Session: SAT 381-386-Steroid Hormone Actions, Biosynthesis & Metabolism
Poster Board SAT-383
We showed previously that post-transcriptional events control renal MR abundance (Viengchareun Mol Endo 2009). Here, using cortical collecting duct KC3AC1 cells, we show that the RNA Binding Protein Tis11b (a member of tristetraprolin/ZFP36 family) induces a dramatic reduction of MR expression under hypertonicity. Consistent with a Tis11b-mediated MR downregulation mechanism, hypertonicity induces a 2-4-fold increase of Tis11b mRNA and protein levels, concomitant with the decreased MR expression. In contrast, RNAi-dependent reduction of Tis11b expression induces the increase of MR expression level. We suggest that Tis11b modulates MR mRNA stability/degradation through binding to Adenine/Uridine Rich Elements (AURE), located in the 3’-UnTranslated Region (3’-UTR) of MR mRNA. Eight highly conserved AURE were indeed identified in the 3’-UTR of MR mRNA.
To examine whether MR transcript was a direct target of Tis11b, the entire 3’-UTR of MR mRNA was subcloned downstream of a luciferase reporter gene and truncated mutants, carrying or lacking AURE, were generated. Cotransfection assays in HEK 293 cells showed that Tis11b induces a 2-fold reduction in luciferase activity of AURE-containing constructs. RNA-ChiP assays demonstrated that endogenously expressed Tis11b physically interacts with MR mRNA AURE in KC3AC1 cells. Finally, to demonstrate the physiological relevance of our findings, we challenged the renal osmotic gradient and demonstrated that mice present with a modification in renal MR expression under water deprivation or diuretic treatment (furosemide, indapamide).
Our data are important to explain the partial aldosterone resistance associated with cyclic variations of renal MR expression during the perinatal period. Whether such regulatory post-transcriptional mechanisms occur in other MR target tissues (cardiovascular and central nervous system) or are altered in kidney diseases and hypertension remains to be established.
Nothing to Disclose: SV, IL, VK, LA, JN, LM, NC, ML
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