Bruce Walcheck

NK cell CD16 surface expression and function is regulated by a disintegrin and metalloprotease-17 (ADAM17)

The Fc receptor CD16 is present on essentially all CD56(dim) peripheral blood natural killer (NK) cells. Upon recognition of antibody-coated cells it delivers a potent signal to NK cells, which eliminate targets through direct killing and cytokine production. Here we investigated the regulation of CD16 surface expression after NK cell activation. Cytokine activation and target cell stimulation led to marked decreases in CD16 expression. Activation of CD56(dim) NK cells by cross-linking CD16 with antibodies resulted in a loss of CD16 and CD62L, which correlated with increased interferon-γ production. A disintegrin and metalloprotease-17 (ADAM17) is shown to be expressed by NK cells, and its selective inhibition abrogated CD16 and CD62L shedding, and led to enhanced interferon-γ production, especially when triggering was delivered through CD16. Fc-induced production of cytokines by NK cells exposed to rituximab-coated B cell targets was also enhanced by ADAM17 inhibition. This supports an important role for targeting ADAM17 to prevent CD16 shedding and improve the efficacy of therapeutic antibodies. Our findings demonstrate that over-activation of ADAM17 in NK cells may be detrimental to their effector functions by down-regulating surface expression of CD16 and CD62L.

Role of ADAM17 in the ectodomain shedding of TNF-α and its receptors by neutrophils and macrophages

TNF‐α and its receptors TNFRI and TNFRII are cleaved from the surface of leukocytes by a proteolytic process referred to as ectodomain shedding. The role of a disintegrin and metalloproteinase 17 (ADAM17) in this process by the major professional phagocytes neutrophils and macrophages, the primary producers of TNF‐α during inflammation induction, is based entirely on indirect evidence, and other sheddases have been implicated as well. As Adam17 gene‐targeting in mice is lethal, we assessed the protease’s relative contribution to TNF‐α, TNFRI, and TNFRII shedding using radiation chimeric mice with leukocytes lacking functional ADAM17. We report ablated, soluble TNF‐α, TNFRI, and TNFRII production by neutrophils and macrophages stimulated with various microbial antigens and greatly reduced TNF‐α levels in vivo following inflammation induction. This is the first simultaneous analysis of TNF‐α, TNFRI, and TNFRII shedding by neutrophils and macrophages and the first direct evidence that ADAM17 is a primary and nonredundant sheddase.

Targeting natural killer cells to acute myeloid leukemia in vitro with a CD16 x 33 bispecific killer cell engager and ADAM17 inhibition.

Purpose: The graft versus leukemia effect by natural killer (NK) cells prevents relapse following hematopoietic stem cell transplantation. We determined whether a novel bispecific killer cell engager (BiKE) signaling through CD16 and targeting CD33 could activate NK cells at high potency against acute myelogenous leukemia (AML) targets. Experimental Design: We investigated the ability of our fully humanized CD16 × CD33 (CD16 × 33) BiKE to trigger in vitro NK cell activation against HL60 (CD33+), RAJI (CD33−), and primary AML targets (de novo and refractory) to determine whether treatment with CD16 × 33 BiKE in combination with an ADAM17 inhibitor could prevent CD16 shedding (a novel inhibitory mechanism induced by NK cell activation) and overcome inhibition of class I MHC recognizing inhibitory receptors. Results: NK cell cytotoxicity and cytokine release were specifically triggered by the CD16 × 33 BiKE when cells were cultured with HL60 targets, CD33+ de novo and refractory AML targets. Combination treatment with CD16 × 33 BiKE and ADAM17 inhibitor resulted in inhibition of CD16 shedding in NK cells, and enhanced NK cell activation. Treatment of NK cells from double umbilical cord blood transplant (UCBT) recipients with the CD16 × 33 BiKE resulted in activation, especially in those recipients with cytomegalovirus reactivation. Conclusion: CD16 × 33 BiKE can overcome self-inhibitory signals and effectively elicit NK cell effector activity against AML. These in vitro studies highlight the potential of CD16 × 33 BiKE ± ADAM17 inhibition to enhance NK cell activation and specificity against CD33+ AML, which optimally could be applied in patients with relapsed AML or for adjuvant antileukemic therapy posttransplantation. Clin Cancer Res; 19(14); 3844–55. ©2013 AACR.

Regulation of mature ADAM17 by redox agents for L-selectin shedding.

