title: Lin-7 targets the Kir 2.3 channel on the basolateral membrane via a L27 domain interaction with CASK.
abstract: Polarized expression of the Kir 2.3 channel in renal epithelial cells is influenced by the opposing activities of two different PDZ proteins. Mammalian Lin-7 (mLin-7) directly interacts with Kir 2.3 to coordinate basolateral membrane expression, whereas the tax interacting protein 1 (TIP-1), composed of a single PDZ domain, competes for interaction with mLin-7 and drives Kir 2.3 into the endocytic pathway. Here we show that the basolateral targeting function of mLin-7 depends on its L27 domain, which directs interaction with a cognate L27 domain in the basolateral membrane-anchoring protein, calcium/calmodulin-dependent serine protein kinase (CASK). In MDCK cells, the expression of an mLin-7 mutant that lacks the L27 domain displaced Kir 2.3 from the mLin-7/CASK complex and caused the channel to accumulate into large intracellular vesicles that partially colocalized with Rab-11. Conversely, transplantation of the mLin-7 L27 domain to TIP-1 conferred CASK interaction and basolateral targeting of Kir 2.3. Expression of the CASK L27 domain redistributed endogenous mLin-7 to an intracellular compartment and caused Kir 2.3 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.
authors.affiliation: Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
authors.forename: Christine
authors.initials: C
authors.lastname: Alewine
authors.forename: Bo-Young
authors.initials: BY
authors.lastname: Kim
authors.forename: Vandana
authors.initials: V
authors.lastname: Hegde
authors.forename: Paul A
authors.initials: PA
authors.lastname: Welling
mesh_terms: D000818:Animals; D019556:COS Cells; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D002522:Chlorocebus aethiops; D004285:Dogs; D051528:Guanylate Kinases / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000502:physiology
chemical_list: C099489:KCNJ4 protein, human; C119588:LIN-7 protein, mammalian; D008565:Membrane Proteins; D024661:Potassium Channels, Inwardly Rectifying; C106868:CASK kinases; D051528:Guanylate Kinases