Platelet DREAM regulates aggregation and ATP secretion following stimulation with numerous agonists. (A) Lysates of gel-filtered mouse and human platelets (hPLT) were immunoblotted. Representative blots were obtained from 3 independent experiments. (B) WT and DREAM KO platelets were treated with or without 0.5 µg/mL CRP, followed by transmission electron micrographs. Original magnification was ×4800 and extension was ×13 000. The arrows show α-granules. Bar, 500 nm. (C-G) Platelet aggregation and ATP secretion were induced by 0.5 µg/mL CRP, 100 nM A23187, 10 µM ADP, 0.0125 U/mL thrombin, and 0.25 µM U46619. In the ADP-induced aggregation assay, 30 µg/mL human FG was added to the platelet suspension before ADP stimulation. (I) Platelet aggregation and quantitative graphs. (II) ATP secretion was monitored with platelet aggregation with a luciferin/luciferase reagent. Data represent the mean ± SD (n = 3). (H-I) WT and DREAM KO platelets were pretreated with (H) 1 U/mL apyrase or (I) 1 µM ADP, and aggregation was induced by CRP, respectively. (J) WT and DREAM KO platelets were pretreated with 1 mM aspirin, followed by stimulation with 0.0125 U/mL thrombin. Platelet aggregation and quantitative graphs are shown. Data represent the mean ± SD (n = 3). **P < .01 and ***P < .001 vs WT platelets after the Student t test.