Synthesis and secretion of procathepsin B and cystatin C by human bronchial epithelial cells in vitro: modulation of cathepsin B activity by neutrophil elastase.
Procathepsin B and cystatin C are found in human lung secretions. We investigated the capacity of human bronchial epithelial cells to synthesize and secrete these proteins. Immunoprecipitation of [35S]methionine-labeled proteins from cultured bronchial epithelial cell lysates, followed by denaturing gel electrophoresis and autoradiography, showed the presence of newly synthesized procathepsin B of M(r) 42,000; no mature form was detected. Cathepsin B in conditioned medium from epithelial cells was tagged with benzyloxycarbonyl-125I-tyrosyl-alanine-diazomethane before and after treatment of the medium with neutrophil elastase. Control medium again showed a predominant form of cathepsin B with a M(r) of 42,000, but upon treatment with neutrophil elastase this protein was converted to a M(r) of 38,000, similar to the active form previously found in lung secretions, and cathepsin B activity was generated. The medium also contained the cathepsin B inhibitor, cystatin C, but cystatins A, B, S, SN, SA, and kininogen were not detected. After removal of cystatin C from the medium, elastase was still required to activate procathepsin B. These results suggest that bronchial epithelial cells are a source of procathepsin B and cystatin C in lung secretions. Cleavage both of cystatin C and procathepsin B by neutrophil elastase is essential for the generation of cathepsin B activity in the medium.
Burnett
D
D
Department of Immunology, University of Birmingham, United Kingdom.
Abrahamson
M
M
Devalia
J L
JL
Sapsford
R J
RJ
Davies
R J
RJ
Buttle
D J
DJ
D001980:Bronchi / Q000378:metabolism*; D002401:Cathepsin B / Q000096:biosynthesis* / Q000378:metabolism; D002478:Cells, Cultured; D003470:Culture Media; D017077:Culture Media, Conditioned; D055316:Cystatin C; D015891:Cystatins / Q000096:biosynthesis* / Q000378:metabolism; D004792:Enzyme Precursors / Q000096:biosynthesis* / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism; D006801:Humans; D019272:Leukocyte Elastase; D010196:Pancreatic Elastase / Q000494:pharmacology*
C525030:CST3 protein, human; D003470:Culture Media; D017077:Culture Media, Conditioned; D055316:Cystatin C; D015891:Cystatins; D004792:Enzyme Precursors; D010196:Pancreatic Elastase; D019272:Leukocyte Elastase; C057832:procathepsin B; D002401:Cathepsin B