EphB2 and ephrin-B1 expressed in the adult kidney regulate the cytoarchitecture of medullary tubule cells through Rho family GTPases

Influenza A virus replicates productively in primary human kidney cells and induces factors and mechanisms related to regulated cell death and renal pathology observed in virus-infected patients

Introduction

Influenza A virus (IAV) infection can cause the often-lethal acute respiratory distress syndrome (ARDS) of the lung. Concomitantly, acute kidney injury (AKI) is frequently noticed during IAV infection, correlating with an increased mortality. The aim of this study was to elucidate the interaction of IAV with human kidney cells and, thereby, to assess the mechanisms underlying IAV-mediated AKI.

Methods

To investigate IAV effects on nephron cells we performed infectivity assays with human IAV, as well as with human isolates of either low or highly pathogenic avian IAV. Also, transcriptome and proteome analysis of IAV-infected primary human distal tubular kidney cells (DTC) was performed. Furthermore, the DTC transcriptome was compared to existing transcriptomic data from IAV-infected lung and trachea cells.

Results

We demonstrate productive replication of all tested IAV strains on primary and immortalized nephron cells. Comparison of our transcriptome and proteome analysis of H1N1-type IAV-infected human primary distal tubular cells (DTC) with existing data from H1N1-type IAV-infected lung and primary trachea cells revealed enrichment of specific factors responsible for regulated cell death in primary DTC, which could be targeted by specific inhibitors.

Discussion

IAV not only infects, but also productively replicates on different human nephron cells. Importantly, multi-omics analysis revealed regulated cell death as potential contributing factor for the clinically observed kidney pathology in influenza.

Isthmin-1: A critical regulator of branching morphogenesis and metanephric mesenchyme condensation during early kidney development

Isthmin-1 (Ism1) was first described to be syn-expressed with Fgf8 in Xenopus. However, its biological role has not been elucidated until recent years. Despite of accumulated evidence that Ism1 participates in angiogenesis, tumor invasion, macrophage apoptosis, and glucose metabolism, the cognate receptors for Ism1 remain largely unknown. Ism1 deficiency in mice results in renal agenesis (RA) with a transient loss of Gdnf transcription and impaired mesenchyme condensation at E11.5. Ism1 binds to and activates Integrin α8β1 to positively regulate Gdnf/Ret signaling, thus promoting mesenchyme condensation and ureteric epithelium branching morphogenesis. Here, we propose the hypothesis underlying the mechanism by which Ism1 regulates branching morphogenesis during early kidney development.

Erythropoietin-producing hepatocellular receptor B6 is highly expressed in non-functioning pituitary neuroendocrine tumors and its expression correlates with tumor size

BACKGROUND

Erythropoietin-producing hepatocellular (EPH) receptors are the largest known family of receptor tyrosine kinases characterized in humans. These proteins are involved in tissue organization, synaptic plasticity, vascular development and the progression of various diseases including cancer. The Erythropoietin-producing hepatocellular receptor tyrosine kinase member EphB6 is a pseudokinase which has not attracted an equivalent amount of interest as its enzymatically-active counterparts. The aim of this study was to assess the expression of EphB6 in pituitary tumors.

METHODS AND RESULTS

Human normal pituitaries and pituitary tumors were examined for EphB6 mRNA expression using real-time PCR and for EphB6 protein by immunohistochemistry and Western blotting. EphB6 was highly expressed in non-functioning pituitary neuroendocrine tumors (NF-PitNETs) versus the normal pituitary and GH-secreting PitNETs. EphB6 mRNA expression was correlated with tumor size.

CONCLUSIONS

Our results suggest EphB6 aberrant expression in NF-PitNETs. Future studies are warranted to determine the role and significance of EphB6 in NF-PitNETs tumorigenesis.

Comprehensive single-cell transcriptional profiling defines shared and unique epithelial injury responses during kidney fibrosis

The underlying cellular events driving kidney fibrogenesis and metabolic dysfunction are incompletely understood. Here, we employed single-cell combinatorial indexing RNA sequencing to analyze 24 mouse kidneys from two fibrosis models. We profiled 309,666 cells in one experiment, representing 50 cell types/states encompassing epithelial, endothelial, immune, and stromal populations. Single-cell analysis identified diverse injury states of the proximal tubule, including two distinct early-phase populations with dysregulated lipid and amino acid metabolism, respectively. Lipid metabolism was defective in the chronic phase but was transiently activated in the very early stages of ischemia-induced injury, where we discovered increased lipid deposition and increased fatty acid β-oxidation. Perilipin 2 was identified as a surface marker of intracellular lipid droplets, and its knockdown in vitro disrupted cell energy state maintenance during lipid accumulation. Surveying epithelial cells across nephron segments identified shared and unique injury responses. Stromal cells exhibited high heterogeneity and contributed to fibrogenesis by epithelial-stromal crosstalk.

Proteomic and metabolomic profiling of urine uncovers immune responses in patients with COVID-19

The utility of the urinary proteome in infectious diseases remains unclear. Here, we analyzed the proteome and metabolome of urine and serum samples from patients with COVID-19 and healthy controls. Our data show that urinary proteins effectively classify COVID-19 by severity. We detect 197 cytokines and their receptors in urine, but only 124 in serum using TMT-based proteomics. The decrease in urinary ESCRT complex proteins correlates with active SARS-CoV-2 replication. The downregulation of urinary CXCL14 in severe COVID-19 cases positively correlates with blood lymphocyte counts. Integrative multiomics analysis suggests that innate immune activation and inflammation triggered renal injuries in patients with COVID-19. COVID-19-associated modulation of the urinary proteome offers unique insights into the pathogenesis of this disease. This study demonstrates the added value of including the urinary proteome in a suite of multiomics analytes in evaluating the immune pathobiology and clinical course of COVID-19 and, potentially, other infectious diseases.

Key role for EphB2 receptor in kidney fibrosis

Erythropoietin producing hepatocellular (Eph)-Eph receptor interacting (Ephrin) receptor-ligand signaling has been implicated in the development of tissue fibrosis, though it has not been well defined in the kidney. We detected substantial up-regulation of expression and phosphorylation of the EphB2 receptor tyrosine kinase in fibrotic kidney tissue obtained both from mice subjected to the unilateral renal ischemia-reperfusion (IR) model at 14 days and in patients suffering from chronic kidney disease (CKD). Knockout (KO) mice lacking EphB2 expression exhibited a normal renal structure and function, indicating no major role for this receptor in kidney development or action. Although IR injury is well-known to cause tissue damage, fibrosis, and renal dysfunction, we found that kidneys from EphB2KO mice showed much less renal tubular injury and retained a more preserved renal function. IR-injured kidneys from EphB2 KOs exhibited greatly reduced fibrosis and inflammation compared with injured wildtype (WT) littermates, and this correlated with a significant reduction in renal expression of profibrotic molecules, inflammatory cytokines, NADPH oxidases, and markers for cell proliferation, tubular epithelial-to-mesenchymal transition (EMT), myofibroblast activation, and apoptosis. A panel of 760 fibrosis-associated genes were further assessed, revealing that 506 genes in WT mouse kidney following IR injury changed their expression. However, 70.9% of those genes were back to or close to normal in expression when EphB2 was deleted. These data indicate that endogenous EphB2 expression and signaling are abnormally activated after kidney injury and subsequently contribute to the development of renal fibrosis via regulation of multiple profibrotic pathways.

