title: Regulation of leading edge microtubule and actin dynamics downstream of Rac1.
abstract: Actin in migrating cells is regulated by Rho GTPases. However, Rho proteins might also affect microtubules (MTs). Here, we used time-lapse microscopy of PtK1 cells to examine MT regulation downstream of Rac1. In these cells, "pioneer" MTs growing into leading-edge protrusions exhibited a decreased catastrophe frequency and an increased time in growth as compared with MTs further from the leading edge. Constitutively active Rac1(Q61L) promoted pioneer behavior in most MTs, whereas dominant-negative Rac1(T17N) eliminated pioneer MTs, indicating that Rac1 is a regulator of MT dynamics in vivo. Rac1(Q61L) also enhanced MT turnover through stimulation of MT retrograde flow and breakage. Inhibition of p21-activated kinases (Paks), downstream effectors of Rac1, inhibited Rac1(Q61L)-induced MT growth and retrograde flow. In addition, Rac1(Q61L) promoted lamellipodial actin polymerization and Pak-dependent retrograde flow. Together, these results indicate coordinated regulation of the two cytoskeletal systems in the leading edge of migrating cells.
authors.affiliation: Department of Cell Biology and Institute for Childhood and Neglected Diseases, La Jolla, CA 92037, USA.
authors.forename: Torsten
authors.initials: T
authors.lastname: Wittmann
authors.forename: Gary M
authors.initials: GM
authors.lastname: Bokoch
authors.forename: Clare M
authors.initials: CM
authors.lastname: Waterman-Storer
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D000818:Animals; D002465:Cell Movement / Q000502:physiology*; D016764:Cell Polarity / Q000502:physiology*; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005057:Eukaryotic Cells / Q000378:metabolism*; D018715:Microscopy, Video; D008870:Microtubules / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D011554:Pseudopodia / Q000378:metabolism*; D054462:p21-Activated Kinases; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D020830:rac1 GTP-Binding Protein