PT  - JOURNAL ARTICLE
AU  - Yanhua Wang
AU  - Lirong Jiang
AU  - Xi Mo
AU  - Yu Lan
AU  - Xiao Yang
AU  - Xinyi Liu
AU  - Jian Zhang
AU  - Li Zhu
AU  - Junling Liu
AU  - Xiaolin Wu
TI  - Megakaryocytic Smad4 Regulates Platelet Function through Syk and ROCK2 Expression
AID  - 10.1124/mol.116.107417
DP  - 2017 Sep 01
TA  - Molecular Pharmacology
PG  - 285--296
VI  - 92
IP  - 3
4099  - http://molpharm.aspetjournals.org/content/92/3/285.short
4100  - http://molpharm.aspetjournals.org/content/92/3/285.full
SO  - Mol Pharmacol2017 Sep 01; 92
AB  - Smad4, a key transcription factor in the transforming growth factor-β signaling pathway, is involved in a variety of cell physiologic and pathologic processes. Here, we characterized megakaryocyte/platelet-specific Smad4 deficiency in mice to elucidate its effect on platelet function. We found that megakaryocyte/platelet-specific loss of Smad4 caused mild thrombocytopenia and significantly extended first occlusion time and tail bleeding time in mice. Smad4-deficient platelets showed reduced agonist-induced platelet aggregation. Further studies showed that a severe defect was seen in integrin αIIbβ3-mediated bidirectional (inside-out and outside-in) signaling in Smad4-deficient platelets, as evidenced by reduced fibrinogen binding and α-granule secretion, suppressed platelet spreading and clot retraction. Microarray analysis showed that the expression levels of multiple genes were altered in Smad4-deficient platelets. Among these genes, spleen tyrosine kinase (Syk) and Rho-associated coiled-coil containing protein kinase 2 (ROCK2) were downregulated several times as confirmed by quantitative reverse-transcription polymerase chain reaction and immunoblotting. Further research showed that Smad4 directly regulates ROCK2 transcription but indirectly regulates Syk. Megakaryocyte/platelet-specific Smad4 deficiency caused decreased expression levels of Syk and ROCK2 in platelets. These results suggest potential links among Smad4 deficiency, attenuated Syk, and ROCK2 expression and defective platelet activation.