M. Haas et al., Involvement of Src and epidermal growth factor receptor in the signal-transducing function of Na+/K+-ATPase, J BIOL CHEM, 275(36), 2000, pp. 27832-27837
Nontoxic concentrations of ouabain, causing partial inhibition of the cardi
ac myocyte Na+/K+-ATPase, induce hypertrophy and several growth-related gen
es through signal pathways that include the activation of Ras and p42/44 mi
togen-activated protein kinase (MAPK). The aim of this work was to examine
the ouabain-induced events upstream of the Ras/MAPK cascade. Treatment of m
yocytes with genistein antagonized ouabain-induced activation of the MAPK,
suggesting that protein tyrosine phosphorylation has a role. Tyrosine phosp
horylation of several myocyte proteins was increased rapidly upon cell expo
sure to ouabain, Lowering of extracellular K+ had a similar ouabain-like ef
fect. Ouabain also increased protein tyrosine phosphorylation in A7r5, HeLa
, and L929 cells. In cardiac myocytes and A7r5 cells, herbimycin A antagoni
zed the ouabain-induced increase in protein tyrosine phosphorylation and MA
PK activation. In both cell types, ouabain stimulated Src kinase activity,
Src translocation to the Triton-insoluble fraction, Src association with th
e epidermal growth factor receptor, and the tyrosine phosphorylation of thi
s receptor on site(s) other than its major autophosphorylation site, Tyr(11
73). The findings suggest that (a) the ouabain-induced activation of Src an
d the Src-induced phosphorylation of the growth factor receptor provide the
scaffolding for the recruitment of adaptor proteins and Ras and the activa
tion 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.