dictyNews Electronic Edition Volume 35, number 6 September 3, 2010 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to dicty@northwestern.edu or by using the form at http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit. Back issues of dictyNews, the Dicty Reference database and other useful information is available at dictyBase - http://dictybase.org. Follow dictyBase on twitter: http://twitter.com/dictybase ========= Abstracts ========= Differential regulation by phosphoinositides of bacterial uptake and Nramp1 (Slc11a1)-induced resistance to Legionella infection in Dictyostelium Barbara Peracino, Alessandra Balest and Salvatore Bozzaro Department of Clinical and Biological Sciences, University of Turin, AOU S. Luigi, 10043 Orbassano (Torino), Italy J Cell Science, in press Membrane phosphatidylinositides recruit cytosolic proteins, regulating phagocytosis, macropinocytosis and endo-lysosomal vesicle maturation. Here we describe effects of PI3K, PTEN or PLC inactivation on Escherichia coli and Legionella pneumophila uptake by the professional phagocyte Dictyostelium discoideum. We show that L. pneumophila is engulfed by macropinocytosis, a process that is partially sensitive, unlike E. coli phagocytosis, to PI3K inactivation. Both processes are blocked by PLC i nhibition. While E. coli is rapidly digested, Legionella proliferates intracellularly. Proliferation is blocked by constitutively expressing Nramp1, an endo-lysosomal iron transporter that confers resistance against invasive bacteria. Inactivating PI3K, but not PTEN or PLC, enhances Legionella infection and suppresses the protective effect of Nramp1 overexpression. PI3K activity is restricted to early infection and is not mediated by effects on the actin cytoskeleton, rather L. pneumophila, in contrast to E. coli, subverts phosphoinositide-sensitive fusion of Legionella-containing macropinosomes with acidic vesicles, without affecting Nramp1 recruitment. A model is presented to explain how Legionella escapes fusion with acidic vesicles and Nramp1-induced resistance to pathogens. Submitted by Salvo Bozzaro [salvatore.bozzaro@unito.it] ============================================================== [End dictyNews, volume 35, number 6]