The EphB6 Receptor: Kinase-Dead but Very Much Alive

The Eph receptor tyrosine kinase member EphB6 is a pseudokinase, and similar to other pseudoenzymes has not attracted an equivalent amount of interest as its enzymatically-active counterparts. However, a greater appreciation for the role pseudoenzymes perform in expanding the repertoire of signals generated by signal transduction systems has fostered more interest in the field. EphB6 acts as a molecular switch that is capable of modulating the signal transduction output of Eph receptor clusters. Although the biological effects of EphB6 activity are well defined, the molecular mechanisms of EphB6 function remain enigmatic. In this review, we use a comparative approach to postulate how EphB6 acts as a scaffold to recruit adaptor proteins to an Eph receptor cluster and how this function is regulated. We suggest that the evolutionary repurposing of EphB6 into a kinase-independent molecular switch in mammals has involved repurposing the kinase activation loop into an SH3 domain-binding site. In addition, we suggest that EphB6 employs the same SAM domain linker and juxtamembrane domain allosteric regulatory mechanisms that are used in kinase-positive Eph receptors to regulate its scaffold function. As a result, although kinase-dead, EphB6 remains a strategically active component of Eph receptor signaling.

Synthetic dysmobility screen unveils an integrated STK40-YAP-MAPK system driving cell migration

Integrating signals is essential for cell survival, leading to the concept of synthetic lethality. However, how signaling is integrated to control cell migration remains unclear. By conducting a "two-hit" screen, we revealed the synergistic reduction of cell migration when serine-threonine kinase 40 (STK40) and mitogen-activated protein kinase (MAPK) were simultaneously suppressed. Single-cell analyses showed that STK40 knockdown reduced cell motility and coordination by strengthening focal adhesion (FA) complexes. Furthermore, STK40 knockdown reduced the stability of yes-associated protein (YAP) and subsequently decreased YAP transported into the nucleus, while MAPK inhibition further weakened YAP activities in the nucleus to disturb FA remodeling. Together, we unveiled an integrated STK40-YAP-MAPK system regulating cell migration and introduced "synthetic dysmobility" as a novel strategy to collaboratively control cell migration.

UniPR1331: Small Eph/Ephrin Antagonist Beneficial in Intestinal Inflammation by Interfering with Type-B Signaling

Eph receptors, comprising A and B classes, interact with cell-bound ephrins generating bidirectional signaling. Although mainly related to carcinogenesis and organogenesis, the role of Eph/ephrin system in inflammation is growingly acknowledged. Recently, we showed that EphA/ephrin-A proteins can modulate the acute inflammatory responses induced by mesenteric ischemia/reperfusion, while beneficial effects were granted by EphB4, acting as EphB/ephrin-B antagonist, in a murine model of Crohn’s disease (CD). Accordingly, we now aim to evaluate the effects of UniPR1331, a pan-Eph/ephrin antagonist, in TNBS-induced colitis and to ascertain whether UniPR1331 effects can be attributed to A- or B-type signaling interference. The potential anti-inflammatory action of UniPR1331 was compared to those of the recombinant proteins EphA2, a purported EphA/ephrin-A antagonist, and of ephrin-A1-Fc and EphA2-Fc, supposedly activating forward and reverse EphA/ephrin-A signaling, in murine TNBS-induced colitis and in stimulated cultured mononuclear splenocytes. UniPR1331 antagonized the inflammatory responses both in vivo, mimicking EphB4 protection, and in vitro; EphA/ephrin-A proteins were inactive or only weakly effective. Our findings represent a further proof-of-concept that blockade of EphB/ephrin-B signaling is a promising pharmacological strategy for CD management and highlight UniPR1331 as a novel drug candidate, seemingly working through the modulation of immune responses.

Endothelial dysfunction and cardiovascular risk in lupus nephritis: New roles for old players?

In systemic lupus erythematosus (SLE) patients, most of the clinical manifestation share a vascular component triggered by endothelial dysfunction. Endothelial cells (ECs) activation occurs both on the arterial and venous side, and the high vascular density of kidneys accounts for the detrimental outcomes of SLE through lupus nephritis (LN). Kidney damage, in turn, exerts a negative feedback on the cardiovascular (CV) system aggravating risk factors for CV diseases such as hypertension, stroke and coronary syndrome among others. Despite the intensive investigation on SLE and LN, the role of endothelial dysfunction, as well as the underlying mechanisms, remains to be fully understood, with no specifically targeted pharmacological treatment. It is not known, in fact, if the activation pathway(s) in venous ECs are similar to the one in arterial ECs and doubts persist on the shared manifestation of microcirculation compared to macrocirculation. In this work, we aim to review the recent literature about the role of endothelial activation and dysfunction in the development of CV complications in SLE and LN patients. We, therefore, focus on arteriovenous similarities and differences and on specific pathways of great vessels compared to capillaries. Critically summarising the available data is of pivotal importance for both basic researchers and clinicians in order to develop and test new pharmacological approaches in the treatment of basic components of SLE and LN.

Partitioning-Defective-6-Ephrin-B1 Interaction Is Regulated by Nephrin-Mediated Signal and Is Crucial in Maintaining Slit Diaphragm of Podocyte

Ephrin-B1 plays a critical role at slit diaphragm. Partitioning-defective (Par)-6 is down-regulated in podocyte of ephrin-B1 knockout mouse, suggesting that Par-6 is associated with ephrin-B1. Par polarity complex, consisting of Par-6, Par-3, and atypical protein kinase C, is essential for tight junction formation. In this study, the expression of Par-6 was analyzed in the normal and nephrotic syndrome model rats, and the molecular association of Par-6, Par-3, ephrin-B1, and nephrin was assessed with the human embryonic kidney 293 cell expression system. Par-6 was concentrated at slit diaphragm. Par 6 interacted with ephrin-B1 but not with nephrin, and Par-3 interacted with nephrin but not with ephrin-B1. The complexes of Par-6-ephrin-B1 and Par-3-nephrin were linked via extracellular sites of ephrin-B1 and nephrin. The Par-6-ephrin-B1 complex was delinked from the Par-3-nephrin complex, and Par-6 and ephrin-B1 were clearly down-regulated already at early phase of nephrotic model. The alteration of Par-6/ephrin-B1 advanced that of Par-3/nephrin. Stimulation to nephrin phosphorylated not only nephrin but also ephrin-B1, and consequently inhibited the interaction between ephrin-B1 and Par-6. Par-6 appeared at presumptive podocyte of early developmental stage and moved to basal area at capillary loop stage to participate in slit diaphragm formation at the final stage. Par-6-ephrin-B1 interaction is crucial for formation and maintenance of slit diaphragm of podocyte.

