DREAM plays an important role in platelet activation and thrombogenesis

Abstract

Downstream regulatory element antagonist modulator (DREAM), a transcriptional repressor, is known to modulate 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 FeCl-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 or DREAM bone marrow chimeric 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 DREAM is important for α-granule secretion, Ca mobilization, and aggregation through PI3K class Iβ (PI3K-Iβ). Genetic and pharmacological studies in human megakaryoblastic MEG-01 cells showed that DREAM is important for A23187-induced Ca mobilization and its regulatory function requires Ca binding and PI3K-Iβ activation. These results suggest that platelet DREAM regulates PI3K-Iβ activity and plays an important role during thrombus formation.

Downstream Regulatory Element Antagonist Modulator (DREAM), a target for anti-thrombotic agents

“…Indeed, we have recently shown that the mRNA and protein of DREAM is expressed in human and mouse platelets and a human megakaryocyte cell line (12). DREAM deletion did not affect blood counts in mice, and DREAM bone marrow chimeric mice showed no difference in their blood counts, suggesting that DREAM is dispensable for hematopoiesis.…”

“…In a series of functional assays, we found that DREAM deletion significantly reduces granule secretion, cytosolic Ca 2+ levels, αIIbβ3 integrin activation, and aggregation in platelets following stimulation with a low concentration of agonists such as thrombin, CRP, U46619, A23187, and ADP (12). Interestingly, our study using isoform-specific PI3K inhibitors (42, 43) in DREAM-null platelets provided evidence that the regulation of platelet function by DREAM results from activation of PI3K class Iβ after agonist stimulation.…”

“…By using in vivo real-time intravital microscopy with DREAM KO mice and their bone marrow chimeras, we demonstrated that both platelet and non-hematopoietic cell DREAM contribute to platelet thrombus formation at the site of laser-induced arteriolar injury (12). In a mouse model of FeCl 3 -induced thrombosis, DREAM KO and hematopoietic cell DREAM KO mice exhibited a delayed time to occlusion, but non-hematopoietic cell DREAM KO mice did not.…”

“…Although our recent report suggested the role of platelet DREAM in regulating PI3K class Iβ activity, it was hard to precisely compare our results with those in platelet-specific PI3K class Iβ-null mice because of the differences in agonists, the concentrations used, and the in vivo models tested. Nevertheless, it is of interest to note that global DREAM deletion prolongs bleeding time (12), whereas the platelet-specific PI3K class Iβ-null mice have no effect on hemostasis (42, 50). This discrepancy implicates the potential role of non-hematopoietic cell DREAM - particularly endothelial cell or leukocyte DREAM - in hemostasis, probably through a mechanism independent of PI3K class Iβ activation.…”

“…Moreover, a previous report that platelet-derived microparticles containing the PPARγ-retinoid X receptor complex induce PPARγ-mediated signaling in a monocytic cell line after internalization (11) suggests that transcription factors in platelets may have a paracrine effect on gene transcription in other nucleated cells. We have recently demonstrated that downstream regulatory element antagonist modulator (DREAM), a transcriptional repressor, is expressed in human and mouse platelets and a human megakaryocytic cell line (12). This review will summarize the known functions of DREAM in nucleated cells and discuss the novel regulatory mechanism of DREAM in platelet activation and its contributions to hemostasis and thrombosis.…”