Latency of cathepsin B secreted by human colon carcinoma cells is not linked to secretion of cystatin C and is relieved by neutrophil elastase.
The lysosomal cysteine proteinase cathepsin B is shown to be secreted by ten human colon carcinoma cell lines and to accumulate in culture media as a latent enzyme. The cell lines also secrete a physiological inhibitor of cathepsin B, cystatin C. A significant correlation was found between secretion of the latent enzyme and the inhibitor (r = 0.755, P < 0.01). The aim of the present study was to modulate the respective secretion of the two antagonists to test whether or not latency of cathepsin B was due to the concomitant secretion of the inhibitor. SW480 colon carcinoma cells were treated with the acidotropic agent ammonium chloride, phorbol 12-myristate 13-acetate, and the inflammatory cytokines TGF-beta, TNF-alpha, and IL-1 beta. Ammonium chloride significantly increased latent cathepsin B levels without affecting the constitutive secretion of cystatin C. Phorbol 12-myristate 13-acetate induced a 4- to 5-fold increase in secreted latent cathepsin B, but did not alter significantly the accumulation of cystatin C in media. The cytokines, TGF-beta, TNF-alpha, and IL-1 beta, had no major effect on the expression of these two antagonists. Latent cathepsin B released from human carcinoma cells could be efficiently activated by neutrophil elastase at neutral pH. It is concluded that latent cathepsin B is a true proenzyme rather than an enzyme-inhibitor complex. In addition, our data from neutrophil elastase activation experiments indicate that a proteolytic system for activation of the tumor cell-secreted latent enzyme may exist in vivo.
Keppler
D
D
Experimental Pathology Unit, Swiss Institute for Experimental Cancer Research, Lausanne.
Waridel
P
P
Abrahamson
M
M
Bachmann
D
D
Berdoz
J
J
Sordat
B
B
D000230:Adenocarcinoma / Q000378:metabolism*; D000643:Ammonium Chloride / Q000494:pharmacology; D002401:Cathepsin B / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D003110:Colonic Neoplasms / Q000378:metabolism*; D055316:Cystatin C; D015891:Cystatins / Q000302:isolation & purification / Q000378:metabolism*; D004789:Enzyme Activation; D006801:Humans; D019272:Leukocyte Elastase / Q000494:pharmacology*; D009504:Neutrophils / Q000201:enzymology; D010196:Pancreatic Elastase / Q000494:pharmacology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured
C525030:CST3 protein, human; D055316:Cystatin C; D015891:Cystatins; D000643:Ammonium Chloride; D010196:Pancreatic Elastase; D019272:Leukocyte Elastase; D002401:Cathepsin B; D013755:Tetradecanoylphorbol Acetate