SYNERGISTIC ACTIVATION OF MAP KINASE (ERK1 2) BY ERYTHROPOIETIN AND STEM-CELL FACTOR IS ESSENTIAL FOR EXPANDED ERYTHROPOIESIS/

Stem cell factor (SCF) and erythropoietin (EPO) work synergistically t o support erythropoiesis, but the mechanism for this synergism is unkn own. By using purified human erythroid colony-forming cells (ECFC), we have found that SCF and EPO synergistically activate MAP kinase (MAPK , ERK1/2), which correlates with the cell growth and thus may be respo nsible for the synergistic effects. Treatment of the cells with PD9805 9 and wortmannin, inhibitors of MEK and PI-3 kinase, respectively, inh ibited the synergistic activation of MAPK and also the cell growth, fu rther supporting this conclusion. Wortmannin only inhibits MAPK activa tion induced by EPO but not that by SCF, suggesting that SCF and EPO m ay activate MAPK through different pathways, which would facilitate sy nergy. Furthermore, EPO, but not SCF led to activation of STATE, where as SCF and wortmannin had no effect on the EPO-induced STATE activatio n, suggesting that STATE is not involved in the synergistic action of SCF and EPO. Together, the data suggest that synergistic activation of MAPK by SCF and EPO is essential for expanded erythropoiesis. (C) 199 8 by The American Society of Hematology.