The Drosophila Toll Pathway in Innate Immunity: from the Core Pathway toward Effector Functions

The fruit fly Drosophila melanogaster Toll signaling pathway has an evolutionarily conserved role in controlling immune responses. Whereas the microbial recognition mechanisms and the core signaling pathway leading to activation of the humoral immune response via the NF-κB transcription factors have been well established for many years, the mechanistic understanding of the effector functions at the molecular level is currently rapidly evolving. In this review, we discuss the current developments in elucidating the role of the Drosophila Toll signaling pathway in immunity. We discuss the emerging role of Toll in viral infections and sex-specific differences in immunity. Mainly, we focus on Toll pathway regulation, the effector molecules, and cellular immunity.

Carbonic Anhydrases in Metazoan Model Organisms: Molecules, Mechanisms, and Physiology

During the past three decades, mice, zebrafish, fruit flies, and Caenorhabditis elegans have been the primary model organisms used for the study of various biological phenomena. These models have also been adopted and developed to investigate the physiological roles of carbonic anhydrases (CAs) and carbonic anhydrase-related proteins (CARPs). These proteins belong to eight CA families and are identified by Greek letters: α, β, γ, δ, ζ, η, θ, and ι. Studies using model organisms have focused on two CA families, α-CAs and β-CAs, which are expressed in both prokaryotic and eukaryotic organisms with species-specific distribution patterns and unique functions. This review covers the biological roles of CAs and CARPs in light of investigations performed in model organisms. Functional studies demonstrate that CAs are not only linked to the regulation of pH homeostasis, the classical role of CAs but also contribute to a plethora of previously undescribed functions.

Proteasome α6 Subunit Negatively Regulates the JAK/STAT Pathway and Blood Cell Activation in Drosophila melanogaster

JAK/STAT signaling regulates central biological functions such as development, cell differentiation and immune responses. In Drosophila, misregulated JAK/STAT signaling in blood cells (hemocytes) induces their aberrant activation. Using mass spectrometry to analyze proteins associated with a negative regulator of the JAK/STAT pathway, and by performing a genome-wide RNAi screen, we identified several components of the proteasome complex as negative regulators of JAK/STAT signaling in Drosophila. A selected proteasome component, Prosα6, was studied further. In S2 cells, Prosα6 silencing decreased the amount of the known negative regulator of the pathway, ET, leading to enhanced expression of a JAK/STAT pathway reporter gene. Silencing of Prosα6 in vivo resulted in activation of the JAK/STAT pathway, leading to the formation of lamellocytes, a specific hemocyte type indicative of hemocyte activation. This hemocyte phenotype could be partially rescued by simultaneous knockdown of either the Drosophila STAT transcription factor, or MAPKK in the JNK-pathway. Our results suggest a role for the proteasome complex components in the JAK/STAT pathway in Drosophila blood cells both in vitro and in vivo.

Osa-Containing Brahma Complex Regulates Innate Immunity and the Expression of Metabolic Genes in Drosophila

Negative regulation of innate immunity is essential to avoid autoinflammation. In Drosophila melanogaster, NF-κB signaling-mediated immune responses are negatively regulated at multiple levels. Using a Drosophila RNA interference in vitro screen, we identified a set of genes inhibiting immune activation. Four of these genes encode members of the chromatin remodeling Osa-containing Brahma (BAP) complex. Silencing additional two genes of the BAP complex was shown to have the same phenotype, confirming its role in immune regulation in vitro. In vivo, the knockdown of osa and brahma was shown to enhance the expression of the Toll pathway-mediated antimicrobial peptides when the flies were challenged with Gram-positive bacteria Micrococcus luteus In this setting, osa knockdown had a particularly strong effect on immune effectors that are predominantly activated by the Imd pathway. Accordingly, Drosophila NF-κB Relish expression was increased by osa silencing. These transcriptional changes were associated with enhanced survival from M. luteus + E. faecalis infection. Besides regulating the expression of immune effector genes, osa RNA interference decreased the expression of a large group of genes involved in metabolism, particularly proteolysis. Of note, the expression of the recently characterized, immune-inducible gene Induced by Infection (IBIN) was diminished in osa knockdown flies. Although IBIN has been shown to modulate metabolism upon infection, the expression of selected Osa-regulated metabolism genes was not rescued by overexpressing IBIN. We conclude that the BAP complex regulates expression of genes involved in metabolism at least partially independent or downstream of IBIN Moreover, Osa affects the NF-κB-mediated immune response by regulating Drosophila NF-κB factor Relish expression.

