ADAM10 sheddase activation is controlled by cell membrane asymmetry

The ectodomain sheddase ADAM10 restricts HIV-1 propagation and is counteracted by Nef

HIV-1 Nef enhances virus propagation by down-regulating CD4 and SERINC5. However, recent evidence points to the existence of an additional Nef-sensitive restriction mechanism. We now show that Nef suppresses the aberrant cleavage of HIV-1 gp41 by ADAM10, a virion-associated cellular ectodomain sheddase, and thus increases the amount of HIV-1 envelope glycoprotein (Env) on virions. Additionally, Nef inhibits the shedding of at least some cellular ADAM10 substrates, resulting in their accumulation on HIV-1 virions. Whereas Nef+ HIV-1 replicated only marginally better in the absence of ADAM10, the propagation of Nef- HIV-1 was notably rescued in ADAM10- T cell lines. Crucially, Nef- HIV-1 also benefited from the absence of ADAM10 in primary CD4+ T cells. Collectively, our results indicate that ADAM10 negatively affects both laboratory-adapted and primary HIV-1 strains by shedding the ectodomains of viral and cellular transmembrane proteins from virions and that Nef rescues virus replication by counteracting ADAM10.

Dys-regulated phosphatidylserine externalization as a cell intrinsic immune escape mechanism in cancer

The negatively charged aminophospholipid, phosphatidylserine (PS), is typically restricted to the inner leaflet of the plasma membrane under normal, healthy physiological conditions. PS is irreversibly externalized during apoptosis, where it serves as a signal for elimination by efferocytosis. PS is also reversibly and transiently externalized during cell activation such as platelet and immune cell activation. These events associated with physiological PS externalization are tightly controlled by the regulated activation of flippases and scramblases. Indeed, improper regulation of PS externalization results in thrombotic diseases such as Scott Syndrome, a defect in coagulation and thrombin production, and in the case of efferocytosis, can result in autoimmunity such as systemic lupus erythematosus (SLE) when PS-mediated apoptosis and efferocytosis fails. The physiological regulation of PS is also perturbed in cancer and during viral infection, whereby PS becomes persistently exposed on the surface of such stressed and diseased cells, which can lead to chronic thrombosis and chronic immune evasion. In this review, we summarize evidence for the dysregulation of PS with a main focus on cancer biology and the pathogenic mechanisms for immune evasion and signaling by PS, as well as the discussion of new therapeutic strategies aimed to target externalized PS. We posit that chronic PS externalization is a universal and agnostic marker for diseased tissues, and in cancer, likely reflects a cell intrinsic form of immune escape. The continued development of new therapeutic strategies for targeting PS also provides rationale for their co-utility as adjuvants and with immune checkpoint therapeutics.

Calcium-sensing receptor- and ADAM10-mediated klotho shedding is regulated by tetraspanin 5

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.

Regulation of ADAM10 activity through microdomain-dependent intracellular calcium changes

A disintegrin and metalloproteinases (ADAMs) are transmembrane proteases that cleave other proteins close to the surface in a process called shedding. The prominent member ADAM10 has been linked to several pathologies such as Alzheimer's disease, bacterial infection, cancer development and metastasis. Although the regulation of the ADAM10 activity by calcium influx and calmodulin inhibition has been reported, the spatiotemporal regulation of Ca2+-dependent ADAM10 activation and the required source of Ca2+ ions have not been thoroughly studied. In the present study, we observed the rapid Ca2+-dependent activation of ADAM10 in A549 lung carcinoma cells upon stimulation with ionomycin. The calmodulin-inhibitors trifluoperazine and ophiobolin A mediated delayed activation of ADAM10, which apparently did not depend on intracellular Ca2+ in the case of trifluoperazine. Furthermore, the surface translocation and release of ADAM10 in extracellular vesicles exhibited different kinetics and were only partially linked to catalytic activation. Finally, ADAM10 activation was observed after the entry of Ca2+ through certain channels, such as canonical members of transient receptor potential (TRP) channels. Therefore, the opening of particular channels for Ca2+ entry points and subsequent Ca2+ flux as well as the temporal aspects of the consequent increase in Ca2+ levels, must be considered for future therapeutic options involving the increasing or decreasing ADAM10 activity.

ADAM10 isoforms: Optimizing usage of antibodies based on protein regulation, structural features, biological activity and clinical relevance to Alzheimer's disease

A Disintegrin and Metalloproteinase 10 (ADAM10) is a crucial transmembrane protein involved in diverse cellular processes, including cell adhesion, migration, and proteolysis. ADAM10's ability to cleave over 100 substrates underscores its significance in physiological and pathological contexts, particularly in Alzheimer's disease (AD). This review comprehensively examines ADAM10's multifaceted roles, highlighting its critical function in the non-amyloidogenic processing of the amyloid precursor protein (APP), which mitigates amyloid beta (Aβ) production, a critical factor in AD development. We summarize the regulation of ADAM10 at multiple levels: transcriptional, translational, and post-translational, revealing the complexity and responsiveness of its expression to various cellular signals. A standardized nomenclature for ADAM10 isoforms is proposed to improve clarity and consistency in research, facilitating better comparison and replication of findings across studies. We address the challenges in detecting ADAM10 isoforms using antibodies, advocating for standardized detection protocols to resolve discrepancies in results from different biological matrices. By highlighting these issues, this review underscores the potential of ADAM10 as a biomarker for early diagnosis and a therapeutic target in AD. By consolidating current knowledge on ADAM10's regulation and function, we aim to provide insights that will guide future research and therapeutic strategies in the AD context.

TRPV4 Mediates Alveolar Epithelial Barrier Integrity and Induces ADAM10-Driven E-Cadherin Shedding

Transient receptor potential vanilloid 4 (TRPV4) channels have been associated with numerous pulmonary pathologies, including hypertension, asthma, and acute lung injury. However, their role in the alveolar epithelium remains unclear. We performed impedance-based resistance measurements in primary differentiated alveolar epithelial type I (AT1) cells from wild-type (WT) and TRPV4-deficient (TRPV4-/-) C57/BL6J mice to detect changes in AT1 barrier integrity upon TRPV4 activation. Both pharmacological (GSK1016790A) and a low pH-driven activation of TRPV4 were quantified, and the downstream effects on adherens junctions were assessed through the Western blotting of epithelial cadherin (E-cadherin) protein levels. Importantly, a drop in pH caused a rapid decrease in AT1 barrier resistance and increased the formation of a ~35 kDa E-cadherin C-terminal fragment, with both effects significantly reduced in TRPV4-/- AT1 cells. Similarly, the pharmacological activation of TRPV4 in AT1 cells triggered an immediate transient loss of barrier resistance and the formation of the same E-cadherin fragment, which was again diminished by TRPV4 deficiency. Moreover, TRPV4-mediated E-cadherin cleavage was significantly reduced by GI254023X, an antagonist of a disintegrin and metalloprotease 10 (ADAM10). Our results confirm the role of TRPV4 in regulating alveolar epithelial barrier permeability and provide insight into a novel signaling pathway by which TRPV4-induced Ca2+ influx stimulates metalloprotease-driven ectodomain shedding.

Overcoming the Tumor Collagen Barriers: A Multistage Drug Delivery Strategy for DDR1-Mediated Resistant Colorectal Cancer Therapy

The extracellular matrix (ECM) is critical for drug resistance in colorectal cancer (CRC). The abundant collagen within the ECM significantly influences tumor progression and matrix-mediated drug resistance (MMDR) by binding to discoidin domain receptor 1 (DDR1), but the specific mechanisms by which tumor cells modulate ECM via DDR1 and ultimately regulate TME remain poorly understand. Furthermore, overcoming drug resistance by modulating the tumor ECM remains a challenge in CRC treatment. In this study, a novel mechanism is elucidated by which DDR1 mediates the interactions between tumor cells and collagen, enhances collagen barriers, inhibits immune infiltration, promotes drug efflux, and leads to MMDR in CRC. To address this issue, a multistage drug delivery system carrying DDR1-siRNA and chemotherapeutic agents is employed to disrupt collagen barriers by silencing DDR1 in tumor, enhancing chemotherapy drugs diffusion and facilitating immune infiltration. These findings not only revealed a novel role for collagen-rich matrix mediated by DDR1 in tumor resistance, but also introduced a promising CRC treatment strategy.

