Mihrshahi Robin, Barclay A Neil, Brown Marion H
Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom.
J Immunol. 2009 Oct 15;183(8):4879-86. doi: 10.4049/jimmunol.0901531. Epub 2009 Sep 28.
The CD200 receptor (CD200R) acts as a negative regulator of myeloid cells by interacting with its widely expressed ligand CD200. Using mutants expressed in U937 cells, we show that inhibition is mediated by the PTB domain binding motif (NPLY) in the receptor's cytoplasmic region. The adaptor protein downstream of tyrosine kinase 2 (Dok2) bound directly to the phosphorylated NPLY motif with a 10-fold higher affinity (K(D) of approximately 1 microM at 37 degrees C) than the closely related Dok1. Both of these proteins have been suggested to play a role in CD200R signaling in murine cells. Dok2 was phosphorylated in response to CD200R engagement and recruited RAS p21 protein activator 1 (RasGAP). Knockdown of Dok2 and RasGAP by RNA interference revealed that these proteins are required for CD200R signaling, while knockdown of Dok1 and the inositol 5-phosphatase SHIP did not affect CD200R-mediated inhibition. We conclude that CD200R inhibits the activation of human myeloid cells through direct recruitment of Dok2 and subsequent activation of RasGAP, which distinguishes this receptor from the majority of inhibitory receptors that utilize ITIMs and recruit phosphatases.
CD200受体（CD200R）通过与其广泛表达的配体CD200相互作用，充当髓样细胞的负调节因子。利用在U937细胞中表达的突变体，我们发现抑制作用是由受体胞质区域中的PTB结构域结合基序（NPLY）介导的。酪氨酸激酶2下游的衔接蛋白（Dok2）直接与磷酸化的NPLY基序结合，其亲和力比密切相关的Dok1高10倍（37℃时的解离常数K(D)约为1 microM）。这两种蛋白都被认为在小鼠细胞的CD200R信号传导中发挥作用。Dok2在CD200R参与时发生磷酸化，并募集RAS p21蛋白激活剂1（RasGAP）。通过RNA干扰敲低Dok2和RasGAP表明，这些蛋白是CD200R信号传导所必需的，而敲低Dok1和肌醇5-磷酸酶SHIP并不影响CD200R介导的抑制作用。我们得出结论，CD200R通过直接募集Dok2和随后激活RasGAP来抑制人髓样细胞的激活，这使该受体与大多数利用免疫受体酪氨酸抑制基序（ITIM）并募集磷酸酶的抑制性受体有所不同。
