A novel heart derived inhibitor of vascular cell proliferation. Purification and biological activity

Abstract

Recently, growth factors with mitogenic properties for vascular wall cells have been isolated from adult heart tissue. Since angiogenesis in the heart typically does not occur under normal physiological conditions, despite the presence of many growth factors, we hypothesized the existence of growth inhibitors. To test this hypothesis, we subjected whole bovine heart extracts to a series of protein purification steps in search of such an inhibitor. The purification procedure consisted of ammonium sulfate precipitation followed by cation exchange chromatography, hydroxylapatite chromatography, ultrafiltration and gelfiltration. We isolated a small protein, which is an inhibitor of cell proliferation from the bovine heart. The inhibitor reversibly suppressed [3H]-thymidine incorporation into nuclei of bovine aortic endothelial and smooth muscle cells. The moiety responsible for the inhibitory activity was identified biochemically (SDS Page, isoelectric focusing, HPEC) as an 11 kD protein with an isoelectric point of 7. The substance is a heat and acetic acid stable protein which does not bind to reversed phase columns because of its hydrophilic character. The inhibitor has no affinity to heparin sepharose. The inhibitory activity was destroyed by hydrolysis. No homology to any hitherto structurally investigated growth inhibitor was observed using the chemical determination of the amino acid sequence by microsequencing after previous trypsin digestion. We conclude that the described growth inhibitor may counteract the activity of mitogens that are abundantly present in normal heart. Vascular cell proliferation may be regulated by inhibition or production of the inhibitor.