PDZRhoGEF and myosin II localize RhoA activity to the back of polarizing neutrophil-like cells

Chemoattractants such as formyl-Met-Leu-Phe (fMLP) induce neutrophils to polarize by triggering divergent pathways that promote formation of a protrusive front and contracting back and sides. RhoA, a Rho GTPase, stimulates assembly of actomyosin contractile complexes at the sides and back. We show here, in differentiated HL60 cells, that PDZRhoGEF (PRG), a guanine nucleotide exchange factor (GEF) for RhoA, mediates RhoA-dependent responses and determines their spatial distribution. As with RNAi knock-down of PRG, a GEF-deleted PRG mutant blocks fMLP-dependent RhoA activation and causes neutrophils to exhibit multiple fronts and long tails. Similarly, inhibition of RhoA, a Rho-dependent protein kinase (ROCK), or myosin II produces the same morphologies. PRG inhibition reduces or mislocalizes monophosphorylated myosin light chains in fMLP-stimulated cells, and myosin II ATPase inhibition reciprocally disrupts normal localization of PRG. We propose a cooperative reinforcing mechanism at the back of cells, in which PRG, RhoA, ROCK, myosin II, and actomyosin spatially cooperate to consolidate attractant-induced contractility and ensure robust cell polarity.