Ouabain-induced signaling and vascular smooth muscle cell proliferation

The hypothesis of this study is that the sodium pump complex acts as an int racellular signal-transducing molecule in canine vascular smooth muscle cel ls through its interaction with other membrane and cytoskeletal proteins. W e have demonstrated that 1 nM ouabain induced transactivation of the epider mal growth factor receptor (EGFR), resulting in increased proliferation and bromodeoxyuridine (BrdUrd) uptake. Immunoprecipitation and Western blottin g showed that the EGFR and Src were phosphorylated within 5 min of 10(-9) M ouabain stimulation. Both ouabain-induced DNA synthesis (BrdUrd uptake) an d MAPK42/44 phosphorylation were inhibited by the Src inhibitor PP2, the EG FR kinase inhibitor AG1478, the tyrosine kinase inhibitor genistein, and th e MEK1 inhibitor PD98059. Ouabain concentrations higher than 1 nM had littl e or no stimulating effect on proliferation or BrdUrd uptake but did minima lly activate ERK1/2. Thus, low concentrations of ouabain, which do not inhi bit the sodium pump sufficiently to perturb the resting cellular ionic mili eu, initiate a transactivational signaling cascade leading to vascular smoo th muscle cell proliferation.