DLX4 stimulates NO levels, VEGF-A production and endothelial cell growth in vitro by inducing iNOS. (A) Flow cytometric analysis of iNOS levels in vector-control and +DLX4 ES2 cells, and in +DLX4 ES2 cells that stably expressed NOS2 shRNA (+DLX4 + shNOS2). (B) NO levels were assayed by using Griess reagent in culture medium that was conditioned by equivalent numbers of cells of each ES2 line. (C) Levels of VEGF-A were assayed by ELISA in tumor-conditioned medium. (D) Growth of endothelial cells cultured in tumor-conditioned medium was evaluated by MTT assay. Shown in B, C and D are average results of three independent experiments.