title: MAPK uncouples cell cycle progression from cell spreading and cytoskeletal organization in cycling cells.
abstract: Integrin-mediated cytoskeletal tension supports growth-factor-induced proliferation, and disruption of the actin cytoskeleton in growth factor-stimulated cells prevents the re-expression of cyclin D and cell cycle re-entry from quiescence. In contrast to cells that enter the cell cycle from G0, cycling cells continuously express cyclin D, and are subject to major cell shape changes during the cell cycle. Here, we investigated the cell cycle requirements for cytoskeletal tension and cell spreading in cycling mammalian cells that enter G1-phase from mitosis. Disruption of the actin cytoskeleton at progressive time-points in G1-phase induced cell rounding, FA disassembly, and attenuated both integrin signaling and growth factor-induced p44/p42 mitogen-activated protein kinase activation. Although cyclin D expression was reduced, the expression of cyclin A and entry into S-phase were not affected. Moreover, expression of cyclin B1, progression through G2- and M-phase, and commitment to a new cell cycle occurred normally. In contrast, cell cycle progression was strongly prevented by inhibition of MAPK activity in G1-phase, whereas cell spreading, cytoskeletal organization, and integrin signaling were not impaired. MAPK inhibition also prevented cytoskeleton-independent cell cycle progression. Thus, these results uncouple the requirements for cell spreading and cytoskeletal organization from MAPK signaling, and show that cycling mammalian cells can proliferate independently of actin stress fibers, focal adhesions, or cell spreading, as long as a threshold level of MAPK activity is sustained.
authors.affiliation: Department of Cell Biology, Faculty of Sciences, University of Utrecht, Padualaan 8, 3584 CH, Utrecht, The Netherlands. c.margadant@nki.nl
authors.forename: Coert
authors.initials: C
authors.lastname: Margadant
authors.forename: Lobke
authors.initials: L
authors.lastname: Cremers
authors.forename: Arnoud
authors.initials: A
authors.lastname: Sonnenberg
authors.forename: Johannes
authors.initials: J
authors.lastname: Boonstra
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D000818:Animals; D016466:CHO Cells; D045744:Cell Line, Tumor; D002465:Cell Movement; D006224:Cricetinae; D019925:Cyclin A / Q000096:biosynthesis; D056744:Cyclin B1 / Q000096:biosynthesis; D056741:Cyclin D / Q000378:metabolism*; D005109:Extracellular Matrix / Q000378:metabolism; D022001:Focal Adhesions / Q000378:metabolism; D016193:G1 Phase; D020935:MAP Kinase Signaling System; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008938:Mitosis; D010446:Peptide Fragments / Q000378:metabolism; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D019925:Cyclin A; D056744:Cyclin B1; D056741:Cyclin D; D010446:Peptide Fragments; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; C503486:WDR77 protein, mouse; D019950:Mitogen-Activated Protein Kinase 1; D020928:Mitogen-Activated Protein Kinases