Sodium pump alpha1 and alpha3 subunit isoforms mediate distinct responses to ouabain and are both essential for survival of human neuroblastoma.

Using SK-N-AS human neuroblastoma cells, which co-express the alpha1 and alpha3 isoforms of the sodium pump alpha subunit, we selectively silenced either the alpha1 or alpha3 subunit by means of transfection with small interfering RNA, and investigated cell survival and the cellular response to ouabain. We found that both of the alpha subunits are essential for cell survival, indicating that substitution of one subunit for the other is not sufficient. In the presence of both alpha subunits, ouabain causes sustained activation of extracellular signal-regulated kinases 1 and 2 (Erk1/2). This activation is not affected when the alpha1 subunit is silenced. However, when alpha3 expression is silenced, ouabain-induced activation of Erk1/2 does not occur, even at a high concentration of ouabain (1 microM). Thus, ouabain-induced Erk1/2 activation is mediated in SK-N-AS cells by alpha3 only, and alpha1 does not participate in this event. This is a clear demonstration of selective involvement of a specific sodium pump alpha subunit isoform in ouabain-induced signaling.