DREAM plays an important role in platelet activation and thrombogenesis

Downstream regulatory element antagonist modulator (DREAM), a transcriptional repressor, is known tomodulate pain responses. However, it is unknown whether DREAM is expressed in anucleate platelets and plays a role in thrombogenesis. By using intravital microscopy with DREAM-null mice and their bone marrow chimeras, we demonstrated that both hematopoietic and nonhematopoietic cell DREAMs are required for platelet thrombus formation following laser-induced arteriolar injury. In a FeCl3-induced thrombosis model, we found that compared with wild-type (WT) control and nonhematopoietic DREAM knockout (KO) mice, DREAM KO control and hematopoietic DREAM KO mice showed a significant delay in time to occlusion. Tail bleeding time was prolonged in DREAM KO control mice, but not in WT orDREAMbonemarrowchimeric mice. In vivo adoptive transfer experiments further indicated the importance of platelet DREAM in thrombogenesis. We found that DREAM deletion does not alter the ultrastructural features of platelets but significantly impairs platelet aggregation and adenosine triphosphate secretion induced by numerous agonists (collagen-related peptide, adenosine 5'-diphosphate, A23187, thrombin, or U46619). Biochemical studies revealed that platelet DREAM positively regulates phosphoinositide 3-kinase (PI3K) activity during platelet activation. Using DREAM-null platelets and PI3K isoform-specific inhibitors, we observed that platelet DREAMis important fora-granule secretion, Ca (2+) mobilization, and aggregation through PI3K class I beta (PI3K-I beta). Genetic and pharmacological studies in human megakaryoblastic MEG-01 cells showed that DREAM is important for A23187-induced Ca (2+) mobilization and its regulatory function requires Ca (2+) binding and PI3K-I beta activation. These results suggest that platelet DREAM regulates PI3K-I beta activity and plays an important role during thrombus formation.