Live‐cell Imaging of Endothelial Cell Tube Formation: Inhibition by Chondrostatin

Abstract

Cartilage tissue is avascular and resistant to tumor invasion. The basis for these properties has been actively sought for the last 35 years. Based on the assumption that cartilage contains inhibitors of angiogenesis, previous studies have focused on isolating potential vascular inhibitors from cartilage. Here we report that the NH2‐propeptide of type IIB procollagen (chondrostatin), a product of collagen biosynthesis, is capable of inhibiting angiogenesis mediated by the integrins, αVß3 or αVß5 present on endothelial cells. Chondrostatin inhibits tube formation by human umbilical vein cells (HUVEC) and inhibits endogenous endothelial cell outgrowth in a rat aortic ring angiogenesis bioassay. The kinetics of formation of vessel tubes by HUVEC cells was investigated by imaging cells as they formed tubes in a collagen gel. As αVß3 and αVß5 integrins are expressed primarily on endothelial cells, cancer cells and osteoclasts, but not on normal chondrocytes, we propose that cartilage chondrostatin protects cartilage by targeting endothelial cells during chondrogenesis, thus inhibiting angiogenesis and rendering the tissue avascular. We show that chondrostatin also binds to chondrosarcoma, breast and cervical cancer cells via the integrins αVß3 and αVß5 and inhibits migration, eventually inducing cell death.Supported by NIH R0136994