Correction: Immune-inducible non-coding RNA molecule lincRNA-IBIN connects immunity and metabolism in Drosophila melanogaster

[This corrects the article DOI: 10.1371/journal.ppat.1007504.].

Immune-inducible non-coding RNA molecule lincRNA-IBIN connects immunity and metabolism in Drosophila melanogaster

Non-coding RNAs have important roles in regulating physiology, including immunity. Here, we performed transcriptome profiling of immune-responsive genes in Drosophila melanogaster during a Gram-positive bacterial infection, concentrating on long non-coding RNA (lncRNA) genes. The gene most highly induced by a Micrococcus luteus infection was CR44404, named Induced by Infection (lincRNA-IBIN). lincRNA-IBIN is induced by both Gram-positive and Gram-negative bacteria in Drosophila adults and parasitoid wasp Leptopilina boulardi in Drosophila larvae, as well as by the activation of the Toll or the Imd pathway in unchallenged flies. We show that upon infection, lincRNA-IBIN is expressed in the fat body, in hemocytes and in the gut, and its expression is regulated by NF-κB signaling and the chromatin modeling brahma complex. In the fat body, overexpression of lincRNA-IBIN affected the expression of Toll pathway -mediated genes. Notably, overexpression of lincRNA-IBIN in unchallenged flies elevated sugar levels in the hemolymph by enhancing the expression of genes important for glucose retrieval. These data show that lncRNA genes play a role in Drosophila immunity and indicate that lincRNA-IBIN acts as a link between innate immune responses and metabolism.

Proprotein convertase Furin1 expression in the Drosophila fat body is essential for a normal antimicrobial peptide response and bacterial host defense

Invading pathogens provoke robust innate immune responses in Dipteran insects, such as Drosophila melanogaster In a systemic bacterial infection, a humoral response is induced in the fat body. Gram-positive bacteria trigger the Toll signaling pathway, whereas gram-negative bacterial infections are signaled via the immune deficiency (IMD) pathway. We show here that the RNA interference-mediated silencing of Furin1-a member of the proprotein convertase enzyme family-specifically in the fat body, results in a reduction in the expression of antimicrobial peptides. This, in turn, compromises the survival of adult fruit flies in systemic infections that are caused by both gram-positive and -negative bacteria. Furin1 plays a nonredundant role in the regulation of immune responses, as silencing of Furin2, the other member of the enzyme family, had no effect on survival or the expression of antimicrobial peptides upon a systemic infection. Furin1 does not directly affect the Toll or IMD signaling pathways, but the reduced expression of Furin1 up-regulates stress response factors in the fat body. We also demonstrate that Furin1 is a negative regulator of the Janus kinase/signal transducer and activator of transcription signaling pathway, which is implicated in stress responses in the fly. In summary, our data identify Furin1 as a novel regulator of humoral immunity and cellular stress responses in Drosophila-Aittomäki, S., Valanne, S., Lehtinen, T., Matikainen, S., Nyman, T. A., Rämet, M., Pesu, M. Proprotein convertase Furin1 expression in the Drosophila fat body is essential for a normal antimicrobial peptide response and bacterial host defense.

