Rapid phosphorylation-dephosphorylation of specific proteins induced by phorbol ester in HL-60 cells. Further characterization of the phosphorylation of 17-kilodalton and 27-kilodalton proteins in myeloid leukemic cells and human monocytes.

Treatment of the promyelocytic leukemic cells, HL-60, with phorbol-12-myristate-13-acetate (PMA) results in arrest of growth and terminal differentiation of the cells into macrophages. We have reported that within minutes following exposure of these cells to PMA there is an increase of severalfold in phosphorylation of two cytosol proteins: 17-20 kDa (pp17, pI approximately 5.5) and 27 kDa (pp27, pI approximately 5.5) as detected in the intact cells by two-dimensional gel electrophoresis. In this report, by analyzing the chase kinetics of 32Pi in cellular proteins, we show that PMA treatment induces a rapid and specific loss of 32Pi from pp17 and pp27. Comparison with kinetics of [3H]leucine loss from these proteins indicates that this effect is due to induction by PMA of rapid turnover of phosphate in pp17 and pp27. This activity persisted in HL-60 for at least 24 h and was also seen in two other cell types studied (U937 leukemia and normal monocytes). The Ca2+ channel blocker, nifedipine, had no effect on PMA-induced 32Pi turnover in pp17, while trifluoroperazine, which is known to inhibit protein kinase C, blocked these events and also inhibited other cellular effects of PMA (adherence and growth arrest). Thus, induction of rapid 32Pi turnover in pp17 and pp27 may be an essential early signal in initiating and maintaining cellular effects of PMA. Myosin light chain (20 kDa), another phosphorylated protein, was shown to be not identical with pp17, although of similar Mr.