KDR and leukemia: Additionally, literature has eluded to the fact that not only VEGF signals through receptor expression VEGFR-1 (Flt-1) and VEGFR-2 (FlK-2/KDR) specifically regulate endothelial function, but are also involved in hematopoietic stem cell and subsets of leukemia cell development[11, 12] Little is known of the mechanisms by which gravitational forces are converted to biochemical functional responses in cells.