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Processing and transport of ROMK1 channel is temperature-sensitive
M Brejon1, S Le Maout, P A Welling
1Department de Biologie Cellulaire, et Moléculaire, Gif/Yvette, 91191, France.
Biochemical and Biophysical Research Communications
|July 30, 1999
Summary
The renal potassium channel ROMK1 (Kir1.1a) is unstable and poorly trafficked to the cell surface at physiological temperatures. Lower temperatures stabilize ROMK1, enabling functional expression, suggesting a need for accessory factors for proper biosynthesis.
Area of Science:
- Biophysics
- Molecular Biology
- Cell Biology
Background:
- The renal epithelial inward rectifier potassium channel ROMK1 (Kir1.1a) plays a critical role in potassium homeostasis.
- Understanding the biosynthesis and trafficking of ROMK1 is essential for comprehending renal potassium transport.
Purpose of the Study:
- To investigate the biosynthetic mechanisms governing the expression of the renal epithelial inward rectifying K(+) channel, ROMK1.
- To determine the stability and trafficking kinetics of ROMK1 in a mammalian epithelial cell system.
Main Methods:
- Introduction of an AU1 epitope tag to the N-terminus of ROMK1 for immunoprecipitation.
- Stable transfection of AU1-ROMK1 into MDCK cells.
- Pulse-chase experiments and whole-cell patch-clamp electrophysiology at 37°C and 26°C.
Main Results:
- At 37°C, ROMK1 protein was rapidly degraded (t(1/2) < 1 hour) and failed to reach the plasma membrane in functional form.
- At 26°C, ROMK1 degradation was significantly reduced (t(1/2) > 4 hours), permitting functional expression at the plasma membrane.
- The AU1 epitope tag did not alter ROMK1 channel function in Xenopus oocytes.
Conclusions:
- Wild-type ROMK1 is bio-synthetically labile and inefficiently trafficked to the plasma membrane at physiological temperatures in mammalian epithelial cells.
- The observed instability resembles temperature-sensitive defects, suggesting ROMK1 may require association with other subunits for proper biosynthetic processing and trafficking.