Publications by authors named "Sylvain Lemeille"

31 Publications

Persistence of self-reactive CD8+ T cells in the CNS requires TOX-dependent chromatin remodeling.

Nat Commun 2021 02 12;12(1):1009. Epub 2021 Feb 12.

Department of Pathology and Immunology, University of Geneva, Geneva, Switzerland.

Self-reactive CD8 T cells are important mediators of progressive tissue damage in autoimmune diseases, but the molecular program underlying these cells' functional adaptation is unclear. Here we characterize the transcriptional and epigenetic landscape of self-reactive CD8 T cells in a mouse model of protracted central nervous system (CNS) autoimmunity and compare it to populations of CNS-resident memory CD8 T cells emerging from acute viral infection. We find that autoimmune CD8 T cells persisting at sites of self-antigen exhibit characteristic transcriptional regulation together with distinct epigenetic remodeling. This self-reactive CD8 T cell fate depends on the transcriptional regulation by the DNA-binding HMG-box protein TOX which remodels more than 400 genomic regions including loci such as Tcf7, which is central to stemness of CD8 T cells. Continuous exposure to CNS self-antigen sustains TOX levels in self-reactive CD8 T cells, whereas genetic ablation of TOX in CD8 T cells results in shortened persistence of self-reactive CD8 T cells in the inflamed CNS. Our study establishes and characterizes the genetic differentiation program enabling chronic T cell-driven immunopathology in CNS autoimmunity.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-021-21109-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7881115PMC
February 2021

Daily Viral Kinetics and Innate and Adaptive Immune Response Assessment in COVID-19: a Case Series.

mSphere 2020 11 11;5(6). Epub 2020 Nov 11.

Geneva Centre for Emerging Viral Diseases, Geneva University Hospitals, Geneva, Switzerland.

Viral shedding patterns and their correlations with immune responses are still poorly characterized in mild coronavirus (CoV) disease 2019 (COVID-19). We monitored shedding of viral RNA and infectious virus and characterized the immune response kinetics of the first five patients quarantined in Geneva, Switzerland. High viral loads and infectious virus shedding were observed from the respiratory tract despite mild symptoms, with isolation of infectious virus and prolonged positivity by reverse transcriptase PCR (RT-PCR) until days 7 and 19 after symptom onset, respectively. Robust innate responses characterized by increases in activated CD14 CD16 monocytes and cytokine responses were observed as early as 2 days after symptom onset. Cellular and humoral severe acute respiratory syndrome (SARS)-CoV-2-specific adaptive responses were detectable in all patients. Infectious virus shedding was limited to the first week after symptom onset. A strong innate response, characterized by mobilization of activated monocytes during the first days of infection and SARS-CoV-2-specific antibodies, was detectable even in patients with mild disease. This work is particularly important because it simultaneously assessed the virology, immunology, and clinical presentation of the same subjects, whereas other studies assess these separately. We describe the detailed viral and immune profiles of the first five patients infected by SARS-CoV-2 and quarantined in Geneva, Switzerland. Viral loads peaked at the very beginning of the disease, and infectious virus was shed only during the early acute phase of disease. No infectious virus could be isolated by culture 7 days after onset of symptoms, while viral RNA was still detectable for a prolonged period. Importantly, we saw that all patients, even those with mild symptoms, mount an innate response sufficient for viral control (characterized by early activated cytokines and monocyte responses) and develop specific immunity as well as cellular and humoral SARS-CoV-2-specific adaptive responses, which already begin to decline a few months after the resolution of symptoms.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1128/mSphere.00827-20DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7657589PMC
November 2020

Immune response of polarized cystic fibrosis airway epithelial cells infected with Influenza A virus.

J Cyst Fibros 2020 Aug 29. Epub 2020 Aug 29.

Faculty of Medicine, Department of Cell Physiology & Metabolism, University of Geneva, Geneva, Switzerland. Electronic address:

Background: Cystic fibrosis (CF), a genetic disease caused by mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene, is characterized by dysfunction of the immune response in the airway epithelium that leads to prolonged infection, colonization and exacerbated inflammation. In this study, we determined the gene expression profile of airway epithelial cells knockdown for CFTR (CFTR KD) in response to bacterial and viral challenges.

Methods: In a first approach, polarized CFTR KD and their control counterpart (CFTR CTL) cells were stimulated with P. aeruginosa-derived virulence factor flagellin. Next, we developed a model of Influenza A virus (IAV) infection in CTL and CFTR KD polarized cells. mRNA was collected for transcriptome analysis.

Results: Beside the expected pro-inflammatory response, Gene Set Enrichment Analysis highlighted key molecular pathways and players involved in IAV and anti-viral interferon signaling. Although IAV replication was similar in both cell types, multiplex gene expression analysis revealed changes of key immune genes dependent on time of infection that were found to be CFTR-dependent and/or IAV-dependent. Interferons are key signaling proteins/cytokines in the antibacterial and antiviral response. To evaluate their impact on the altered gene expression profile in CFTR responses to pathogens, we measured transcriptome changes after exposure to Type I-, Type II- and Type III-interferons.

Conclusions: Our findings reveal target genes in understanding the defective immune response in the CF airway epithelium in the context of viral infection. Information provided in this study would be useful to understand the dysfunctional immune response of the CF airway epithelium during infection.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.jcf.2020.08.012DOI Listing
August 2020

Interplay of RFX transcription factors 1, 2 and 3 in motile ciliogenesis.

Nucleic Acids Res 2020 09;48(16):9019-9036

Univ Lyon, Université Claude Bernard Lyon-1, CNRS UMR-5310, INSERM U-1217, Institut NeuroMyoGène, F-69008, Lyon, France.

