Role of δ-PKC on the differentiation process of murine erythroleukemia cells

In murine erythroleukemia (MEL) cells the length of the latent period before the onset of hexamethylenebisacetamide induced terminal erythroid differentiation is inversely correlated to the intracellular level of δ- PKC. This is supported by the following experimental evidence. V3.17[44] MEL cell line, characterized by a very high rate of differentiation, contains an amount of δ-PKC protein one third lower than that present in the N23 MEL cell line, characterized by a very low rate of differentiation. A similar difference in the amount of δ-PKC mRNA is present in the two cell lines. In N23 cells, following addition of HMBA, the amount of δ-PKC protein and δ- PKC mRNA is down-regulated to one third its original value, which now corresponds to that constitutively present in V3.17[44] cells. Furthermore, in these cells the levels of δ-PKC protein and of its specific mRNA are unaffected by treatment with HMBA. Following introduction of homologous purified δ-PKC both MEL cell variants display a longer latent period before the onset of differentiation: from 50 to 75 hours in N23 cell line and from 20 to 40 hours in V3.17[44] cells, respectively. Taken together, these results suggest that a δ-PKC related signal plays a negative role in the early stages of MEL cell differentiation and that the level of the kinase is controlled through a down-regulation process upon exposure to the chemical inducer.