protein_function: Endostatin potently inhibits endothelial cellproliferation and angiogenesis. May inhibit angiogenesis bybinding to the heparan sulfate proteoglycans involved in growthfactor signaling.
Endostatin is a naturally-occurring 20-kDa C-terminal fragment derived from type XVIII collagen. It is reported to serve as an anti-angiogenic agent, similar to angiostatin and thrombospondin. And It is produced by proteolytic cleavage of collagen XVIII, a member of the multiplexin family that is characterized by interruptions in the triple helix creating multiple domains, by proteases such as cathepsins. Using a genomic clone as a probe for fluorescence in situ hybridization, Endostatin was mapped the COL18A1 gene to 21q22.3. By immunoprecipitation analysis using membrane fractions of human mammary epithelial cells, It showed that endostatin specifically bound to cell surface nucleolin with high affinity. Blockage of nucleolin with neutralizing antibody or knockdown of nucleolin by RNA interference countered the antiendothelial activity of endostatin and abrogated its antiangiogenic and antitumor activity in vivo.