Sada K, Zhang J, Siraganian R P
Receptors and Signal Transduction Section, Oral Infection and Immunity Branch, National Institutes of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892, USA.
Blood. 2001 Mar 1;97(5):1352-9. doi: 10.1182/blood.v97.5.1352.
Aggregation of the high-affinity IgE receptor induces the tyrosine phosphorylation of subunits of the receptor and the subsequent association with the receptor of the cytosolic protein tyrosine kinase Syk. The current experiments examined the functional importance of membrane association of Syk and the role of the SH2 domain in receptor-mediated signal transduction. Wild-type Syk and chimeric Syk molecules with the c-Src myristylation sequence at the amino-terminus were expressed in a Syk-negative mast cell line. Chimeric Syk with the myristylation sequence was membrane associated, and a small fraction was constitutively colocalized with FcepsilonRI, Lyn, and LAT (linker for T-cell activation) in the glycolipid-enriched microdomains or rafts. However, even under these conditions, the tyrosine phosphorylation of Syk and the downstream propagation of signals required FcepsilonRI aggregation. This chimeric Syk was less active than wild-type Syk in FcepsilonRI-mediated signal transduction. In contrast, a truncated membrane-associated form of Syk that lacked the SH2 domains was not tyrosine phosphorylated by receptor aggregation and failed to transduce intracellular signals. These findings suggest that SH2 domain-mediated membrane translocation of Syk is essential for the FcepsilonRI-mediated activation of Syk for downstream signaling events leading to histamine release. Furthermore, the localization of Syk in glycolipid-enriched microdomains by itself is not enough to generate or enhance signaling events.
高亲和力IgE受体的聚集诱导受体亚基的酪氨酸磷酸化，并随后与胞质蛋白酪氨酸激酶Syk的受体结合。当前实验研究了Syk膜结合的功能重要性以及SH2结构域在受体介导的信号转导中的作用。野生型Syk和在氨基末端带有c-Src肉豆蔻酰化序列的嵌合Syk分子在Syk阴性肥大细胞系中表达。带有肉豆蔻酰化序列的嵌合Syk与膜结合，并且一小部分在富含糖脂的微结构域或脂筏中与FcepsilonRI、Lyn和LAT（T细胞激活连接蛋白）组成性共定位。然而，即使在这些条件下，Syk的酪氨酸磷酸化和信号的下游传播仍需要FcepsilonRI聚集。这种嵌合Syk在FcepsilonRI介导的信号转导中比野生型Syk活性更低。相比之下，一种缺少SH2结构域的截短的膜相关形式的Syk不会因受体聚集而发生酪氨酸磷酸化，并且无法转导细胞内信号。这些发现表明，SH2结构域介导的Syk膜易位对于FcepsilonRI介导的Syk激活以引发导致组胺释放的下游信号事件至关重要。此外，Syk自身在富含糖脂的微结构域中的定位不足以产生或增强信号事件。
