Overexpression of EPHA2 receptor destabilizes adherens junctions via a RhoA-dependent mechanism

Abstract

EPHA2 receptor tyrosine kinase is overexpressed in several human cancer types and promotes malignancy. However, the mechanisms by which EPHA2 promotes tumor progression are not completely understood. Here we report that overexpression of a wild-type EPHA2, but not a signaling-defective cytoplasmic truncation mutant (ΔC), in human mammary epithelial cells weakens E-cadherin-mediated cell-cell adhesion. Interestingly, the total level of cadherins and the composition of the adherens junction complexes were not affected, nor was the tyrosine phosphorylation of the cadherin complex components changed. By contrast, RhoA GTPase activity was significantly affected by modulating the EPHA2 activity in MCF-10A cells. Treatment with a ROCK kinase inhibitor rescued cell-cell adhesion defects in EPHA2-overexpressing cells, whereas expression of constitutively activated Rho disrupted adherens junctions in ΔC-expressing cells. EPHA2-dependent Rho activation and destabilization of adherens junctions appeared to be regulated via a signaling pathway involving Src kinase, low molecular weight phosphotyrosine phosphatase (LMW-PTP) and p190 RhoGAP. EPHA2 interacted with both Src and LMW-PTP, and the interactions increased in EPHA2-overexpressing cells. In addition, LMW-PTP phosphatase activity was elevated, and this elevation was accompanied by a decrease in tyrosine phosphorylation of p190 RhoGAP and destabilization of cell-cell adhesion. Expression of either a dominant negative LMW-PTP mutant, C12S, or a wild-type p190 RhoGAP rescued adhesion defects in EPHA2-overexpressing cells. Together, these data suggest that EPHA2 promotes tumor malignancy through a mechanism involving RhoA-dependent destabilization of adherens junctions.

Major Role of Epidermal Growth Factor Receptor and Src Kinases in Promoting Oxidative Stress-dependent Loss of Adhesion and Apoptosis in Epithelial Cells

“…oxidant-induced activation of Src and EGFR leading to hyper-phosphorylation of AJ proteins (E-cadherin, catenins, cortactin, and afadin), junctional disruption, and cell de-adhesion. A previous study also showed that overexpression of ephrin type A2 receptor (also identified herein) can destabilize AJs via a Src-and RhoA-dependent mechanism (33). Thus, hyper-activation of receptor tyrosine kinases other than EGFR may also promote loss of adhesion.…”

Eph receptor and ephrin function in breast, gut, and skin epithelia

“…48,70 Similarly, EphA2 overexpression was capable of disrupting adherens junctions through a RhoA-mediated mechanism in breast epithelial cells but, in this case, without altering adherens junction protein or phosphorylation levels. 74 Since 48 This migratory phenotype also depended on a serine 897 residue present on the EphA2 cytoplasmic tail, a site directly phosphorylated by Akt in the absence of ephrin binding. 76,77 EphA2 and Akt signaling may also intersect in normal mammary epithelial development since loss of Akt1 and Akt2 in mice disrupted expansion of the epithelial mammary tree during pregnancy and lactation similar to EphA2 loss.…”

EphA2 overexpression promotes ovarian cancer growth

“…7,9,42,43 A recent study has shown that overexpression of EphA2 destabilizes adherens junctions via a RhoA-dependent mechanism. 44 EphA2 has been also shown to promote tumorigenesis by enhancing angiogenesis. The effects on angiogenesis may be direct (EphA2 overexpression has been noted in angiogenic blood vessels and may contribute to vasculogenic mimicry) 18 or indirect (role in VEGF mediated angiogenesis).…”