ESSAY Molecular Reproduction & Development 83:12–18 (2016) Role of EFNB2/EPHB4 Signaling in Spiral Artery Development During Pregnancy: An Appraisal HONGMEI DONG,* CHAORAN YU, JIAO MU, JI ZHANG, AND WEI LIN Department of Forensic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, People’s Republic of China SUMMARY EFNB2 and EPHB4, which belong to a large tyrosine kinase receptor superfamily, are molecular markers of arterial and venous blood vessels, respectively. EFNB2/ EPHB4 signaling plays an important role in physiological and pathological angiogen- esis, and its role in tumor vessel development has been extensively studied. [W]e hypothesize that changing Pregnancy and tumors share similar features, including continuous cell proliferation the distinct spatiotemporal and increased demand for a blood supply. Our previous studies showed that Efnb2 expression of EFNB2/ Ephb4 and were expressed dynamically in the spiral arteries, uterine natural killer EPHB4...contributes to spiral À cells, and trophoblasts during mouse gestation Days 6.5 12.5. Moreover, uterine artery remodeling. natural killer cells and trophoblasts are required for the modification of spiral arteries. Oxygen tension within the pregnant uterus, which contributes to the vascular development, also affects EFNB2 and EPHB4 expression. Considering the role of ÃCorresponding author: EFNB2/EPHB4 signaling in embryonic and tumor vascular development, and its Department of Forensic Medicine Tongji Medical College of dynamic expression in the decidua and placenta, we hypothesize that EFNB2 and Huazhong University of EPHB4 are involved in the regulation of spiral artery remodeling. Investigating this Science and Technology hypothesis will help clarify the mechanisms of pathological pregnancy that may 13 Hangkong Road Wuhan, Hubei 430030, P. R. China. underlie abnormal spiral artery development. Email: [email protected] Grant sponsor: National Natural Science Foundation of China; Grant numbers: 30872323, 81471821; Grant sponsor: Scientific Research Foundation for the Returned Overseas Chinese Scholars of the State Education Ministry Mol. Reprod. Dev. 83: 12À18, 2016. ß 2015 Wiley Periodicals, Inc. Published online 13 November 2015 in Wiley Online Library (wileyonlinelibrary.com). Received 6 December 2014; Accepted 22 October 2015 DOI 10.1002/mrd.22593 INTRODUCTION Erythropoietin-producing hepatocellular receptor B4 (EPHB4) and Eph-family receptor-interacting protein B2 (EFNB2) are members of the receptor tyrosine kinase superfamily. EFNB2 and EPHB4 represent arterial and Abbreviations: ANGPT, angiopoietin; EFNB2, Eph family receptor interact- venous markers, respectively (le Noble et al., 2004; Adams ing protein B2; EPHB4, erythropoietin producing hepatocellular receptor; HIF1A, and Alitalo, 2007). EFNB2 is specifically expressed in hypoxia inducible factor 1 alpha; HTR 8/SVneo cells, extravillous trophoblastic cell line; HUVECs, human umbilical vein endothelial cells; PGF, placental growth endothelial cells, vascular smooth muscle cells, and peri- factor; uNK cell, uterine natural killer cell; VEGF, vascular endothelial growth cytes of the artery, whereas EPHB4 is expressed in factor ß 2015 WILEY PERIODICALS, INC. ROLE OF EFNB2/EPHB4 SIGNALING IN SPIRAL ARTERY DEVELOPMENT endothelial cells of all diameters of the venous lineage with VEGF and other angiogenic factors to modulate an- (Lawson and Weinstein, 2002; Hirashima and Suda giogenic processes. 2006). Both EFNB2 and EPHB4 are membrane-bound proteins composed of extracellular, transmembrane, and intracellular domains. Cell-cell contact is required for their EFNB2/EPHB4 SIGNAL TRANSDUCTION IN interaction, which induces bidirectional signaling in both TUMOR ANGIOGENESIS receptor- and ligand-expressing cells: EFNB2 activates the downstream EPHB4 receptor in ‘‘forward’’ signaling, The overexpression of Eph family members has been whereas EPHB4 signaling through EFNB2 is ‘‘reverse’’ documented in a variety of human cancers. EPHB2 and signaling (Fuller et al., 2003; Hamada et al., 2003). EPHB4 abundance, for example, is associated with the EFNB2 is the ligand for EPHB2, EPHB4, and other kinases, histological grade, differentiation, progression, metastatic whereas EPHB4 can only be activated by EFNB2. Bidirec- status, and prognosis of cancer (Alam et al., 2007; Kumar tional EFNB2/EPHB4 signaling results in attractive and et al., 2009). The correlation between EFNB2/EPHB4 and repulsive processes that guide cell adhesion, migration, tumors, however, is not entirely consistent: Lee et al. and repulsionÀÀparticularly in tissue boundary formation (2005) reported that EPHB4 expression in vivo was sig- (Poliakov et al., 2004), axonal guidance (Reber et al., nificantly greater in human