Phosphorylation of 64-kDa Protein, Enzyme Release, and Increase in Intracellular cAMP Level of Human Polymorphonuclear Leukocytes Induced by fMet-Leu-Phe Stimulation

The chemotactic peptide fMet-Leu-Phe induced specific protein phosphorylation of human polymorphonuclear leukocytes. The major phosphorylated protein was observed to have a molecular size of 64kDa judged from sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The phosphorylated 64-kDa protein was definitely detected from 45s after fMet-Leu-Phe treatment and then increased in quantity with the incubation time. When the 64-kDa protein was phosphorylated, its pI decreased, as demonstrated by two-dimensional electrophoresis. On the other hand, sensitivity of polymorphonuclear leukocytes to cytochalasin B remained at a low level for 30s after fMet-Leu-Phe treatment when it was determined by release of myeloperoxidase and O2- production. But the cytochalasin B-dependent myeloperoxidase release and O2- production increased with the extension of the incubation time in the presence of fMet-Leu-Phe, reaching their maximal levels over a 180-300s period. Furthermore, fMet-Leu-Phe also induced a temporal increase in the intracellular CAMP level with its peak at 15s, which thereafter returned to its initial level; whereas no major change was observed in the level of cGMP. Phosphorylation of the 64-kDa protein was slightly enhanced with dibutyryl-cAMP, but not with dibutyryl-cGMP. 12-O-Tetradecanoylphorbol 13-acetate and A23187 also stimulated phosphorylation of this protein with slow responses. These results suggest that phosphorylation of the 64-kDa protein is related to the cytochalasin B-dependent release of enzymes from and O2- production by polymorphonuclear leukocytes.