TMEM16F scramblase regulates angiogenesis via endothelial intracellular signaling

TMEM16F (also known as ANO6), a Ca2+-activated lipid scramblase (CaPLSase) that dynamically disrupts lipid asymmetry, plays a crucial role in various physiological and pathological processes, such as blood coagulation, neurodegeneration, cell-cell fusion and viral infection. However, the mechanisms through which it regulates these processes remain largely elusive. Using endothelial cell-mediated angiogenesis as a model, here we report a previously unknown intracellular signaling function of TMEM16F. We demonstrate that TMEM16F deficiency impairs developmental retinal angiogenesis in mice and disrupts angiogenic processes in vitro. Biochemical analyses indicate that the absence of TMEM16F enhances the plasma membrane association of activated Src kinase. This in turn increases VE-cadherin phosphorylation and downregulation, accompanied by suppressed angiogenesis. Our findings not only highlight the role of intracellular signaling by TMEM16F in endothelial cells but also open new avenues for exploring the regulatory mechanisms for membrane lipid asymmetry and their implications in disease pathogenesis.

Unraveling the dual role of ADAM10: Bridging the gap between cancer and Alzheimer's disease

An inverse association between Alzheimer's disease (AD) and cancer has been proposed. Patients with a cancer history have a decreased risk of developing AD, and AD patients have a reduced cancer incidence, which is not seen in vascular dementia patients. Given this association, common molecular and biological mechanisms that could explain this inverse relationship have been proposed before, such as Peptidylprolyl Cis/Trans Isomerase, NIMA-Interacting 1 (Pin1), Wingless and Int-1 (Wnt), and transformation-related protein 53 (p53)-mediated pathways, along with inflammation and oxidative stress-related proteins. A Disintegrin And Metalloprotease 10 (ADAM10) is a protease responsible for the cleavage of key AD- and cancer-related substrates, and it has inverse roles in those diseases: neuroprotective and disease-promoting, respectively. Thus, herein, we review the relevant literature linking AD and cancer and propose how ADAM10 activity might modulate the inverse association between the diseases. Understanding how this protease mediates those two conditions might raise some considerations in the ADAM10 pharmacological modulation for treating AD and cancer.

A type I interferon regulatory network for human plasmacytoid dendritic cells based on heparin, membrane-bound and soluble BDCA-2

Plasmacytoid dendritic cells (pDCs) produce type I interferons (IFNs) after sensing viral/bacterial RNA or DNA by toll-like receptor (TLR) 7 or TLR9, respectively. However, aberrant pDCs activation can cause adverse effects on the host and contributes to the pathogenesis of type I IFN-related autoimmune diseases. Here, we show that heparin interacts with the human pDCs-specific blood dendritic cell antigen 2 (BDCA-2) but not with related lectins such as DCIR or dectin-2. Importantly, BDCA-2-heparin interaction depends on heparin sulfation and receptor glycosylation and results in inhibition of TLR9-driven type I IFN production in primary human pDCs and the pDC-like cell line CAL-1. This inhibition is mediated by unfractionated and low-molecular-weight heparin, as well as endogenous heparin from plasma, suggesting that the local blood environment controls the production of IFN-α in pDCs. Additionally, we identified an activation-dependent soluble form of BDCA-2 (solBDCA-2) in human plasma that functions as heparin antagonist and thereby increases TLR9-driven IFN-α production in pDCs. Of importance, solBDCA-2 levels in the serum were increased in patients with scrub typhus (an acute infectious disease caused by Orientia tsutsugamushi) compared to healthy control subjects and correlated with anti-dsDNA antibodies titers. In contrast, solBDCA-2 levels in plasma from patients with bullous pemphigoid or psoriasis were reduced. In summary, this work identifies a regulatory network consisting of heparin, membrane-bound and solBDCA-2 modulating TLR9-driven IFN-α production in pDCs. This insight into pDCs function and regulation may have implications for the treatment of pDCs-related autoimmune diseases.

The mechanistic basis of the membrane-permeabilizing activities of the virulence-associated protein A (VapA) from Rhodococcus equi

Pathogenic Rhodococcus equi release the virulence-associated protein A (VapA) within macrophage phagosomes. VapA permeabilizes phagosome and lysosome membranes and reduces acidification of both compartments. Using biophysical techniques, we found that VapA interacts with model membranes in four steps: (i) binding, change of mechanical properties, (ii) formation of specific membrane domains, (iii) permeabilization within the domains, and (iv) pH-specific transformation of domains. Biosensor data revealed that VapA binds to membranes in one step at pH 6.5 and in two steps at pH 4.5 and decreases membrane fluidity. The integration of VapA into lipid monolayers was only significant at lateral pressures <20 mN m-1 indicating preferential incorporation into membrane regions with reduced integrity. Atomic force microscopy of lipid mono- and bilayers showed that VapA increased the surface heterogeneity of liquid disordered domains. Furthermore, VapA led to the formation of a new microstructured domain type and, at pH 4.5, to the formation of 5 nm high domains. VapA binding, its integration and lipid domain formation depended on lipid composition, pH, protein concentration and lateral membrane pressure. VapA-mediated permeabilization is clearly distinct from that caused by classical microbial pore formers and is a key contribution to the multiplication of Rhodococcus equi in phagosomes.

Apoptosis-mediated ADAM10 activation removes a mucin barrier promoting T cell efferocytosis

Efferocytic clearance of apoptotic cells in general, and T cells in particular, is required for tissue and immune homeostasis. Transmembrane mucins are extended glycoproteins highly expressed in the cell glycocalyx that function as a barrier to phagocytosis. Whether and how mucins may be regulated during cell death to facilitate efferocytic corpse clearance is not well understood. Here we show that normal and transformed human T cells express a subset of mucins which are rapidly and selectively removed from the cell surface during apoptosis. This process is mediated by the ADAM10 sheddase, the activity of which is associated with XKR8-catalyzed flipping of phosphatidylserine to the outer leaflet of the plasma membrane. Mucin clearance enhances uptake of apoptotic T cells by macrophages, confirming mucins as an enzymatically-modulatable barrier to efferocytosis. Together these findings demonstrate a glycocalyx regulatory pathway with implications for therapeutic intervention in the clearance of normal and transformed apoptotic T cells.

The matrix metalloproteinase ADAM10 supports hepatitis C virus entry and cell-to-cell spread via its sheddase activity

Hepatitis C virus (HCV) exploits the four entry factors CD81, scavenger receptor class B type I (SR-BI, also known as SCARB1), occludin, and claudin-1 as well as the co-factor epidermal growth factor receptor (EGFR) to infect human hepatocytes. Here, we report that the disintegrin and matrix metalloproteinase 10 (ADAM10) associates with CD81, SR-BI, and EGFR and acts as HCV host factor. Pharmacological inhibition, siRNA-mediated silencing and genetic ablation of ADAM10 reduced HCV infection. ADAM10 was dispensable for HCV replication but supported HCV entry and cell-to-cell spread. Substrates of the ADAM10 sheddase including epidermal growth factor (EGF) and E-cadherin, which activate EGFR family members, rescued HCV infection of ADAM10 knockout cells. ADAM10 did not influence infection with other enveloped RNA viruses such as alphaviruses and a common cold coronavirus. Collectively, our study reveals a critical role for the sheddase ADAM10 as a HCV host factor, contributing to EGFR family member transactivation and as a consequence to HCV uptake.

The basis of complications in the context of SARS-CoV-2 infection: Pathological activation of ADAM17

The virulence of SARS-CoV-2 decreases with increasing infectivity, the primary approaches for antiviral treatments will be preventing or minimizing the complications resulting from virus infection. ADAM metallopeptidase domain 17 (ADAM17) activation by SARS-CoV-2 infection has a dual effect on the development of the disease: increased release of inflammatory cytokines and dysregulation of Angiotensin converting enzyme II (ACE2) on cell surfaces, inflammatory cytokine infiltration and loss of ACE2 protective function lead to a significant increase in the incidence of related complications. Importantly, pathologically activated ADAM17 showed superior features than S protein in regulating ACE2 expression and participating in the intra cellular replication of SARS-CoV-2. In short, SARS-CoV-2 elicits only a limited immune response when it promotes its own replication and pathogenicity through ADAM17. Therefore, the pathological activation of ADAM17 may also represent a diminished innate antiviral defense and an altered strategy of SARS-CoV-2 infection. In this review, we summarized recent advances in our understanding of the pathophysiology of ADAM17, with a focus on the new findings that SARS-CoV-2 affects ADAM17 expression through Furin protein converting enzyme and Mitogen-activated protein kinase (MAPK) pathway, and raises the hypothesis that SARS-CoV-2 may mediates the pathological activation of ADAM17 by hijacking the actin regulatory pathway, and discussed the underlying biological principles.

