The amiloride-sensitive epithelial sodium channel alpha-subunit is transcriptionally down-regulated in rat parotid cells by the extracellular signal-regulated protein kinase pathway.
Previous studies have shown that an inducible Raf-1 kinase protein, DeltaRaf-1:ER, activates the mitogen-activated protein kinase/extracellular signal-regulated protein kinase (ERK)-signaling pathway, which is required for the transformation of the rat salivary epithelial cell line, Pa-4. Differential display polymerase chain reaction was employed to search for mRNAs repressed by DeltaRaf-1:ER activation. Through this approach, the gene encoding the alpha-subunit of the amiloride-sensitive epithelial sodium channel (alpha-ENaC) was identified as a target of activated Raf-1 kinases. alpha-ENaC down-regulation could also be seen in cells treated with 12-O-tetradecanoyl-1-phorbol-13-acetate (TPA), indicating that the repression of steady-state alpha-ENaC mRNA level was dependent upon the activity of protein kinase C, the target of TPA, as well. Pretreatment of cells with a specific inhibitor of the ERK kinase pathway, PD 98059, markedly abolished the down-regulation of alpha-ENaC expression, consistent with the hypothesis that the ERK kinase-signaling pathway is involved in TPA-mediated repression. Moreover, through the use of transient transfection assays with alpha-ENaC-reporter and activated Raf expression construct(s), we provide the first evidence that activation of the ERK pathway down-regulates alpha-ENaC expression at the transcriptional level. Elucidating the molecular programming that modulates the expression of the alpha-subunit may provide new insights into the modulation of sodium reabsorption across epithelia.
Zentner
M D
MD
Department of Molecular Pharmacology and Toxicology, Los Angeles, California 90033, USA.
Lin
H H
HH
Wen
X
X
Kim
K J
KJ
Ann
D K
DK
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002478:Cells, Cultured; D015536:Down-Regulation; D004789:Enzyme Activation; D004847:Epithelial Cells / Q000378:metabolism; D053503:Epithelial Sodium Channels; D005786:Gene Expression Regulation / Q000187:drug effects; D010306:Parotid Gland / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D015222:Sodium Channels / Q000096:biosynthesis / Q000235:genetics*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014158:Transcription, Genetic
D053503:Epithelial Sodium Channels; D012333:RNA, Messenger; D015222:Sodium Channels; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D013755:Tetradecanoylphorbol Acetate