Targeting the Eph/Ephrin System as Anti-Inflammatory Strategy in IBD

Besides their long-known critical role in embryonic growth and in cancer development and progression, erythropoietin-producing hepatocellular carcinoma type B (EphB) receptor tyrosine kinases and their ephrin-B ligands are involved in the modulation of immune responses and in remodeling and maintaining the integrity of the intestinal epithelial layer. These processes are critically involved in the pathogenesis of inflammatory-based disorders of the gut, like inflammatory bowel diseases (IBDs). Accordingly, our aim was to investigate the role of the EphB/ephrin-B system in intestinal inflammation by assessing the local and systemic effects produced by its pharmacological manipulation in 2,4,6-trinitrobenzenesulfonic acid (TNBS)- (Th1-dependent model) and dextran sulphate sodium (DSS)- (innate response model) induced colitis in mice. To this purpose, we administered chimeric Fc-conjugated proteins, allegedly able to uni-directionally activate either forward (ephrin-B1-Fc) or reverse (EphB1-Fc) signaling, and the soluble monomeric EphB4 extracellular domain protein, that, simultaneously interfering with both signaling pathways, acts as EphB/ephrin-B antagonist.The blockade of the EphB/ephrin-B forward signaling by EphB4 and EphB1-Fc was ineffective against DSS-induced colitis while it evoked remarkable beneficial effects against TNBS colitis: it counteracted all the evaluated inflammatory responses and the changes elicited on splenic T lymphocytes subpopulations, without preventing the appearance of a splice variant of ephrin-B2 gene elicited by the haptenating agent in the colon. Interestingly, EphB4, preferentially displacing EphB4/ephrin-B2 interaction over EphB1/ephrin-B1 binding, was able to promote Tumor Necrosis Factor alpha (TNFα) release by splenic mononuclear cells in vitro. On the whole, the collected results point to a potential role of the EphB/ephrin-B system as a pharmacological target in intestinal inflammatory disorders and suggest that the therapeutic efficacy of its blockade seemingly works through the modulation of immune responses, independent of the changes at the transcriptional and translational level of EphB4 and ephrin-B2 genes.

Changing expression profiles of long non-coding RNAs, mRNAs and circular RNAs in ethylene glycol-induced kidney calculi rats

Background

To explore long non-coding RNA (lncRNA), mRNA and circular RNA (circRNA) expression profiles and their biological functions in the pathogenesis of kidney stones in ethylene glycol-induced urolithiasis rats.

Results

The expression of 1440 lncRNAs, 2455 mRNAs and 145 circRNAs was altered in the kidneys of urolithiasis rats. GO and KEGG biological pathway analysis were performed to predict the functions of differentially expressed lncRNAs, circRNAs and co-expressed potential targeting genes. Co-expression networks of lncRNA-mRNA and circRNA-miRNA were constructed based on correlation analysis between differentially expressed RNAs. mRNAs coexpressed with lncRNAs were involved in many kidney diseases, e.g., Ephb6 was associated with the reabsorption ability of the kidney. Arl5b was associated with the dynamic changes in the podocyte foot process in podocyte injury. miRNAs co-expressed with circRNAs, such as rno-miR-138-5p and rno-miR-672-5p, have been proven to be functional in hypercalciuria urolithiasis.

Conclusion

The expression profile provided a systematic perspective on the potential functions of lncRNAs and circRNAs in the pathogenesis of kidney stones. Differentially expressed lncRNAs and circRNAs might serve as treatment targets for kidney stones.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5052-8) contains supplementary material, which is available to authorized users.

EphA7 regulates claudin6 and pronephros development in Xenopus

Eph/ephrin molecules are widely expressed during embryonic development, and function in a variety of developmental processes. Here we studied the roles of the Eph receptor EphA7 and its soluble form in Xenopus pronephros development. EphA7 is specifically expressed in pronephric tubules at tadpole stages and knockdown of EphA7 by a translation blocking morpholino led to defects in tubule cell differentiation and morphogenesis. A soluble form of EphA7 (sEphA7) was also identified. Interestingly, the membrane level of claudin6 (CLDN6), a tetraspan transmembrane tight junction protein, was dramatically reduced in the translation blocking morpholino injected embryos, but not when a splicing morpholino was used, which blocks only the full length EphA7. In cultured cells, EphA7 binds and phosphorylates CLDN6, and reduces its distribution at the cell surface. Our work suggests a role of EphA7 in the regulation of cell adhesion during pronephros development, whereas sEphA7 works as an antagonist.

Truncated EphA2 likely potentiates cell adhesion via integrins as well as infiltration and/or lodgment of a monocyte/macrophage cell line in the red pulp and marginal zone of the mouse spleen, where ephrin-A1 is prominently expressed in the vasculature

We previously established a J774.1 monocyte/macrophage subline expressing a truncated EphA2 construct lacking the kinase domain. We demonstrated that following ephrin-A1 stimulation, endogenous EphA2 promotes cell adhesion through interaction with integrins and integrin ligands such as ICAM1 and that truncated EphA2 potentiates the adhesion and becomes associated with the integrin/integrin ligand complex. Based on these findings, we hypothesized that the EphA/ephrin-A system, particularly EphA2/ephrin-A1, regulates transendothelial migration/tissue infiltration of monocytes/macrophages, because ephrin-A1 is widely recognized to be upregulated in inflammatory vasculatures. To evaluate whether this hypothesis is applicable in the spleen, we screened for EphA2/ephrin-A1 expression and reexamined the cellular properties of the J774.1 subline. We found that ephrin-A1 was expressed in the vasculature of the marginal zone and the red pulp and that its expression was upregulated in response to phagocyte depletion; further, CD115, F4/80, and CXCR4 were expressed in J774.1 cells, which serve as a usable substitute for monocytes/macrophages. Moreover, following ephrin-A1 stimulation, truncated EphA2 did not detectably interfere with the phosphorylation of endogenous EphA2, and it potentiated cell adhesion possibly through modulation of integrin avidity. Accordingly, by intravenously injecting mice with equal numbers of J774.1 and the subline cells labeled with distinct fluorochromes, we determined that truncated EphA2 markedly potentiated preferential cell infiltration into the red pulp and the marginal zone. Thus, modulation of EphA2 signaling might contribute to effective transplantation of tissue-specific resident macrophages and/or monocytes.