Endothelial TMEM16F lipid scramblase regulates angiogenesis

Dynamic loss of lipid asymmetry through the activation of TMEM16 Ca2+-activated lipid scramblases (CaPLSases) has been increasingly recognized as an essential membrane event in a wide range of physiological and pathological processes, including blood coagulation, microparticle release, bone development, pain sensation, cell-cell fusion, and viral infection. Despite the recent implications of TMEM16F CaPLSase in vascular development and endothelial cell-mediated coagulation, its signaling role in endothelial biology remains to be established. Here, we show that endothelial TMEM16F regulates in vitro and in vivo angiogenesis through intracellular signaling. Developmental retinal angiogenesis is significantly impaired in TMEM16F deficient mice, as evidenced by fewer vascular loops and larger loop areas. Consistent with our in vivo observation, TMEM16F siRNA knockdown in human umbilical vein endothelial cells compromises angiogenesis in vitro. We further discovered that TMEM16F knockdown enhances VE-cadherin phosphorylation and reduces its expression. Moreover, TMEM16F knockdown also promotes Src kinase phosphorylation at tyrosine 416, which may be responsible for downregulating VE-cadherin expression. Our study thus uncovers a new biological function of TMEM16F in angiogenesis and provides a potential mechanism for how the CaPLSase regulates angiogenesis through intracellular signaling.

Breakdown of Phospholipid Asymmetry Triggers ADAM17-Mediated Rescue Events in Cells Undergoing Apoptosis

ADAM17, a prominent member of the "Disintegrin and Metalloproteinase" (ADAM) family, controls vital cellular functions through the cleavage of transmembrane substrates, including epidermal growth factor receptor (EGFR) ligands such as transforming growth factor (TGF)-alpha and Epiregulin (EREG). Several ADAM17 substrates are relevant to oncogenesis and tumor growth. We have presented evidence that surface exposure of phosphatidylserine (PS) is pivotal for ADAM17 to exert sheddase activity. The scramblase Xkr8 is instrumental for calcium-independent exposure of PS in apoptotic cells. Xkr8 can be dually activated by caspase-3 and by kinases. In this investigation, we examined whether Xkr8 would modulate ADAM17 activity under apoptotic and non-apoptotic conditions. Overexpression of Xkr8 in HEK293T cells led to significantly increased caspase-dependent as well as PMA-induced release of EREG and TGF-alpha. Conversely, siRNA-mediated downregulation of Xkr8 in colorectal Caco-2 cancer cells led to decreased PS externalization upon induction of apoptosis, which was accompanied by reduced shedding of endogenously expressed EREG and reduced cell survival. We conclude that Xkr8 shares with conventional scramblases the propensity to upmodulate the ADAM-sheddase function. Liberation of growth factors could serve a rescue function in cells on the pathway to apoptotic death.

TMEM16A/F support exocytosis but do not inhibit Notch-mediated goblet cell metaplasia of BCi-NS1.1 human airway epithelium

Cl- channels such as the Ca2+ activated Cl- channel TMEM16A and the Cl- permeable phospholipid scramblase TMEM16F may affect the intracellular Cl- concentration ([Cl-]i), which could act as an intracellular signal. Loss of airway expression of TMEM16A induced a massive expansion of the secretory cell population like goblet and club cells, causing differentiation into a secretory airway epithelium. Knockout of the Ca2+-activated Cl- channel TMEM16A or the phospholipid scramblase TMEM16F leads to mucus accumulation in intestinal goblet cells and airway secretory cells. We show that both TMEM16A and TMEM16F support exocytosis and release of exocytic vesicles, respectively. Lack of TMEM16A/F expression therefore causes inhibition of mucus secretion and leads to goblet cell metaplasia. The human basal epithelial cell line BCi-NS1.1 forms a highly differentiated mucociliated airway epithelium when grown in PneumaCult™ media under an air liquid interface. The present data suggest that mucociliary differentiation requires activation of Notch signaling, but not the function of TMEM16A. Taken together, TMEM16A/F are important for exocytosis, mucus secretion and formation of extracellular vesicles (exosomes or ectosomes) but the present data do no not support a functional role of TMEM16A/F in Notch-mediated differentiation of BCi-NS1.1 cells towards a secretory epithelium.

Topical Alginate Protection against Pepsin-Mediated Esophageal Damage: E-Cadherin Proteolysis and Matrix Metalloproteinase Induction

Epithelial barrier dysfunction is a hallmark of gastroesophageal reflux disease (GERD) related to symptom origination, inflammatory remodeling and carcinogenesis. Alginate-based antireflux medications were previously shown to topically protect against peptic barrier disruption, yet the molecular mechanisms of injury and protection were unclear. Herein, Barrett's esophageal (BAR-T) cells were pretreated with buffered saline (HBSS; control), dilute alginate medications (Gaviscon Advance or Gaviscon Double Action, Reckitt Benckiser), a viscosity-matched placebo, or ADAM10 and matrix metalloproteinase (MMP) inhibitors before exposure to HBSS pH7.4 or pH4 ± 1 mg/mL pepsin for 10-60 min. Cell viability was assessed by ATP assay; mediators of epithelial integrity, E-cadherin, ADAM10, and MMPs were examined by Western blot and qPCR. Alginate rescued peptic reduction of cell viability (p < 0.0001). Pepsin-pH4 yielded E-cadherin fragments indicative of regulated intramembrane proteolysis (RIP) which was not rescued by inhibitors of known E-cadherin sheddases. Transcriptional targets of E-cadherin RIP fragments were elevated at 24 h (MMP-1,2,9,14; p < 0.01). Alginate rescued E-cadherin cleavage, ADAM10 maturation, and MMP induction (p < 0.01). Results support RIP as a novel mechanism of peptic injury during GERD. Alginate residue after wash-out to mimic physiologic esophageal clearance conferred lasting protection against pepsin-induced molecular mechanisms that may exacerbate GERD severity and promote carcinogenesis in the context of weakly acidic reflux.

Regulation of phospholipid distribution in the lipid bilayer by flippases and scramblases

Cellular membranes function as permeability barriers that separate cells from the external environment or partition cells into distinct compartments. These membranes are lipid bilayers composed of glycerophospholipids, sphingolipids and cholesterol, in which proteins are embedded. Glycerophospholipids and sphingolipids freely move laterally, whereas transverse movement between lipid bilayers is limited. Phospholipids are asymmetrically distributed between membrane leaflets but change their location in biological processes, serving as signalling molecules or enzyme activators. Designated proteins - flippases and scramblases - mediate this lipid movement between the bilayers. Flippases mediate the confined localization of specific phospholipids (phosphatidylserine (PtdSer) and phosphatidylethanolamine) to the cytoplasmic leaflet. Scramblases randomly scramble phospholipids between leaflets and facilitate the exposure of PtdSer on the cell surface, which serves as an important signalling molecule and as an 'eat me' signal for phagocytes. Defects in flippases and scramblases cause various human diseases. We herein review the recent research on the structure of flippases and scramblases and their physiological roles. Although still poorly understood, we address the mechanisms by which they translocate phospholipids between lipid bilayers and how defects cause human diseases.

ADAM10-a "multitasker" in sepsis: focus on its posttranslational target

BACKGROUND

Sepsis has a complex pathogenesis in which the uncontrolled systemic inflammatory response triggered by infection leads to vascular barrier disruption, microcirculation dysfunction and multiple organ dysfunction syndrome. Numerous recent studies reveal that a disintegrin and metalloproteinase 10 (ADAM10) acts as a "molecular scissor" playing a pivotal role in the inflammatory response during sepsis by regulating proteolysis by cleaving various membrane protein substrates, including proinflammatory cytokines, cadherins and Notch, which are involved in intercellular communication. ADAM10 can also act as the cellular receptor for Staphylococcus aureus α-toxin, leading to lethal sepsis. However, its substrate-specific modulation and precise targets in sepsis have not yet to be elucidated.

