Cell Surface Metalloprotease Research Articles

DIFFERENTIAL CELL SURFACE PROTEOMICS OF FLOTILLIN-1, HMGB1 AND AMINOPEPTIDASE N IN H3 MUTATED PAEDIATRIC HIGH-GRADE GLIOMAS

Abstract AIMS High-grade gliomas (HGG) are central nervous system tumour in children, where treatment options remain elusive, leaving children with a dismal prognosis. Histone H3.3 mutations, K27M and G34V/R have been identified as the two most common recurrent somatic mutations in paediatric HGG (pHGG). These mutations are present in 50% of pHGG compared to only 1% in adult gliomas. Our previous proteomic research on cell membrane protein through protein MS data analyses have identified different signatures of differentially expressed cell membrane proteins in H3-G34R/V mutated pHGG cells, in comparison to H3 wild type tumour cells in culture. Among these proteins we have identified flotillin-1, HMGB1 (High mobility group box 1) and aminopeptidase N. Flotillin-1 is associated with numerous malignancies and HMGB1 also functions as an oncogene and aminopeptidase N is a cell surface metalloprotease involved in tumour progression. Our aim is to study the expression and localisation of these cell surface proteins in H3 mutated and wild type tumour cells, to validate them as targets for developing novel therapeutics. METHOD Expression and localisation of flotillin-1, HMGB1 and aminopeptidase N in H3.3 mutated pHGG cell lines in comparison to H3 wildtype glioma and control cells was analysed, using different protein expression assays including immunofluorescence microscopy and western blotting. RESULTS Results showed statistically significant differential protein expression and localisation of these proteins. Flotillin-1 had increased cell membrane localization in H3 mutated cells. HMGB1 expression was increased, while aminopeptidase N expression was decreased in the H3 mutated cells in comparison to wildtype pHGG. CONCLUSION This new knowledge of the cell membrane proteomics of H3 mutated pHGG may help us utilise Flotillin- 1,HMGB1 and aminopeptidase N, as potential therapeutic targets for these unique H3 mutated children’s brain tumours.

ADAM interact with large protein complexes to regulate Histone modification, gene expression and splicing.

Cranial neural crest (CNC) cells are key stem cells that contribute to most of the facial structures in all vertebrates. Previous work has shown that multiple ADAM (A Disintegrin And Metalloprotease) cell surface metalloproteases are essential for the induction and migration of the CNC in multiple vertebrate animal models. In Xenopus, we have shown that Adam13 associates with the transcription factor Arid3a to regulate gene expression. Here we show that Adam13 regulates gene expression by modulating Histone modifications globally in the CNC. Furthermore, we show that Arid3a binding to the tfap2a; promoter depends on the presence of Adam13. This association promotes the expression of one tfap2a; variant predominantly expressed in the CNC that uniquely activates the expression of calpain-8, a gene critical for CNC migration. This tfap2a; variant selectively associates with proteins involved with mRNA splicing, a function that is critically affected by the loss of Adam13 in the CNC. Our results suggest that ADAM metalloproteases may act as sensors of the environment that can modulate chromatin availability, leading to changes in gene expression and splicing.

HGG-24. DIFFERENTIAL CELL SURFACE PROTEOMICS OF FLOTILLIN-1, HMGB1 AND AMINOPEPTIDASE N IN H3 MUTATED PAEDIATRIC HIGH-GRADE GLIOMAS

