title: Proteolytic activation of latent TGF-beta precedes caspase-3 activation and enhances apoptotic death of lung epithelial cells.
abstract: Transforming growth factors beta (TGF-betas) are multifunctional cytokines, which are secreted in latent forms in large latent TGF-beta complexes (LL-TGF-beta) with subsequent deposition to the extracellular matrix (ECM). While a variety of mechanisms capable of activating latent TGF-beta in vitro have been described, the physiological conditions, which promote the activation of TGF-beta in vivo are poorly understood. Mink lung epithelial cells (Mv1Lu) are a widely used model for evaluation of the effects of exogenous TGF-beta both in transcriptional and growth inhibitor assays. We find here that apoptosis of Mv1Lu cells, induced either by staurosporine or serum deprivation, is accompanied by proteolytic processing of LL-TGF-beta and the activation of endogenous TGF-beta. Activation of TGF-beta preceded caspase-3 activation and was almost completely suppressed by the serine protease inhibitor, AEBSF. Both exogenous and endogenously activated TGF-betas were able to enhance the apoptotic response of Mv1Lu cells leading to potentiation of cell death. Potentiation of cell death by activated TGF-beta was associated with downregulation of Akt and p38 MAPK, which were both activated at the initial stages of Mv1Lu apoptosis and were suppressed by exogenous TGF-beta. Pharmacological interruption of either phosphoinositide-3-kinase (PI-3K)/Akt or p38 MAPK signaling by the specific inhibitors mimicked the effect of TGF-beta leading to potentiation of cell death. Current results suggest that proteolytic activation of endogenous TGF-beta is a component of the apoptotic response, capable of modulating the death of Mv1Lu cells by inhibition of both PI-3K/Akt and p38 MAPK-dependent survival pathways.
authors.affiliation: Department of Pathology, Haartman Institute, University of Helsinki, Biomedicum Helsinki and Helsinki University Hospital, Helsinki, Finland. Victor.Soloyvan@uku.fi
authors.forename: Victor T
authors.initials: VT
authors.lastname: Solovyan
authors.forename: Jorma
authors.initials: J
authors.lastname: Keski-Oja
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002448:Cell Adhesion / Q000187:drug effects; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D017077:Culture Media, Conditioned / Q000494:pharmacology; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D053779:Latent TGF-beta Binding Proteins; D008168:Lung / Q000166:cytology; D008907:Mink; D008954:Models, Biological; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017395:Plasminogen Activator Inhibitor 1 / Q000235:genetics; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism; D051899:Smad2 Protein / Q000378:metabolism; D019311:Staurosporine / Q000494:pharmacology; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism* / Q000494:pharmacology; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D061945:Caspase Inhibitors; D017077:Culture Media, Conditioned; D016895:Culture Media, Serum-Free; D047908:Intracellular Signaling Peptides and Proteins; D053779:Latent TGF-beta Binding Proteins; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017395:Plasminogen Activator Inhibitor 1; D051899:Smad2 Protein; D016212:Transforming Growth Factor beta; D051057:Proto-Oncogene Proteins c-akt; D048051:p38 Mitogen-Activated Protein Kinases; D014568:Urokinase-Type Plasminogen Activator; D053148:Caspase 3; D020169:Caspases; D019311:Staurosporine