METHODS

We performed a computer-based online search using PubMed and Google Scholar for published articles concerning ADAM10 and sepsis.

CONCLUSIONS

In this review, we focus on the functions of ADAM10 in sepsis-related complex endothelium-immune cell interactions and microcirculation dysfunction through the diversity of its substrates and its enzymatic activity. In addition, we highlight the posttranslational mechanisms of ADAM10 at specific subcellular sites, or in multimolecular complexes, which will provide the insight to intervene in the pathophysiological process of sepsis caused by ADAM10 dysregulation.

Dysregulation of ADAM10 shedding activity in naked mole-rat fibroblasts is due to deficient phosphatidylserine externalization

The naked mole-rat (NMR, Heterocephalus glaber) is of significant interest to biogerontological research, rarely developing age-associated diseases, such as cancer. The transmembrane glycoprotein CD44 is upregulated in certain cancers and CD44 cleavage by a disintegrin and metalloproteinase 10 (ADAM10) regulates cellular migration. Here we provide evidence that mature ADAM10 is expressed in NMR primary skin fibroblasts (NPSF), and that ionomycin increases cell surface ADAM10 localization. However, we observed an absence of ADAM10 mediated CD44 cleavage, as well as shedding of exogenous and overexpressed betacellulin in NPSF, whereas in mouse primary skin fibroblasts ionomycin induced ADAM10-dependent cleavage of both CD44 and betacellulin. Overexpressing a hyperactive form of the Ca²⁺ -dependent phospholipid scramblase ANO6 in NPSF increased phosphatidylserine (PS) externalization, which rescued the ADAM10 sheddase activity and promoted cell migration in NPSF in an ADAM10-dependent manner. These findings suggest that dysregulation of ADAM10 shedding activity is due to a deficient PS externalization in NMR.

A Bioengineering Strategy to Control ADAM10 Activity in Living Cells

A Disintegrin and Metalloprotease 10, also known as ADAM10, is a cell surface protease ubiquitously expressed in mammalian cells where it cuts several membrane proteins implicated in multiple physiological processes. The dysregulation of ADAM10 expression and function has been implicated in pathological conditions, including Alzheimer's disease (AD). Although it has been suggested that ADAM10 is expressed as a zymogen and the removal of the prodomain results in its activation, other potential mechanisms for the ADAM10 proteolytic function and activation remain unclear. Another suggested mechanism is post-translational modification of the cytoplasmic domain, which regulates ADAM10-dependent protein ectodomain shedding. Therefore, the precise and temporal activation of ADAM10 is highly desirable to reveal the fine details of ADAM10-mediated cleavage mechanisms and protease-dependent therapeutic applications. Here, we present a strategy to control prodomain and cytosolic tail cleavage to regulate ADAM10 shedding activity without the intervention of small endogenous molecule signaling pathways. We generated a series of engineered ADAM10 analogs containing Tobacco Etch Virus protease (TEV) cleavage site (TEVcs), rendering ADAM10 cleavable by TEV. This strategy revealed that, in the absence of other stimuli, the TEV-mediated removal of the prodomain could not activate ADAM10. However, the TEV-mediated cleavage of the cytosolic domain significantly increased ADAM10 activity. Then, we generated ADAM10 with a minimal constitutively catalytic activity that increased significantly in the presence of TEV or after activating a chemically activatable TEV. Our results revealed a bioengineering strategy for controlling the ADAM10 activity in living cells, paving the way to obtain spatiotemporal control of ADAM10. Finally, we proved that our approach of controlling ADAM10 promoted α-secretase activity and the non-amyloidogenic cleavage of amyloid-β precursor protein (APP), thereby increasing the production of the neuroprotective soluble ectodomain (sAPPα). Our bioengineering strategy has the potential to be exploited as a next-generation gene therapy for AD.

Ectodomain shedding of EGFR ligands serves as an activation readout for TRP channels

Transient receptor potential (TRP) channels are activated by various extracellular and intracellular stimuli and are involved in many physiological events. Because compounds that act on TRP channels are potential candidates for therapeutic agents, a simple method for evaluating TRP channel activation is needed. In this study, we demonstrated that a transforming growth factor alpha (TGFα) shedding assay, previously developed for detecting G-protein-coupled receptor (GPCR) activation, can also detect TRP channel activation. This assay is a low-cost, easily accessible method that requires only an absorbance microplate reader. Mechanistically, TRP-channel-triggered TGFα shedding is achieved by both of a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) and 17 (ADAM17), whereas the GPCR-induced TGFα shedding response depends solely on ADAM17. This difference may be the result of qualitative or quantitative differences in intracellular Ca2+ kinetics between TRP channels and GPCRs. Use of epidermal growth factor (EGF) and betacellulin (BTC), substrates of ADAM10, improved the specificity of the shedding assay by reducing background responses mediated by endogenously expressed GPCRs. This assay for TRP channel measurement will not only facilitate the high-throughput screening of TRP channel ligands but also contribute to understanding the roles played by TRP channels as regulators of membrane protein ectodomain shedding.

Investigating isoform switching in RHBDF2 and its role in neoplastic growth in breast cancer

Background

Breast cancer is the second leading cause of cancer-related deaths globally, and its prevalence rates are increasing daily. In the past, studies predicting therapeutic drug targets for cancer therapy focused on the assumption that one gene is responsible for producing one protein. Therefore, there is always an immense need to find promising and novel anti-cancer drug targets. Furthermore, proteases have an integral role in cell proliferation and growth because the proteolysis mechanism is an irreversible process that aids in regulating cellular growth during tumorigenesis. Therefore, an inactive rhomboid protease known as iRhom2 encoded by the gene RHBDF2 can be considered an important target for cancer treatment. Speculatively, previous studies on gene expression analysis of RHBDF2 showed heterogenous behaviour during tumorigenesis. Consistent with this, several studies have reported the antagonistic role of iRhom2 in tumorigenesis, i.e., either they are involved in negative regulation of EGFR ligands via the ERAD pathway or positively regulate EGFR ligands via the EGFR signalling pathway. Additionally, different opinions suggest iRhom2 mediated cleavage of EGFR ligands takes place TACE dependently or TACE independently. However, reconciling these seemingly opposing roles is still unclear and might be attributed to more than one transcript isoform of iRhom2.

Methods

To observe the differences at isoform resolution, the current strategy identified isoform switching in RHBDF2 via differential transcript usage using RNA-seq data during breast cancer initiation and progression. Furthermore, interacting partners were found via correlation and enriched to explain their antagonistic role.

Results

Isoform switching was observed at DCIS, grade 2 and grade 3, from canonical to the cub isoform. Neither EGFR nor ERAD was found enriched. However, pathways leading to TACE-dependent EGFR signalling pathways were more observant, specifically MAPK signalling pathways, GPCR signalling pathways, and toll-like receptor pathways. Nevertheless, it was noteworthy that during CTCs, the cub isoform switches back to the canonical isoform, and the proteasomal degradation pathway and cytoplasmic ribosomal protein pathways were significantly enriched. Therefore, it could be inferred that cub isoform functions during cancer initiation in EGFR signalling. In contrast, during metastasis, where invasion is the primary task, the isoform switches back to the canonical isoform.

Protein-Labeling Fluorescent Probe Reveals Ectodomain Shedding of Transmembrane Carbonic Anhydrases

Ectodomain shedding is a form of limited proteolysis in which a protease cleaves a transmembrane protein, releasing the extracellular domain from the cell surface. Cells use this process to regulate a wide variety of biological events. Typically, immunological detection methods are employed for the analysis of ectodomains secreted into the cultured media. In this paper, we describe a new strategy using an affinity-based protein-labeling fluorescent probe to study ectodomain shedding. We analyzed the ectodomain shedding of cell surface carbonic anhydrases (CAIX and CAXII), which are important biomarkers for tumor hypoxia. Using both chemical and genetic approaches, we identified that the ADAM17 metalloprotease is responsible for the shedding of carbonic anhydrases. Compared to current immunological methods, this protein-labeling approach not only detects ectodomain released into the culture media but also allows real-time living cell tracking and quantitative analysis of remnant proteins on the cell surface, thereby providing a more detailed insight into the mechanism of ectodomain shedding as well as protein lifetime on the cell surface.

