Identification and categorization of inducible mast cell genes in a subtraction library

Applying genomics tools to identify therapeutic targets for asthma

Asthma is a chronic inflammatory disease of the airways, the susceptibility to which is strongly influenced by genetics. Genomics, the study of the human genome, is redefining the process for rapidly identifying novel therapeutic targets for asthma and other diseases. One approach is to search for polymorphisms in genes that increase susceptibility to the disease in order to identify genes and cellular pathways relevant to the disease process. In asthma, for example, regardless of the genetic factors that contribute to susceptibility, good drug targets could be found that affect epithelial integrity, allergic response, and the recruitment or activity of inflammatory cells. Such targets may consist of proteins that are specifically expressed in certain cell types, proteins whose expression is regulated during the disease process or proteins involved in the destructive process. This review discusses some of the genomics tools that can be used to identify new molecular targets, which in turn are useful in screening for novel compounds likely to affect diseases such as asthma.

TLR3-induced activation of mast cells modulates CD8+ T-cell recruitment

Mast cells play an important role in host defense against various pathogens, but their role in viral infection has not been clarified in detail. dsRNA, synthesized by various types of viruses and mimicked by polyinosinic-polycytidylic acid (poly(I:C)) is recognized by Toll-like receptor 3 (TLR3). In this study, we demonstrate that poly(I:C) injection in vivo potently stimulates peritoneal mast cells to up-regulate a number of different costimulatory molecules. Therefore, we examined the expression and the functional significance of TLR3 activation in mast cells. Mast cells express TLR3 on the cell surface and intracellularly. After stimulation of mast cells with poly(I:C) and Newcastle disease virus (NDV), TLR3 is phosphorylated and the expression of key antiviral response cytokines (interferon beta, ISG15) and chemokines (IP10, RANTES) is upregulated. Interestingly, mast cells activated via TLR3-poly(I:C) potently stimulate CD8+ T-cell recruitment. Indeed, mast-cell-deficient mice (KitW/KitW-v) given an intraperitoneal injection of poly(I:C) show a decreased CD8+ T-cell recruitment, whereas granulocytes normally migrate to the peritoneal cavity. Mast-cell reconstitution of KitW/KitW-v mice normalizes the CD8+ T-cell influx. Thus, mast cells stimulated through engagement of TLR3 are potent regulators of CD8+ T-cell activities in vitro and in vivo.

Strategies for identifying genes that play a role in spinal cord regeneration

A search for genes that promote or block CNS regeneration requires numerous approaches; for example, tests can be made on individual candidate molecules. Here, however, we describe methods for comprehensive identification of genes up- and down-regulated in neurons that can and cannot regenerate after injury. One problem concerns identification of low-abundance genes out of the 30,000 or so genes expressed by neurons. Another difficulty is knowing whether a single gene or multiple genes are necessary. When microchips and subtractive differential display are used to identify genes turned on or off, the numbers are still too great to test which molecules are actually important for regeneration. Candidates are genes coding for trophic, inhibitory, receptor and extracellular matrix molecules, as well as unknown genes. A preparation useful for narrowing the search is the neonatal opossum. The spinal cord and optic nerve can regenerate after injury at 9 days but cannot at 12 days after birth. This narrow window allows genes responsible for the turning off of regeneration to be identified. As a next step, sites at which they are expressed (forebrain, midbrain, spinal cord, neurons or glia, intracellular or extracellular) must be determined. An essential step is to characterize proteins, their levels of expression, and their importance for regeneration. Comprehensive searches for molecular mechanisms represent a lengthy series of experiments that could help in devising strategies for repairing injured spinal cord.

Plasminogen activator inhibitor-1 in the pathogenesis of asthma

Plasminogen activator inhibitor (PAI)-1 is the main inhibitor of the fibrinolytic system and is known to play an essential role in tissue remodeling. Recent evidence indicates that chronic asthma may lead to tissue remodeling such as subepithelial fibrosis and extracellular matrix (ECM) deposition in the airways. However, the role of PAI-1 in asthma is unknown. Recently the mast cell (MC), which plays a major role in asthma, was found as a novel source of PAI-1, and a large number of MCs expressing PAI-1 are infiltrated in the airways of patients with severe asthma. Furthermore, PAI-1-deficient mice show reduced ECM deposition in the airways of a murine model of chronic asthma by inhibiting MMP-9 activity and fibrinolysis. In a human study, the 4G allele frequency was significantly higher in the asthmatic patients than in the control group. In view of the findings that the 4G allele is associated with elevated plasma PAI-1 level, elevated PAI-1 level in the lung may contribute to the development of asthma. In summary, PAI-1 may play an important role in the pathogenesis of asthma and further studies evaluating the mechanisms of PAI-1 action may lead to the development of a novel therapeutic target for the treatment and prevention of asthma.

Transcriptional response of human mast cells stimulated via the Fc(epsilon)RI and identification of mast cells as a source of IL-11

BACKGROUND

In asthma and other allergic disorders, the activation of mast cells by IgE and antigen induces the cells to release histamine and other mediators of inflammation, as well as to produce certain cytokines and chemokines. To search for new mast cell products, we used complementary DNA microarrays to analyze gene expression in human umbilical cord blood-derived mast cells stimulated via the high-affinity IgE receptor (Fc(epsilon)RI).

