Mahir Karababa

University Hospital of Lausanne, Lausanne, VD, Switzerland

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Publications (6)27.01 Total impact

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    ABSTRACT: Because IL-1beta plays an important role in inflammation in human and murine arthritis, we investigated the contribution of the inflammasome components ASC, NALP-3, IPAF, and caspase-1 to inflammatory arthritis. We first studied the phenotype of ASC-deficient and wild-type mice during Ag-induced arthritis (AIA). ASC(-/-) mice showed reduced severity of AIA, decreased levels of synovial IL-1beta, and diminished serum amyloid A levels. In contrast, mice deficient in NALP-3, IPAF, or caspase-1 did not show any alteration of joint inflammation, thus indicating that ASC associated effects on AIA are independent of the classical NALP-3 or IPAF inflammasomes. Because ASC is a ubiquitous cytoplasmic protein that has been implicated in multiple cellular processes, we explored other pathways through which ASC may modulate inflammation. Ag-specific proliferation of lymph node and spleen cells from ASC-deficient mice was significantly decreased in vitro, as was the production of IFN-gamma, whereas IL-10 production was enhanced. TCR ligation by anti-CD3 Abs in the presence or absence of anti-CD28 Abs induced a reduction in T cell proliferation in ASC(-/-) T cells compared with wild-type ones. In vivo lymph node cell proliferation was also significantly decreased in ASC(-/-) mice, but no effects on apoptosis were observed either in vitro or in vivo in these mice. In conclusion, these results strongly suggest that ASC modulates joint inflammation in AIA through its effects on cell-mediated immune responses but not via its implication in inflammasome formation.
    The Journal of Immunology 10/2009; 183(6):4003-12. · 5.52 Impact Factor
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    ABSTRACT: Nicotinamide phosphoribosyltransferase (NAMPT), also known as visfatin, is the rate-limiting enzyme in the salvage pathway of NAD biosynthesis from nicotinamide. Since its expression is upregulated during inflammation, NAMPT represents a novel clinical biomarker in acute lung injury, rheumatoid arthritis, and Crohn's disease. However, its role in disease progression remains unknown. We report here that NAMPT is a key player in inflammatory arthritis. Increased expression of NAMPT was confirmed in mice with collagen-induced arthritis, both in serum and in the arthritic paw. Importantly, a specific competitive inhibitor of NAMPT effectively reduced arthritis severity with comparable activity to etanercept, and decreased pro-inflammatory cytokine secretion in affected joints. Moreover, NAMPT inhibition reduced intracellular NAD concentration in inflammatory cells and circulating TNFalpha levels during endotoxemia in mice. In vitro pharmacological inhibition of NAMPT reduced the intracellular concentration of NAD and pro-inflammatory cytokine secretion by inflammatory cells. Thus, NAMPT links NAD metabolism to inflammatory cytokine secretion by leukocytes, and its inhibition might therefore have therapeutic efficacy in immune-mediated inflammatory disorders.
    PLoS ONE 02/2008; 3(5):e2267. · 3.53 Impact Factor
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    ABSTRACT: In Candida albicans UTR2 (CSF4), CRH11, and CRH12 are members of a gene family (the CRH family) that encode glycosylphosphatidylinositol-dependent cell wall proteins with putative transglycosidase activity. Deletion of genes of this family resulted in additive sensitivity to compounds interfering with normal cell wall formation (Congo red, calcofluor white, SDS, and high Ca(2+) concentrations), suggesting that these genes contribute to cell wall organization. A triple mutant lacking UTR2, CRH11, and CRH12 produced a defective cell wall, as inferred from increased sensitivity to cell wall-degrading enzymes, decreased ability of protoplasts to regenerate a new wall, constitutive activation of Mkc1p, the mitogen-activated protein kinase of the cell wall integrity pathway, and an increased chitin content of the cell wall. Importantly, this was accompanied by a decrease in alkali-insoluble 1,3-beta-glucan but not total glucan content, suggesting that formation of the linkage between 1,3-beta-glucan and chitin might be affected. In support of this idea, localization of a Utr2p-GFP fusion protein largely coincided with areas of chitin incorporation in C. albicans. As UTR2 and CRH11 expression is regulated by calcineurin, a serine/threonine protein phosphatase involved in tolerance to antifungal drugs, cell wall morphogenesis, and virulence, this points to a possible relationship between calcineurin and the CRH family. Deletion of UTR2, CRH11, and CRH12 resulted in only a partial overlap with calcineurin-dependent phenotypes, suggesting that calcineurin has additional targets. Interestingly, cells deleted for UTR2, CRH11, and CRH12 were, like a calcineurin mutant, avirulent in a mouse model of systemic infection but retained the capacity to colonize target organs (kidneys) as the wild type. In conclusion, this work establishes the role of UTR2, CRH11, and CRH12 in cell wall organization and integrity.
    Journal of Biological Chemistry 01/2007; 281(52):40399-411. · 4.65 Impact Factor
