Low molecular weight polysialic acid binds to properdin and reduces the activity of the alternative complement pathway.

Sialic acids as the terminal caps of the cellular glycocalyx play an essential role in self-recognition and were shown to modulate complement processes via interaction between α2,3-linked sialic acids and complement factor H. Previously, it was suggested that low molecular weight α2,8-linked polysialic acid (polySia avDP20) interferes with complement activation, but the exact molecular mechanism is still unclear. Here, we show that soluble polySia avDP20 (molecular weight of ~ 6 kDa) reduced the binding of serum-derived alternative pathway complement activator properdin to the cell surface of lesioned Hepa-1c1c7 and PC-12 neuroblastoma cells.

Presenilin/γ-secretase-dependent EphA3 processing mediates axon elongation through non-muscle myosin IIA.

EphA/ephrin signaling regulates axon growth and guidance of neurons, but whether this process occurs also independently of ephrins is unclear. We show that presenilin-1 (PS1)/γ-secretase is required for axon growth in the developing mouse brain. PS1/γ-secretase mediates axon growth by inhibiting RhoA signaling and cleaving EphA3 independently of ligand to generate an intracellular domain (ICD) fragment that reverses axon defects in PS1/γ-secretase- and EphA3-deficient hippocampal neurons.

EphA3 targeting reduces in vitro adhesion and invasion and in vivo growth and angiogenesis of multiple myeloma cells.

Purpose: Multiple myeloma (MM) is a hematologic malignancy characterized by a clonal expansion of plasma cells (PCs) in the bone marrow (BM). Since MM has so far remained incurable, further insights into its pathogenesis and the concomitant identification of new therapeutic targets are urgently needed. The tyrosine kinase receptor EphA3 is known to be involved in various cellular processes including cell viability, cell movement and cell-cell interactions.

EphA3 as a target for antibody immunotherapy in acute lymphoblastic leukemia.

The human EphA3 gene was discovered in a pre-B acute lymphoblastic leukemia (pre-B-ALL) using the EphA3-specific monoclonal antibody (mAb), IIIA4, which binds and activates both human and mouse EphA3. We use two models of human pre-B-ALL to examine EphA3 function, demonstrating effects on pre-B-cell receptor signaling. In therapeutic targeting studies, we demonstrated antitumor effects of the IIIA4 mAb in EphA3-expressing leukemic xenografts and no antitumor effect in the xenografts with no EphA3 expression providing evidence that EphA3 is a functional therapeutic target in pre-B-ALL.

PTP-PEST controls EphA3 activation and ephrin-induced cytoskeletal remodelling.

Eph receptors and their corresponding membrane-bound ephrin ligands regulate cell positioning and establish tissue patterns during embryonic and oncogenic development. Emerging evidence suggests that assembly of polymeric Eph signalling clusters relies on cytoskeletal reorganisation and underlies regulation by protein tyrosine phosphatases (PTPs). PTP-PEST (also known as PTPN12) is a central regulator of actin cytoskeletal dynamics.

The role of proteases in regulating Eph/ephrin signaling.

Proteases regulate a myriad of cell functions, both in normal and disease states. In addition to protein turnover, they regulate a range of signaling processes, including those mediated by Eph receptors and their ephrin ligands. A variety of proteases is reported to directly cleave Ephs and/or ephrins under different conditions, to promote receptor and/or ligand shedding, and regulate receptor/ligand internalisation and signaling.

A mathematical model for eph/ephrin-directed segregation of intermingled cells.

Eph receptors, the largest family of receptor tyrosine kinases, control cell-cell adhesion/de-adhesion, cell morphology and cell positioning through interaction with cell surface ephrin ligands. Bi-directional signalling from the Eph and ephrin complexes on interacting cells have a significant role in controlling normal tissue development and oncogenic tissue patterning. Eph-mediated tissue patterning is based on the fine-tuned balance of adhesion and de-adhesion reactions between distinct Eph- and ephrin-expressing cell populations, and adhesion within like populations (expressing either Eph or ephrin).

Hypoxia-controlled EphA3 marks a human endometrium-derived multipotent mesenchymal stromal cell that supports vascular growth.

Eph and ephrin proteins are essential cell guidance cues that orchestrate cell navigation and control cell-cell interactions during developmental tissue patterning, organogenesis and vasculogenesis. They have been extensively studied in animal models of embryogenesis and adult tissue regeneration, but less is known about their expression and function during human tissue and organ regeneration. We discovered the hypoxia inducible factor (HIF)-1α-controlled expression of EphA3, an Eph family member with critical functions during human tumour progression, in the vascularised tissue of regenerating human endometrium and on isolated human endometrial multipotent mesenchymal stromal cells (eMSCs), but not in other highly vascularised human organs.

