IL-2 Signaling Involves Recruitment and Activation of Multiple Protein Tyrosine Kinases by the IL-2 Receptor

The IL-2 receptor (IL-2R) consists of three subunits, the IL-2R alpha, IL-2R beta, and IL-2R gamma chains, the last of which is also used in the receptors for IL-4, IL-7, IL-9, IL-13, and IL-15. The IL-2-induced proliferative signals emanate from the cytoplasmic domains of IL-2R beta and IL-2R gamma, but the nature and function of the signaling molecules that transmit these signals are not fully understood. Here we summarize our current understanding of the mechanisms by which IL-2R transmit signals by using multiple protein kinases. In fact, at least four protein tyrosine kinases (PTKs) are physically associated with IL-2R: p56lck (and its members), Syk PTK, and the Janus kinases, Jak1 and Jak3. cDNA expression studies revealed that the activation of these PTKs is critical for IL-2-induced proliferative signal transmission. Our findings indicate that a unique property of the IL-2R cytoplasmic domains is to recruit a variety of signaling molecules, which may suggest a mechanism by which these PTKs and other signaling molecules function in concert.