Extracellular Shedding Research Articles

Giant worm-shaped ESCRT scaffolds surround actin-independent integrin clusters.

Endosomal Sorting Complex Required for Transport (ESCRT) proteins can be transiently recruited to the plasma membrane for membrane repair and formation of extracellular vesicles. Here, we discovered micrometer-sized worm-shaped ESCRT structures that stably persist for multiple hours at the plasma membrane of macrophages, dendritic cells, and fibroblasts. These structures surround clusters of integrins and known cargoes of extracellular vesicles. The ESCRT structures are tightly connected to the cellular support and are left behind by the cells together with surrounding patches of membrane. The phospholipid composition is altered at the position of the ESCRT structures, and the actin cytoskeleton is locally degraded, which are hallmarks of membrane damage and extracellular vesicle formation. Disruption of actin polymerization increased the formation of the ESCRT structures and cell adhesion. The ESCRT structures were also present at plasma membrane contact sites with membrane-disrupting silica crystals. We propose that the ESCRT proteins are recruited to adhesion-induced membrane tears to induce extracellular shedding of the damaged membrane.

Role of redox-sensitive catalytic interaction with ADAM10 in mutant-selective extracellular shedding of prion protein

Misfolded glycosylphosphatidylinositol-anchored prion protein (PrP) is primarily degraded in lysosomes but is often rapidly removed from the cell surface before endocytosis in a preemptive manner. However, this mechanism is poorly understood. In this study, we discovered a disease-causing prion mutation (Q212P) that exceptionally promoted the extracellular release of PrP. Spatiotemporal analyses combined with genome editing identified the role of sheddase ADAM10 in Q212P shedding from the cell surface. ADAM10 was observed to catalytically interacts with Q212P but non-catalytically with wild-type PrP (wtPrP). This intrinsic difference in the interaction of ADAM10 between Q212P and wtPrP allowed Q212P to selectively access the sheddase activity of ADAM10 in a redox-sensitive manner. In addition, redox perturbation instigated the latent misfolding propensity of Q212P and disrupted the catalytic interaction between PrP and ADAM10, resulting in the accumulation of misfolded PrP on the cell surface. Upon recovery, active ADAM10 was able to reversibly release the surface Q212P. However, it might prove detrimental if unregulated resulting in unexpected proteotoxicity. This study provides a molecular basis of the mutant-selective shedding of PrP by demonstrating the catalytic interaction of ADAM10 with Q212P.

Abstract 1889: Dual-specific antibodies that bind to BCMA and TACI (HMBD-009) enable better targeting of multiple myeloma in pre-clinical models

Abstract Existing immunotherapies for multiple myelomas (MM), including bispecific antibodies, antibody-drug conjugates and chimeric antigen receptor-based strategies, have targeted the B-cell maturation antigen (BCMA) that is expressed at the surface of malignant plasma cells (PCs). Although promising, clinical outcomes are hampered by resistance mechanisms that include BCMA extracellular domain shedding and cell-surface downregulation. In addition, BCMA expression is known to be variable among MM patients. Transmembrane activator and CAML interactor (TACI), another member of the tumor necrosis factor receptor (TNFR) super family, represents another viable drug target. TACI expression largely overlaps with BCMA and expression is also increased in PCs of MM patients. Interestingly, TACI may have a role in maintaining an immunosuppressive tumor microenvironment as its expression was observed to be upregulated in Tregs in MM patient's tumor load. Activation of TACI in Tregs triggers their proliferation and survival further supporting a pro-tumoral role for this receptor. Altogether, the dual targeting of both BCMA and TACI should be beneficial to the efficient removal of malignant PCs. Despite low sequence homology, BCMA and TACI share a similar 3D structure, which is likely the reason that APRIL (A proliferation-Inducing ligand) binds to both receptors. We applied our proprietary Rational Antibody Discovery platform to successfully direct the generation of mouse IgG clones able to bind a conserved epitope on BCMA and TACI with sub-nanomolar affinities. In addition, these antibodies were able to inhibit the binding of BCMA to APRIL - an interaction known to favor MM tumor growth and survival. Two IgG clones were successfully humanized and retained their capacity to bind to both BCMA and TACI when heterologously expressed on HEK293, or endogenously expressed in MM cancer cell lines such as H929. No cross-reactivity to other TNFR family members was observed. In antibody-dependent cell-mediated cytotoxicity (ADCC) assays, these clones were able to induce efficient cell killing by binding either BCMA or TACI. Moreover, our lead dual-specific anti-BCMA/anti-TACI antibody (HMBD-009) showed better tumor control compared to other anti-BCMA only antibodies in pre-clinical tumor models of MM. Dual-specific antibodies able to efficiently target both BCMA and TACI represent a promising new avenue to improve the elimination of malignant PCs from MM patients. Citation Format: Fabien M. Decaillot, Dipti Thakkar, Siyu Guan, Konrad Paszkiewicz, Piers J. Ingram, Jerome D. Boyd-Kikurp. Dual-specific antibodies that bind to BCMA and TACI (HMBD-009) enable better targeting of multiple myeloma in pre-clinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1889.

