Siglec-7 mediates nonapoptotic cell death independently of its immunoreceptor tyrosine-based inhibitory motifs in monocytic cell line U937
Siglec-7 mediates nonapoptotic cell death independently of its immunoreceptor tyrosine-based inhibitory motifs in monocytic cell line U937
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DOI：
10.1093/glycob/cwp195
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发表时间：
2010-03-01
期刊：
影响因子：
4.3
通讯作者：
Hashimoto, Yasuhiro
中科院分区：
文献类型：
--
作者：
Mitsuki, Motoaki;Nara, Kiyomitsu;Hashimoto, Yasuhiro
Siglec-7是一种唾液酸结合免疫球蛋白样凝集素，主要通过细胞溶质免疫受体酪氨酸基序（ITIM）转导抑制信号。在此，我们报道了Siglec-7与特异性F（ab '）（2）的聚类引起细胞死亡。有趣的是，缺乏胞质ITIM结构域的截短的Siglec-7仍然诱导细胞死亡，表明ITIM对于死亡信号传导不是必需的。对死亡信号的进一步分析显示，氧自由基清除剂N-乙酰半胱氨酸完全抑制了细胞死亡，而pancaspase抑制剂则没有。此外，在死亡过程中没有检测到caspase-3激活、DNA梯状条带形成和核浓缩，表明细胞死亡是非凋亡性的。为了鉴定死亡信号传导的关键区域，我们制备了Siglec-7和Siglec-9之间的一系列改组嵌合体，后者不表达死亡信号。关键区域被定位到近膜C2-set结构域的中间，其在Siglec-7和Siglec-9之间仅包含6个氨基酸差异。对这六种氨基酸中的每一种的点突变分析揭示，六种氨基酸中的四种对于死亡信号是关键的。计算机辅助的3D建模显示，这四个氨基酸位于C2-set结构域表面的近端。总之，Siglec-7诱导非凋亡性细胞死亡，其信号由细胞外C2-set结构域转导。
Siglec-7, a sialic acid binding immunoglobulin-like lectin, predominantly transduces inhibitory signals through cytosolic immunoreceptor tyrosine-based inhibitory motifs (ITIMs). Here, we report that clustering of Siglec-7 with a specific F(ab')(2) elicited cell death. Interestingly, a truncated Siglec-7 lacking the cytosolic ITIM domain still induced the cell death, suggesting that the ITIMs are not essential for the death signaling. Further analyses of the death signaling revealed that an oxygen radical scavenger, N-acetyl cysteine, completely inhibited the cell death, whereas a pancaspase inhibitor did not. In addition, caspase-3 activation, DNA ladder formation, and nuclear condensation were not detected during the death process, suggesting that the cell death is nonapoptotic. To identify the critical region for the death signaling, we prepared a series of shuffling chimeras between Siglec-7 and Siglec-9, the latter of which did not transduce a death signal. The critical region was mapped to the middle of the membrane-proximal C2-set domain, which contained only six amino acid differences between Siglec-7 and Siglec-9. Point mutation analyses of each of these six amino acids revealed that four of the six amino acids were critical for the death signal. A computer-assisted 3D modeling revealed that these four amino acids were proximally located on the surface of the C2-set domain. In conclusion, Siglec-7 induces nonapoptotic cell death, the signal for which is transduced by an extracellular C2-set domain.