Protein Phosphatase 2A Interacts with the Na+,K+-ATPase and Modulates Its Trafficking by Inhibition of Its Association with Arrestin

Background: The P-type ATPase family constitutes a collection of ion pumps that form phosphorylated intermediates during ion transport. One of the best known members of this family is the Na +,K +-ATPase. The catalytic subunit of the Na +,K +-ATPase includes several functional domains that determine its enzymatic and trafficking properties. Methodology/Principal Findings: Using the yeast two-hybrid system we found that protein phosphatase 2A (PP2A) catalytic C-subunit is a specific Na +,K +-ATPase interacting protein. PP-2A C-subunit interacted with the Na +,K +-ATPase, but not with the homologous sequences of the H +,K +-ATPase. We confirmed that the Na +,K +-ATPase interacts with a complex of A- and C-subunits in native rat kidney. Arrestins and G-protein coupled receptor kinases (GRKs) are important regulators of G-protein coupled receptor (GPCR) signaling, and they also regulate Na +,K +-ATPase trafficking through direct association. PP2A inhibits association between the Na +,K +-ATPase and arrestin, and diminishes the effect of arrestin on Na +,K +-ATPase trafficking. GRK phosphorylates the Na +,K +-ATPase and PP2A can at least partially reverse this phosphorylation. Conclusions/Significance: Taken together, these data demonstrate that the sodium pump belongs to a growing list of io

Are there several isoforms of Na,K-ATPase alpha subunit in the rabbit kidney?

International audiencePrevious pharmacologic and kinetic studies have demonstrated the axial heterogeneity of the rabbit kidney tubule with regard to Na,K-ATPase. To evaluate whether this heterogeneity might reflect the presence of distinct isoforms of the alpha subunit of Na,K-ATPase, we used two monoclonal antibodies, IIC9 and IIE2 (G8), specific for the alpha 1 and alpha 3 isoforms, respectively, as probes for changes in the specific activity of Na,K-ATPase at the level of successive segments of the rabbit nephron. Single, well defined nephron segments were obtained by microdissection of collagenase-treated kidney. Results indicate that IIC9 antibody inhibited Na,K-ATPase activity by > 90% in all the segments of the nephron except the collecting duct. Conversely, IIE2 (G8) antibody abolished Na,K-ATPase activity in the collecting duct, whereas it had no effect in other nephron segments. These findings suggest that the rabbit collecting duct preferentially expresses a distinct isoform of Na,K-ATPase catalytic subunit, which is presumably alpha 3-like, in agreement with previous pharmacologic and kinetic observations, whereas other nephron segments would express the alpha 1 isoform

Presence of two isoforms of Na, K-ATPase with different pharmacological and immunological properties in the rat kidney

International audiencePrevious studies have demonstrated the presence of two populations of Na,K-ATPase with distinct kinetic, pharmacological and immunological characteristics along the rabbit nephron, indicating that the proximal segments of the nephron express exclusively the alpha 1 isoform of the catalytic subunit, whereas the collecting duct expresses an alpha 3-like isoform. Because pharmacological studies have shown the existence of two populations of Na,K-ATPase with different sensitivities to ouabain in the rat cortical collecting duct, which may result from the presence in the same nephron segment of the two isoforms demonstrated in the different segments of the rabbit nephron, the present study was undertaken to characterize the properties of Na,K-ATPase along the rat nephron. Results indicate that each segment of the rat nephron contains two subpopulations of Na,K-ATPase: a component highly sensitive to ouabain (IC50 approximately 5.10(-6) M) which is recognized by an anti-alpha 3 antibody and another moiety of lower affinity for ouabain (IC50 approximately 5.10(-4) M) which is recognized by an anti-alpha 1 antibody. Whether these two subpopulations correspond to different isoforms of the alpha subunit of Na,K-ATPase (alpha 1 and alpha 3-like) remains to be determined

The FXYD1 protein plays a protective role against pulmonary hypertension and arterial remodeling via redox and inflammatory mechanisms

First published December 22, 2023Pulmonary hypertension (PH) consists of a heterogenous group of diseases that culminate in increased pulmonary arterial pressure and right ventricular (RV) dysfunction. We sought to investigate the role of FXYD1, a small membrane protein that modulates Na⁺- K⁺-ATPase function, in the pathophysiology of PH. We mined online transcriptome databases to assess FXYD1 expression in PH. We characterized the effects of FXYD1 knockout (KO) in mice on right and left ventricular (RV and LV) function using echocardiography and measured invasive hemodynamic measurements under normal conditions and after treatment with bleomycin sulfate or chronic hypoxia to induce PH. Using immunohistochemistry, immunoblotting, and functional assays, we examined the effects of FXYD1 KO on pulmonary microvasculature and RV and LV structure and assessed signaling via endothelial nitric oxide synthase (eNOS) and inflammatory pathways. FXYD1 lung expression tended to be lower in samples from patients with idiopathic pulmonary arterial hypertension (IPAH) compared with controls, supporting a potential pathophysiological role. FXYD1 KO mice displayed characteristics of PH including significant increases in pulmonary arterial pressure, increased muscularization of small pulmonary arterioles, and impaired RV systolic function, in addition to LV systolic dysfunction. However, when PH was stimulated with standard models of lung injury-induced PH, there was no exacerbation of disease in FXYD1 KO mice. Both the lungs and left ventricles exhibited elevated nitrosative stress and inflammatory milieu. The absence of FXYD1 in mice results in LV inflammation and cardiopulmonary redox signaling changes that predispose to pathophysiological features of PH, suggesting FXYD1 may be protective. NEW & NOTEWORTHY This is the first study to show that deficiency of the FXYD1 protein is associated with pulmonary hypertension. FXYD1 expression is lower in the lungs of people with idiopathic pulmonary artery hypertension. FXYD1 deficiency results in both left and right ventricular functional impairment. Finally, FXYD1 may endogenously protect the heart from oxidative and inflammatory injury.Thomas S. Hansen, Keyvan Karimi Galougahi, Owen Tang, Michael Tsang, Marielle Scherrer-Crosbie, Elena Arystarkhova, Kathleen Sweadner, Christina Bursill, Kristen J. Bubb, and Gemma A. Figtre