| Research Abstract |
Murine interleukin 5 (IL-5) binds to its receptor with high and low affinity. It has been shown that the high affinity IL-5 receptor (IL-5R) is composed of at least two membrane protein subunits, p60 and p130, which are designated alpha chain and beta chain, respectively. The murine IL-5R alpha chain (IL-5Ralpha) was purified from IL-5 dependent early B cell line (T88-M) by using an immobilized monoclonal antibody against the murine IL-5Ralpha. The determined N-terminal sequence of the immunoaffinity-purified IL-5Ralpha corresponded precisely to the deduced primary sequence from cDNA encoding the IL-5Ralpha. Our data indicate that the signal peptide is N-terminal 17 aminoacids of the deduced sequence from the IL-5Ralpha cDNA. The high affinity IL-5R was reconstituted on an L-cells transfectant co-expressing IL-5Ralpha and AIC2B, which is the homologue of IL-3 receptor (AIC2A) and does not bind IL-5 its self. AIC2B is a component of the high affinity IL-5R, which is called beta chain. The rapid phosphorylation of a p60, which is not IL-5Ralpha, at serine residues and of p140, p92, p53, p48 and p45 at tyrosine residues were induced by the stimulation of T88-M cells with IL-5. Furthermore we investigated IL-5-induced tyrosine phosphorylation of IL-5Rbeta with an monoclonal antibody against the murine IL-5Rbeta. IL-5Rbeta appeared to be phosphorylated at tyrosine residues within 30 min after the stimulation with IL-5. The tyrosine-phosphorylated IL-5Rbeta disappeared 30 min after the stimulation. Interestingly, molecular weight of the tyrosine- phosphorylated IL-5Rbeta at 5 min after the stimulation was heavier than that at 1 min after the stimulation. Now we investigate association between IL-5Rbeta and other phosphorylated proteins with transfectants expressing mutant IL-5Ralpha and IL-5Rbeta.
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