Phospholipid- and Ca2+-dependent protein kinase activity and protein phosphorylation patterns in the differentiation of human promyelocytic leukemia cell line HL-60.

The effects of differentiating agents on the activity and phosphorylation pattern produced by phospholipid- and Ca2+-dependent protein kinase (PL-Ca-PK) were examined in human promyelocytic leukemia cell line HL-60. Dimethyl sulfoxide (DMSO), retinoic acid (RA), and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] increased the appearance of mature myelocytic (DMSO and RA) or monocytic [1,25(OH)2D3] cells. The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) increased the appearance of adherent macrophage-like cells. Coincident with the appearance of differentiated cells induced by DMSO, RA, and 1,25(OH)2D3 was an increase in PL-Ca-PK activity. In contrast, TPA treatment resulted in the rapid disappearance of PL-Ca-PK and the induction of phospholipid- and Ca2+- (PL-Ca-) independent protein kinase activity. The phosphorylation pattern resulting from endogenous PL-Ca-PK in extracts from cells treated with DMSO, RA, or 1,25(OH)2D3 showed a prominent phosphorylated protein of molecular weight 37,000 (pp37) and 38,000 (pp38) which was related to the appearance of the myelocyte/monocyte phenotype. pp37 and pp38 were also present in TPA-treated cells, but their phosphorylation was no longer dependent on the presence of phospholipid and calcium. Cells treated with DMSO and RA also exhibited a PL-Ca-dependent pp21 which was barely evident in 1,25(OH)2D3-treated cells and thus represented a myeloid cell marker. Also present was a prominent PL-Ca-dependent pp19 which remained unchanged following treatment with DMSO, RA, and 1,25(OH)2D3, but which diminished markedly in TPA-treated cells. On the other hand, TPA-treated cells exhibited a characteristic pp130 which was antigenically related to the actin binding protein, vinculin. These results indicate that there are characteristic PL-Ca-dependent phosphorylated proteins indicative of mature myelocytic and monocytic cells, as well as PL-Ca-independent phosphorylated proteins characteristic of the macrophage-like phenotype.