenic mice with mice with null mutations of p50 to generate mice that overproduced IL-13 in the presence and absence of this NF-kappaB component. These studies demonstrate that all these interventions reduced IL-13-induced tissue inflammation, fibrosis and alveolar remodeling. In addition, we show that both PS1145 and wild-type NBD inhibit lung inflammatory and structural cell apoptosis. PS1145 inhibits caspase activation and up-regulates inhibitor of apoptosis protein cellular-inhibitor of apoptosis protein 1 (c-IAP-1). Therefore, NF-kappaB is an attractive target for immunotherapy of IL-13-mediated diseases.

Cutting edge: Modulation of intestinal autoimmunity and IL-2 signaling by sphingosine kinase 2 independent of sphingosine 1-phosphate

Sphingosine kinase (Sphk) phosphorylates sphingosine into sphingosine-1-phosphate (S1P), but its recently identified isoform Sphk2 has been suggested to have distinct subcellular localization and substrate specificity. We demonstrate here that, surprisingly, Sphk2(-/-) CD4(+) T cells exhibit a hyperactivated phenotype with significantly enhanced proliferation and cytokine secretion in response to IL-2 as well as reduced sensitivity to regulatory T cell-mediated suppression in vitro, apparently independent of effects upon S1P. Such findings appear to reflect a requirement for Sphk2 to suppress IL-2 signaling because, in Sphk2(-/-) CD4(+) T cells, IL-2 induced abnormally accentuated STAT5 phosphorylation and small interfering RNA knockdown of STAT5 abrogated their hyperactive phenotype. This pathway physiologically modulates autoinflammatory responses, because Sphk2(-/-) T cells induced more rapid and robust inflammatory bowel disease in scid recipients. Thus, Sphk2 regulates IL-2 pathways in T cells, and the modulation of Sphk2 activity may be of therapeutic utility in inflammatory and/or infectious diseases.

Coordinated involvement of mast cells and T cells in allergic mucosal inflammation: critical role of the CC chemokine ligand 1:CCR8 axis

CCL1 is the predominant chemokine secreted from IgE-activated human and mouse mast cells in vitro, colocalizes to mast cells in lung biopsies, and is elevated in asthmatic airways. CCR8, the receptor for CCL1, is expressed by approximately 70% of CD4(+) T lymphocytes recruited to the asthmatic airways, and the number of CCR8-expressing cells is increased 3-fold in the airways of asthmatic subjects compared with normal volunteers. In vivo, CCL1 expression in the lung is reduced in mast cell-deficient mice after aeroallergen provocation. Neutralization of CCL1 or CCR8 deficiency results in reduced mucosal lung inflammation, airway hyperresponsiveness, and mucus hypersecretion to a similar degree as detected in mast cell-deficient mice. Adenoviral delivery of CCL1 to the lungs of mast cell-deficient mice restores airway hyperresponsiveness, lung inflammation, and mucus hypersecretion to the degree observed in wild-type mice. The consequences of CCR8 deficiency, including a marked reduction in Th2 cytokine levels, are comparable with those observed by depletion of CD4(+) T lymphocytes. Thus, mast cell-derived CCL1- and CCR8-expressing CD4(+) effector T lymphocytes play an essential role in orchestrating lung mucosal inflammatory responses.

