Our current research interests are aimed toward examining the mechanism by which Eph receptor tyrosine kinases and their ephrin ligands signal events affecting cell-cell adhesion and morphogenetic movements. From the elucidation of these signal transduction pathways we may improve our understanding of oncogenesis. The cell-cell adhesion system plays a major role in normal development and morphogenesis. Inactivation of this adhesion system is thought to play a critical role in cancer invasion and metastasis. The Xenopus embryo is well suited for investigations of these processes because the frog has a well characterized and invariant cell fate map and cell lineage can be easily traced during experiments. Mutant receptors, ligands, and other proteins can be ectopically expressed in embryos. Thus, their effects on signal transduction, motility, and differentiation can be assessed morphologically and histologically as well as biochemically in a developing vertebrate. Our laboratory is currently investigating the role of the Xenopus Eph receptor tyrosine kinases and ephrinB transmembrane ligands in cell signaling and function using the Xenopus oocyte and embryo systems, as well as human cultured cell lines. At present, our emphasis is placed upon the mechanism by which these Eph family members send signals affecting morphogenetic movements. Members of the Eph family have been implicated in regulating numerous developmental processes and have been found to be de-regulated in metastatic cancers, for example, prostate, ovarian, breast, colon, neuroblastoma, lung, and melanoma. Our laboratory has continued these studies examining proximal and distal signaling from ephrinB1 that controls cell adhesion and cell movement. We recently found evidence that ephrinB1 signals via its intracellular domain to control retinal progenitor movement into the eye field by interacting with Dishevelled (dsh), and co-opting the planar cell polarity (PCP) pathway. Using biochemical analysis and gain or loss of function experiments, our data suggest that dsh associates with ephrinB1 and mediates ephrinB1 signaling via downstream members of the PCP pathway during eye field formation. thus, we have used the eye field as a model system for understanding how ephrinB1 controls cell movement. Most recently we have examined the mechanisms by which ephrinB1 affects cell-cell junctions. A body of evidence is emerging that shows a requirement for ephrin ligands in the proper migration of cells, and the formation of cell and tissue boundaries. These processes are dependent on the cellcell adhesion system, which plays a crucial role in normal morphogenetic processes during development, as well as in invasion and metastasis19. Although ephrinB ligands are bi-directional signalling molecules, the precise mechanism by which ephrinB1 signals through its intracellular domain to regulate cell-cell adhesion in epithelial cells remains unclear. Here, we present evidence that ephrinB1 associates with the Par polarity complex protein Par-6 (a scaffold protein required for establishing tight junctions) and can compete with the small GTPase Cdc42 for association with Par-6. This competition causes inactivation of the Par complex, resulting in the loss of tight junctions. Moreover, the interaction between ephrinB1 and Par-6 is disrupted by tyrosine phosphorylation of the intracellular domain of ephrinB1. Thus, we have identified a mechanism by which ephrinB1 signalling regulates cell-cell junctions in epithelial cells, and this may influence how we devise therapeutic interventions regarding these molecules in metastatic disease.

National Institute of Health (NIH)
National Cancer Institute (NCI)
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National Cancer Institute Division of Basic Sciences
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Hwang, Yoo-Seok; Daar, Ira O (2017) A frog's view of EphrinB signaling. Genesis 55:
Gaur, Shailly; Mandelbaum, Max; Herold, Mona et al. (2016) Neural transcription factors bias cleavage stage blastomeres to give rise to neural ectoderm. Genesis 54:334-49
Lu, Quanlong; Insinna, Christine; Ott, Carolyn et al. (2015) Early steps in primary cilium assembly require EHD1/EHD3-dependent ciliary vesicle formation. Nat Cell Biol 17:228-240
Cho, Hee Jun; Hwang, Yoo-Seok; Mood, Kathleen et al. (2014) EphrinB1 interacts with CNK1 and promotes cell migration through c-Jun N-terminal kinase (JNK) activation. J Biol Chem 289:18556-68
Ji, Yon Ju; Hwang, Yoo-Seok; Mood, Kathleen et al. (2014) EphrinB2 affects apical constriction in Xenopus embryos and is regulated by ADAM10 and flotillin-1. Nat Commun 5:3516
Hwang, Yoo-Seok; Lee, Hyun-Shik; Kamata, Teddy et al. (2013) The Smurf ubiquitin ligases regulate tissue separation via antagonistic interactions with ephrinB1. Genes Dev 27:491-503
Singh, Arvinder; Winterbottom, Emily F; Ji, Yon Ju et al. (2013) Abelson interactor 1 (ABI1) and its interaction with Wiskott-Aldrich syndrome protein (wasp) are critical for proper eye formation in Xenopus embryos. J Biol Chem 288:14135-46
Klein, Steven L; Neilson, Karen M; Orban, John et al. (2013) Conserved structural domains in FoxD4L1, a neural forkhead box transcription factor, are required to repress or activate target genes. PLoS One 8:e61845
Daar, Ira O (2012) Human cancer. Preface. Adv Cancer Res 114:xi
Lee, Hyun-Shik; Sokol, Sergei Y; Moody, Sally A et al. (2012) Using 32-cell stage Xenopus embryos to probe PCP signaling. Methods Mol Biol 839:91-104

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