Aberrant expression of erythropoietin-producing hepatocellular carcinoma cell (EPH) receptors has been reported in a variety of human cancer types. In addition to modulating cell proliferation and migration, EPH receptors are also involved in tumor progression. The transcriptional activation and silencing of EPH receptors are also associated with tumorigenesis. However, the mechanisms underlying the involvement of EPH receptors in tumorigenesis have not been completely deciphered. We have investigated and described the role of EPHB6, a kinase-deficient receptor, in modulating the abundance of cadherin 17 and activation of other intracellular signaling proteins. We previously showed that EPHB6 alters the tumor phenotype of breast carcinoma cells. However, the mechanisms underlying these phenotypic changes had not previously been investigated. Herein we demonstrated the downstream effects of EPHB6 expression on the abundance of cadherin 17, mitogen-activated protein kinase (MEK2), extracellular signal-regulated kinase (ERK), phospho-ERK, β-catenin, phospho- glycogen synthase kinase 3 beta (GSK3β) (ser21/9), cell morphology and actin cytoskeleton. These comparisons were made between EPHB6-deficient MDA-MB-231 cells transfected with an empty pcDNA3 vector and cells stably transfected with an expression construct of EPHB6. The results indicate elevated levels of MEK2 and phospho-ERK. While there was no change in the amount of ERK, the abundance of cadherin 17, β-catenin and phospho-GSK3β was significantly reduced in EPHB6-transfected cells. These studies clearly demonstrate an inverse relationship between the levels of phospho-ERK and the abundance of cadherin 17, β-catenin and phospho-GSK3β in EPHB6-expressing MDA-MB-231 cells. From these data we conclude that EPHB6-mediated alterations arise due to changes in abundance and localization of cadherin 17 and activation of WNT signaling pathway. Transcriptional silencing of EPHB6 in native MDA-MB-231 cells and consequent effects on cadherin 17 and WNT pathway may, thus, be responsible for the invasive behavior of these cells.
Keywords: CDH17; EPHB6; ERK; GSK3β; WNT; breast carcinoma; cadherin 17; β-catenin.
Copyright© 2014, International Institute of Anticancer Research (Dr. John G. Delinasios), All rights reserved.