Changes in glycosylation on
proteins or
lipids are one of the hallmarks of
tumorigenesis. In many cases, it is still not understood how
glycan information is translated into biological function. In this review, we discuss at the example of specific
cancer-related
glycoproteins how their endocytic uptake into eukaryotic cells is tuned by
carbohydrate modifications. For this, we not only focus on overall uptake rates, but also illustrate how different uptake processes-dependent or not on the conventional
clathrin machinery-are used under given glycosylation conditions. Furthermore, we discuss the role of certain
sugar-
binding proteins, termed
galectins, to tune
glycoprotein uptake by inducing their crosslinking into lattices, or by co-clustering them with
glycolipids into raft-type membrane nanodomains from which the so-called
clathrin-independent carriers (CLICs) are formed for
glycoprotein internalization into cells. The latter process has been termed
glycolipid-
lectin (GL-Lect) hypothesis, which operates in a complementary manner to the
clathrin pathway and
galectin lattices.