Fbp17 and cip4 recruit ship2 and lamellipodin to prime the plasma membrane for fast endophilin-mediated endocytosis

Abstract

Endocytosis mediates the cellular uptake of micronutrients and the turnover of plasma membrane proteins. Clathrin-mediated endocytosis is the major uptake pathway in resting cells 1 , but several clathrin-independent endocytic routes exist in parallel 2,3 . One such pathway, fast endophilin-mediated endocytosis (FEME), is not constitutive but triggered upon activation of certain receptors, including the β 1 adrenergic receptor 4 . FEME activates promptly following stimulation as endophilin is pre-enriched by the phosphatidylinositol-3,4-bisphosphate-binding protein lamellipodin 4,5 . However, in the absence of stimulation, endophilin foci abort and disassemble after a few seconds. Looking for additional proteins involved in FEME, we found that 20 out of 65 BAR domain-containing proteins tested colocalized with endophilin spots. Among them, FBP17 and CIP4 prime the membrane of resting cells for FEME by recruiting the 5′-lipid phosphatase SHIP2 and lamellipodin to mediate the local production of phosphati-dylinositol-3,4-bisphosphate and endophilin pre-enrichment. Membrane-bound GTP-loaded Cdc42 recruits FBP17 and CIP4, before being locally deactivated by RICH1 and SH3BP1 GTPase-activating proteins. This generates the transient assembly and disassembly of endophilin spots, which lasts 5–10 seconds. This mechanism periodically primes patches of the membrane for prompt responses upon FEME activation.