Sanchez-Lockhart Mariano, Graf Beth, Miller Jim
The David H Smith Center for Vaccine Biology and Immunology, University of Rochester, Rochester, NY 14642, USA.
J Immunol. 2008 Dec 1;181(11):7639-48. doi: 10.4049/jimmunol.181.11.7639.
During T cell interaction with APC, CD28 is recruited to the central region (cSMAC) of the immunological synapse. CD28-mediated signaling through PI3K results in the recruitment of protein kinase C-theta (PKCtheta) to the cSMAC, activation of NF-kappaB, and up-regulation of IL-2 transcription. However, the mechanism that mediates CD28 localization to the cSMAC and the functional consequences of CD28 localization to the cSMAC are not understood. In this report, we show that CD28 recruitment and persistence at the immunological synapse requires TCR signals and CD80 engagement. Addition of mAb to either MHC class II or CD80 results in the rapid displacement of CD28 from the immunological synapse. Ligand binding is not sufficient for CD28 localization to the immunological synapse, as truncation of the cytosolic tail of CD28 disrupts synapse localization without effecting the ability of CD28 to bind CD80. Furthermore, a single point mutation in the CD28 cytosolic tail (tyrosine 188) interferes with the ability of CD28 to preferentially accumulate at the cSMAC. PKCtheta distribution at the immunological synapse mirrors the distribution of tyrosine 188-mutated CD28, indicating that CD28 drives the localization of PKCtheta even when CD28 is not localized to the cSMAC. Mutation of tyrosine 188 also results in diminished activation of NF-kappaB, suggesting that CD28-mediated localization of PKCtheta to the cSMAC is important for efficient signal transduction. These data reinforce the importance of the interplay of signals between TCR and CD28 and suggest that CD28 signaling through PCKtheta may be mediated through localization to the cSMAC region of the immunological synapse.
在T细胞与抗原呈递细胞（APC）相互作用期间，CD28被募集到免疫突触的中央区域（cSMAC）。CD28通过磷脂酰肌醇-3激酶（PI3K）介导的信号传导导致蛋白激酶C-θ（PKCθ）被募集到cSMAC，激活核因子κB（NF-κB）并上调白细胞介素-2（IL-2）转录。然而，介导CD28定位于cSMAC的机制以及CD28定位于cSMAC的功能后果尚不清楚。在本报告中，我们表明CD28在免疫突触处的募集和持续存在需要T细胞受体（TCR）信号和CD80结合。向主要组织相容性复合体II类（MHC II类）或CD80添加单克隆抗体（mAb）会导致CD28从免疫突触快速移位。配体结合不足以使CD28定位于免疫突触，因为CD28胞质尾部的截断会破坏突触定位，而不影响CD28结合CD80的能力。此外，CD28胞质尾部的单点突变（酪氨酸188）会干扰CD28优先在cSMAC积累的能力。PKCθ在免疫突触处的分布反映了酪氨酸188突变的CD28的分布，表明即使CD28不定位于cSMAC，CD28也会驱动PKCθ的定位。酪氨酸188的突变还会导致NF-κB的激活减少，这表明CD28介导的PKCθ定位于cSMAC对于有效的信号转导很重要。这些数据强化了TCR和CD28之间信号相互作用的重要性，并表明通过PKCθ的CD28信号传导可能是通过定位于免疫突触的cSMAC区域介导的。
