Human breast cancer cells contain a phosphoramidon-sensitive metalloproteinase which can process exogenous big endothelin-1 to endothelin-1: a proposed mitogen for human breast fibroblasts.
Endothelin-1 (ET-1) levels are elevated in human breast tumours compared with normal and benign tissues, and in the presence of insulin-like growth factor 1 (IGF-I) ET-1 is a potent mitogen for human breast fibroblasts. In this study we have examined the ability of intact human breast cancer cell lines to process exogenously added big ET-1 (1-38) to the active mature ET-1 peptide by using a specific radioimmunometric assay. In both hormome-dependent (MCF-7, T47-D) and hormone-independent (MDA-MB-231) breast cancer cell lines the putative endothelin-converting enzyme (ECE) exhibited apparent Michaelis-Menten kinetics when converting added big ET-1 to ET-1. Both basal ET-1 production and exogenously added big ET-1 to ET-1 conversion were greatly reduced in all three cell lines in response to the metalloproteinase inhibitor phosphoramidon but were insensitive to other classes of protease inhibitors. Inhibition was also observed when cells were incubated in the presence of the divalent cation chelators 1,10-phenanthroline and EDTA. In MCF-7 cells the optimal pH for the ECE activity using a saponin cell permeabilisation procedure was found to residue within a narrow range of 6.2-7.26. Our results indicate that human breast cancer cells contain a neutral phosphoramidon-sensitive metalloproteinase which can process big ET-1 to ET-1. In the breast this conversion could contribute substantially to the local extracellular levels of this proposed paracrine breast fibroblast mitogen.
Patel
K V
KV
Unit of Metabolic Medicine, St Mary's Hospital Medical School, Imperial College of Science, Technology and Medicine, London.
Schrey
M P
MP
D016282:Aspartic Acid Endopeptidases / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism*; D001940:Breast / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D001943:Breast Neoplasms / Q000201:enzymology* / Q000473:pathology; D002851:Chromatography, High Pressure Liquid; D003470:Culture Media; D004492:Edetic Acid / Q000494:pharmacology; D019332:Endothelin-1; D000072396:Endothelin-Converting Enzymes; D016232:Endothelins / Q000378:metabolism* / Q000493:pharmacokinetics; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D006020:Glycopeptides / Q000494:pharmacology*; D006133:Growth Substances / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007502:Iron Chelating Agents / Q000494:pharmacology; D007700:Kinetics; D008666:Metalloendopeptidases; D008934:Mitogens / Q000378:metabolism*; D010618:Phenanthrolines / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology*; D011498:Protein Precursors / Q000378:metabolism* / Q000493:pharmacokinetics; D012680:Sensitivity and Specificity; D014407:Tumor Cells, Cultured / Q000187:drug effects
D003470:Culture Media; D019332:Endothelin-1; D016232:Endothelins; D006020:Glycopeptides; D006133:Growth Substances; D007502:Iron Chelating Agents; D008934:Mitogens; D010618:Phenanthrolines; D011480:Protease Inhibitors; D011498:Protein Precursors; D004492:Edetic Acid; D016282:Aspartic Acid Endopeptidases; D008666:Metalloendopeptidases; D000072396:Endothelin-Converting Enzymes; C008890:phosphoramidon; C025205:1,10-phenanthroline