Cilia assembly is under strict transcriptional control during animal development. In vertebrates, a hierarchy of transcription factors (TFs) are involved in controlling the specification, differentiation and function of multiciliated epithelia. RFX TFs play key functions in the control of ciliogenesis in animals. Whereas only one RFX factor regulates ciliogenesis in C. elegans, several distinct RFX factors have been implicated in this process in vertebrates. However, a clear understanding of the specific and redundant functions of different RFX factors in ciliated cells remains lacking. Using RNA-seq and ChIP-seq approaches we identified genes regulated directly and indirectly by RFX1, RFX2 and RFX3 in mouse ependymal cells. We show that these three TFs have both redundant and specific functions in ependymal cells. Whereas RFX1, RFX2 and RFX3 occupy many shared genomic loci, only RFX2 and RFX3 play a prominent and redundant function in the control of motile ciliogenesis in mice. Our results provide a valuable list of candidate ciliary genes. They also reveal stunning differences between compensatory processes operating in vivo and ex vivo.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/nar/gkaa625DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7498320PMC
September 2020

Vav3 Mediates Pseudomonas aeruginosa Adhesion to the Cystic Fibrosis Airway Epithelium.

Cell Rep 2020 07;32(1):107842

Faculty of Medicine, Department of Pediatrics, Gynecology & Obstetrics, University of Geneva, Geneva 1211, Switzerland; Faculty of Medicine, Department of Cell Physiology & Metabolism, University of Geneva, Geneva 1211, Switzerland. Electronic address:

Pseudomonas aeruginosa (Pa) represents the leading cause of airway infection in cystic fibrosis (CF). Early airways colonization can be explained by enhanced adhesion of Pa to the respiratory epithelium. RNA sequencing (RNA-seq) on fully differentiated primary cultures of airway epithelial cells from CF and non-CF donors predict that VAV3, β1 INTEGRIN, and FIBRONECTIN genes are significantly enriched in CF. Indeed, Vav3 is apically overexpressed in CF, associates with active β1 integrin luminally exposed, and increases fibronectin deposition. These luminal microdomains, rich in fibronectin and β1 integrin and regulated by Vav3, mediate the increased Pa adhesion to the CF epithelium. Interestingly, Vav3 inhibition normalizes the CF-dependent fibronectin and β1-integrin ectopic expression, improves the CF epithelial integrity, and prevents the enhanced Pa trapping to the CF epithelium. Through its capacity to promote a luminal complex with active β1 integrin and fibronectin that favors bacteria trapping, Vav3 may represent a new target in CF.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.celrep.2020.107842DOI Listing
July 2020

IL-36 signaling in keratinocytes controls early IL-23 production in psoriasis-like dermatitis.

Life Sci Alliance 2020 06 28;3(6). Epub 2020 Apr 28.

Department of Pathology-Immunology, University of Geneva Faculty of Medicine, Geneva, Switzerland

IL-36R signaling plays an important role in the pathogenesis of psoriasis. We ought to assess the specific function of IL-36R in keratinocytes for the pathology of Aldara-induced psoriasis-like dermatitis. mice presenting deletion of IL-36R in keratinocytes were similarly resistant to Aldara-induced ear inflammation as mice, but acanthosis was only prevented in mice. FACS analysis revealed that IL-36R signaling in keratinocytes is mandatory for early neutrophil infiltration in Aldara-treated ears. RNASeq and qRT-PCR experiments demonstrated the crucial role of IL-36R signaling in keratinocytes for induction of IL-23, IL-17, and IL-22 at early time points. Taken together, our results demonstrate that IL-36R signaling in keratinocytes plays a major role in the induction of Aldara-induced psoriasis-like dermatitis by triggering early production of IL-23/IL-17/IL-22 cytokines and neutrophil infiltration.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.26508/lsa.202000688DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7190273PMC
June 2020

Human fetal mesoangioblasts reveal tissue-dependent transcriptional signatures.

Stem Cells Transl Med 2020 05 23;9(5):575-589. Epub 2020 Jan 23.

Department of Pathology and Immunology, Faculty of Medicine, University of Geneva, Geneva, Switzerland.

Mesoangioblasts (MABs) derived from adult skeletal muscles are well-studied adult stem/progenitor cells that already entered clinical trials for muscle regeneration in genetic diseases; however, the transcriptional identity of human fetal MABs (fMABs) remains largely unknown. Herein we analyzed the transcriptome of MABs isolated according to canonical markers from fetal atrium, ventricle, aorta, and skeletal muscles (from 9.5 to 13 weeks of age) to uncover specific gene signatures correlating with their peculiar myogenic differentiation properties inherent to their tissue of origin. RNA-seq analysis revealed for the first time that human MABs from fetal aorta, cardiac (atrial and ventricular), and skeletal muscles display subsets of differentially expressed genes likely representing distinct expression signatures indicative of their original tissue. Identified GO biological processes and KEGG pathways likely account for their distinct differentiation outcomes and provide a set of critical genes possibly predicting future specific differentiation outcomes. This study reveals novel information regarding the potential of human fMABs that may help to improve specific differentiation outcomes relevant for therapeutic muscle regeneration.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/sctm.19-0209DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7180296PMC
May 2020

Gestation and lactation exposure to nicotine induces transient postnatal changes in lung alveolar development.

Am J Physiol Lung Cell Mol Physiol 2020 04 22;318(4):L606-L618. Epub 2020 Jan 22.

Department of Pediatrics, Gynecology, and Obstetrics, Faculty of Medicine, University of Geneva, Geneva, Switzerland.

