Identification of genes and proteins specifically regulated by costimulation of mast cell Fcε Receptor I and chemokine receptor 1

Mast cell function is a critical component of allergic reactions. Mast cell responses mediated by the high-affinity immunoglobulin E receptor FcεRI can be enhanced by co-activation of additional receptors such as CC chemokine receptor 1 (CCR1). To examine the downstream effects of FcεRI-CCR1 costimulation, rat basophilic leukemia cells stably transfected with CCR1 (RBL-CCR1 cells) were sensitized and activated with antigen and/or the CCR1 ligand CC chemokine ligand (CCL) 3. Gene and protein expression were determined at 3h and 24h post-activation, respectively, using GeneChip and Luminex bead assays. Gene microarray analysis demonstrated that 32 genes were differentially regulated in response to costimulation, as opposed to stimulation with antigen or CCL3 alone. The genes most significantly up-regulated by FcεRI-CCR1 costimulation were Ccl7, Rgs1, Emp1 and RT1-S3. CCL7 protein was also expressed at higher levels 24h after dual receptor activation, although RGS1, EMP1 and RT1-S3 were not. Of the panel of chemokines and cytokines tested, only CCL2, CCL7 and interleukin (IL)-6 were expressed at higher levels following costimulation. IL-6 expression was seen only after FcεRI-CCR1 costimulation, although the amount expressed was very low. CCL7, CCL2 and IL-6 might play roles in mast cell regulation of late-phase allergic responses.

Insulin signaling regulates fatty acid catabolism at the level of CoA activation

The insulin/IGF signaling pathway is a highly conserved regulator of metabolism in flies and mammals, regulating multiple physiological functions including lipid metabolism. Although insulin signaling is known to regulate the activity of a number of enzymes in metabolic pathways, a comprehensive understanding of how the insulin signaling pathway regulates metabolic pathways is still lacking. Accepted knowledge suggests the key regulated step in triglyceride (TAG) catabolism is the release of fatty acids from TAG via the action of lipases. We show here that an additional, important regulated step is the activation of fatty acids for beta-oxidation via Acyl Co-A synthetases (ACS). We identify pudgy as an ACS that is transcriptionally regulated by direct FOXO action in Drosophila. Increasing or reducing pudgy expression in vivo causes a decrease or increase in organismal TAG levels respectively, indicating that pudgy expression levels are important for proper lipid homeostasis. We show that multiple ACSs are also transcriptionally regulated by insulin signaling in mammalian cells. In sum, we identify fatty acid activation onto CoA as an important, regulated step in triglyceride catabolism, and we identify a mechanistic link through which insulin regulates lipid homeostasis.

Type 2 diabetes, which is reaching epidemic proportions worldwide, is often associated with obesity and an imbalance in organismal lipid homeostasis. Therefore, understanding how insulin regulates lipid biosynthesis and breakdown is necessary. Surprisingly, the molecular mechanisms by which insulin regulates fatty acid catabolism are not entirely understood. We show here that insulin signaling regulates expression of acyl-CoA Synthetases (ACS). ACSs couple fatty acids to Coenzyme A, thereby activating them for subsequent biochemical reactions. In Drosophila, we find that insulin signaling modulates expression of one ACS called Pudgy, which activates fatty acids for beta-oxidation. Modulation of pudgy expression leads to changes in overall organismal lipid homeostasis. Likewise, we show that in mammalian cells insulin signaling regulates expression of a number of ACSs and that ACS expression modulates steady-state lipid levels.

CCR1 expression and signal transduction by murine BMMC results in secretion of TNF-alpha, TGFbeta-1 and IL-6

