Aim: 

TRPC proteins assemble into homo- or hetero-multimeric channel complexes that participate in capacitative Ca²⁺ entry (CCE) or non-capacitative Ca²⁺ entry (NCCE). hTRPC6 has been postulated as a point of convergence between both pathways. It was initially presented as a non-capacitative channel activated by diacylglycerol (DAG) but hTRPC6 also forms capacitative channels by interaction with hTRPC1 (Redondo et al. 2008). Here we report dynamic interactions between endogenously expressed hTRPC6 with either Orai1 and STIM1 or hTRPC3 to participate in CCE or NCCE.

Methods: 

Cytosolic Ca²⁺ concentration, reversible electroporation, immunoprecipitation and Western blotting were performed as previously described (López et al. 2006).

Results: 

Cell electrotransjection with anti-hTRPC6 antibody reduces CCE induced by N,N,N',N'-tetrakis-(2-pyridylmethyl)-ethylenediamine (TPEN), an intraluminal Ca²⁺ chelator. Thrombin and thapsigargin plus ionomycin enhanced interaction between hTRPC6, Orai1 and STIM1. The DAG analog, 1-oleoyl-2-acetyl-sn-glycerol (OAG) displaces hTRPC6 from Orai1/STIM1 and enhances its association with hTRPC3. The interaction between hTRPC6 and hTRPC3 was abolished by dimethyl-BAPTA loading.

Conclusion: 

Our results demonstrate that hTRPC6 participates both in CCE and NCCE through its interaction with the Orai1/STIM1 complex or hTRPC3, respectively.

References: López, J.J., Salido, G.M., Pariente, J.A., Rosado, J.A. 2006. Interaction of STIM1 with endogenously expressed human canonical TRP1 upon depletion of intracellular Ca²⁺ stores. J Biol Chem 281, 28254-28264.

Redondo, P.C., Jardin, I., Lopez, J.J., Salido, G.M. & Rosado, J.A. 2008. Intracellular Ca²⁺ store depletion induces the formation of macromolecular complexes involving hTRPC1, hTRPC6, the type II IP₃ receptor and SERCA3 in human platelets. Biochim Biophys Acta 1783, 1163-1176.

Supported by BFU2007-60104; I.J. supported by BES-2008-002875.