Abstract High-grade gliomas (HGG) are the deadliest central nervous system tumour in children. Despite this, treatment options remain elusive, leaving children with a dismal prognosis. Histone H3.3 mutations, K27M and G34V/R have been identified as the two most common recurrent somatic mutations in paediatric HGG (pHGG). These mutations are present in 50% of pHGG compared to only 1% in adult gliomas. Our previous proteomic research on cell membrane protein through protein MS data analyses have identified different signatures of differentially expressed cell membrane proteins in H3-G34R/V mutated pHGG cells, in comparison to H3 wild type tumour cells in culture. Among these proteins we have identified flotillin-1, HMGB1 (High mobility group box 1) and aminopeptidase N. Flotillin-1 is associated with numerous malignancies and HMGB1 also functions as an oncogene and aminopeptidase N is a cell surface metalloprotease involved in tumour progression. We have now verified the expression and localisation of these cell surface proteins in H3 mutated and wild type tumour cells, in order to validate as targets for developing novel therapeutics. Expression and localisation of flotillin-1, HMGB1 and aminopeptidase N in H3.3 mutated pHGG cell lines in comparison to H3 wildtype glioma and control cells was analysed, using different protein expression assays including immunofluorescence microscopy and western blotting. Experimental analyses showed statistically significant differential protein expression and localisation of these proteins. Flotillin-1 had increased cell membrane localization in H3 mutated cells.HMGB1 expression was increased, while aminopeptidase N expression was decreased in the H3 mutated cells in comparison to wildtype pHGG. This new knowledge of the cell membrane proteomics of H3 mutated pHGG may help us utilise Flotillin-1, HMGB1 and aminopeptidase N, as potential therapeutic targets for these unique H3 mutated children’s brain tumours.

Role of iRhom2 in Olfaction: Implications for Odorant Receptor Regulation and Activity-Dependent Adaptation.

The cell surface metalloprotease ADAM17 (a disintegrin and metalloprotease 17) and its binding partners iRhom2 and iRhom1 (inactive Rhomboid-like proteins 1 and 2) modulate cell-cell interactions by mediating the release of membrane proteins such as TNFα (Tumor necrosis factor α) and EGFR (Epidermal growth factor receptor) ligands from the cell surface. Most cell types express both iRhoms, though myeloid cells exclusively express iRhom2, and iRhom1 is the main iRhom in the mouse brain. Here, we report that iRhom2 is uniquely expressed in olfactory sensory neurons (OSNs), highly specialized cells expressing one olfactory receptor (OR) from a repertoire of more than a thousand OR genes in mice. iRhom2-/- mice had no evident morphological defects in the olfactory epithelium (OE), yet RNAseq analysis revealed differential expression of a small subset of ORs. Notably, while the majority of ORs remain unaffected in iRhom2-/- OE, OSNs expressing ORs that are enriched in iRhom2-/- OE showed fewer gene expression changes upon odor environmental changes than the majority of OSNs. Moreover, we discovered an inverse correlation between the expression of iRhom2 compared to OSN activity genes and that odor exposure negatively regulates iRhom2 expression. Given that ORs are specialized G-protein coupled receptors (GPCRs) and many GPCRs activate iRhom2/ADAM17, we investigated if ORs could activate iRhom2/ADAM17. Activation of an olfactory receptor that is ectopically expressed in keratinocytes (OR2AT4) by its agonist Sandalore leads to ERK1/2 phosphorylation, likely via an iRhom2/ADAM17-dependent pathway. Taken together, these findings point to a mechanism by which odor stimulation of OSNs activates iRhom2/ADAM17 catalytic activity, resulting in downstream transcriptional changes to the OR repertoire and activity genes, and driving a negative feedback loop to downregulate iRhom2 expression.

ADAM12 abrogation alters immune cell infiltration and improves response to checkpoint blockade therapy in the T11 murine model of triple-negative breast cancer

