DNA-binding phosphoproteins induced after T cell activation: Effects of cyclosporin A

To define novel proteins involved in the early transcriptional response during the activation of human T lymphocytes, we used a high-resolution, two-dimensional gel electrophoresis system to identify nuclear, deoxyribonucleic acid (DNA)-binding proteins exhibiting rapid changes in phosphorylation following cell stimulation. We identified 18 nuclear proteins whose phosphorylation level changed more than 5-fold upon activation. Of these, 11 were found to possess DNA-binding properties. The 11 phosphoproteins with DNA-binding activity, along with Br others, were analyzed further. Phosphoamino acid analysis revealed several sets of proteins with different phosphorylated residues. Kinetic analysis of the phosphorylation of the selected proteins was performed and revealed a complex group of transient and sustained responses to cell activation. Finally, the activation-induced changes in one set of phosphoproteins were dramatically inhibited by cyclosporin A. We suggest that these phosphoproteins may be directly involved in regulating the transcriptional response to cellular activation by external stimuli.