L-selectin is constitutively expressed by neutrophils and plays a key role in directing these cells to sites of inflammation. Upon neutrophil activation, L-selectin is rapidly and efficiently down-regulated from the cell surface by ectodomain shedding. We have directly shown that A disintegrin and metalloprotease 17 (ADAM17) is a primary and nonredundant sheddase of L-selection by activated neutrophils in vivo. Following cell activation, intracellular signals lead to the induction of ADAM17’s enzymatic activity; however, the target of this inducer mechanism remains unclear. Our study provides evidence of an activation mechanism that involves the extracellular region of the mature form of cell surface ADAM17 and not its intracellular region. We demonstrate that the catalytic activity of purified ADAM17 lacking a prodomain and its intracellular region is diminished under mild reducing conditions by DTT and enhanced by H2O2 oxidation. Moreover, H2O2 reversed ADAM17 inhibition by DTT. The treatment of neutrophils with H2O2 also induced L-selectin shedding in an ADAM17-dependent manner. These findings suggest that thiol-disulfide conversion occurring in the extracellular region of ADAM17 may be involved in its activation. An analysis of ADAM17 revealed that within its disintegrin/cysteine-rich region are two highly conserved, vicinal cysteine sulfhydryl motifs (cysteine-X-X-cysteine), which are well-characterized targets for thiol-disulfide exchange in various other proteins. Using a cell-based ADAM17 reconstitution assay, we demonstrate that the cysteine-X-X-cysteine motifs are critical for L-selectin cleavage. Taken together, our findings suggest that reduction-oxidation modifications of cysteinyl sulfhydryl groups in mature ADAM17 may serve as a mechanism for regulating the shedding of L-selectin following neutrophil stimulation.

Regulation of expression of major histocompatibility antigens by bovine macrophages infected with Mycobacterium avium subsp. paratuberculosis or Mycobacterium avium subsp. avium.

ABSTRACT Mycobacterium avium subsp. paratuberculosisand Mycobacterium avium subsp. avium are antigenically and genetically very similar organisms; however, they differ markedly in their virulence for cattle. We evaluated the capacity of bovine macrophages infected with M. aviumsubsp. paratuberculosis or M. avium subsp.avium to express major histocompatibility complex (MHC) class I and class II antigens on their surface and to interact with primed autologous lymphocytes. Our results indicate that infection of bovine macrophages with M. avium subsp.paratuberculosis promoted the downregulation of MHC class I and class II molecules on the macrophage surface within 24 and 12 h, respectively. Alternatively, MHC class II expression by M. avium subsp. avium-infected macrophages was not detected until 24 h after infection, and the magnitude of the decrease was smaller. Decreased MHC class I expression by M. avium subsp. avium-infected macrophages was not detected. Unlike M. avium subsp.paratuberculosis-infected macrophages, M. aviumsubsp. avium-infected macrophages upregulated MHC class I and class II expression after activation by gamma interferon or tumor necrosis factor alpha. Further, M. avium subsp.avium-infected macrophages were lysed by primed autologous lymphocytes, whereas M. avium subsp.paratuberculosis-infected macrophages were not. Overall, the results support the hypothesis that the difference in the virulence of M. avium subsp. paratuberculosis andM. avium subsp. avium for cattle is dependent on a difference in the capacity of the organisms to suppress mycobacterial antigen presentation to T lymphocytes.

The Cytoplasmic Domain of L-Selectin Participates in Regulating L-Selectin Endoproteolysis

Neutrophil recruitment at sites of inflammation is regulated by a series of adhesion and activation events. L-selectin (CD62L) is a leukocyte expressed adhesion protein that is important for neutrophil accumulation and rolling along the vascular endothelium. L-selectin is unique from other adhesion molecules involved in leukocyte transmigration in that its adhesiveness appears to be regulated partly by rapid endoproteolysis. Cleavage of L-selectin occurs within a membrane-proximal region that results in ectodomain shedding and retention of a 6-kDa transmembrane fragment. The cleavage domain of L-selectin has been well characterized through mutational analysis. Whether the cytoplasmic domain of L-selectin also plays a role in regulating shedding is controversial. We have previously shown that the Ca2+-sensing protein calmodulin (CaM) constitutively associates with the cytoplasmic domain of L-selectin in transfected cell lines. However, in the absence of mapping and mutational analysis of the CaM-binding region of L-selectin, there remains no direct evidence that this interaction affects shedding. Using synthesized peptides and expressed L-selectin constructs, we demonstrate that CaM binding activity occurs in the membrane-proximal region of the cytoplasmic domain. Mutations engineered in this region that prevent CaM binding increase the proteolytic turnover of L-selectin. Moreover, we demonstrate that CaM binding to the 6-kDa transmembrane fragment is greatly reduced compared with intact L-selectin in neutrophils, suggesting that CaM binding is regulated. These data imply that the cytoplasmic domain of L-selectin can regulate shedding by a mechanism in which bound CaM may operate as a negative effector.

ADAM17 activity during human neutrophil activation and apoptosis

Substrates of the metalloprotease ADAM17 (also known as TNF‐α converting enzyme or TACE) undergo ectodomain shedding and include various inflammatory modulators. Though polymorphonuclear leukocytes contribute significantly to inflammation, direct analyses of ADAM17 on human neutrophils are very limited. In addition, the current understanding of the processes regulating ADAM17 activity primarily relate to its rapid activation. Therefore, to extend insights into the mechanisms of ADAM17 activity, we examined its surface expression and the shedding of its substrates during extended periods of neutrophil activation and apoptosis. Contrary to studies with immortalized hematopoietic cell lines, we report that surface expression of ADAM17 is maintained by human neutrophils activated with formyl peptides or by FcR/complement receptor‐mediated phagocytosis. Interestingly, bacterial phagocytosis resulted in a significant increase in ADAM17 expression several hours after pathogen engulfment. We provide novel evidence that ADAM17 surface expression is also maintained during spontaneous and anti‐Fas‐induced neutrophil apoptosis. The well‐validated ADAM17 substrates L‐selectin and proTNF‐α were shed efficiently by neutrophils under each of the conditions tested. Our data thus indicate prolonged ADAM17 expression during neutrophil effector functions. The implications of this may be a role by ADAM17 in both the induction and down‐regulation of neutrophil activity.

