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 erythr oid and megakaryocytic differentiation of the erythroleukemia cell lin e K562 was examined. Cells were stably transfected with expression vec tors encoding either a tetracycline-responsive dominant negative c-Jun (Jun(DN)) or a hybrid Raf protein inducible by estrogen. Down-regulat ion of AP-1 activity by induction of Jun(DN) enhanced erythroid differ entiation by two agents, cytosine arabinoside and activin A. Induction of AP-1 activity by elevated Raf activity inhibited erythroid differe ntion, thus mimicking the well-known effect of tetradecanoyl phorbol a cetate (TPA) on this process. Induced Raf activity also brought about partial megakaryocytic differentiation of the line. However, inhibitio n of TPA-induced AP-1 activity by induction of Jun(DN) gave mixed resu lts. While the cytological effects of TPA treatment observed on cytoch emical staining were inhibited by Jun(DN), two protein markers for meg akaryocytic differentiation were increased. These results, while suppo rtive of current models of hematopoietic lineage-specific gene express ion, suggest a complex and temporal mechanism of lineage commitment. ( C) 1998 Academic Press.