Alterations of Na+/K+-ATPase function in caveolin-1 knockout cardiac fibroblasts

Abstract

Recent studies have demonstrated that the Na+/K+-ATPase is not only an ion pump, but also a membrane receptor that confers the ligand-like effects of cardiotonic steroids (CTS) such as ouabain on protein kinases and cell growth. Because CTS have been implicated in cardiac fibrosis, this study examined the role of caveolae in the regulation of Na+/K+-ATPase function and CTS signaling in cardiac fibroblasts. In cardiac fibroblasts prepared from wild-type and caveolin-1 knockout [Cav-1(−/−)] mice, we found that the absence of caveolin-1 did not affect total cellular amount or surface expression of Na+/K+-ATPase α1 subunit. However, it did increase ouabain-sensitive 86Rb+ uptake. While knockout of caveolin-1 increased basal activities of Src and ERK1/2, it abolished activation of these kinases induced by ouabain but not angiotensin II. Finally, ouabain stimulated collagen synthesis and cell proliferation in wild type but not Cav-1(−/−) cardiac fibroblasts. Thus, we conclude that caveolae are important for regulating both pumping and signal transducing functions of Na+/K+-ATPase. While depletion of caveolae increases the pumping function of Na+/K+-ATPase, it suppresses CTS-induced signal transduction, growth, and collagen production in cardiac fibroblasts.

Loss of Caveolin-1 Impairs Retinal Function Due to Disturbance of Subretinal Microenvironment

“…Surprisingly, as shown in Fig. 6A, total Na ϩ /K ϩ -ATPase activity in RPE microsomes measured at saturating concentrations of all ligands was enhanced in Cav-1 KO microsomes, as has been recently observed in cardiac fibroblasts from Cav-1 KO mice (74). The increased total activity in RPE could not be explained by increases in levels of Na ϩ /K ϩ -ATPase because Western blots from microsomal fractions indicated similar levels of enzyme (Fig.…”

“…6). Surprisingly, V max was significantly higher in Cav-1 KO membranes, a finding recently observed in Cav-1 KO cardiac fibroblasts (74). These results indicate that the loss of Cav-1 affects Na ϩ /K ϩ ATPase activity, but we cannot yet determine whether this effect is due to disruption of a complex containing Cav-1 and the Na ϩ /K ϩ -ATPase or is due to indirect changes in either membrane composition or ion concentrations.…”

Cardiotonic Steroids Stabilize Regulator of G Protein Signaling 2 Protein Levels

“…It is not clear whether these effects are a direct result of ouabain inhibiting Na ϩ /K ϩ -ATPase pump function or inducing signal transduction cascades. It was suggested that acute effects (5-10 min) of CTSs require much higher concentrations (micromolar) than the long-term effects (hours to days; nanomolar) observed in the present study (Quintas et al, 2010).…”

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

“…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). When cardiotonic steroids at low picomolar to nanomolar concentrations bind to Na C /K C ATPase in the caveolae, this activates Src, which in turn results in transactivation of EGFR and activation of the PI3K-Akt pathway, the Ras-Raf-ERK MAP kinase pathway, IP3R activation, and calcium oscillations, resulting in regulation of earlyresponse genes associated with cell growth, motility, and metabolic pathways (Peng et al 1996, Kometiani et al 1998, Contreras et al 1999, Aizman et al 2001, Abramowitz et al 2003, Dmitrieva & Doris 2003, Dong et al 2004, Khundmiri et al 2006, Liu & Askari 2006, Liu et al 2007a,b, 2011, Pierre et al 2008, Quintas et al 2010, Morrill et al 2012, Bai et al 2013, Wu et al 2013, Rincon-Heredia et al 2014.…”