In vivo role of leukocyte ADAM17 in the inflammatory and host responses during E. coli-mediated peritonitis

Inflammation is the bodys initial response to infection, which is harmful when excessive, as exemplified in sepsis inflammatory syndromes. Ectodomain shedding by the membrane metalloprotease ADAM17 is an emerging regulator of inflammation, as it directs the activity of various inflammatory modulators. At this time, however, little is known about the in vivo function of ADAM17. Here, we show that ADAM17‐deficient leukocytes afforded mice a survival benefit following Escherichia coli‐mediated peritoneal sepsis, which was associated with a reduction in systemic proinflammatory cytokine levels and bacterial burden. A more rapid yet transitory neutrophil infiltration into the peritoneal cavity of conditional ADAM17 knockout mice was observed when compared with control mice, suggesting a mechanism for their enhanced clearance of bacteria. Preventing the shedding of L‐selectin augments neutrophil recruitment, and we show that L‐selectin shedding by peritoneal neutrophils in conditional ADAM17 knockout mice was impaired. Moreover, their peritoneal TNF‐α levels were markedly lower than control mice following E. coli challenge. These events indicate key molecular processes involved in the altered time course of neutrophil recruitment in conditional ADAM17 knockout mice. Overall, our study provides novel in vivo evidence of the instrumental role of ADAM17 in modulating inflammation and host resistance during Gram‐negative bacterial infection.

ADAM-17-independent shedding of L-selectin

L‐selectin is expressed by leukocytes and facilitates their adhesion under flow along the walls of blood vessels. As do a variety of membrane proteins, L‐selectin undergoes ectodomain shedding. Using approaches that monitor full‐length L‐selectin in short‐term assays, it has been determined that L‐selectin shedding is defective in tumor necrosis factor α‐converting enzyme (ADAM‐17)‐deficient cells. In this study, we examined the steady‐state levels of L‐selectin on ADAM‐17‐deficient cells using a monoclonal antibody to the cytoplasmic region of L‐selectin, which allows for the detection of total L‐selectin (full‐length and the membrane‐associated cleavage fragment). We demonstrate that ADAM‐17‐deficient cells generate a 6‐kDa transmembrane fragment of L‐selectin. Although inducible L‐selctin shedding by phorbol 12‐myristate 13‐acetate stimulation was not observed by these cells in short‐term assays, basal turnover did occur, resulting in the production of soluble L‐selectin, as determined by enzyme‐linked immunosorbent assay. L‐selectin turnover was greatly increased upon ADAM‐17 reconstitution. Truncating the juxtamembrane region of L‐selectin blocked ADAM‐17‐independent shedding as did a hydroxymate metalloprotease inhibitor. Together, these findings demonstrate that a metalloprotease activity separate from ADAM‐17 can use the cleavage domain of L‐selectin. We speculate that separate proteolytic mechanisms of L‐selectin shedding may regulate distinct antiadhesive mechanisms, such as inducible shedding for the rapid dissociation of cell–cell interactions and constitutive shedding for the homeostatic maintenance of high serum levels of soluble L‐selectin, a potential adhesion buffer.

ADAM17 activity and other mechanisms of soluble L-selectin production during death receptor-induced leukocyte apoptosis

L-selectin is an adhesion molecule expressed by neutrophils that broadly directs their infiltration in to sites of inflammation. It is also present at relatively high levels in the serum of normal individuals. It is well established that L-selectin is efficiently shed from the surface of neutrophils upon their activation, a process that regulates its density and binding activity. Neutrophil programmed cell death is critical for the resolution of inflammation, and L-selectin downregulation is induced during this process as well. The mechanisms underpinning this latter process are much less understood, and were investigated in this study. Using a disintegrin and metalloprotease (ADAM)-17 radiation chimeric mice, we demonstrate for the first time that during early events of death receptor-mediated neutrophil apoptosis, L-selectin downregulation occurs primarily by ADAM17-mediated shedding. This was observed as well upon using shRNA to knock down ADAM17 expression in Jurkat cells, a well-studied cell line in terms of the molecular processes involved in the induction of apoptosis. These findings directly reveal that ADAM17 activity occurs during programmed cell death. Hence, the cleavage of particular ADAM17 substrates may be an additional component of the anti-inflammatory program initiated by apoptotic neutrophils. Of interest was that during later stages of induced leukocyte apoptosis, soluble L-selectin production occurred independent of ADAM17, as well as membrane events, such as blebbing and microparticle production. This process may provide an explanation for the lack of diminished serum L-selectin levels in ADAM17-null mice, and suggests a mechanism for the homeostatic maintenance of soluble L-selectin levels in the blood of healthy individuals.