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Mode of action of erythropoietin (Epo) in an Epo-dependent murine cell line. II. Cell cycle dependency of Epo action.

Erythropoietin (Epo), a glycoprotein hormone, regulates the proliferation and differentiation of committed erythroid progenitor cells. We investigated the effect of Epo on the kinetics of an Epo-dependent cell line (DA-1ER), which was cloned from the murine interleukin 3-dependent cell line, DA-1. Flow cytometry and [3H]thymidine incorporation were used to analyze the cell cycle. Removal of Epo from the culture medium resulted in the accumulation of the cells in the G1 phase. Eighteen hours after the removal of Epo, 75%-80% of the cells were arrested in G1 phase. Readdition of Epo to these quiescent cells allowed them to progress from the G1 to the S phase with a lag period of 10 h. Epo was required throughout the lag period in order to achieve maximal DNA synthesis. When the cells were arrested in the G2/M phase or the G1/S interphase by colcemid and thymidine, respectively, and then released from the arrest, they could complete the cell cycle in the absence of Epo. These findings suggest that Epo is only required in the G1 phase for the cells to progress through the cell cycle.