THE MOLECULAR ROLE OF THE COMMON GAMMA(C) SUBUNIT IN SIGNAL-TRANSDUCTION REVEALS FUNCTIONAL ASYMMETRY WITHIN MULTIMERIC CYTOKINE RECEPTOR COMPLEXES

The specific signal transduction function of the gamma(c) subunit in t he interleukin (IL) 2, IL-4, IL-7, IL-9, and IL-15 receptor complexes remains undefined. The present structure-function analyses demonstrate d that the entire cytoplasmic tail of gamma(c) could be functionally r eplaced in the IL-2 receptor (IL-2R) signaling complex by a severely t runcated erythropoietin receptor cytoplasmic domain lacking tyrosine r esidues, Heterodimerization of IL-2R beta with either gamma(c) or the truncated erythropoietin receptor chain Led to an array of specific si gnals normally derived from the native IL-2R despite the substitution of Janus kinase JAK2 for JAK3 in the receptor complex, These findings thus suggest a model in which the gamma(c) subunit serves as a common aad generic ''trigger'' chain by providing a nonspecific Janus kinase for signaling program initiation, while signal specificity is determin ed by the unique ''driver'' subunit in each of the gamma(c)-containing receptor complexes, Furthermore, these results may have important fun ctional implications for the asymmetric design of many cytokine recept or complexes and the evolutionary design of receptor subfamilies that share common trigger or driver subunits.