Cells Lacking β-Actin are Genetically Reprogrammed and Maintain Conditional Migratory Capacity

• Published in: Molecular & cellular proteomics 2012-08, Vol.11 (8), p.255-271
• Main Authors: Tondeleir, Davina, Lambrechts, Anja, Müller, Matthias, Jonckheere, Veronique, Doll, Thierry, Vandamme, Drieke, Bakkali, Karima, Waterschoot, Davy, Lemaistre, Marianne, Debeir, Olivier, Decaestecker, Christine, Hinz, Boris, Staes, An, Timmerman, Evy, Colaert, Niklaas, Gevaert, Kris, Vandekerckhove, Joël, Ampe, Christophe
• Format: Article
• Language: English
• Subjects: Actins - genetics; Actins - metabolism; Amides - pharmacology; Animals; Blotting, Western; Cell Adhesion - drug effects; Cell Adhesion - genetics; Cell Adhesion - physiology; Cell Movement - drug effects; Cell Movement - genetics; Cell Movement - physiology; Cells, Cultured; Embryo, Mammalian - cytology; Embryo, Mammalian - embryology; Embryo, Mammalian - metabolism; Fibroblasts - cytology; Fibroblasts - metabolism; Gene Expression Regulation, Developmental; Mice; Mice, Knockout; Protein Isoforms - genetics; Protein Isoforms - metabolism; Proteomics - methods; Pseudopodia - genetics; Pseudopodia - metabolism; Pseudopodia - physiology; Pyridines - pharmacology; Reverse Transcriptase Polymerase Chain Reaction; rho-Associated Kinases - antagonists & inhibitors; rho-Associated Kinases - genetics; rho-Associated Kinases - metabolism; Signal Transduction - drug effects; Signal Transduction - genetics; Signal Transduction - physiology; Transforming Growth Factor beta - genetics; Transforming Growth Factor beta - metabolism
• ISSN: 1535-9476; 1535-9484
• DOI: 10.1074/mcp.M111.015099

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.