Phosphorylation of a Mr 70,000 protein is associated with interleukin 2 receptor expression

The human T cell hybrid II23 was isolated from fusions between human peripheral blood lymphocytes which had been stimulated with phytohemagglutinin (PHA) and a subline of the human T cell line CEM called CEM.TET1. This hybrid does not constitutively express detectable levels of interleukin 2 (IL 2) receptors but can be induced to express receptors by stimuli shown to activate T cells. Antibody to CD3 (a component of the T cell receptor) coupled to agarose or PHA (greater than 3 micrograms/ml) induced both IL 2 production and receptor expression on II23 cells. Phorbol 12-myristate 13-acetate (PMA) induced IL 2 receptor expression on II23 cells but not IL 2 secretion. Because PMA is a known activator of the Ca2+/phospholipid-dependent enzyme protein kinase C, proteins of stimulated and unstimulated cells were analyzed by two-dimensional gel electrophoresis for changes in phosphoprotein patterns. A Mr 70,000 protein with a pI of 6.2 was phosphorylated in hybrids stimulated by PMA, anti-CD3 antibody coupled to agarose or PHA, i.e. by the same stimuli which induce IL 2 receptors on these cells. The immunosuppressive drug cyclosporin A inhibited IL 2 release without altering induction of IL 2 receptors or phosphorylation of the Mr 70,000 protein. The 70-kDa protein was located in the cytosol, where it remained phosphorylated for at least 4 h after stimulation. A protein with the same migratory properties on two-dimensional gels was similarly phosphorylated after stimulation of normal peripheral blood T lymphocytes, indicating that the phenomenon was not due to hybridization or transformation. This 70-kDA protein may therefore be involved in the pathway which leads to the transcription and expression of IL 2 receptors.