Bidirectional signalling between EphA2 and ephrinA1 increases tubular cell attachment, laminin secretion and modulates erythropoietin expression after renal hypoxic injury

Acute kidney injury (AKI) is common in hospitalized patients and has a poor prognosis, the severity of AKI being linked to progression to chronic kidney disease. This stresses the need to search for protective mechanisms during the acute phase. We investigated kidney repair after hypoxic injury using a rat model of renal artery branch ligation, which led to an oxygen gradient vertical to the corticomedullary axis. Three distinct zones were observed: tubular necrosis, infarction border zone and preserved normal tissue. EphA2 is a receptor tyrosine kinase with pivotal roles in cell architecture, migration and survival, upon juxtacrine contact with its membrane-bound ligand EphrinA1. Following hypoxia, EphA2 was up-regulated in cortical and medullary tubular cells, while EphrinA1 was up-regulated in interstitial cells adjacent to peritubular capillaries. Moreover, erythropoietin (EPO) messenger RNA (mRNA) was strongly expressed in the border zone of infarcted kidney within the first 6 h. To gain more insight into the biological impact of EphA2 and EphrinA1 up-regulation, we activated the signalling pathways in vitro using recombinant EphrinA1/Fc or EphA2/Fc proteins. Stimulation of EphA2 forward signalling in the proximal tubular cell line HK2 increased cell attachment and laminin secretion at the baso-lateral side. Conversely, activation of reverse signalling through EphrinA1 expressed by Hep3B cells promoted EPO production at both the transcriptional and protein level. Strikingly, in co-culture experiments, juxtacrine contact between EphA2 expressing MDCK and EphrinA1 expressing Hep3B was sufficient to induce a significant up-regulation of EPO mRNA production in the latter cells, even in the absence of hypoxic conditions. The synergistic effects of EphA2 and hypoxia led to a 15-20-fold increase of EPO expression. Collectively, our results suggest an important role of EphA2/EphrinA1 signalling in kidney repair after hypoxic injury through stimulation of (i) tubular cell attachment, (ii) secretion of basal membrane proteins and (iii) EPO production. These findings could thus pave the way to new therapeutic approaches.

Eph/ephrin signaling in the kidney and lower urinary tract

Development and homeostasis of the highly specialized cell types and tissues that constitute the organs of the urinary system, the kidneys and ureters, the bladder, and the urethra, require the tightly regulated exchange of signals in and between these tissues. Eph/ephrin signaling is a bidirectional signaling pathway that has been functionally implicated in many developmental and homeostatic contexts, most prominently in the vascular and neural system. Expression and knockout analyses have now provided evidence that Eph/ephrin signaling is of crucial relevance for cell and tissue interactions in the urinary system as well. A clear requirement has emerged in the formation of the vesicoureteric junction, in urorectal septation and glomerulogenesis during embryonic development, in maintenance of medullary tubular cells and podocytes in homeostasis, and in podocyte and glomerular injury responses. Deregulation of Eph/ephrin signaling may also contribute to the formation and progression of tumors in the urinary system, most prominently bladder and renal cell carcinoma. While in the embryonic contexts Eph/ephrin signaling regulates adhesion of epithelial cells, in the adult setting, cell-shape changes and cell survival seem to be the primary cellular processes mediated by this signaling module. With progression of the genetic analyses of mice conditionally mutant for compound alleles of Eph receptor and ephrin ligand genes, additional essential functions are likely to arise in the urinary system.

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. They also cleave other adhesion proteins in response to Eph-ephrin interactions, to indirectly facilitate Eph-mediated functions. Proteases thus contribute to Eph/ephrin mediated changes in cell-cell and cell-matrix interactions, in cell morphology and in cell migration and invasion, in a manner which appears to be tightly regulated by, and co-ordinated with, Eph signaling. This review summarizes the current literature describing the function and regulation of protease activities during Eph/ephrin-mediated cell signaling.

EphB2 activation is required for ependymoma development as well as inhibits differentiation and promotes proliferation of the transformed cell

Our intracranial implantation mouse model of ependymoma clearly demonstrates overexpression of the ephrin receptor EphB2 in Ink4a/Arf^(−/−) supratentorial embryonic neural stem cells (STeNSCs) to be essential for transformation and disease development; however the requirement for and consequence of receptor activation on transformation and neural stem cell function were not examined. We definitively illustrate the necessity for receptor activation in cellular transformation and the importance of implantation site and microenvironment in directing ependymoma development. In vitro assays of EphB2 overexpressing Ink4a/Arf^(−/−) STeNSCs showed no changes in their neural stem cell characteristics (stem cell marker expression and self-renewal) upon receptor activation, but EphB2 driven tumor cells were inhibited significantly in differentiation and exhibited increased tumorsphere formation and cellular proliferation in response to ephrin-B ligand mediated receptor activation. Additionally, we observed substantial differences in the phosphorylation state of several key proteins involved in Ras and p38 MAPK signaling when comparing EphB2 overexpressing Ink4a/Arf^(−/−) STeNSCs and tumor cells with relatively little change in total protein levels. We propose that EphB2 mediated ependymoma development is a multifactorial process requiring microenvironment directed receptor activation, resulting in changes in the phosphorylation status of key regulatory proteins, maintenance of a stem-like state and cellular proliferation.

Aberrant EphB/ephrin-B expression in experimental gastric lesions and tumor cells

AIM: To determine whether the expression profiles of EphB receptor and ephrin-B ligand can be used as markers for dysplastic/oncogenic transformation in gastric mucosa.

METHODS: The protein expression and localization of EphB and ephrin-B in normal, ulcerated regenerating, and dysplastic gastric mucosa were examined in a rat experimental model by immunolabeling, and mRNA expression was assessed in four human gastric carcinoma cell lines by reverse transcription-polymerase chain reaction.

RESULTS: Ephrin-B- and EphB-expressing regions were divided along the pit-gland axis in normal gastric units. EphB2 was transiently upregulated in the experimental ulcer, and its expression domain extended to gastric pits and/or the luminal surface where ephrin-B-expressing pit cells reside. EphB2, B3, and B4 and ephrin-B1 were coexpressed in the experimental gastric dysplasia, and more than one ligand-receptor pair was highly expressed in each of the gastric carcinoma cell lines.

CONCLUSION: Robust and stable coexpression of EphB and ephrin-B is a feature common to experimentally induced gastric dysplasia and human gastric carcinoma cell lines as compared to normal gastric and ulcerated regenerating epithelia. Thus, EphB/ephrin-B may be a useful marker combination for dysplastic/oncogenic transformation in gastric cancer.

Quantitative proteomics reveals novel therapeutic and diagnostic markers in hypertension

Hypertension is a prevalent disorder in the world representing one of the major risk factors for heart attack and stroke. These risks are increased in salt sensitive individuals. Hypertension and salt sensitivity are complex phenotypes whose pathophysiology remains poorly understood and, remarkably, salt sensitivity is still laborious to diagnose.

