The human erythroleukemia (K562) cell line is induced to differentiate into megakaryocytic cells by treatment with the tumor promoter phorbol myristate acetate (PMA). PMA-induced differentiation is characterized by (1) almost complete cessation of cellular proliferation, (2) expression of the megakaryocytic cell surface marker glycoprotein IIb/IIIa (gpIIIa), (3) increased secretion of granulocyte/macrophage-colony stimulating factor (GM-CSF) and (4) increased secretion of interleukin-6 (IL-6). PMA-induced differentiation is dose-dependent with maximal activity seen at 10 nM PMA. In contrast, bryostatin (bryo), a structurally distinct protein kinase C (PKC) activator, fails to induce megakaryocytic differentiation or growth arrest at the concentrations tested (0.01-100 nM). Rather, bryo inhibits PMA-induced growth arrest and megakaryocytic differentiation in a dose-dependent fashion (full inhibition at 100 nM). The divergent biological effects of PMA and bryo correspond to the differential activation and translocation of PKC isotypes in K562 cells. PKC isotype analysis demonstrates that undifferentiated cells express both alpha and beta II PKC but no detectable beta I, gamma or epsilon PKC. Treatment of cells with either PMA or bryo leads to rapid translocation of both alpha and beta II PKC from the cytosol to the non-nuclear particulate fraction. However, bryo also induces selective translocation of beta II PKC to the nuclear membrane.(ABSTRACT TRUNCATED AT 250 WORDS)
Daphnoretin, a novel protein kinase C activator, induces growth arrest irreversibly on Human Hepatoma HepG2 Cells
