Effects of phorbol ester on translocation and down-regulation of protein kinase C and phosphorylation of endogenous proteins in human acute myeloid leukemia cell line KG-1 and its phorbol ester-resistant subline KG-1a.

ABSTRACT

12-O-Tetradecanoylphorbol-13-acetate (TPA) induced decreases in the catalytic activity and immunoreactivity of protein kinase C (PK-C) in the soluble fraction, accompanied by increases in their activities in the particulate fraction, of a human myeloid leukemia cell line KG-1. TPA also caused a similar down-regulation and translocation of PK-C in KG-1a, a cloned subline shown to be resistant to the differentiating effect of TPA. The activity levels of enzyme in the soluble and particulate fractions from KG-1 cells, however, were about three times higher than those from KG-1a cells. Immunocytochemical studies showed that, when KG-1 cells were treated with 10 nM TPA for 30 min, PK-C was translocated to the plasma membrane in the adherent subpopulation of cells, whereas the enzyme remained largely in the cytoplasm and perinuclear area of the nonadherent cells. TPA, in contrast, caused a PK-C translocation primarily to the perinuclear region in KG-1a cells. Phosphorylation patterns of PK-C substrate proteins in the two cell lines were similar, except that phosphorylation of the Mr 33,000 and 97,000 proteins were predominant in KG-1 and KG-1a cells, respectively. The present findings showed existence of certain differential effects of TPA on the PK-C system in the two leukemia cell lines, suggesting a molecular basis for the selective resistance of KG-1a cells to the differentiating action of TPA.