Here we present a urinary proteomic study specifically designed to identify urinary proteins relevant for the pathogenesis of hypertension and salt sensitivity. Despite previous studies that underlined the association of UMOD gene variants with hypertension, this work provides novel evidence showing different uromodulin protein level in the urine of hypertensive patients compared to healthy individuals. Notably, we also show that patients with higher level of uromodulin are homozygous for UMOD risk variant and display a decreased level of salt excretion, highlighting the essential role of UMOD in the regulation of salt reabsorption in hypertension. Additionally, we found that urinary nephrin 1, a marker of glomerular slit diaphragm, may predict a salt sensitive phenotype and positively correlate with increased albuminuria associated with this type of hypertension.

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We identified urinary proteins differently excreted in hypertensive patients.

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Nephrin 1 might predict salt sensitive phenotype and glomerular complications.

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Uromodulin impacts salt homeostasis in hypertension.

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We provide new insights into the pathogenesis of hypertension and salt sensitivity.

Nephric duct insertion requires EphA4/EphA7 signaling from the pericloacal mesenchyme

The vesico-ureteric junction (VUJ) forms through a complex developmental program that connects the primordium of the upper urinary tract [the nephric duct (ND)] with that of the lower urinary tract (the cloaca). The signals that orchestrate the various tissue interactions in this program are poorly understood. Here, we show that two members of the EphA subfamily of receptor tyrosine kinases, EphA4 and EphA7, are specifically expressed in the mesenchyme surrounding the caudal ND and the cloaca, and that Epha4−/−;Epha7+/− and Epha4−/−;Epha7−/− (DKO) mice display distal ureter malformations including ureterocele, blind and ectopically ending ureters with associated hydroureter, megaureter and hydronephrosis. We trace these defects to a late or absent fusion of the ND with the cloaca. In DKO embryos, the ND extends normally and approaches the cloaca but the tip subsequently looses its integrity. Expression of Gata3 and Lhx1 and their downstream target Ret is severely reduced in the caudal ND. Conditional deletion of ephrin B2 from the ND largely phenocopies these changes, suggesting that EphA4/EphA7 from the pericloacal mesenchyme signal via ephrin B2 to mediate ND insertion. Disturbed activity of this signaling module may entail defects of the VUJ, which are frequent in the spectrum of congenital anomalies of the kidney and the urinary tract (CAKUT) in human newborns.

Synthesis and in vitro evaluation of thiododecaborated α, α- cycloalkylamino acids for the treatment of malignant brain tumors by boron neutron capture therapy

Boron-neutron capture therapy (BNCT) is an attractive technique for cancer treatment. As such, α, α-cycloalkyl amino acids containing thiododecaborate ([B12H11](2-)-S-) units were designed and synthesized as novel boron delivery agents for BNCT. In the present study, new thiododecaborate α, α-cycloalkyl amino acids were synthesized, and biological evaluation of the boron compounds as boron carrier for BNCT was carried out.

Eph receptors and ephrins as targets for cancer therapy

Eph receptor tyrosine kinases and their ephrin ligands are involved in various signalling pathways and mediate critical steps of a wide variety of physiological and pathological processes. Increasing experimental evidence demonstrates that both Eph receptor and ephrin ligands are overexpressed in a number of human tumours, and are associated with tumour growth, invasiveness and metastasis. In this regard, the Eph/ephrin system provides the foundation for potentially exciting new targets for anticancer therapies for Eph-expressing tumours. The purpose of this review is to outline current advances in the role of Eph receptors and ephrin ligands in cancer, and to discuss novel therapeutic approaches of anticancer therapies.

Complementary expression and repulsive signaling suggest that EphB2 and ephrin-B1 are possibly involved in epithelial boundary formation at the squamocolumnar junction in the rodent stomach

Eph receptors and ephrin ligands are cell-cell communication molecules with well-defined roles in cell adhesion, migration, and tissue boundary formation. However, their expression levels in the squamocolumnar epithelial junction region at the distal esophagus are completely unknown. We examined EphB2 and ephrin-B1 localization in the squamocolumnar epithelial junction region between the proximal and distal stomach of the rodents. Immunostaining showed complimentary expression patterns along the proximal-to-distal axis of the gastric epithelia across the junction: EphB2 expression was maximal around the epithelial junction and sharply decreased in the stratified squamous epithelium at a short distance from the junction, whereas ephrin-B1 was strongly expressed in the stratified squamous epithelium at a distance from the junction and sharply decreased toward the junction. These expression patterns suggest that EphB2/ephrin-B1 signaling occurs preferentially in the epithelia across the junction, where the receptor and ligand expression highly overlap. We also show that (1) EphB2 preferentially binds ephrin-B1, and (2) cell repulsion/lateral migration was induced in primary cultured gastric keratinocytes on ephrin-B1-Fc- and EphB2-Fc-coated surfaces. On the basis of these findings, we propose that EphB2 and ephrin-B1 are possibly involved in epithelial boundary formation at the squamocolumnar junction.

Characteristics of genomic signatures derived using univariate methods and mechanistically anchored functional descriptors for predicting drug- and xenobiotic-induced nephrotoxicity

ABSTRACT The ideal toxicity biomarker is composed of the properties of prediction (is detected prior to traditional pathological signs of injury), accuracy (high sensitivity and specificity), and mechanistic relationships to the endpoint measured (biological relevance). Gene expression-based toxicity biomarkers ("signatures") have shown good predictive power and accuracy, but are difficult to interpret biologically. We have compared different statistical methods of feature selection with knowledge-based approaches, using GeneGo's database of canonical pathway maps, to generate gene sets for the classification of renal tubule toxicity. The gene set selection algorithms include four univariate analyses: t-statistics, fold-change, B-statistics, and RankProd, and their combination and overlap for the identification of differentially expressed probes. Enrichment analysis following the results of the four univariate analyses, Hotelling T-square test, and, finally out-of-bag selection, a variant of cross-validation, were used to identify canonical pathway maps-sets of genes coordinately involved in key biological processes-with classification power. Differentially expressed genes identified by the different statistical univariate analyses all generated reasonably performing classifiers of tubule toxicity. Maps identified by enrichment analysis or Hotelling T-square had lower classification power, but highlighted perturbed lipid homeostasis as a common discriminator of nephrotoxic treatments. The out-of-bag method yielded the best functionally integrated classifier. The map "ephrins signaling" performed comparably to a classifier derived using sparse linear programming, a machine learning algorithm, and represents a signaling network specifically involved in renal tubule development and integrity. Such functional descriptors of toxicity promise to better integrate predictive toxicogenomics with mechanistic analysis, facilitating the interpretation and risk assessment of predictive genomic investigations.

