AP-1 Activity Affects the Levels of Induced Erythroid and Megakaryocytic Differentiation of K562 Cells

The effect of modulating AP-1 activity on the levels of induced erythroid and megakaryocytic differentiation of the erythroleukemia cell line K562 was examined. Cells were stably transfected with expression vectors encoding either a tetracycline-responsive dominant negative c-Jun (JunDN) or a hybrid Raf protein inducible by estrogen. Down-regulation of AP-1 activity by induction of JunDNenhanced erythroid differentiation by two agents, cytosine arabinoside and activin A. Induction of AP-1 activity by elevated Raf activity inhibited erythroid differention, thus mimicking the well-known effect of tetradecanoyl phorbol acetate (TPA) on this process. Induced Raf activity also brought about partial megakaryocytic differentiation of the line. However, inhibition of TPA-induced AP-1 activity by induction of JunDNgave mixed results. While the cytological effects of TPA treatment observed on cytochemical staining were inhibited by JunDN, two protein markers for megakaryocytic differentiation were increased. These results, while supportive of current models of hematopoietic lineage-specific gene expression, suggest a complex and temporal mechanism of lineage commitment.