Dynasore does not inhibit the endocytosis of transferrin but impairs its endosomal trafficking in HeLa cell line

Transferrin (Tf) is an iron-binding glycoprotein (molecular weight 80 kDa) that takes role in iron-uptake in cells and therefore regulates the free iron level in our body. Transferrin, loaded with iron, binds to the surface expressed transferrin receptor (TfR) and enters the cell through receptor mediated, clathrin-dependent endocytosis that requires the unimpaired function of protein dynamin. Inside the cell, Tf/TfR complex is directed to early endosomes where iron is released. On the other hand, apoTf/TfR is subsequently targeted to the plasma membrane either directly or indirectly via juxtanuclear recycling compartment. Although the main endocytic pathway of Tf/TfR has been extensively investigated, a lot of data are rather controversial. Considering that, the aim of this study was to better elucidate the less known links of its intracellular trafficking in HeLa cell line. To achieve that goal we used a palette of inhibitors that remodel cellular endosomal network and have followed internalized molecules by flow cytometry and confocal microscopy. Aluminium fluoride, but not dynasore, retards the endocytosis of Tf/TfR. However, both inhibitors (together with PLD and PLA inhibitors) affect the structure and function (e.g. recycling) of endosomal compartments. These results implicates that dynamin is not essential for endocytosis of Tf/TfR but is important for its recycling. Furthermore, small Arf GTPases are involved both in endocytosis and recycling of Tf/TfR.