Mast cells have been implicated in the pathogenesis of both atopic and non-atopic asthma. Ras guanine nucleotide-releasing protein 4 (RasGRP4) is a mast cell-restricted guanine nucleotide exchange factor and diacylglycerol (DAG)/ phorbol ester receptor whose function has not been deduced. RT-PCR analysis of 40 asthmatic patients and 40 non-asthmatic controls demonstrated a higher hRasGRP4 mRNA expression in a subgroup of the asthmatics. A RasGRP4-defective variant of the human mast cell line HMC-1 was used to create stable clones expressing green fluorescent protein-labeled human RasGRP4 for monitoring the movement of this signaling protein inside mast cells before and after exposure to phorbol-12-myristate 13-acetate (PMA) and for evaluating the protein???s ability to control the development, phenotype, and function of mast cells. Transcript-profiling approaches revealed hRasGRP4 constitutively regulates the expression of numerous genes in the HMC-1 cell line. For example, expression of hRasGRP4 in HMC-1 cells substantially decreased GATA-1 levels without altering GATA-2 levels, suggesting that hRasGRP4 regulates mast cell commitment of multipotential progenitors in part by controlling the intracellular levels of at least one lineage-dependent transcription factor for hematopoietic cells. hRasGRP4 resided primarily in the cytosol before HMC-1 cells were stimulated with PMA. After exposure to PMA, hRasGRP4 translocated to the inner leaflet of the cell???s plasma membrane and then to perinuclear and Golgi compartments. Extracellular signal-regulated kinases 1 and 2 were activated during this translocation process, and the PMA-treated cells transiently increased their expression of the transcripts encoding the interleukin 13 receptor IL-13R??2 and numerous other proteins. The accumulated data in our mast cell model suggest hRasGRP4 translocates to various intracellular compartments via its DAG/PMA-binding domain to regulate those signaling pathways that allow mast cells to respond quickly to changes in their tissue microenvironments.
| Identifer | oai:union.ndltd.org:ADTP/225439 |
| Date | January 2006 |
| Creators | Katsoulotos, Gregory Peter, St George Clinical School, UNSW |
| Publisher | Awarded by:University of New South Wales. St George Clinical School |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Gregory Peter Katsoulotos, http://unsworks.unsw.edu.au/copyright |
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