Ohnishi H, Ledbetter J A, Kanner S B, Linsley P S, Tanaka T, Geller A M, Kotb M
Veteran's Administration Medical Center, Memphis, TN 38104.
J Immunol. 1995 Apr 1;154(7):3180-93.
The CD28 molecule expressed on the surface of T cells plays a pivotal role in transducing costimulatory signals necessary for cell activation. CD28 coligation enhances tyrosine phosphorylation and phosphoinositol 3-kinase association in responsive cells. CD28 cross-linking has also been reported to activate inositol phospholipid turnover and to cause release of intracellular calcium. Here we examine the effects of CD28 cross-linking on early activation of protein kinase C (PKC). We have reported recently that either PMA or CD28 cross-linking synergizes with signals delivered by superantigen and cytokines to induce the proliferation of APC-depleted T cells. Unlike PMA, CD28 cross-linking alone failed to induce an increase in membrane-associated PKC activity. However, PKC activation was seen in resting T cells when CD28 was cross-linked in the presence of superantigen plus APC-derived supernatant, which by themselves had no effect on PKC activity. Inhibition of PKC activity using calphostin C blocked the response of pure T cells to superantigen in the presence of either autologous APC, PMA, or CD28 cross-linking. This effect was specific; it was only seen when calphostin C was added within the first hour of stimulation. Assays of [Ca2+]i levels showed that CD28 cross-linking augmented and prolonged the rise in [Ca2+]i induced in T cells by superantigen and APC-derived cytokines. In the presence of superantigen, the proliferative response of T cells costimulated by CD28 cross-linking was cyclosporin A-sensitive, whereas in the presence of PMA, CD28 cross-linking conferred resistance to cyclosporin A. Both the phosphorylation of phospholipase C gamma 1 at tyrosine and the rise in [Ca2+]i induced by CD28 cross-linking in preactivated T cells were blocked by herbimycin A. Herbimycin A treatment also blocked the ability of CD28 cross-linking to induce a rise in [Ca2+]i in resting T cells. We conclude that CD28 costimulatory signals augment superantigen-induced TCR signals by converging onto common TCR effector pathways involving the activation of phospholipase C gamma 1 and PKC and by generating a cyclosporin A-sensitive pathway.
表达于T细胞表面的CD28分子在转导细胞活化所需的共刺激信号中起关键作用。CD28共连接增强反应性细胞中的酪氨酸磷酸化和磷酸肌醇3激酶结合。据报道，CD28交联还可激活肌醇磷脂周转并导致细胞内钙释放。在此，我们研究CD28交联对蛋白激酶C（PKC）早期活化的影响。我们最近报道，佛波酯（PMA）或CD28交联与超抗原和细胞因子传递的信号协同作用，诱导APC缺失的T细胞增殖。与PMA不同，单独的CD28交联未能诱导膜相关PKC活性增加。然而，当在超抗原加APC来源的上清液存在下进行CD28交联时，静息T细胞中可见PKC活化，而超抗原和上清液本身对PKC活性无影响。使用钙泊三醇C抑制PKC活性可阻断纯T细胞在存在自体APC、PMA或CD28交联时对超抗原的反应。这种作用具有特异性；仅在刺激的第一小时内加入钙泊三醇C时才可见。[Ca2+]i水平测定表明，CD28交联增强并延长了超抗原和APC来源的细胞因子在T细胞中诱导的[Ca2+]i升高。在存在超抗原的情况下，CD28交联共刺激的T细胞增殖反应对环孢素A敏感，而在存在PMA的情况下，CD28交联赋予对环孢素A的抗性。CD28交联在预活化T细胞中诱导的磷脂酶Cγ1酪氨酸磷酸化和[Ca2+]i升高均被赫曲霉素A阻断。赫曲霉素A处理也阻断了CD28交联在静息T细胞中诱导[Ca2+]i升高的能力。我们得出结论，CD28共刺激信号通过汇聚到涉及磷脂酶Cγ1和PKC活化的共同TCR效应器途径并通过产生对环孢素A敏感的途径来增强超抗原诱导的TCR信号。