ABSTRACT Immunosuppressive tumor microenvironment (TME) impedes anti-tumor immune responses and contributes to immunotherapy resistance in triple-negative breast cancer (TNBC). ADAM12, a member of cell surface metalloproteases, is selectively upregulated in mesenchymal/claudin-low TNBCs, where its expression is largely restricted to tumor cells. The role of cancer cell-expressed ADAM12 in modulating the immune TME is not known. We show that Adam12 knockout in the T11 mouse syngeneic transplantation model of claudin-low TNBC leads to decreased numbers of tumor-infiltrating neutrophils (TINs)/polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) and increased numbers of tumor-infiltrating B cells and T cells. ADAM12 loss in cancer cells increases chemotaxis of B cells in vitro and this effect is eliminated by inhibition of CXCR4, a receptor for CXCL12, or anti-CXCL12 blocking antibody. Importantly, ADAM12 loss in T11 cancer cells sensitizes tumors to anti-PD1/anti-CTLA4 combination therapy, although the initial responsiveness is followed by acquired therapy resistance. Depletion of B cells in mice eliminates the improved response to immune checkpoint blockade of Adam12 knockout T11 tumors. Analysis of gene expression data for claudin-low TNBCs from the METABRIC patient cohort shows significant inverse correlations between ADAM12 and gene expression signatures of several anti-tumor immune cell populations, as well as a significant positive correlation between ADAM12 and gene expression signature of TINs/PMN-MDSCs. Collectively, these results implicate ADAM12 in immunosuppression within the TME in TNBC.

Targeted truncation of the ADAM17 cytoplasmic domain in mice results in protein destabilization and a hypomorphic phenotype

A disintegrin and metalloprotease 17 (ADAM17) is a cell-surface metalloprotease that serves as the principle sheddase for tumor necrosis factor α (TNFα), interleukin-6 receptor (IL-6R), and several ligands of the epidermal growth factor receptor (EGFR), regulating these crucial signaling pathways. ADAM17 activation requires its transmembrane domain, but not its cytoplasmic domain, and little is known about the role of this domain in vivo. To investigate, we used CRISPR-Cas9 to mutate the endogenous Adam17 locus in mice to produce a mutant ADAM17 lacking its cytoplasmic domain (Adam17Δcyto). Homozygous Adam17Δcyto animals were born at a Mendelian ratio and survived into adulthood with slightly wavy hair and curled whiskers, consistent with defects in ADAM17/EGFR signaling. At birth, Adam17Δcyto mice resembled Adam17−/− mice in that they had open eyes and enlarged semilunar heart valves, but they did not have bone growth plate defects. The deletion of the cytoplasmic domain resulted in strongly decreased ADAM17 protein levels in all tissues and cells examined, providing a likely cause for the hypomorphic phenotype. In functional assays, Adam17Δcyto mouse embryonic fibroblasts and bone-marrow-derived macrophages had strongly reduced ADAM17 activity, consistent with the reduced protein levels. Nevertheless, ADAM17Δcyto could be stimulated by PMA, a well-characterized posttranslational activator of ADAM17, corroborating that the cytoplasmic domain of endogenous ADAM17 is not required for its rapid response to PMA. Taken together, these results provide the first evidence that the cytoplasmic domain of ADAM17 plays a pivotal role in vivo in regulating ADAM17 levels and function.

Proteolytic processing of PD-L1 by ADAM proteases in breast cancer cells.

Expression of programmed death ligand 1 (PD-L1) on the surface of tumor cells and its interaction with programmed cell death protein 1 (PD-1) on tumor-infiltrating lymphocytes suppress anti-tumor immunity. In breast tumors, PD-L1 expression levels are the highest in estrogen receptor-negative, progesterone receptor-negative, and human epidermal growth factor receptor 2-negative (triple-negative) cancers. In this study, we show that a portion of PD-L1 exogenously expressed in several triple-negative breast cancer cell lines, as well as endogenous PD-L1, is proteolytically cleaved by cell surface metalloproteases. The cleavage generates an ~ 37-kDa N-terminal PD-L1 fragment that is released to the media and a C-terminal PD-L1 fragment that remains associated with cells but is efficiently eliminated by lysosomal degradation. We identify ADAM10 and ADAM17, two closely related members of the ADAM family of cell surface metalloproteases, as enzymes mediating PD-L1 cleavage. Notably, treatment of cells with ionomycin, a calcium ionophore and a known activator of ADAM10, or with phorbol 12-myristate 13-acetate, an activator of ADAM17, dramatically increases the release of soluble PD-L1 to the media. We postulate that ADAM10 and/or ADAM17 may contribute to the regulation of the PD-L1/PD-1 pathway and, ultimately, to anti-tumor immunity in triple-negative breast cancer.

