Mechanisms of Cross-talk Between EphrinB and Alternate Signaling Pathways

在正常发育期间，许多组织的祖细胞经历多能性、上皮-间充质转化、增殖、迁移和分化的进行性限制。这些事件中的大多数（如果不是全部）涉及细胞-细胞和细胞-基质粘附的修饰，并且这些粘附系统的异常修饰通常与肿瘤的形成相关。受体酪氨酸激酶的Eph家族及其配体肝配蛋白在多种癌症中经常过表达，包括乳腺癌、小细胞肺癌和胃肠癌、黑色素瘤和神经母细胞瘤。使用非洲爪蟾胚胎系统，我们已经证明，ephrinB的细胞内结构域介导的信号传导影响细胞-细胞粘附，并且这种活性可以通过与活化的FGF受体的相互作用来调节。 跨膜ephrinB 1蛋白是一种双向信号分子，通过其胞质结构域发出信号以促进细胞运动进入眼区，而成纤维细胞生长因子受体（FGFR）的激活抑制这些运动和视网膜命运。在非洲爪蟾胚胎中，ephrinB 1通过与支架蛋白Dishevelled（Dsh）的相互作用在视网膜祖细胞移动到眼区中发挥作用。然而，FGFR调节这种细胞运动的机制尚不清楚。在这里，我们提供了证据表明FGFR诱导的视网膜命运抑制依赖于埃甫蛋白B 1细胞内结构域内的磷酸化。我们证明了ephrinB 1内酪氨酸324和325的磷酸化破坏了ephrinB 1/Dsh相互作用，从而调节依赖于平面细胞极性（PCP）途径的视网膜祖细胞运动。这些结果为FGF信号如何调节ephrinB 1对眼内视网膜祖细胞运动的控制提供了机制性的见解。

During normal development progenitor cells of many tissues undergo progressive restriction of pluripotency, epithelial-to-mesenchymal transition, proliferation, migration, and differentiation. Most, if not all, of these events involve modifications of cell-cell and cell-matrix adhesion, and abnormal modifications of these adhesion systems are often associated with the formation of tumors. The Eph family of receptor tyrosine kinases and their ligands, the ephrins, are frequently over-expressed in a wide variety of cancers, including breast, small-cell lung and gastrointestinal cancers, melanomas, and neuroblastomas. 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 interaction with an activated FGF receptor. The transmembrane ephrinB1 protein is a bi-directional signaling molecule that signals through its cytoplasmic domain to promote cellular movements into the eye field, whereas activation of the fibroblast growth factor receptor (FGFR) represses these movements and retinal fate. In Xenopus embryos, ephrinB1 plays a role in retinal progenitor cell movement into the eye field through an interaction with the scaffold protein Dishevelled (Dsh). However, the mechanism by which the FGFR may regulate this cell movement is unknown. Here we present evidence that FGFR-induced repression of retinal fate is dependent upon phosphorylation within the intracellular domain of ephrinB1. We demonstrate that phosphorylation of tyrosines 324 and 325 within ephrinB1 disrupts the ephrinB1/Dsh interaction, thus modulating retinal progenitor movement that is dependent on the planar cell polarity (PCP) pathway. These results provide mechanistic insight into how FGF signaling modulates ephrinB1 control of retinal progenitor movement within the eye field.