Actin-binding proteins mediate regulation by calcium of polycystin-2

CANTERO MR, CANTIELLO HF

Baltimore, Maryland, USA

Congreso; 55th biophysical annual meeting; 2011

Polycystin-2 (PC2, TRPP2) is a member of the TRP superfamily that acts as a non-selective cation channel, with permeability to calcium. PC2 is implicated in calcium transport, and therefore, its regulation by calcium is relevant to its role(s) in cell function. Recent studies (Cantero & Cantiello, BJ 98(3):340a, 2010) demonstrated that PC2 channel activity from human syncytiotrophoblast is regulated by cytoplasmic calcium, such that low calcium (< 0.3 nM) renders the channel inactive. Titration of cytoplasmic calcium recovers PC2 channel activity, with a Hill coefficient of 4 and an apparent affinity constant of 1-5 nM. Interestingly, in vitro in vitro translated PC2, devoid of regulatory proteins was completely insensitive to intracellular calcium (ibid). In this  study we further explored the nature of this regulation by assessing potential calcium-sensitive target proteins in the channel complex. Several calcium sensitive and insensitive actin-binding proteins (ABP) were studiedin the in vitro translated protein. The actin-bundling protein á-actinin (250 nM) increased PC2 channel activity in the presence of high (10 ìM) cytoplasmic calcium, but instead was inhibitory in its absence. The calcium insensitive G-actin binding protein profiling (4 nM), increased PC2 channel activity both in presence and absence of calcium, while the calcium-sensitive, actin-severing protein gelsolina (4 nM), regulated PC2 channel function in the presence, but not absence of calcium (10 ìM). These data suggest that the formation of ABP-PC2 complexes confer distinct calcium regulatory functions to the channel, thus providing a novel cytoskeletal pathway for channel regulation. This response to cytoplasmic calcium by PC2 may provide functional diversity to the channel by choosing, and possibly exchanging ABP-structural partners.