Phorbol diesters increase the phosphorylation of the leukocyte common antigen CD45 in human T cells

We have studied the phosphorylation of the human leukocyte surface glycoprotein CD45, formerly known as leukocyte common antigen or T200, following activation of peripheral T cells with tumor-promoting phorbol diesters. The cells were incubated with [32P]orthophosphate, treated with phorbol diesters, and the CD45 was immunoprecipitated using the monoclonal antibody T29/33. CD45 was weakly phosphorylated in nonactivated T cells, but a treatment of the cells with 10, 60 or 200 nM phorbol 12,13-dibutyrate (PDBu) markedly increased the phosphorylation of the glycoprotein. This effect of PDBu was relatively selective for CD45 since the activation of the cells did not affect the phosphorylation of all membrane phosphoglycoproteins. The effect of another tumor promoter, phorbol 12-myristate 13-acetate (PMA), was comparable to that of PDBu, but a nontumor-promoting phorbol derivative, 4 alpha-phorbol 12,13-didecanoate, did not change the level of CD45 phosphorylation. The phosphorylation of CD45 was found to clearly increase after a treatment of T cells with 60 nM PDBu for only 30 s, and the phosphorylation reached its maximum in about 5 min.