UP-REGULATION OF SYK ACTIVITY DURING HL60 CELL-DIFFERENTIATION INTO GRANULOCYTE BUT NOT INTO MONOCYTE MACROPHAGE-LINEAGE/

Following induction of cell differentiation in vitro, an increase in S yk activity was observed only in HL60 cells differentiation into granu locytes induced by all trans retinoic acid (RA) but not into macrophag es induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) or monocytes induced by sodium butyrate. This elevation of Syk activity was the spe cific increase in kinase activity because the Syk amount was not alter ed before and after differentiation. Anti-phosphotyrosine blot reveale d that tyrosine phosphorylation of Syk was significantly increased as the function of induction time by RA, but not by TPA and sodium butyra te, suggesting that tyrosine phosphorylation might account for Syk act ivation. More importantly, Syk tyrosine phosphorylation and Syk activi ty were not altered in U937 and K562 cells which undergo monocyte diff erentiation and no differentiation, respectively, in response to RA in duction. Taken together, Syk might exert a unique role in directing HL 60 cells toward granulocyte differentiation. (C) 1997 Academic Press.