Regulation of electrogenic Na+ /HCO3- cotransporter 1 (NBCe1) function and its dependence on m-TOR mediated phosphorylation of Ser245.

Abstract

Astrocytes are pivotal responders to alterations of extracellular pH, primarily by regulation of their principal acid-base transporter, the membrane-bound electrogenic Na+ /bicarbonate cotransporter 1 (NBCe1). Here, we describe amammalian target of rapamycin (mTOR)-dependent and NBCe1-mediated astroglial response to extracellular acidosis. Using primary mouse cortical astrocytes, we investigated the effect of long-term extracellular metabolic acidosis on regulation of NBCe1 and elucidated the underlying molecular mechanisms by immunoblotting, biotinylation of surface proteins, intracellular H+ recording using the H+ -sensitive dye 2',7'-bis-(carboxyethyl)-5-(and-6)-carboxyfluorescein, and phosphoproteomic analysis. The results showed significant increase of NBCe1-mediated recovery of intracellular pH from acidification in WT astrocytes, but not in cortical astrocytes from NBCe1-deficient mice. Acidosis-induced upregulation of NBCe1 activity was prevented following inhibition of mTOR signaling by rapamycin. Yet, during acidosis or following exposure of astrocytes to rapamycin, surface protein abundance of NBCe1 remained -unchanged. Mutational analysis in HeLa cells suggested that NBCe1 activity was dependent on phosphorylation state of Ser245 , a residue conserved in all NBCe1 variants. Moreover, phosphorylation state of Ser245 is regulated by mTOR and is inversely correlated with NBCe1 transport activity. Our results identify pSer245 as a novel regulator of NBCe1 functional expression. We propose that context-dependent and mTOR-mediated multisite phosphorylation of serine residues of NBCe1 is likely to be a potent mechanism contributing to the response of astrocytes to acid/base challenges during pathophysiological conditions.

• Authors: Marina Giannaki, Christina Ludwig, Stephan Heermann, Eleni Roussa
• Journal: Journal of cellular physiology (J Cell Physiol) Vol. 237 Issue 2 Pg. 1372-1388 (02 2022) ISSN: 1097-4652 [Electronic] United States
• PMID: 34642952 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: © 2021 The Authors. Journal of Cellular Physiology published by Wiley Periodicals LLC.

Chemical References

• Sodium-Bicarbonate Symporters
• Symporters
• Sodium
• TOR Serine-Threonine Kinases
• Sirolimus

Topics

• Acidosis (metabolism)
• Animals
• Cerebral Cortex
• HeLa Cells
• Humans
• Mice
• Mice, Inbred C57BL
• Mice, Knockout
• Phosphorylation
• Sirolimus (pharmacology)
• Sodium (metabolism)
• Sodium-Bicarbonate Symporters (genetics, metabolism)
• Symporters (metabolism)
• TOR Serine-Threonine Kinases (metabolism)