Protein kinase C isotypes in human erythroleukemia cell proliferation and differentiation

Barbara A. Hocevar, Dwight M. Morrow, Mark L. Tykocinski, Alan P. Fields

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89 Scopus citations


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 α and βII PKC but no detectable βI γ or ∈ PKC. Treatment of cells with either PMA or bryo leads to rapid translocation of both α and βII PKC from the cytosol to the non-nuclear particulate fraction. However, bryo also induces selective translocation of βII PKC to the nuclear membrane. Nuclear βII PKC is functionally active as evidenced by the time-dependent phosphorylation of Iamin B, a previously identified nuclear PKC substrate. These data indicate that the divergent effects of PMA and bryo on erythroleukemia cell proliferation and differentiation correspond to differential activation of βII PKC at the nuclear membrane. Nuclear activation of βII PKC by bryo appears to generate a dominant, proliferative signal that overrides the PMA-induced differentiation signal. Therefore, the a and βII PKC isotypes exhibit distinct translocation and activation profiles during megakaryocytic differentiation and proliferation, indicating that they play distinct roles in these cellular processes.

Original languageEnglish (US)
Pages (from-to)671-679
Number of pages9
JournalJournal of cell science
Issue number3
StatePublished - 1992


  • Bryostatin 1
  • Lamin B phosphorylation
  • Nuclear protein kinase C

ASJC Scopus subject areas

  • Cell Biology


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