TY - JOUR
T1 - Distinct roles for Rap1b protein in platelet secretion and integrin α IIbβ 3 outside-in signaling
AU - Zhang, Guoying
AU - Xiang, Binggang
AU - Ye, Shaojing
AU - Chrzanowska-Wodnicka, Magdalena
AU - Morris, Andrew J.
AU - Gartner, T. Kent
AU - Whiteheart, Sidney W.
AU - White, Gilbert C.
AU - Smyth, Susan S.
AU - Li, Zhenyu
PY - 2011/11/11
Y1 - 2011/11/11
N2 - Rap1b is activated by platelet agonists and plays a critical role in integrin α IIbβ 3 inside-out signaling and platelet aggregation. Here we show that agonist-induced Rap1b activation plays an important role in stimulating secretion of platelet granules. We also show that α IIbβ 3 outside-in signaling can activate Rap1b, and integrin outside-in signaling-mediated Rap1b activation is important in facilitating platelet spreading on fibrinogen and clot retraction. Rap1b-deficient platelets had diminished ATP secretion and P-selectin expression induced by thrombin or collagen. Importantly, addition of low doses of ADP and/or fibrinogen restored aggregation of Rap1b-deficient platelets. Furthermore, we found that Rap1b was activated by platelet spreading on immobilized fibrinogen, a process that was not affected by P2Y 12 or TXA 2 receptor deficiency, but was inhibited by the selective Src inhibitor PP2, the PKC inhibitor Ro-31-8220, or the calcium chelator demethyl-1,2-bis(2-aminophenoxy) ethane-N,N,N′,N′-tetraacetic acid tetrakis. Clot retraction was abolished, and platelet spreading on fibrinogen was diminished in Rap1b-deficient platelets compared with wild-type controls. The defects in clot retraction and spreading on fibrinogen of Rap1b-deficient platelets were not rescued by addition of MnCl 2, which elicits α IIbβ 3 outside-in signaling in the absence of inside-out signaling. Thus, our results reveal two different activation mechanisms of Rap1b as well as novel functions of Rap1b in platelet secretion and in integrin α IIbβ 3 outside-in signaling.
AB - Rap1b is activated by platelet agonists and plays a critical role in integrin α IIbβ 3 inside-out signaling and platelet aggregation. Here we show that agonist-induced Rap1b activation plays an important role in stimulating secretion of platelet granules. We also show that α IIbβ 3 outside-in signaling can activate Rap1b, and integrin outside-in signaling-mediated Rap1b activation is important in facilitating platelet spreading on fibrinogen and clot retraction. Rap1b-deficient platelets had diminished ATP secretion and P-selectin expression induced by thrombin or collagen. Importantly, addition of low doses of ADP and/or fibrinogen restored aggregation of Rap1b-deficient platelets. Furthermore, we found that Rap1b was activated by platelet spreading on immobilized fibrinogen, a process that was not affected by P2Y 12 or TXA 2 receptor deficiency, but was inhibited by the selective Src inhibitor PP2, the PKC inhibitor Ro-31-8220, or the calcium chelator demethyl-1,2-bis(2-aminophenoxy) ethane-N,N,N′,N′-tetraacetic acid tetrakis. Clot retraction was abolished, and platelet spreading on fibrinogen was diminished in Rap1b-deficient platelets compared with wild-type controls. The defects in clot retraction and spreading on fibrinogen of Rap1b-deficient platelets were not rescued by addition of MnCl 2, which elicits α IIbβ 3 outside-in signaling in the absence of inside-out signaling. Thus, our results reveal two different activation mechanisms of Rap1b as well as novel functions of Rap1b in platelet secretion and in integrin α IIbβ 3 outside-in signaling.
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U2 - 10.1074/jbc.M111.239608
DO - 10.1074/jbc.M111.239608
M3 - Article
C2 - 21940635
AN - SCOPUS:80655144733
SN - 0021-9258
VL - 286
SP - 39466
EP - 39477
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 45
ER -