Phosphoinositide Lipid Posphatase SHIP1 and PTEN Coordinate to Regulate Cell Migration and Adhesion

The second messenger phosphatidylinositol(3,4,5)P3 (PtdIns(3,4,5)P3) is formed by stimulation of various receptors, including G protein–coupled receptors and integrins. The lipid phosphatases PTEN and SHIP1 are critical in regulating the level of PtdIns(3,4,5)P3 dur­ ing chemotaxis. Observations that loss of PTEN had minor and loss of SHIP1 resulted in a severe chemotaxis defect in neutrophils led to the belief that SHIP1 rather than PTEN acts as a predominant phospholipid phosphatase in establishing a PtdIns(3,4,5)P3 compass. In this study, we show that SHIP1 regulates PtdIns(3,4,5)P3 production in response to cell adhesion and plays a limited role when cells are in suspension. SHIP1−/− neutrophils lose their polarity upon cell adhesion and are extremely adherent, which impairs chemotaxis. However, chemo­ taxis can be restored by reducing adhesion. Loss of SHIP1 elevates Akt activation following cell adhesion due to increased PtdIns(3,4,5)P3 production. From our observations, we con­ clude that SHIP1 prevents formation of top­down PtdIns(3,4,5)P3 polarity to facilitate proper cell attachment and detachment during chemotaxis. INTRODUCTION Neutrophils are responsible for controlling pathogen invasion and are therefore an important component of the innate immune system. Neutrophils are the most abundant cell type among circulating white blood cells and are normally quiescent as they travel within blood vessels (Borregaard, 2010). Neutrophils migrate into the infected tissue by responding to a variety of chemokines (e.g., interleukin-8 [IL-8]), cytokines (e.g., tumor necrosis factor α [TNFα]), leukotrienes (e.g., leukotriene B4 [LTB4]), complement peptides (e.g., C5a, C3a), and chemicals released by bacteria directly, such as peptides bearing the N-formyl group (N-formyl-methionine-leucinephenylalanine [fMLP]), by a process known as chemotaxis. During chemotaxis, the cell becomes morphologically polarized, with the front of the cell (pseudopod) constantly protruding and retracting motile membranous structures toward the direction of the chemoattractant gradient. This movement is largely driven by the outward extension of actin filaments (Pollard and Borisy, 2003). Actin filaments can also be associated through clutch-like complexes of proteins to adhesion complexes at the base of the cell, against which actin-polymerization–mediated protrusive forces can operate (Hu et al., 2007; Hoffman et al., 2011). Studies on the mechanisms of chemotaxis have shown that phosphatidylinositol(3,4,5)P3 (PtdIns(3,4,5)P3) plays a pivotal role in establishing cell polarity (Stephens et al., 2002; Weiner, 2002). Phosphoinositide 3-kinases (PI3Ks) are evolutionary conserved lipid kinases that convert phosphatidylinositol 4,5-bisphosphate (PtIns(4,5)P2) to PtdIns(3,4,5)P3. PI3Kα, β, and δ (class 1a) isoforms are activated by tyrosine kinases, whereas PI3Kγ (class 1b) is activated by G protein–coupled receptors (GPCRs). In neutrophils that sense a chemoattractant gradient like fMLP, GPCRs and G proteins (Gαi/o) downstream of these receptors are activated, leading to formation of PtdIns(3,4,5)P3 at the leading edge, predominantly by the activity of PI3Kγ (Ferguson et al., 2007; Stephens et al., 2008). However, class 1a PI3Kδ activity is also believed to be involved in fMLP-mediated responses (Condliffe et al., 2005). In addition, cell adhesion resulting from the interaction of integrins (αLβ2 and αMβ2) with extracellular matrix Monitoring Editor Peter Van Haastert University of Groningen Received: Oct 31, 2011 Revised: Jan 4, 2012 Accepted: Feb 2, 2012 This article was published online ahead of print in MBoC in Press (http://www .molbiolcell.org/cgi/doi/10.1091/mbc.E11-10-0889) on February 9, 2012. Address correspondence to: Hongbo R. Luo ([email protected]). © 2012 Mondal et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0). “ASCB®,“ “The American Society for Cell Biology®,” and “Molecular Biology of the Cell®” are registered trademarks of The American Society of Cell Biology. Abbreviations used: EGFP, enhanced green fluorescent protein; FAK, focal adhesion kinase; HBSS, Hank’s balanced salt solution; PH, pleckstrin homology domain; PTEN, phosphatase and tensin homologue deleted in chromosome 10; RGD, arginine–glycine–aspartic acid peptide; SHIP1, SH2 domain containing inositol-5-phosphatase.