PCSK9 deficiency results in a specific shedding of excess LDLR in female mice only: Role of hepatic cholesterol

PCSK9 promotes the lysosomal degradation of cell surface LDL receptor (LDLR). We analyzed how excess LDLR generated by PCSK9 deficiency is differently handled in male and female mice to possibly unveil the mechanism leading to the lower efficacy of PCSK9 mAb on LDL-cholesterol levels in women. Analysis of intact or ovariectomized PCSK9 knockout (KO) mice supplemented with placebo or 17β-estradiol (E2) demonstrated that female, but not male mice massively shed the soluble ectodomain of the LDLR in the plasma. Liver-specific PCSK9 KO or alirocumab-treated WT mice exhibit the same pattern. This shedding is distinct from the basal one and is inhibited by ZLDI-8, a metalloprotease inhibitor pointing at ADAM10/ADAM17. In PCSK9 KO female mice, ZLDI-8 raises by 80 % the LDLR liver content in a few hours. This specific shedding is likely cholesterol-dependent: it is prevented in PCSK9 KO male mice that exhibit low intra-hepatic cholesterol levels without activating SREBP-2, and enhanced by mevalonate or high cholesterol feeding, or by E2 known to stimulate cholesterol synthesis via the estrogen receptor-α. Liver transcriptomics demonstrates that critically low liver cholesterol in ovariectomized female or knockout male mice also hampers the cholesterol-dependent G2/M transition of the cell cycle. Finally, higher levels of shed LDLR were measured in the plasma of women treated with PCSK9 mAb. PCSK9 knockout female mice hormonally sustain cholesterol synthesis and shed excess LDLR, seemingly like women. In contrast, male mice rely on high surface LDLR to replenish their stocks, despite 80 % lower circulating LDL.

Paneth Cell Secretion in vivo Requires Expression of Tmem16a and Tmem16f

Background and Aims

Paneth cells play a central role in intestinal innate immune response. These cells are localized at the base of small intestinal crypts of Lieberkuhn. The calcium-activated chloride channel TMEM16A and the phospholipid scramblase TMEM16F control intracellular Ca2+ signaling and exocytosis. We analyzed the role of TMEM16A and TMEM16F for Paneth cells secretion.

Methods

Mice with intestinal epithelial knockout of Tmem16a (Tmem16a-/-) and Tmem16f (Tmem16f-/-) were generated. Tissue structures and Paneth cells were analyzed, and Paneth cell exocytosis was examined in small intestinal organoids in vitro. Intracellular Ca2+ signals were measured and were compared between wild-type and Tmem16 knockout mice. Bacterial colonization and intestinal apoptosis were analyzed.

Results

Paneth cells in the crypts of Lieberkuhn from Tmem16a-/- and Tmem16f-/- mice demonstrated accumulation of lysozyme. Tmem16a and Tmem16f were localized in wild-type Paneth cells but were absent in cells from knockout animals. Paneth cell number and size were enhanced in the crypt base and mucus accumulated in intestinal goblet cells of knockout animals. Granule fusion and exocytosis on cholinergic and purinergic stimulation were examined online. Both were strongly compromised in the absence of Tmem16a or Tmem16f and were also blocked by inhibition of Tmem16a/f. Purinergic Ca2+ signaling was largely inhibited in Tmem16a knockout mice. Jejunal bacterial content was enhanced in knockout mice, whereas cellular apoptosis was inhibited.

Conclusion

The present data demonstrate the role of Tmem16 for exocytosis in Paneth cells. Inhibition or activation of Tmem16a/f is likely to affect microbial content and immune functions present in the small intestine.

Phospholipid Scramblases: Role in Cancer Progression and Anticancer Therapeutics

Phospholipid scramblases (PLSCRs) that catalyze rapid mixing of plasma membrane lipids result in surface exposure of phosphatidyl serine (PS), a lipid normally residing to the inner plasma membrane leaflet. PS exposure provides a chemotactic eat-me signal for phagocytes resulting in non-inflammatory clearance of apoptotic cells by efferocytosis. However, metastatic tumor cells escape efferocytosis through alteration of tumor microenvironment and apoptotic signaling. Tumor cells exhibit altered membrane features, high constitutive PS exposure, low drug permeability and increased multidrug resistance through clonal evolution. PLSCRs are transcriptionally up-regulated in tumor cells leading to plasma membrane remodeling and aberrant PS exposure on cell surface. In addition, PLSCRs interact with multiple cellular components to modulate cancer progression and survival. While PLSCRs and PS exposed on tumor cells are novel drug targets, many exogenous molecules that catalyze lipid scrambling on tumor plasma membrane are potent anticancer therapeutic molecules. In this review, we provide a comprehensive analysis of scramblase mediated signaling events, membrane alteration specific to tumor development and possible therapeutic implications of scramblases and PS exposure.

The collectrin-like part of the SARS-CoV-1 and -2 receptor ACE2 is shed by the metalloproteinases ADAM10 and ADAM17

The transmembrane protease angiotensin converting enzyme 2 (ACE2) is a protective regulator within the renin angiotensin system and additionally represents the cellular receptor for SARS‐CoV. The release of soluble ACE2 (sACE2) from the cell surface is hence believed to be a crucial part of its (patho)physiological functions, as both, ACE2 protease activity and SARS‐CoV binding ability, are transferred from the cell membrane to body fluids. Yet, the molecular sources of sACE2 are still not completely investigated. In this study, we show different sources and prerequisites for the release of sACE2 from the cell membrane. By using inhibitors as well as CRISPR/Cas9‐derived cells, we demonstrated that, in addition to the metalloprotease ADAM17, also ADAM10 is an important novel shedding protease of ACE2. Moreover, we observed that ACE2 can also be released in extracellular vesicles. The degree of either ADAM10‐ or ADAM17‐mediated ACE2 shedding is dependent on stimulatory conditions and on the expression level of the pro‐inflammatory ADAM17 regulator iRhom2. Finally, by using structural analysis and in vitro verification, we determined for the first time that the susceptibility to ADAM10‐ and ADAM17‐mediated shedding is mediated by the collectrin‐like part of ACE2. Overall, our findings give novel insights into sACE2 release by several independent molecular mechanisms.

Scramblases as Regulators of Proteolytic ADAM Function

Proteolytic ectodomain release is a key mechanism for regulating the function of many cell surface proteins. The sheddases ADAM10 and ADAM17 are the best-characterized members of the family of transmembrane disintegrin-like metalloproteinase. Constitutive proteolytic activities are low but can be abruptly upregulated via inside-out signaling triggered by diverse activating events. Emerging evidence indicates that the plasma membrane itself must be assigned a dominant role in upregulation of sheddase function. Data are discussed that tentatively identify phospholipid scramblases as central players during these events. We propose that scramblase-dependent externalization of the negatively charged phospholipid phosphatidylserine (PS) plays an important role in the final activation step of ADAM10 and ADAM17. In this manuscript, we summarize the current knowledge on the interplay of cell membrane changes, PS exposure, and proteolytic activity of transmembrane proteases as well as the potential consequences in the context of immune response, infection, and cancer. The novel concept that scramblases regulate the action of ADAM-proteases may be extendable to other functional proteins that act at the cell surface.

How tetraspanin-mediated cell entry of SARS-CoV-2 can dysregulate the shedding of the ACE2 receptor by ADAM17

COVID-19, the respiratory infection caused by the novel coronavirus SARS-CoV-2, presents a clinical picture consistent with the dysregulation of many of the pathways mediated by the metalloprotease ADAM17. ADAM17 is a sheddase that plays a key role in the modulation of ACE2, the receptor which also functions as the point of attachment leading to cell entry by the virus. This work investigates the possibility that ADAM17 dysregulation and attachment of the SARS-CoV-2 virion to the ACE2 receptor are linked events, with the latter causing the former. Tetraspanins, the transmembrane proteins that function as scaffolds for the construction of viral entry platforms, are mooted as key components in this connection.