Targeting EphA3 inhibits cancer growth by disrupting the tumor stromal microenvironment.

Eph receptor tyrosine kinases are critical for cell-cell communication during normal and oncogenic tissue patterning and tumor growth. Somatic mutation profiles of several cancer genomes suggest EphA3 as a tumor suppressor, but its oncogenic expression pattern and role in tumorigenesis remain largely undefined. Here, we report unexpected EphA3 overexpression within the microenvironment of a range of human cancers and mouse tumor xenografts where its activation inhibits tumor growth.

Therapeutic targeting of EPH receptors and their ligands.

Critical roles for EPH receptor (EPH)-ephrin signalling in a range of chronic and regenerative diseases are increasingly being recognized. In particular, the complex roles of EPHs and ephrins in tumour growth and progression, and in nerve injury and regeneration have been studied extensively. This has led to considerable progress in developing strategies for their therapeutic targeting, with some anticancer agents already in clinical trials.

Vascular remodeling in cancer.

The growth and dissemination of tumors rely on an altered vascular network, which supports their survival and expansion and provides accessibility to the vasculature and a route of transport for metastasizing tumor cells. The remodeling of vascular structures through generation of new vessels (for example, via tumor angiogenesis) is a well studied, even if still quite poorly understood, process in human cancer. Antiangiogenic therapies have provided insight into the contribution of angiogenesis to the biology of human tumors, yet have also revealed the ease with which resistance to antiangiogenic drugs can develop, presumably involving alterations to vascular signaling mechanisms.

EphA3 maintains tumorigenicity and is a therapeutic target in glioblastoma multiforme.

Significant endeavor has been applied to identify functional therapeutic targets in glioblastoma (GBM) to halt the growth of this aggressive cancer. We show that the receptor tyrosine kinase EphA3 is frequently overexpressed in GBM and, in particular, in the most aggressive mesenchymal subtype. Importantly, EphA3 is highly expressed on the tumor-initiating cell population in glioma and appears critically involved in maintaining tumor cells in a less differentiated state by modulating mitogen-activated protein kinase signaling.

Antibodies binding the ADAM10 substrate recognition domain inhibit Eph function.

The ADAM10 transmembrane metalloprotease cleaves a variety of cell surface proteins that are important in disease, including ligands for receptor tyrosine kinases of the erbB and Eph families. ADAM10-mediated cleavage of ephrins, the ligands for Eph receptors, is suggested to control Eph/ephrin-mediated cell-cell adhesion and segregation, important during normal developmental processes, and implicated in tumour neo-angiogenesis and metastasis. We previously identified a substrate-binding pocket in the ADAM10 C domain that binds the EphA/ephrin-A complex thereby regulating ephrin cleavage.

Eph/Ephrin signaling in injury and inflammation.

The Eph/ephrin receptor-ligand system plays an important role in embryogenesis and adult life, principally by influencing cell behavior through signaling pathways, resulting in modification of the cell cytoskeleton and cell adhesion. There are 10 EphA receptors, and six EphB receptors, distinguished on sequence difference and binding preferences, that interact with the six glycosylphosphatidylinositol-linked ephrin-A ligands and the three transmembrane ephrin-B ligands, respectively. The Eph/ephrin proteins, originally described as developmental regulators that are expressed at low levels postembryonically, are re-expressed after injury to the optic nerve, spinal cord, and brain in fish, amphibians, rodents, and humans.

Targeting of EPH receptor tyrosine kinases for anticancer therapy.

Intense research over the past 15 years has demonstrated Eph receptors and their cell surface ephrin ligands to be one of the most prevalent and complex cell-cell communication systems; this system guides cell positioning and orchestrates tissue patterning in multicellular organisms by coordinating synchronised cell-cell adhesion or segregation of interacting cells. The expression of many Eph and ephrin family members together with their embryonic patterning functions often re-emerge during oncogenesis and have generated considerable interest as targets for anticancer therapies. The first generation of monoclonal antibodies, kinase inhibitors, and vaccines suggests considerable promise in preclinical and early clinical development, but there is little doubt that successful clinical use will rely on a comprehensive understanding of the complex and sometimes puzzling activities of Eph receptors during tumor progression.

Concepts and consequences of Eph receptor clustering.

