title: Thrombospondin 2 regulates cell proliferation induced by Rac1 redox-dependent signaling.
abstract: Thrombospondin 2 (TSP2) is a matricellular protein controlling the apoptosis-proliferation balance in endothelial cells. Little is known about its transcriptional regulation compared with that of TSP1. We found that overexpression of a constitutively active mutant of Rac (Rac(V12)) specifically increases TSP2 mRNA levels without affecting TSP1 in human aortic endothelial cells (HAEC). Moreover, TSP2 induction by Rac(V12) is dependent upon reactive oxygen species (ROS) production, as gp91ds-tat peptide, an inhibitor of NADPH oxidase, and the flavoprotein inhibitor diphenylene iodinium (DPI) block TSP2 synthesis. Furthermore, we found that increasing Rac(V12) expression results in a biphasic proliferative curve, with proliferation initially increasing as Rac(V12) expression increases and then returning to levels less than that of control cells at higher expression. This growth inhibition is mediated by TSP2, as either DPI treatment, which blocks TSP2 synthesis, or pan-TSP blocking antibodies restore the proliferative ability of HAEC with high expression. Mechanistically, we show that the effect of TSP2 on cell proliferation is independent of the antiangiogenic TSP2 Hep1 sequence, which is capable of altering actin cytoskeletal reorganization but not proliferation in our experimental conditions. Finally, we show in vivo that Rac-induced TSP2 expression is observed in the aorta of transgenic mice selectively expressing Rac(V12) in smooth muscle cells. These results identify Rac-induced ROS as a new pathway involved in the regulation of TSP2 expression.
authors.affiliation: Division of Cardiology, Department of Medicine, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: Neuza
authors.initials: N
authors.lastname: Lopes
authors.forename: David
authors.initials: D
authors.lastname: Gregg
authors.forename: Sanjay
authors.initials: S
authors.lastname: Vasudevan
authors.forename: Hamdy
authors.initials: H
authors.lastname: Hassanain
authors.forename: Pascal
authors.initials: P
authors.lastname: Goldschmidt-Clermont
authors.forename: Hervé
authors.initials: H
authors.lastname: Kovacic
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D001011:Aorta / Q000166:cytology; D017209:Apoptosis; D002453:Cell Cycle; D002455:Cell Division; D002460:Cell Line; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000378:metabolism; D004247:DNA / Q000096:biosynthesis; D004730:Endothelium, Vascular / Q000166:cytology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation; D006801:Humans; D015151:Immunoblotting; D051379:Mice; D008822:Mice, Transgenic; D009130:Muscle, Smooth / Q000166:cytology; D019255:NADPH Oxidases / Q000378:metabolism; D009861:Onium Compounds / Q000494:pharmacology; D010084:Oxidation-Reduction; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D017382:Reactive Oxygen Species; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D019699:Thrombospondins / Q000502:physiology*; D013997:Time Factors; D014018:Tissue Distribution; D014158:Transcription, Genetic; D015854:Up-Regulation; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*; D000099262:Thrombospondin 2
chemical_list: D000199:Actins; D004247:DNA; D004791:Enzyme Inhibitors; D019255:NADPH Oxidases; D009861:Onium Compounds; D012313:RNA; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D019699:Thrombospondins; D020830:rac1 GTP-Binding Protein; D000099262:Thrombospondin 2; C007517:diphenyleneiodonium