Interleukin-2 receptor heterotrimer complex and intracellular signaling.

Identification of a third component of the IL-2 receptor complex, gamma-chain, has established that the high-affinity complex consists of at least three distinct subunits, alpha-, beta- and gamma-chains. The alpha-chain specifies the low-affinity IL-2 binding. The beta- or gamma-chains alone do not show any appreciable IL-2 binding activity, however simultaneous existence of both chains generates a functional receptor complex that is suggested to associate with a non-receptor type protein tyrosine kinase that may deliver IL-2-induced signals further downstream. Mutation studies have revealed that discrete cytoplasmic regions of the beta- and gamma-chains transduce at least two independent signaling pathways.