Ezrin Regulates Hematopoietic Stem/Progenitor Cell Motility

Abstract 1282

Ezrin is a member of the ERM (ezrin, moesin and radixin) protein family that links plasma membrane proteins to the actin cytoskeleton. Ezrin in other in vitro cell systems has been hypothesized to participate in cell-cell contact and could have a role in stem/ progenitor cell mobilization and adhesion. To test this hypothesis, we crossed ezrin^flox/flox mice with Mx1 cre transgenic mice to generate an inducible ezrin knock out mouse model. Inducible disruption of the ezrin gene in hematopoietic cells was achieved by the administration of polyIC. Ezrin knock out HSPCs exhibited a 30–40% decrease in baseline and chemokine stromal cell-derived factor-1 (SDF-1) stimulated motility in transwell migration assays in vitro. In addition, loss of ezrin led to a 60% decrease in the homing capacity of HSPCs in lethally irradiated recipient mice following transplantation. There was a 40–55% decrease in colony forming cells in peripheral blood and spleen of the mice following ezrin knock out, suggesting that ezrin knock out HSPCs may be deficient in egressing out of the bone marrow. To further understand the cause of the impaired motility of ezrin knock out HSPCs, we examined F-actin level of HSPCs at baseline and in response to SDF-1. Ezrin knock out HSPCs displayed 1.5 to 2 fold higher level of F-actin at baseline when compared with wild type cells. Following stimulation with SDF-1, wild type HSPCs that migrated to the bottom compartment of the transwell demonstrated a 2 time greater decrease in F-actin level when compared with ezrin knock out cells, suggesting that ezrin may participate in the regulation of F-actin depolymerization in HSPCs. In summary, we demonstrate that ezrin modulates HSPC migration and homing likely through its regulation on F-actin organization.