Agonist- and T(H)2 cytokine-induced up-regulation of cysteinyl leukotriene receptor messenger RNA in human monocytes

A review of non-prostanoid, eicosanoid receptors: expression, characterization, regulation, and mechanism of action

Eicosanoid signaling controls a wide range of biological processes from blood pressure homeostasis to inflammation and resolution thereof to the perception of pain and to cell survival itself. Disruption of normal eicosanoid signaling is implicated in numerous disease states. Eicosanoid signaling is facilitated by G-protein-coupled, eicosanoid-specific receptors and the array of associated G-proteins. This review focuses on the expression, characterization, regulation, and mechanism of action of non-prostanoid, eicosanoid receptors.

Increased expression of bitter taste receptors in human allergic nasal mucosa and their contribution to the shrinkage of human nasal mucosa

OBJECTIVE

Bitter taste receptors (TAS2Rs) are expressed in the extraoral tissues, where they possess various physiological functions. This study is to characterize TAS2Rs expression in normal and allergic nasal mucosa and analyse nasal symptom after challenge with bitter tastes to evaluate their pathophysiological function in normal and allergic nasal mucosa.

METHODS

The expression levels of TAS2Rs (TAS2R4, 5, 7, 10, 14, 39, and 43) in nasal mucosa were investigated by real-time PCR, Western blot, and immunohistochemistry. The expression levels of TAS2Rs and Ca(2+) imaging in cultured epithelial cells were measured after stimulation with type 2 cytokines (IL-4, IL-5, and IL-13) or bitter tastes. Nasal symptoms in control subjects and allergic rhinitis patients using visual analogue score and acoustic rhinometry were evaluated before and after stimulation with bitter tastes. Vascular diameter of rat nasal septum was measured before and after treatment with bitter tastes.

RESULTS

TAS2Rs tested here were expressed in nasal mucosa where they were commonly distributed in superficial epithelium, submucosal glands, and endothelium. Their expression levels are increased in allergic nasal mucosa and up-regulated in cultured epithelial cells simulated with type 2 cytokines. After treatment with bitter tastes, intracellular Ca(2+) signalling was increased in cultured epithelial cells, and vascular constriction was found in rat nasal septum. Increased nasal patency was observed in human nasal mucosa without pain or sneezing.

CONCLUSION AND CLINICAL RELEVANCE

TAS2Rs are constitutively expressed in human nasal mucosa and their expression levels are increased in allergic nasal mucosa, where they could potentially contribute to shrinkage of normal and allergic nasal mucosa.

Cellular signalling of cysteinyl leukotriene type 1 receptor variants CysLT₁-G300S and CysLT₁-I206S

Cysteinyl-leukotrienes are pro-inflammatory lipid mediators, involved in allergic asthma, that bind the G-protein-coupled receptors CysLT1, CysLT2 and GPR99. A polymorphism in one of these receptors, CysLT1-G300S was strongly associated with atopy, whereas the CysLT1-I206S polymorphism was not. In the present work, our aim was to characterize these two variants by studying their cellular signalling. Cell surface expression of mutant receptors in transfected HEK-293 cells was comparable to that of the wild-type receptor. Compared to CysLT1-WT, production of inositol phosphates as well as IL-8 and IL-13 promoter transactivation in response to either LTD4 or LTC4 was significantly increased in CysLT1-G300S-transfected cells. Moreover, LTD4-induced phosphorylation of the signalling effector Erk, but not p38, p65 or c-Jun was higher in CysLT1-G300S-transfected cells. On the other hand, the variant CysLT1-I206S did not show a significant difference in its signal transduction compared to the wild-type receptor. Taken together, our results indicate that the variant CysLT1-G300S can induce a greater signal than the CysLT1-WT receptor, a feature that may be relevant to its association with atopy.

Pharmacotherapy in the management of asthma in the elderly: a review of clinical studies

Asthma in the elderly is a disease with emerging concern. Despite some recent advances in our understanding of epidemiology and pathophysiology, there is a considerable lack of clinical evidence specific to elderly patients. Currently available high quality clinical evidence has been mostly obtained from younger adults, but rarely from elderly patients. Under-representation of elderly patients in previous randomized trials may have been due to being, old age, or having comorbidities. Thus, a question may be raised whether current clinical evidence could be well generalized into elderly patients. Further clinical trials should address clinical issues raised in elderly population. In this review, we aimed to overview the efficacy and safety of pharmacological management, and also to summarize the literature relevant to elderly asthma.

