ACTIVATION OF STAT5 BY INTERLEUKIN-2 REQUIRES A CARBOXYL-TERMINAL REGION OF THE INTERLEUKIN-2 RECEPTOR-BETA CHAIN BUT IS NOT ESSENTIAL FOR THE PROLIFERATIVE SIGNAL TRANSMISSION

The high-affinity interleukin 2 (IL-2) receptor (IL-2R) consists of th ree subunits: the IL-2R alpha, IL-2R beta c, and IL-2R gamma c chains, Two members of the Janus kinase family, Jak1 and Jak3, are associated with IL-2R beta c and IL-2R gamma c, respectively, and they are activ ated upon IL-2 stimulation. The cytokine-mediated Jak kinase activatio n usually results in the activation of a family of latent transcriptio n factors termed Stat (signal transducer and activator of transcriptio n) proteins. Recently, the IL-2-induced Stat protein was purified from human lymphocytes and found to be the homologue of sheep Stat5/mammar y gland factor. We demonstrate that the human Stat5 is activated by IL -2 and that Jak3 is required for the efficient activation. The cytopla smic region of the IL-2R beta c chain required for activation of Stat5 is mapped within the carboxyl-terminal 147 amino acids. On the other hand, this region is not essential for IL-2-induced cell proliferation .