ADAM10 Knockout Cell Line (HEK293)

The platelet-activating collagen receptor GPVI represents the focus of clinical trials as an antiplatelet target for arterial thrombosis, and soluble GPVI is a plasma biomarker for several human diseases. A disintegrin and metalloproteinase 10 (ADAM10) acts as a 'molecular scissor' that cleaves the extracellular region from GPVI and many other substrates. ADAM10 interacts with six regulatory tetraspanin membrane proteins, Tspan5, Tspan10, Tspan14, Tspan15, Tspan17 and Tspan33, which are collectively termed the TspanC8s. These are emerging as regulators of ADAM10 substrate specificity. Human platelets express Tspan14, Tspan15 and Tspan33, but which of these regulates GPVI cleavage remains unknown. To address this, CRISPR/Cas9 knockout human cell lines were generated to show that Tspan15 and Tspan33 enact compensatory roles in GPVI cleavage, with Tspan15 bearing the more important role. To investigate this mechanism, a series of Tspan15 and GPVI mutant expression constructs were designed. The Tspan15 extracellular region was found to be critical in promoting GPVI cleavage, and appeared to achieve this by enabling ADAM10 to access the cleavage site at a particular distance above the membrane. These findings bear implications for the regulation of cleavage of other ADAM10 substrates, and provide new insights into post-translational regulation of the clinically relevant GPVI protein.

The renin-angiotensin-aldosterone system (RAAS) plays a critical role in the regulation of blood pressure and fluid balance, with angiotensin-converting enzyme (ACE) being a key transmembrane enzyme that converts angiotensin I to angiotensin II. Hence, ACE activity is an important drug target in cardiovascular pathologies such as hypertension. Our study demonstrates that human pulmonary microvascular endothelial cells (HPMECs) are an important source of proteolytically released ACE. The proteolytic release of transmembrane proteins, a process known as ectodomain shedding, is facilitated by membrane proteases called sheddases. By knockout and inhibition studies, we identified ADAM10 (A disintegrin and metalloprotease 10) as a primary sheddase responsible for ACE release in HEK293 cells. The function of ADAM10 as primary, constitutive sheddase of ACE was confirmed in HPMECs. Moreover, we demonstrated the physiological relevance of ADAM10 for ACE shedding in ex vivo precision cut lung slices (PCLS) from human and mouse lungs. Notably, ADAM17 activity is not directly involved in ACE shedding but indirectly by regulating ACE mRNA and protein levels, leading to increased ADAM10-mediated ACE shedding. Importantly, soluble ACE generated by shedding is enzymatically active and can thereby participate in systemic RAAS functions. Taken together, our findings highlight the critical role of ADAM10 (directly) and ADAM17 (indirectly) in ACE shedding and RAAS modulation.

GPR37 is an orphan G protein-coupled receptor (GPCR) implicated in several neurological diseases and important physiological pathways in the brain. We previously reported that its long N-terminal ectodomain undergoes constitutive metalloprotease-mediated cleavage and shedding, which have been rarely described for class A GPCRs. Here, we demonstrate that the protease that cleaves GPR37 at Glu167↓Gln168 is a disintegrin and metalloprotease 10 (ADAM10). This was achieved by employing selective inhibition, RNAi-mediated downregulation, and genetic depletion of ADAM10 in cultured cells as well as in vitro cleavage of the purified receptor with recombinant ADAM10. In addition, the cleavage was restored in ADAM10 knockout cells by overexpression of the wild type but not the inactive mutant ADAM10. Finally, postnatal conditional depletion of ADAM10 in mouse neuronal cells was found to reduce cleavage of the endogenous receptor in the brain cortex and hippocampus, confirming the physiological relevance of ADAM10 as a GPR37 sheddase. Additionally, we discovered that the receptor is subject to another cleavage step in cultured cells. Using site-directed mutagenesis, the site (Arg54↓Asp55) was localized to a highly conserved region at the distal end of the ectodomain that contains a recognition site for the proprotein convertase furin. The cleavage by furin was confirmed by using furin-deficient human colon carcinoma LoVo cells and proprotein convertase inhibitors. GPR37 is thus the first multispanning membrane protein that has been validated as an ADAM10 substrate and the first GPCR that is processed by both furin and ADAM10. The unconventional N-terminal processing may represent an important regulatory element for GPR37.

