Vasohibin is a newly identified negative feedback regulator for angiogenesis. When expressed in cultured human endothelial cells, vasohibin polypeptides were detected in multiple distinct molecular weight forms, suggesting that some proteolytic events may occur within cells or the pericellular milieu. In order to identify the proteolysis sites, vasohibin cDNA mutants were Generated to substitute some basic amino acids with alanine and then were transfected into endothelial cells. Western blots with anti-vasohibin monoclonal antibody following the transfection showed that there were at least two cleaving sites in the amino terminal region. Purified recombinant protein of the amino terminal truncated forms not only retained its inhibitory activity on angiogenesis in mouse corneal assay but also showed strong affinity to heparin. Moreover, deletion of some basic residues at the carboxyl terminal resulted in abrogation of both antiangiogenic and heparin-binding activities. Processing patterns and biological activities of the processed forms of this novel antiangiogenic factor are discussed. (c) 2006 Elsevier Inc. All rights reserved.