Novel pathogenic mechanism of microbial metalloproteinases: liberation of membrane-anchored molecules in biologically active form exemplified by studies with the human interleukin-6 receptor.
Certain membrane-anchored proteins, including several cytokines and cytokine receptors, can be released into cell supernatants through the action of endogenous membrane-bound metalloproteinases. The shed molecules are then able to fulfill various biological functions; for example, soluble interleukin-6 receptor (sIL-6R) can bind to bystander cells, rendering these cells sensitive to the action of IL-6. Using IL-6R as a model substrate, we report that the metalloproteinase from Serratia marcescens mimics the action of the endogenous shedding proteinase. Treatment of human monocytes with the bacterial protease led to a rapid release of sIL-6R into the supernatant. This effect was inhibitable with TAPI [N-(D,L-[2-(hydroxyaminocarbonyl)methyl]-4-methylpentanoyl) L-3-(2' naphthyl)-alanyl-L-alanine, 2-aminoethyl amide], a specific inhibitor of the membrane-bound intrinsic metalloproteinase, but not with other conventional proteinase inhibitors. sIL-6R-liberating activity was also detected in culture supernatants of Staphylococcus aureus, Pseudomonas aeruginosa, and Listeria monocytogenes, organisms that are known to produce metalloproteinases. sIL-6R released through the action of S. marcescens metalloproteinase retained biological activity and rendered IL-6-unresponsive human hepatoma cells sensitive to stimulation with IL-6. This was shown by Northern (RNA) blot detection of haptoglobin mRNA and by quantitative measurements of de novo-synthesized haptoglobin in cell supernatants. Analysis of immunoprecipitated, radiolabeled sIL-6R revealed that the bacterial protease cleaved IL-6R at a site distinct from that utilized by the endogenous protease. These studies show that membrane-anchored proteins can be released in active form through cleavage at multiple sites, and they uncover a novel mechanism via which microbial proteases possibly provoke long-range biological effects in the host organism.
Vollmer
P
P
First Department of Medicine-Pathophysiology Section, Johannes Gutenberg-University of Mainz, Germany.
Walev
I
I
Rose-John
S
S
Bhakdi
S
S
D000818:Animals; D015703:Antigens, CD / Q000378:metabolism*; D001424:Bacterial Infections / Q000201:enzymology*; D002522:Chlorocebus aethiops; D006801:Humans; D008089:Listeria monocytogenes / Q000276:immunology; D008565:Membrane Proteins / Q000378:metabolism; D008666:Metalloendopeptidases / Q000378:metabolism*; D009000:Monocytes / Q000378:metabolism*; D011550:Pseudomonas aeruginosa / Q000276:immunology; D018123:Receptors, Interleukin / Q000378:metabolism*; D019947:Receptors, Interleukin-6; D011994:Recombinant Proteins; D012706:Serratia marcescens / Q000201:enzymology; D015398:Signal Transduction; D012995:Solubility; D013211:Staphylococcus aureus / Q000201:enzymology; D013379:Substrate Specificity
D015703:Antigens, CD; D008565:Membrane Proteins; D018123:Receptors, Interleukin; D019947:Receptors, Interleukin-6; D011994:Recombinant Proteins; D008666:Metalloendopeptidases