Phospholipase A2 receptor 1 (PLA2R1) is a 180-kDa transmembrane protein that plays a role in inflammation and cancer and is the major autoantigen in membranous nephropathy, a rare but severe autoimmune kidney disease. A soluble form of PLA2R1 has been detected in mouse and human serum. It is likely produced by proteolytic shedding of membrane-bound PLA2R1 but the mechanism is unknown. Here, we show that human PLA2R1 is cleaved by A Disintegrin And Metalloprotease 10 (ADAM10) and ADAM17 in HEK293 cells, mouse embryonic fibroblasts, and human podocytes. By combining site-directed mutagenesis and sequencing, we determined the exact cleavage site within the extracellular juxtamembrane stalk of human PLA2R1. Orthologs and paralogs of PLA2R1 are also shed. By using pharmacological inhibitors and genetic approaches with RNA interference and knock-out cellular models, we identified a major role of ADAM10 in the constitutive shedding of PLA2R1 and a dual role of ADAM10 and ADAM17 in the stimulated shedding. We did not observe evidence for cleavage by β- or γ-secretase, suggesting that PLA2R1 may not be a substrate for regulated intramembrane proteolysis. PLA2R1 shedding occurs constitutively and can be triggered by the calcium ionophore ionomycin, the protein kinase C activator PMA, cytokines, and lipopolysaccharides, in vitro and in vivo. Altogether, our results show that PLA2R1 is a novel substrate for ADAM10 and ADAM17, producing a soluble form that is increased in inflammatory conditions and likely exerts various functions in physiological and pathophysiological conditions including inflammation, cancer, and membranous nephropathy.

Soluble, circulating Klotho (sKlotho) is essential for normal health and renal function. sKlotho is shed from the renal distal convoluted tubule (DCT), its primary source, via enzymatic cleavage. However, the physiologic mechanisms that control sKlotho production, trafficking, and shedding are not fully defined. We previously found that the G protein-coupled calcium-sensing receptor (CaSR) co-localizes with membrane-bound αKlotho and the disintegrin/metalloprotease ADAM10 in the DCT and controls sKlotho in response to CaSR ligands and pHo by activating ADAM10. Here, we advance understanding of this process by showing that tetraspanin 5 (Tspan5), a scaffolding and chaperone protein, contributes to the cell surface expression and specificity of a protein complex that includes Tspan5, ADAM10, Klotho, and CaSR. These results support a model of multiprotein complexes that confer signaling specificity beyond CaSR on G protein-coupled processes. Impact statement Systemic circulating sKlotho is a determinant for normal physiology. Studies of knockout animals established its role as an anti-aging protein. The regulatory mechanisms for Klotho production and secretion are largely unknown. We report that Tspan 5 contributes to CaSR- and ADAM10-dependent Klotho shedding from the kidney, its primary source.

A disintegrin and metalloproteinases 10 (ADAM10) and ADAM17 are transmembrane metalloproteinases that cleave the membrane-anchored proteins. They act as α-secretase that cleaves amyloid precursor protein (APP), precluding the production of amyloid-β, thus protecting against the onset of Alzheimer's disease (AD). However, the degradation pathway of ADAM10 and ADAM17 remains unknown. In this study, we show that ADAM10 and ADAM17 are degraded through the lysosomal pathway. The lysosomal cysteine protease, AEP, plays an important role in the degradation of ADAM10/17. AEP directly cleaves ADAM10/17. Knockout of AEP increases the content of ADAM10/17 in the brain. Given the protective role of ADAM10 and ADAM17 against AD, AEP-mediated degradation of ADAM10/17 may be involved in the pathogenesis of AD.