PROTEIN-KINASE-C ISOFORMS IN MURINE ERYTHROLEUKEMIA-CELLS AND THEIR INVOLVEMENT IN THE DIFFERENTIATION PROCESS

In addition to α, δ and ε-protein kinase C, murine erythroleukemia cells contain ζ-PKC and also a c-PKC isoform, named α₁, which shows cross-reactivity with an anti-α-PKC antipeptide antibody. In a C44 MEL cell clone, characterized by a high rate of differentiation, both c-PKC forms are expressed at a level higher than that of the N23 MEL cell clone which differentiates at a low rate and contains higher levels of ε-PKC and particularly of the δ-PKC isozyme. In the course of MEL cell differentiation, δ-PKC in N23 cells and α₁-PKC in C44 cells are rapidly down-regulated and the overall process is almost completed before cell commitment. Of the other three PKC isozymes present in both clones, only α-PKC is down-regulated to a significant extent. It is proposed that modulation of the signal delivered by each PKC isozyme is one of the biochemical mechanisms involved in MEL cell differentiation.