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    ABSTRACT: Calcineurin is a major player in calcium-dependent signal transduction pathways of eukaryotes. Calcineurin acts on transcription factors (e.g. CRZ1 in Saccharomyces cerevisiae) and governs the expression of genes in a species-dependent fashion. In Candida albicans, the calcineurin pathway is involved in tolerance to antifungal agents, cation homeostasis and virulence. However, the components of the calcineurin pathway are still poorly investigated in this yeast species. Taking S. cerevisiae as a model to reconstitute this pathway, two CRZ1-like genes, CRZ1 and CRZ2 (for calcineurin-responsive zinc finger 1 and 2 genes), were found with C(2)H(2) zinc finger domains. Only CRZ1 was able to restore the calcium hypersusceptibility of a S. cerevisiae crz1Delta mutant and to mediate calcium-dependent gene expression in this yeast species. Several experiments showed that CRZ1 was dependent on calcineurin in C. albicans: (i) phenotypic analysis of a crz1Delta/Delta mutant showed impaired growth as compared with the wild type in the presence of cations (Ca(2+), Mn(2+)) as does a mutant lacking calcineurin subunit A (cnaDelta/Delta) and (ii) a green fluorescent protein (GFP)-Crz1p fusion protein showed a calcium- and calcineurin-dependent nuclear localization. To further analyse the relationship between calcineurin and CRZ1, a comprehensive analysis of calcineurin/Crz1p-dependent gene expression following addition of Ca(2+) (200 mM) was performed. Among the expression of 264 genes altered by at least twofold, the upregulation of 60 genes was dependent on both calcineurin and CRZ1. Interestingly, a motif [5'-G(C/T)GGT-3'] with similarity to the target sequence of Crz1p (GNGGCG/TCA) from S. cerevisiae was identified as a putative regulatory sequence in the upstream regions of these calcineurin/Crz1p-dependent genes. However, additional experiments showed that calcineurin may have other targets in addition to CRZ1. First, CRZ1 was not involved in tolerance to antifungal agents (fluconazole, terbinafine) on the opposite to calcineurin. Second, CRZ1 was only moderately influencing virulence in a mice model of infection which is in sharp contrast to the strong avirulence of cnaDelta/Delta mutant in the same animal model. Even though this work establishes CRZ1 as a calcineurin target, further studies are needed to identify other calcineurin-dependent elements in C. albicans.
    Molecular Microbiology 04/2006; 59(5):1429-51. · 4.96 Impact Factor
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    ABSTRACT: The ABC transporter genes CDR1 and CDR2 can be upregulated in Candida albicans developing resistance to azoles or can be upregulated by exposing cells transiently to drugs such as fluphenazine. The cis-acting drug-responsive element (DRE) present in the promoters of both genes and necessary for their upregulation contains 5'-CGG-3' triplets that are often recognized by transcriptional activators with Zn(2)-Cys(6) fingers. In order to isolate regulators of CDR1 and CDR2, the C. albicans genome was searched for genes encoding proteins with Zn(2)-Cys(6) fingers. Interestingly, three of these genes were tandemly arranged near the mating locus. Their involvement in CDR1 and CDR2 upregulation was addressed because a previous study demonstrated a link between mating locus homozygosity and azole resistance. The deletion of only one of these genes (orf19.3188) was sufficient to result in a loss of transient CDR1 and CDR2 upregulation by fluphenazine and was therefore named TAC1 (transcriptional activator of CDR genes). Tac1p has a nuclear localization, and a fusion of Tac1p with glutathione S-transferase could bind the cis-acting regulatory DRE in both the CDR1 and the CDR2 promoters. TAC1 is also relevant for azole resistance, since a TAC1 allele (TAC1-2) recovered from an azole-resistant strain could trigger constitutive upregulation of CDR1 and CDR2 in an azole-susceptible laboratory strain. Transcript profiling experiments performed with a TAC1 mutant and a revertant containing TAC1-2 revealed not only CDR1 and CDR2 as targets of TAC1 regulation but also other genes (RTA3, IFU5, and HSP12) that interestingly contained a DRE-like element in their promoters. In conclusion, TAC1 appears to be the first C. albicans transcription factor involved in the control of genes mediating antifungal resistance.
    Eukaryotic Cell 01/2005; 3(6):1639-52. · 3.59 Impact Factor
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    ABSTRACT: Azole resistance in Candida albicans can be due to upregulation of multidrug transporters belonging to ABC (ATP-binding cassette) transporters (CDR1 and CDR2) or major facilitators (CaMDR1). Upregulation of these genes can also be achieved by exposure to fluphenazine, resulting in specific upregulation of CDR1 and CDR2 and by exposure to benomyl, resulting in specific CaMDR1 upregulation. In this study, these two different states of gene upregulation were used to determine coregulated genes that often share similar functions or similar regulatory regions. The transcript profiles of a laboratory strain exposed to these drugs were therefore determined and compared with those of two matched pairs of azole-susceptible and -resistant strains expressing CDR1 and CDR2 (CDR strains) or CaMDR1 (MDR isolates). The results obtained revealed that, among 42 commonly regulated genes (8.6% of all regulated genes) between fluphenazine-exposed cells and CDR isolates, the most upregulated were CDR1 and CDR2 as expected, but also IFU5, RTA3 (which encodes putative membrane proteins), HSP12 (which encodes heat shock protein), and IPF4065 (which is potentially involved in stress response). Interestingly, all but HSP12 and IPF4065 contain a putative cis-acting drug responsive element in their promoters. Among the 57 genes (11.5% of all regulated genes) commonly regulated between benomyl-exposed cells and MDR isolates, the most upregulated were CaMDR1 as expected but also genes with oxido-reductive functions such as IFD genes, IPF5987, GRP2 (all belonging to the aldo-keto reductase family), IPF7817 [NAD(P)H oxido-reductase], and IPF17186. Taken together, these results show that in vitro drug-induced gene expression only partially mimics expression profiles observed in azole-resistant clinical strains. Upregulated genes in both drug-exposed conditions and clinical strains are drug resistance genes but also genes that could be activated under cell damage conditions.
    Antimicrobial Agents and Chemotherapy 09/2004; 48(8):3064-79. · 4.57 Impact Factor