Harmful consequences of cigarette smoke (CS) exposure during lung development can already manifest in infancy. In particular, early life exposure to nicotine, the main component of CS, was shown to affect lung development in animal models. We aimed to characterize the effect of nicotine on alveoli formation. We analyzed the kinetics of normal alveolar development during the alveolarization phase and then looked at the effect of nicotine in a mouse model of gestational and early life exposure. Immunohistochemical staining revealed that the wave of cell proliferation [i.e., vascular endothelial cells, alveolar epithelial cells (AEC) type II and mesenchymal cell] occurs at postnatal day (pnd) 8 in control and nicotine-exposed lungs. However, FACS analysis of individual epithelial alveolar cells revealed nicotine-induced transient increase of AEC type I proliferation and decrease of vascular endothelial cell proliferation at pnd8. Furthermore, nicotine increased the percentage of endothelial cells at pnd2. Transcriptomic data also showed significant changes in nicotine samples compared with the controls on cell cycle-associated genes at pnd2 but not anymore at pnd16. Accordingly, the expression of survivin, involved in cell cycle regulation, also follows a different kinetics in nicotine lung extracts. These changes resulted in an increased lung size detected by stereology at pnd16 but no longer in adult age, suggesting that nicotine can act on the pace of lung maturation. Taken together, our results indicate that early life nicotine exposure could be harmful to alveolar development independently from other toxicants contained in CS.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1152/ajplung.00228.2019DOI Listing
April 2020

Intracellular IL-1 Receptor Antagonist Isoform 1 Released from Keratinocytes upon Cell Death Acts as an Inhibitor for the Alarmin IL-1α.

J Immunol 2020 02 13;204(4):967-979. Epub 2020 Jan 13.

Department of Pathology and Immunology, School of Medicine, University of Geneva, 1211 Geneva 4, Switzerland; and

The inflammatory effects of IL-1α/β are controlled by IL-1R antagonist (IL-1Ra). One IL-1Ra isoform is secreted, whereas three other isoforms (intracellular IL-1Ra [icIL-1Ra] 1, 2, and 3) are supposed to remain intracellular because of the absence of a signal peptide. In contrast to the well-characterized function of the secreted isoform, the biological role of the intracellular isoforms remains largely unclear. icIL-1Ra1 represents the major isoform in keratinocytes. We created icIL-1Ra1 mice and investigated the role of icIL-1Ra1 in Aldara (5% imiquimod)-induced psoriasis-like skin inflammation. Naive icIL-1Ra1 mice bred habitually and exhibited a normal phenotype. icIL-1Ra1 deficiency aggravated Aldara-induced skin inflammation, as demonstrated by increased ear thickness and increased mRNA levels of key proinflammatory cytokines. No intracellular effect of icIL-1Ra1 could be detected in isolated keratinocytes using RNA-sequencing analysis; however, Aldara treatment led to caspase 1/11-, caspase 8-, and RIPK3-independent keratinocyte cell death accompanied by the release of both icIL-1Ra1 and IL-1α. Furthermore, blocking IL-1α attenuated the clinical severity of Aldara-induced ear thickening in icIL-1Ra1 mice. Our data suggest that upon keratinocyte damage icIL-1Ra1 acts extracellularly as an antagonist of the alarmin IL-1α to immediately counteract its inflammatory effects.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.4049/jimmunol.1901074DOI Listing
February 2020

Mitochondrial arginase-2 is a cell‑autonomous regulator of CD8+ T cell function and antitumor efficacy.

JCI Insight 2019 11 21;4(24). Epub 2019 Nov 21.

Department of Pathology and Immunology, Faculty of Medicine, University of Geneva, Geneva, Switzerland.

As sufficient extracellular arginine is crucial for T cell function, depletion of extracellular arginine by elevated arginase 1 (Arg1) activity has emerged as a hallmark immunosuppressive mechanism. However, the potential cell-autonomous roles of arginases in T cells have remained unexplored. Here, we show that the arginase isoform expressed by T cells, the mitochondrial Arg2, is a cell-intrinsic regulator of CD8+ T cell activity. Both germline Arg2 deletion and adoptive transfer of Arg2-/- CD8+ T cells significantly reduced tumor growth in preclinical cancer models by enhancing CD8+ T cell activation, effector function, and persistence. Transcriptomic, proteomic, and high-dimensional flow cytometry characterization revealed a CD8+ T cell-intrinsic role of Arg2 in modulating T cell activation, antitumor cytoxicity, and memory formation, independently of extracellular arginine availability. Furthermore, specific deletion of Arg2 in CD8+ T cells strongly synergized with PD-1 blockade for the control of tumor growth and animal survival. These observations, coupled with the finding that pharmacologic arginase inhibition accelerates activation of ex vivo human T cells, unveil Arg2 as a potentially new therapeutic target for T cell-based cancer immunotherapies.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1172/jci.insight.132975DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6975264PMC
November 2019

Maternal Antibodies Inhibit Neonatal and Infant Responses to Vaccination by Shaping the Early-Life B Cell Repertoire within Germinal Centers.

Cell Rep 2019 08;28(7):1773-1784.e5

WHO Collaborative Center for Vaccine Immunology, Department of Pathology and Immunology, University of Geneva, Geneva 1211, Switzerland.

Maternal antibodies (MatAbs) protect offspring from infections but limit their responses to vaccination. The mechanisms of this inhibition are still debated. Using murine early-life immunization models mimicking the condition prevailing in humans, we observed the induction of CD4-T, T follicular helper, and germinal center (GC) B cell responses even when early-life antibody responses were abrogated by MatAbs. GC B cells induced in the presence of MatAbs form GC structures and exhibit canonical GC changes in gene expression but fail to differentiate into plasma cells and/or memory B cells in a MatAb titer-dependent manner. Furthermore, GC B cells elicited in the presence or absence of MatAbs use different V and V genes and show differences in genes associated with B cell differentiation and isotype switching. Thus, MatAbs do not prevent B cell activation but control the output of the GC reaction both quantitatively and qualitatively, shaping the antigen-specific B cell repertoire.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.celrep.2019.07.047DOI Listing
August 2019

Macroautophagy in Dendritic Cells Controls the Homeostasis and Stability of Regulatory T Cells.

