ECSM2, an endothelial specific filamin A binding protein that mediates chemotaxis

Objective-We aimed to characterize the expression and function of a novel transcript that bioinformatics analysis predicted to be endothelial specific, called endothelial-specific molecule-2 (ECSM2). Methods and Results-A full-length cDNA was isolated and predicted ECSM2 to be a putative 205-amino acid transmembrane protein that bears no homology to any known protein. Quantitative polymerase chain reaction analysis in vitro and in situ hybridization analysis in vivo confirmed ECSM2 expression to be exclusively endothelial, and localization to the plasma membrane was shown. Knockdown of ECSM2 expression in human umbilical vein endothelial cells using siRNA resulted in both reduced chemotaxis and impaired tube formation on matrigel, a solubilized basement membrane, both processes involved in angiogenesis. A yeast 2 hybrid analysis using the ECSM2 intracellular domain identified filamin A as an interacting protein. This interaction was confirmed by precipitation of filamin-A from endothelial cell lysates by a GST-tagged intracellular domain of ECSM2. Conclusion-This study is the first to characterize a novel cell surface protein ECSM2 that regulates endothelial chemotaxis and tube formation, and interacts with filamin A. These studies implicate a role for ECSM2 in angiogenesis via modulation of the actin cytoskeleton.