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Oxidative Medicine and Cellular Longevity
Volume 2016 (2016), Article ID 1607092, 9 pages
http://dx.doi.org/10.1155/2016/1607092
Research Article

Functional Interactions between BKCaα-Subunit and Annexin A5: Implications in Apoptosis

Division of Pathophysiology and Repair, School of Biosciences, Sir Martin Evans Building, Museum Avenue, Cardiff University, Cardiff CF10 3AX, UK

Received 14 April 2016; Revised 4 July 2016; Accepted 10 July 2016

Academic Editor: Yong Ji

Copyright © 2016 Stephen P. Brazier et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Proteomic studies have suggested a biochemical interaction between α subunit of the large conductance, voltage- and Ca2+-activated potassium channel (α), and annexin A5 (ANXA5), which we verify here by coimmunoprecipitation and double labelling immunocytochemistry. The observation that annexin is flipped to the outer membrane leaflet of the plasma membrane during apoptosis, together with the knowledge that the intracellular C-terminal of α contains both Ca2+-binding and a putative annexin-binding motif, prompted us to investigate the functional consequences of this protein partnership to cell death. Membrane biotinylation demonstrated that ANXA5 was flipped to the outer membrane leaflet of HEK 293 cells early in serum deprivation-evoked apoptosis. As expected, serum deprivation caused caspase-3/7 activation and this was accentuated in α expressing HEK 293 cells. The functional consequences of ANXA5 partnership with α were striking, with ANXA5 knockdown causing an increase and ANXA5 overexpression causing a decrease, in single channel Ca2+-sensitivity, measured in inside-out membrane patches by patch-clamp. Taken together, these data suggest a novel model of the early stages of apoptosis where membrane flippage results in removal of the inhibitory effect of ANXA5 on K+ channel activity with the consequent amplification of Ca2+ influx and augmented activation of caspases.