PI(3)K gamma has an important context-dependent role in neutrophil chemokinesis

The directional movement of cells in a gradient of external stimulus is termed chemotaxis and is important in many aspects of development and differentiated cell function. Phophoinositide 3-kinases (PI(3)Ks) are thought to have critical roles within the gradient-sensing machinery of a variety of highly motile cells(1,2), such as mammalian phagocytes(3), allowing these cells to respond quickly and efficiently to shallow gradients of soluble stimuli. Our analysis of mammalian neutrophil migration towards ligands such as fMLP shows that, although PtdIns(3,4)P-2 and PtdIns(3,4,5)P-3 accumulate in a PI(3)K gamma-dependent fashion at the up-gradient leading-edge, this signal is not required for efficient gradient-sensing and gradient-biased movement. PI(3)K gamma activity is however, a critical determinant of the proportion of cells that can move, that is, respond chemokinetically, in reaction to fMLP. Furthermore, this dependence of chemokinesis on PI(3)K gamma activity is context dependent, both with respect to the state of priming of the neutrophils and the type of surface on which they are migrating. We propose this effect of PI(3)K gamma is through roles in the regulation of some aspects of neutrophil polarization that are relevant to movement, such as integrin-based adhesion and the accumulation of polymerized (F)-actin at the leading-edge.