EB1 contributes to proper front-to-back polarity in neutrophil-like HL-60 cells

Directed migration of leukocytes towards a chemotactic source is largely dependent on coordinated actin cytoskeleton functions that provide the driving forces at the cell front and enable contractility at the rear. In contrast to the force-generating properties of the actin cytoskeleton, the microtubule network assumes a regulatory function in balancing front-to-back polarity. In migrating neutrophils, microtubules are mostly concentrated at the cell rear, and previously published work suggested that microtubules are stabilized and kept in place by a mechanism involving Cdc42, WASP, CD11b, and the end-binding protein 1 (EB1). EB1, as a microtubule plus-end tracking protein (+TIP), is a potential candidate to bridge the gap between microtubule and actomyosin dynamics. After knockdown of EB1 in neutrophil-like HL-60 cells, both directionality and straightness of migration while moving through 3D collagen gels are impaired. An increased number of lateral protrusions are observed in EB1-knockdown cells, indicating an inability to balance cell polarity in the absence of EB1. Moreover, in EB1-deficient cells, substrate adhesion on fibrinogen-coated surfaces is significantly reduced. EB1-knockdown cells show significant changes in levels of GEF-H1, a microtubule-associated guanine nucleotide exchange factor that links microtubule integrity to RhoA-dependent regulation of the actin cytoskeleton, suggesting that GEF-H1 might constitute one element of the microtubule-actin crosstalk in migrating leukocytes.