Tumor Necrosis Factor-α-converting Enzyme (TACE/ADAM-17) Mediates the Ectodomain Cleavage of Intercellular Adhesion Molecule-1 (ICAM-1)*

Ectodomain shedding has emerged as an important regulatory step in the function of transmembrane proteins. Intercellular adhesion molecule-1 (ICAM-1), an adhesion receptor that mediates inflammatory and immune responses, undergoes shedding in the presence of inflammatory mediators and phorbol 12-myristate 13-acetate (PMA). The shedding of ICAM-1 in ICAM-1-transfected 293 cells upon PMA stimulation and in endothelialcellsupontumornecrosisfactorstimulationwasblockedby metalloproteinase inhibitors, whereas serine protease inhibitors were ineffective. p-Aminophenylmercuric acetate, a mercuric compound that is knowntoactivatematrixmetalloproteinases,up-regulatedICAM-1shedding. TIMP-3 (but not TIMP-1 or -2) effectively blocked cleavage. This profile suggests the involvement of the ADAM family of proteases in the cleavage of ICAM-1. The introduction of enzymatically active tumor necrosis factor-converting enzyme (TACE) into ICAM-1-expressing cells up-regulated cleavage. Small interfering RNA directed against TACE blockedICAM-1cleavage. ICAM-1transfected intoTACE / fibroblasts didnotshowincreasedsheddingoverconstitutivelevels inthepresenceof PMA,whereas cleavagedidoccur in ICAM-1-transfectedTACE / cells. TheseresultsindicatethatICAM-1sheddingismediatedbyTACE.Blocking the shedding of ICAM-1 altered the cell adhesive function, as ICAM1-mediatedcelladhesionwasup-regulatedinthepresenceofTACEsmall interfering RNA and TIMP-3, but not TIMP-1. However, cleavage was found to occur at multiple sites within the stalk domain of ICAM-1, and numerouspointmutationswithin the regiondidnot affect cleavage, indicating that TACE-mediated cleavage of ICAM-1 may not be sequence-specific.