Chemokine receptors (CCRs) are important co-stimulatory molecules found on many blood cells and associated with various diseases. The expression and function of CCRs on mast cells has been quite controversial. In this study, we report for the first time that murine bone marrow-derived mast cells (BMMC) express messenger RNA and protein for CCR1. BMMC cultured in the presence of murine recombinant stem cell factor and murine IL-3 expressed CCR1 after 5-6 weeks. We also report for the first time that mBMMC(CCR1+) cells endogenously express neurokinin receptor-1 and intercellular adhesion molecule-1. To examine the activity of CCR1 on these BMMC, we simultaneously stimulated two receptors: CCR1 by its ligand macrophage inflammatory protein-1alpha and the IgE receptor FcepsilonRI by antigen cross-linking. We found that co-stimulation enhanced BMMC degranulation compared with FcepsilonRI stimulation alone, as assessed by beta-hexosaminidase activity (85 versus 54%, P < 0.0001) and Ca(2+) influx (223 versus 183 nM, P < 0.05). We also observed significant increases in mast cell secretion of key growth factors, cytokines and chemokine mediators upon CCR1-FcepsilonRI co-stimulation. These factors include transforming growth factor beta-1, tumor necrosis factor-alpha and the cytokine IL-6. Taken together, our data indicate that CCR1 plays a key role in BMMC function. These findings contribute to our understanding of mechanisms for immune cell trafficking during inflammation.

CCR1 expression and signal transduction by murine BMMC results in secretion of TNF-α, TGFβ-1 and IL-6 (98.10)

Chemokine receptors are important co-stimulatory molecules found on many blood cells. Chemokine receptor 1 (CCR1) is one of the important chemokine receptor identified in different immune cells known for its function in various diseases. The expression and functions of chemokine receptors on mast cells has been quite controversial. In this study, we report for the first time that murine bone marrow-derived mast cells (BMMC) express mRNA and protein for CCR1. BMMC cultured in the presence of murine recombinant stem cell factor and murine interleukin-3 expressed CCR1 after 5-6 weeks. Co-stimulation of CCR1 by its ligand macrophage inflammatory protein 1α (MIP-1α) and the IgE receptor FceRI enhanced BMMC degranulation compared to FceRI stimulation alone (85% vs. 54%, p &lt; 0.0001) and Ca2+ influx. We report for the first time that mBMMCCCR1+ cells endogenously express neurokinin receptor-1 and intercellular adhesion molecule-1. We also observed significant increases in mast cell secretion of key growth factors, cytokines and chemokine mediators upon CCR1- FceRI co-stimulation. These factors include transforming growth factor β-1, tumor necrosis factor-α, ciliary neurotrophic factor and the cytokine interleukin-6. Taken together, our data indicate that CCR1 plays a key role in BMMC function. These findings contribute to our understanding of mechanisms for immune cell trafficking during inflammation.

Role of beta-chemokines in mast cell activation and type I hypersensitivity reactions in the conjunctiva: in vivo and in vitro studies

Chemokines have a clearly defined role in mobilizing the recruitment of leukocytes to both healthy and inflamed tissues. This review details work from our and other laboratories, indicating that beta-chemokines may play important roles (i) in driving the terminal differentiation of mast cell precursors in mucosal tissues and (ii) in providing priming or costimulatory signals required for mast cell activation, leading to an antigen-driven inflammatory response. These data stem from in vivo, ex vivo, and in vitro studies. Data are also presented that suggest that Fc epsilon RI:chemokine receptor cross talk may involve spatiotemporal dynamics that may control the strength and nature of the complex activating signals controlling mast cell effector function.

Chemokine receptor signaling in mast cells (89.27)

Mast cells play an important role in IgE-associated allergic disorders and immune response to parasites.

In a former study, we demonstrated that chemokine CCL3 (MIP-1α) acted as a co-stimulator for FcεRI-mediated activation on mast cells. To advance our understanding on this finding, we studied gene profiles in Rat Basophilic Leukaemia mast cells after co-activation of CCR1 (a receptor of CCL3) and FcεRI using the Affymetrix GeneChip Arrays. Emp1 (Epithelial Membrane protein 1), RT1-S3 (non-classical type 1 MHC gene), and Slc35e4 (solute carrier family 35, member E4) were found to be the top possible synergy-related genes. Validations of this data are being carried out using real time PCR, western-blotting and siRNA technologies.

Further to our in vivo findings of the inhibition of the immediate hypersensitivity reactions in the conjunctiva and the attenuation of mast cell degranulation in MIP-1α deficient mice, we would like to check if MIP-1α and CCR1 play a critical role to produce these effects. We reconstituted the bone marrow-derived mice mast cells (BMMC) from naïve mice into mast cell-deficient mice and confirmed that the reconstituted BMMC home to their eye. The next step is to examine whether CCR1 and CCL3 are critical for mast cell activation and allergic conjunctivitis-like symptoms following induction of murine allergic conjunctivitis using CCR1- and CCL3- deficient mice.