The functional role of cell adhesion molecules in tumor angiogenesis

Cell adhesion molecules (CAMs) are cell surface glycoproteins that mediate the physical interactions between adjacent cells and between cells and the surrounding extracellular matrix. CAMs belong to different protein families, depending on their structural and functional properties. Furthermore, the expression of certain CAMs under physiological conditions is restricted to specific cell types. Besides playing a key homeostatic role in maintaining the architecture of quiescent tissues, CAMs have also to adapt to the microenvironmental changes that occur during certain physiological and pathological processes. This is best exemplified by cancer vascularization, where the expression and function of vascular CAMs are dynamically regulated in response to tissue alterations induced by tumor growth as well as by changes in the surrounding stroma. This enables endothelial cells (ECs) to leave the quiescent state and re-enter the angiogenic cascade. The latter is a multistep process carried out by different types of specialized ECs. This review describes the actual or supposed function of the various CAM subsets in the sequential series of events that underlie vascular changes during tumor angiogenesis. Notably, elucidating the mechanism of action of endothelial CAMs in cancer vasculature is expected to open new therapeutic avenues aimed at interfering with tumor growth and dissemination.