O-glycan truncation enhances cancer-related functions of CD44 in gastric cancer.

CD44 isoforms are often upregulated in gastric cancer and have been associated with increased metastatic potential and poor survival. To evaluate the functional impact of O-glycan truncation on CD44 we have analysed glyco-engineered cancer cell models displaying shortened O-glycans. Here, we demonstrate that induction of aberrant O-glycan termination through various molecular mechanisms affects CD44 molecular features. We show that CD44 is a major carrier of truncated O-glycans and that this truncation is accompanied by an increased hyaluronan binding capacity and affects extracellular shedding. In addition, short O-glycans promoted the colocalization of CD44v6 with the receptor tyrosine kinase RON and concomitantly increased activation. Our invitro findings were validated in gastric cancer clinical samples.

Epidermal growth factor-mediated Rab25 pathway regulates integrin \u03b21 trafficking in colon cancer

BackgroundIntegrins play a critical role in carcinogenesis. Integrin β1 localization is regulated by the guanosine-5′-triphosphate hydrolase Rab25 and integrin β1 levels are elevated in the serum of colon cancer patients; thus, the present study examined the effects of epidermal growth factor (EGF) and Rab25 on integrin β1 localization in colon cancer cells.MethodsHCT116 human colon cancer cells were treated with increasing concentrations of EGF, and cell proliferation and protein expression were monitored by MTT and western blot analyses, respectively. Cell fractionation was performed to determine integrin β1 localization in the membrane and cytosol. Integrin β1 extracellular shedding was monitored by enzyme-linked immunosorbent assays (ELISAs) with culture supernatants from stimulated cells. HCT116 cells were transfected with Rab25-specific siRNA to determine the significance of Rab25 in integrin β1 trafficking in the presence of EGF.ResultsTotal integrin β1 expression increased in response to EGF and subsequently decreased at 24 h post-stimulation. A similar decrease was observed in purified membrane fractions, whereas no changes were observed in cytosolic levels. ELISAs using media from stimulated cell cultures demonstrated increased integrin β1 levels corresponding to the decrease observed in membrane fractions, suggesting that EGF induces integrin receptor shedding. EGF stimulation in Rab25-knockdown cells resulted in integrin β1 accumulation in the membrane, suggesting that Rab25 promotes integrin endocytosis.ConclusionsIntegrin β1 is shed from colon cancer cells in response to EGF stimulation in a Rab25-dependent manner. These results further the present understanding of the role of integrin β1 in colon cancer progression.

Targeting Human Astrocytes' Calcium-sensing Receptors for Treatment of Alzheimer's Disease.

