Calreticulin positively regulates the expression and function of epithelial sodium channel.
Epithelial sodium channel (ENaC) is a heteromultimeric Na(+) channel at the apical membrane in the kidney, colon, and lung. Because ENaC plays a crucial role in regulating Na(+) absorption and extracellular fluid volume, its dysregulation causes severe phenotypes including hypertension, hypokalemia, and airway obstruction. Despite the importance of ENaC, its protein quality control mechanism remains less established. Here we firstly show the role of calreticulin (CRT), a lectin-like molecular chaperone in the endoplasmic reticulum (ER), on the regulation of ENaC. Overexpression and knockdown analyses clearly indicated that CRT positively affects the expression of each ENaC subunit (alpha, beta and gamma). CRT overexpression also up-regulated the cell surface expression of alpha-, beta- and gamma-ENaC. Moreover, we found that CRT directly interacts with each ENaC subunit. Although CRT knockdown did not affect the de novo synthesis of ENaC subunits, CRT overexpression decreased alpha-, beta- and gamma-ENaC expression in the detergent (RIPA)-insoluble fraction, suggesting that CRT enhanced the solubility of ENaC subunits. Consistent with the increased intracellular and cell surface expression of ENaC subunits, increased channel activity of ENaC was also observed upon overexpression of CRT. Our study thus identifies CRT as an ER chaperone that regulates ENaC expression and function.
Sugahara
Takuya
T
Department of Molecular Medicine, Graduate School of Pharmaceutical Sciences, Kumamoto University, Kumamoto, Japan.
Koga
Tomoaki
T
Ueno-Shuto
Keiko
K
Shuto
Tsuyoshi
T
Watanabe
Eriko
E
Maekawa
Ai
A
Kitamura
Kenichiro
K
Tomita
Kimio
K
Mizuno
Ai
A
Sato
Takashi
T
Suico
Mary Ann
MA
Kai
Hirofumi
H
D000818:Animals; D016466:CHO Cells; D037282:Calreticulin / Q000235:genetics / Q000494:pharmacology*; D006224:Cricetinae; D003412:Cricetulus; D018076:DNA, Complementary; D004721:Endoplasmic Reticulum; D053503:Epithelial Sodium Channels / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D005786:Gene Expression Regulation / Q000187:drug effects*; D018832:Molecular Chaperones; D011485:Protein Binding; D021122:Protein Subunits; D014162:Transfection
D037282:Calreticulin; D018076:DNA, Complementary; D053503:Epithelial Sodium Channels; D018832:Molecular Chaperones; D021122:Protein Subunits