Involvement of Src and Epidermal Growth Factor Receptor in the Signal-transducing Function of Na+/K+-ATPase

Abstract

Nontoxic concentrations of ouabain, causing partial inhibition of the cardiac myocyte Na(+)/K(+)-ATPase, induce hypertrophy and several growth-related genes through signal pathways that include the activation of Ras and p42/44 mitogen-activated protein kinase (MAPK). The aim of this work was to examine the ouabain-induced events upstream of the Ras/MAPK cascade. Treatment of myocytes with genistein antagonized ouabain-induced activation of the MAPK, suggesting that protein tyrosine phosphorylation has a role. Tyrosine phosphorylation of several myocyte proteins was increased rapidly upon cell exposure to ouabain. Lowering of extracellular K(+) had a similar ouabain-like effect. Ouabain also increased protein tyrosine phosphorylation in A7r5, HeLa, and L929 cells. In cardiac myocytes and A7r5 cells, herbimycin A antagonized the ouabain-induced increase in protein tyrosine phosphorylation and MAPK activation. In both cell types, ouabain stimulated Src kinase activity, Src translocation to the Triton-insoluble fraction, Src association with the epidermal growth factor receptor, and the tyrosine phosphorylation of this receptor on site(s) other than its major autophosphorylation site, Tyr(1173). The findings suggest that (a) the ouabain-induced activation of Src and the Src-induced phosphorylation of the growth factor receptor provide the scaffolding for the recruitment of adaptor proteins and Ras and the activation of Ras/MAPK cascade; and (b) the activation of such pathways may be a common feature of the signal-transducing function of Na(+)/K(+)-ATPase in most cells.

Na,K-ATPase signal transduction triggers CREB activation and dendritic growth

“…The other mechanism suggests that inhibition of Na,K-ATPase pumping activity is not in itself required for a signaling event to occur; instead, Na,K-ATPase is proposed to function via a microdomain where ouabain-induced signaling occurs via physical association of Na,K-ATPase with a host of binding partners. Na,K-ATPase has been reported to associate with the inositol 1,4,5-trisphosphate receptor to generate intracellular Ca 2ϩ oscillations (44) and to form a complex with the epidermal growth factor receptor, leading to MAP kinase activation (16). Dendritic growth via Na,K-ATPase signal transduction might be modulated by either or both of these signaling pathways.…”

“…Previous reports indicate that Na,K-ATPase signal transduction stimulates proliferation in smooth muscle cells (11) and apoptosis in prostate cancer cells (12). Ouabain, an endogenously synthesized hormone (13,14), is Na,K-ATPase's ligand and forms a hormone-receptor complex capable of inducing mitogen-activated protein (MAP) kinase phosphorylation (15,16) and intracellular Ca 2ϩ signaling (17)(18)(19).…”

Expression of Mutant α1 Na/K-ATPase Defective in Conformational Transition Attenuates Src-mediated Signal Transduction*

“…The clue suggesting the ␣1 Na/K-ATPase⅐Src interaction came from our early studies of ouabain-induced protein tyrosine phosphorylation (4). These studies demonstrated that ouabain activated Src by stimulating the phosphorylation of Tyr-418 and that the activation of Src was required for ouabaininduced transactivation of EGF receptors and many other protein kinase and lipase cascades (4,8,31).…”

Transactivation of the epidermal growth factor receptor in responses to myocardial stress and cardioprotection

“…Additionlly, interaction of ouabain with cardiomyocyte Na + /K + ATPase triggers EGFR transactivation and Ras/ERK1/2 activation (Haas et al, 2000), with PKC essential to this signalling (Mohammadi et al, 2001), though whether up-and/or downstream of EGFR is untested.…”