Understanding the pathophysiology of Alzheimer's disease (AD) in the principal human neural cells is necessary for finding therapeutics for this illness. To help do this, we have been using freshly cultured functionally normal cerebral cortical adult human astrocytes (NAHAs) and postnatal neurons. The findings show that amyloid-β oligomers (Aβ-os) binding to calcium-sensing receptors (CaSRs) on NAHAs and neuron surfaces trigger signals capable of driving AD pathogenesis. This Aβ•CaSR signalling shifts the amyloid precursor protein (APP) from its α-secretase shedding producing neurotrophic/neuroprotective soluble (s)APPα to its β-secretase cleaving engendering AD-driving Aβ42/Aβ42-os peptides. Aβ•CaSR signalling in NAHAs also drives the release of toxic hyper-phosphorylated Tau proteins in exosomes, and of nitric oxide, and VEGF-A. These several harmful agents comprise the neuron-killing machinery, driving the very slowly spreading AD neurocontagion. VEGF-A over-secretion from Aβ-exposed blood vessel-attached astrocytes induces a functional magnetic resonance imaging- detectable hippocampal neoangiogenesis which indicates approaching AD in amnestic minor cognitive impairment (aMCI) patients. Most important in AD's regard, selective allosteric CaSR antagonists (calcylitics) added to Aβ42/Aβ42-os-exposed NAHAs (or to human neuron cultures) rescue the extracellular shedding of neurotrophic/ neuroprotective sAPPα and suppress all the neurotoxic effects of Aβ•CaSR signalling even when multiple microglial cytokines are also present. Therefore, since the multipotent calcilytics would be reasonably safe and inexpensive drugs for humans, it is worthwhile testing them as AD therapeutics in clinical trials especially in persons in the earliest detectable stages of AD neuropathology progression such as aMCI.

Calcium-Sensing Receptor Antagonist NPS 2143 Restores Amyloid Precursor Protein Physiological Non-Amyloidogenic Processing in A\u03b2-Exposed Adult Human Astrocytes

Physiological non-amyloidogenic processing (NAP) of amyloid precursor holoprotein (hAPP) by α-secretases (e.g., ADAM10) extracellularly sheds neurotrophic/neuroprotective soluble (s)APPα and precludes amyloid-β peptides (Aβs) production via β-secretase amyloidogenic processing (AP). Evidence exists that Aβs interact with calcium-sensing receptors (CaSRs) in human astrocytes and neurons, driving the overrelease of toxic Aβ42/Aβ42-os (oligomers), which is completely blocked by CaSR antagonist (calcilytic) NPS 2143. Here, we investigated the mechanisms underlying NPS 2143 beneficial effects in human astrocytes. Moreover, because Alzheimer’s disease (AD) involves neuroinflammation, we examined whether NPS 2143 remained beneficial when both fibrillary (f)Aβ25–35 and a microglial cytokine mixture (CMT) were present. Thus, hAPP NAP prevailed over AP in untreated astrocytes, which extracellularly shed all synthesized sAPPα while secreting basal Aβ40/42 amounts. Conversely, fAβ25–35 alone dramatically reduced sAPPα extracellular shedding while driving Aβ42/Aβ42-os oversecretion that CMT accelerated but not increased, despite a concurring hAPP overexpression. NPS 2143 promoted hAPP and ADAM10 translocation to the plasma membrane, thereby restoring sAPPα extracellular shedding and fully suppressing any Aβ42/Aβ42-os oversecretion, but left hAPP expression unaffected. Therefore, as anti-AD therapeutics calcilytics support neuronal viability by safeguarding astrocytes neurotrophic/neuroprotective sAPPα shedding, suppressing neurons and astrocytes Aβ42/Aβ42-os build-up/secretion, and remaining effective even under AD-typical neuroinflammatory conditions.

Syndecan-2 enhances E-cadherin shedding and fibroblast-like morphological changes by inducing MMP-7 expression in colon cancer cells