Cysteinyl leukotrienes regulate Th2 cell-dependent pulmonary inflammation

The Th2 cell-dependent inflammatory response is a central component of asthma, and the ways in which it is regulated is a critical question. The cysteinyl leukotrienes (cys-LTs) are 5-lipoxygenase pathway products implicated in asthma, in particular, by their function as smooth muscle constrictors of airways and microvasculature. To elucidate additional roles for cys-LTs in the pathobiology of pulmonary inflammation, we used an OVA sensitization and challenge protocol with mice lacking leukotriene C(4) synthase (LTC(4)S), the terminal enzyme for cys-LT generation. Ag-induced pulmonary inflammation, characterized by eosinophil infiltration, goblet cell hyperplasia with mucus hypersecretion, and accumulation and activation of intraepithelial mast cells was markedly reduced in LTC(4)S(null) mice. Furthermore, Ag-specific IgE and IgG1 in serum, Th2 cell cytokine mRNA expression in the lung, and airway hyperresponsiveness to methacholine were significantly reduced in LTC(4)S(null) mice compared with wild-type controls. Finally, the number of parabronchial lymph node cells from sensitized LTC(4)S(null) mice and their capacity to generate Th2 cell cytokines ex vivo after restimulation with Ag were also significantly reduced. In contrast, delayed-type cutaneous hypersensitivity, a prototypic Th1 cell-dependent response, was intact in LTC(4)S(null) mice. These findings provide direct evidence of a role for cys-LTs in regulating the initiation and/or amplification of Th2 cell-dependent pulmonary inflammation.

Role of CCR5 in the Pathogenesis of IL-13-Induced Inflammation and Remodeling

IL-13 is a major effector at sites of Th2 inflammation and tissue remodeling. In these locations, it frequently coexists with the CCR5 chemokine receptor and its ligands MIP-1alpha/CCL3 and MIP-1beta/CCL4. We hypothesized that CCR5 induction and activation play important roles in the pathogenesis of IL-13-induced tissue responses. To test this hypothesis, we evaluated the effects of IL-13 on the expression of CCR5 in the murine lung. We also compared the effects of lung-targeted transgenic IL-13 in mice treated with anti-CCR5 or an Ab control and mice with wild-type or null CCR5 loci. These studies demonstrate that IL-13 is a potent stimulator of epithelial cell CCR5 expression. They also demonstrate that CCR5 neutralization or a deficiency of CCR5 significantly decreases IL-13-induced inflammation, alveolar remodeling, structural and inflammatory cell apoptosis, and respiratory failure and death. Lastly, these studies provide mechanistic insights by demonstrating that CCR5 is required for optimal IL-13 stimulation of select chemokines (MIP-1alpha/CCL3, MIP-1beta/CCL4, MCP-1/CCL-2), matrix metalloproteinase-9 and cell death regulators (Fas, TNF, TNFR1, TNFR2, Bid), optimal IL-13 inhibition of alpha1-antitrypsin, and IL-13-induction of and activation of caspases-3, -8, and-9. Collectively, these studies demonstrate that CCR5 plays a critical role in the pathogenesis of IL-13-induced inflammation and tissue remodeling.

Expression of the type 2 receptor for cysteinyl leukotrienes (CysLT2R) by human mast cells: Functional distinction from CysLT1R

Cysteinyl leukotrienes (cysLTs) mediate vascular leakage and bronchoconstriction through the smooth muscle-associated CysLT type 1 receptor (CysLT1R), one of at least two loosely homologous cysLT-binding G protein-coupled receptors. We previously reported that CysLT1R is expressed by cultured human mast cells (hMCs), and that priming these cells with IL-4 enhances their sensitivity to calcium flux and cytokine generation in response to cys-LTs and the nucleotide ligand, uridine diphosphate (UDP), without increasing their surface expression of CysLT1R. We now report that hMCs express the type 2 receptor for cysLTs (CysLT2R) as well, and that the amount of surface CysLT2R protein increases in response to priming with IL-4. The selective function of CysLT2R was evident based on uninhibited IL-8 secretion by IL-4-primed hMCs stimulated with cys-LTs or UDP in the presence of the selective CysLT1R antagonist MK571. MK571 did inhibit IL-5 generation, calcium flux, and phosphorylation of extracellular signal-regulated kinase. IL-8 secretion was inhibited by pertussis toxin and a selective p38 kinase inhibitor, SB203580. The CysLT2 response may permit the cys-LTs and nucleotides generated in infection and tissue injury to elicit IL-8 generation by hMCs, potentially leading to neutrophilic infiltration, a characteristic of aerosol challenge-induced late-phase responses and of sudden death associated with asthma.

