Inhibition of epidermal growth factor signaling by the cardiac glycoside ouabain in medulloblastoma

Abstract

Epidermal growth factor (EGF) signaling regulates cell growth, proliferation, and differentiation. Upon receptor binding, EGF triggers cascades of downstream signaling, including the MAPK and phosphoinositide-3-kinase (PI3K)/Akt signaling pathways. Aberrant expression/activation of EGFR is found in multiple human cancers, including medulloblastoma, the most prevalent pediatric brain cancer, and often has been associated with metastasis, poor prognosis, and resistance to chemotherapy. Na,K-ATPase is an ion pump well known for its role in intracellular ion homeostasis. Recent studies showed that Na,K-ATPase also functions as a signaling platform and revealed a role in EGFR, MAPK, and PI3K signaling. While both EGFR and Na,K-ATPase seem to modulate similar signaling pathways, cardiac glycosides that are steroid-like inhibitors of Na,K-ATPase, exhibit antiproliferative and proapoptotic properties in cancer cells. Thus, we sought to better understand the relationship between EGF and cardiac glycoside signaling. Here, we show that in medulloblastoma cells, both EGF and ouabain activate Erk1/2 and PI3K/Akt signaling. Nevertheless, in medulloblastoma cells ouabain did not transactivate EGFR as has been reported in various other cell lines. Indeed, ouabain inhibited EGF-induced Erk1/2 and Akt activation and, moreover, prevented EGF-induced formation of actin stress fibers and cell motility, probably by activating a stress signaling response. Na,K-ATPase has been proposed to act as a signaling scaffold and our studies suggest that in medulloblastoma cells Na,K-ATPase might act as a check point to integrate EGF-associated signaling pathways. Thus, Na,K-ATPase might serve as a valid target to develop novel therapeutic approaches in tumors with aberrant activation of the EGFR signaling cascades.

Synthesizing Signaling Pathways from Temporal Phosphoproteomic Data

“…ATP1A1 is the catalytic subunit of Na + ,K + -ATPase, an ion pump that also plays a role in signal transduction when inhibited by ouabain (Reinhard et al, 2013), making it a candidate therapeutic target for diseases such as medulloblastoma (Wolle et al, 2014). MAPK1 26, 2017; phosphorylates ATP1A1 in response to insulin (Al-Khalili et al, 2004) and proinsulinconnecting peptide (C-peptide) (Zhong et al, 2004) stimulation, potentially on T81.…”

Targeting Na+/K+‐translocating adenosine triphosphatase in cancer treatment

“…found that treatment of digoxin through the inhibition of hypoxia‐inducible factor (HIF)1 α inhibited mesenchymal transition and invasion in glioblastoma SNB75 and U87 cells. Wolle et al . reported that ouabain did not transactivate EGFR but inhibited its effect via promotion of the activation of PI3K/Akt and ERK1/2 in medulloblastoma cells.…”

Fenofibrate inhibits tumour intravasation by several independent mechanisms in a 3-dimensional co-culture model

“…For example, the overexpression of voltage gated K + channels was observed in breast-, colon-and prostate cancer and medullablastoma (11,12) and their inhibition attenuates neuroblastoma and endothelial cell migration (13,14). Consistently, the Na + /K + -ATPase inhibitor ouabain (also known as g-strophanthin) attenuates medullablastoma cell migration and the localisation of Tyr397-phosphorylated FAK to lammelipodia (15). Furthermore, the voltage gated K + v1.2 channel induces directional migration of mesenchymal bone marrow or CHO cells through phosphorylation of Tyr397-FAK (16) as well as wound healing in an animal model (17).…”