Induction of immunomodulator transcriptional responses by cholera toxin

Gene expression profiling identifies STAT3 as a novel pathway for immunomodulation by cholera toxin adjuvant

Earlier studies have reported on both proinflammatory and anti-inflammatory activities of cholera toxin (CT). As CT is a powerful adjuvant, we were interested in identifying genes with a possible involvement in these functions. A global gene expression analysis in mouse B cells showed that CT regulated <100 annotated genes, which encoded transcription factors, G proteins, cell-cycle regulators, and immunoregulating molecules. Interestingly, CT regulated the expression of the signal transducer and activator of transcription (STAT)3 gene and influenced the level and activation of both isoforms STAT3 alpha and STAT3 beta, in vitro in a B-cell line and in Peyer's patch (PP) B cells and in vivo in freshly isolated splenic B cells from CT-treated mice. This effect was cAMP dependent and was not seen with CTB. B cells pre-exposed to CT were significantly more susceptible to the activation of STAT3 by interleukin (IL)-6 and IL-10. This exerted a stronger inhibitory effect of IL-10 on lipopolysaccharide (LPS)-stimulated B-cell proliferation and cytokine production (IL-6). Moreover, IgG1 and IgA production induced by LPS and IL-10 were enhanced by the addition of CT to cultures of PP or splenic B cells. This is the first study to provide a molecular mechanism that can reconcile previous findings of proinflammatory and anti-inflammatory effects by CT adjuvant.

Toxins-useful biochemical tools for leukocyte research

Leukocytes are a heterogeneous group of cells that display differences in anatomic localization, cell surface phenotype, and function. The different subtypes include e.g., granulocytes, monocytes, dendritic cells, T cells, B cells and NK cells. These different cell types represent the cellular component of innate and adaptive immunity. Using certain toxins such as pertussis toxin, cholera toxin or clostridium difficile toxin, the regulatory functions of Gα_i, Gαs and small GTPases of the Rho family in leukocytes have been reported. A summary of these reports is discussed in this review.

Toxicogenomics: transcription profiling for toxicology assessment

Toxicogenomics, the application of transcription profiling to toxicology, has been widely used for elucidating the molecular and cellular actions of chemicals and other environmental stressors on biological systems, predicting toxicity before any functional damages, and classification of known or new toxicants based on signatures of gene expression. The success of a toxicogenomics study depends upon close collaboration among experts in different fields, including a toxicologist or biologist, a bioinformatician, statistician, physician and, sometimes, mathematician. This review is focused on toxicogenomics studies, including transcription profiling technology, experimental design, significant gene extraction, toxicological results interpretation, potential pathway identification, database input and the applications of toxicogenomics in various fields of toxicological study.

Bacterial exotoxins downregulate cathelicidin (hCAP-18/LL-37) and human beta-defensin 1 (HBD-1) expression in the intestinal epithelial cells

Cathelicidin (hCAP-18/LL-37) and beta-defensin 1 (HBD-1) are human antimicrobial peptides (AMPs) with high basal expression levels, which form the first line of host defence against infections over the epithelial surfaces. The antimicrobial functions owe to their direct microbicidal effects as well as the immunomodulatory role. Pathogenic microorganisms have developed multiple modalities including transcriptional repression to combat this arm of the host immune response. The precise mechanisms and the pathogen-derived molecules responsible for transcriptional downregulation remain unknown. Here, we have shown that enteric pathogens suppress LL-37 and HBD-1 expression in the intestinal epithelial cells (IECs) with Vibrio cholerae and enterotoxigenic Escherichia coli (ETEC) exerting the most dramatic effects. Cholera toxin (CT) and labile toxin (LT), the major virulence proteins of V. cholerae and ETEC, respectively, are predominantly responsible for these effects, both in vitro and in vivo. CT transcriptionally downregulates the AMPs by activating several intracellular signalling pathways involving protein kinase A (PKA), ERK MAPKinase and Cox-2 downstream of cAMP accumulation and inducible cAMP early repressor (ICER) may mediate this role of CT, at least in part. This is the first report to show transcriptional repression of the AMPs through the activation of cellular signal transduction pathways by well-known virulence proteins of pathogenic microorganisms.

2D-QSAR and HQSAR of the inhibition of calcineurin-NFAT signaling by blocking protein-protein interaction with N-(4-oxo-1(4H)-naphthalenylidene)benzenesulfonamide analogues

The inhibition of calcineurin-NFAT signaling by blocking protein-protein interaction with N-(4-oxo-1(4H)-naphthalenylidene)benzenesulfonamide analogues was studied in order to obtain mechanistic information about the effects of structural modification and molecular design of immunomodulation agents. The study was carried out by quantitative structure-activity relationship (QSAR) analysis using 2D-QSAR and hologram QSAR (HQSAR) methods. The statistical results of the two models showed the best prediction and fitness (r2 > 0.900) for the inhibition activities. The inhibitory activities from the 2D-QSAR models were dependent upon the electronic affinity of electron acceptor and optimum dipole moment (DM opt = 4.491 Debye). In addition, the HQSAR model provided information about which structural distinctions could be significant contributors the inhibition.

Toxicogenomics in the assessment of immunotoxicity

Microarray analysis is used for simultaneous measurement of expression of thousands of genes in a given sample and as such extends and deepens our understanding of biological processes. Application of the technique in toxicology is referred to as toxicogenomics. The examples of assessment of immunotoxicity by gene expression profiling presented and discussed here, show that microarray analysis is able to detect known and novel effects of a wide range of immunomodulating agents. Besides the elucidation of mechanisms of action, toxicogenomics is also applied to predict consequences of exposing biological systems to toxic agents. Successful attempts to classify compounds using signature gene expression profiles have been reported. These did, however, not specifically focus on immunotoxicity. Databases containing expression profiles can facilitate the applications of toxicogenomics. Platforms and methodologies for gene expression profiling may vary, however, hampering data compiling across different laboratories. Therefore, attention is paid to standardization of the generation, reporting, and management of microarray data. Obtained gene expression profiles should be anchored to pathological and functional endpoints for correct interpretation of results. These issues are also important when using toxicogenomics in risk assessment. The application of toxicogenomics in evaluation of immunotoxicity is thus not yet without challenges. It already contributes to the understanding of immunotoxic processes and the development of in vitro screening assays, though, and is therefore expected to be of value for mechanistic insight into immunotoxicity and hazard identification of existing and novel compounds.

Cholera toxin induced novel genes in human lymphocytes and monocytes

Cholera toxin (CT) is well known as an inducer of the accumulation of cellular cAMP through the ADP-ribosylation of the Gs protein by CT. CT is also one of the most powerful mucosal adjuvants. However, the molecular mechanisms of the CT adjuvanticity are not well understood. Here, the transcriptional responses of cultured human lymphocytes and monocytes in response to CT were analyzed using differential display-PCR. The full complement of cellular mRNA was examined by high resolution polyarylamide gel electrophoresis and sequence analyses of the PCR products of 240 primer sets. Over 100 genes with altered expression were initially identified. The expressions of 65 of these genes were further analyzed and confirmed using custom glass cDNA arrays, RT-PCR and real-time PCR. Immunomodulatory genes such as CD2, HIF1, CXCL2, L-plastin, LILR and IFI30 were affected by CT. In addition, 14 novel genes with previously unknown functions were found to be CT induced. These CT induced gene expression alterations provide more insight in the mechanisms of CT actions. The CT induced gene expressions alterations could contribute to the CT adjuvanticity.