|M.Sc Student||Tal Osnat|
|Subject||Regulation of the Anion Exchanger (Pendrin) Gene by|
|Department||Department of Medicine||Supervisors||Professor Israel Zelikovic|
|Dr. Julia Rozenfeld|
|Full Thesis text|
Pendrin (SLC26A4), a Cl-/anion exchanger encoded by the gene PDS is highly expressed in the kidney, thyroid and inner ear epithelia. Mutations in human PDS (hPDS) lead to Pendred syndrome, characterized by sensorineural hearing defect and thyroid goiter. In the kidney, pendrin functions as an apical Cl-/HCO3- exchanger in β-intercalated cells of the cortical collecting duct (CCD). In addition to its role in secreting bicarbonate and maintaining acid-base balance, pendrin is also involved in NaCl balance and blood pressure regulation in the mouse. However, the cellular and molecular mechanisms controlling pendrin activity in the renal epithelium remain to be established.
In this study, we have explored the effects of the peptide uroguanylin (UGN; the "intestinal natriuretic hormone") and ambient Cl-, known modulators of electrolyte balance, on transcription and translation of the pendrin gene in vitro and in vivo.
Real time-PCR analysis of human embryonic kidney (HEK293) cells showed a UGN- induced decrease in endogenous pendrin mRNA levels compared to control cells.
received UGN intravenously. Two or 24hrs later, their kidneys were harvested
for pendrin mRNA quantification (real time PCR) and pendrin protein
visualization (immunofluorescence). UGN- injected animals displayed a decrease
in pendrin mRNA and protein expression in renal tubules.
The effect of UGN and ambient Cl- on the hPDS promoter was examined. Luciferase reporter plasmids containing different length fragments of this promoter were transfected into HEK293 cells that were exposed to UGN or different Cl- levels. UGN and high Cl- decreased, whereas low Cl- increased hPDS promoter activity compared to activity in control cells. Furthermore, the findings provided evidence for the presence of distinct UGN -, and Cl - response elements on the hPDS promoter.
In conclusion, the peptide UGN and Cl- availability influence pendrin - mediated Cl-/ HCO3- exchange in the renal tubule at the transcriptional level in vitro and in vivo. These modulators exert their effect on the PDS promoter by acting on distinct response elements on this promoter, which remain to be identified and characterized. The UGN- induced effects on pendrin activity occurs along the entire pathway of pendrin production, namely DNA, RNA, and protein. The effect of UGN and ambient Cl- on pendrin gene activity demonstrated in this study may play an important role in extracellular fluid homeostasis and blood pressure control in health and disease.