The IL-4 receptor: Signaling mechanisms and biologic functions

Interleukin-4 is a multifunctional cytokine that plays a critical role in t he regulation of immune responses. Its effects depend upon binding to and s ignaling through a receptor complex consisting of the IL-4R alpha chain and the common gamma chain (gamma c), resulting in a series of phosphorylation events mediated by receptor-associated kinases. In turn, these cause the r ecruitment of mediators of cell growth, of resistance to apoptosis, and of gene activation and differentiation. Here we describe our current understan ding of the organization of the IL-4 receptor, of the signaling pathways th at are induced as a result of receptor occupancy, and of the various mechan isms through which receptor function is modulated. We particularly emphasiz e the modular nature of the receptor and the specialization of different re ceptor regions for distinct functions, most notably the independent regulat ion of cell growth and gene activation.