Gangliosides (GS) are sialylated glycolipids mainly expressed at the outer leaflet of the plasma membrane. They have been implicated in many physiological and pathological processes, e.g. in cell growth, cell adhesion and endocytosis; including its capacity to function as receptor for several toxins, viruses and antibodies. While clathrin-mediated endocytosis has been widely studied, the specific role of GS in this cellular process has not been well established. By biochemical and cell biology techniques, we found an increased internalization of the transferrin-receptor (Tf-R) complex, the archetypical cargo for internalization through clathrin-mediated endocytosis, in cell lines expressing GS with higher level of sialylation. The ectopic expression of Neu3, a GS-specific sialidase, led to a drastic decrease in Tf endocytosis, suggesting a participation of GS in this process. However, the expression of Neu3 in GS-depleted cells maintained its effect on Tf-R endocytosis. Kinetic assays carried out in Neu3-over expressing cells showed a significant reduction in the sorting of endocytosed Tf-R complex to early and recycling endosomes. Overall, the results indicate that the effect of Neu3 on the internalization of Tf is independent of its action on GS, suggesting a novel role of this sialidase on clathrin-mediated endocytosis.
