Role of ERK activation in growth and erythroid differentiation of K562 cells

Inhibition of signaling through has in BCR-ABL-positive pluripotent K562 ce lls leads to apoptosis and spontaneous differentiation. However, Has-induce d activation of the mitogen-activated protein kinase ERK has been suggested to play a critical role in either growth or differentiation in different m odel systems. We studied the role of ERK activation in the growth-promoting and anti-apoptotic effect of Has and its involvement in hemin-induced nont erminal erythroid differentiation using the BCR-ABL-positive K562 cell line as a model. K562 cells were stably transfected with ERK1 or the dominant i nhibitory mutant of ERK1 (ERK1-KR). Overexpression of ERK1-KR inhibited cel l growth with an approximately fourfold increase in doubling time and induc ed apoptosis in K562 cells, Incubation with the MEK1 inhibitor UO126 inhibi ted cell growth and induced apoptosis in K562 cells in a dose-dependent man ner as well. In the presence of exogenously added hemin, K562 cells differe ntiate into erythroblasts, as indicated by the production of large amounts of fetal hemoglobin. We examined the activation of MAP kinases during hemin -induced differentiation, The ERK1 and 2 activity increased within 2 h post hemin treatment and remained elevated for 24-48 h, During this time, fetal hemoglobin synthesis also increases from 0.8 to 10 pg/cell. There was no a ctivation of JNK or p38 protein kinases, The hemin-induced accumulation of hemoglobin was inhibited in ERK1-KR overexpressing cells and was enhanced i n the wild-type ERK1 transfectants. Our results suggest that ERK activation is involved in both growth and hemin-induced erythroid differentiation in the BCR-ABL-positive K562 cell line, (C) 2001 Academic Press.