This project aims to investigate the function of the receptors for granulocyte-macrophage colony stimulating factor (GM-CSF), Interleukin-3 (IL-3) and Interleukin-5 (IL-5). These factors exert strong proliferative and differentiative effects on myeloid hemopoietic cells, and moreover, autocrine GM-CSF production has been implicated in some leukemias, while IL-5 is involved in many allergic reactions. The cell-surface receptors for GM-CSF, IL-3 and IL-5 are members of the cytokine receptor family and are comprised of two different subunits, alpha and beta. The alpha subunit is unique to each factor while the beta subunit (h-beta-c) is shared by the three factors. Specifically, it is proposed to utilize a unique set of constitutively active mutants of the h-beta-c to examine the structure, composition and activity of the functional receptor complexes. These studies will test a model which predicts that there are actually two distinct types of functional receptor complex. This will be carried out by: (i) Examining association between receptor subunits expressed in cell lines; (ii) Studying the molecular structure of a critical region of h-beta-c in both normal and mutant forms. This will use both directed mutations and nuclear magnetic resonance spectroscopy; (iii) Attempting to correlate different receptor subunit associations with tyrosine phosphorylation of h-beta-c. In addition, it is proposed that novel reagents (e.g., monoclonal antibodies and peptides) can be generated which interact with critical regions of h-beta-c and which can trigger its signalling activity. As well as providing tools to probe receptor structure, these reagents may provide a proof-of-principle for the isolation of novel agonists for these and other members of the cytokine receptor family.