Functional screening of five PYPAF family members identifies PYPAF5 as a novel regulator of NF-kappaB and caspase-1

PYRIN-containing Apaf-1-like proteins (PYPAFs) are a recently identified family of proteins thought to function in apoptotic and inflammatory signaling pathways. PYPAF1 and PYPAF7 proteins have been found to assemble with the PYRIN-CARD protein ASC and coordinate the activation of NF-kappaB and pro-caspase-1. To determine if other PYPAF family members function in pro-inflammatory signaling pathways, we screened five other PYPAF proteins (PYPAF2, PYPAF3, PYPAF4, PYPAF5 and PYPAF6) for their ability to activate NF-kappaB and pro-caspase-1. Co-expression of PYPAF5 with ASC results in a synergistic activation of NF-kappaB and the recruitment of PYPAF5 to punctate structures in the cytoplasm. The expression of PYPAF5 is highly restricted to granulocytes and T-cells, indicating a role for this protein in inflammatory signaling. In contrast, PYPAF2, PYPAF3, PYPAF4 and PYPAF6 failed to colocalize with ASC and activate NF-kappaB. PYPAF5 also synergistically activated caspase-1-dependent cytokine processing when co-expressed with ASC. These findings suggest that PYPAF5 functions in immune cells to coordinate the transduction of pro-inflammatory signals to the activation of NF-kappaB and pro-caspase-1.

PYPAF7, a novel PYRIN-containing Apaf1-like protein that regulates activation of NF-kappa B and caspase-1-dependent cytokine processing

PYRIN-containing Apaf1-like proteins (PYPAFs) are members of the nucleotide-binding site/leucine-rich repeat (NBS/LRR) family of signal transduction proteins. We report here that PYPAF7 is a novel PYPAF protein that activates inflammatory signaling pathways. The expression of PYPAF7 is highly restricted to immune cells, and its gene maps to chromosome 19q13.4, a locus that contains a cluster of genes encoding numerous PYPAF family members. Co-expression of PYPAF7 with ASC results in the recruitment of PYPAF7 to distinct cytoplasmic loci and a potent synergistic activation of NF-kappa B. To identify other proteins involved in PYPAF7 and ASC signaling pathways, we performed a mammalian two-hybrid screen and identified pro-caspase-1 as a binding partner of ASC. Co-expression of PYPAF7 and ASC results in the synergistic activation of caspase-1 and a corresponding increase in secretion of interleukin-1 beta. In addition, PYPAF1 induces caspase-1-dependent cytokine processing when co-expressed with ASC. These findings indicate that PYPAF family members participate in inflammatory signaling by regulating the activation of NF-kappa B and cytokine processing.

PYPAF1, a PYRIN-containing Apaf1-like protein that assembles with ASC and regulates activation of NF-kappa B

The PYRIN domain is a recently identified protein-protein interaction domain that is found at the N terminus of several proteins thought to function in apoptotic and inflammatory signaling pathways. We report here that PYPAF1 (PYRIN-containing Apaf1-like protein 1) is a novel PYRIN-containing signaling protein that belongs to the nucleotide-binding site/leucine-rich repeat (NBS/LRR) family of signaling proteins. The expression of PYPAF1 is highly restricted to immune cells, and its gene maps to chromosome 1q44, a locus that is associated with the rare inflammatory diseases Muckle-Wells syndrome and familial cold urticaria. To identify downstream signaling partners of PYPAF1, we performed a mammalian two-hybrid screen and identified ASC as a PYRIN-containing protein that interacts selectively with the PYRIN domain of PYPAF1. When expressed in cells, ASC recruits PYPAF1 to distinct cytoplasmic loci and induces the activation of NF-kappaB. Furthermore, coexpression of PYPAF1 with ASC results in a potent synergistic activation of NF-kappaB. These findings suggest that PYPAF1 and ASC function as upstream activators of NF-kappaB signaling.

