PKR regulates survival of clonogenic BM progenitor cells in vitro after hematopoietic growth factor deprivation, inflammatory cytokine treatment, or γ-irradiation. The colony formation data are expressed as percent of maximal numbers of colonies. Mean actual maximal colony counts per 2 × 10⁴ cells were WT = 70.4, TgPKR = 53.4, TgDNPKR = 77, and PKRKO = 111.6. (A) BM cells were cultured in media without growth factors for the indicated times. Cells (2 × 10⁴) were then plated in methylcellulose-based media containing 1× growth factors (50 ng/mL SCF, 10 ng/mL IL-3, 10 ng/mL IL-6, and 3U/mL EPO) and colonies scored after 7 days (n = 3). (B) Lin⁻c-Kit⁺ cells were isolated from BM of WT, TgPKR, TgDNPKR, or PKRKO mice and cultured in media without growth factors. At the indicated times, measurement of Annexin V staining was performed by flow cytometry to determine apoptosis. (n = 3). (C) BM cells (2 × 10⁴) were plated in methylcellulose-based media containing various concentrations of the hematopoietic growth factor cocktail (0.0675× to 1×, 1× = 50 ng/mL SCF, 10 ng/mL IL-3, 10 ng/mL IL-6, and 3U/mL EPO) and hematopoietic colony formation scored. (D-G) Cells (2 × 10⁴) were plated in methylcellulose-based media containing various concentrations of the hematopoietic growth factor cocktail and 300nM of either PKRI or inactive control. (H) Hematopoietic colony formation was assayed in medium containing 1× growth factors and the indicated concentration of IFN-γ. (I) Hematopoietic colony formation was assayed in medium containing 1× growth factors and the indicated concentration of TNF-α. (J) Hematopoietic colony formation was assayed after irradiation of BM cells with the indicated doses of γ-irradiation. (For all colony-formation assays, colonies were scored after 7 days’ growth and results are the average of BM from 3 mice [n = 3] for each genotype.)