Cell Rep 2019 07;28(1):21-29.e6

Department of Pathology and Immunology, School of Medicine, University of Geneva, 1211, Geneva 4, Switzerland; Division of Rheumatology, Department of Internal Medicine, University Hospital, 1211 Geneva 4, Switzerland. Electronic address:

Regulatory T cells (Tregs) play a crucial role in controlling autoimmune and inflammatory responses. Recent studies have demonstrated that dendritic cells (DCs) contribute to the homeostasis of peripheral Tregs. Autophagy, a critical pathway for cellular homeostasis, is active in DCs and is upregulated in different inflammatory conditions. We have shown that Tregs are expanded and have phenotypic alterations and impaired suppressive functions in mice with autophagy-deficient DCs. RNA profiling of Tregs revealed that autophagy in DCs is required to stabilize Treg expression signatures. This phenotype is linked to the downregulation of ICOS-Ligand expression in autophagy-deficient DCs, a consequence of the accumulation of ADAM10, the metalloproteinase responsible for its cleavage. Upon inflammation, in antigen-induced arthritis, mice with autophagy-deficient DCs exhibit increased synovial inflammation and cartilage and bone erosion correlating with Treg-to-Th17 conversion. Our data reveal a mechanism that couples autophagy deficiency in DCs to the function, homeostasis, and stability of Tregs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.celrep.2019.05.110DOI Listing
July 2019

KLF4-Induced Connexin40 Expression Contributes to Arterial Endothelial Quiescence.

Front Physiol 2019 12;10:80. Epub 2019 Feb 12.

Department of Pathology and Immunology, University of Geneva, Geneva, Switzerland.

Shear stress, a blood flow-induced frictional force, is essential in the control of endothelial cell (EC) homeostasis. High laminar shear stress (HLSS), as observed in straight parts of arteries, assures a quiescent non-activated endothelium through the induction of Krüppel-like transcription factors (KLFs). Connexin40 (Cx40)-mediated gap junctional communication is known to contribute to a healthy endothelium by propagating anti-inflammatory signals between ECs, however, the molecular basis of the transcriptional regulation of Cx40 as well as its downstream effectors remain poorly understood. Here, we show that flow-induced KLF4 regulated Cx40 expression in a mouse EC line. Chromatin immunoprecipitation in ECs revealed that KLF4 bound to three predicted KLF consensus binding sites in the Cx40 promoter. HLSS-dependent induction of Cx40 expression was confirmed in primary human ECs. The downstream effects of Cx40 modulation in ECs exposed to HLSS were elucidated by an unbiased transcriptomics approach. Cell cycle progression was identified as an important downstream target of Cx40 under HLSS. In agreement, an increase in the proportion of proliferating cell nuclear antigen (PCNA)-positive ECs and a decrease in the proportion of ECs in the G0/G1 phase were observed under HLSS after Cx40 silencing. Transfection of communication-incompetent HeLa cells with Cx40 demonstrated that the regulation of proliferation by Cx40 was not limited to ECs. Using a zebrafish model, we finally showed faster intersegmental vessel growth and branching into the dorsal longitudinal anastomotic vessel in embryos knock-out for the Cx40 orthologs and . Most significant effects were observed in embryos with a mutant encoding for a channel with reduced gap junctional function. Faster intersegmental vessel growth in mutant embryos was associated with increased EC proliferation as assessed by PH3 immunostaining. Our data shows a novel evolutionary-conserved role of flow-driven KLF4-dependent Cx40 expression in endothelial quiescence that may be relevant for the control of atherosclerosis and diseases involving sprouting angiogenesis.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3389/fphys.2019.00080DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6379456PMC
February 2019

Expression of the DNA-Binding Factor TOX Promotes the Encephalitogenic Potential of Microbe-Induced Autoreactive CD8 T Cells.

Immunity 2018 05;48(5):937-950.e8

Department of Pathology and Immunology, University of Geneva, Geneva, Switzerland; Division of Clinical Pathology, Geneva University Hospital, Geneva, Switzerland. Electronic address:

Infections are thought to trigger CD8 cytotoxic T lymphocyte (CTL) responses during autoimmunity. However, the transcriptional programs governing the tissue-destructive potential of CTLs remain poorly defined. In a model of central nervous system (CNS) inflammation, we found that infection with lymphocytic choriomeningitis virus (LCMV), but not Listeria monocytogenes (Lm), drove autoimmunity. The DNA-binding factor TOX was induced in CTLs during LCMV infection and was essential for their encephalitogenic properties, and its expression was inhibited by interleukin-12 during Lm infection. TOX repressed the activity of several transcription factors (including Id2, TCF-1, and Notch) that are known to drive CTL differentiation. TOX also reduced immune checkpoint sensitivity by restraining the expression of the inhibitory checkpoint receptor CD244 on the surface of CTLs, leading to increased CTL-mediated damage in the CNS. Our results identify TOX as a transcriptional regulator of tissue-destructive CTLs in autoimmunity, offering a potential mechanistic link to microbial triggers.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.immuni.2018.04.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6040915PMC
May 2018

Intratumoral CpG-B Promotes Antitumoral Neutrophil, cDC, and T-cell Cooperation without Reprograming Tolerogenic pDC.

Cancer Res 2018 06 27;78(12):3280-3292. Epub 2018 Mar 27.

Department of Pathology and Immunology, University of Geneva Medical School, Geneva, Switzerland.

