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The signalling factor PI3K is a specific regulator of the clathrin-independent dynamin-dependent endocytosis of IL-2 receptors
Cyril Basquin, Valérie Malardé, Paul Mellor, Deborah H. Anderson, Vannary Meas-Yedid, Jean-Christophe Olivo-Marin, Alice Dautry-Varsat, Nathalie Sauvonnet


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.


  • Author contributions

    C.B. performed the experiments and participated in the writing of the manuscript; V.M. performed experiments; P.M. and D.H.A. performed experiments and corrected the manuscript; V.M.Y. and J.C.O.M. designed algorithms to quantify the data; A.D.V. corrected the manuscript and N.S. performed and designed experiments and wrote the manuscript.

  • Funding

    This work was supported by the Conseil Pasteur-Weizmann [grant to N.S.]; and the Canadian Cancer Society Research Institute [grant to D.H.A.]. C.B. is supported by ED no. 426 ‘Gènes, Génomes, Cellules’ and ‘La Ligue Contre le Cancer’ fellowships. P.M. is supported by a post-doctoral fellowship from the Saskatchewan Health Research Foundation.

  • Supplementary material available online at

  • Accepted December 10, 2012.
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