Protein Profiling of the secretome of Fc sigma RI Activated RBL-2H3.1 cells

Secretory proteins of IgE receptor activated mast cells and basophils play a pivotal role in the generation of immediate and long term immune responses in allergy and type I hypersensitivity. The present study aims to generate a 2-D map and profile of proteins secreted from a high secretory variant of the rat basophilic leukemia cell line, RBL-2H3.1, which in view of the difficulty associated with gaining adequate numbers of pure primary mast cell and basophiles, represents an accepted model system for the study and standardization of the methodology to characterize the secretome of these cell types. A 2-D map of secretory proteins was generated by 2-D PAGE and a shotgun mass spectrometric approach carried out for protein identification. Study resulted into identification of 299 proteins released from resting and IgE receptor activated RBL-2H3.1 cells after 90 s, 30 min and 3 h antigen challenge. Further sequence analysis identified 53% of total proteins as secretory proteins which could be attributed to classical and non-classical secretory pathways. Additionally, functional classification of classic secretory proteins verified the presence of proteins belonged to cytokines, receptors, membrane proteins, lysosomal proteins and proteins associated with specific sub-cellular localizations such as endoplasmic reticulum, mitochondria, nucleus, cytoplasm and ribosome. According to this data the presence of some secretory proteins such as cytokines [e.g. MCP-2, PF-4, CSF-1 and TGF-beta1] are all subject to Ag challenge which may point to their importance toward pathogenesis in allergic diseases. In view of both a beneficial and adverse role of mast cell mediators in health and disease, an identification of temporal changes in the secretory pattern may form the basis for future tailor made intervention strategies that may enable us to harvest the therapeutic potential inherent in mast cell exocytosis while inhibiting/attenuating negative outcomes

novel insight to the functional role of stathmin 1 in IgE-mediated activation of RBL-2H3 cells

IgE-mediated cell signaling, induced by cross-linking of high affinity receptor for IgE [FepsilonRI] in the presence of antigen [Ag], is a well known mechanism described for mast cell activation in allergy and hypersensitivity reactions, which induces a spectrum of cellular responses such as secretion and up-regulation of cell surface FepsilonRL Although for several years IgE binding to FepsilonRI was considered to be a passive sensitization process, the outcomes of several recent studies have revealed a variety of different cellular responses to IgE binding compared to IgE plus Antigen binding. The present study applied a functional proteomics-based approach to investigate mast cell signaling events and provided new insights to FcsRI-mediated cell signaling in RBL-2H3.1 cells, and may point to the activation of alternative signaling pathways in response to IgE or IgE plus Ag. Comparative analysis by 2-D PAGE of RBL cells activated with IgE plus Ag for three and four hours compared to non-activated cells was followed by mass spectrometric protein identification and provided evidence for the induction of Stathmin 1 [STMN1] gene expression in response to IgE plus Ag activation. Complementary SDS-PAGE analysis showed a distinct up-regulation of STMN1 induction in response to challenge with IgE plus Ag compared to sensitization with IgE only. Phosphoproteomics analysis gave evidence for significant increase at phosphorylation of STMN1 on ser16 after 1min, though a slight rise at 5 min, and on ser38 after 1 and 5min sensitization with IgE and a similar result was observed for 1min IgE plus Ag-activation. IgE plus Ag-activation was also found to induce the phosphorylation of ser38 to a greater extent than sensitization with IgE. In contrast, IgE alone was more effective than IgE plus Ag at inducing phosphorylation of ser 16. Collectively this study provides further insights into the role of Stathmin 1 in FepsilonRI-mediated activation of cells of mast cell lineage and might shed light on the diverse response of these cells to IgE or IgE plus Ag