Ouabain Binds with High Affinity to the Na,K-ATPase in Human Polycystic Kidney Cells and Induces Extracellular Signal–Regulated Kinase Activation and Cell Proliferation

Abstract

In autosomal dominant polycystic kidney disease (ADPKD), cyst formation and enlargement require proliferation of mural renal epithelial cells and the transepithelial secretion of fluid into the cyst cavity. Na,K-ATPase is essential for solute and water transport in ADPKD cells, and ouabain blocks fluid secretion in these cells. By binding to the Na,K-ATPase, ouabain also induces proliferation in some cell types. Surprisingly, it was found that nanomolar concentrations of ouabain, similar to those circulating in blood, induced ADPKD cell proliferation but had no statistically significant effect on normal human kidney (NHK) cells. Ouabain, acting from the basolateral side of the cells, also caused an increase in the level of phosphorylated extracellular signal-regulated kinases (ERK). Mitogen-activated protein kinase kinase (MEK) inhibitor U0126 blocked ouabain-induced ERK activation and cell proliferation, suggesting that ouabain effect is mediated through the MEK-ERK pathway. In contrast to NHK cells, the dose-response curve for ouabain inhibition of Na,K-ATPase activity indicated that approximately 20% of the enzyme in ADPKD cells exhibits a higher affinity for ouabain. The increased ouabain affinity of ADPKD cells was not due to differences in Na,K-ATPase isoform expression because these cells, like NHK cells, possess only the ␣1 and ␤1 subunits. The ␥ variants of the Na,K-ATPase also are expressed in the cells but are elevated in ADPKD cells. Currently, the basis for the differences in ouabain sensitivity of NHK and ADPKD cells is unknown. It is concluded that ouabain stimulates proliferation in ADPKD cells by binding to the Na,K-ATPase with high affinity and via activation of the MEK-ERK pathway.

The Cleaved Cytoplasmic Tail of Polycystin-1 Regulates Src-Dependent STAT3 Activation

“…19,20 Similarly, ouabain-a hormone that activates EGFR, Src, and mitogen-activated kinase kinase-ERK pathways-stimulates proliferation in ADPKD cyst cells but not in normal renal tubule cells. 56 Overall, our results suggest that accumulation of the cleaved PC1 tail in renal epithelial cells in ADPKD changes their response to cAMP stimuli. Although normal cells would respond by dampening STAT3 activation via EPAC/SOCS3, ADPKD cells respond to cAMP by activating STAT3 via PKA/PC1-p30/Src, resulting in a proliferative response.…”

Potentially Modifiable Factors Affecting the Progression of Autosomal Dominant Polycystic Kidney Disease

“…Atrial natriuretic peptide could have a cystogenic effect via generation of cGMP (20). Cardiotonic steroids induce extracellular signalregulated kinase activation and proliferation of human AD-PKD cyst-derived epithelial cells (18). TGF-␤ plays a role in the development of epithelial-mesenchymal transition and interstitial fibrosis in ADPKD (17).…”

Advances in understanding the role of cardiac glycosides in control of sodium transport in renal tubules

“…In addition to its transporting function, Na C /K C ATPase plays an important role in cell signaling (Xie & Askari 2002). The elegant work from the laboratories of Xie and Askari has elucidated this important role of Na C /K C ATPase that is probably involved in diverse cellular functions and pathophysiological states such as cell growth, hypertrophy, ischemia, development and postnatal maturation of kidneys, and as yet undefined processes (Kometiani et al 1998, 2005, Xie et al 1999, Liu et al 2000,b, Aizman et al 2001, Mohammadi et al 2001, Aizman & Aperia 2003, Andersson et al 2004, Li et al 2006, Liang et al 2006, Aperia 2007, Nguyen et al 2007, Kennedy et al 2008, Tian & Xie 2008, Khodus et al 2011, Brashear et al 2012, Blanco & Wallace 2013, Burlaka et al 2013, Fontana et al 2013, Wu et al 2013. The laboratory of Zijian Xie made an important discovery by demonstrating that a population of non-ion-transporting and highaffinity Na C /K C ATPase resides in caveolae, forming a signaling complex with Src kinase (Pierre & Xie 2006).…”

“…Therefore, it remains to be determined whether different Na C /K C ATPase isoforms play such different roles in cardiotonic steroid-mediated blood pressure development in humans. This review highlights recent exciting studies investigating the effects of physiological and pathophysiological concentrations of cardiotonic steroids on renal salt reabsorption (Aizman et al 2001, Abramowitz et al 2003, Aizman & Aperia 2003, Contreras et al 2006, Khundmiri et al 2006, Aperia 2007, Nguyen et al 2007, Holthouser et al 2010, Jansson et al 2012, Bignami et al 2013, Blanco & Wallace 2013). …”