The cAMP-binding Popdc proteins have a redundant function in the heart

Popdc (Popeye-domain-containing) genes encode membrane-bollind proteins and are abundantly present in cardiac myocytes and in skeletal muscle fibres. Functional analysis of Popdc1 (Byes) and Popdc2 in mice and of popdc2 in zebrafish revealed an overlapping role for proper electrical conduction in the heart and maintaining structural integrity of skeletal muscle. Popdc proteins mediate cAMP signalling and modulate the biological activity of interacting proteins. The two-pore channel TREK-1 interacts with all three Popdc proteins. In Xenopus oocytes, the presence of Popdc proteins causes an enhanced membrane transport leading to an increase in TREK-1 current, which is blocked when cAMP levels are increased. Another important Popdc-interacting protein is caveolin 3, and the loss of Popdc1 affects caveolar size. Thus a family of membrane-bound cAMP-binding proteins has been identified, which modulate the subcellular localization of effector proteins involved in organizing signalling complexes and assuring proper membrane physiology of cardiac myocytes.