Tamir A, Granot Y, Isakov N
Department of Microbiology and Immunology, Faculty of Health Sciences, Ben Gurion University of the Negev, Beer Sheva, Israel.
J Immunol. 1996 Aug 15;157(4):1514-22.
The induction of T cell proliferation requires signals from the TCR and a co-receptor molecule, such as CD28, that activate parallel and partially cross-reactive signaling pathways. These pathways are disrupted by agonists that utilize adenylate cyclase and cAMP-dependent protein kinase A (PKA). We found that the adenylate cyclase activator, forskolin, inhibits anti-CD3-induced shift in Lck electrophoretic mobility, suggesting an intervention at the TCR-coupled phosphoinositide turnover that precedes the activation of PKC. The shift of Lck following direct PKC activation by 12-O-tetradecanoyl phorbol 13-acetate, which bypasses early receptor-triggered biochemical events, is insensitive to forskolin. Nevertheless, forskolin also inhibits PKC downstream events, such as c-jun expression, which is critical for the activation process of T cells. To further analyze potential cross points between positively and negatively regulating signaling pathways in T cells, we tested the effects of activators of the adenylate cyclase or PKA on two parallel mitogen-activated protein kinase signaling pathways mediated by extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase. Using a PKC-specific inhibitor, GF109203X, or PKC-depleted T cells, we found that a large part of the anti-CD3-induced ERK activation is PKC dependent. Both PKC-dependent and -independent activation of ERK were sensitive to inhibition by forskolin or a cell-permeable cAMP analogue, dbcAMP. Furthermore, the effect of 12-O-tetradecanoyl phorbol 13-acetate and ionomycin, which synergized to fully activate c-Jun N-terminal kinase, was also sensitive to inhibition by forskolin. Our results suggest that PKA inhibits T cell activation by interfering with multiple events along the two signaling pathways operating downstream of the TCR and the CD28 co-receptor molecules.
T细胞增殖的诱导需要来自TCR和共受体分子（如CD28）的信号，这些信号激活平行且部分交叉反应的信号通路。这些通路会被利用腺苷酸环化酶和cAMP依赖性蛋白激酶A（PKA）的激动剂破坏。我们发现，腺苷酸环化酶激活剂福斯高林可抑制抗CD3诱导的Lck电泳迁移率变化，提示其干预了TCR偶联的磷脂酰肌醇代谢，该代谢先于PKC的激活。12 - O - 十四烷酰佛波醇13 - 乙酸酯直接激活PKC后导致的Lck迁移率变化（该激活绕过了早期受体触发的生化事件）对福斯高林不敏感。然而，福斯高林也抑制PKC的下游事件，如对T细胞激活过程至关重要的c - jun表达。为了进一步分析T细胞中正向和负向调节信号通路之间的潜在交叉点，我们测试了腺苷酸环化酶或PKA激活剂对由细胞外信号调节激酶（ERK）和c - Jun N末端激酶介导的两条平行的丝裂原活化蛋白激酶信号通路的影响。使用PKC特异性抑制剂GF109203X或PKC缺失的T细胞，我们发现抗CD3诱导的ERK激活很大一部分依赖于PKC。ERK的PKC依赖性和非依赖性激活均对福斯高林或细胞可渗透的cAMP类似物二丁酰环磷腺苷（dbcAMP）的抑制敏感。此外，12 - O - 十四烷酰佛波醇13 - 乙酸酯和离子霉素协同作用完全激活c - Jun N末端激酶的效应也对福斯高林的抑制敏感。我们的结果表明，PKA通过干扰TCR和CD28共受体分子下游两条信号通路中的多个事件来抑制T细胞激活。