Genetic Screen in Drosophila Larvae Links ird1 Function to Toll Signaling in the Fat Body and Hemocyte Motility

To understand how Toll signaling controls the activation of a cellular immune response in Drosophila blood cells (hemocytes), we carried out a genetic modifier screen, looking for deletions that suppress or enhance the mobilization of sessile hemocytes by the gain-of-function mutation Toll10b (Tl10b). Here we describe the results from chromosome arm 3R, where five regions strongly suppressed this phenotype. We identified the specific genes immune response deficient 1 (ird1), headcase (hdc) and possibly Rab23 as suppressors, and we studied the role of ird1 in more detail. An ird1 null mutant and a mutant that truncates the N-terminal kinase domain of the encoded Ird1 protein affected the Tl10b phenotype, unlike mutations that affect the C-terminal part of the protein. The ird1 null mutant suppressed mobilization of sessile hemocytes, but enhanced other Tl10b hemocyte phenotypes, like the formation of melanotic nodules and the increased number of circulating hemocytes. ird1 mutants also had blood cell phenotypes on their own. They lacked crystal cells and showed aberrant formation of lamellocytes. ird1 mutant plasmatocytes had a reduced ability to spread on an artificial substrate by forming protrusions, which may explain why they did not go into circulation in response to Toll signaling. The effect of the ird1 mutation depended mainly on ird1 expression in hemocytes, but ird1-dependent effects in other tissues may contribute. Specifically, the Toll receptor was translocated from the cell membrane to intracellular vesicles in the fat body of the ird1 mutant, and Toll signaling was activated in that tissue, partially explaining the Tl10b-like phenotype. As ird1 is otherwise known to control vesicular transport, we conclude that the vesicular transport system may be of particular importance during an immune response.

Cytokines in Drosophila immunity

Cytokines are a large and diverse group of small proteins that can affect many biological processes, but most commonly cytokines are known as mediators of the immune response. In the event of an infection, cytokines are produced in response to an immune stimulus, and they function as key regulators of the immune response. Cytokines come in many shapes and sizes, and although they vary greatly in structure, their functions have been well conserved in evolution. The immune signaling pathways that respond to cytokines are remarkably conserved from fly to man. Therefore, Drosophila melanogaster, provides an excellent platform for studying the biology and function of cytokines. In this review, we will describe the cytokines and cytokine-like molecules found in the fly and discuss their roles in host immunity.

β carbonic anhydrase is required for female fertility in Drosophila melanogaster

Background

Carbonic anhydrases (CAs, EC 4.2.1.1) are ubiquitous enzymes that catalyze the reversible hydration reaction of carbon dioxide. CAs are present as six structurally divergent enzyme families: α, β, γ, δ, ζ and η. β-CAs have a wide distribution across different species including invertebrates. Previously, we showed that Drosophila melanogaster β-CA is a highly active mitochondrial enzyme. In this study, we investigated the function of Drosophila β-CA by silencing the expression of the β-CA gene using UAS/GAL4-based RNA interference (RNAi) in Drosophila in vivo.

Results

Crossing β-CA RNAi lines over ubiquitous Actin driver flies did not produce any viable progeny, indicating that β-CA expression is required for fly development. RNAi silencing of β-CA ubiquitously in adult flies did not affect their survival rate or function of mitochondrial electron transport chain. Importantly, β-CA RNAi led to impaired reproduction. All β-CA knockdown females were sterile, and produced few or no eggs. Whole ovaries of knockdown females looked normal but upon cadherin staining, there was an apparent functional defect in migration of border cells, which are considered essential for normal fertilization.

Conclusions

These results indicate that although Drosophila β-CA is dispensable for survival of adult flies, it is essential for female fertility.

Electronic supplementary material

The online version of this article (doi:10.1186/s12983-015-0111-3) contains supplementary material, which is available to authorized users.