Cancer immunotherapies utilize distinct mechanisms to harness the power of the immune system to eradicate cancer cells. Therapeutic vaccines, aimed at inducing active immune responses against an existing cancer, are highly dependent on the immunological microenvironment, where many immune cell types display high levels of plasticity and, depending on the context, promote very different immunologic outcomes. Among them, plasmacytoid dendritic cells (pDC), known to be highly immunogenic upon inflammation, are maintained in a tolerogenic state by the tumor microenvironment. Here, we report that intratumoral (i.t.) injection of established solid tumors with CpG oligonucleotides-B (CpG-B) inhibits tumor growth. Interestingly, control of tumor growth was independent of tumor-associated pDC, which remained refractory to CpG-B stimulation and whose depletion did not alter the efficacy of the treatment. Instead, tumor growth inhibition subsequent to i.t. CpG-B injection depended on the recruitment of neutrophils into the milieu, resulting in the activation of conventional dendritic cells, subsequent increased antitumor T-cell priming in draining lymph nodes, and enhanced effector T-cell infiltration in the tumor microenvironment. These results reinforce the concept that i.t. delivery of TLR9 agonists alters the tumor microenvironment by improving the antitumor activity of both innate and adaptive immune cells. Intratumoral delivery of CpG-B disrupts the tolerogenic tumor microenvironment and inhibits tumor growth. .
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1158/0008-5472.CAN-17-2549DOI Listing
June 2018

Overexpression of the human antigen R suppresses the immediate paradoxical proliferation of melanoma cell subpopulations in response to suboptimal BRAF inhibition.

Cancer Med 2017 Jul 1;6(7):1652-1664. Epub 2017 Jun 1.

Department of Pathology and Immunology, University of Geneva, Switzerland.

Tumor plasticity and the heterogeneous response of melanoma cells to targeted therapies are major limits for the long-term efficacy of this line of therapy. Targeting tumor plasticity is theoretically possible through the modulation of the expression of RNA-binding proteins which can affect many different compensatory mechanisms of the adaptive response of malignant cells to targeted therapies. Human antigen R (HuR) is a modulator of gene expression and a transacting factor in the mRNA-processing machinery used in the cell stress response, and is a potential target for reducing tumor plasticity. In this experiment, we exploit the inherent heterogeneous response of the A375 melanoma line to suboptimal BRAF inhibition as a model of immediate adaptive response. We first observe that HuR overexpression can prevent the heterogeneous response and thus the immediate paradoxical proliferation induced by low-doses vemurafenib treatment. We then use single-cell mass cytometry to characterize subpopulations, including those that paradoxically proliferate, based on their proliferation rate and the expression patterns of markers involved in the reversible adaptive resistance to BRAF inhibition and/or recognized as HuR targets involved in cell cycle regulation. Under suboptimal BRAF inhibition, HuR overexpression affects these subpopulations and their expression pattern with contrasting responses depending on their proliferation rate: faster-proliferating vemurafenib-sensitive or -resistant subpopulations showed higher death tendency and reduced size, and slower-proliferating subpopulations showed an attenuated resistant expression response and their paradoxical proliferation was inhibited. These observations pave the way to new therapeutic strategies for preventing the heterogeneous response of tumors to targeted therapies.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/cam4.1091DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5504324PMC
July 2017

The Pkn22 Ser/Thr kinase in Nostoc PCC 7120: role of FurA and NtcA regulators and transcript profiling under nitrogen starvation and oxidative stress.

BMC Genomics 2015 Jul 29;16:557. Epub 2015 Jul 29.

Aix-Marseille University and CNRS, Laboratoire de Chimie Bactérienne - UMR7283, IMM, 31 Chemin Joseph Aiguier, 13402, Marseille cedex 20, France.

Background: The filamentous cyanobacterium Nostoc sp. strain PCC 7120 can fix N2 when combined nitrogen is not available. Furthermore, it has to cope with reactive oxygen species generated as byproducts of photosynthesis and respiration. We have previously demonstrated the synthesis of Ser/Thr kinase Pkn22 as an important survival response of Nostoc to oxidative damage. In this study we wished to investigate the possible involvement of this kinase in signalling peroxide stress and nitrogen deprivation.

Results: Quantitative RT-PCR experiments revealed that the pkn22 gene is induced in response to peroxide stress and to combined nitrogen starvation. Electrophoretic motility assays indicated that the pkn22 promoter is recognized by the global transcriptional regulators FurA and NtcA. Transcriptomic analysis comparing a pkn22-insertion mutant and the wild type strain indicated that this kinase regulates genes involved in important cellular functions such as photosynthesis, carbon metabolism and iron acquisition. Since metabolic changes may lead to oxidative stress, we investigated whether this is the case with nitrogen starvation. Our results rather invalidate this hypothesis thereby suggesting that the function of Pkn22 under nitrogen starvation is independent of its role in response to peroxide stress.

Conclusions: Our analyses have permitted a more complete functional description of Ser/Thr kinase in Nostoc. We have decrypted the transcriptional regulation of the pkn22 gene, and analysed the whole set of genes under the control of this kinase in response to the two environmental changes often encountered by cyanobacteria in their natural habitat: oxidative stress and nitrogen deprivation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1186/s12864-015-1703-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4518582PMC
July 2015

RFX2 Is a Major Transcriptional Regulator of Spermiogenesis.

PLoS Genet 2015 Jul 10;11(7):e1005368. Epub 2015 Jul 10.

Department of Pathology and Immunology, University of Geneva Medical School, CMU, Geneva, Switzerland.

Spermatogenesis consists broadly of three phases: proliferation of diploid germ cells, meiosis, and finally extensive differentiation of the haploid cells into effective delivery vehicles for the paternal genome. Despite detailed characterization of many haploid developmental steps leading to sperm, only fragmentary information exists on the control of gene expression underlying these processes. Here we report that the RFX2 transcription factor is a master regulator of genes required for the haploid phase. A targeted mutation of Rfx2 was created in mice. Rfx2-/- mice are perfectly viable but show complete male sterility. Spermatogenesis appears to progress unperturbed through meiosis. However, haploid cells undergo a complete arrest in spermatid development just prior to spermatid elongation. Arrested cells show altered Golgi apparatus organization, leading to a deficit in the generation of a spreading acrosomal cap from proacrosomal vesicles. Arrested cells ultimately merge to form giant multinucleated cells released to the epididymis. Spermatids also completely fail to form the flagellar axoneme. RNA-Seq analysis and ChIP-Seq analysis identified 139 genes directly controlled by RFX2 during spermiogenesis. Gene ontology analysis revealed that genes required for cilium function are specifically enriched in down- and upregulated genes showing that RFX2 allows precise temporal expression of ciliary genes. Several genes required for cell adhesion and cytoskeleton remodeling are also downregulated. Comparison of RFX2-regulated genes with those controlled by other major transcriptional regulators of spermiogenesis showed that each controls independent gene sets. Altogether, these observations show that RFX2 plays a major and specific function in spermiogenesis.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1371/journal.pgen.1005368DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4498915PMC
July 2015

The C-terminal region of the RNA helicase CshA is required for the interaction with the degradosome and turnover of bulk RNA in the opportunistic pathogen Staphylococcus aureus.