Influence of Anoctamin-4 and -9 on ADAM10 and ADAM17 Sheddase Function

Ca2+-activated Cl− channels (TMEM16, also known as anoctamins) perform important functions in cell physiology, including modulation of cell proliferation and cancer growth. Many members, including TMEM16F/ANO6, additionally act as Ca2+-activated phospholipid scramblases. We recently presented evidence that ANO6-dependent surface exposure of phosphatidylserine (PS) is pivotal for the disintegrin-like metalloproteases ADAM10 and ADAM17 to exert their sheddase function. Here, we compared the influence of seven ANO family members (ANO1, 4, 5, 6, 7, 9, and 10) on ADAM sheddase activity. Similar to ANO6, overexpression of ANO4 and ANO9 led to increased release of ADAM10 and ADAM17 substrates, such as betacellulin, TGFα, and amphiregulin (AREG), upon ionophore stimulation in HEK cells. Inhibitor experiments indicated that ANO4/ANO9-mediated enhancement of TGFα-cleavage broadened the spectrum of participating metalloproteinases. Annexin V-staining demonstrated increased externalisation of PS in ANO4/ANO9-overexpressing cells. Competition experiments with the soluble PS-headgroup phosphorylserine indicated that the ANO4/ANO9 effects were due to increased PS exposure. Overexpression of ANO4 or ANO9 in human cervical cancer cells (HeLa), enhanced constitutive shedding of the growth factor AREG and increased cell proliferation. We conclude that ANO4 and ANO9, by virtue of their scramblase activity, may play a role as important regulators of ADAM-dependent cellular functions.

Physiologic Regulation of Systemic Klotho Levels by Renal CaSR Signaling in Response to CaSR Ligands and pH o

BACKGROUND

The kidney is the source of sKlotho and kidney-specific loss of Klotho leads to a phenotype resembling the premature multiorgan failure phenotype in Klotho-hypomorphic mice ( kl/kl mice). Klotho and the Ca-sensing receptor (CaSR) are highly expressed in the distal convoluted tubule (DCT). The physiologic mechanisms that regulate sKlotho levels are unknown.

METHODS

We measured sKlotho in WT and tubule-specific CaSR -/- (TS-CaSR -/- ) mice treated with calcimimetics, alkali, or acid, and Klotho shed from minced mouse kidneys, and from HEK-293 cells expressing the CaSR and Klotho, in response to calcimimetics, calcilytics, alkalotic and acidic pH, and ADAM protease inhibitors. The CaSR, Klotho, and ADAM10 were imaged in mouse kidneys and cell expression systems using confocal microscopy.

RESULTS

The CaSR, Klotho, and ADAM10 colocalize on the basolateral membrane of the DCT. Calcimimetics and HCO 3 increase serum sKlotho levels in WT but not in CaSR -/- mice, and acidic pH suppresses sKlotho levels in WT mice. In minced kidneys and cultured cells, CaSR activation with high Ca, calcimimetics, or alkali increase shed Klotho levels via ADAM10, as demonstrated using the ADAM10 inhibitor GI254023X and siRNA. In cultured cells, the CaSR, Klotho, and ADAM10 form cell surface aggregates that disperse after CaSR activation.

CONCLUSIONS

We identify a novel physiologic mechanism for regulation of sKlotho levels by the renal CaSR-ADAM10-Klotho pathway. We show that CaSR activators, including alkali, increase renal CaSR-stimulated Klotho shedding and predict that this mechanism is relevant to the effects of acidosis and alkali therapy on CKD progression.

Gating and Regulatory Mechanisms of TMEM16 Ion Channels and Scramblases

The transmembrane protein 16 (TMEM16) family consists of Ca2+-activated ion channels and Ca2+-activated phospholipid scramblases (CaPLSases) that passively flip-flop phospholipids between the two leaflets of the membrane bilayer. Owing to their diverse functions, TMEM16 proteins have been implicated in various human diseases, including asthma, cancer, bleeding disorders, muscular dystrophy, arthritis, epilepsy, dystonia, ataxia, and viral infection. To understand TMEM16 proteins in health and disease, it is critical to decipher their molecular mechanisms of activation gating and regulation. Structural, biophysical, and computational characterizations over the past decade have greatly advanced the molecular understanding of TMEM16 proteins. In this review, we summarize major structural features of the TMEM16 proteins with a focus on regulatory mechanisms and gating.

A model for COVID-19-induced dysregulation of ACE2 shedding by ADAM17

The angiotensin Converting Enzyme 2 (ACE2) receptor is a key component of the renin-angiotensin-aldesterone system (RAAS) that mediates numerous effects in the cardiovascular system. It is also the cellular point of contact for the coronavirus spike protein. Cleavage of the receptor is both important to its physiological function as well as being necessary for cell entry by the virus. Shedding of ACE2 by the metalloprotease ADAM17 releases a catalytically active soluble form of ACE2, but cleavage by the serine protease TMPRSS2 is necessary for virion internalization. Complicating the issue is the observation that circulating ACE2 can also bind to the virus effectively blocking attachment to the membrane-bound receptor. This work investigates the possibility that the inflammatory response to coronavirus infection can abrogate shedding by ADAM17, thereby favoring cleavage by TMPRSS2 and thus cell entry by the virion.

ADAM10-Mediated Ectodomain Shedding Is an Essential Driver of Podocyte Damage

BACKGROUND

Podocytes embrace the glomerular capillaries with foot processes, which are interconnected by a specialized adherens junction to ultimately form the filtration barrier. Altered adhesion and loss are common features of podocyte injury, which could be mediated by shedding of cell-adhesion molecules through the regulated activity of cell surface-expressed proteases. A Disintegrin and Metalloproteinase 10 (ADAM10) is such a protease known to mediate ectodomain shedding of adhesion molecules, among others. Here we evaluate the involvement of ADAM10 in the process of antibody-induced podocyte injury.

METHODS

Membrane proteomics, immunoblotting, high-resolution microscopy, and immunogold electron microscopy were used to analyze human and murine podocyte ADAM10 expression in health and kidney injury. The functionality of ADAM10 ectodomain shedding for podocyte development and injury was analyzed, in vitro and in vivo, in the anti-podocyte nephritis (APN) model in podocyte-specific, ADAM10-deficient mice.

RESULTS

ADAM10 is selectively localized at foot processes of murine podocytes and its expression is dispensable for podocyte development. Podocyte ADAM10 expression is induced in the setting of antibody-mediated injury in humans and mice. Podocyte ADAM10 deficiency attenuates the clinical course of APN and preserves the morphologic integrity of podocytes, despite subepithelial immune-deposit formation. Functionally, ADAM10-related ectodomain shedding results in cleavage of the cell-adhesion proteins N- and P-cadherin, thus decreasing their injury-related surface levels. This favors podocyte loss and the activation of downstream signaling events through the Wnt signaling pathway in an ADAM10-dependent manner.

CONCLUSIONS

ADAM10-mediated ectodomain shedding of injury-related cadherins drives podocyte injury.

ADAM10 Site-Dependent Biology: Keeping Control of a Pervasive Protease

Enzymes, once considered static molecular machines acting in defined spatial patterns and sites of action, move to different intra- and extracellular locations, changing their function. This topological regulation revealed a close cross-talk between proteases and signaling events involving post-translational modifications, membrane tyrosine kinase receptors and G-protein coupled receptors, motor proteins shuttling cargos in intracellular vesicles, and small-molecule messengers. Here, we highlight recent advances in our knowledge of regulation and function of A Disintegrin And Metalloproteinase (ADAM) endopeptidases at specific subcellular sites, or in multimolecular complexes, with a special focus on ADAM10, and tumor necrosis factor-α convertase (TACE/ADAM17), since these two enzymes belong to the same family, share selected substrates and bioactivity. We will discuss some examples of ADAM10 activity modulated by changing partners and subcellular compartmentalization, with the underlying hypothesis that restraining protease activity by spatial segregation is a complex and powerful regulatory tool.

Proteomic Studies of Primary Acute Myeloid Leukemia Cells Derived from Patients Before and during Disease-Stabilizing Treatment Based on All-Trans Retinoic Acid and Valproic Acid

All-trans retinoic acid (ATRA) and valproic acid (VP) have been tried in the treatment of non-promyelocytic variants of acute myeloid leukemia (AML). Non-randomized studies suggest that the two drugs can stabilize AML and improve normal peripheral blood cell counts. In this context, we used a proteomic/phosphoproteomic strategy to investigate the in vivo effects of ATRA/VP on human AML cells. Before starting the combined treatment, AML responders showed increased levels of several proteins, especially those involved in neutrophil degranulation/differentiation, M phase regulation and the interconversion of nucleotide di- and triphosphates (i.e., DNA synthesis and binding). Several among the differentially regulated phosphorylation sites reflected differences in the regulation of RNA metabolism and apoptotic events at the same time point. These effects were mainly caused by increased cyclin dependent kinase 1 and 2 (CDK1/2), LIM domain kinase 1 and 2 (LIMK1/2), mitogen-activated protein kinase 7 (MAPK7) and protein kinase C delta (PRKCD) activity in responder cells. An extensive effect of in vivo treatment with ATRA/VP was the altered level and phosphorylation of proteins involved in the regulation of transcription/translation/RNA metabolism, especially in non-responders, but the regulation of cell metabolism, immune system and cytoskeletal functions were also affected. Our analysis of serial samples during the first week of treatment suggest that proteomic and phosphoproteomic profiling can be used for the early identification of responders to ATRA/VP-based treatment.

