The p85 recruitment site of EPO-R is required for EPO-dependent suppression of γ-IR–induced cell-cycle arrest.

(A) 32D cells expressing wild-type (wt) or mutated EPO-R were cultured in medium that contained either 1.4 ng/mL IL-3 or 5 U/mL EPO. Subsequently, cultures were exposed to 4 Gy γ-IR (+γ) or were left untreated (−γ). Twenty-four hours after irradiation, cells were stained with PI and analyzed by FACS. Before PI staining, the viability of the cells was determined by trypan blue exclusion and was 94% or greater in all experiments. Percentage of S-phase cells is indicated for each culture. (B) Percentage of G2/M cells in γ-IR–treated cultures versus nonirradiated cultures shown in panel A was determined, and the fold increase in G2/M was calculated (G2+γ/G2−γ). Values presented represent the average of 3 independent experiments. Similar results were obtained with at least 3 independent clones of each cell type. ▪, EPO; ■, IL-3.