RABEP1 regulates neutrophil migration via endosomal recycling and actin polymerization

Neutrophils are the first responders of our innate immune system, crucial for defense against various infections. The intricate regulation of neutrophil migration is essential for neutrophil function. However, a complete mechanistic understanding is missing. We previously performed a miRNA overexpression screen and identified miR-190 as a potent suppressor of neutrophil migration in zebrafish. Through a second round of small-scale screening using neutrophil-specific knockouts of putative miR-190 targets, we identified that rabep1 (encoding Rabaptin, RAB GTPase binding effector protein 1) is essential for neutrophil motility and chemotaxis in zebrafish. Re-expressing full-length Rabaptin, but not its truncation lacking the Rab4/Rab5 binding domain, rescued cell motility in the knockout. Knocking down RABEP1 in differentiated human leukemia (dHL-60) cells consistently reduced cell motility. RABAPTIN-deficient dHL-60 cells are defective with fast recycling, yet maintain a normal Rab5 GTP level. The RABAPTIN-deficient cells displayed reduced PAK phosphorylation and decreased F-actin levels, yet still appropriately polarized upon chemokine stimulation. Overexpression of dominant-negative Rab4 or Rab5 has a similar inhibitory effect on neutrophil migration. Our data suggest that RABAPTIN drives endosomal recycling, Rac activation, and leading-edge actin polymerization, providing significant insights into the role of the endocytic pathway in neutrophil motility.