DIFFERING KINASE-ACTIVITY OF THE C-YES AND C-SRC GENE PROTEINS IN TPA-INDUCED MEGAKARYOCYTIC DIFFERENTIATION OF T-33 AND K562 CELL-LINES

We examined the protein kinase (PK) activity of the c-yes and c-src ge ne proteins (c-YES, c-SRC) at an early phase of 12-O-tetradecanoyl pho rbol-13-acetate (TPA)-induced megakaryocytic differentiation of T-33 a nd K562 cells with use of immunoprecipitation and in vitro kinase assa y. We found that c-SRC PK activity of TPA-treated T-33 and K562 cell l ines had been enhanced compared with the untreated ones, but in contra st, no enhancement of c-YES PK activity by the TPA treatment was obser ved in these cell lines. We also examined PK activity in TPA-induced m onocytic differentiation of U937 monoblastic cells that exhibited no m egakaryocytic markers and found that both the c-YES and c-SRC PK activ ity was enhanced by the TPA treatment. Our data suggest that c-YES and c-SRC play different and unique roles in TPA-induced megakaryocytic d ifferentiation in T-33 and K562 cells.