Cysteinyl leukotrienes and their receptors; emerging concepts

Cysteinyl leukotrienes (cys-LTs) are potent mediators of inflammation derived from arachidonic acid through the 5-lipoxygenase/leukotriene C4 synthase pathway. The derivation of their chemical structures and identification of their pharmacologic properties predated the cloning of their classical receptors and the development of drugs that modify their synthesis and actions. Recent studies have revealed unanticipated insights into the regulation of cys-LT synthesis, the function of the cys-LTs in innate and adaptive immunity and human disease, and the identification of a new receptor for the cys-LTs. This review highlights these studies and summarizes their potential pathobiologic and therapeutic implications.

The cysteinyl leukotriene 2 receptor contributes to all-trans retinoic acid-induced differentiation of colon cancer cells

Background

Cysteinyl leukotrienes (CysLTs) are potent pro-inflammatory mediators that are increased in samples from patients with inflammatory bowel diseases (IBDs). Individuals with IBDs have enhanced susceptibility to colon carcinogenesis. In colorectal cancer, the balance between the pro-mitogenic cysteinyl leukotriene 1 receptor (CysLT₁R) and the differentiation-promoting cysteinyl leukotriene 2 receptor (CysLT₂R) is lost. Further, our previous data indicate that patients with high CysLT₁R and low CysLT₂R expression have a poor prognosis. In this study, we examined whether the balance between CysLT₁R and CysLT₂R could be restored by treatment with the cancer chemopreventive agent all-trans retinoic acid (ATRA).

Methods

To determine the effect of ATRA on CysLT₂R promoter activation, mRNA level, and protein level, we performed luciferase gene reporter assays, real-time polymerase chain reactions, and Western blots in colon cancer cell lines under various conditions.

Results

ATRA treatment induces CysLT₂R mRNA and protein expression without affecting CysLT₁R levels. Experiments using siRNA and mutant cell lines indicate that the up-regulation is retinoic acid receptor (RAR) dependent. Interestingly, ATRA also up-regulates mRNA expression of leukotriene C₄ synthase, the enzyme responsible for the production of the ligand for CysLT₂R. Importantly, ATRA-induced differentiation of colorectal cancer cells as shown by increased expression of MUC-2 and production of alkaline phosphatase, both of which could be reduced by a CysLT₂R-specific inhibitor.

Conclusions

This study identifies a novel mechanism of action for ATRA in colorectal cancer cell differentiation and demonstrates that retinoids can have anti-tumorigenic effects through their action on the cysteinyl leukotriene pathway.

Localization and up-regulation of cysteinyl leukotriene-2 receptor in human allergic nasal mucosa

BACKGROUND

Cysteinyl leukotrienes (CysLTs) are lipid mediators that have been implicated in the pathogenesis of allergic rhinitis. Pharmacological studies using CysLTs indicate that 2 classes of receptors exist, namely, CysLT1 and CysLT2 receptors. The former class of receptors is sensitive to the CysLT1 antagonists currently used to treat asthma and allergic rhinitis, and its localization has been previously examined by our group using immunohistochemistry and in situ hybridization techniques. We investigated the expression and localization of the CysLT2 receptor in human nasal mucosa by western blot and immunohistochemical analyses.

METHODS

Human turbinates were obtained after turbinectomy from 16 patients with nasal obstruction refractory to medical therapy. To identify the cells expressing the CysLT2 receptor, double immunostaining was performed by using anti-CysLT2 receptor antibody and anti-CD31 (endothelial cell) antibody or anti-smooth muscle actin antibody.

RESULTS

A 39 kDa band was detected on the western blots of human turbinates samples by using the anti-CysLT2 receptor antibody. The expression level of the CysLT2 receptor in patients with nasal allergy was higher than that in patients with non-allergic rhinitis. The immunohistochemical study also showed an intense immunoreactivity for CysLT2 receptor in both vascular endothelial cells and vascular smooth muscles.

CONCLUSIONS

The results indicated that the CysLT2 receptor plays a primary role in the vascular responses in the upper respiratory tract.

Regulation of cysteinyl leukotriene receptor 2 expression--a potential anti-tumor mechanism

Background

The cysteinyl leukotrienes receptors (CysLTRs) are implicated in many different pathological conditions, such as inflammation and cancer. We have previously shown that colon cancer patients with high CysLT₁R and low CysLT₂R expression demonstrate poor prognosis. Therefore, we wanted to investigate ways for the transcriptional regulation of CysLT₂R, which still remains to be poorly understood.

