Signaling Mechanisms of EphrinB1 in Cell Adhesion, Migration and Invasion

Division Of Basic Sciences - Nci

Investigators

Linked publications, trials & patents

Abstract

Using the Xenopus embryonic system, we have demonstrated that signaling mediated by the intracellular domain of ephrinB affects cell-cell adhesion, and that this activity can be modulated by tyrosine phosphorylation initiated by binding to the extracellular domain of a cognate Eph receptor or by an interaction with an activated FGF receptor. Using the epithelial cells of early-stage Xenopus embryos, we previously showed through loss- and gain-of function approaches that ephrinB1 can regulate cell-cell contacts and tight junctions (Lee et al, Nature Cell Biol. 2008). Although many of our studies allowed us to gain some mechanistic insight into how ephrinBs regulate cell movement and cell-cell boundaries, we understood little of how ephrinBs are regulated. Thus, several years ago, we focused on those issues. In one study we discovered a system of differential interactions between ephrinB1 and the E3 ubiquitin ligases, Smurf1 and Smurf2, that regulates the maintenance of tissue boundaries through the control of ephrinB protein levels (Hwang et al, Genes and Development 2013). In another study examining regulation of ephrinB2, we identified a new ephrinB2 interacting protein, the flotillin-1 scaffold protein, and showed that the presence of this protein is critical to maintain ephrinB2 protein levels. Reduction in ephrinB2 protein due to the loss of flotillin-1 leads to the failure of neural tube closure, an important morphogenetic event (Ji et al, Nature Comm. 2014). We also showed that the small GTPase Rab11 associates with ephrinB1, linking it to the Rab11Fip5 adaptor protein in an endosome recycling complex (Yoon et al, Development, 2021). Rab11Fip5 null and nonsense mutations are associated with Autism Spectrum disorders in humans. We showed that loss of Rab11fip5 causes decreased expression of ephrinB1, leading to reduced cell proliferation and reduction in the size of the embryonic telencephalon. This study provides insight into how ephrinB1 is regulated by the Rab11/Rab11fip5 complex and shows that the ephrinB1 protein is involved in maintaining forebrain size (Yoon et al, Development, 2021). In addition to our interest in cell-cell adhesion, we have focused on the role of ephrinB1 in cell movement. We reported that Dishevelled (Dvl), which is a scaffold central to the Wnt signaling pathway, mediates ephrinB signaling that controls retinal progenitor cell movement into the eye field (Lee et al, Nature Cell Biol. 2006). We discovered that FGFR or Eph-induced phosphorylation of ephrinB1 disrupts the ephrinB1/Dvl interaction, leading to a loss of ephrinB1-induced planar cell polarity (PCP) signaling (Moore et al, Dev Cell 2004; Lee et al, Mol. Biol. Cell 2009). Thus, cross-talk between FGF signaling and the ephrinB1/Dsh/PCP pathway can regulate the movements and positioning of specific progenitor cells during embryogenesis. During the previous review period we extended our studies to examine neural crest migration, which undergoes many of the same processes and hallmarks observed in cancer metastasis. In our studies, we found that ephrinB2 regulates contact inhibition of locomotion (CIL) in migrating neural crests through its association with TBC1d24, a Rab-GAP protein that negatively regulates E-cadherin recycling via Rab35. This association is mediated by the interaction of ephrinB2 with Dvl (Yoon et al, Nature Comm. 2018). These findings importantly bridge two signaling pathways that control cell-cell adhesion and cell migration, while providing significant insight into how ephrinB reverse signaling may regulate contact inhibition of locomotion (CIL), a process critical to collective cell migration and cancer metastasis. As part of our interest in the intersection with the Wnt/PCP pathway, we have directed our attention to ephrinB/Dvl as it plays a critical role in several morphogenetic events. To this end, we initiated a mass spectrometric analysis of ephrinB2 in the neural plate since our previous study indicated that ephrinB2 played a role in neural tube closure (Ji et al Nat. Comm. 2014). Our newest effort provided mechanistic insight into how ephrinB2 along with Wnt4 plays an instructive role in neural tube closure. These experiments led us to the discovery of the WERDS signaling complex that is responsible for this critical embryonic process. Moreover, as part of this mechanism, we made the exciting revelation that ephrinB2 antagonizes Wnt/beta-catenin signaling through a conformational change in the main Wnt signaling scaffold, Dvl. This interaction acts as a switch that changes Dvl from canonical to non-canonical Wnt signaling that is required for apical constriction in the neural tube (Yoon et al, Nat. Comm 2023).