E-cadherin plays a mechanical role in mediating cell-cell interactions and maintaining epithelial tissue integrity, and the loss of E-cadherin function has been implicated in cancer progression and metastasis. Syndecan-2, a cell-surface heparan sulfate proteoglycan, is upregulated during the development of colon cancer. Here, we assessed the functional relationship between E-cadherin and syndecan-2. We found that stable overexpression of syndecan-2 in a human colorectal adenocarcinoma cell line (HT29) enhanced the proteolytic shedding of E-cadherin to conditioned-media. Either knockdown of matrix metalloproteinase 7 (MMP-7) or inhibition of MMP-7 activity using GM6001 significantly reduced the extracellular shedding of E-cadherin, suggesting that syndecan-2 mediates E-cadherin shedding via MMP-7. Consistent with this notion, enhancement of MMP-7 expression by interleukin-1α treatment increased the shedding of E-cadherin. Conversely, the specific reduction of either syndecan-2 or MMP-7 reduced the shedding of E-cadherin. HT29 cells overexpressing syndecan-2 showed significantly lower cell-surface expression of E-cadherin, decreased cell-cell contact, a more fibroblastic cell morphology, and increased expression levels of ZEB-1. Taken together, these data suggest that syndecan-2 induces extracellular shedding of E-cadherin and supports the acquisition of a fibroblast-like morphology by regulating MMP-7 expression in a colon cancer cell line.

Soluble CD146 boosts therapeutic effect of endothelial progenitors through proteolytic processing of short CD146 isoform.

Endothelial colony-forming cells (ECFC) constitute an endothelial progenitor fraction with a promising interest for the treatment of ischaemic cardiovascular diseases. As soluble CD146 (sCD146) is a new factor promoting angiogenesis, we examined whether sCD146 priming could improve the therapeutic potential of ECFC and defined the involved mechanism. We investigated the effects of sCD146 priming on regenerative properties of ECFC in vivo. In a mouse model of hindlimb ischaemia, the homing of radiolabelled cells to ischaemic tissue was assessed by SPECT-CT imaging. Soluble CD146 priming did not modify the number of engrafted ECFC but improved their survival capacity, leading to an enhanced revascularization. The mechanism of action of sCD146 on ECFC was studied in vitro. We showed that sCD146 acts in ECFC through a signalosome, located in lipid rafts, containing angiomotin, the short isoform of CD146 (shCD146), VEGFR1, VEGFR2, and presenilin-1. Soluble CD146 induced a sequential proteolytic cleavage of shCD146, with an extracellular shedding followed by an intramembrane cleavage mediated by matrix metalloprotease (MMP)/ADAM and presenilin-1, respectively. The generated intracellular part of shCD146 was directed towards the nucleus where it associated with the transcription factor CSL and modulated the transcription of genes involved in cell survival (FADD, Bcl-xl) and angiogenesis (eNOS). This effect was dependent on both VEGFR1 and VEGFR2, which were rapidly phosphorylated by sCD146. These findings establish that activation of the proteolytic processing of shCD146, in particular by sCD146, constitutes a promising pathway to improve endothelial progenitors' regenerative properties for the treatment of cardiovascular diseases.

UDP-sugar substrates of HAS3 regulate its O-GlcNAcylation, intracellular traffic, extracellular shedding and correlate with melanoma progression.

Hyaluronan content is a powerful prognostic factor in many cancer types, but the molecular basis of its synthesis in cancer still remains unclear. Hyaluronan synthesis requires the transport of hyaluronan synthases (HAS1-3) from Golgi to plasma membrane (PM), where the enzymes are activated. For the very first time, the present study demonstrated a rapid recycling of HAS3 between PM and endosomes, controlled by the cytosolic levels of the HAS substrates UDP-GlcUA and UDP-GlcNAc. Depletion of UDP-GlcNAc or UDP-GlcUA shifted the balance towards HAS3 endocytosis, and inhibition of hyaluronan synthesis. In contrast, UDP-GlcNAc surplus suppressed endocytosis and lysosomal decay of HAS3, favoring its retention in PM, stimulating hyaluronan synthesis, and HAS3 shedding in extracellular vesicles. The concentration of UDP-GlcNAc also controlled the level of O-GlcNAc modification of HAS3. Increasing O-GlcNAcylation reproduced the effects of UDP-GlcNAc surplus on HAS3 trafficking, while its suppression showed the opposite effects, indicating that O-GlcNAc signaling is associated to UDP-GlcNAc supply. Importantly, a similar correlation existed between the expression of GFAT1 (the rate limiting enzyme in UDP-GlcNAc synthesis) and hyaluronan content in early and deep human melanomas, suggesting the association of UDP-sugar metabolism in initiation of melanomagenesis. In general, changes in glucose metabolism, realized through UDP-sugar contents and O-GlcNAc signaling, are important in HAS3 trafficking, hyaluronan synthesis, and correlates with melanoma progression.

