JAG1 and leukemia: Combined with findings that PERK down-regulation suppressed PERK-eIF2a- ATF4 activation and JAG1 expression (Fig. 2), these observations suggest that endothelial down-regulation of PERK attenuated leukemia progression and improved survival by suppressing PERK-eIF2a- ATF4-JAG1 activation, thereby decreasing angiogenic factor expression, reducing leukemia cell survival, and preserving the residual hematopoiesis.