The signalling factor PI3K is a specific regulator of the clathrin-independent dynamin-dependent endocytosis of IL-2 receptors.
Receptor-mediated endocytosis is an essential process used by eukaryotic cells to internalise many molecules. Several clathrin-independent endocytic routes exist, but the molecular mechanism of each pathway remains to be uncovered. The present study focuses on a clathrin-independent dynamin-dependent pathway used by interleukin 2 receptors (IL-2R), essential players of the immune response. Ras-related C3 botulinum toxin substrate (Rac1) and its targets, the p21-activated kinases (Pak), are specific regulators of this pathway, acting on cortactin and actin polymerization. The present study reveals a dual and specific role of phosphatidylinositol 3-kinase (PI3K) in IL-2R endocytosis. Inhibition of the catalytic activity of PI3K strongly affects IL-2R endocytosis, in contrast to transferrin (Tf) uptake, a marker of the clathrin-mediated pathway. Moreover, Vav2, a GTPase exchange factor (GEF) induced upon PI3K activation, is specifically involved in IL-2R entry. The second action of PI3K is through its regulatory subunit, p85α, which binds to and recruits Rac1 during IL-2R internalisation. Indeed, the overexpression of a p85α mutant missing the Rac1 binding motif leads to the specific inhibition of IL-2R endocytosis. The inhibitory effect of this p85α mutant could be rescued by the overexpression of either Rac1 or the active form of Pak, indicating that p85α acts upstream of the Rac1-Pak cascade. Finally, biochemical and fluorescent microscopy techniques reveal an interaction between p85α, Rac1 and IL-2R that is enhanced by IL-2. In summary, our results indicate a key role of class I PI3K in IL-2R endocytosis that creates a link with IL-2 signalling.
Institut Pasteur, Unité de Biologie des Interactions Cellulaires, 25 rue du Docteur Roux, 75724 Paris Cedex 15, France.
Cyril
C
Basquin
Valérie
V
Malardé
Paul
P
Mellor
Deborah H
DH
Anderson
Vannary
V
Meas-Yedid
Jean-Christophe
JC
Olivo-Marin
Alice
A
Dautry-Varsat
Nathalie
N
Sauvonnet
D015153:Blotting, Western; D002460:Cell Line; D002966:Clathrin / Q000378:metabolism*; D016207:Cytokines / Q000378:metabolism; D034281:Dynamins / Q000378:metabolism*; D004705:Endocytosis / Q000235:genetics / Q000502:physiology*; D005455:Fluorescent Antibody Technique; D006801:Humans; D047468:Immunoprecipitation; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D015375:Receptors, Interleukin-2 / Q000378:metabolism*; D015398:Signal Transduction
D002966:Clathrin; D016207:Cytokines; D015375:Receptors, Interleukin-2; D019869:Phosphatidylinositol 3-Kinases; D034281:Dynamins