Methodology/Principal Findings

We investigated the potential role of the anti-tumorigenic interferon α (IFN-α) and the mitogenic epidermal growth factor (EGF) on CysLT₂R regulation using non-transformed intestinal epithelial cell lines and colon cancer cells to elucidate the effects on the CysLT₂R expression and regulation. This was done using Western blot, qPCR, luciferase reporter assay and a colon cancer patient array. We found a binding site for the transcription factor IRF-7 in the putative promoter region of CysLT₂R. This site was involved in the IFN-α induced activity of the CysLT₂R luciferase reporter assay. In addition, IFN-α induced the activity of the differentiation marker alkaline phosphatase along with the expression of mucin-2, which protects the epithelial layer from damage. Interestingly, EGF suppressed both the expression and promoter activity of the CysLT₂R. E-boxes present in the CysLT₂R putative promoter region were involved in the suppressing effect. CysLT₂R signaling was able to suppress cell migration that was induced by EGF signaling.

Conclusions/Significance

The patient array showed that aggressive tumors generally expressed less IFN-α receptor and more EGFR. Interestingly, there was a negative correlation between CysLT₂R and EGFR expression. Our data strengthens the idea that there is a protective role against tumor progression for CysLT₂R and that it highlights new possibilities to regulate the CysLT₂R.

IL-2-controlled expression of multiple T cell trafficking genes and Th2 cytokines in the regulatory T cell-deficient scurfy mice: implication to multiorgan inflammation and control of skin and lung inflammation

Scurfy (Sf) mice bear a mutation in the Foxp3 transcription factor, lack regulatory T cells (Treg), develop multiorgan inflammation, and die prematurely. The major target organs affected are skin, lungs, and liver. “Sf mice lacking the Il2 gene (Sf.Il2–/–), despite being devoid of Treg, did not develop skin and lung inflammation, but the inflammation in liver remained [corrected]. Genome-wide microarray analysis revealed hundreds of genes that were differentially regulated among Sf, Sf.Il2(-/-), and B6 CD4(+) T cells, but the most significant changes were those encoding receptors for trafficking/chemotaxis/retention and cytokines. Our study suggests that IL-2 controls the skin and lung inflammation in Sf mice in an apparent "organ-specific" manner through two novel mechanisms: by regulating the expression of genes encoding a variety of receptors for T cell trafficking/chemotaxis/retention and by regulating Th2 cell expansion and cytokine production. Thus, IL-2 is potentially a master regulator for multiorgan inflammation and an underlying etiological factor for various diseases associated with skin and lung inflammation.

On the biosynthesis and biological role of eoxins and 15-lipoxygenase-1 in airway inflammation and Hodgkin lymphoma

This mini-review is focused on the enzyme 15-lipoxygenase-1 (15-LO-1) and eoxins in airway inflammatory diseases and Hodgkin lymphoma. Several studies have demonstrated increased expression and activity of 15-LO-1 in the respiratory tissue from asthma patients , indicating a pathophysiological role of this enzyme in airway inflammation. Eoxins were recently identified as pro-inflammatory metabolites of arachidonic acid, formed through the 15-LO-1 pathway, in human eosinophils, mast cells, airway epithelial cells and Hodgkin lymphoma. Mice deficient of 12/15-LO, the ortholog to human 15-LO-1, had an attenuated allergic airway inflammation compared to wild type controls, also indicating a pathophysiological role of this enzyme in respiratory inflammation. The putative therapeutic implications of 15-LO-1 inhibitors in the treatment of asthma, chronic obstructive pulmonary disorder and Hodgkin lymphoma are discussed.

Cysteinyl leukotriene receptor CysLT1 as a novel therapeutic target for allergic rhinitis treatment

BACKGROUND

Cysteinyl leukotrienes (cys-LTs) play an important role in allergic rhinitis because CysLT(1) receptor antagonists relieve the symptoms of allergic rhinitis.

OBJECTIVE

I overview the clinical pharmacology of CysLT(1) receptor antagonists and their potential role in patients with allergic rhinitis.

METHODS

I review the evidence regarding the release of cys-LTs and localization of CysLT(1) receptor on nasal mucosa, and evaluate the clinical efficacy of CysLT(1) receptor antagonist in allergic rhinitis.

RESULTS/CONCLUSION

Immunohistochemical studies show that in allergic rhinitis, the major target of CysLT(1) receptor antagonists are the vascular bed and infiltrated leukocytes such as mast cells, eosinophils and macrophages. CysLT(1) receptor antagonists provide a new opportunity for simultaneous management of allergic diseases of the upper and lower respiratory tract.