Endocytosis of G protein-coupled receptors is regulated by clathrin light chain phosphorylation

Ferreira, Filipe and Foley, Matthew and Cooke, Alex and Cunningham, Margaret and Smith, Gemma and Woolley, Robert and Henderson, Graeme and Kelly, Eamonn and Mundell, Stuart and Smythe, Elizabeth (2012) Endocytosis of G protein-coupled receptors is regulated by clathrin light chain phosphorylation. Current Biology, 22 (15). pp. 1361-1370. ISSN 0960-9822 (https://doi.org/10.1016/j.cub.2012.05.034)

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Signaling by transmembrane receptors such as G protein-coupled receptors (GPCRs) occurs at the cell surface and throughout the endocytic pathway, and signaling from the cell surface may differ in magnitude and downstream output from intracellular signaling. As a result, the rate at which signaling molecules traverse the endocytic pathway makes a significant contribution to downstream output. Modulation of the core endocytic machinery facilitates differential uptake of individual cargoes. Clathrin-coated pits are a major entry portal where assembled clathrin forms a lattice around invaginating buds that have captured endocytic cargo. Clathrin assembles into triskelia composed of three clathrin heavy chains and associated clathrin light chains (CLCs). Despite the identification of clathrin-coated pits at the cell surface over 30 years ago, the functions of CLCs in endocytosis have been elusive.  In this work, we identify a novel role for CLCs in the regulated endocytosis of specific cargoes. Small interfering RNA-mediated knockdown of either CLCa or CLCb inhibits the uptake of GPCRs. Moreover, we demonstrate that phosphorylation of Ser204 in CLCb is required for efficient endocytosis of a subset of GPCRs and identify G protein-coupled receptor kinase 2 (GRK2) as a kinase that can phosphorylate CLCb on Ser204. Overexpression of CLCb(S204A) specifically inhibits the endocytosis of those GPCRs whose endocytosis is GRK2-dependent.  Together, these results indicate that CLCb phosphorylation acts as a discriminator for the endocytosis of specific GPCRs.