Protein Kinase Cα Is an Effector of Hexamethylene Bisacetamide-Induced Differentiation of Friend Erythroleukemia Cells

Abstract

The program of biochemical and molecular events necessary for commitment to erythroid cell differentiation is particularly well characterized in murine Friend erythroleukemia cell lines. Commitment to hemoglobin synthesis in response to a variety of chemical inducers, including hexamethylene bisacetamide and dimethyl sulfoxide is completed by 24 h and proceeds to terminal differentiation by 96 h. Phorbol 12-myristate 13-acetate, a classical tumor promoter phorbol ester that binds to protein kinase C, blocks differentiation in a reversible manner, suggesting an important role for protein kinase C signaling pathways. The classical protein kinase C isoforms α, βI, and βII, play distinct roles in the transduction of proliferative and differentiative signals in human, as well as in murine, erythroleukemia cells. Protein kinase Cα has been implicated in differentiation of human erythroleukemia cells although its translocation to the nucleus has not been observed. Taking advantage of the ability of phorbol 12-myristate 13-acetate to block differentiation in Friend erythroleukemia cells, we determined the localization of the predominant protein kinase C isoforms α and βI during differentiation and in response to their blockade. The ability of phorbol myristate acetate to preferentially diminish protein kinase Cα-protein localization to the nucleus by 24 h and thereby block differentiation induced by hexamethylene bisacetamide was paralleled by the ability of protein kinase Cα antisense transfection to block differentiation. In addition, β-globin transcription, assessed by polymerase chain reaction, was significantly decreased in protein kinase Cα antisense-transfected cells compared to that seen in vector transfected ones. Taken together, these data suggest an important temporal role for nuclear protein kinase Cα localization in Friend erythroleukemia cell differentiation.