Kato Hisashi, Honda Shigenori, Yoshida Hitoshi, Kashiwagi Hirokazu, Shiraga Masamichi, Honma Nakayuki, Kurata Yoshiyuki, Tomiyama Yoshiaki
Department of Internal Medicine and Molecular Science, Graduate School of Medicine B5, Osaka University, Osaka, Japan.
J Thromb Haemost. 2005 Apr;3(4):763-74. doi: 10.1111/j.1538-7836.2005.01235.x.
CD47 (integrin-associated protein) serves as a receptor for thrombospondin-1 (TSP-1) and Src homology 2 domain-containing protein tyrosine phosphatase substrate-1 (SHPS-1), and the TSP-1/CD47 interaction has been believed to augment integrin-mediated platelet function. Here, employing SHPS-1-immunoglobulin (Ig) as a ligand, we have newly demonstrated that CD47 acts as an inhibitory receptor for platelet function. The binding of SHPS-1-Ig was solely mediated by CD47, because CD47-deficient platelets failed to bind murine SHPS-1-Ig. The human SHPS-1/CD47 interaction inhibited the platelet aggregation induced by several kinds of agonists at a low concentration. Moreover, human SHPS-1 expressed on the cell surface as well as soluble SHPS-1-Ig markedly inhibited the platelet spreading on, but not initial adhesion to, immobilized fibrinogen. Again, neither murine SHPS-1 expressed on the cell surface nor murine SHPS-1-Ig inhibited the spreading of CD47-deficient platelets. We further investigated the tyrosine phosphorylation of signaling proteins during platelet spreading on immobilized fibrinogen. Unexpectedly, SHPS-1 inhibited alpha(IIb)beta(3)-mediated platelet spreading without disturbing focal adhesion kinase (FAK) tyrosine phosphorylation. Further examination revealed that SHPS-1 inhibited the tyrosine phosphorylation of alpha-actinin, a downstream effector of FAK, but not of cortactin. Thus, it is likely that the SHPS-1/CD47 interaction inhibits alpha(IIb)beta(3)-mediated outside-in signaling by interfering with the downstream pathway of FAK. Taken together, our data suggest that SHPS-1 negatively regulates platelet function via CD47, especially alpha(IIb)beta(3)-mediated outside-in signaling.
CD47(整合素相关蛋白)作为血小板反应蛋白-1(TSP-1)和含Src同源2结构域蛋白酪氨酸磷酸酶底物-1(SHPS-1)的受体,TSP-1/CD47相互作用被认为可增强整合素介导的血小板功能。在此,我们使用SHPS-1免疫球蛋白(Ig)作为配体,首次证明CD47作为血小板功能的抑制性受体。SHPS-1-Ig的结合仅由CD47介导,因为缺乏CD47的血小板无法结合鼠源SHPS-1-Ig。人源SHPS-1/CD47相互作用在低浓度时可抑制多种激动剂诱导的血小板聚集。此外,细胞表面表达的人源SHPS-1以及可溶性SHPS-1-Ig可显著抑制血小板在固定化纤维蛋白原上的铺展,但不影响其初始黏附。同样,细胞表面表达的鼠源SHPS-1或鼠源SHPS-1-Ig均不抑制缺乏CD47的血小板的铺展。我们进一步研究了血小板在固定化纤维蛋白原上铺展过程中信号蛋白的酪氨酸磷酸化情况。出乎意料的是,SHPS-1抑制α(IIb)β(3)介导的血小板铺展,而不影响粘着斑激酶(FAK)的酪氨酸磷酸化。进一步研究发现,SHPS-1抑制FAK下游效应分子α-辅肌动蛋白的酪氨酸磷酸化,但不抑制皮层肌动蛋白的酪氨酸磷酸化。因此,SHPS-1/CD47相互作用可能通过干扰FAK的下游途径抑制α(IIb)β(3)介导的由外向内信号传导。综上所述,我们的数据表明SHPS-1通过CD47负向调节血小板功能,尤其是α(IIb)β(3)介导的由外向内信号传导。