Cleavage and cell adhesion properties of human epithelial cell adhesion molecule (HEPCAM).

Human epithelial cell adhesion molecule (HEPCAM) is a tumor-associated antigen frequently expressed in carcinomas, which promotes proliferation after regulated intramembrane proteolysis. Here, we describe extracellular shedding of HEPCAM at two α-sites through a disintegrin and metalloprotease (ADAM) and at one β-site through BACE1. Transmembrane cleavage by γ-secretase occurs at three γ-sites to generate extracellular Aβ-like fragments and at two ϵ-sites to release human EPCAM intracellular domain HEPICD, which is efficiently degraded by the proteasome. Mapping of cleavage sites onto three-dimensional structures of HEPEX cis-dimer predicted conditional availability of α- and β-sites. Endocytosis of HEPCAM warrants acidification in cytoplasmic vesicles to dissociate protein cis-dimers required for cleavage by BACE1 at low pH values. Intramembrane cleavage sites are accessible and not part of the structurally important transmembrane helix dimer crossing region. Surprisingly, neither chemical inhibition of cleavage nor cellular knock-out of HEPCAM using CRISPR-Cas9 technology impacted the adhesion of carcinoma cell lines. Hence, a direct function of HEPCAM as an adhesion molecule in carcinoma cells is not supported and appears to be questionable.

Abstract A86: Extracellular domain shedding influences specific tumor uptake and kinetics of EGFR PET tracer 89Zr-imgatuzumab

Abstract Background Overexpression and mutations of epidermal growth factor receptor (EGFR) are associated with tumor cell growth, differentiation, proliferation, apoptosis and cellular invasiveness. Imgatuzumab is a novel EGFR monoclonal antibody (mAb), glycoengineered for enhanced antibody-dependent cellular cytotoxicity. Molecular imaging using radiolabeled mAbs can potentially support decision making during (pre)clinical development and clinical practice. However, preclinical EGFR imaging studies revealed a mismatch between in vivo EGFR expression levels and tumor tracer uptake. Factors suggested causing the mismatch include differences in perfusion rates, vascularity, vascular permeability, interstitial pressure and mAb plasma half-life. Another factor that might influence tracer kinetics is shed EGFR (sEGFR) extracellular domain (ECD), which is found in sera of cancer patients with EGFR expressing tumors. We radiolabeled imgatuzumab with zirconium-89 (89Zr) and determined the influence of sEGFR on 89Zr-imgatuzumab tracer kinetics and tumor uptake in xenograft models. Methods Imgatuzumab was conjugated to N-Suc-desferal and radiolabeled with 89Zr. MicroPET imaging was performed 24, 72 and 144 hours post injection of 10, 25 and 160 μg 89Zr-imgatuzumab (5 MBq). As a non-specific control, 111In-DTPA-IgG (1 MBq) was used in equal doses in the same animals. Imaging studies were performed in A431 (human epidermoid carcinoma, EGFR overexpressing) and A549 and H441 (both human non-small cell lung cancer, medium EGFR expressing) subcutaneous xenograft bearing mice. Ex vivo biodistribution analysis was performed after the last scan. sEGFR levels in liver lysates and plasma were obtained using a human EGFR ECD ELISA assay. Results Increasing 89Zr-imgatuzumab dose from 10 to 160 μg enhanced tumor uptake in A431 bearing mice from 8.7 ± 3.1 to 31.4 ± 11.6% ID/g. On contrary, dose escalation between 10 and 160 μg 89Zr-imgatuzumab lowered tumor uptake from 13.8 ± 5.9 to 6.7 ± 0.8% ID/g in A549 and from 27.6 ± 3.6 to 15.5 ± 3.2% ID/g in H441 bearing mice. High liver uptake of 22.0 ± 5.4% ID/g was observed in A431 tumors at 10 μg 89Zr-imgatuzumab, this was higher than A549 (7.4 ± 1.5% ID/g, p<0.0001) and H441 (8.4 ± 2.1% ID/g, p<0.001) bearing mice. Liver uptake in A431 bearing mice could be blocked with 160 μg 89Zr-imgatuzumab to 7.1 ± 1.6% ID/g. Human EGFR ECD ELISA showed presence of 790 ± 267 ng/g protein sEGFR in liver lysates and 831 ± 173 ng/ml in plasma of A431 bearing mice, while sEGFR levels in liver and plasma of A549 and H441 tumor bearing mice were comparable to non tumor bearing control mice. Conclusion 89Zr-imgatuzumab effectively accumulates in EGFR expressing tumors. A431 tumors extensively shedded EGFR, which highly influenced 89Zr-imgatuzumab kinetics in A431 bearing mice. These results support the use of shed antigen measurements and subsequent tracer dose adjustment in future EGFR imaging studies. Citation Format: Martin Pool, Arjan Kol, Marjolijn N. Lub-de Hooge, Christian A. Gerdes, Steven de Jong, Elisabeth G.E. de Vries, Anton G.T. Terwisscha van Scheltinga. Extracellular domain shedding influences specific tumor uptake and kinetics of EGFR PET tracer 89Zr-imgatuzumab. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A86.

