PKR expression cooperates with the NHD13 transgene to shorten survival and promote MDS evolution to acute leukemia in the NHD13 mouse. (A) NHD13 mice were crossed with mice expressing a PKR transgene specifically in hematopoietic cells (TgPKR) or PKRKO mice, to produce NHD13-TgPKR and NHD13-PKRKO mice. NHD13 (n = 12), NHD13-TgPKR (n = 12), and NHD13-PKRKO (n = 12) mice were aged until physical deterioration led to death or required euthanasia (defined as body condition score ≤2). (A) Kaplan–Meier analysis demonstrates that PKR expression cooperates with NHD13 to significantly shorten the survival of mice. (B) NHD13-TgPKR mice more frequently die of acute leukemia than NHD13 mice. Acute leukemia or MDS was determined by hematoxylin and eosin staining and flow cytometry of BM cells collected at time of death. (C) Kaplan–Meier analysis demonstrates superior survival in NHD13 mice with low-level PKR expression vs NHD13 mice with high-level PKR expression (RQ >2) relative to age-matched WT controls. PKR expression in PB mononuclear cells collected as NHD13 mice aged was measured by quantitative real-time polymerase chain reaction. Circles represent mice that were censored at 350 days. (D-E) At 3 and 6 months of age, BM was collected from WT, NHD13, NHD13-TgPKR, and NHD13-PKRKO mice for comparison by flow cytometry analysis. (D) BM blasts were measured using CD45⁺ expression and side scatter. NHD13-TgPKR mice had significantly increased BM blasts compared with NHD13 mice at 6 months, whereas in PKRKO mice, this was significantly reduced. (E) BM from NHD13-PKRKO mice had significantly increased CFU-GEMM activity compared with NHD13 or NHD13-TgPKR. (F) Lin⁻ BM cells were isolated from 8 NHD13 mice and PKR level determined by flow cytometry. Some 30 minutes after IR, p-ATM was measured by flow cytometry and plotted vs PKR expression to reveal that relative PKR expression was inversely proportional to p-ATM. Each point represents an individual mouse. *P < .05; **P < .01.