OSR1 regulates a subset of inward rectifier potassium channels via a binding motif variant

Area of Science:

• Molecular Biology
• Cell Physiology
• Biochemistry

Background:

• The With-No-Lysine (WNK) signaling pathway is crucial for regulating cell volume and ion transport.
• SPAK (STE20/SPS1-related proline- and alanine-rich kinase) and OSR1 (oxidative stress-responsive 1) kinases are key components of the WNK pathway.
• These kinases interact with substrates via C-terminal domains and specific linear sequence motifs (R-F-x-V/I).

Purpose of the Study:

• To investigate novel interaction motifs for SPAK and OSR1.
• To determine the role of these motifs in the function of inward rectifier K+ (Kir) channels.
• To elucidate the mechanism by which the WNK-OSR1 pathway regulates Kir channel activity and plasma membrane localization.

Main Methods:

• Bioinformatic analysis to identify sequence motifs in Kir channels.
• In vitro kinase assays to assess OSR1 activation of Kir channels.
• Site-directed mutagenesis to disrupt the identified motif in Kir2.3.
• siRNA knockdown of OSR1 and chemical inhibition of WNK activity.
• Confocal microscopy to examine plasma membrane localization of Kir2.3.

Main Results:

• SPAK and OSR1 interact with a variant motif (R-x-F-x-V/I) with similar affinity to the known motif.
• Eight of 16 human inward rectifier K+ channels contain the R-x-F-x-V motif.
• OSR1 activates Kir2.1 and Kir2.3 channels, which possess the motif, but not Kir4.1, which lacks it.
• Mutation of the motif in Kir2.3 abolishes OSR1-mediated activation.
• Disruption of OSR1 or WNK activity impairs NaCl-induced plasma membrane localization of Kir2.3.

Conclusions:

• The WNK-OSR1 pathway enhances Kir2.1 and Kir2.3 channel activity, likely by increasing their plasma membrane localization.
• The identified R-x-F-x-V/I motif is critical for this regulation.
• This finding expands the understanding of the WNK pathway's physiological impact on ion transport through the regulation of inward rectifier K+ channels.