title: TSG-6 potentiates the antitissue kallikrein activity of inter-alpha-inhibitor through bikunin release.
abstract: TSG-6 (the protein product of TNF-stimulated gene-6), an inflammation-associated protein, forms covalent complexes with heavy chains (HCs) from inter-alpha-inhibitor and pre-alpha-inhibitor and associates noncovalently with their common bikunin chain, potentiating the antiplasmin activity of this serine protease inhibitor. We show that TSG-6 and TSG-6.HC complexes are present in bronchoalveolar lavage fluid from patients with asthma and increase after allergen challenge. Immunodetection demonstrated elevated TSG-6 in the airway tissue and secretions of smokers. Experiments conducted in vitro with purified components revealed that bikunin.HC complexes (byproducts of TSG-6.HC formation) release bikunin. Immunoprecipitation revealed that bikunin accounts for a significant proportion of tissue kallikrein inhibition in bronchoalveolar lavage after allergen challenge but not in baseline conditions, confirming that bikunin in its free state, but not when associated with HCs, is a relevant protease inhibitor in airway secretions. In primary cultures of differentiated human airway epithelial and submucosal gland cells, TSG-6 is induced by TNF-alpha and IL-1beta, which suggests that these cells are responsible for TSG-6 release in vivo. Bikunin and HC3 (i.e., pre-alpha-inhibitor) were also induced by TNF-alpha in primary cultures. Our results suggest that TSG-6 may play an important protective role in bronchial epithelium by increasing the antiprotease screen on the airway lumen.
authors.affiliation: Division of Pulmonary and Critical Care Medicine (R-47), University of Miami School of Medicine, RMSB 7072A, Miami, FL 33136, USA. rforteza@miami.edu
authors.forename: Rosanna
authors.initials: R
authors.lastname: Forteza
authors.forename: Susana M
authors.initials: SM
authors.lastname: Casalino-Matsuda
authors.forename: Maria Elena
authors.initials: ME
authors.lastname: Monzon
authors.forename: Erik
authors.initials: E
authors.lastname: Fries
authors.forename: Marilyn S
authors.initials: MS
authors.lastname: Rugg
authors.forename: Caroline M
authors.initials: CM
authors.lastname: Milner
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Day
mesh_terms: D000293:Adolescent; D000328:Adult; D000510:Alpha-Globulins / Q000502:physiology*; D001249:Asthma / Q000378:metabolism*; D018893:Bronchoalveolar Lavage; D015815:Cell Adhesion Molecules / Q000502:physiology*; D002478:Cells, Cultured; D004789:Enzyme Activation; D004847:Epithelial Cells / Q000378:metabolism; D005088:Exocrine Glands / Q000166:cytology; D005260:Female; D006801:Humans; D053583:Interleukin-1beta / Q000502:physiology; D008297:Male; D008562:Membrane Glycoproteins / Q000502:physiology*; D008875:Middle Aged; D011485:Protein Binding; D021122:Protein Subunits / Q000378:metabolism*; D012907:Smoking / Q000378:metabolism; D020840:Tissue Kallikreins / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology
chemical_list: D000510:Alpha-Globulins; D015815:Cell Adhesion Molecules; D053583:Interleukin-1beta; D008562:Membrane Glycoproteins; D021122:Protein Subunits; C109148:SPINT2 protein, human; C072273:TNFAIP6 protein, human; D014409:Tumor Necrosis Factor-alpha; C011877:inter-alpha-inhibitor; D020840:Tissue Kallikreins