RESULTS

One to two hours after Fc(epsilon)RI-dependent stimulation, more than 2,400 genes (about half of which are of unknown function) exhibited 2-200 fold changes in expression. The transcriptional program included changes in the expression of IL-11 and at least 30 other cytokines and chemokines. Human mast cells secreted 130-529 pg of IL-11/106 cells by 6 h after stimulation with anti-IgE.

CONCLUSION

Our initial analysis of the transcriptional program induced in in vitro-derived human mast cells stimulated via the Fc(epsilon)RI has identified many products that heretofore have not been associated with this cell type, but which may significantly influence mast cell function in IgE-associated host responses. We also have demonstrated that mast cells stimulated via the Fc(epsilon)RI can secrete IL-11. Based on the previously reported biological effects of IL-11, our results suggest that production of IL-11 may represent one link between IgE-dependent mast cell activation in subjects with allergic asthma and the development of a spectrum of structural changes in the airways of these individuals; such changes, collectively termed "airway remodeling," can constitute an important long term consequence of asthma.

Upregulation of collagens detected by gene array in a model of flow-induced pulmonary vascular remodeling

We recently reported localized increased pulmonary arterial resistance, neointimal lesions, and medial thickening induced by aortopulmonary anastomosis in young pigs. This model was used to investigate changes in expression of genes potentially involved in pulmonary vascular remodeling employing a high throughput Atlas Human Cardiovascular Array carrying approximately 600 cardiovascular-related cDNA sequences. Data were confirmed by Northern analysis, Western blots, and histological examination. With the use of lower stringency conditions for hybridization, 56% of the 588 human genes on the array showed visible signal after autoradiography. Approximately 10% of the genes with visible hybridization were altered by shunt-induced high flow. Extracellular matrix and cell adhesion molecules were the most highly represented group of upregulated genes. To our knowledge, our data are the first to demonstrate flow-induced changes in gene expression using a combination of cross species cDNA arrays, homologous hybridization, immunospecific protein, and histology. Our observations expand the list of genes as putative candidates in pulmonary vascular remodeling and support the utility of cross-species microarray analysis in such applications.

Chemical reverse transformation of CHO-K1 cells induces changes in expression of a candidate tumour suppressor and of a gene not previously characterised as transformation related

Chemical reverse transformation of CHO-K1 and other cells is a well-established phenomenon, in which oncogenically transformed cells re-acquire fibroblastoid morphology, contact inhibition and anchorage-dependent growth, in response to cyclic AMP and other agents. A limited number of changes in gene transcription and enzyme activity have been demonstrated to coincide with these morphological and physiological changes. We have used a partial differential display to identify four genes that are transcriptionally modulated in reverse transformation. One of these, encoding ribosomal protein S18, is transcriptionally suppressed, probably as a result of the detransforming process. Three others are transcriptionally activated. One has homology to NADH-ubiquinone oxidoreductase chain 4 protein, and is also probably changed as a result of the detransforming process. Another is homologous to a human sequence which encodes a 27 kDa protein, p27(BBP/eIF6), that is involved in the biogenesis of 60S ribosomal subunit, and in cell lines of epithelial origin binds to beta integrin. This has not previously been described as transformation-related, and could have a causative role in reverse transformation. The third has homology, with transcriptional or processing variations, to a human genomic sequence, a positional candidate for a tumour suppressor gene, encoding the Krit1 protein which interacts with the Ras-family GTPase Krev-1.

Mast cells express connexins on their cytoplasmic membrane

BACKGROUND

Because of the close association between mast cells and fibroblasts in the microenvironment and the importance of connexins (Cxs) in fibroblast communication with other cells, we hypothesized that mast cells also express Cxs, allowing them to similarly communicate with other cells through gap junctions.

OBJECTIVES

We sought to identify the expression of Cxs (particularly Cx43, Cx32, and Cx26) by murine mast cells.

METHODS

The expression of Cxs was studied by RT-PCR, Northern blot analysis, Western blot analysis, flow cytometry, and confocal laser scanning microscopy.

RESULTS

In this report we demonstrate that murine bone marrow cultured mast cells and the growth factor-independent murine mast cell line C57, express Cx43 and Cx32 as assessed by RT-PCR, Northern blot analysis, Western blot analysis, and flow cytometry, but do not express Cx26. We also show, by confocal laser scanning microscopy, that Cx43 localizes to the cytoplasmic membrane of mast cells in a pattern similar to that seen in fibroblasts.

CONCLUSIONS

Mast cells express Cx43 and Cx32, and Cx43 is associated with the cytoplasmic membrane, suggesting that mast cells have the potential to communicate with other cells in their microenvironment in part through gap junctions.

Characterization of gene expression in resting and activated mast cells

To characterize gene expression in activated mast cells more comprehensively than heretofore, we surveyed the changes in genetic transcripts by the method of serial analysis of gene expression in the RBL-2H3 line of rat mast cells before and after they were stimulated through their receptors with high affinity for immunoglobulin E (FcepsilonRI). A total of 40,759 transcripts derived from 11,300 genes were analyzed. Among the diverse genes that had not been previously associated with mast cells and that were constitutively expressed were those for the cytokine macrophage migration inhibitory factor neurohormone receptors such as growth hormone- releasing factor and melatonin and components of the exocytotic machinery. In addition, several dozen transcripts were differentially expressed in response to antigen-induced clustering of the FcepsilonRI. Included among these were the genes for preprorelaxin, mitogen-activated protein kinase kinase 3, and the dual specificity protein phosphatase, rVH6. Significantly, the majority of genes differentially expressed in this well-studied model of mast cell activation have not been identified before this analysis.