An important, irreversible step in many signalling pathways is the shedding of membrane-anchored proteins. A Disintegrin And Metalloproteinase (ADAM) 17 is one of the major sheddases involved in a variety of physiological and pathophysiological processes including regeneration, differentiation, and cancer progression. This central role in signalling implies that ADAM17 activity has to be tightly regulated, including at the level of localisation. Most mature ADAM17 is localised intracellularly, with only a small amount at the cell surface. We found that ADAM17 is constitutively internalised by clathrin-coated pits and that physiological stimulators such as GPCR ligands induce ADAM17-mediated shedding, but do not alter the cell-surface abundance of the protease. In contrast, the PKC-activating phorbol ester PMA, often used as a strong inducer of ADAM17, causes not only proteolysis by ADAM17 but also a rapid increase of the mature protease at the cell surface. This is followed by internalisation and subsequent degradation of the protease. Eventually, this leads to a substantial downregulation of mature ADAM17. Our results therefore imply that physiological activation of ADAM17 does not rely on its relocalisation, but that PMA-induced PKC activity drastically dysregulates the localisation of ADAM17.

Background: A disintegrin and metalloprotease 17 (ADAM17) releases many proinflammatory mediators. Results: The conserved ADAM seventeen dynamic interaction sequence (CANDIS) mediates effective substrate binding and is controlled by the disulfide-regulated conformation of the preceding membrane-proximal domain (MPD). Conclusion: CANDIS, together with the MPD, represents a novel key regulatory element. Significance: We investigate the molecular details of a novel kind of regulation.

A wide variety of biological processes including differentiation, regeneration, and cancer progression are regulated by shedding of membrane-anchored proteins. One of the major sheddases is A Disintegrin And Metalloprotease-17 (ADAM17) whose extracellular region consists of a pro-, a catalytic, a disintegrin-, and a membrane-proximal domain (MPD) as well as a short juxtamembrane segment of 17 amino acid residues that has been named "Conserved ADAM-seventeeN Dynamic Interaction Sequence" (CANDIS). This segment is involved in substrate recognition. Key mediators of inflammation including interleukin-6 receptor (IL-6R) and tumor necrosis factor (TNF-α) are substrates of ADAM17. The shedding activity of ADAM17 is regulated by the conformation of the membrane-proximal domain preceding the CANDIS segment. Here, we show that CANDIS, besides being involved in substrate recognition, is able to interact with lipid bilayers in vitro and that this property could be involved in regulating ADAM17 shedding activity.

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To avoid malformation and disease, tissue development and homoeostasis are co-ordinated precisely in time and space. Secreted Frizzled-related protein 3 (sFRP3), encoded by the Frizzled-related protein gene (FRZB), acts as an antagonist of Wnt signalling in bone development by delaying the maturation of proliferative chondrocytes into hypertrophic chondrocytes. A disintegrin and metalloprotease 17 (ADAM17) is a transmembrane protease that is essential for developmental processes and promotes cartilage maturation into bone. sFRP3 is chondroprotective and is expressed in chondrocytes of healthy articular cartilage. Upon damage to cartilage, sFRP3 is down-regulated. Rare variants of sFRP3 are associated with osteoarthritis. The present study demonstrates a novel function of sFRP3 in suppression of the enzymatic activity of ADAM17 which results in the inhibition of ADAM17-meditated interleukin-6 receptor (IL-6R) shedding. By contrast, the rare double variant of sFRP3 failed to suppress ADAM17. The shed soluble IL-6R (sIL-6R) is linked to inflammation, cartilage degeneration and osteolysis. Accordingly, enhanced activity of ADAM17 in cartilage, caused by the expression of the rare double sFRP3 variant, provides an explanation for the genetic effect of sFRP3 variants in joint disease. The finding that sFRP3 interacts with the ADAM17 substrate IL-6R also suggests a new regulatory mechanism by which the substrate is protected against shedding.