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PDZ-Binding and Di-Hydrophobic Motifs Regulate Distribution of Kir4.1 Channels in Renal Cells

Masayuki Tanemoto^*, Takaaki Abe^*, and Sadayoshi Ito^*

^* Division of Nephrology, Hypertension and Endocrinology, Department of Medicine, Tohoku University Graduate School of Medicine, Sendai, Japan; and PRESTO, Japan Science and Technology Agency, Kawaguchi, Japan

Address correspondence to: Dr. Masayuki Tanemoto, Division of Nephrology, Hypertension, and Endocrinology, Department of Medicine, Tohoku University Graduate School of Medicine, 1-1 Seiryo-cho, Aoba-ku, Sendai 980-8574, Japan. Phone: 81-22-717-7163; Fax: 81-22-717-7168; mtanemoto-tky{at}umin.ac.jp

Received for publication March 10, 2005. Accepted for publication June 17, 2005.

It was shown previously that the carboxyl-terminal cytoplasmic portion of Kir4.1 determines the localization of basolateral K⁺ channel in renal distal tubules, which is composed from the assembly of Kir4.1 and Kir5.1. For clarifying the signals for this localization, specific sequence motifs of Kir4.1 were sought. In HEK293T cells, where Kir4.1 showed linear expression on the cell surface, disruption of the carboxyl-terminal PDZ-binding motif induced mostly clustered distribution but did not reduce whole-cell channel activity. Point mutation analysis revealed that serine³⁷⁷ in this motif was responsible for the surface vicinity expression. Disruption of the di-hydrophobic array of valine³³³/valine³³⁴ induced diffuse cytoplasmic distribution and diminished channel activity. Both valine³³³ and valine³³⁴ contributed to this effect. In contrast to the di-hydrophobic motifs of other membrane proteins that facilitate the sorting, valine³³³/valine³³⁴ supported the cell-surface retention. Because both the PDZ-binding and di-hydrophobic motifs participated in the basolateral expression of both Kir4.1 homomer and Kir5.1/Kir4.1 heteromer in MDCK cells, they are thought to be responsible for the localization of basolateral K⁺ channel in renal distal tubules.

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