title: Transforming growth factor-beta-induced mobilization of actin cytoskeleton requires signaling by small GTPases Cdc42 and RhoA.
abstract: Transforming growth factor-beta (TGF-beta) is a potent regulator of cell growth and differentiation in many cell types. The Smad signaling pathway constitutes a main signal transduction route downstream of TGF-beta receptors. We studied TGF-beta-induced rearrangements of the actin filament system and found that TGF-beta 1 treatment of PC-3U human prostate carcinoma cells resulted in a rapid formation of lamellipodia. Interestingly, this response was shown to be independent of the Smad signaling pathway; instead, it required the activity of the Rho GTPases Cdc42 and RhoA, because ectopic expression of dominant negative mutant Cdc42 and RhoA abrogated the response. Long-term stimulation with TGF-beta 1 resulted in an assembly of stress fibers; this response required both signaling via Cdc42 and RhoA, and Smad proteins. A known downstream effector of Cdc42 is p38(MAPK); treatment of the cells with the p38(MAPK) inhibitor 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(pyridyl)1H-imidazole (SB203580), as well as ectopic expression of a kinase-inactive p38(MAPK), abrogated the TGF-beta-induced actin reorganization. Moreover, treatment of cells with the inhibitors of the RhoA target-protein Rho-associated coiled-coil kinase (+)-R-trans-4-(aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide (Y-27632) and 1-5(-isoquinolinesulfonyl)homopiperazine (HA-1077), as well as ectopic expression of kinase-inactive Rho coiled-coil kinase-1, abrogated the TGF-beta 1-induced formation of stress fibers. Collectively, these data indicate that TGF-beta-induced membrane ruffles occur via Rho GTPase-dependent pathways, whereas long-term effects require cooperation between Smad and Rho GTPase signaling pathways.
authors.affiliation: Ludwig Institute for Cancer Research, Biomedical Center, S-751 24 Uppsala, Sweden.
authors.forename: Sofia
authors.initials: S
authors.lastname: Edlund
authors.forename: Maréne
authors.initials: M
authors.lastname: Landström
authors.forename: Carl-Henrik
authors.initials: CH
authors.lastname: Heldin
authors.forename: Pontus
authors.initials: P
authors.lastname: Aspenström
mesh_terms: D000199:Actins / Q000378:metabolism*; D000577:Amides / Q000494:pharmacology; D000818:Animals; D022081:Cell Surface Extensions / Q000378:metabolism; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D051901:Smad4 Protein; D022502:Stress Fibers / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases; D020830:rac1 GTP-Binding Protein / Q000378:metabolism; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein / Q000378:metabolism*
chemical_list: D000199:Actins; D000577:Amides; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D007093:Imidazoles; D047908:Intracellular Signaling Peptides and Proteins; D011725:Pyridines; D011993:Recombinant Fusion Proteins; C497796:SMAD4 protein, human; D051901:Smad4 Protein; C490811:Smad4 protein, rat; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; C108830:Y 27632; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein; C093642:SB 203580