Cleavage and Cell Adhesion Properties of Human Epithelial Cell Adhesion Molecule (HEPCAM)

Human epithelial cell adhesion molecule (HEPCAM) is a tumor-associated antigen frequently expressed in carcinomas, which promotes proliferation after regulated intramembrane proteolysis. Here, we describe extracellular shedding of HEPCAM at two α-sites through a disintegrin and metalloprotease (ADAM) and at one β-site through BACE1. Transmembrane cleavage by γ-secretase occurs at three γ-sites to generate extracellular Aβ-like fragments and at two ϵ-sites to release human EPCAM intracellular domain HEPICD, which is efficiently degraded by the proteasome. Mapping of cleavage sites onto three-dimensional structures of HEPEX cis-dimer predicted conditional availability of α- and β-sites. Endocytosis of HEPCAM warrants acidification in cytoplasmic vesicles to dissociate protein cis-dimers required for cleavage by BACE1 at low pH values. Intramembrane cleavage sites are accessible and not part of the structurally important transmembrane helix dimer crossing region. Surprisingly, neither chemical inhibition of cleavage nor cellular knock-out of HEPCAM using CRISPR-Cas9 technology impacted the adhesion of carcinoma cell lines. Hence, a direct function of HEPCAM as an adhesion molecule in carcinoma cells is not supported and appears to be questionable.

Proteomic Identification of Cysteine Cathepsin Substrates Shed from the Surface of Cancer Cells

Extracellular cysteine cathepsins are known to drive cancer progression, but besides degradation of extracellular matrix proteins little is known about their physiological substrates and thus the molecular mechanisms they deploy. One of the major mechanisms used by other extracellular proteases to facilitate cancer progression is proteolytic release of the extracellular domains of transmembrane proteins or ectodomain shedding. Here we show using a mass spectrometry-based approach that cathepsins L and S act as sheddases and cleave extracellular domains of CAM adhesion proteins and transmembrane receptors from the surface of cancer cells. In cathepsin S-deficient mouse pancreatic cancers, processing of these cathepsin substrates is highly reduced, pointing to an essential role of cathepsins in extracellular shedding. In addition to influencing cell migration and invasion, shedding of surface proteins by extracellular cathepsins impacts intracellular signaling as demonstrated for regulation of Ras GTPase activity, thereby providing a putative mechanistic link between extracellular cathepsin activity and cancer progression. The MS data is available via ProteomeXchange with identifier PXD002192.

Gangliosides drive the tumor infiltration and function of myeloid-derived suppressor cells.

