| Abstract: | The tyrosine kinases Jak1 and Jak3 are known to be associated with the β and γ chains of interleukin-2 receptor (IL-2R). They are activated by stimulation with IL-2, IL-4, IL-7, IL-9, or IL-15, receptors of which share the γ chain of the IL-2R. We have obtained direct evidence of Jak1 association with the α chains of receptors for IL-4, IL-7 and IL-9 and with the β chain of IL-2R, which is also common to the IL-15R. Furthermore, we have prepared mutant IL-2R β chains with a mutation in the box 1 region, which is conserved among the IL-2R β chain and the α chains of the other cytokine receptors sharing the IL-2R γ chain. Using MOLT-4 transfectants with the mutant β chains, we found that two conserved proline residues within the box 1 region are essentially involved in association with Jak1. The MOLT-4 transfectants with the mutant β chains lacking Jak1 association showed IL-2 responsiveness, in terms of activation of Jak3 and Stat5 and induction of cell growth, indicating that Jak1 is dispensable for IL-2-mediated cell growth signaling and that Jak1 activation is not required for activation of Jak3 and Stat5 in the MOLT-4 transfectants. |