Polymeric receptor-ligand complexes between interacting Eph and ephrin-expressing cells are regarded as dynamic intercellular signalling scaffolds that control cell-to-cell contact: the resulting Eph-ephrin signalling clusters function as positional cues that facilitate cell navigation and tissue patterning during normal and oncogenic development. The considerable complexity of this task, coordinating a multitude of cell movements and cellular interactions, is achieved by accurate translation of spatial information from Eph and ephrin expression gradients into fine-tuned changes in cell-cell adhesion and position. Here we review emerging evidence suggesting that the required combinatorial diversity is not only achieved by the large number of possible Eph-ephrin interactions and selective use of Eph forward and ephrin reverse signals, but in particular through the composition and signal capacity of Eph-ephrin clusters, which is adjusted dynamically to reflect overall Eph and ephrin surface densities on interacting cells.

Eph-dependent cell-cell adhesion and segregation in development and cancer.

Numerous studies attest to essential roles for Eph receptors and their ephrin ligands in controlling cell positioning and tissue patterning during normal and oncogenic development. These studies suggest multiple, sometimes contradictory, functions of Eph-ephrin signalling, which under different conditions can promote either spreading and cell-cell adhesion or cytoskeletal collapse, cell rounding, de-adhesion and cell-cell segregation. A principle determinant of the balance between these two opposing responses is the degree of receptor/ligand clustering and activation.

Eph receptor function is modulated by heterooligomerization of A and B type Eph receptors.

Eph receptors interact with ephrin ligands on adjacent cells to facilitate tissue patterning during normal and oncogenic development, in which unscheduled expression and somatic mutations contribute to tumor progression. EphA and B subtypes preferentially bind A- and B-type ephrins, respectively, resulting in receptor complexes that propagate via homotypic Eph-Eph interactions. We now show that EphA and B receptors cocluster, such that specific ligation of one receptor promotes recruitment and cross-activation of the other.

PTP1B regulates Eph receptor function and trafficking.

Eph receptors orchestrate cell positioning during normal and oncogenic development. Their function is spatially and temporally controlled by protein tyrosine phosphatases (PTPs), but the underlying mechanisms are unclear and the identity of most regulatory PTPs are unknown. We demonstrate here that PTP1B governs signaling and biological activity of EphA3.

Architecture of Eph receptor clusters.

Eph receptor tyrosine kinases and their ephrin ligands regulate cell navigation during normal and oncogenic development. Signaling of Ephs is initiated in a multistep process leading to the assembly of higher-order signaling clusters that set off bidirectional signaling in interacting cells. However, the structural and mechanistic details of this assembly remained undefined.

Expression of nodal signalling components in cycling human endometrium and in endometrial cancer.

Background: The human endometrium is unique in its capacity to remodel constantly throughout adult reproductive life. Although the processes of tissue damage and breakdown in the endometrium have been well studied, little is known of how endometrial regeneration is achieved after menstruation. Nodal, a member of the transforming growth factor-beta superfamily, regulates the processes of pattern formation and differentiation that occur during early embryo development.

Cytoplasmic relaxation of active Eph controls ephrin shedding by ADAM10.

Release of cell surface-bound ligands by A-Disintegrin-And-Metalloprotease (ADAM) transmembrane metalloproteases is essential for signalling by cytokine, cell adhesion, and tyrosine kinase receptors. For Eph receptor ligands, it provides the switch between cell-cell adhesion and repulsion. Ligand shedding is tightly controlled by intrinsic tyrosine kinase activity, which for Eph receptors relies on the release of an inhibitory interaction of the cytoplasmic juxtamembrane segment with the kinase domain.

Eph/ephrin signalling and function in oncogenesis: lessons from embryonic development.

Eph receptors and their membrane-bound ephrin ligands are developmental cell guidance cues that direct cell migration and orchestrate patterning processes by modulating adhesive or repulsive cell properties. During the past two decades, an exponentially growing interest in their function has resulted in a considerably advanced understanding of the cellular and molecular principles of Eph function in normal and oncogenic development. Ephs not only accurately guide the path of migrating cells, but also facilitate contact and communication between neighbouring cell populations, in particular at epithelial/mesenchymal boundaries.

Eph, a protein family coming of age: more confusion, insight, or complexity?

Since the mid-1980s, Eph receptors have evolved from being regarded as orphan receptors with unknown functions and ligands to becoming one of the most complex "global positioning systems" that regulates cell traffic in multicellular organisms. During this time, there has been an exponentially growing interest in Ephs and ephrin ligands, coinciding with important advances in the way biological function is interrogated through mapping of genomes and manipulation of genes. As a result, many of the original concepts that used to define Eph signaling and function went overboard.