Role of ADAM10 and ADAM17 in Regulating CD137 Function

Human CD137 (4-1BB), a member of the TNF receptor family, and its ligand CD137L (4-1BBL), are expressed on immune cells and tumor cells. CD137/CD137L interaction mediates bidirectional cellular responses of potential relevance in inflammatory diseases, autoimmunity and oncology. A soluble form of CD137 exists, elevated levels of which have been reported in patients with rheumatoid arthritis and various malignancies. Soluble CD137 (sCD137) is considered to represent a splice variant of CD137. In this report, however, evidence is presented that A Disintegrin and Metalloproteinase (ADAM)10 and potentially also ADAM17 are centrally involved in its generation. Release of sCD137 by transfected cell lines and primary T cells was uniformly inhibitable by ADAM10 inhibition. The shedding function of ADAM10 can be blocked through inhibition of its interaction with surface exposed phosphatidylserine (PS), and this effectively inhibited sCD137 generation. The phospholipid scramblase Anoctamin-6 (ANO6) traffics PS to the outer membrane and thus modifies ADAM10 function. Overexpression of ANO6 increased stimulated shedding, and hyperactive ANO6 led to maximal constitutive shedding of CD137. sCD137 was functionally active and augmented T cell proliferation. Our findings shed new light on the regulation of CD137/CD137L immune responses with potential impact on immunotherapeutic approaches targeting CD137.

ADAM10 Plasma and CSF Levels Are Increased in Mild Alzheimer's Disease

ADAM10 is the main α-secretase that participates in the non-amyloidogenic cleavage of amyloid precursor protein (APP) in neurons, inhibiting the production of β-amyloid peptide (Aβ) in Alzheimer’s disease (AD). Strong recent evidence indicates the importance of the localization of ADAM10 for its activity as a protease. In this study, we investigated ADAM10 activity in plasma and CSF samples of patients with amnestic mild cognitive impairment (aMCI) and mild AD compared with cognitively healthy controls. Our results indicated that plasma levels of soluble ADAM10 were significantly increased in the mild AD group, and that in these samples the protease was inactive, as determined by activity assays. The same results were observed in CSF samples, indicating that the increased plasma ADAM10 levels reflect the levels found in the central nervous system. In SH-SY5Y neuroblastoma cells, ADAM10 achieves its major protease activity in the fraction obtained from plasma membrane lysis, where the mature form of the enzyme is detected, confirming the importance of ADAM10 localization for its activity. Taken together, our results demonstrate the potential of plasma ADAM10 to act as a biomarker for AD, highlighting its advantages as a less invasive, easier, faster, and lower-cost processing procedure, compared to existing biomarkers.

Flagging fusion: Phosphatidylserine signaling in cell-cell fusion

Formations of myofibers, osteoclasts, syncytiotrophoblasts, and fertilized zygotes share a common step, cell–cell fusion. Recent years have brought about considerable progress in identifying some of the proteins involved in these and other cell-fusion processes. However, even for the best-characterized cell fusions, we still do not know the mechanisms that regulate the timing of cell-fusion events. Are they fully controlled by the expression of fusogenic proteins or do they also depend on some triggering signal that activates these proteins? The latter scenario would be analogous to the mechanisms that control the timing of exocytosis initiated by Ca²⁺ influx and virus-cell fusion initiated by low pH- or receptor interaction. Diverse cell fusions are accompanied by the nonapoptotic exposure of phosphatidylserine at the surface of fusing cells. Here we review data on the dependence of membrane remodeling in cell fusion on phosphatidylserine and phosphatidylserine-recognizing proteins and discuss the hypothesis that cell surface phosphatidylserine serves as a conserved “fuse me” signal regulating the time and place of cell-fusion processes.

Notch Signaling in B Cell Immune Responses

The Notch signaling pathway is highly evolutionarily conserved, dictating cell fate decisions and influencing the survival and growth of progenitor cells that give rise to the cells of the immune system. The roles of Notch signaling in hematopoietic stem cell maintenance and in specification of T lineage cells have been well-described. Notch signaling also plays important roles in B cells. In particular, it is required for specification of marginal zone type B cells, but Notch signaling is also important in other stages of B cell development and activation. This review will focus on established and new roles of Notch signaling during B lymphocyte lineage commitment and describe the function of Notch within mature B cells involved in immune responses.

ADAM10 plasma levels predict worsening in cognition of older adults: a 3-year follow-up study

BACKGROUND

Blood-based biomarkers for Alzheimer's disease (AD) are highly needed in clinic practice. So far, the gold standards for AD diagnosis are brain neuroimaging and beta-amyloid peptide, total tau, and phosphorylated tau in cerebrospinal fluid (CSF); however, they are not attractive for large-scale screening. Blood-based biomarkers allow an initial large-scale screening of patients under suspicion that could later be tested for the already established CSF biomarkers. To this regard, in this study, we evaluated whether plasma ADAM10 levels would be predictors of declines in cognition in community-dwelling older adults after a 3-year period follow-up.

METHODS

This was a 3-year longitudinal cohort study that included 219 community-dwelling older adults. Sociodemographic, clinical, lifestyle, depressive symptoms (GDS), and cognitive data (Mini-Mental State Examination, MMSE; Clock Drawing test, CDT) were gathered. The measurement of ADAM10 plasma levels was performed using a sandwich ELISA kit. Bivariate comparisons between groups were performed using Wilcoxon-Mann-Whitney for continuous data and Pearson's chi-square tests with Yates continuity correction for categorical data. Longitudinal analyzes of changes in the MMSE scores were performed using linear mixed-effects modeling.

RESULTS

Baseline MMSE scores and ADAM10 levels were significantly associated with MMSE scores on the follow-up assessment. When analyzing the interaction with time, normal MMSE scores and the ADAM10 plasma levels at baseline presented a significant and independent negative association with MMSE score values on the follow-up assessment. The analyses also showed that the predictive effect of ADAM10 plasma levels on decreasing MMSE scores on follow-up seems to be more pronounced in participants with normal MMSE, when compared with those with altered MMSE scores at baseline.

CONCLUSIONS

Considering that ADAM10 increase in plasma is detected as soon as in mild cognitive impairment (MCI) patients, the results presented here may support the complementary clinical use of this biomarker, in addition to the classical AD biomarkers. Taken together, these results provide the first direct evidence that changes in ADAM10 plasma levels are predictors of cognitive worsening in older adults. Moreover, this work can shed light on the study of blood biomarkers for AD and contribute to the advancement of the area.

Phosphatidylserine inside out: a possible underlying mechanism in the inflammation and coagulation abnormalities of COVID-19

The rapid ability of SARS-CoV-2 to spread among humans, along with the clinical complications of coronavirus disease 2019-COVID-19, have represented a significant challenge to the health management systems worldwide. The acute inflammation and coagulation abnormalities appear as the main causes for thousands of deaths worldwide. The intense inflammatory response could be involved with the formation of thrombi. For instance, the presence of uncleaved large multimers of von Willebrand (vWF), due to low ADAMTS13 activity in plasma could be explained by the inhibitory action of pro-inflammatory molecules such as IL-1β and C reactive protein. In addition, the damage to endothelial cells after viral infection and/or activation of endothelium by pro-inflammatory cytokines, such as IL-1β, IL-6, IFN-γ, IL-8, and TNF-α induces platelets and monocyte aggregation in the vascular wall and expression of tissue factor (TF). The TF expression may culminate in the formation of thrombi, and activation of cascade by the extrinsic pathway by association with factor VII. In this scenario, the phosphatidylserine-PtdSer exposure on the outer leaflet of the cell membrane as consequence of viral infection emerges as another possible underlying mechanism to acute immune inflammatory response and activation of coagulation cascade. The PtdSer exposure may be an important mechanism related to ADAM17-mediated ACE2, TNF-α, EGFR and IL-6R shedding, and the activation of TF on the surface of infected endothelial cells. In this review, we address the underlying mechanisms involved in the pathophysiology of inflammation and coagulation abnormalities. Moreover, we introduce key biochemical and pathophysiological concepts that support the possible participation of PtdSer exposure on the outer side of the SARS-CoV-2 infected cells membrane, in the pathophysiology of COVID-19. Video Abstract.

