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Molecular & Cellular Proteomics 8:1972-1987, 2009.
© 2009 by The American Society for Biochemistry and Molecular Biology, Inc.

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Research

A Protein Interaction Network for the Large Conductance Ca²⁺-activated K⁺ Channel in the Mouse Cochlea^*,

Thandavarayan Kathiresan, Margaret Harvey, Sandra Orchard, Yoshihisa Sakai and Bernd Sokolowski^,¶

From the Department of Otolaryngology – Head and Neck Surgery, University of South Florida, College of Medicine, Tampa, Florida 33612 and
European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton Cambridge, CB10 1SD, United Kingdom

The large conductance Ca²⁺-activated K⁺ or BK channel has a role in sensory/neuronal excitation, intracellular signaling, and metabolism. In the non-mammalian cochlea, the onset of BK during development correlates with increased hearing sensitivity and underlies frequency tuning in non-mammals, whereas its role is less clear in mammalian hearing. To gain insights into BK function in mammals, coimmunoprecipitation and two-dimensional PAGE, combined with mass spectrometry, were used to reveal 174 putative BKAPs from cytoplasmic and membrane/cytoskeletal fractions of mouse cochlea. Eleven BKAPs were verified using reciprocal coimmunoprecipitation, including annexin, apolipoprotein, calmodulin, hippocalcin, and myelin P0, among others. These proteins were immunocolocalized with BK in sensory and neuronal cells. A bioinformatics approach was used to mine databases to reveal binary partners and the resultant protein network, as well as to determine previous ion channel affiliations, subcellular localization, and cellular processes. The search for binary partners using the IntAct molecular interaction database produced a putative global network of 160 nodes connected with 188 edges that contained 12 major hubs. Additional mining of databases revealed that more than 50% of primary BKAPs had prior affiliations with K⁺ and Ca²⁺ channels. Although a majority of BKAPs are found in either the cytoplasm or membrane and contribute to cellular processes that primarily involve metabolism (30.5%) and trafficking/scaffolding (23.6%), at least 20% are mitochondrial-related. Among the BKAPs are chaperonins such as calreticulin, GRP78, and HSP60 that, when reduced with siRNAs, alter BK expression in CHO cells. Studies of BK in mitochondria revealed compartmentalization in sensory cells, whereas heterologous expression of a BK-DEC splice variant cloned from cochlea revealed a BK mitochondrial candidate. The studies described herein provide insights into BK-related functions that include not only cell excitation, but also cell signaling and apoptosis, and involve proteins concerned with Ca²⁺ regulation, structure, and hearing loss.

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