Interleukin 2 (IL-2) rapidly induces phosphorylation of a cellular protein, pp67, in an IL-2 dependent murine cell line.

We have investigated interleukin 2 (IL-2)-induced protein phosphorylation in an IL-2 dependent murine cell line by the two-dimensional gel electrophoresis. IL-2 rapidly and markedly induced phosphorylation of a cellular protein distinct from the IL-2 receptor, with a molecular weight of 67,000 daltons and an isoelectric point of 5.8, named pp67. IL-2 dose-responses of pp67 phosphorylation and cell proliferation were well correlated. Phosphoamino acid analysis showed that the phosphorylation site of pp67 was a serine residue. Further, when the cells were treated with 12-O-tetradecanoylphorbol-13-acetate (TPA) instead of IL-2, similar increase of pp67 phosphorylation was observed. Such IL-2 dependent protein phosphorylation was also detected in various human IL-2 receptor bearing T cells. Thus we speculate that the phosphorylation of pp67 could be regulated by protein kinase C and it could be a common feature in an early event of the intracellular growth signaling from the IL-2 receptor.