Trimer carboxyl propeptide of collagen I produced by mature osteoblasts ischemotactic for endothelial cells

During the second phase of osteogenesis in vitro, rat osteoblasts secrete i nducer(s) of chemotaxis and chemoinvasion of endothelial and tumor cells. W e report here the characterization and purification from mature osteoblast conditioned medium of the agent chemotactic for endothelial cells. The chem oactive conditioned medium specifically induces directional migration of en dothelial cells, not affecting the expression and activation of gelatinases , cell proliferation, and scattering. Directional migration induced in endo thelial cells by conditioned medium from osteoblasts is inhibited by pertus sis toxin, by blocking antibodies to integrins alpha (1), beta (1), and bet a (3), and by antibodies to metalloproteinase 2 and 9. The biologically act ive purified protein has two sequences, coincident with the amino-terminal amino acids, respectively, of the alpha (2) and of the alpha (2) carboxyl p ropeptides of type I collagen, as physiologically produced by procollagen C proteinase. Antibodies to type I collagen and to the carboxyl terminus of alpha (1) or alpha (2) chains inhibit chemotaxis. The chemoattractant is th e propeptide trimer carboxyl-terminal to type I collagen, and its activity is lost upon reduction. These data illustrate a previously unknown function for the carboxyl-terminal trimer, possibly relevant in promoting endotheli al cell migration and vascularization of tissues producing collagen type I.