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Am J Physiol Cell Physiol (October 3, 2007). doi:10.1152/ajpcell.00323.2007
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Submitted on July 24, 2007
Accepted on September 24, 2007

Lin-7 Targets the Kir 2.3 Channel on the Basolateral Membrane via a L27 Domain Interaction with CASK

Christine Alewine1, Vandana Hegde1, Bo-young Kim1, and Paul A. Welling1*

1 Physiology, Univ. MD Medical School, Baltimore, Maryland, United States

* To whom correspondence should be addressed. E-mail: pwelling{at}umaryland.edu.

Polarized expression of the Kir2.3 channel in renal epithelial cells is influenced by the opposing activities of two different PDZ proteins. mLin-7 directly interacts with Kir 2.3 to coordinate basolateral membrane expression whereas the Tax Interacting Protein-1 (TIP-1), comprised of a single PDZ domain, competes for interaction with mLin-7 and drives Kir2.3 into the endocytic pathway. Here, we show that the basolateral targeting function of mLin-7 depends upon its L27 domain, which directs interaction with a cognate L27 domain in the basolateral membrane anchoring protein, CASK. In MDCK cells, expression of a mLin-7 mutant that lacks the L27 domain displaced Kir2.3 from the mLin-7/CASK complex and caused the channel to accumulate into large intracellular vesicles which partially co-localized with Rab-11. Conversely, transplantation of the mLin-7 L27 domain to TIP-1 conferred CASK interaction and basolateral targeting of Kir2.3. Expression of the CASK L27 domain redistributed endogenous mLin-7 to an intracellular compartment and caused Kir2.3 to accumulate in subapical endosomes. Taken together, these data support a model whereby mLin-7 acts as a PDZ-to-L27 adapter, mediating indirect association of Kir 2.3 with a basolateral membrane scaffold, and thereby stabilizing Kir 2.3 at the basolateral membrane.




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