TPA-induced differentiation of rat aortic endothelial cells is substrate-specific and receptor mediated.

Under normal conditions, the morphology of cultured endothelial cells (EC) is characterized by a contact-inhibited monolayer with a distinct cobblestone appearance. However, when treated with phorbol esters, EC acquire fibroblast-like growth characteristics, are no longer contact-inhibited in growth, become invasive and form pre-capillary, tubular structures within collagen matrices. These events describe the basic processes of angiogenesis. We characterized the early effects of phorbol-12-myristate-13-acetate (TPA) on the attachment and spreading of rat aortic endothelial cells (RAEC) to purified extracellular matrix proteins by analyzing the distribution of fibronectin integrin receptors and the organization of cytoskeleton microfilaments during RAEC spreading on four different extracellular matrix peptides (i.e., Collagen Types I and IV, fibronectin and laminin). Type IV collagen appeared to be the best substrate for RAEC adhesion and spreading while laminin proved to be the poorest. TPA (0.1 micron) decreased the rate of RAEC spreading on Type IV collagen with a subsequent delay in cell-cell contact formation. In contrast, TPA increases the rate of spreading and cell-cell contact formation of RAEC plated on laminin.