Edin Expression in the Fat Body Is Required in the Defense Against Parasitic Wasps in Drosophila melanogaster

The cellular immune response against parasitoid wasps in Drosophila involves the activation, mobilization, proliferation and differentiation of different blood cell types. Here, we have assessed the role of Edin (elevated during infection) in the immune response against the parasitoid wasp Leptopilina boulardi in Drosophila melanogaster larvae. The expression of edin was induced within hours after a wasp infection in larval fat bodies. Using tissue-specific RNAi, we show that Edin is an important determinant of the encapsulation response. Although edin expression in the fat body was required for the larvae to mount a normal encapsulation response, it was dispensable in hemocytes. Edin expression in the fat body was not required for lamellocyte differentiation, but it was needed for the increase in plasmatocyte numbers and for the release of sessile hemocytes into the hemolymph. We conclude that edin expression in the fat body affects the outcome of a wasp infection by regulating the increase of plasmatocyte numbers and the mobilization of sessile hemocytes in Drosophila larvae.

The events leading to a successful encapsulation of parasitoid wasp eggs in the larvae of the fruit fly Drosophila melanogaster are insufficiently understood. The formation of a capsule seals off the wasp egg, and this process is often functionally compared to the formation of granulomas in vertebrates. Like granuloma formation in humans, the encapsulation process in fruit flies requires the activation, mobilization, proliferation and differentiation of different blood cell types. Here, we have studied the role of Edin (elevated during infection) in the immune defense against the parasitoid wasp Leptopilina boulardi in Drosophila larvae. We demonstrate that edin expression in the fat body (an immune-responsive organ in Drosophila functionally resembling the mammalian liver) is required for a normal defense against wasp eggs. Edin is required for the release of blood cells from larval tissues and for the subsequent increase in circulating blood cell numbers. Our results provide new knowledge of how the encapsulation process is regulated in Drosophila, and how blood cells are activated upon wasp parasitism. Understanding of the encapsulation process in invertebrates may eventually lead to a better knowledge of the pathophysiology of granuloma formation in human diseases, such as tuberculosis.

Functional genomic analysis of the Drosophila immune response

Drosophila melanogaster has been widely used as a model organism for over a century now, and also as an immunological research model for over 20 years. With the emergence of RNA interference (RNAi) in Drosophila as a robust tool to silence genes of interest, large-scale or genome-wide functional analysis has become a popular way of studying the Drosophila immune response in cell culture. Drosophila immunity is composed of cellular and humoral immunity mechanisms, and especially the systemic, humoral response pathways have been extensively dissected using the functional genomic approach. Although most components of the main immune pathways had already been found using traditional genetic screening techniques, important findings including pathway components, positive and negative regulators and modifiers have been made with RNAi screening. Additionally, RNAi screening has produced new information on host-pathogen interactions related to the pathogenesis of many microbial species.

Uracil debases pathogenic but not commensal bacteria

The metazoan gut harbors microbial communities on its mucosal surfaces, yet the mechanisms by which gut immunity tolerates symbiotic and commensal bacteria while eliminating pathogens is insufficiently understood. In a recent Cell paper, Lee et al. (2013) show that bacterial uracil, not secreted by commensal bacteria, triggers dual oxidase-dependent immunity.

The RhoGEF Zizimin-related acts in the Drosophila cellular immune response via the Rho GTPases Rac2 and Cdc42

Zizimin-related (Zir), a Rho guanine nucleotide exchange factor (RhoGEF) homologous to the mammalian Dock-C/Zizimin-related family, was identified in a screen to find new genes involved in the Drosophila melanogaster cellular immune response against eggs from the parasitoid wasp Leptopilina boulardi. RhoGEFs activate Rho-family GTPases, which are known to be central regulators of cell migration, spreading and polarity. When a parasitoid wasp is recognized as foreign, multiple layers of circulating immunosurveillance cells (haemocytes) should attach to the egg. In Zir mutants this process is disrupted and lamellocytes, a haemocyte subtype, fail to properly encapsulate the wasp egg. Furthermore, macrophage-like plasmatocytes exhibit a strong reduction in their ability to phagocytise Escherichia coli and Staphylococcus aureus bacteria. During encapsulation and phagocytosis Zir genetically interacts with two Rho-family GTPases, Rac2 and Cdc42. Finally, Zir is dispensable for the humoral immune response against bacteria. We propose that Zir is necessary to activate the Rho-family GTPases Rac2 and Cdc42 during the Drosophila cellular immune response.

