title: Cells lacking β-actin are genetically reprogrammed and maintain conditional migratory capacity.
abstract: Vertebrate nonmuscle cells express two actin isoforms: cytoplasmic β- and γ-actin. Because of the presence and localized translation of β-actin at the leading edge, this isoform is generally accepted to specifically generate protrusive forces for cell migration. Recent evidence also implicates β-actin in gene regulation. Cell migration without β-actin has remained unstudied until recently and it is unclear whether other actin isoforms can compensate for this cytoplasmic function and/or for its nuclear role. Primary mouse embryonic fibroblasts lacking β-actin display compensatory expression of other actin isoforms. Consistent with this preservation of polymerization capacity, β-actin knockout cells have unchanged lamellipodial protrusion rates despite a severe migration defect. To solve this paradox we applied quantitative proteomics revealing a broad genetic reprogramming of β-actin knockout cells. This also explains why reintroducing β-actin in knockout cells does not restore the affected cell migration. Pathway analysis suggested increased Rho-ROCK signaling, consistent with observed phenotypic changes. We therefore developed and tested a model explaining the phenotypes in β-actin knockout cells based on increased Rho-ROCK signaling and increased TGFβ production resulting in increased adhesion and contractility in the knockout cells. Inhibiting ROCK or myosin restores migration of β-actin knockout cells indicating that other actins compensate for β-actin in this process. Consequently, isoactins act redundantly in providing propulsive forces for cell migration, but β-actin has a unique nuclear function, regulating expression on transcriptional and post-translational levels, thereby preventing myogenic differentiation.
authors.affiliation: Department of Medical Protein Research, VIB, Ghent, Belgium.
authors.forename: Davina
authors.initials: D
authors.lastname: Tondeleir
authors.forename: Anja
authors.initials: A
authors.lastname: Lambrechts
authors.forename: Matthias
authors.initials: M
authors.lastname: Müller
authors.forename: Veronique
authors.initials: V
authors.lastname: Jonckheere
authors.forename: Thierry
authors.initials: T
authors.lastname: Doll
authors.forename: Drieke
authors.initials: D
authors.lastname: Vandamme
authors.forename: Karima
authors.initials: K
authors.lastname: Bakkali
authors.forename: Davy
authors.initials: D
authors.lastname: Waterschoot
authors.forename: Marianne
authors.initials: M
authors.lastname: Lemaistre
authors.forename: Olivier
authors.initials: O
authors.lastname: Debeir
authors.forename: Christine
authors.initials: C
authors.lastname: Decaestecker
authors.forename: Boris
authors.initials: B
authors.lastname: Hinz
authors.forename: An
authors.initials: A
authors.lastname: Staes
authors.forename: Evy
authors.initials: E
authors.lastname: Timmerman
authors.forename: Niklaas
authors.initials: N
authors.lastname: Colaert
authors.forename: Kris
authors.initials: K
authors.lastname: Gevaert
authors.forename: Joël
authors.initials: J
authors.lastname: Vandekerckhove
authors.forename: Christophe
authors.initials: C
authors.lastname: Ampe
mesh_terms: D000199:Actins / Q000235:genetics / Q000378:metabolism*; D000577:Amides / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D002448:Cell Adhesion / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D002465:Cell Movement / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D002478:Cells, Cultured; D004622:Embryo, Mammalian / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D051379:Mice; D018345:Mice, Knockout; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D040901:Proteomics / Q000379:methods*; D011554:Pseudopodia / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D011725:Pyridines / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism; D054460:rho-Associated Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
chemical_list: D000199:Actins; D000577:Amides; D020033:Protein Isoforms; D011725:Pyridines; D016212:Transforming Growth Factor beta; C108830:Y 27632; C515854:Rock1 protein, mouse; C515855:Rock2 protein, mouse; D054460:rho-Associated Kinases