title: BCL6 suppresses RhoA activity to alter macrophage morphology and motility.
abstract: BCL6 is a potent transcriptional repressor that plays important roles in germinal center formation, T helper cell differentiation and lymphomagenesis and regulates expression of several chemokine genes in macrophages. In a further investigation of its role in macrophages, we show that BCL6 inactivation in primary bone marrow-derived macrophages leads to decreased polarization, motility and cell spreading accompanied by an increase in peripheral focal complexes, anchored F-actin bundles and cortical F-actin density. These changes were associated with excess RhoA activation. C3 transferase inhibition of RhoA activity reverted the adhesion structure phenotype, which was not affected by Rho kinase inhibitors, suggesting that other downstream effectors of Rho maintain this Bcl6(-/-) phenotype. Excess RhoA activation in BCL6-deficient macrophages is associated with a decrease in the p120RasGAP (RASA1)-mediated translocation of p190RhoGAP (GRLF1) to active RhoA at the plasma membrane and a reduction in cell surface expression of the CSF1R that has been reported to recruit RasGAP to the plasma membrane. Reconstitution of BCL6 expression in Bcl6(-/-) macrophages results in complete reversion of the morphological phenotype and a significant increase in cell surface CSF1R expression whereas overexpression of the CSF1R corrects the polarization and adhesion structure defects. These results demonstrate that BCL6 suppresses RhoA activity, largely through upregulation of surface CSF1R expression, to modulate cytoskeletal and adhesion structures and increase the motility of macrophages.
authors.affiliation: Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA. pixley@aecom.yu.edu
authors.forename: Fiona J
authors.initials: FJ
authors.lastname: Pixley
authors.forename: Ying
authors.initials: Y
authors.lastname: Xiong
authors.forename: Raymond Yick-Loi
authors.initials: RY
authors.lastname: Yu
authors.forename: Erik A
authors.initials: EA
authors.lastname: Sahai
authors.forename: E Richard
authors.initials: ER
authors.lastname: Stanley
authors.forename: B Hilda
authors.initials: BH
authors.lastname: Ye
mesh_terms: D036002:ADP Ribose Transferases / Q000378:metabolism; D000199:Actins / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D001854:Bone Marrow Cells / Q000166:cytology; D001905:Botulinum Toxins / Q000378:metabolism; D002448:Cell Adhesion; D002462:Cell Membrane / Q000378:metabolism; D002465:Cell Movement; D002469:Cell Separation; D002478:Cells, Cultured; D018925:Chemokines / Q000378:metabolism; D002633:Chemotaxis; D004268:DNA-Binding Proteins / Q000502:physiology*; D005434:Flow Cytometry; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D008853:Microscopy; D010641:Phenotype; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D021381:Protein Transport; D051560:Proto-Oncogene Proteins c-bcl-6; D016186:Receptor, Macrophage Colony-Stimulating Factor / Q000096:biosynthesis; D012190:Retroviridae / Q000235:genetics; D013997:Time Factors; D014158:Transcription, Genetic; D020729:p120 GTPase Activating Protein / Q000378:metabolism; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein / Q000378:metabolism / Q000502:physiology*
chemical_list: D000199:Actins; C084103:BCL6 protein, human; D018925:Chemokines; D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D051560:Proto-Oncogene Proteins c-bcl-6; D020729:p120 GTPase Activating Protein; D036002:ADP Ribose Transferases; C063007:exoenzyme C3, Clostridium botulinum; D016186:Receptor, Macrophage Colony-Stimulating Factor; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D001905:Botulinum Toxins; D020742:rhoA GTP-Binding Protein