Regulation of Na,K-ATPase Subunit Abundance by Translational Repression

Clifford, Rebecca J.; Kaplan, Jack H.

doi:10.1074/jbc.m109.030536

Cited by 12 publications

(15 citation statements)

References 57 publications

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“…Similar to our data, expression of flag-conjugated sheep β 1 subunit in MDCK cells did not alter mRNA level of endogenous subunits or the amount of the α 1 subunit but decreased the level of the endogenous β 1 subunit (37). Based on these results, the authors concluded that translation of the endogenous β 1 subunit is repressed by expression of the exogenous β 1 subunit by an unknown mechanism (37).…”

Section: Discussionsupporting

confidence: 90%

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Assembly with the Na,K-ATPase α₁ Subunit Is Required for Export of β₁ and β₂ Subunits from the Endoplasmic Reticulum

2009

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The level of the heterodimeric Na,K-ATPase is tightly controlled in epithelia to maintain appropriate transport function. The catalytic Na,K-ATPase α subunit is not able to exit the ER or catalyze ion transport unless assembled with the β subunit. However, requirements for the ER exit of the Na,KATPase β subunit that plays an additional, ion-transport-independent, role in intercellular adhesion are not clear. Exogenous β 1 or β 2 subunits expressed in renal MDCK cells replace endogenous β 1 subunits in the α-β complexes in the ER, resulting in a decrease in the amount of the α 1 -bound endogenous β 1 subunits by 47-61% with no change in the amount of α 1 subunits. Disruption of the α 1 -β association by mutations in defined α 1 -interacting regions of either β 1 or β 2 subunits results in the ER retention and rapid degradation of unassembled mutants. Hence, the ER quality control system allows export only of assembled α-β complexes to the Golgi, thereby maintaining an equimolar ratio of α and β subunits in the plasma membrane, whereas the number of α 1 subunits in the ER determines the amount of the α-β complexes.

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Section: Discussionsupporting

confidence: 90%

“…Based on these results, the authors concluded that translation of the endogenous β 1 subunit is repressed by expression of the exogenous β 1 subunit by an unknown mechanism (37). …”

Section: Discussionmentioning

confidence: 99%

Assembly with the Na,K-ATPase α₁ Subunit Is Required for Export of β₁ and β₂ Subunits from the Endoplasmic Reticulum

2009

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“…As suggested by previous reports 21, 24 , we demonstrate that a true overexpression of either α isoform is impossible, since increased expression of one isoform results in compensatory down-regulation of the other endogenous α isoform. However, increased expression of the α2 isoform, which effectively results in replacement of α1 with α2, attenuated the hypertrophic response after transverse aortic constriction (TAC) and was associated with faster Ca 2+ extrusion via NCX1.…”

Section: Introductionsupporting

confidence: 78%

“…Previous work has suggested that a change in expression of a particular NKA isoform is balanced by altered expression of the other, such that a constant level of NKA protein is maintained 21, 24 . In agreement with these previous observations, our Western blot experiments from whole-cell extracts of NKA-α1, NKA-α2 and Wt hearts demonstrated that overexpression of one NKA isoform elicited downregulation of the other isoform in a manner that preserved total levels of NKA (Figure 4A).…”

Section: Resultsmentioning

confidence: 99%

Overexpression of the Na ⁺ /K ⁺ ATPase α2 But Not α1 Isoform Attenuates Pathological Cardiac Hypertrophy and Remodeling

Correll

Eder

Burr

et al. 2014

Circulation Research

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Rationale The Na+/K+ ATPase (NKA) directly regulates intracellular Na+ levels, which in turn indirectly regulates Ca2+ levels by proximally controlling flux through the Na+/Ca2+ exchanger (NCX1). Elevated Na+ levels have been reported during heart failure, which permits some degree of reverse mode Ca2+ entry through NCX1, as well as less efficient Ca2+ clearance. Objective To determine if maintaining lower intracellular Na+ levels by NKA overexpression in the heart would enhance forward-mode Ca2+ clearance and prevent reverse-mode Ca2+ entry through NCX1 to protect the heart. Methods and Results Cardiac-specific transgenic mice overexpressing either the NKA-α1 or α2 were generated and subjected to pressure overload hypertrophic stimulation. We found that while increased expression of NKA-α1 had no protective effect, overexpression of NKA-α2 significantly decreased cardiac hypertrophy after pressure overload in mice at 2, 10 and 16 weeks of stimulation. Remarkably, total NKA protein expression and activity were not altered in either of these two transgenic models, as increased expression of one isoform led to a concomitant decrease in the other endogenous isoform. NKA-α2 overexpression, but not NKA-α1, led to significantly faster removal of bulk Ca2+ from the cytosol in a manner requiring NCX1 activity. Mechanistically, overexpressed NKA-α2 showed greater affinity for Na+ compared with NKA-α1, leading to more efficient clearance of this ion. Moreover, overexpression of NKA-α2, but not NKA-α1, was coupled to a decrease in phospholemman expression and phosphorylation, which would favor greater NKA activity, NCX1 activity and Ca2+ removal. Conclusions Our results suggest that the protective effect produced by increased expression of NKA-α2 on the heart after pressure overload is due to more efficient Ca2+ clearance because this isoform of NKA preferentially enhances NCX1 activity compared with NKA-α1.

