Store depletion stimulates POST-dependent STIM1 binding to multiple transporters. (Left) POST binds SERCA2, PMCA, and Na/K-ATPase on store depletion. The POST immunoprecipitate from HEK 293 cells was probed with antibodies to the indicated proteins. Store depletion conditions were as described in Fig. 1. (Center) STIM1 binds POST targets on store depletion. HEK 705 (not induced with tetracycline) cell lysates were immunoprecipitated with rabbit STIM1 antibody and probed with antibody to the indicated proteins. (Right) POST is required for store depletion-dependent STIM1 binding to SERCA2, PMCA, Na/K-ATPase, importin-β1, and exportin-1. HEK 705 cells were transfected with nonsilencing (NS) or POST siRNA; 4 d after transfection, cells were treated with thapsigargin (TG) and cell lysates were immunoprecipitated with anti-STIM1 rabbit antibody and probed with the indicated antibody.