Although it is now widely appreciated that antitumor immunity is critical to impede tumor growth and progression, there remain significant gaps in knowledge about the mechanisms used by tumors to escape immune control. In tumor cells, we hypothesized that one mechanism of immune escape used by tumors involves the synthesis and extracellular shedding of gangliosides, a class of biologically active cell surface glycosphingolipids with known immunosuppressive properties. In this study, we report that tumor cells engineered to be ganglioside deficient exhibit impaired tumorigenicity, supporting a link between ganglioside-dependent immune escape and tumor outgrowth. Notably, we documented a dramatic reduction in the numbers and function of tumor-infiltrating myeloid-derived suppressor cells (MDSC) in ganglioside-deficient tumors, in contrast with the large MDSC infiltrates seen in ganglioside-rich littermate control tumors. Transient ganglioside reconstitution of the tumor cell inoculum was sufficient to increase MDSC infiltration, supporting a direct connection between ganglioside production by tumor cells and the recruitment of immunosuppressive MDSC into the tumor microenvironment. Our results reveal a novel mechanism of immune escape that supports tumor growth, with broad implications given that many human tumors produce and shed high levels of gangliosides.

Interleukin-1α promotes extracellular shedding of syndecan-2 via induction of matrix metalloproteinase-7 expression

The cell surface heparan sulfate proteoglycan, syndecan-2, is known to play an important role in the tumorigenic activity of colon cancer cells. In addition, the extracellular domain of syndecan-2 is cleaved by matrix metalloproteinase-7 (MMP-7) in various colon cancer cells, but factors involved in regulating this process remain unknown. Here, we demonstrate a role for interleukin-1α (IL-1α) in syndecan-2 shedding in colon cancer cells. Treatment of low metastatic (HT-29) and highly metastatic (HCT-116) colon cancer cells with various soluble growth factors and cytokines revealed that IL-1α specifically increased extracellular shedding of syndecan-2 in a concentration- and time-dependent manner. IL-1α did not affect the expression of syndecan-2, but did significantly reduce its cell surface levels. Notably, IL-1α increased the mRNA expression and subsequent secreted levels of MMP-7 protein and enhanced the phosphorylation of p38 and ERK mitogen-activated protein kinases. Furthermore, increased syndecan-2 shedding was dependent on the mitogen-activated protein kinase-mediated MMP-7 expression. Taken together, these data suggest that IL-1α regulates extracellular domain shedding of syndecan-2 through regulation of the MAP kinase-mediated MMP-7 expression in colon cancer cells.

Helping Eve Overcome ADAM: G-Quadruplexes in the ADAM-15 Promoter as New Molecular Targets for Breast Cancer Therapeutics

ADAM-15, with known zymogen, secretase, and disintegrin activities, is a catalytically active member of the ADAM family normally expressed in early embryonic development and aberrantly expressed in various cancers, including breast, prostate and lung. ADAM-15 promotes extracellular shedding of E-cadherin, a soluble ligand for the HER2/neu receptor, leading to activation, increased motility, and proliferation. Targeted downregulation of both ADAM-15 and HER2/neu function synergistically kills breast cancer cells, but to date there are no therapeutic options for decreasing ADAM-15 function or expression. In this vein, we have examined a unique string of guanine-rich DNA within the critical core promoter of ADAM-15. This region of DNA consists of seven contiguous runs of three or more consecutive guanines, which, under superhelical stress, can relax from duplex DNA to form an intrastrand secondary G-quadruplex (G4) structure. Using biophysical and biological techniques, we have examined the G4 formation within the entire and various truncated regions of the ADAM-15 promoter, and demonstrate strong intrastrand G4 formation serving to function as a biological silencer element. Characterization of the predominant G4 species formed within the ADAM-15 promoter will allow for specific drug targeting and stabilization, and the further development of novel, targeted therapeutics.

Mapping of matrix metalloproteinase cleavage sites on syndecan‐1 and syndecan‐4 ectodomains

Syndecans are transmembrane heparan sulfate proteoglycans with roles in cell proliferation, differentiation, adhesion, and migration. They have been associated with multiple functions in tumour progression, through their ability to interact with a wide range of ligands as well as other receptors, which makes them key effectors in the pericellular microenvironment. Extracellular shedding of syndecans by tumour-associated matrix metalloproteinases (MMPs) may have an important role in tumour progression. Such ectodomain shedding generates soluble ectodomains that may function as paracrine or autocrine effectors, or as competitive inhibitors of the intact proteoglycan. Tumour-associated MMPs are shown here to cleave the ectodomains of human syndecan-1 and syndecan-4. Two membrane proximal regions of both syndecan-1 and syndecan-4 are favoured MMP cleavage sites, six and 15 residues from the transmembrane domain. Other sites are 35-40 residues C-terminal from the heparan sulfate chain substitution sites in both syndecans. The MT1-MMP cleavage sites in syndecan-1 and syndecan-4 were confirmed by site-directed mutagenesis. These findings provide insights into the characteristics of syndecan shedding.