CD10 expression identifies a subset of human perivascular progenitor cells with high proliferation and calcification potentials.

The tunica adventitia ensheathes arteries and veins and contains presumptive mesenchymal stem cells (MSCs) involved in vascular remodeling. We show here that a subset of human adventitial cells express the CD10/CALLA cell surface metalloprotease. Both CD10+ and CD10- adventitial cells displayed phenotypic features of MSCs when expanded in culture. However, CD10+ adventitial cells exhibited higher proliferation, clonogenic and osteogenic potentials in comparison to their CD10- counterparts. CD10+ adventitial cells increased expression of the cell cycle protein CCND2 via ERK1/2 signaling and osteoblastogenic gene expression via NF-κB signaling. CD10 expression was upregulated in adventitial cells through sonic hedgehog-mediated GLI1 signaling. These results suggest that CD10, which marks rapidly dividing cells in other normal and malignant cell lineages, plays a role in perivascular MSC function and cell fate specification. These findings also point to a role for CD10+ perivascular cells in vascular remodeling and calcification.

Proximal Tubule-Derived Amphiregulin Amplifies and Integrates Profibrotic EGF Receptor Signals in Kidney Fibrosis.

Sustained activation of EGF receptor (EGFR) in proximal tubule cells is a hallmark of progressive kidney fibrosis after AKI and in CKD. However, the molecular mechanisms and particular EGFR ligands involved are unknown. We studied EGFR activation in proximal tubule cells and primary tubular cells isolated from injured kidneys in vitro. To determine in vivo the role of amphiregulin, a low-affinity EGFR ligand that is highly upregulated with injury, we used ischemia-reperfusion injury or unilateral ureteral obstruction in mice with proximal tubule cell-specific knockout of amphiregulin. We also injected soluble amphiregulin into knockout mice with proximal tubule cell-specific deletion of amphiregulin's releasing enzyme, the transmembrane cell-surface metalloprotease, a disintegrin and metalloprotease-17 (ADAM17), and into ADAM17 hypomorphic mice. Yes-associated protein 1 (YAP1)-dependent upregulation of amphiregulin transcript and protein amplifies amphiregulin signaling in a positive feedback loop. YAP1 also integrates signals of other moderately injury-upregulated, low-affinity EGFR ligands (epiregulin, epigen, TGFα), which also require soluble amphiregulin and YAP1 to induce sustained EGFR activation in proximal tubule cells in vitro. In vivo, soluble amphiregulin injection sufficed to reverse protection from fibrosis after ischemia-reperfusion injury in ADAM17 hypomorphic mice; injected soluble amphiregulin also reversed the corresponding protective proximal tubule cell phenotype in injured proximal tubule cell-specific ADAM17 knockout mice. Moreover, the finding that proximal tubule cell-specific amphiregulin knockout mice were protected from fibrosis after ischemia-reperfusion injury or unilateral ureteral obstruction demonstrates that amphiregulin was necessary for the development of fibrosis. Our results identify amphiregulin as a key player in injury-induced kidney fibrosis and suggest therapeutic or diagnostic applications of soluble amphiregulin in kidney disease.

Integrin-Like Tethering of Motility Complexes at Bacterial Focal Adhesions

Directed surface motility of metazoan cells and protozoan parasites involves substratum engagement by surface-exposed integrin(-like) adhesins, directionally transported by molecular motors via coupling to the internal cytoskeleton. The predatory deltaproteobacterium Myxococcus xanthus uses a helically-trafficked motor at bacterial focal adhesions to power gliding motility. However, the mechanisms of gliding machinery-substratum coupling and force mechanotransduction between innermembrane motors and substratum are unknown. Herein, we use bead force spectroscopy and TIRF microscopy to characterize CglB as the essential substratum-coupling integrin αI-domain-like adhesin. Protease susceptibility reveals that CglB interacts with a globular-protein-accessorized β-barrel OM display platform, which regulates the cell-surface conformational state and accessibility of the adhesin. Surface retention of CglB is further regulated by a cell-surface metalloprotease, a phenomenon also modulated by the OM display platform. These data depict a complex mechanism for bacterial gliding adhesin secretion, cell-surface anchoring, and processing, with conserved themes between prokaryotic and eukaryotic cell motility.

