Serum- and glucocorticoid-regulated kinase isoform-1 and epithelial sodium channel subunits in human ocular ciliary epithelium.
OBJECTIVE
In peripheral sodium-transporting tissues, the serum- and glucocorticoid-regulated kinase (SGK) isoform-1 is an early corticosteroid target gene in the activation of epithelial sodium channels (ENaCs). Sodium transport across the human ocular nonpigmented and pigmented ciliary epithelial bilayer (NPE-PE) is essential for aqueous humor production, but the expression of SGK1 and ENaC subunits remain to be defined.


METHODS
SGK1 and ENaC subunits were evaluated by in situ hybridization and RT-PCR analysis on human NPE-PE sections and an NPE cell line (ODM-2). Northern blot analyses were conducted on ODM-2 cells incubated with dexamethasone (DEX) or aldosterone (ALDO) and RU38486 (a glucocorticoid receptor [GR] antagonist) or RU26752 (a mineralocorticoid receptor [MR] antagonist) or both inhibitors. The affinity of the GRs and MRs for DEX and ALDO was assessed by radioligand-binding assays.


RESULTS
Expression of SGK1 and ENaC subunits was confirmed in NPE-PE tissues and ODM-2 cells. Dose-dependent induction of SGK1 mRNA in the ODM-2 cells was demonstrated after incubation with DEX or ALDO. While response to DEX was not inhibited by RU38486 or RU26752, there was a moderate reduction in induction by ALDO in the presence of RU26752 that was completely abolished in the presence of both inhibitors. Specific binding of (3)[H]DEX and (3)[H]ALDO was established, revealing greater expression of GRs than MRs.


CONCLUSIONS
The expression of ENaCs within the NPE-PE and corticosteroid regulation of SGK1 through the GR and MR, indicate that this mechanism may be a feature of sodium transport in the human ocular ciliary epithelium.
Rauz
Saaeha
S
Academic Unit of Ophthalmology, Division of Immunity and Infection, University of Birmingham, Birmingham, United Kingdom.
Walker
Elizabeth A
EA
Hughes
Susan V
SV
Coca-Prados
Miguel
M
Hewison
Martin
M
Murray
Philip I
PI
Stewart
Paul M
PM
D000450:Aldosterone / Q000494:pharmacology; D015152:Blotting, Northern; D002460:Cell Line; D002924:Ciliary Body / Q000187:drug effects / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D053503:Epithelial Sodium Channels; D005786:Gene Expression Regulation / Q000187:drug effects; D005938:Glucocorticoids / Q000494:pharmacology; D006727:Hormone Antagonists / Q000494:pharmacology; D006801:Humans; D017874:Immediate-Early Proteins; D017403:In Situ Hybridization; D007527:Isoenzymes; D015735:Mifepristone / Q000494:pharmacology; D000451:Mineralocorticoid Receptor Antagonists; D009687:Nuclear Proteins; D010857:Pigment Epithelium of Eye / Q000187:drug effects / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011965:Receptors, Glucocorticoid / Q000037:antagonists & inhibitors; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015222:Sodium Channels / Q000235:genetics* / Q000378:metabolism; D013148:Spironolactone / Q000031:analogs & derivatives* / Q000494:pharmacology; D000099184:Serum-Glucocorticoid Regulated Kinases
D000450:Aldosterone; D003907:Dexamethasone; D004338:Drug Combinations; D053503:Epithelial Sodium Channels; D005938:Glucocorticoids; D006727:Hormone Antagonists; D017874:Immediate-Early Proteins; D007527:Isoenzymes; D015735:Mifepristone; D000451:Mineralocorticoid Receptor Antagonists; D009687:Nuclear Proteins; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger; D011965:Receptors, Glucocorticoid; D015222:Sodium Channels; D013148:Spironolactone; D000099184:Serum-Glucocorticoid Regulated Kinases; C047175:7-propyl spirolactone