RNA Biol 2015 ;12(6):658-74

a Department of Microbiology and Molecular Medicine ; Medical Faculty; University of Geneva ; Michel Servet , Geneva , Switzerland.

Staphylococcus aureus is a versatile opportunistic pathogen that adapts readily to a variety of different growth conditions. This adaptation requires a rapid regulation of gene expression including the control of mRNA abundance. The CshA DEAD-box RNA helicase was previously shown to be required for efficient turnover of the agr quorum sensing mRNA. Here we show by transcriptome-wide RNA sequencing and microarray analyses that CshA is required for the degradation of bulk mRNA. Moreover a subset of mRNAs is significantly stabilised in absence of CshA. Deletion of the C-terminal extension affects RNA turnover similar to the full deletion of the cshA gene. In accordance with RNA decay data, the C-terminal region of CshA is required for an RNA-independent interaction with components of the RNA degradation machinery. The C-terminal truncation of CshA reduces its ATPase activity and this reduction cannot be compensated at high RNA concentrations. Finally, the deletion of the C-terminal extension does affect growth at low temperatures, but to a significantly lesser degree than the full deletion, indicating that the core of the helicase can assume a partial function and opening the possibility that CshA is involved in different cellular processes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1080/15476286.2015.1035505DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4615653PMC
October 2015

NLRC5 exclusively transactivates MHC class I and related genes through a distinctive SXY module.

PLoS Genet 2015 Mar 26;11(3):e1005088. Epub 2015 Mar 26.

Department of Biochemistry, University of Lausanne, Epalinges, Switzerland.

MHC class II (MHCII) genes are transactivated by the NOD-like receptor (NLR) family member CIITA, which is recruited to SXY enhancers of MHCII promoters via a DNA-binding "enhanceosome" complex. NLRC5, another NLR protein, was recently found to control transcription of MHC class I (MHCI) genes. However, detailed understanding of NLRC5's target gene specificity and mechanism of action remained lacking. We performed ChIP-sequencing experiments to gain comprehensive information on NLRC5-regulated genes. In addition to classical MHCI genes, we exclusively identified novel targets encoding non-classical MHCI molecules having important functions in immunity and tolerance. ChIP-sequencing performed with Rfx5(-/-) cells, which lack the pivotal enhanceosome factor RFX5, demonstrated its strict requirement for NLRC5 recruitment. Accordingly, Rfx5-knockout mice phenocopy Nlrc5 deficiency with respect to defective MHCI expression. Analysis of B cell lines lacking RFX5, RFXAP, or RFXANK further corroborated the importance of the enhanceosome for MHCI expression. Although recruited by common DNA-binding factors, CIITA and NLRC5 exhibit non-redundant functions, shown here using double-deficient Nlrc5(-/-)CIIta(-/-) mice. These paradoxical findings were resolved by using a "de novo" motif-discovery approach showing that the SXY consensus sequence occupied by NLRC5 in vivo diverges significantly from that occupied by CIITA. These sequence differences were sufficient to determine preferential occupation and transactivation by NLRC5 or CIITA, respectively, and the S box was found to be the essential feature conferring NLRC5 specificity. These results broaden our knowledge on the transcriptional activities of NLRC5 and CIITA, revealing their dependence on shared enhanceosome factors but their recruitment to distinct enhancer motifs in vivo. Furthermore, we demonstrated selectivity of NLRC5 for genes encoding MHCI or related proteins, rendering it an attractive target for therapeutic intervention. NLRC5 and CIITA thus emerge as paradigms for a novel class of transcriptional regulators dedicated for transactivating extremely few, phylogenetically related genes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1371/journal.pgen.1005088DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4374748PMC
March 2015

Unravelling the cross-talk between iron starvation and oxidative stress responses highlights the key role of PerR (alr0957) in peroxide signalling in the cyanobacterium Nostoc PCC 7120.

Environ Microbiol Rep 2014 Oct;6(5):468-75

The cyanobacterial phylum includes oxygenic photosynthetic prokaryotes of a wide variety of morphologies, metabolisms and ecologies. Their adaptation to their various ecological niches is mainly achieved by sophisticated regulatory mechanisms and depends on a fine cross-talk between them. We assessed the global transcriptomic response of the filamentous cyanobacterium Nostoc PCC 7120 to iron starvation and oxidative stress. More than 20% of the differentially expressed genes in response to iron stress were also responsive to oxidative stress. These transcripts include antioxidant proteins-encoding genes that confirms that iron depletion leads to reactive oxygen accumulation. The activity of the Fe-superoxide dismutase was not significantly decreased under iron starvation, indicating that the oxidative stress generated under iron deficiency is not a consequence of (SOD) deficiency. The transcriptional data indicate that the adaptation of Nostoc to iron-depleted conditions displays important differences with what has been shown in unicellular cyanobacteria. While the FurA protein that regulates the response to iron deprivation has been well characterized in Nostoc, the regulators in charge of the oxidative stress response are unknown. Our study indicates that the alr0957 (perR) gene encodes the master regulator of the peroxide stress. PerR is a peroxide-sensor repressor that senses peroxide by metal-catalysed oxidation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/1758-2229.12157DOI Listing
October 2014

Extensive remodeling of DC function by rapid maturation-induced transcriptional silencing.