Dual control of pcdh8l/PCNS expression and function in Xenopus laevis neural crest cells by adam13/33 via the transcription factors tfap2α and arid3a.

Adam13/33 is a cell surface metalloprotease critical for cranial neural crest (CNC) cell migration. It can cleave multiple substrates including itself, fibronectin, ephrinB, cadherin-11, pcdh8 and pcdh8l (this work). Cleavage of cadherin-11 produces an extracellular fragment that promotes CNC migration. In addition, the adam13 cytoplasmic domain is cleaved by gamma secretase, translocates into the nucleus and regulates multiple genes. Here, we show that adam13 interacts with the arid3a/dril1/Bright transcription factor. This interaction promotes a proteolytic cleavage of arid3a and its translocation to the nucleus where it regulates another transcription factor: tfap2α. Tfap2α in turn activates multiple genes including the protocadherin pcdh8l (PCNS). The proteolytic activity of adam13 is critical for the release of arid3a from the plasma membrane while the cytoplasmic domain appears critical for the cleavage of arid3a. In addition to this transcriptional control of pcdh8l, adam13 cleaves pcdh8l generating an extracellular fragment that also regulates cell migration.

Increased Potency of a Bi-specific TL1A-ADAM17 (TACE) Inhibitor by Cell Surface Targeting.

Inflammatory bowel disease (IBD) is a multifactorial disease characterized by the dysregulated activity of many pro-inflammatory factors. Thus, bi-specific inhibitors for the simultaneous inhibition of two pro-inflammatory factors can exhibit high therapeutic potential. Here, we developed a novel bi-specific inhibitor targeting the TL1A cytokine and ADAM17/TACE metalloprotease. Biochemical analysis of the bi-specific inhibitor revealed high TL1A binding and TACE inhibition that is similar to the two respective mono-specific inhibitors. Interestingly, cell based assays for TL1A inhibition revealed strong synergism between the inhibitory domains showing an up to 80-fold increase in potency of the bi-specific inhibitor. The dramatic increase in potency is associated with binding to cell membranes through the TACE inhibitory domain leading to increased concentration of the inhibitor on the cell surface. Our study highlights the high potential of the simultaneous targeting of cell surface metalloprotease (TACE) and soluble pro-inflammatory cytokine (TL1A) as a potential therapeutic approach in IBD.

Quantitative proteomics screen identifies a substrate repertoire of rhomboid protease RHBDL2 in human cells and implicates it in epithelial homeostasis

Rhomboids are intramembrane serine proteases conserved in all kingdoms of life. They regulate epidermal growth factor receptor signalling in Drosophila by releasing signalling ligands from their transmembrane tethers. Their functions in mammals are poorly understood, in part because of the lack of endogenous substrates identified thus far. We used a quantitative proteomics approach to investigate the substrate repertoire of rhomboid protease RHBDL2 in human cells. We reveal a range of novel substrates that are specifically cleaved by RHBDL2, including the interleukin-6 receptor (IL6R), cell surface protease inhibitor Spint-1, the collagen receptor tyrosine kinase DDR1, N-Cadherin, CLCP1/DCBLD2, KIRREL, BCAM and others. We further demonstrate that these substrates can be shed by endogenously expressed RHBDL2 and that a subset of them is resistant to shedding by cell surface metalloproteases. The expression profiles and identity of the substrates implicate RHBDL2 in physiological or pathological processes affecting epithelial homeostasis.

