AKAP5 Knockout Cell Line (HEK293)

To avoid conflicting and deleterious outcomes, eukaryotic cells often confine second messengers to spatially restricted subcompartments. The smallest signaling unit is the Ca nanodomain, which forms when Ca channels open. Ca nanodomains arising from store-operated Orai1 Ca channels stimulate the protein phosphatase calcineurin to activate the transcription factor nuclear factor of activated T cells (NFAT). Here, we show that NFAT1 tethered directly to the scaffolding protein AKAP79 (A-kinase anchoring protein 79) is activated by local Ca entry, providing a mechanism to selectively recruit a transcription factor. We identify the region on the N terminus of Orai1 that interacts with AKAP79 and demonstrate that this site is essential for physiological excitation-transcription coupling. NMR structural analysis of the AKAP binding domain reveals a compact shape with several proline-driven turns. Orai2 and Orai3, isoforms of Orai1, lack this region and therefore are less able to engage AKAP79 and activate NFAT. A shorter, naturally occurring Orai1 protein that arises from alternative translation initiation also lacks the AKAP79-interaction site and fails to activate NFAT1. Interfering with Orai1-AKAP79 interaction suppresses cytokine production, leaving other Ca channel functions intact. Our results reveal the mechanistic basis for how a subtype of a widely expressed Ca channel is able to activate a vital transcription pathway and identify an approach for generation of immunosuppressant drugs.