Nucleic Acids Res 2014 Sep 7;42(15):9641-55. Epub 2014 Aug 7.

Department of Pathology and Immunology, University of Geneva Medical School, CH-1211 Geneva, Switzerland

The activation, or maturation, of dendritic cells (DCs) is crucial for the initiation of adaptive T-cell mediated immune responses. Research on the molecular mechanisms implicated in DC maturation has focused primarily on inducible gene-expression events promoting the acquisition of new functions, such as cytokine production and enhanced T-cell-stimulatory capacity. In contrast, mechanisms that modulate DC function by inducing widespread gene-silencing remain poorly understood. Yet the termination of key functions is known to be critical for the function of activated DCs. Genome-wide analysis of activation-induced histone deacetylation, combined with genome-wide quantification of activation-induced silencing of nascent transcription, led us to identify a novel inducible transcriptional-repression pathway that makes major contributions to the DC-maturation process. This silencing response is a rapid primary event distinct from repression mechanisms known to operate at later stages of DC maturation. The repressed genes function in pivotal processes--including antigen-presentation, extracellular signal detection, intracellular signal transduction and lipid-mediator biosynthesis--underscoring the central contribution of the silencing mechanism to rapid reshaping of DC function. Interestingly, promoters of the repressed genes exhibit a surprisingly high frequency of PU.1-occupied sites, suggesting a novel role for this lineage-specific transcription factor in marking genes poised for inducible repression.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/nar/gku674DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4150779PMC
September 2014

Transcriptome-wide analyses of 5'-ends in RNase J mutants of a gram-positive pathogen reveal a role in RNA maturation, regulation and degradation.

PLoS Genet 2014 Feb 27;10(2):e1004207. Epub 2014 Feb 27.

Department of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland.

RNA decay and maturation have in recent years been recognised as major regulatory mechanisms in bacteria. In contrast to Escherichia coli, the Firmicute (Gram-positive) bacteria often do not encode the well-studied endonuclease RNase E, but instead rely on the endonucleases RNase Y, RNase J1 and RNase J2, of which the latter two have additionally been shown to have 5' to 3' exonucleolytic activity. We have previously demonstrated that these RNases could be deleted individually in the pathogenic Firmicute Staphylococcus aureus; however, we here present that, outside a narrow permissive window of growth conditions, deleting one or both of the RNase J genes presents serious difficulties for the cell. Moreover, an active site mutant of RNase J1 behaved like a deletion, whereas no phenotypes were detected for the RNase J2 active site mutant. Furthermore, in order to study the in vivo enzymatic activity of RNase J1 and J2, a method was developed to map the exact 5'-ends of mature and processed RNA, on a global scale. An enrichment of 5' RNA ends could be seen in the RNase J mutants, suggesting that their exonucleolytic activity is crucial for normal degradation of bulk RNA. Using the data to examine specific RNAs, we demonstrated that RNase J activity is needed for correct 5' maturation of both the 16S rRNA and the RNase P ribozyme, and can also inactivate the latter, possibly as quality control. Additional examples show that RNase J perform initial cleavages, apparently competing with ribosomes for access to mRNAs. The novel 5' mapping assay offers an exceptionally detailed view of RNase activity, and reveals that the roles of RNase J proteins are diverse, ranging from maturation and post-transcriptional regulation to degradation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1371/journal.pgen.1004207DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3937233PMC
February 2014

Protein kinases and phosphatases involved in the acclimation of the photosynthetic apparatus to a changing light environment.

Philos Trans R Soc Lond B Biol Sci 2012 Dec;367(1608):3466-74

Departments of Molecular Biology and Plant Biology, University of Geneva, 30 Quai Ernest Ansermet, Geneva 4, Switzerland.

Photosynthetic organisms are subjected to frequent changes in light quality and quantity and need to respond accordingly. These acclimatory processes are mediated to a large extent through thylakoid protein phosphorylation. Recently, two major thylakoid protein kinases have been identified and characterized. The Stt7/STN7 kinase is mainly involved in the phosphorylation of the LHCII antenna proteins and is required for state transitions. It is firmly associated with the cytochrome b(6)f complex, and its activity is regulated by the redox state of the plastoquinone pool. The other kinase, Stl1/STN8, is responsible for the phosphorylation of the PSII core proteins. Using a reverse genetics approach, we have recently identified the chloroplast PPH1/TAP38 and PBPC protein phosphatases, which counteract the activity of STN7 and STN8 kinases, respectively. They belong to the PP2C-type phosphatase family and are conserved in land plants and algae. The picture that emerges from these studies is that of a complex regulatory network of chloroplast protein kinases and phosphatases that is involved in light acclimation, in maintenance of the plastoquinone redox poise under fluctuating light and in the adjustment to metabolic needs.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1098/rstb.2012.0064DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3497069PMC
December 2012

State transitions at the crossroad of thylakoid signalling pathways.

Photosynth Res 2010 Nov 9;106(1-2):33-46. Epub 2010 Mar 9.

Department of Molecular Biology and Plant Biology, University of Geneva, 30, Quai Ernest Ansermet, 1211 Geneva, Switzerland.

In order to maintain optimal photosynthetic activity under a changing light environment, plants and algae need to balance the absorbed light excitation energy between photosystem I and photosystem II through processes called state transitions. Variable light conditions lead to changes in the redox state of the plastoquinone pool which are sensed by a protein kinase closely associated with the cytochrome b(6)f complex. Preferential excitation of photosystem II leads to the activation of the kinase which phosphorylates the light-harvesting system (LHCII), a process which is subsequently followed by the release of LHCII from photosystem II and its migration to photosystem I. The process is reversible as dephosphorylation of LHCII on preferential excitation of photosystem I is followed by the return of LHCII to photosystem II. State transitions involve a considerable remodelling of the thylakoid membranes, and in the case of Chlamydomonas, they allow the cells to switch between linear and cyclic electron flow. In this alga, a major function of state transitions is to adjust the ATP level to cellular demands. Recent studies have identified the thylakoid protein kinase Stt7/STN7 as a key component of the signalling pathways of state transitions and long-term acclimation of the photosynthetic apparatus. In this article, we present a review on recent developments in the area of state transitions.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s11120-010-9538-8DOI Listing
November 2010

Stt7-dependent phosphorylation during state transitions in the green alga Chlamydomonas reinhardtii.