Biological evaluation of dodecaborate-containing L-amino acids for boron neutron capture therapy

To develop a boron carrier for practical purposes, new boron-containing amino acids with an undecahydro-closo-dodecaboranylthio ([(10)B(12)H(11)S](2-)-) unit in the side chain of the α-amino acid have already been designed and synthesized. In the present paper, cytotoxicity, the incorporation amounts into tumor cells, and the tumor cell killing effects of these compounds were elucidated to evaluate their usefulness as boron carriers. Furthermore, the microdistribution of the amino acids in tumor cells was established.

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. This equilibrium is likely altered in cancers and modulated by somatic mutations of key Eph family members that have emerged as candidate cancer markers in recent profiling studies. In addition, cross-talk amongst Ephs and with other signalling pathways significantly modulates cell-cell adhesion, both between and within Eph- and ephrin-expressing cell populations. This review summarises our current understanding of how Eph receptors control cell adhesion and morphology, and presents examples demonstrating the importance of these events in normal development and cancer.

Podocyte EphB4 signaling helps recovery from glomerular injury

Eph receptor tyrosine kinases and their ligands (ephrins) have a pivotal role in the homeostasis of many adult organs and are widely expressed in the kidney. Glomerular diseases beginning with mesangiolysis can recover, with podocytes having a critical role in this healing process. We studied here the role of Eph signaling in glomerular disease recovery following mesangiolytic Thy1.1 nephritis in rats. EphB4 and ephrinBs were expressed in healthy glomerular podocytes and were upregulated during Thy1.1 nephritis, with EphB4 strongly phosphorylated around day 9. Treatment with NPV-BHG712, an inhibitor of EphB4 phosphorylation, did not cause glomerular changes in control animals. Nephritic animals treated with vehicle did not have morphological evidence of podocyte injury or loss; however, application of this inhibitor to nephritic rats induced glomerular microaneurysms, podocyte damage, and loss. Prolonged NPV-BHG712 treatment resulted in increased albuminuria and dysregulated mesangial recovery. Additionally, NPV-BHG712 inhibited capillary repair by intussusceptive angiogenesis (an alternative to sprouting angiogenesis), indicating a previously unrecognized role of podocytes in regulating intussusceptive vessel splitting. Thus, our results identify EphB4 signaling as a pathway allowing podocytes to survive transient capillary collapse during glomerular disease.

Ephrin-B1 Is a Novel Specific Component of the Lateral Membrane of the Cardiomyocyte and Is Essential for the Stability of Cardiac Tissue Architecture Cohesion

Rationale:

Cardiac tissue cohesion relying on highly ordered cardiomyocytes (CM) interactions is critical because most cardiomyopathies are associated with tissue remodeling and architecture alterations.

Objective:

Eph/ephrin system constitutes a ubiquitous system coordinating cellular communications which recently emerged as a major regulator in adult organs. We examined if eph/ephrin could participate in cardiac tissue cyto-organization.

Methods and Results:

We reported the expression of cardiac ephrin-B1 in both endothelial cells and for the first time in CMs where ephrin-B1 localized specifically at the lateral membrane. Ephrin-B1 knock-out (KO) mice progressively developed cardiac tissue disorganization with loss of adult CM rod-shape and sarcomeric and intercalated disk structural disorganization confirmed in CM-specific ephrin-B1 KO mice. CMs lateral membrane exhibited abnormal structure by electron microscopy and notably increased stiffness by atomic force microscopy. In wild-type CMs, ephrin-B1 interacted with claudin-5/ZO-1 complex at the lateral membrane, whereas the complex disappeared in KO/CM-specific ephrin-B1 KO mice. Ephrin-B1 deficiency resulted in decreased mRNA expression of CM basement membrane components and disorganized fibrillar collagen matrix, independently of classical integrin/dystroglycan system. KO/CM-specific ephrin-B1 KO mice exhibited increased left ventricle diameter and delayed atrioventricular conduction. Under pressure overload stress, KO mice were prone to death and exhibited striking tissue disorganization. Finally, failing CMs displayed downregulated ephrin-B1/claudin-5 gene expression linearly related to the ejection fraction.

Conclusions:

Ephrin-B1 is necessary for cardiac tissue architecture cohesion by stabilizing the adult CM morphology through regulation of its lateral membrane. Because decreased ephrin-B1 is associated with molecular/functional cardiac defects, it could represent a new actor in the transition toward heart failure.

Complementary expression and repulsive signaling suggest that EphB receptors and ephrin-B ligands control cell positioning in the gastric epithelium

Eph receptors and ephrin ligands are membrane-bound cell-cell communication molecules with well-defined roles in development. However, their expression and functions in the gastric epithelium are virtually unknown. We detected several EphB receptors and ephrin-Bs in the gastric corpus mucosa of the adult rodent stomach by RT-PCR amplification. Immunostaining showed complementary expression patterns, with EphB receptors preferentially expressed in the deeper regions and ephrin-Bs in the superficial regions of the gastric units. EphB1, EphB2 and EphB3 are expressed in mucous neck, chief and parietal cells, respectively. In contrast, ephrin-B1 is in pit cells and proliferating cells of the isthmus. In a mouse ulcer model, EphB2 expression was upregulated in the regenerating epithelium and expanded into the isthmus. Thus, EphB/ephrin-B signaling likely occurs preferentially in the isthmus, where receptor-ligand overlap is highest. We show that EphB signaling in primary gastric epithelial cells promotes cell retraction and repulsion at least in part through RhoA activation. Based on these findings, we propose that the EphB-positive progeny of gastric stem cells migrates from the isthmus toward the bottom of the gastric glands due to repulsive signals arising from contact with ephrin-Bs, which are preferentially expressed in the more superficial regions of the isthmus and gastric pits.

Complementary expression of EphB receptors and ephrin-B ligand in the pyloric and duodenal epithelium of adult mice

Eph receptors and ephrin ligands are membrane-bound cell-cell communication molecules that regulate the spatial organisation of cells in various tissues by repulsive or adhesive signals arising from contact between EphB- and ephrin-bearing cells. However, the expression and functions of Eph receptors in the gastric epithelium and Brunner's glands are virtually unknown. We detected several EphB receptors and ephrin-B ligands in the pyloric and duodenal mucosa of the adult mouse by RT-PCR amplification. Immunostaining showed complementary expression patterns, with ephrin-B1 being preferentially expressed in the superficial part and EphB receptors in the deeper part of both epithelia. In the gastric pylorus, ephrin-B1 was expressed in pit cells and proliferating cells of the isthmus. In contrast, EphB2, EphB3, and EphB4 were expressed in pyloric glandular cells and proliferating cells of the isthmus. In the duodenum, ephrin-B1 was expressed in cells lining the ducts of Brunner's glands as well as those covering villi and the upper portion of the crypts of Lieberkühn. In contrast, EphB2 and EphB3 were expressed in the gland segment of Brunner's glands and the lower portion of the crypts and EphB4, in the crypts. In both mucosae, EphB2, EphB3, and EphB4 were found to be tyrosine phosphorylated, suggesting that EphB/ephrin-B signalling might occur preferentially in the isthmus, crypts, and duct-gland transition of Brunner's glands, where the receptor and ligand expression overlaps. Based on these findings, we propose that EphB/ephrin-B signalling may regulate cell positioning within the pyloric and duodenal epithelium.

