Interleukin 2 (IL-2) is the major growth factor for T lymphocytes and plays a critical role in the regulation of specific immune responses. IL-2 initiates its biological response by specifically binding to its glycoprotein receptor (lL-2R). Recent studies have demonstrated that the functional IL-2R is a multicomponent complex of at least two and as many as four distinct subunits. These include the well characterized 55 kDa IL-2 binding alpha subunit, the 75 kDa IL-2 binding beta subunit, a 22 kDa gamma subunit that co-precipitates with the beta subunit. The latter two subunits have been just recently identified in our biochemical characterization of the mouse lL-2R and the human equivalents of these proteins have not yet been found. The major objectives of this proposal are to biochemically characterize these newly described beta, gamma and delta subunits and to establish the role of each subunit in the formation of a functional high affinity lL-2R complex. Binding studies of wild type and mutant mouse IL-2 will be used to characterize the ligand-binding properties of lL-2Rbeta and define the ligand contact sites of IL2R alpha and lL-2R beta. Biochemical studies will be performed for cell surface and metabolically labeled IL-2R subunits to more fully describe the biochemical properties of lL-2Rbeta, gamma and delta and to determine the cellular site of assembly of the lL-2R complex. These experiments will take advantage of our recently prepared monoclonal antibody that efficiently precipitates the lL-2R beta/gamma heterodimer. The role of each subunit in the formation of a functional lL-2R will be assessed by attempting to reconstitute functional lL-2R in non-lymphoid cells. These experiments will require the cDNA cloning and sequencing of each subunit and the subsequent expression of these cDNAs in non-lymphoid cells by transfection. Mutant cell lines will also be produced that express abnormal lL-2R to facilitate the identification and characterization of the assembly of the components required for the formation of functional lL-2R and to also assess the possibility that one or more of the three other lL-2R associated proteins, plOO, pl35 and pl8O, might be important for a functional lL-2R. These studies will provide information relating to the molecular mechanisms controlling high and low affinity ligand-binding and may provide clues into the mechanism of IL-2 signal transduction. This work will help define normal cellular growth control which is important for our understanding of abnormal, or malignant cell growth. Since IL-2 has been implicated in various T and B cell responses, these studies are also relevant to the basis by which an immune response is regulated.
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