TNF-induced shedding of TNF receptors in human polymorphonuclear leukocytes: Role of the 55-kDa TNF receptor and involvement of a membrane-bound and non-matrix metalloproteinase

A down-modulation of both the 55-kDa (TNF-R55) and the 75-kDa (TNF-R75) TNF receptors is observed in neutrophils exposed to a variety of stimuli. Prot eolytic cleavage of the extracellular region of both receptors (shedding) a nd, with TNF, internalization of TNF-R55 and shedding of TNF-R75 are the pr oposed mechanisms, We have characterized the TNF-induced shedding of TNF re ceptors in neutrophils and determined the nature of the involved proteinase , Neutrophils exposed to TNF release both TNF receptors, A release of TNF r eceptors comparable to that observed with TNF was induced with TNF-R55-spec ific reagents (mAbs and a mutant of TNF) but not with the corresponding TNF -R75-specific reagents. A hydroxamic acid compound (KB8301) almost complete ly inhibited shedding of TNF-R55 and to a lesser degree shedding of TNF-R75 , KB8301 also inhibited FMLP-induced shedding to a similar extent. Shedding was also inhibited by 1,10-phenanthroline, but this effect was considered nonspecific as the compound, at variance with KB8301, almost completely inh ibited TNF and FMLP-induced PMN activation, Diisopropylfluorophosphate part ially inhibited shedding of TNF-R75, suggesting the contribution of a serin e proteinase to the release of this receptor. Shedding activity was not aff ected by matrix metalloproteinases inhibitors nor was it released in the su pernatants of FMLP-stimulated neutrophils. These results suggest that TNF i nduces release of its receptors, that such a release is mediated via TNF-R5 5, and that a membrane-bound and non-matrix metalloproteinase is involved i n the process. The possibility that ADAM-17, which we show to be expressed in neutrophils, might be the involved proteinase is discussed.