Lipid products of PI(3)Ks maintain persistent cell polarity and directed motility in neutrophils

In gradients of external chemo-attractant, mammalian neutrophilic leukocytes (neutrophils)(1) and Dictyostelium discoideum amoebae 2 adopt a polarized morphology and selectively accumulate lipid products of phosphatidylinositol-3-OH kinases (PI(3) Ks), including PtdIns(3,4,5) P-3, at their up-gradient edges; the internal PtdIns(3,4,5) P-3 gradient substantially exceeds that of the external attractant. An accompanying report 3 presents evidence for a positive feedback loop that amplifies the gradient of internal signal: PtdIns(3,4,5) P-3 at the leading edge stimulates its own accumulation by inducing activation of one or more Rho GTPases (Rac, Cdc42, and/or Rho), which in turn increase PtdIns(3,4,5) P-3 accumulation. Here we show that interruption of this feedback by treatment with PI(3) K inhibitors reduces the size and stability of pseudopods and causes cells to migrate in jerky trajectories that deviate more from the up-gradient direction than do those of controls. Moreover, amplification of the internal PtdIns(3,4,5) P-3 gradient is markedly impaired by latrunculin or jasplakinolide, toxins that inhibit polymerization (4,5) or depolymerization(6) of actin, respectively. Thus reciprocal interplay between PtdIns(3,4,5) P-3 and polymerized actin initiates and maintains the asymmetry of intracellular signals responsible for cell polarity and directed motility.