Soulet F, Yarar D, Leonard M, Schmid SL

Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037, USA.

Dynamin, a central player in clathrin-mediated endocytosis, interacts with several functionally diverse SH3 domain-containing proteins. However, the role of these interactions with regard to dynamin function is poorly defined. We have investigated a recently identified protein partner of dynamin, SNX9, sorting nexin 9. SNX9 binds directly to both dynamin-1 and dynamin-2. Moreover by stimulating dynamin assembly, SNX9 stimulates dynamin's basal GTPase activity and potentiates assembly-stimulated GTPase activity on liposomes. In fixed cells, we observe that SNX9 partially localizes to clathrin-coated pits. Using total internal reflection fluorescence microscopy in living cells, we detect a transient burst of EGFP-SNX9 recruitment to clathrin-coated pits that occurs during the late stages of vesicle formation and coincides spatially and temporally with a burst of dynamin-mRFP fluorescence. Transferrin internalization is inhibited in HeLa cells after siRNA-mediated knockdown of SNX9. Thus, our results establish that SNX9 is required for efficient clathrin-mediated endocytosis and suggest that it functions to regulate dynamin activity.

Mesh Terms:
Carrier Proteins, Cell Membrane, Clathrin, Coated Pits, Cell-Membrane, Dynamin I, Dynamin II, Endocytosis, GTP Phosphohydrolases, HeLa Cells, Humans, Liposomes, Protein Binding, Receptors, Transferrin, Sorting Nexins, Vesicular Transport Proteins

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