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“…It is important to note a major difference between our expression system and commonly used mammalian expression systems. For example, studies that have specifically investigated this issue have reported that the level of expression of endogenous ␣1 in COS-1, HEK-293, or MDCK cells is about 50% of total Na-K-ATPase ␣1 (8,43). Given the high level of endogenous ␣1, most assays have to be conducted in the presence of ouabain (e.g., 10 M) to eliminate the contribution from endogenous ␣1 Na-K-ATPase.…”

Section: Discussionmentioning

confidence: 99%

Expression of rat Na-K-ATPase α2 enables ion pumping but not ouabain-induced signaling in α1-deficient porcine renal epithelial cells

Xie

Cui

et al. 2015

American Journal of Physiology-Cell Physiology

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Pase is a fundamental component of ion transport. Four ␣ isoforms of the Na-K-ATPase catalytic ␣ subunit are expressed in human cells. The ubiquitous Na-K-ATPase ␣1 was recently discovered to also mediate signal transduction through Src kinase. In contrast, ␣2 expression is limited to a few cell types including myocytes, where it is coupled to the Na ϩ /Ca 2ϩ exchanger. To test whether rat Na-KATPase ␣2 is capable of cellular signaling like its ␣1 counterpart in a recipient mammalian system, we used an ␣1 knockdown pig renal epithelial cell (PY-17) to create an ␣2-expressing cell line with no detectable level of ␣1 expression. These cells exhibited normal ouabain-sensitive ATPase, but failed to effectively regulate Src. In contrast to ␣1-expressing cells, ouabain did not stimulate Src kinase or downstream effectors such as ERK and Akt in ␣2 cells, although their signaling apparatus was intact as evidenced by EGF-mediated signal transduction. Additionally, ␣2 cells were unable to rescue caveolin-1. Unlike the NaKtide sequence derived from Na-K-ATPase ␣1, which downregulates basal Src activity, the corresponding ␣2 NaKtide was unable to inhibit Src in vitro. Finally, coimmunoprecipitation of cellular Src was diminished in ␣2 cells. These findings indicate that Na-K-ATPase ␣2 does not regulate Src and, therefore, may not serve the same role in signal transduction as ␣1. This further implies that the signaling mechanism of Na-K-ATPase is isoform specific, thereby supporting a model where ␣1 and ␣2 isoforms play distinct roles in mediating contraction and signaling in myocytes.rat Na-K-ATPase isoforms; Src tyrosine kinase; membrane transporters; ouabain; signal transduction THE NA-K-ATPASE, discovered in 1957 by Jens Skou, is a member of the P-type ATPase family and an integral membrane protein maintaining cellular ion homeostasis by pumping Na ϩ and K ϩ across the cell membrane (32). The protein consists of two noncovalently linked subunits, ␣ and ␤. The ␣-subunit contains the binding sites for substrates (e.g., ions and ATP) and ligands (e.g., ouabain) as it undergoes E1 and E2 conformational changes during a transport cycle. Four isoforms of the Na-K-ATPase ␣-subunit are expressed in humans. While ␣1 is expressed ubiquitously, ␣2 and ␣3 are primarily found in myocytes and neurons, respectively, and ␣4 is detected in sperm (3,4,31,45,50). Recent studies have revealed major differences in the physiological functions of each isoform. For example, the ␣2 isoform appears to possess the unique ability to regulate intracellular Ca 2ϩ levels in myocytes and coresides with the Na ϩ /Ca 2ϩ exchanger (5, 24). In addition, recent experiments using SWAP mice (ouabainsensitive ␣1 Na-K-ATPase mutant and ouabain-resistant ␣2 Na-K-ATPase mutant) suggest that the ␣2 isoform plays a more prominent role in calcium release in cardiac and smooth muscle myocytes than ␣1 (12).Over the last decade, we have also come to realize that the Na-K-ATPase may have many regulatory functions other than pumping ions across cell membranes. Studies fr...

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Regulation of Na,K-ATPase Subunit Abundance by Translational Repression

Cited by 12 publications

References 57 publications

Assembly with the Na,K-ATPase α₁ Subunit Is Required for Export of β₁ and β₂ Subunits from the Endoplasmic Reticulum

Assembly with the Na,K-ATPase α₁ Subunit Is Required for Export of β₁ and β₂ Subunits from the Endoplasmic Reticulum

Overexpression of the Na ⁺ /K ⁺ ATPase α2 But Not α1 Isoform Attenuates Pathological Cardiac Hypertrophy and Remodeling

Expression of rat Na-K-ATPase α2 enables ion pumping but not ouabain-induced signaling in α1-deficient porcine renal epithelial cells

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Regulation of Na,K-ATPase Subunit Abundance by Translational Repression

Cited by 12 publications

References 57 publications

Assembly with the Na,K-ATPase α1 Subunit Is Required for Export of β1 and β2 Subunits from the Endoplasmic Reticulum

Assembly with the Na,K-ATPase α1 Subunit Is Required for Export of β1 and β2 Subunits from the Endoplasmic Reticulum

Overexpression of the Na + /K + ATPase α2 But Not α1 Isoform Attenuates Pathological Cardiac Hypertrophy and Remodeling

Expression of rat Na-K-ATPase α2 enables ion pumping but not ouabain-induced signaling in α1-deficient porcine renal epithelial cells

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Assembly with the Na,K-ATPase α₁ Subunit Is Required for Export of β₁ and β₂ Subunits from the Endoplasmic Reticulum

Assembly with the Na,K-ATPase α₁ Subunit Is Required for Export of β₁ and β₂ Subunits from the Endoplasmic Reticulum

Overexpression of the Na ⁺ /K ⁺ ATPase α2 But Not α1 Isoform Attenuates Pathological Cardiac Hypertrophy and Remodeling