Keeping in touch with contact inhibition of locomotion

Contact inhibition of locomotion (CIL) is the process by which cells in vitro change their direction of migration upon contact with another cell. Here, we revisit the concept that CIL plays a central role in the migration of single cells and in collective migration, during both health and disease. Importantly, malignant cells exhibit a diminished CIL behaviour which allows them to invade healthy tissues. Accumulating evidence indicates that CIL occurs in vivo and that regulation of small Rho GTPases is important in the collapse of cell protrusions upon cell contact, the first step of CIL. Finally, we propose possible cell surface proteins that could be involved in the initial contact that regulates Rho GTPases during CIL.

Angiogenesis and chronic kidney disease

The number of patients requiring renal replacement therapy due to end-stage renal disease (ESRD) is increasing worldwide. The prevalence of chronic kidney disease (CKD), and the importance of CKD as a risk factor in development of ESRD and in complicating cardiovascular disease (CVD) have been confirmed. In recent years, the involvement of angiogenesis-related factors in the progression of CKD has been studied, and the potential therapeutic effects on CKD of modulating these factors have been identified. Vascular endothelial growth factor (VEGF)-A, a potent pro-angiogenic factor, is involved in the development of the kidney, in maintenance of the glomerular capillary structure and filtration barrier, and in the renal repair process after injury. VEGF-A is also involved in the development of early diabetic nephropathy, demonstrated by the therapeutic effects of anti-VEGF-A antibody. Angiopoietin (Ang)-1 induces the maturation of newly formed blood vessels, and the therapeutic effects of Ang-1 in diabetic nephropathy have been described. In experimental models of diabetic nephropathy, the therapeutic effects of angiogenesis inhibitors, including angiostatin, endostatin and tumstatin peptides, the isocoumarin NM-3, and vasohibin-1, have been reported.

Further analysis of the involvement of angiogenesis-related factors in the development of CKD is required. Determining the disease stage at which therapy is most effective and developing an effective drug delivery system targeting the kidney will be essential for pro-or anti-angiogenic strategies for patients with CKD.

Identification of EphrinB1 expression in prostatic mesenchyme and a role for EphB-EphrinB signalling in prostate development

Paracrine signalling from mesenchyme to epithelium plays a key role in regulating prostate organogenesis and it is important to identify the mesenchymally expressed molecules that regulate organ growth, though currently few such molecules are known. Tyrosine kinase signalling via EphB receptors has been characterised in many developmental processes, and EphB3 mRNA expression was detected in prostate inductive mesenchyme in previous gene profiling studies. This led us to examine the expression and function of EphrinB signalling in prostate development, to determine if EphrinB ligands might function as mesenchymal paracrine regulators of prostate growth. Using PCR, wholemount in situ hybridisation, and immunohistochemistry we examined the expression of EphB receptors and EphrinB ligands in rat prostate during development to determine which showed mesenchymal expression. EphB3 and EphrinB1 transcripts and proteins were expressed in the mesenchyme of developing prostate and in female urogenital mesenchyme and smooth muscle. The function of EphrinB signalling was examined using in vitro organ culture assays of ventral prostate (VP), which were treated with EphB3-Fc and EphrinB1-Fc proteins to inhibit or augment Ephrin signalling. Addition of recombinant EphB3-Fc resulted in a significant decrease in VP organ size, while recombinant EphrinB1-Fc resulted in a significant increase in VP organ size and epithelial proliferation. Additionally, EphrinB1-Fc reduced the degree of epithelial branching in VP organs and increased ductal tip size, though without disrupting normal differentiation. We have identified expression of EphrinB1 in prostatic mesenchyme and suggest that the EphrinB signalling system acts as a regulator of prostate growth. EphrinB-EphB signalling may function as an autocrine regulator of mesenchyme and/or as a paracrine regulator of epithelia.

Eph-ephrin signalling in adult tissues and cancer

Eph receptor tyrosine kinases and their ligands, the ephrins, play key roles in the regulation of migration and cell adhesion during development, thereby influencing cell fate, morphogenesis and organogenesis. Recent findings suggest that Eph signalling also controls the architecture and physiology of different tissues in the adult body under normal and pathological conditions such as cancer. A prime example is the intestinal epithelium where EphB-ephrinB interactions regulate both cell positioning and tumor progression. Here, we will review recent advances on the role of Eph-ephrin signalling in the intestine and other organs.

Three-dimensional structure of the EphB2 receptor in complex with an antagonistic peptide reveals a novel mode of inhibition

The Eph family of receptor tyrosine kinases has been implicated in tumorigenesis as well as pathological forms of angiogenesis. Understanding how to modulate the interaction of Eph receptors with their ephrin ligands is therefore of critical interest for the development of therapeutics to treat cancer. Previous work identified a set of 12-mer peptides that displayed moderate binding affinity but high selectivity for the EphB2 receptor. The SNEW antagonistic peptide inhibited the interaction of EphB2 with ephrinB2, with an IC50 of approximately 15 microm. To gain a better molecular understanding of how to inhibit Eph/ephrin binding, we determined the crystal structure of the EphB2 receptor in complex with the SNEW peptide to 2.3-A resolution. The peptide binds in the hydrophobic ligand-binding cleft of the EphB2 receptor, thus competing with the ephrin ligand for receptor binding. However, the binding interactions of the SNEW peptide are markedly different from those described for the TNYL-RAW peptide, which binds to the ligand-binding cleft of EphB4, indicating a novel mode of antagonism. Nevertheless, we identified a conserved structural motif present in all known receptor/ligand interfaces, which may serve as a scaffold for the development of therapeutic leads. The EphB2-SNEW complex crystallized as a homodimer, and the residues involved in the dimerization interface are similar to those implicated in mediating tetramerization of EphB2-ephrinB2 complexes. The structure of EphB2 in complex with the SNEW peptide reveals novel binding determinants that could serve as starting points in the development of compounds that modulate Eph receptor/ephrin interactions and biological activities.

