Allosteric feed-forward activation of AP-2 via FCHO-BMP2K axis promotes clathrin-mediated endocytosis

Spatio-temporal regulation of central adaptor complex, AP-2 is pivotal for clathrin-mediated endocytosis (CME). We recently discovered that FCHO proteins trigger clathrin-coated pit (CCP) formation by allosterically activating AP-2 on plasma membrane (). Here, we demonstrate that this activation promotes AP-2 phosphorylation recruitment and stabilization of BMP-2 inducible kinase (BMP2K), a AP-2 kinase leading to CCP maturation. Accordingly, BMP2K mislocalizes and degrades in FCHO knockout/ AP-2 depleted cells. Functional inactivation of kinase impairs AP-2 phosphorylation leading to altered lattice morphology and CME phenotypes reminiscent of CCP maturation defects. Reexpression of FCHO rescues AP-2 phosphorylation defects in FCHO knockout cells implying membrane activation of AP-2 is a prerequisite for kinase function. Furthermore, gain- and loss-of function phenotypes of FCHO and BMP2K are analogous and mirror altered AP-2 functions during zebrafish embryogenesis. Together, our findings reveal an allosteric feed-forward axis for operation of CME.