Small heat shock protein alphaA-crystallin regulates epithelial sodium channel expression.
Integral membrane proteins are synthesized on the cytoplasmic face of the endoplasmic reticulum (ER). After being translocated or inserted into the ER, they fold and undergo post-translational modifications. Within the ER, proteins are also subjected to quality control checkpoints, during which misfolded proteins may be degraded by proteasomes via a process known as ER-associated degradation. Molecular chaperones, including the small heat shock protein alphaA-crystallin, have recently been shown to play a role in this process. We have now found that alphaA-crystallin is expressed in cultured mouse collecting duct cells, where apical Na(+) transport is mediated by epithelial Na(+) channels (ENaC). ENaC-mediated Na(+) currents in Xenopus oocytes were reduced by co-expression of alphaA-crystallin. This reduction in ENaC activity reflected a decrease in the number of channels expressed at the cell surface. Furthermore, we observed that the rate of ENaC delivery to the cell surface of Xenopus oocytes was significantly reduced by co-expression of alphaA-crystallin, whereas the rate of channel retrieval remained unchanged. We also observed that alphaA-crystallin and ENaC co-immunoprecipitate. These data are consistent with the hypothesis that small heat shock proteins recognize ENaC subunits at ER quality control checkpoints and can target ENaC subunits for ER-associated degradation.
Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
Ossama B
OB
Kashlan
Gunhild M
GM
Mueller
Mohammad Z
MZ
Qamar
Paul A
PA
Poland
Annette
A
Ahner
Ronald C
RC
Rubenstein
Rebecca P
RP
Hughey
Jeffrey L
JL
Brodsky
Thomas R
TR
Kleyman
D000818:Animals; D004285:Dogs; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism*; D005786:Gene Expression Regulation; D006360:Heat-Shock Proteins / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D018832:Molecular Chaperones / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012964:Sodium / Q000737:chemistry; D015222:Sodium Channels / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism; D014981:Xenopus; D038202:alpha-Crystallin A Chain / Q000378:metabolism* / Q000502:physiology*
D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D015222:Sodium Channels; D038202:alpha-Crystallin A Chain; D012964:Sodium