Abstract
The level of expression of the α5/β1 integrin fibronectin receptor(FnR) strongly affects the growth rate of CHO cell tumors in nude mice. Here we report that α5/β1 expression also influences the organization of the tumor vasculature. Tumors formed from CHO clones defective in FnR expression have a leaky vasculature that gives them a hemorrhagic appearance. Tumors from wild‐type CHO cells, or from FnR‐deficient CHO clones transfected with constructs coding for the α5 integrin subunit, have an intact, non‐leaky vasculature. In tumors from FnR‐deficient cells, the endothelial lining of blood vessels is sparse, and red cells and plasma proteins can be detected in the tumor parenchyma. In tumors from cells expressing the α5/β1 FnR, tumor vessels are circumscribed by a lining of von‐Willebrand‐factor‐positive endothelial cells, and blood cells and proteins are confined to the vessel lumina. Thus, the level of expression of the α5/β1 FnR in the tumor parenchymal cells can influence the development of tumor vasculature. Since α5/β1 is vital to the organization of the extracellular matrix, one possibility is that altered matrix assembly contributes to the defective vascularization seen in α5/β1 ‐deficient tumors.