CONSTITUTIVE C-JUN EXPRESSION INDUCES PARTIAL MACROPHAGE DIFFERENTIATION IN U-937 CELLS

Previous studies have shown that phorbol ester induced macrophage diff erentiation in the leukemic cell line U-937 is tightly linked to the e xpression of the c-jun protooncogene and the generation of AP-1 transc riptional activity. We expressed the c-jun protooncogene in U-937 cell s to examine the role of c-jun in the differentiation of these cells. AP-1 DNA binding activity and the expression of AP-1 controlled downst ream genes were increased in all clones expressing exogenous cJun. Mor e importantly, these transfectants showed evidence of differentiation as measured by the acquisition of phagocytic capacity, although they d id not develop morphological changes associated with differentiation s uch as adherence. Furthermore, they became committed to terminal diffe rentiation after significantly shorter exposures to phorbol esters tha n did control cell lines. These data show that cJun expression induces partial differentiation along the macrophage pathway in U-937 cells.