JIP4 is recruited by the phosphoinositide-binding protein Phafin2 to promote recycling tubules on macropinosomes

Macropinocytosis allows cells to take up extracellular material in a non-selective manner. The molecular mechanisms that mediate recycling of membranes and transmembrane proteins from macropinosomes still need to be defined. Here we report that JIP4, a coiled-coil containing protein previously described to bind to microtubule motors, is recruited to retromer- and actin-containing tubulating subdomains on macropinosomes by binding to the PH domain of the phosphatidylinositol 3-phosphate (PtdIns3P)-binding protein Phafin2. This recruitment is not shared by the closely related isoforms JIP3 and Phafin1. Disruption of Phafin2 or PtdIns3P impairs JIP4 recruitment to macropinosomes whereas forced localization of Phafin2 to mitochondria causes mitochondrial targeting of JIP4. While knockout of JIP4 suppresses tubulation, overexpression enhances tubulation from macropinosomes. JIP4 knockout cells display increased retention of macropinocytic cargo in both early and late macropinosomes, consistent with a recycling defect. Collectively, these data identify JIP4 and Phafin2 as components of a tubular recycling pathway that operates from macropinosomes.