Over-expression of ATF4 led to further increased JAG1 level (Fig. 3C) while down-regulation of ATF4 by siRNA decreased JAG1 level in ECs co-cultured with ICN1 leukemia cells (Fig. 3D-3E), indicating that EC JAG1 expression is regulated by ATF4 in the leukemia microenvironment. This evidence concerns the gene ATF4 and leukemia.