Production of IGF-binding proteins by vascular endothelial cells

Conditioned serum-free media from cultured human, bovine and rodent endothelial cells contained binding proteins with high affinity for the insulin-like growth factors (IGFs). After partial purifications on heparin or Multiplication Stimulating Activity (MSA)-affinity columns, 2 species of binding protein were identified, a major protein having Mr approximately 35,000 and a minor 22-28,000 protein. The binding proteins had greater affinity for IGF-I than IGF-II with no affinity for insulin or proinsulin. Substantial amounts of the binding proteins remained cell-associated, loosely bound to the outer cell surface of the endothelial cell. Binding protein(s) from human endothelial cells cross-reacted with antibodies to the 53,000 dalton acid-stable human serum binding protein. Production of endothelial binding proteins was not stimulated by growth hormone or insulin. We conclude that endothelial cells in culture produce large quantities of specific IGF binding proteins. Such binding proteins should be relevant in understanding the complex metabolism and function of the IGFs in the intact host.