Short-term TNFα shedding is independent of cytoplasmic phosphorylation or furin cleavage of ADAM17

Proteolysis of transmembrane molecules is an irreversible post-translational modification enabling autocrine, paracrine and endocrine signaling of many cytokines. The pro-inflammatory activities of membrane bound TNF alpha (pro-TNF alpha) strongly depend on ectodomain shedding mediated by the A Disintegrin And Metalloprotease family member ADAM17. Despite the well-documented role of ADAM17 in pro-TNF alpha cleavage during inflammation, little is known about its regulation. Mitogen-activated protein kinase-induced phosphorylation of the ADAM17 cytoplasmic tail has been described to be required for proper activation. To address, if pro-TNF alpha shedding depends on cytosolic phosphorylation we analyzed ADAM17 mutants lacking the cytoplasmic domain. ADAM17 mediated shedding of pro-TNF alpha was induced by PMA, Anisomycin and the phosphatase inhibitors Cantharidin and Calyculin A. Deletion of the entire cytoplasmic portion of ADAM17 abolished furin-dependent proteolytic maturation and pro-TNFa cleavage. Interestingly, we could exclude that resistance to proconvertase processing is the reason for the enzymatic inactivity of ADAM17 lacking the cytoplasmic portion as furin-resistant ADAM17 mutants rescued genetic ADAM17 deficiency after mitogen-activated protein kinase activation. Adding only 6 cytoplasmic amino acids completely restored ADAM17 maturation and shedding of pro-TNF alpha as well as of both TNF-receptors Finally, we showed that a pro-TNF alpha mutant lacking the cytoplasmic portion was also shed from the cell surface. We conclude that pro-TNF alpha cleavage by its major sheddase ADAM17 does not depend on cytosolic phosphorylation and/or interaction. These results have general implications on understanding the activation mechanism controlling the activity of ADAM17. (C) 2013 Elsevier B.V. All rights reserved.