DIFFERENTIATION OF HL-60 PROMYELOCYTIC CELLS IS PROMOTED BY A DIFFERENTIATION ENHANCING FACTOR PRODUCED BY ERYTHROLEUKEMIA-CELLS

A differentiation enhancing factor isolated from murine erythroleukemi a cells is also a potent enhancer of the differentiation of HL60 human promyelocytic leukemia cells, induced by retinoic acid and by phorbol ester. This stimulating effect is the result of a large increase in t he sensitivity of HL60 cells for retinoic acid and for phorbol 12-myri state 13-acetate (20-fold and 40-fold, respectively). Accelerated diff erentiation induced by the protein factor, and monitored by the appear ance of marker enzymes, is accompanied by a large increase in the fluc tuation of the levels of protein kinase C (PKC) isozymes in HL60 cells . These results provide further support for the role of this new prote in factor in cell differentiation and indicate that other cell types a re susceptible to its biological effect.