Interaction of STIM1 with endogenously expressed human canonical TRP1 upon depletion of intracellular Ca2+ stores

STIM1 ((s) under bar tromal (i) under bar nteraction (m) under bar olecule (1) under bar) has recently been proposed to communicate the intracellular Ca2+ stores with the plasma membrane to mediate store-operated Ca2+ entry. Here we describe for the first time that Ca2+ store depletion stimulates rapid STIM1 surface expression and association with endogenously expressed human canonical TRP1 (hTRPC1) independently of rises in cytosolic free Ca2+ concentration. These events require the support of the actin cytoskeleton in human platelets, as reported for the coupling between type II inositol 1,4,5-trisphosphate receptor in the Ca2+ stores and hTRPC1 in the plasma membrane, which has been suggested to underlie the activation of store-operated Ca2+ entry in these cells. Electrotransjection of cells with anti-STIM1 antibody, directed toward the N-terminal sequence that includes the Ca2+- binding region, prevented the migration of STIM1 toward the plasma membrane, the interaction between STIM1 and hTRPC1, the coupling between hTRPC1 and type II inositol 1,4,5-trisphosphate receptor, and reduced store-operated Ca2+ entry. These findings provide evidence for a role of STIM1 in the activation of store- operated Ca2+ entry probably acting as a Ca2+ sensor.