Mol Cell Proteomics 2010 Jun 1;9(6):1281-95. Epub 2010 Feb 1.

Department of Molecular Biology and Plant Biology, University of Geneva, 1211 Geneva, Switzerland.

Photosynthetic organisms are able to adapt to changes in light conditions by balancing the light excitation energy between the light-harvesting systems of photosystem (PS) II and photosystem I to optimize the photosynthetic yield. A key component in this process, called state transitions, is the chloroplast protein kinase Stt7/STN7, which senses the redox state of the plastoquinone pool. Upon preferential excitation of photosystem II, this kinase is activated through the cytochrome b(6)f complex and required for the phosphorylation of the light-harvesting system of photosystem II, a portion of which migrates to photosystem I (state 2). Preferential excitation of photosystem I leads to the inactivation of the kinase and to dephosphorylation of light-harvesting complex (LHC) II and its return to photosystem II (state 1). Here we compared the thylakoid phosphoproteome of the wild-type strain and the stt7 mutant of Chlamydomonas under state 1 and state 2 conditions. This analysis revealed that under state 2 conditions several Stt7-dependent phosphorylations of specific Thr residues occur in Lhcbm1/Lhcbm10, Lhcbm4/Lhcbm6/Lhcbm8/Lhcbm9, Lhcbm3, Lhcbm5, and CP29 located at the interface between PSII and its light-harvesting system. Among the two phosphorylation sites detected specifically in CP29 under state 2, one is Stt7-dependent. This phosphorylation may play a crucial role in the dissociation of CP29 from PSII and/or in its association to PSI where it serves as a docking site for LHCII in state 2. Moreover, Stt7 was required for the phosphorylation of the thylakoid protein kinase Stl1 under state 2 conditions, suggesting the existence of a thylakoid protein kinase cascade. Stt7 itself is phosphorylated at Ser(533) in state 2, but analysis of mutants with a S533A/D change indicated that this phosphorylation is not required for state transitions. Moreover, we also identified phosphorylation sites that are redox (state 2)-dependent but independent of Stt7 and additional phosphorylation sites that are redox-independent.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1074/mcp.M000020-MCP201DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2877987PMC
June 2010

Analysis of the chloroplast protein kinase Stt7 during state transitions.

PLoS Biol 2009 Mar;7(3):e45

Department of Molecular Biology University of Geneva, Geneva, Switzerland.

State transitions allow for the balancing of the light excitation energy between photosystem I and photosystem II and for optimal photosynthetic activity when photosynthetic organisms are subjected to changing light conditions. This process is regulated by the redox state of the plastoquinone pool through the Stt7/STN7 protein kinase required for phosphorylation of the light-harvesting complex LHCII and for the reversible displacement of the mobile LHCII between the photosystems. We show that Stt7 is associated with photosynthetic complexes including LHCII, photosystem I, and the cytochrome b6f complex. Our data reveal that Stt7 acts in catalytic amounts. We also provide evidence that Stt7 contains a transmembrane region that separates its catalytic kinase domain on the stromal side from its N-terminal end in the thylakoid lumen with two conserved Cys that are critical for its activity and state transitions. On the basis of these data, we propose that the activity of Stt7 is regulated through its transmembrane domain and that a disulfide bond between the two lumen Cys is essential for its activity. The high-light-induced reduction of this bond may occur through a transthylakoid thiol-reducing pathway driven by the ferredoxin-thioredoxin system which is also required for cytochrome b6f assembly and heme biogenesis.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1371/journal.pbio.1000045DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2650728PMC
March 2009

Iron starvation leads to oxidative stress in Anabaena sp. strain PCC 7120.

J Bacteriol 2005 Sep;187(18):6596-8

Laboratoire de Chimie Bactérienne, IBSM-CNRS, 31 chemin Joseph Aiguier, 13402 Marseille cedex 20, France.

We establish here that iron deficiency causes oxidative stress in the cyanobacterium Anabaena sp. strain PCC 7120. Iron starvation leads to a significant increase in reactive oxygen species, whose effect can be abolished by treatment with the antioxidant tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl). Oxidative stress induced by iron starvation could be a common feature of photosynthetic bacteria.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1128/JB.187.18.6596-6598.2005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1236655PMC
September 2005

Inferring the connectivity of a regulatory network from mRNA quantification in Synechocystis PCC6803.

Nucleic Acids Res 2005 8;33(10):3381-9. Epub 2005 Jun 8.

Laboratoire Adaptation et Pathogénie des Micro-Organismes, CNRS UMR5163 Université Joseph Fourier Bâtiment Jean Roget, Faculté Médecine-Pharmacie, Domaine de la Merci 38700 La Tronche, France.

A major task of contemporary biology is to understand and predict the functioning of regulatory networks. We use expression data to deduce the regulation network connecting the sigma factors of Synechocystis PCC6803, the most global regulators in bacteria. Synechocystis contains one group 1 (SigA) and four group 2 (SigB, SigC, SigD and SigE) sigma factors. From the relative abundance of the sig mRNA measured in the wild-type and the four group 2 sigma mutants, we derive a network of the influences of each sigma factor on the transcription of all other sigma factors. Internal or external stimuli acting on only one of the sigma factors will thus indirectly modify the expression of most of the others. From this model, we predict the control points through which the circadian time modulates the expression of the sigma factors. Our results show that the cross regulation between the group 1 and group 2 sigma factors is very important for the adaptation of the bacterium to different environmental and physiological conditions.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1093/nar/gki654DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1145192PMC
June 2005