The synovial sarcoma SYT-SSX2 oncogene remodels the cytoskeleton through activation of the ephrin pathway

Synovial sarcoma is a soft tissue cancer associated with a recurrent t(X:18) translocation that generates one of two fusion proteins, SYT-SSX1 or SYT-SSX2. In this study, we demonstrate that SYT-SSX2 is a unique oncogene. Rather than confer enhanced proliferation on its target cells, SYT-SSX2 instead causes a profound alteration of their architecture. This aberrant morphology included elongation of the cell body and formation of neurite-like extensions. We also observed that cells transduced with SYT-SSX2 often repulsed one another. Notably, cell repulsion is a known component of ephrin signaling. Further analysis of SYT-SSX2-infected cells revealed significant increases in the expression and activation of Eph/ephrin pathway components. On blockade of EphB2 signaling SYT-SSX2 infectants demonstrated significant reversion of the aberrant cytoskeletal phenotype. In addition, we discovered, in parallel, that SYT-SSX2 induced stabilization of the microtubule network accompanied by accumulation of detyrosinated Glu tubulin and nocodazole resistance. Glu tubulin regulation was independent of ephrin signaling. The clinical relevance of these studies was confirmed by abundant expression of both EphB2 and Glu tubulin in SYT-SSX2-positive synovial sarcoma tissues. These results indicate that SYT-SSX2 exerts part of its oncogenic effect by altering cytoskeletal architecture in an Eph-dependent manner and cytoskeletal stability through a concurrent and distinct pathway.

Ephrin-B1 localizes at the slit diaphragm of the glomerular podocyte

Ephs and ephrins are a family of membrane-bound proteins that function as receptor-ligand pairs. Members of the Eph-ephrin-B family have recently been reported to regulate the paracellular permeability of epithelial cells. In this study, we analyzed the expression and the function of ephrin-B1 in glomeruli. Using immunofluorescence (IF), we found that ephrin-B1 was expressed along the glomerular capillary loop. Immunoelectron microscopy revealed that ephrin-B1 expression was restricted at the slit diaphragm. Dual labeled IF showed ephrin-B1 colocalized with the slit diaphragm proteins nephrin and CD2-associated protein. Ephrin-B1 colocalized with nephrin at the late capillary loop stage of kidney development. Additionally, injection of rats with a nephritogenic anti-nephrin antibody (ANA) reduced ephrin-B1 expression. When podocytes were cultured in vitro, they extruded processes that co-stained for ephrin-B1 and for CD2-associated protein. When these podocytes were treated in culture with small interfering RNA for ephrin-B1, CD2-associated protein was reduced in the processes, with a remaining faint perinuclear staining. We suggest that ephrin-B1 has a role in maintaining barrier function at the slit diaphragm.

Marked disturbance of calcium homeostasis in mice with targeted disruption of the Trpv6 calcium channel gene

We report the phenotype of mice with targeted disruption of the Trpv6 (Trpv6 KO) epithelial calcium channel. The mice exhibit disordered Ca(2+) homeostasis, including defective intestinal Ca(2+) absorption, increased urinary Ca(2+) excretion, decreased BMD, deficient weight gain, and reduced fertility. Although our Trpv6 KO affects the closely adjacent EphB6 gene, the phenotype reported here is not related to EphB6 dysfunction.

INTRODUCTION

The mechanisms underlying intestinal Ca(2+) absorption are crucial for overall Ca(2+) homeostasis, because diet is the only source of all new Ca(2+) in the body. Trpv6 encodes a Ca(2+)-permeable cation channel responsible for vitamin D-dependent intestinal Ca(2+) absorption. Trpv6 is expressed in the intestine and also in the skin, placenta, kidney, and exocrine organs.

MATERIALS AND METHODS

To determine the in vivo function of TRPV6, we generated mice with targeted disruption of the Trpv6 (Trpv6 KO) gene.

RESULTS

Trpv6 KO mice are viable but exhibit disordered Ca(2+) homeostasis, including a 60% decrease in intestinal Ca(2+) absorption, deficient weight gain, decreased BMD, and reduced fertility. When kept on a regular (1% Ca(2+)) diet, Trpv6 KO mice have deficient intestinal Ca(2+) absorption, despite elevated levels of serum PTH (3.8-fold) and 1,25-dihydroxyvitamin D (2.4-fold). They also have decreased urinary osmolality and increased Ca(2+) excretion. Their serum Ca(2+) is normal, but when challenged with a low (0.25%) Ca(2+) diet, Trpv6 KO mice fail to further increase serum PTH and vitamin D, ultimately developing hypocalcemia. Trpv6 KO mice have normal urinary deoxypyridinoline excretion, although exhibiting a 9.3% reduction in femoral mineral density at 2 months of age, which is not restored by treatment for 1 month with a high (2%) Ca(2+) "rescue" diet. In addition to their deranged Ca(2+) homeostasis, the skin of Trpv6 KO mice has fewer and thinner layers of stratum corneum, decreased total Ca(2+) content, and loss of the normal Ca(2+) gradient. Twenty percent of all Trpv6 KO animals develop alopecia and dermatitis.

CONCLUSIONS

Trpv6 KO mice exhibit an array of abnormalities in multiple tissues/organs. At least some of these are caused by tissue-specific mechanisms. In addition, the kidneys and bones of Trpv6 KO mice do not respond to their elevated levels of PTH and 1,25-dihydroxyvitamin D. These data indicate that the TRPV6 channel plays an important role in Ca(2+) homeostasis and in other tissues not directly involved in this process.

The EphB4 receptor-tyrosine kinase promotes the migration of melanoma cells through Rho-mediated actin cytoskeleton reorganization

Several studies have reported the up-regulation of EphB receptor-tyrosine kinases and ephrin-B ligands in a variety of tumors, suggesting a functional relation between EphB/ephrin-B signaling and tumor progression. The ability of the EphB receptors to regulate cell migration and promote angiogenesis likely contributes to tumor progression and metastasis. Here we show that EphB receptors, and especially EphB4, regulate the migration of murine melanoma cells. Highly malignant melanoma cells express the highest levels of EphB4 receptor and migrate faster than less malignant melanoma cells. Furthermore, inhibition of EphB receptor forward signaling by overexpression of a form of EphB4 lacking the cytoplasmic portion or by treatment with competitively acting soluble EphB2-Fc results in slower melanoma cell migration. In contrast, overexpression of active EphB4 significantly enhances cell migration. The effects of EphB4 receptor on cell migration and cell morphology require its kinase activity because the inhibition of EphB4 kinase activity by overexpression of kinase dead EphB4 inhibits cell migration and affects the organization of actin cytoskeleton. Activation of EphB4 receptor with its ligand ephrin-B2-Fc enhances the migratory ability of melanoma cells and increases RhoA activity, whereas inhibiting EphB receptor forward signaling decreases RhoA activity. Moreover, expression of dominant negative RhoA blocks the effects of active EphB4 on cell migration and actin organization. These data suggest that EphB4 forward signaling contributes to the high migratory ability of invasive melanoma cells by influencing RhoA-mediated actin cytoskeleton reorganization.