IRhoms in the brain – a new frontier?

The cell surface metalloprotease ADAM17 (a disintegrin and metalloprotease 17) orchestrates cell-cell interactions and has a key role in inflammation, development and in diseases such as Rheumatoid...

The Wnt receptor Frizzled-4 modulates ADAM13 metalloprotease activity.

Cranial neural crest (CNC) cells are a transient population of stem cells that originate at the border of the neural plate and the epidermis, and migrate ventrally to contribute to most of the facial structures including bones, cartilage, muscles and ganglia. ADAM13 is a cell surface metalloprotease that is essential for CNC cell migration. Here, we show in Xenopus laevis embryos that the Wnt receptor Fz4 binds to the cysteine-rich domain of ADAM13 and negatively regulates its proteolytic activity in vivo. Gain of Fz4 function inhibits CNC cell migration and can be rescued by gain of ADAM13 function. Loss of Fz4 function also inhibits CNC cell migration and induces a reduction of mature ADAM13, together with an increase in the ADAM13 cytoplasmic fragment that is known to translocate into the nucleus to regulate gene expression. We propose that Fz4 associates with ADAM13 during its transport to the plasma membrane to regulate its proteolytic activity.

Cell surface metalloproteases as targets in glioblastoma: implications for tumor growth and therapy resistance

Background: Despite multimodal therapy, Glioblastoma (GBM) chemotherapy with Temozolomide (TMZ) remains inefficient due to chemoresistance. MMP and ADAM metalloproteases (MPs) are increased in GBM and could contribute to chemoresistance and TMZ induced recurrence of glioblastoma. Methods: TMZ sensitivity of GBM cells was assessed with MP inhibitors batimastat (BB-94) and marimastat (BB-2516). Induction of MPs by TMZ was determined by qPCR and activity assays. MP-dependent effects of TMZ on mitochondria and intracellular kinase (Akt/PI3K, ERK1/2) pathway were investigated by FACS, morphological analysis and Western blotting. Invasiveness of TMZ/BB-94 treated GBM cells was determined by Matrigel invasion assays. Potential MP substrates were identified by proteomic analysis and MP expression levels were compared in primary vs. recurrent GBM.

GSK3 and Polo-like kinase regulate ADAM13 function during cranial neural crest cell migration.

ADAMs are cell surface metalloproteases that control multiple biological processes by cleaving signaling and adhesion molecules. ADAM13 controls cranial neural crest (CNC) cell migration both by cleaving cadherin-11 to release a promigratory extracellular fragment and by controlling expression of multiple genes via its cytoplasmic domain. The latter activity is regulated by γ-secretase cleavage and the translocation of the cytoplasmic domain into the nucleus. One of the genes regulated by ADAM13, the protease calpain8, is essential for CNC migration. Although the nuclear function of ADAM13 is evolutionarily conserved, it is unclear whether the transcriptional regulation is also performed by other ADAMs and how this process may be regulated. We show that ADAM13 function to promote CNC migration is regulated by two phosphorylation events involving GSK3 and Polo-like kinase (Plk). We further show that inhibition of either kinase blocks CNC migration and that the respective phosphomimetic forms of ADAM13 can rescue these inhibitions. However, these phosphorylations are not required for ADAM13 proteolysis of its substrates, γ-secretase cleavage, or nuclear translocation of its cytoplasmic domain. Of significance, migration of the CNC can be restored in the absence of Plk phosphorylation by expression of calpain-8a, pointing to impaired nuclear activity of ADAM13.

