Thrombospondin 1 Expression in Transformed Endothelial Cells Restores a Normal Phenotype and Suppresses Their Tumorigenesis

• Published in: Proceedings of the National Academy of Sciences - PNAS 1995-07, Vol.92 (15), p.6788-6792
• Main Authors: Sheibani, Nader, Frazier, William A.
• Format: Article
• Language: English
• Subjects: Animals; Cell Differentiation; Cell growth; Cell lines; Cell Transformation, Neoplastic; Cells; Cellular biology; Cultured cells; Endothelial cells; Endothelium, Vascular - pathology; Gene Expression Regulation, Neoplastic; Hemangioma; Hemangioma - etiology; Humans; Mast cells; Membrane Glycoproteins - biosynthesis; Messenger RNA; Mice; Neoplasms, Experimental; Phenotype; Phenotypes; Plasminogen Activator Inhibitor 1 - biosynthesis; Recombinant Proteins - biosynthesis; Suppression, Genetic; Thrombospondins; Transfection; Transforming Growth Factor beta - analysis; Tumors; Urokinase-Type Plasminogen Activator - biosynthesis
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.92.15.6788

Murine endothelial cells are readily transformed in a single step by the polyomavirus oncogene encoding middle-sized tumor antigen. These cells (bEND.3) form tumors (hemangiomas) in mice which are lethal in newborn animals. The bEND.3 cells rapidly proliferate in culture and express little or no thrombospondin 1 (TS1). To determine the role of TS1 in regulation of endothelial cell phenotype, we stably transfected bEND.3 cells with a human TS1 expression vector. The cells expressing human TS1 were readily identified by their altered morphology and exhibited a slower growth rate and lower saturation density than the parental bEND.3 cells. The TS1-expressing cells also formed aligned cords of cells instead of clumps or cysts in Matrigel. Moreover, while the bEND.3 cells formed large tumors in nude mice within 48 hr, the TS1-expressing cells failed to form tumors even after 1 month. The TS1-transfected cells expressed transforming growth factor β mRNA and bioactivity at levels similar to those of the parental or vector-transfected bEND.3 cells, indicating that the effects of TS1 expression are not due to the activation of transforming growth factor β by TS1. TS1 expression resulted in a >100-fold decrease in net fibrinolytic (urokinase-type plasminogen activator, uPA) activity due to more plasminogen-activator inhibitor 1 and less uPA secretion. TS1 thus appears to be an important regulator of endothelial cell phenotype required for maintaining the quiescent, differentiated state.