title: LTBP-1 blockade in dioxin receptor-null mouse embryo fibroblasts decreases TGF-beta activity: Role of extracellular proteases plasmin and elastase.
abstract: In mouse embryonic fibroblasts (MEF) lacking dioxin receptor (AhR), high levels of latent transforming growth factor-beta (TGF-beta)-binding protein-1 (LTBP-1) correlated with increased TGF-beta1 activity, an observation suggesting that LTBP-1 could contribute to maintain TGF-beta1 levels. Here, using small interfering RNAs (siRNA), we have first analyzed if LTBP-1 expression affected TGF-beta1 activity in MEF cells. We have then determined how LTBP-1 levels could alter the activity of extracellular proteases known to activate TGF-beta1, and finally, whether protease inhibition could reduce TGF-beta1 activation. LTBP-1 inhibition by siRNA in AhR-/- MEF decreased the amount of active TGF-beta1 and reduced plasminogen activators (PA)/plasmin and elastase activities and thrombospondin-1 (TSP-1) expression, without significantly affecting their mRNA levels. On the contrary, LTBP-1 siRNA restored matrix metalloproteinase-2 (MMP-2) activity in AhR-/- MEF. Interestingly, whereas a TGF-beta1 neutralizing antibody mimicked many of the LTBP-1 siRNA effects on extracellular proteases, addition of recombinant TGF-beta1 protein increased proteases activity over basal levels in AhR-/- MEF. These proteases contributed to TGF-beta activation since their specific inhibitors reduced active TGF-beta levels in these cells. These results suggest that LTBP-1 contributes to TGF-beta1 activation in MEF, possibly by influencing the activities of PA/plasmin, elastase, TSP-1, and MMP-2. TGF-beta1, on the other hand, could be also involved in maintaining the activity of these extracellular proteases. Thus, LTBP-1 appears to play a role in TGF-beta1 activation through a process involving extracellular protease activities, which, in turn, could be affected by TGF-beta1 levels.
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Extremadura, Avenida de Elvas s/n, 06071-Badajoz, Spain.
authors.forename: Aurea
authors.initials: A
authors.lastname: Gomez-Duran
authors.forename: Sonia
authors.initials: S
authors.lastname: Mulero-Navarro
authors.forename: Xiaoqing
authors.initials: X
authors.lastname: Chang
authors.forename: Pedro M
authors.initials: PM
authors.lastname: Fernandez-Salguero
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D015536:Down-Regulation; D005341:Fibrinolysin / Q000502:physiology*; D005347:Fibroblasts / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000502:physiology*; D053779:Latent TGF-beta Binding Proteins; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D010196:Pancreatic Elastase / Q000502:physiology*; D010447:Peptide Hydrolases / Q000502:physiology; D011480:Protease Inhibitors / Q000494:pharmacology; D034741:RNA, Small Interfering; D018336:Receptors, Aryl Hydrocarbon / Q000235:genetics*; D016212:Transforming Growth Factor beta / Q000378:metabolism*
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D053779:Latent TGF-beta Binding Proteins; C509033:Ltbp1 protein, mouse; D011480:Protease Inhibitors; D034741:RNA, Small Interfering; D018336:Receptors, Aryl Hydrocarbon; D016212:Transforming Growth Factor beta; D010447:Peptide Hydrolases; D010196:Pancreatic Elastase; D005341:Fibrinolysin; D020778:Matrix Metalloproteinase 2