Cardiotonic steroids stabilize regulator of G protein signaling 2 protein levels.

Regulator of G protein signaling 2 (RGS2), a G(q)-specific GTPase-activating protein, is strongly implicated in cardiovascular function. RGS2(-/-) mice are hypertensive and prone to heart failure, and several rare human mutations that accelerate RGS2 degradation have been identified among patients with hypertension. Therefore, pharmacological up-regulation of RGS2 protein levels might be beneficial. We used a β-galactosidase complementation method to screen several thousand compounds with known pharmacological functions for those that increased RGS2 protein levels. Several cardiotonic steroids (CTSs), including ouabain and digoxin, increased RGS2 but not RGS4 protein levels. CTSs increased RGS2 protein levels through a post-transcriptional mechanism, by slowing protein degradation. RGS2 mRNA levels in primary vascular smooth muscle cells were unaffected by CTS treatment, whereas protein levels were increased 2- to 3-fold. Na(+)/K(+)-ATPase was required for the increase in RGS2 protein levels, because the effect was lost in Na(+)/K(+)-ATPase-knockdown cells. Furthermore, we demonstrated that CTS-induced increases in RGS2 levels were functional and reduced receptor-stimulated, G(q)-dependent, extracellular signal-regulated kinase phosphorylation. Finally, we showed that in vivo treatment with digoxin led to increased RGS2 protein levels in heart and kidney. CTS-induced increases in RGS2 protein levels and function might modify several deleterious mechanisms in hypertension and heart failure. This novel CTS mechanism might contribute to the beneficial actions of low-dose digoxin treatment in heart failure. Our results support the concept of small-molecule modulation of RGS2 protein levels as a new strategy for cardiovascular therapy.