The matrix metalloproteinase-7 regulates the extracellular shedding of syndecan-2 from colon cancer cells

The cell surface heparan sulfate proteoglycan syndecan-2 regulates the activation of matrix metalloproteinase-7 (MMP-7) as a docking receptor. Here, we demonstrate the role of MMP-7 on syndecan-2 shedding in colon cancer cells. Western blot analysis showed that shed syndecan-2 was found in the culture media from various colon cancer cells. Overexpression of MMP-7 enhanced syndecan-2 shedding, whereas the opposite was true when MMP-7 levels were knocked-down using small inhibitory RNAs. Consistently, HT29 cells treated with MMP-7, but neither MMP-2 nor MMP-9, showed increased shed syndecan-2 in a time- and concentration-dependent manner. Furthermore, MALDI-TOF MS analysis and N-terminal amino acid sequencing revealed that MMP-7 cleaved both recombinant syndecan-2 and an endogenously glycosylated syndecan-2 ectodomain in the N-terminus at Leu149 residue in vitro. Taken together, the data suggest that MMP-7 directly mediates shedding of syndecan-2 from colon cancer cells.

Abstract 3681: Helping Eve overcome ADAM: Characterization of the G-quadruplex in the ADAM15 core promoter

Abstract Breast cancer is the most common form of cancer in women, whose lethality is only surpassed by lung cancer. Through the last quarter-century there have been significant advances in detection and treatment options, such as Herceptin for HER2/neu positive cancers. While the development of targeted biological agents has greatly improved patient outcome, up to 70% of patients remain de novo refractory, relapse on therapy, or develop resistance. There is a pressing and eminent need for novel therapies to synergize with, or resensitize to, standard treatments. Enter ADAM15, with known zymogen, secretase, and disintegrin activies. This catalytically active member of the ADAM family is normally expressed in early embryonic development and is aberrantly expressed in various cancers, including breast. ADAM15 promotes extracellular shedding of E-cadherin, a soluble ligand for the HER2/neu receptor, leading to activation, increased motility, and proliferation. Seven independent microarray studies have shown that ADAM15 and HER2/neu are simultaneously upregulated in several stages of breast cancer, where their overexpression correlates with more aggressive and invasive disease. We have examined a unique string of GC-rich DNA within the critical core promoter of ADAM15. This region of DNA consists of seven tandem runs of three or more consecutive guanines. Under superhelical stress produced by the transcriptional complex, this region can relax from duplex DNA to form an intrastrand secondary structure known as a G-quadruplex. These globular entities generally serve as silencing elements for gene transcription. Furthermore, the topology of each G-quadruplex is as unique as a fingerprint. This allows for specific therapeutic targeting, offering a unique opportunity for treatment and selectivity over normal cells thus providing a potentially wide therapeutic window. Circular dichroism (CD) studies have confirmed the formation of a mixed parallel/anti-parallel G-quadruplex. Further CD analysis of the minimal G-quadruplex forming fragments has shown the capability of forming four unique thermally stable species. Electrophoretic mobility shift assay indicates the strongest intramolecular G-quadruplex formation in the 5′- and 3′-end runs of guanine, with minor intermolecular formations in the 3′-mid sequence, and a relatively unstable 5′-mid formation. To specifically determine which guanines are involved in the formation of the G-quadruplex and predict biologically relevant three-dimensional structures, DMS footprinting was performed on the full-length sequence and each of the four dissected regions. The pursuant data was used to build a molecular model of the structure. Full characterization of the G-quadruplex species formed will allow for specific drug targeting and stabilization, and the further development of novel, targeted therapeutics. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3681.