Referenced in: none

Automatically associated channels: Kir6.2

Title: Molecular identification and functional characterization of a mitochondrial sulfonylurea receptor 2 splice variant generated by intraexonic splicing.

Authors: Bin Ye, Stacie L Kroboth, Jie-Lin Pu, Jason J Sims, Nitin T Aggarwal, Elizabeth M McNally, Jonathan C Makielski, Nian-Qing Shi

Journal, date & volume: Circ. Res., 2009 Nov 20 , 105, 1083-93

PubMed link: http://www.ncbi.nlm.nih.gov/pubmed/19797704

Abstract
Cardioprotective pathways may involve a mitochondrial ATP-sensitive potassium (mitoK(ATP)) channel but its composition is not fully understood.We hypothesized that the mitoK(ATP) channel contains a sulfonylurea receptor (SUR)2 regulatory subunit and aimed to identify the molecular structure.Western blot analysis in cardiac mitochondria detected a 55-kDa mitochondrial SUR2 (mitoSUR2) short form, 2 additional short forms (28 and 68 kDa), and a 130-kDa long form. RACE (Rapid Amplification of cDNA Ends) identified a 1.5-Kb transcript, which was generated by a nonconventional intraexonic splicing (IES) event within the 4th and 29th exons of the SUR2 mRNA. The translated product matched the predicted size of the 55-kDa short form. In a knockout mouse (SUR2KO), in which the SUR2 gene was disrupted, the 130-kDa mitoSUR2 was absent, but the short forms remained expressed. Diazoxide failed to induce increased fluorescence of flavoprotein oxidation in SUR2KO cells, indicating that the diazoxide-sensitive mitoK(ATP) channel activity was associated with 130-kDa-based channels. However, SUR2KO mice displayed similar infarct sizes to preconditioned wild type, suggesting a protective role for the remaining short form-based channels. Heterologous coexpression of the SUR2 IES variant and Kir6.2 in a K(+) transport mutant Escherichia coli strain permitted improved cell growth under acidic pH conditions. The SUR2 IES variant was localized to mitochondria, and removal of a predicted mitochondrial targeting sequence allowed surface expression and detection of an ATP-sensitive current when coexpressed with Kir6.2.We identify a novel SUR2 IES variant in cardiac mitochondria and provide evidence that the variant-based channel can form an ATP-sensitive conductance and may contribute to cardioprotection.