Characterization of two novel lipocalins expressed in the Drosophila embryonic nervous system

We have found two novel lipocalins in the fruit fly Drosophila melanogaster that are homologous to the grasshopper Lazarillo, a singular lipocalin within this protein family which functions in axon guidance during nervous system development. Sequence analysis suggests that the two Drosophila proteins are secreted and possess peptide regions unique in the lipocalin family. The mRNAs of DNLaz (for Drosophila neural Lazarillo) and DGLaz (for Drosophila glial Lazarillo) are expressed with different temporal patterns during embryogenesis. They show low levels of larval expression and are highly expressed in pupa and adult flies. DNLaz mRNA is transcribed in a subset of neurons and neuronal precursors in the embryonic CNS. DGLaz mRNA is found in a subset of glial cells of the CNS: the longitudinal glia and the medial cell body glia. Both lipocalins are also expressed outside the nervous system in the developing gut, fat body and amnioserosa. The DNLaz protein is detected in a subset of axons in the developing CNS. Treatment with a secretion blocker enhances the antibody labeling, indicating the DNLaz secreted nature. These findings make the embryonic nervous system expression of lipocalins a feature more widespread than previously thought. We propose that DNLaz and DGLaz may have a role in axonal outgrowth and pathfinding, although other putative functions are also discussed.

Alpha3beta1-integrin as a critical mediator of the hepatic differentiation response to the extracellular matrix

The extracellular matrix (ECM) promotes the differentiation of many cell types, and ECM remodeling in the liver has been implicated in embryonic development, tissue injury, and oncogenesis. Integrins are heterodimeric ECM receptors that play critical roles in transducing the composition of the ECM in the cell environment. We previously showed that mouse H2.35 cells, a conditionally transformed, liver-derived cell line, assume a more differentiated hepatocyte morphology and enhanced liver-specific gene expression when the cells are cultured on gelatinous ECM substrata. Here we show that H2. 35 cells express relatively high levels of alpha3beta1-integrins, similar to that previously shown for immature hepatocytes, transformed hepatocytes, and biliary cells. However, the cell morphological responses that depend on alpha3beta1-integrin have not been defined. We found that transfecting H2.35 cells with antisense RNA construct directed to alpha3-subunit messenger RNA perturbs the initial cell attachment to laminin and collagen, and strongly inhibits cell morphological, proliferative, and gene expression responses to a collagen gel substratum. In situ hybridization to mouse embryo tissues demonstrates the presence of alpha3-subunit messenger RNAs in newly formed hepatocytes. We suggest that alpha3beta1-integrins are important for immature and transformed hepatocytes to respond morphologically to the extracellular matrix.

Primary structure and expression pattern of the 33-kDa chitinase gene from the mycoparasitic fungus Trichoderma harzianum

A gene (chit33) from the mycoparasitic fungus Trichoderma harzianum, coding for a chitinase of 33 kDa, has been isolated and characterized. Partial amino-acid sequences from the purified 33-kDa chitinase were obtained. The amino-terminal peptide sequence was employed to design an oligonucleotide probe and was used as a primer to isolate a 1.2-kb cDNA. The cDNA codes for a protein of 321 amino acids, which includes a putative signal peptide of 19 amino acids. All microsequenced peptides found in this sequence, indicate that this cDNA codes for the 33-kDa chitinase. A high homology (approximately 43% identity) was found with fungal and plant chitinases, including yeast chitinases. However enzyme characteristics suggest a nutritional (saprophytic or mycoparasitic), rather than a morphogenetic, role for this chitinase. The chit33 gene appears as a single copy in the T. harzianum genome, is strongly suppressed by glucose, and de-repressed under starvation conditions as well as in the presence of autoclaved mycelia and/or fungal cell walls. The 33-kDa chitinase seems to be very stable except under starvation conditions. The independent regulation of each of the chitinases in T. harzianum indicates different specific roles.

