Changes in sodium pump expression dictate the effects of ouabain on cell growth
Jiang Tian1, Xin Li, Man Liang
1Department of Physiology and Pharmacology, University of Toledo College of Medicine, Toledo, Ohio 43614, USA.
Abstract:
Here we show that ouabain-induced cell growth regulation is intrinsically coupled to changes in the cellular amount of Na/K-ATPase via the phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway. Ouabain increases the endocytosis and degradation of Na/K-ATPase in LLC-PK1, human breast (BT20), and prostate (DU145) cancer cells. However, ouabain stimulates the PI3K/Akt/mTOR pathway and consequently up-regulates the expression of Na/K-ATPase in LLC-PK1 but not BT20 and DU145 cells. This up-regulation is sufficient to replete the plasma membrane pool of Na/K-ATPase and to stimulate cell proliferation in LLC-PK1 cells. On the other hand, ouabain causes a gradual depletion of Na/K-ATPase and an increased expression of cell cycle inhibitor p21(cip), which consequently inhibits cell proliferation in BT20 and DU145 cells. Consistently, we observe that small interfering RNA-mediated knockdown of Na/K-ATPase is sufficient to induce the expression of p21(cip) and slow the proliferation of LLC-PK1 cells. Moreover, this knockdown converts the growth stimulatory effect of ouabain to growth inhibition in LLC-PK1 cells. Mechanistically, both Src and caveolin-1 are required for ouabain-induced activation of Akt and up-regulation of Na/K-ATPase. Furthermore, inhibition of the PI3K/Akt/mTOR pathway by rapamycin completely blocks ouabain-induced expression of Na/K-ATPase and converts ouabain-induced growth stimulation to growth inhibition in LLC-PK1 cells. Taken together, we conclude that changes in the expression of Na/K-ATPase dictate the growth regulatory effects of ouabain on cells.
Insights
Ouabain
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- Ouabain is a cardiac glycoside known to affect cell physiology.
- The Na/K-ATPase is a crucial ion pump involved in cell function and growth.
- The phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway regulates cell growth and survival.
Purpose of the Study:
- To elucidate the mechanism by which ouabain regulates cell growth.
- To investigate the role of Na/K-ATPase and the PI3K/Akt/mTOR pathway in ouabain's effects.
- To determine how ouabain differentially affects cell proliferation in various cancer cell lines.
Main Methods:
- Cell culture of LLC-PK1, BT20, and DU145 cells.
- Analysis of Na/K-ATPase expression and localization via endocytosis and degradation studies.
- Western blotting to assess PI3K/Akt/mTOR pathway activation and p21(cip) expression.
- Small interfering RNA (siRNA) mediated knockdown of Na/K-ATPase.
- Inhibition of the PI3K/Akt/mTOR pathway using rapamycin.
Main Results:
- Ouabain increases Na/K-ATPase endocytosis and degradation in all tested cell lines.
- Ouabain stimulates the PI3K/Akt/mTOR pathway, up-regulating Na/K-ATPase in LLC-PK1 cells, promoting proliferation.
- In BT20 and DU145 cells, ouabain leads to Na/K-ATPase depletion and p21(cip) induction, inhibiting proliferation.
- Na/K-ATPase knockdown mimics ouabain's inhibitory effects and converts ouabain's growth stimulation to inhibition in LLC-PK1 cells.
- Src and caveolin-1 are essential for ouabain-induced Akt activation and Na/K-ATPase up-regulation.
- Rapamycin blocks ouabain-induced Na/K-ATPase expression and shifts growth stimulation to inhibition in LLC-PK1 cells.
Conclusions:
- Cellular Na/K-ATPase levels, modulated by the PI3K/Akt/mTOR pathway, dictate ouabain's growth regulatory effects.
- Ouabain's impact on cell proliferation is dependent on its differential regulation of Na/K-ATPase expression in cancer cells.
- Targeting Na/K-ATPase or the PI3K/Akt/mTOR pathway could offer therapeutic strategies for cancers exhibiting differential responses to ouabain.
Related Concept Videos
01:26Regulation of Sodium and Potassium
Sodium Regulation
Sodium ions make up approximately 90% of extracellular cations, with a normal blood plasma concentration of 136–148 mEq/L. A decrease in blood volume and pressure triggers the release of renin from granular cells in the juxtaglomerular complex (JGC), primarily in...
01:45Endocrine Signaling
01:27Feedback Regulation of Calcium Concentration
Various transmembrane receptors, such as G protein-coupled receptors (GPCRs), elicit a response to extracellular signals by increasing cytosolic calcium. Activated GPCRs...
01:26Voltage-gated Ion Channels
Generally, all voltage-gated ion channels have a 'voltage-sensing domain' that spans the lipid bilayer. The charged residues in the sensor move in response to the membrane potential changes that open the channel allowing ions movement. There are several types of...
01:22Antiarrhythmic Drugs: Class I Agents as Sodium Channel Blockers
Class 1A Antiarrhythmic Drugs: These drugs work by moderately blocking sodium channels,...
01:24Generation of Action Potential in Skeletal Muscles
Like neurons, muscle cells are also regarded as excitable due to their capacity to change in response to stimuli, primarily due to voltage-gated ion channels embedded in their plasma membranes, which get activated by alterations in the cell's...