ADAM10 is involved in the proteolytic processing and shedding of proteins such as the amyloid precursor protein (APP), cadherins, and the Notch receptors, thereby initiating the regulated intramembrane proteolysis (RIP) of these proteins. Here, we demonstrate that the sheddase ADAM10 is also subject to RIP. We identify ADAM9 and -15 as the proteases responsible for releasing the ADAM10 ectodomain, and Presenilin/␥-Secretase as the protease responsible for the release of the ADAM10 intracellular domain (ICD). This domain then translocates to the nucleus and localizes to nuclear speckles, thought to be involved in gene regulation. Thus, ADAM10 performs a dual role in cells, as a metalloprotease when it is membrane-bound, and as a potential signaling protein once cleaved by ADAM9/15 and the ␥-Secretase.
ADAMs8 (A disintegrin and metalloprotease) are type 1 transmembrane proteins related to snake venom integrin ligands and metalloproteases. All 38 different family members feature a common modular ectodomain structure (1-4) (Fig. 1A). In addition to the membrane-bound, full-length prototype, soluble ADAM variants have also been identified, consisting of only the ectodomain or fragments thereof that are released into the intercellular space. Such variants are generated by partial gene duplication (ADAM9) (5), alternative splicing (ADAM12) (6, 7), or proteolysis (ADAMs 8, 13, and 19) (8 -10). ADAMs can be grouped either by their tissue distribution and/or functional properties. One major group (ADAMs 2, 3, 5, 6, 16, 18, 20, 21, 24, 25, 26, 29, and 30) is expressed exclusively in the male gonad, with an emerging role in sperm maturation. A second group (ADAMs 2,7,11,18,22,23,and 29) is characterized by an inactive protease domain, and they seem to be mainly important for cell adhesion and fusion. A large third group of ADAMs displays a broad expression profile and has demonstrated (ADAMs 8,9,10,12,17,19, and 28) or predicted (ADAMs 15,20,21,30, and 33) proteolytic activity. These proteases play a major role in the ectodomain shedding of proteins involved in paracrine signaling, cell adhesion, and intracellular signaling (reviewed in Refs. 11 and 12). The site specificity of the cleavage of these substrates is rather relaxed, and apparently different family members can mutually compensate for each other. This has been illustrated particularly well for the amyloid precursor protein (APP) (13-17).ADAM10 is one of the proteolytically active ADAM members (15, 18 -21). The list of ADAM10 substrates is still growing, confirming the central role of ADAM10 in many important biological processes, such as cell migration and axonal navigation (robo receptors and ephrins (22, 23), cell adhesion (cadherins (19, 21), CD44 and L1 (24)), and regulation of immune reactions, and control of apoptosis (FasL) (25). Importantly, genetic ablation of ADAM10 in vertebrates (15) and invertebrates (26 -29) mainly results in loss of Notch phenotypes, indicating the crucial role for this protease in the Notch signaling pathway (30,31). Finally, AD...