2048

EPHB2

EphB2, a receptor tyrosine kinase for ephrin ligands, is overexpressed in various cancers and plays an important role in tumor progression. However, the expression and functions of EphB2 in cervical cancer remain unknown. In this study, we performed immunohistochemistry in clinical cervical specimens and found that EphB2 was overexpressed in the cervical cancer specimens, and its expression correlated with cancer progression. The percentage of EphB2-positive cells increased gradually from 28% in the normal cervix to 40% in high-grade squamous intraepithelial lesions, and ultimately to 69.8% in squamous cell carcinomas (P < .05). We overexpressed EphB2 in HeLa cells and silenced EphB2 in cervical cancer (C33A) cells, which expressed low and high levels of EphB2, respectively. Exogenous EphB2 promoted cell migration, invasion, and an epithelial-mesenchymal transition (EMT) signature, which is a complex process that occurs during organogenesis and cancer metastasis, whereas EphB2 silencing had the opposite effect (P < .05). Furthermore, HeLa cells with exogenous EphB2 exhibited a stem cell-like state that promoted tumorsphere formation in vitro and exhibited tumorigenesis potential in vivo (P < .05), whereas EphB2 silencing in C33A cells inhibited these stem cell properties (P < .05). In addition, we investigated the intracellular signaling pathways in cervical cancer and found that R-Ras expression correlated positively with EphB2 in clinical samples, and its activity was regulated by EphB2 in cervical cancer. These findings demonstrate that EphB2 plays an important role in cervical cancer progression by orchestrating an EMT program through R-Ras activation.CI - (c) 2014.

Transcriptional silencing is a major cause for the inactivation of tumor suppressor genes, however, the underlying mechanisms are only poorly understood. The EPHB2 gene encodes a receptor tyrosine kinase that controls epithelial cell migration and allocation in intestinal crypts. Through its ability to restrict cell spreading, EPHB2 functions as a tumor suppressor in colorectal cancer whose expression is frequently lost as tumors progress to the carcinoma stage. Previously we reported that EPHB2 expression depends on a transcriptional enhancer whose activity is diminished in EPHB2 non-expressing cells. Here we investigated the mechanisms that lead to EPHB2 enhancer inactivation. We show that expression of EPHB2 and SNAIL1 - an inducer of epithelial-mesenchymal transition (EMT) - is anti-correlated in colorectal cancer cell lines and tumors. In a cellular model of Snail1-induced EMT, we observe that features of active chromatin at the EPHB2 enhancer are diminished upon expression of murine Snail1. We identify the transcription factors FOXA1, MYB, CDX2 and TCF7L2 as EPHB2 enhancer factors and demonstrate that Snail1 indirectly inactivates the EPHB2 enhancer by downregulation of FOXA1 and MYB. In addition, Snail1 induces the expression of Lymphoid enhancer factor 1 (LEF1) which competitively displaces TCF7L2 from the EPHB2 enhancer. In contrast to TCF7L2, however, LEF1 appears to repress the EPHB2 enhancer. Our findings underscore the importance of transcriptional enhancers for gene regulation under physiological and pathological conditions and show that SNAIL1 employs a combinatorial mechanism to inactivate the EPHB2 enhancer based on activator deprivation and competitive displacement of transcription factors.CI - Copyright (c) 2016 Elsevier B.V. All rights reserved.