Leishmania Evades Host Immunity by Inhibiting Antigen Cross-Presentation through Direct Cleavage of the SNARE VAMP8

During phagocytosis, microorganisms are taken up by immune cells into phagosomes. Through membrane-trafficking events mediated by SNARE proteins, phagosomes fuse with lysosomes, generating degradative phagolysosomes. Phagolysosomes contribute to host immunity by linking microbial killing within these organelles with antigen processing for presentation on MHC class I or II molecules to Tcells. We show that the intracellular parasite Leishmania evades immune recognition by inhibiting phagolysosome biogenesis. The Leishmania cell surface metalloprotease GP63 cleaves a subset of SNAREs, including VAMP8. GP63-mediated VAMP8 inactivation or Vamp8 disruption prevents the NADPH oxidase complex from assembling on phagosomes, thus altering their pH and degradative properties. Consequently, the presentation of exogenous Leishmania antigens on MHC class I molecules, also known as cross-presentation, is inhibited, resulting in reduced Tcell activation. These findings indicate that Leishmania subverts immune recognition by altering phagosome function and highlight the importance of VAMP8 in phagosome biogenesis and antigen cross-presentation.

CD10 expression in urothelial bladder carcinomas: staining patterns and relationship with pathologic parameters*

CD10 is a cell surface metalloprotease that inactivates various bioactive neuropeptides. CD10 has been suggested as a useful prognostic marker for urothelial carcinoma, but there are only a few studies of CD10 in urothelial tumors and they have shown varying results. The aims of this study were to investigate the expression of CD10 in urothelial bladder carcinomas and to clarify its association with pathologic parameters. Materials and methods: A total of 50 urothelial bladder carcinomas were selected from archival material. All cases were reevaluated histopathologically and graded according to the WHO/ISUP 1998 classification. The TNM system was used for their pathological staging. CD 10 immunohistochemical staining was performed on one representative tissue block for each case. Results: 35 of the 50 (70%) tumors showed positive CD10 immunostaining. We found a statistically significant difference in terms of CD10 extent between low grade and high grade tumors. No association was detected between CD10 expression and other pathologic parameters. No relationship was found between CD10 expression and tumor size, lymphovascular invasion, or pathological stage. Conclusion: According to our findings, high grade carcinomas showed a wider CD10 expression than that in low grade carcinomas. CD10 may play an important role in the progression and differentiation of bladder urothelial carcinomas.

Constitutive Endocytosis of the Chemokine CX3CL1 Prevents Its Degradation by Cell Surface Metalloproteases

CX(3)CL1, a chemokine with transmembrane and soluble species, plays a key role in inflammation by acting as both chemoattractant and adhesion molecule. CX(3)CL1 is the only chemokine known to undergo constitutive internalization, raising the possibility that dynamic equilibrium between the endocytic compartment and the plasma membrane critically regulates the availability and processing of CX(3)CL1 at the cell surface. We therefore investigated how transmembrane CX(3)CL1 is internalized. Inhibition of dynamin using a nonfunctional allele or of clathrin using specific small interfering RNA prevented endocytosis of the chemokine in CX(3)CL1-expressing human ECV-304 cells. Perusal of the cytoplasmic domain of CX(3)CL1 revealed two putative adaptor protein-2 (AP-2)-binding motifs. Accordingly, CX(3)CL1 co-localized with AP-2 at the plasma membrane. We generated a mutant allele of CX(3)CL1 lacking the cytoplasmic tail. Deletion of the cytosolic tail precluded internalization of the chemokine. We used site-directed mutagenesis to disrupt AP-2-binding motifs, singly or in combination, which resulted in diminished internalization of CX(3)CL1. Although CX(3)CL1 was present in both superficial and endomembrane compartments, ADAM10 (a disintegrin and metalloprotease 10) and tumor necrosis factor-converting enzyme, the two metalloproteases that cleave CX(3)CL1, localized predominantly to the plasmalemma. Inhibition of endocytosis using the dynamin inhibitor, Dynasore, promoted rapid metalloprotease-dependent shedding of CX(3)CL1 from the cell surface into the surrounding medium. These findings indicate that the cytoplasmic tail of CX(3)CL1 facilitates its constitutive clathrin-mediated endocytosis. Such regulation enables intracellular storage of a sizable pool of presynthesized CX(3)CL1 that protects the chemokine from degradation by metalloproteases at the plasma membrane.