Large-scale RNAi screens add both clarity and complexity to Drosophila NF-κB signaling

NF-κB signaling is an immune response mechanism remarkably conserved through phylogeny. The genetically tractable model animal Drosophila melanogaster is an important model organism for studying NF-κB signaling in the immune response. Fruit flies have two NF-κB signaling pathways: the Toll and the Imd pathway. Traditional genetic screens have revealed many important aspects about the regulation of Drosophila NF-κB signaling and have helped us to also understand the immune response in humans. For example, the discovery that Toll like receptors are the main immune signaling molecules in mammals was based on work in flies. During the past decade high throughput RNA interference (RNAi)-based screening in cultured Drosophila cells has become a common method for identifying novel genes required for numerous cellular processes including NF-κB signaling. These screens have identified many novel positive and negative regulators of Drosophila NF-κB signaling thus enhancing our understanding of these signaling cascades.

The Drosophila Toll signaling pathway

The identification of the Drosophila melanogaster Toll pathway cascade and the subsequent characterization of TLRs have reshaped our understanding of the immune system. Ever since, Drosophila NF-κB signaling has been actively studied. In flies, the Toll receptors are essential for embryonic development and immunity. In total, nine Toll receptors are encoded in the Drosophila genome, including the Toll pathway receptor Toll. The induction of the Toll pathway by gram-positive bacteria or fungi leads to the activation of cellular immunity as well as the systemic production of certain antimicrobial peptides. The Toll receptor is activated when the proteolytically cleaved ligand Spatzle binds to the receptor, eventually leading to the activation of the NF-κB factors Dorsal-related immunity factor or Dorsal. In this study, we review the current literature on the Toll pathway and compare the Drosophila and mammalian NF-κB pathways.

[Fruit fly--genetically excellent model animal for research]

Drosophila melanogaster, i.e., the fruit fly is a familiar nuisance in late summer. For those living in a country plagued by myriads of flying insects, it is difficult to think any other model animal as an ethically more suitable research tool. Due to its genetic manipulability, the fruit fly is an excellent research model, but mainly due to lack of experience, has been utilized only to a small extent in medical research in Finland. For instance, the readily available transgenic RNAi strains have made functional, genome-wide screening possible in a complete organism or in a designated tissue.

Eye transformer is a negative regulator of Drosophila JAK/STAT signaling

JAK/STAT signaling pathway is evolutionarily conserved and tightly regulated. We carried out a reporter-based genome-wide RNAi in vitro screen to identify genes that regulate Drosophila JAK/STAT pathway and found 5 novel regulators. Of these, CG14225 is a negative regulator structurally related to the Drosophila JAK/STAT pathway receptor Domeless, especially in the extracellular domain, and to the mammalian IL-6 receptor and the signal transducer gp130. CG14225 coimmunoprecipitates with Domeless and its associated kinase hopscotch in S2 cells. CG14225 RNAi caused hyperphosphorylation of the transcription factor Stat92E in S2 cells on stimulation with the Drosophila JAK/STAT pathway ligand unpaired. CG14225 RNAi in vivo hyperactivated JAK/STAT target genes on septic injury and enhanced unpaired-induced eye overgrowth, and was thus named the eye transformer (ET). In the gastrointestinal infection model, where JAK/STAT signaling is important for stem cell renewal, CG14225/ET RNAi was protective in vivo. In conclusion, we have identified ET as a novel negative regulator of the Drosophila JAK/STAT pathway both in vitro and in vivo, and it functions in regulating Stat92E phosphorylation.

