Phosphatidylinositol 3-kinase is involved in the protection of primary cultured human erythroid precursor cells from apoptosis

Little is known about the physiologic role of phosphatidylinositol 3-kinase (PI-3K) in the development of erythrocytes. Previous studies have shown th at the effects of the PI-3K inhibitor wortmannin on erythropoietin (EPO)-de pendent cell lines differed depending on the cell type used. Wortmannin inh ibited EPO-induced differentiation of some cell lines without affecting the ir proliferation; however, the EPO-induced proliferation of other cell line s was inhibited by wortmannin. In neither case were signs of apoptosis obse rved. We have previously reported that signaling in highly purified human c olony forming units-erythroid (CFU-E), generated in vitro from CD34(+) cell s, differed from that in EPO-dependent cell lines. In the current study, we examined the effects of a more specific PI-3K inhibitor (LY294002) on huma n CFU-E. We found that LY294002 dose-dependently inhibits the proliferation of erythroid progenitor cells with a half-maximal effect at 10 mu mol/L LY 294002. LY294002 at similar concentrations also induces apoptosis of these cells, as evidenced by the appearance of annexin V-binding cells and DNA fr agmentation. The steady state phosphorylation of AKT at Ser-473 that occurs as a result of PI-3K activation was also inhibited by LY294002 at similar concentrations, suggesting that the effects of LY294002 are specific. Inter estingly, the acceleration of apoptosis by LY294002 was observed in the pre sence or absence of EPO. Further, deprivation of EPO resulted in accelerate d apoptosis irrespective of the presence of LY294002. Our study confirms an d extends the finding that signaling in human primary cultured erythroid ce lls is significantly different from that in EPO-dependent cell lines. These data suggest that PI-3K has an antiapoptotic role in erythroid progenitor cells. In addition, 2 different pathways for the protection of primary eryt hroid cells from apoptosis likely exist: 1 independent of EPO that is LY294 002-sensitive and one that is EPO-dependent and at least partly insensitive to LY294002. (C) 1999 by The American Society of Hematology.