Research Institute for Biomedical Sciences, Tokyo University of Science, 2669 Yamazaki, Noda, Chiba 278-0022, Japan.
Int Immunol. 2013 Dec;25(12):671-81. doi: 10.1093/intimm/dxt028. Epub 2013 Sep 18.
In addition to TCR signaling, the activation and proliferation of naive T cells require CD28-mediated co-stimulation. Once engaged, CD28 is phosphorylated and can then activate signaling pathways by recruiting molecules to its YMNM motif and two PxxP motifs. In this study, we analyzed the relationship between tyrosine phosphorylation and the co-stimulatory function of CD28 in murine primary CD4(+) T cells. Tyrosine phosphorylation is decreased in CD28 where the N-terminal PxxP motif is mutated (nPA). In cells expressing nPA, activation of Akt and functional co-stimulation were decreased. In contrast, where the C-terminal PxxP motif is mutated, tyrosine phosphorylation and activation of the ERK, Akt and NF-κB were intact, but proliferation and IL-2 production were decreased. Using the Y(189) to F mutant, we also demonstrated that in naive CD4(+) T cells, tyrosine at position 189 in the YMNM motif is critical for both tyrosine phosphorylation and the functional co-stimulatory effects of CD28. This mutation did not affect unfractionated T-cell populations. Overall, our data suggest that CD28 signaling uses tyrosine phosphorylation-dependent and phosphorylation-independent pathways.
除了 TCR 信号，初始 T 细胞的激活和增殖还需要 CD28 介导的共刺激。一旦结合，CD28 被磷酸化，然后可以通过募集分子到其 YMNM 基序和两个 PxxP 基序来激活信号通路。在这项研究中，我们分析了小鼠原代 CD4(+) T 细胞中 CD28 的酪氨酸磷酸化与共刺激功能之间的关系。在 N 端 PxxP 基序发生突变的 CD28(nPA)中，酪氨酸磷酸化减少。在表达 nPA 的细胞中，Akt 的激活和功能性共刺激减少。相比之下，C 端 PxxP 基序发生突变时，ERK、Akt 和 NF-κB 的酪氨酸磷酸化和激活是完整的，但增殖和 IL-2 产生减少。使用 Y(189)到 F 突变体，我们还表明在初始 CD4(+) T 细胞中，YMNM 基序中位置 189 的酪氨酸对于 CD28 的酪氨酸磷酸化和功能共刺激效应都是至关重要的。该突变不影响未分选的 T 细胞群体。总的来说，我们的数据表明 CD28 信号使用依赖于和不依赖于磷酸化的途径。
