THE ROLE OF SHARED RECEPTOR MOTIFS AND COMMON STAT PROTEINS IN THE GENERATION OF CYTOKINE PLEIOTROPY AND REDUNDANCY BY IL-2, IL-4, IL-7, IL-13, AND IL-15

To understand the molecular bases for cytokine redundancy and pleiotropy, we have compared the Stat proteins activated In peripheral blood lymphocytes (PBLs) by cytokines with shared and distinct actions. Interleukin-2 (IL-2) rapidly activated Stat5 in fresh PBL, and Stat3 and Stat5 in preactivated PBL. IL-7 and IL-15 induced the same complexes as IL-2, a feature explained by the existence of similar tyrosine-phosphorylated motifs in the cytoplasmic domains of IL-PRP and IL-7R that can serve as docking sites for Stat proteins. IL-13 induced the same complexes as IL-4, a finding explained by our studies implicating IL-4R as a shared component of the receptors. These studies demonstrate that a single cytokine can activate different combinations of Stat proteins under different physiological conditions, and also indicate two mechanisms by which distinct cytokines can activate the same Stat protein.