prostate cancers than in 2007), lymphangiogenesis, and angiogenesis (Mosch matched normal prostate epithelial cells, whereas Berclaz et al., 2010). EFNB2/EPHB4 signaling is regulated by their et al. (2002) showed that loss of EPHB4 expression was abundance on the cell surface and their asymmetric characteristic of human breast carcinoma and correlated distribution. with tumor progression. A role for EFNB2/EPHB4 signal- The angiogenic role of EFNB2/EPHB4 signaling was ing in tumor angiogenesis and growth was also demon- first described in embryonic development. Loss of Efnb2 strated in multiple mouse models (Kertesz et al., 2006; (Wang et al., 1998; Adams et al., 1999) or Ephb4 (Gerety Kimura et al., 2009; Krasnoperov et al., 2010; Abengozar et al., 1999) in mice leads to early embryonic lethality, et al., 2012). due to impaired remodeling of the embryonic vascular Considering the overlapping data that support a role for system. The angiogenesis phenotype of the Efnb2 or EFNB2/EPHB4 signaling in tumor progression, this path- Ephb4 single mutants is also almost indistinguishable, way has been vetted as a potential therapeutic target which further supports their close relationship in vascula- (Kertesz et al., 2006; Abengozar et al., 2012). Inhibition of ture development. EFNB2/EPHB4 signaling suppressed tumor growth in murine tumor xenograft models by preventing endothelial cell migration, adhesion, and tube formation in vitro, and INTERPLAY BETWEEN EFNB2/EPHB4 SIGNALING inhibited the pro-angiogenic effects of VEGF and basic AND OTHER ANGIOGENIC MOLECULES fibroblast growth factor (FGF2) in vivo (Kertesz et al., 2006). Activation of EPHB4 by soluble EFNB2-Fc, on the Pro-angiogenic factors are needed to form a complex, other hand, suppressed the growth of head and neck collaborative network for blood vessel formation. Vascular squamous cell carcinoma xenografts by inducing tumor endothelial growth factor (VEGF) signaling is a key path- vessel maturation (Kimura et al., 2009). The regulatory way that regulates angiogenesis and morphogenesis. For mechanism of EFNB2/EPHB4 signaling on tumor angio- example, VEGF- and angiopoietin-1 (ANGPT1)-induced genesis was investigated further by Erber et al. (2006), proliferation and migration of human umbilical vein endo- who found that tumors overexpressing EPHB4 variants thelial cells (HUVECs) are suppressed by the activation of reorganize the vascular system to achieve parallel vessel endogenous EPHB kinases, via EFNB2-Fc through Ras/ alignment and unidirectional blood flow, whereas control mitogen-activated protein kinase (MAPK) signaling (Kim tumors were characterized by a chaotic microvascular et al., 2002). On the other hand, Martiny-Baron et al. (2010) network. Active EPHB4 signaling was also able to reduce demonstrated that an EPHB4 kinase inhibitor blocks both vascular permeability and decrease edema formation, EPHB4 kinase activity and VEGF-induced angiogenesis, resultinginenlargedbloodvesselsratherthanincreased revealing the intimate relationship between EFNB2 and vessel number to increase blood flow to the tumor. To- VEGF signaling. Indeed, EFNB2 is a likely modulator of gether, the data suggested that enhancing EPHB4 sig- VEGF that functions in all endothelial cells by controlling the naling in tumor endothelial cells does not affect initial internalization and signaling of two VEGF receptors during tumor angiogenesis, but instead markedly influences physiological and pathological angiogenesis (Sawamiphak subsequent morphogenesis and remodeling of the tumor et al., 2010; Wang et al., 2010) as well as an influencing vascular system, similar to observations made in the factor in the expression of angiogenic factors such as developing embryo. Noren et al. (2004) also reported ANGPT1, ANGPT2, and the angiopoietin receptor 2 that EPHB4 promotes vascular formation and remodeling (TEK or TIE2) (Kim et al., 2002; Erber et al., 2006). On via EFNB2. Indeed, the role of EFNB2/EPHB4 signaling in the other hand, VEGF can up-regulate EFNB2 (Mu- tumor vascular morphogenesis, as a modification or re- kouyama et al., 2002) while VEGFA inhibited EPHB4 application of process, is also involved in normal postnatal expression in adult venous endothelial cells (Yang et al., angiogenesis (Zamora et al., 2005; Erber et al., 2006; 2013). Therefore, EFNB2/EPHB4 signaling likely works Davies et al., 2009). Mol. Reprod. Dev. 83:12–18 (2016) 13 Molecular Reproduction & Development DONG ET AL. SPIRAL ARTERY REMODELING AND ITS induced cytotrophoblast invasion in vitro (Zhou et al., MODULATION 2002). Oxygen concentration within the uteroplacental environ- Malignant tumors and implanted embryos both need a ment varies with gestational age (Tuuli et al., 2011), rich blood supply to