On the role of cell surface carbohydrates and their binding proteins (lectins) in tumor metastasis

This review focuses on the recent advances in investigations of the role of cell surface carbohydrates in tumor metastasis. It also summarizes the results of extensive studies of endogenous lectins, their structure, carbohydrate specificity and biological functions with the major emphasis on the significance of lectin-cell surface carbohydrate interactions in a metastatic process. Numerous data demonstrate that malignant transformation is associated with various and complex alterations in the glycosylation process. Some of these changes might provide a selective advantage for tumor cells during their progression to more invasive and metastatic phenotype. Cell glycosylation depends on the expression and function of various glycosyltransferases and glycosidases. Recently, transfection of genes encoding various glysosyltransferases gene in sense and antisense orientation helped to bring direct evidence that changes in cell surface carbohydrates are important for the metastatic behavior of tumor cells. Cell surface carbohydrates affect tumor cell interactions with normal cells or with the extracellular matrix during metastatic spread and growth. These interactions can be mediated via tumor cell carbohydrates and their binding proteins known as endogenous lectins. The family of the discovered endogenous lectins is rapidly expanding. The number of C-type lectins has reached 50 and at least 10 galectins have been identified. The biological significance of the endogenous lectins and their possible role in tumor growth and metastasis formation has started to unravel. Some lectins recognize the 'foreign' patterns of cell surface carbohydrates expressed by microorganisms and tumor cells, and play a role in innate and adaptive immunity. It was shown that lectins affect tumor cell survival, adhesion to the endothelium or extracellular matrix, as well as tumor vascularization and other processes that are crucial for metastatic spread and growth.