Ectopic localizations of Golgi glycosyltransferases.

Glycosyltransferases involved in N- and O-glycan chain elongation and termination are localized in the Golgi apparatus. Early evidence in support of this rule was based on fractionation techniques and was corroborated by numerous immunocytochemical studies. Usually these studies were confined to cultured cell lines exhibiting little differentiation features, such as HeLa cells. However, localization studies conducted in primary cell cultures (e.g., human umbilical vein endothelial cells), cells obtained ex vivo (e.g., sperm cells), and tissue sections (e.g., intestinal, renal, or hepatic tissue) often reveal ectopic localizations of glycosyltransferases usually at post-Golgi sites, including the plasma membrane. Hence, extracellular cues resulting from specific adhesion sites may influence post-Golgi trafficking routes, which may be reflected by ectopic localization of Golgi enzymes.