An immunomodulatory role for the Mycobacterium tuberculosis Acr protein in the formation of the tuberculous granuloma

The tuberculous granuloma is a compact aggregate of dormant bacteria encapsulated by host macrophages. It is commonly regarded as a product of the host defense designed to isolate infectious mycobacteria. This work demonstrates that exposure of macrophages to the Mtb heat-shock protein Acr leads to overproduction of the chemokine CXCL16, allowing the mycobacterium to exploit the innate immune response. This induction of chemokine expression is hypothesized to occur through activation of ADAM proteases, providing an immunomodulatory role for Mtb Acr in the formation of the granuloma.

Structural and functional consequences of reversible lipid asymmetry in living membranes

Maintenance of lipid asymmetry across the two leaflets of the plasma membrane (PM) bilayer is a ubiquitous feature of eukaryotic cells. Loss of this asymmetry has been widely associated with cell death. However, increasing evidence points to the physiological importance of non-apoptotic, transient changes in PM asymmetry. Such transient scrambling events are associated with a range of biological functions, including intercellular communication and intracellular signaling. Thus, regulation of interleaflet lipid distribution in the PM is a broadly important but underappreciated cellular process with key physiological and structural consequences. Here, we compile the mounting evidence revealing multifaceted, functional roles of PM asymmetry and transient loss thereof. We discuss the consequences of reversible asymmetry on PM structure, biophysical properties and interleaflet coupling. We argue that despite widespread recognition of broad aspects of membrane asymmetry, its importance in cell biology demands more in-depth investigation of its features, regulation, and physiological and pathological implications.

Mitochondrial Targeting of the Enteropathogenic Escherichia coli Map Triggers Calcium Mobilization, ADAM10-MAP Kinase Signaling, and Host Cell Apoptosis

Enteropathogenic E. coli (EPEC) is an important human diarrhea-causing bacterium. The pathogenic effects of EPEC largely depend upon its ability to inject a series of proteins, termed effectors, into the host cells. One such effector is the mitochondrion-associated protein (Map). Map has been shown to induce actin-rich projections (i.e., filopodia) on the infected cell surface and activate a Rho GTPase enzyme termed Cdc42. Nonetheless, although most injected Map localizes to host mitochondria, its functions in the mitochondria remain unknown. Here, we show that Map targeting of mitochondria stimulates the disruption of mitochondrial membrane potential to induce Ca²⁺ efflux into the host cytoplasm. The efflux stimulates the activity of a protein termed ADAM10, which induces activation of a mitogen-activated protein kinase cascade leading to host cell apoptosis. As apoptosis plays a central role in host-pathogen interactions, our findings provide novel insights into the functions of mitochondrial Map in promoting the EPEC disease.

The ability of diarrheagenic bacterial pathogens, such as enteropathogenic Escherichia coli (EPEC), to modulate the activity of mitogen-activated protein kinases (MAPKs) and cell survival has been suggested to benefit bacterial colonization and infection. However, our understanding of the mechanisms by which EPEC modulate these functions is incomplete. In this study, we show that the EPEC type III secreted effector Map stimulates the sheddase activity of the disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) and the ERK and p38 MAPK signaling cascades. Remarkably, all these activities were dependent upon the ability of Map to target host mitochondria, mainly via its mitochondrial toxicity region (MTR). Map targeting of mitochondria disrupted the mitochondrial membrane potential, causing extrusion of mitochondrial Ca²⁺ into the host cell cytoplasm. We also found that Map targeting of mitochondria is essential for triggering host cell apoptosis. Based on these findings, we propose a model whereby Map imported into mitochondria causes mitochondrial dysfunction and Ca²⁺ efflux into the host cytoplasm. Since Ca²⁺ has been reported to promote ADAM10 activation, the acute elevation of Ca²⁺ in the cytoplasm may stimulate the ADAM10 sheddase activity, resulting in the release of epidermal growth factors that stimulate the ERK signaling cascade. As p38 activity is also Ca²⁺ sensitive, elevation in cytoplasmic Ca²⁺ may independently also activate p38. We hypothesize that Map-dependent MAPK activation, combined with Map-mediated mitochondrial dysfunction, evokes mitochondrial host cell apoptosis, potentially contributing to EPEC colonization and infection of the gut.

ADAM-Mediated Signalling Pathways in Gastrointestinal Cancer Formation

Tumour growth is not solely driven by tumour cell-intrinsic mechanisms, but also depends on paracrine signals provided by the tumour micro-environment. These signals comprise cytokines and growth factors that are synthesized as trans-membrane proteins and need to be liberated by limited proteolysis also termed ectodomain shedding. Members of the family of A disintegrin and metalloproteases (ADAM) are major mediators of ectodomain shedding and therefore initiators of paracrine signal transduction. In this review, we summarize the current knowledge on how ADAM proteases on tumour cells but also on cells of the tumour micro-environment contribute to the formation of gastrointestinal tumours, and discuss how these processes can be exploited pharmacologically.

Early Diagnosis of Alzheimer's Disease in Blood Using a Disposable Electrochemical Microfluidic Platform

Alzheimer's disease (AD) is a neurodegenerative condition that affects a large number of elderly people worldwide and has a high social and economic impact. The diagnosis of AD in early stage can significantly improve the evolution and prognosis of the disease. We report the use of A Disintegrin And Metalloprotease 10 (ADAM10) as a blood biomarker for the early diagnosis of AD. A simple, low-cost, sensitive, and disposable microfluidic platform (DμP) was developed for ADAM10 detection in plasma and cerebrospinal fluid based on electrochemical immunosensors. The assay was designed to accurately detect ADAM10 in serum, with a limit of detection of 0.35 fg/mL. ADAM10 was detected in subjects divided into cognitively healthy subjects, subjects with mild cognitive impairment, and AD patients in different disease stages. An increase in protein levels was found throughout the disease, and good DμP accuracy in differentiating individuals was observed. The DμP provided significantly better sensitivity than the well-established enzyme-linked immunosorbent assay test. ADAM10 and its detection using the DμP were proven to be an alternative tool for the early diagnosis and monitoring of AD, bringing new exciting possibilities to improve the quality of life of AD patients.

Role of ADAM10 as a CD30 Sheddase in Classical Hodgkin Lymphoma

Cancer cells generally recruit and influence non-malignant immune cells to support the tumor growth. Classical Hodgkin lymphoma (cHL) is a good example because the affected lymphoid tissue contains only a few malignant Hodgkin and Reed-Sternberg (H-RS) cells, which are supported by a massive infiltrate of lymphocytes, fibroblasts, and innate immune cells. The transmembrane receptor CD30, which is selectively expressed on the H-RS cells, plays an important role, not only in cell stimulation and intercellular communication but also in tumor diagnosis and targeted tumor therapy. Different protein processing pathways influence its functionality. Depending on the conditions, the receptor is internalized or released. The release of CD30 occurs either as an intact molecule, embedded in the membrane of extracellular vesicles (EVs), or as a cleaved soluble ectodomain (sCD30). CD30 cleavage is predominantly catalyzed by ADAM10. The enzyme is catalytically active in cells as well as in EVs and gradually releases sCD30. Because the circulation contains no CD30⁺ donor cells, this mechanism explains that the cleaved ectodomain represents the predominant form of CD30 in the plasma of cHL patients. CD30 processing might influence the impact of CD30 antibody-drug conjugates, such as Brentuximab Vedotin (BV). Whereas, ADAM10-degraded CD30 impedes the BV efficacy, tumor-derived EVs load bystander cells with CD30 and generate new targets among supporter cells. This crossfire effect might contribute to the enormous clinical impact of BV, whereas the ADAM10-dependent cleavage to the mild systemic off-target effects of the treatment with BV.