A METALLOPROTEASE INHIBITOR BLOCKS SHEDDING OF THE 80-KD TNF RECEPTOR AND TNF PROCESSING IN T-LYMPHOCYTES

TNF is synthesized as a 26-kD membrane-anchored precursor and is proteolytically processed at the cell surface to yield the mature secreted 17-kD polypeptide. The 80-kD tumor necrosis factor (TNF) receptor (TNFR(80)) is also proteolytically cleaved at the cell surface (shed), releasing a soluble ligand-binding receptor fragment. Since processing of TNF and TNFR(80) occurs concurrently in activated T cells, we asked whether a common protease may be involved. Here, we present evidence that a recently described inhibitor of TNF processing N-{(D,L-[2-(hydroxyaminocarbonyl)methyl]-4-methylpentanoyl}L-3-(2'naphthyl)-alanyl-L-alanine, 2-aminoethyl amide (TAPI) also blocks shedding of TNFR(80), suggesting that these processes may be coordinately regulated during T cell activation. In addition, studies of murine fibroblasts transfected with human TNFR(80), or a cytoplasmic deletion form of TNFR(80), reveal that inhibition of TNFR(80) shedding by TAPI is independent of receptor phosphorylation and does not require the receptor cytoplasmic domain.