AN ALPHA-2-BETA-1 INTEGRIN-DEPENDENT PINOCYTIC MECHANISM INVOLVING INTRACELLULAR VACUOLE FORMATION AND COALESCENCE REGULATES CAPILLARY LUMEN AND TUBE FORMATION IN 3-DIMENSIONAL COLLAGEN MATRIX

Human endothelial cells, when suspended within three-dimensional colla gen matrices, develop intracellular vacuoles that coalesce to form cap illary lumens and tubes. Vacuole and lumen formation are completely de pendent on the collagen-binding integrin alpha 2 beta 1, while other e ndothelial cell integrins had no apparent influence. Vacuole formation occurs by a pinocytic process with internalization of plasma membrane and molecules from the extracellular space, such as fluorescent trace rs. By immunofluorescence, vacuole membranes were found to contain ass ociated cell. surface proteins, proteins involved in endosomal traffic king (i.e., caveolin and annexin II), and F-actin. Furthermore, some v acuole compartments contained von Willebrand factor. Integrin-regulate d vacuole formation and coalescence are major mechanisms controlling c apillary lumen and tube formation within a three-dimensional extracell ular matrix. (C) 1996 Academic Press, Inc.