Drosophila as a model for antiviral immunity

The fruit fly Drosophila melanogaster has been successfully used to study numerous biological processes including immune response. Flies are naturally infected with more than twenty RNA viruses making it a valid model organism to study host-pathogen interactions during viral infections. The Drosophila antiviral immunity includes RNA interference, activation of the JAK/STAT and other signaling cascades and other mechanisms such as autophagy and interactions with other microorganisms. Here we review Drosophila as an immunological research model as well as recent advances in the field of Drosophila antiviral immunity.

Genome-wide RNA interference in Drosophila cells identifies G protein-coupled receptor kinase 2 as a conserved regulator of NF-kappaB signaling

Because NF-kappaB signaling pathways are highly conserved in evolution, the fruit fly Drosophila melanogaster provides a good model to study these cascades. We carried out an RNA interference (RNAi)-based genome-wide in vitro reporter assay screen in Drosophila for components of NF-kappaB pathways. We analyzed 16,025 dsRNA-treatments and identified 10 novel NF-kappaB regulators. Of these, nine dsRNA-treatments affect primarily the Toll pathway. G protein-coupled receptor kinase (Gprk)2, CG15737/Toll pathway activation mediating protein, and u-shaped were required for normal Drosomycin response in vivo. Interaction studies revealed that Gprk2 interacts with the Drosophila IkappaB homolog Cactus, but is not required in Cactus degradation, indicating a novel mechanism for NF-kappaB regulation. Morpholino silencing of the zebrafish ortholog of Gprk2 in fish embryos caused impaired cytokine expression after Escherichia coli infection, indicating a conserved role in NF-kappaB signaling. Moreover, small interfering RNA silencing of the human ortholog GRK5 in HeLa cells impaired NF-kappaB reporter activity. Gprk2 RNAi flies are susceptible to infection with Enterococcus faecalis and Gprk2 RNAi rescues Toll(10b)-induced blood cell activation in Drosophila larvae in vivo. We conclude that Gprk2/GRK5 has an evolutionarily conserved role in regulating NF-kappaB signaling.

Pirk is a negative regulator of the Drosophila Imd pathway

NF-kappaB transcription factors are involved in evolutionarily conserved signaling pathways controlling multiple cellular processes including apoptosis and immune and inflammatory responses. Immune response of the fruit fly Drosophila melanogaster to Gram-negative bacteria is primarily mediated via the Imd (immune deficiency) pathway, which closely resembles the mammalian TNFR signaling pathway. Instead of cytokines, the main outcome of Imd signaling is the production of antimicrobial peptides. The pathway activity is delicately regulated. Although many of the Imd pathway components are known, the mechanisms of negative regulation are more elusive. In this study we report that a previously uncharacterized gene, pirk, is highly induced upon Gram-negative bacterial infection in Drosophila in vitro and in vivo. pirk encodes a cytoplasmic protein that coimmunoprecipitates with Imd and the cytoplasmic tail of peptidoglycan recognition protein LC (PGRP-LC). RNA interference-mediated down-regulation of Pirk caused Imd pathway hyperactivation upon infection with Gram-negative bacteria, while overexpression of pirk reduced the Imd pathway response both in vitro and in vivo. Furthermore, pirk-overexpressing flies were more susceptible to Gram-negative bacterial infection than wild-type flies. We conclude that Pirk is a negative regulator of the Imd pathway.

