Expression of BRG1, a human SWI/SNF component, affects the organisation of actin filaments through the RhoA signalling pathway.
The human BRG1 (brahma-related gene 1) protein is a component of the SWI/SNF family of the ATP-dependent chromatin remodelling complexes. We show here that expression of the BRG1 protein, but not of an ATPase-deficient BRG1 protein, in BRG1-deficient SW13 cells alters the organisation of actin filaments. BRG1 expression induces the formation of thick actin filament bundles resembling stress-fibres, structures that are rarely seen in native SW13 cells. BRG1 expression does not influence the activity state of the RhoA-GTPase, which is involved in stress-fibre formation. We find that RhoA is equally activated by stimuli, such as serum, in BRG1-expressing cells, ATPase-deficient BRG1-expressing cells and native SW13 cells. However, the activation of RhoA by lysophosphatidic acid and serum does not trigger the formation of stress-fibre-like structures in SW13 cells. Activation of the RhoA-GTPase in BRG1-expressing cells induces stress-fibre-like structures, indicating that the BRG1 can couple RhoA activation to stress-fibre formation. At least two downstream effectors are involved in stress-fibre formation, Rho-kinase/ROCK and Dia. BRG1 expression, but not the expression of the ATP-deficient BRG1, increases the protein level of ROCK1, one form of the Rho-kinase/ROCK. That this is of importance is supported by the findings that an increased Rho-kinase/ROCK activity in SW13 cells, obtained by overexpressing wild-type ROCK1 and ROCK2, induces stress-fibre formation. No specificity between the two Rho-kinase/ROCK forms exists. Our results suggest that the BRG1 protein affects the RhoA pathway by increasing the protein level of ROCK1, which allows stress-fibre-like structures to form.
Asp
Patrik
P
Department of Zoological Cell Biology, The Wenner-Gren Institute, Stockholm University, SE-106 91 Stockholm, Sweden.
Wihlborg
Margareta
M
Karlén
Mattias
M
Farrants
Ann-Kristin Ostlund
AK
D008841:Actin Cytoskeleton / Q000378:metabolism*; D000818:Animals; D048429:Cell Size / Q000235:genetics; D002478:Cells, Cultured; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics / Q000378:metabolism*; D004265:DNA Helicases; D005057:Eukaryotic Cells / Q000166:cytology / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D005786:Gene Expression Regulation / Q000502:physiology; D005809:Genes, Regulator / Q000235:genetics; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D011930:Reaction Time / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics; D013314:Stress, Mechanical; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation / Q000235:genetics; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
D002868:Chromosomal Proteins, Non-Histone; D047908:Intracellular Signaling Peptides and Proteins; D009687:Nuclear Proteins; C445179:SWI-SNF-B chromatin-remodeling complex; D014157:Transcription Factors; D017346:Protein Serine-Threonine Kinases; C515851:ROCK1 protein, human; C515852:ROCK2 protein, human; D054460:rho-Associated Kinases; C084108:SMARCA4 protein, human; D004265:DNA Helicases; D020742:rhoA GTP-Binding Protein