MECHANISMS OF SIGNAL TRANSDUCTION THROUGH SURFACE RECEPTORS

白细胞介素5(IL-5)通过与其受体(IL-5R)相互作用而诱导B细胞和嗜酸性粒细胞的增殖和分化，IL-5R由两个不同的多肽链组成，即α和β(β)。IL-5以高亲和力(Kd，10-150 pm)和低亲和力(Kd，2-10 nM)与特定的细胞表面受体(IL-5R)结合。IL-5Rpha单独以低亲和力与IL-5结合。Betac本身不与IL-5结合，但与IL-5Rα结合形成高亲和力的IL-5R。阿尔法链是IL-5所特有的，而Betac是IL-3和GM-CSF受体所共有的。与一些生长因子受体家族不同的是，细胞因子受体具有内在的激酶结构域，与任何参与受体介导的信号转导的已知酶没有细胞质结构域的同源性。然而，细胞蛋白的酪氨酸磷酸化在各种细胞因子/细胞因子受体系统中被观察到，并被认为在它们的信号转导中起关键作用。最近发现的一个家庭…更多的非受体酪氨酸激酶，包括TYK2、JAK1和JAK2，被认为与细胞因子受体包括GM-CSF和IL-3有关。我们发现在依赖IL-5的早期B细胞系T88-M中，IL-5可以诱导约130 kDa到140 kDa、92 kDa、53 kDa、48 kDa和45 kDa的蛋白质的酪氨酸磷酸化。在这个项目中，我们使用依赖IL-5的早期B细胞系Y16和表达完整或突变的IL-5Rpha和完整的Betac的转染体，研究了IL-5Rpha在IL-5信号转导相关分子酪氨酸磷酸化中的作用。结果表明，表达完全缺乏胞浆结构域的截短型IL-5Rpha和BC的转染体对IL-5既没有蛋白酪氨酸磷酸化，也没有细胞增殖。这证实了IL-5Rpha在蛋白质酪氨酸磷酸化启动细胞生长中的关键作用。IL-5刺激导致Betac和含有Src同源2(SH2)和/或SH3结构域的蛋白如磷脂酰肌醇-3(PI-3)激酶、Shc、Vav和HS1的快速酪氨酸磷酸化，提示它们参与了IL-5介导的信号转导。IL-5刺激可显著增强JAK2和B细胞特异性Bruton‘s酪氨酸激酶(BTK)的活性，并增加JAK2的酪氨酸磷酸化水平。这些结果和最近有关生长因子信号转导的数据结合在一起，JAK2和BTK等酪氨酸激酶驱动的多个生化通路参与了IL-5的信号转导。较少

Interleukin 5 (IL-5) induces proliferation and differentiation of B cells and eosinophils by interacting with its receptor (IL-5R) which consists of two distinct polypeptide chains, alpha and beta (betac). IL-5 binds to a specific cell surface receptor (IL-5R) with both high (Kd, 10-150 pM) and low affinity (Kd, 2-10 nM). The IL-5Ralpha alone binds IL-5 with low affinity. The betac does not bind IL-5 by itself, but does form a high affinity IL-5R in combination with IL-5Ralpha. The alpha chain is specific for IL-5 while betac is common to receptors for IL-3 and GM-CSF,as well. Unlike several growth factor receptor families that possess intrinsic kinase domains, the receptors for cytokines have no cytoplasmic domain homology with any known enzymes involved in receptor-mediated signal transduction. However, tyrosine phosphorylation of cellular proteins has been observed in various cytokine/cytokine receptor systems and believed to be crucial in their signaling. A recently discovered fami … More ly of nonreceptor-tyrosine kinases, including Tyk2, JAK1 and JAK2, was suggested to be associated with cytokine receptors including GM-CSF and IL-3. We have shown that IL-5 induces distinct tyrosine phosphorylation of proteins migrating at about 130 to 140,92,53,48 and 45 kDa in the IL-5-dependent early B cell line, T88-M.In this project, we investigated the role of IL-5Ralpha in tyrosine phosphorylation of molecules involved in IL-5 signal transduction, using an IL-5-dependent early B cell line, Y16 and transfectants expressing intact or mutant IL-5Ralpha together with intact betac. The results revealed that the transfectants expressing truncated IL-5Ralpha, which entirely lacks a cytoplasmic domain, together with bc showed neither protein-tyrosine phosphorylation nor proliferation in response to IL-5. This confirms the critical role of IL-5Ralpha in the protein-tyrosine phosphorylation initiates cell growth. IL-5 stimulation results in rapid tyrosine phosphorylation of betac and proteins containing Src-homology 2 (SH2) and/or SH3 domains such as phosphatidyl-inositol-3 (PI-3) kinase, Shc, Vav and HS1, suggesting their involvement in IL-5 mediated signal transduction. IL-5 stimulation significantly enhanced activities of JAK2 kinase and B-cell specific Bruton's tyrosine kinase (Btk) and increased the tyrosine phosphorylation of JAK2 kinase. These results and recent data on signaling of growth factors taken together, multiple biochemical pathways driven by tyrosine kinases such as JAK2 and Btk are involved in IL-5 signal transduction. Less