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.