SU1498, an Inhibitor of Vascular Endothelial Growth Factor Receptor 2, Causes Accumulation of Phosphorylated ERK Kinases and Inhibits Their Activity in Vivo and in Vitro

SU1498, an inhibitor of vascular endothelial growth factor receptor 2, has been used successfully to study the physiological manifestations of receptor functions. Here we report that in addition to its anti-receptor activity, SU1498 stimulates accumulation of phosphorylated ERKs in human umbilical vein endothelial cells and in human aortic endothelial cells in a manner that is dependent on the functioning of the upstream components of the MAPK pathway, B-Raf, and MEK kinases. The enhanced accumulation of phospho-ERKs is observed only in cells that have been stimulated with sphingosine 1-phosphate or protein growth factors; SU1498 by itself is ineffective. We show that the inhibitor acts by blocking the kinase activity of phospho-ERK both in a direct assay and in immunoprecipitates from cells treated with the compound. The data reveal a novel and unique way in which MAPK signaling pathway may be blocked in human endothelial cells.