Iap2 is required for a sustained response in the Drosophila Imd pathway

Fruit flies have effective immune response against Gram-negative bacteria. Upon infection, early JNK-signaling pathway mediated response is followed by the action of the Immune deficiency (Imd) signaling cascade, a Drosophila equivalent of mammalian TNF-receptor pathway, leading to the release of antimicrobial peptides. Recently, Tak1-binding protein 2 (Tab2) and Inhibitor of apoptosis 2 (Iap2) were identified as components of the Imd pathway. In this study, we carried out a genome-wide kinetic analysis of the role of Tab2 and Iap2 for immune response in Drosophila S2 cells using oligonucleotide microarrays. Tab2 RNAi abolished the induction of all immune response genes in S2 cells indicating its requirement for signaling both via the Imd and the JNK pathway. The role of Iap2 was more specific. Kinetic analysis indicated that Iap2 is required to sustain antimicrobial peptide gene expression in S2 cells. Furthermore, inactivation of Iap2 by RNAi resulted in impaired microbial resistance in Drosophila in vivo.

Inhibitor of apoptosis 2 and TAK1-binding protein are components of the Drosophila Imd pathway

The Imd signaling cascade, similar to the mammalian TNF-receptor pathway, controls antimicrobial peptide expression in Drosophila. We performed a large-scale RNAi screen to identify novel components of the Imd pathway in Drosophila S2 cells. In all, 6713 dsRNAs from an S2 cell-derived cDNA library were analyzed for their effect on Attacin promoter activity in response to Escherichia coli. We identified seven gene products required for the Attacin response in vitro, including two novel Imd pathway components: inhibitor of apoptosis 2 (Iap2) and transforming growth factor-activated kinase 1 (TAK1)-binding protein (TAB). Iap2 is required for antimicrobial peptide response also by the fat body in vivo. Both these factors function downstream of Imd. Neither TAB nor Iap2 is required for Relish cleavage, but may be involved in Relish nuclear localization in vitro, suggesting a novel mode of regulation of the Imd pathway. Our results show that an RNAi-based approach is suitable to identify genes in conserved signaling cascades.

CAMP factor homologues in Propionibacterium acnes: a new protein family differentially expressed by types I and II

Analysis of the draft genome sequence of the opportunistic pathogenPropionibacterium acnestype strain NCTC 737 (=ATCC 6919) revealed five genes with sequence identity to the co-haemolytic Christie–Atkins–Munch-Peterson (CAMP) factor ofStreptococcus agalactiae. The predicted molecular masses for the expressed proteins ranged from 28 to 30 kDa. The genes were present in each of the three recently identifiedrecA-based phylogenetic groupings ofP. acnes(IA, IB and II), as assessed by PCR amplification. Conserved differences in CAMP factor gene sequences between these three groups were also consistent with their previous phylogenetic designations. All type IA, IB and II isolates were positive for the co-haemolytic reaction on sheep blood agar. Immunoblotting and silver staining of SDS-PAGE gels, however, revealed differential protein expression of CAMP factors amongst the different groups. Type IB and II isolates produced an abundance of CAMP factor 1, detectable by specific antibody labelling and silver staining of SDS-PAGE gels. In contrast, abundant CAMP factor production was lacking in type IA isolates, although larger amounts of CAMP factor 2 were detectable by immunoblotting compared with type II isolates. While the potential role of the abundant CAMP factor 1 in host colonization or virulence remains to be determined, it should be noted that the type strain ofP. acnesused in much of the published literature is a type IA isolate and is, therefore, lacking in this attribute.

Functional analysis of immune response genes in Drosophila identifies JNK pathway as a regulator of antimicrobial peptide gene expression in S2 cells

The templates of innate immunity have ancient origins. Thus, such model animals as the fruit fly, Drosophila melanogaster, can be used to identify gene products that also play a key role in the innate immunity in mammals. We have used oligonucleotide microarrays to identify genes that are responsive to gram-negative bacteria in Drosophila macrophage-like S2 cells. In total, 53 genes were induced by greater than threefold in response to Escherichia coli. The induction of all these genes was peptidoglycan recognition protein LC (PGRP-LC) dependent. Twenty-two genes including 10 of the most strongly induced genes are also known to be up-regulated by septic injury in vivo. Importantly, we identified 31 genes that are not known to respond to bacterial challenge. We carried out targeted dsRNA treatments to assess the functional importance of these gene products for microbial recognition, phagocytosis and antimicrobial peptide release in Drosophila S2 cells in vitro. RNAi targeting three of these genes, CG7097, CG15678 and beta-Tubulin 60D, caused altered antimicrobial peptide release in vitro. Our results indicate that the JNK pathway is essential for normal antimicrobial peptide release in Drosophila in vitro.

