Stim1 and Orai1 Mediate CRAC Currents and Store-Operated Calcium Entry Important for Endothelial Cell Proliferation

Recent breakthroughs in the store-operated calcium (Ca2+) entry (SOCE) pathway have identified Stim1 as the endoplasmic reticulum Ca2+ sensor and Orai1 as the pore forming subunit of the highly Ca2+ -selective CRAC channel expressed in hematopoietic cells. Previous studies, however, have suggested that endothelial cell (EC) SOCE is mediated by the nonselective canonical transient receptor potential channel (TRPC) family, TRPC1 or TRPC4. Here, we show that passive store depletion by thapsigargin or receptor activation by either thrombin or the vascular endothelial growth factor activates the same pathway in primary ECs with classical SOCE pharmacological features. ECs possess the archetypical Ca2+ release-activated Ca2+ current (ICRAC), albeit of a very small amplitude. Using a maneuver that amplifies currents in divalent-free bath solutions, we show that EC CRAC has similar characteristics to that recorded from rat basophilic leukemia cells, namely a similar time course of activation, sensitivity to 2-aminoethoxydiphenyl borate, and low concentrations of lanthanides, and large Na+ currents displaying the typical depotentiation. RNA silencing of either Stim1 or Orai1 essentially abolished SOCE and ICRAC in ECs, which were rescued by ectopic expression of either Stim1 or Orai1, respectively. Surprisingly, knockdown of either TRPC1 or TRPC4 proteins had no effect on SOCE and ICRAC. Ectopic expression of Stim1 in ECs increased their ICRAC to a size comparable to that in rat basophilic leukemia cells. Knockdown of Stim1, Stim2, or Orai1 inhibited EC proliferation and caused cell cycle arrest at S and G2/M phase, although Orai1 knockdown was more efficient than that of Stim proteins. These results are first to our knowledge to establish the requirement of Stim1/Orai1 in the endothelial SOCE pathway. (Circ Res. 2008; 23: 1289-1299.)