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Lin-7 targets the Kir 2.3 channel on the basolateral membrane via a L27 domain interaction with CASK

Christine Alewine1, Bo-Young Kim, Vandana Hegde

  • 1Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.

American Journal of Physiology. Cell Physiology
|October 5, 2007
PubMed

Insights

Mammalian Lin-7 (mLin-7) protein uses its L27 domain to anchor the Kir 2.3 channel to the basolateral membrane in renal cells. This interaction is crucial for proper channel localization and function.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Renal Physiology

Background:

  • Polarized expression of ion channels like Kir 2.3 in renal epithelial cells is critical for kidney function.
  • PDZ proteins regulate membrane protein localization through specific protein-protein interactions.
  • Mammalian Lin-7 (mLin-7) and tax interacting protein 1 (TIP-1) are PDZ proteins that influence Kir 2.3 channel trafficking.

Purpose of the Study:

  • To elucidate the role of the L27 domain of mLin-7 in the basolateral targeting of the Kir 2.3 channel.
  • To investigate the interaction between mLin-7, CASK (calcium/calmodulin-dependent serine protein kinase), and Kir 2.3.
  • To understand how the L27 domain mediates the adapter function of mLin-7.

Main Methods:

  • Utilized mutant mLin-7 lacking the L27 domain in MDCK cells.
  • Investigated the effect of TIP-1 with a transplanted mLin-7 L27 domain.
  • Examined the impact of expressing the CASK L27 domain on endogenous mLin-7 and Kir 2.3 localization.
  • Employing immunofluorescence microscopy and co-localization studies with Rab-11.

Main Results:

  • mLin-7's basolateral targeting function for Kir 2.3 is dependent on its L27 domain.
  • Loss of the mLin-7 L27 domain causes Kir 2.3 to accumulate in intracellular vesicles.
  • Transplanting the mLin-7 L27 domain to TIP-1 enables basolateral targeting of Kir 2.3.
  • Expression of the CASK L27 domain disrupts mLin-7 localization and leads to Kir 2.3 accumulation in subapical endosomes.

Conclusions:

  • mLin-7 functions as a PDZ-to-L27 adapter protein.
  • mLin-7 mediates indirect association of Kir 2.3 with a basolateral membrane scaffold via CASK.
  • This interaction stabilizes Kir 2.3 at the basolateral membrane, ensuring proper renal epithelial cell function.

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