Polycystin-2 (TRPP2) Function is Regulated by Calcium Microdomains, a Feedback Mechanism and Ligand Binding

CANTERO MR AND CANTIELLO HF

Congreso; 56th Annual Meeting Biophysical Society; 2012

Polycystin-2 (PC2, TRPP2) is a member of the TRP superfamily that acts as a non-selective cation channel, with permeability to Ca2+. Ca2+ transport by PC2 is relevant in cell signaling. Recent studies (Cantero & Cantiello, BJ 98(3):340a, 2010; ibid, 99(3):106a, 2011) demonstrated that PC2 channel activity from human syncytiotrophoblast (PC2hst) is inhibited by low Ca2+ (~0.3 nM). Addition of the Ca2+ quelators EGTA andBAPTA had different time responses of current decay (7:1) in reconstituted PC2hst, suggesting the presence of Ca2+ microdomains. The in vitro translated PC2 (PC2ptv), devoid of regulatory proteins is insensitive to intracellular Ca2+, but instead Ca2+ regulation is conferred by Ca2+-dependent actin binding proteins (ABPs), such as á-actinin that inhibited channel function in the absence, but stimulated it in the presence of Ca2+. We modeled Ca2+ regulation by assessing Ca2+ microdomains in the PC2hst preparation. The differential equations were solved with MATLAB®. Diffusional models did not reproduce channel behavior after Ca2+ sequestering. Thus, we explored a three-state channel model that reproduced several experimental conditions but failed to explain PC2ptv channel inhibition in the presence of a fixed buffer (ABPs). A five-state ?ligand-activated? channel model mimicked the effect of á-actinin on the PC2ptv. This model also reproduced the temporal decrease in the channel?s open probability in the presence of Ca2+ chelators. The model supports the idea that a fixed buffer bound as a Ca2+-sensitive ligand to the channel, acts as a local Ca2+ source that regulates Ca2+ influx through the channel. This novel cytoskeletal regulation of PC2 may provide functional diversity