Intracellular maturation and localization of the tumour necrosis factor alpha convertase (TACE)

Tumour necrosis factor alpha convertase (TACE) is a metallo-protease/disint egrin involved in the ectodomain shedding of several proteins, a process th ought to be important in inflammation, rheumatoid arthritis and murine deve lopment. The characterization of the intracellular maturation and subcellul ar localization of endogenous TACE is decribed in the present study. Simila rly to other proteolytically active metalloprotease/ disintegrins, two form s of TACE are found in cells; a full-length precursor and a mature form lac king the prodomain. Prodomain removal occurs in a late Golgi compartment, c onsistent with the proposed role of a furin type proprotein convertase in t his process. An additional form of TACE, lacking the pro and cytoplasmic do mains, is detected when cell lysates are prepared in the presence of EDTA i nstead of a hydroxamate-based metalloprotease inhibitor or 1,10-phenanthrol ine. This form appears to be generated by mature TACE cleaving its own cyto plasmic tail and may explain why little mature TACE has been detected in pr evious studies. In cell-surface labelling experiments, mature TACE was dete cted on the cell surface but immunofluorescence data indicate that TACE is predominantly localized to a perinuclear compartment similar to that descri bed for tumour necrosis factor (TNF)alpha. This raises the possibility that TACE-mediated ectodomain shedding may occur in an intracellular compartmen t in addition to the cell surface.