Interleukin 2 activates a receptor-associated protein kinase

The interleukin 2 (IL 2) receptor complex has been shown to consist of at least two IL 2 binding molecules, one of 55 to 57 kd (gp57(Tac)) and one of 75 to 78 kd apparent m.w. The data presented here indicate that a protein of m.w. 78,000 (pp78) co-immunoprecipitates with gp57(Tac) when a monoclonal antibody against gp57(Tac) is used. The 78 kd molecule is phosphorylated in vitro within the immune complex only in the presence of exogenously added IL 2, whereas the 57 kd molecule is phosphorylated equally in the presence or absence of IL 2. Phosphorylation in vitro of pp78 was demonstrated in extracts of human peripheral blood T cells (PBL-T) and the human T cell line Jurkat, but not in extracts of the human macrophage line U937 or the murine T cell line 2.8.2. Metabolic phosphorylation in intact cells reflects results observed in vitro; both pp78 and gp57(Tac) are phosphorylated in PBL-T and Jurkat, but not in U937. These data demonstrate that the IL 2 receptor complex contains an IL 2 responsive protein kinase activity and may signal the cell through a phosphorylation event.