Propionibacterium acnes types I and II represent phylogenetically distinct groups

Although two phenotypes of the opportunistic pathogen Propionibacterium acnes (types I and II) have been described, epidemiological investigations of their roles in different infections have not been widely reported. Using immunofluorescence microscopy with monoclonal antibodies (MAbs) QUBPa1 and QUBPa2, specific for types I and II, respectively, we investigated the prevalences of the two types among 132 P. acnes isolates. Analysis of isolates from failed prosthetic hip implants (n = 40) revealed approximately equal numbers of type I and II organisms. Isolates from failed prosthetic hip-associated bone (n = 6) and tissue (n = 38) samples, as well as isolates from acne (n = 22), dental infections (n = 8), and skin removed during surgical incision (n = 18) were predominately of type I. A total of 11 (8%) isolates showed atypical MAb labeling and could not be conclusively identified. Phylogenetic analysis of P. acnes by nucleotide sequencing revealed the 16S rRNA gene to be highly conserved between types I and II. In contrast, sequence analysis of recA and a putative hemolysin gene (tly) revealed significantly greater type-specific polymorphisms that corresponded to phylogenetically distinct cluster groups. All 11 isolates with atypical MAb labeling were identified as type I by sequencing. Within the recA and tly phylogenetic trees, nine of these isolates formed a cluster distinct from other type I organisms, suggesting a further phylogenetic subdivision within type I. Our study therefore demonstrates that the phenotypic differences between P. acnes types I and II reflect deeper differences in their phylogeny. Furthermore, nucleotide sequencing provides an accurate method for identifying the type status of P. acnes isolates.

Induction and regulation of xenobiotic-metabolizing cytochrome P450s in the human A549 lung adenocarcinoma cell line

Several cytochrome P450 (CYP) enzymes are expressed in the human lung, where they participate in metabolic inactivation and activation of numerous exogenous and endogenous compounds. In this study, the expression pattern of all known xenobiotic-metabolizing CYP genes was characterized in the human alveolar type II cell-derived A549 adenocarcinoma cell line using qualitative reverse transcriptase/polymerase chain reaction (RT-PCR). In addition, the mechanisms of induction by chemicals of members in the CYP1 and CYP3A subfamilies were assessed by quantitative RT-PCR. The expression of messenger RNAs (mRNAs) of CYPs 1A1, 1B1, 2B6, 2C, 2E1, 3A5, and 3A7 was detected in the A549 cells. The amounts of mRNAs of CYPs 1A2, 2A6, 2A7, 2A13, 2F1, 3A4, and 4B1 were below the limit of detection. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced CYP1A1 and CYP1B1 mRNAs 56-fold and 2.5-fold, respectively. CYP3A5 was induced 8-fold by dexamethasone and 11-fold by phenobarbital. CYP3A4 was not induced by any of the typical CYP3A4 inducers used. The tyrosine kinase inhibitor genistein and the protein kinase C inhibitor staurosporine blocked TCDD-elicited induction of CYP1A1, but they did not affect CYP1B1 induction. Protein phosphatase inhibitors okadaic acid and calyculin A enhanced TCDD-induction of CYP1B1 slightly, but had negligible effects on CYP1A1 induction. These results suggest that CYP1A1 and CYP1B1 are differentially regulated in human pulmonary epithelial cells and give the first indication of the induction of CYP3A5 by glucocorticoids in human lung cells. These results establish that having retained several characteristics of human lung epithelial cell CYP expression, the A549 lung cell line is a valuable model for mechanistic studies on induction of the pulmonary CYP system.