Molecular characterization and heterologous expression of an endo-beta-1,6-glucanase gene from the mycoparasitic fungus Trichoderma harzianum

Hydrolytic enzymes from the filamentous fungus Trichoderma harzianum have been described as critical elements of the mycoparasitic action of Trichoderma against fungal plant pathogens. In this report we describe the first genomic and cDNA clones encoding a beta-1,6-endoglucanase gene. The deduced protein sequence has limited homology with other beta-glucanases. Northern experiments show a marked repression of mRNA accumulation by glucose. The protein has been successfully produced in Saccharomyces cerevisiae upon construction of a transcriptional fusion of the cDNA with a yeast promoter. This S. cerevisiae recombinant strain shows a strong lytic action on agar plates containing beta-1,6-glucan.

Cloning and characterization of a chitinase (chit42) cDNA from the mycoparasitic fungus Trichoderma harzianum

A cDNA of Trichoderma harzianum (chit42), coding for an endochitinase of 42 kDa, has been cloned using synthetic oligonucleotides corresponding to amino-acid sequences of the purified chitinase. The cDNA codes for a protein of 423 amino acids. Analysis of the N-terminal amino-acid sequence of the chitinase, and comparison with that deduced from the nucleotide sequence, revealed post-translational processing of a putative signal peptide of 22 amino acids and a second peptide of 12 amino acids. The chit42 sequence presents overall similarities with filamentous fungal and bacterial chitinases and to a lesser extent with yeast and plant chitinases. The deduced amino-acid sequence has putative catalytic, phosphorylation and glycosylation domains. Expression of chit42 mRNA is strongly induced by chitin and chitin-containing cell walls and is subjected to catabolite repression. Southern analysis shows that it is present as a single-copy gene in T. harzianum. chit42 is also detected in several tested mycoparasitic and non-mycoparasitic fungal strains.

A putative catabolite-repressed cell wall protein from the mycoparasitic fungus Trichoderma harzianum

A cDNA clone encoding a putative cell wall protein (Qid3) was isolated from a library prepared from chitin-induced mRNA in cultures of the mycoparasitic fungus Trichoderma harzianum. The predicted 14 kDa protein shows a potential signal peptide, several hydrophobic domains and certain motifs that are structurally similar to proline-rich and glycine-rich plant cell wall proteins. Expression of the qid3 gene is derepressed in the absence of glucose. When introduced in yeast, qid3 expression causes cell division arrest into cytokinesis and cell separation, probably due to its cell wall localization.

Isolation and characterization of three chitinases from Trichoderma harzianum

Three proteins which display chitinase activity were purified from the supernatants of Trichoderma harzianum CECT 2413 grown in minimal medium supplemented with chitin as the sole carbon source. Purification was carried out after protein precipitation with ammonium sulphate, adsorption to colloidal chitin and digestion, and, finally, chromatofocusing. By this procedure, two chitinases of 42 kDa (CHIT42) and 37 kDa (CHIT37) were purified to homogeneity, as judged by SDS/PAGE and gel filtration, whereas a third, of 33 kDa (CHIT33), was highly purified. The isoelectric points for CHIT42, CHIT37 and CHIT33 were 6.2, 4.6 and 7.8, respectively. The three enzymes displayed endochitinase activities and showed different kinetic properties. CHIT33 was able to hydrolyze chitin oligomers of a polymerization degree higher than n = 4, its Km for colloidal chitin being 0.3 mg/ml. CHIT42 and CHIT37 were able to hydrolyze chitin oligomers with a minimal polymerization degree of n = 3, their Km values for colloidal chitin being 1.0 mg/ml and 0.5 mg/ml respectively. With regard to their lytic activity with purified cell walls of the phytopathogenic fungus Botrytis cinerea, a hydrolytic action was observed only when CHIT42 was present. Antibodies against CHIT42 and CHIT37 specifically recognized the proteins and did not display cross-reaction, suggesting that each protein is encoded by a different gene.