Peter Daniel, Jin S L Catherine, Conti Marco, Hatzelmann Armin, Zitt Christof
Department of Biochemistry, Altana Pharma, Konstanz, Germany.
J Immunol. 2007 Apr 15;178(8):4820-31. doi: 10.4049/jimmunol.178.8.4820.
Type 4 phosphodiesterases (PDE4) are critical regulators in TCR signaling by attenuating the negative constraint of cAMP. In this study, we show that anti-CD3/CD28 stimulation of human primary CD4(+) T cells increases the expression of the PDE4 subtypes PDE4A, PDE4B, and PDE4D in a specific and time-dependent manner. PDE4A and PDE4D mRNAs as well as enzyme activities were up-regulated within 5 days, PDE4B showed a transient up-regulation with highest levels after 24 h. The induction was shown to be independent of different stimulation conditions and was similar in naive and memory T cell subpopulations. To elucidate the functional impact of individual PDE4 subtypes on T cell function, we used PDE4 subtype-specific short-interfering RNAs (siRNAs). Knockdown of either PDE4B or PDE4D inhibited IL-2 release 24 h after stimulation (time point of maximal IL-2 concentrations) to an extent similar to that observed with the panPDE4 inhibitor RP73401 (piclamilast). Substantial amounts of IFN-gamma or IL-5 were measured only at later time points. siRNA targeting PDE4D showed a predominant inhibitory effect on these cytokines measured after 72 h. However, the inhibition of all cytokines was most effective when PDE4 siRNAs were applied in combination. Although the effect of PDE4 inhibition on T cell proliferation is small, the PDE4D-targeting siRNA alone was as effective as the panPDE4 inhibitor, whereas PDE4A or PDE4B siRNAs had hardly an effect. In summary, individual PDE4 subtypes have overall nonredundant, but complementary, time-dependent roles in propagating various T cell functions and PDE4D is the form likely playing a predominant role.
4型磷酸二酯酶（PDE4）通过减弱cAMP的负向抑制作用，成为TCR信号传导中的关键调节因子。在本研究中，我们发现抗CD3/CD28刺激人原代CD4(+) T细胞，会以一种特定的、时间依赖性方式增加PDE4亚型PDE4A、PDE4B和PDE4D的表达。PDE4A和PDE4D的mRNA以及酶活性在5天内上调，PDE4B则表现出短暂上调，在24小时后达到最高水平。这种诱导作用显示与不同刺激条件无关，在初始和记忆T细胞亚群中相似。为了阐明单个PDE4亚型对T细胞功能的功能影响，我们使用了PDE4亚型特异性小干扰RNA（siRNA）。敲低PDE4B或PDE4D均可在刺激后24小时（IL-2浓度最高的时间点）抑制IL-2释放，其程度与使用泛PDE4抑制剂RP73401（匹伐米司特）时观察到的相似。仅在较晚时间点检测到大量的IFN-γ或IL-5。靶向PDE4D的siRNA对72小时后检测的这些细胞因子显示出主要抑制作用。然而，当联合应用PDE4 siRNA时，对所有细胞因子的抑制最为有效。尽管PDE4抑制对T细胞增殖的影响较小，但单独使用靶向PDE4D的siRNA与泛PDE4抑制剂一样有效，而PDE4A或PDE4B siRNA几乎没有作用。总之，单个PDE4亚型在传播各种T细胞功能方面具有总体非冗余但互补的时间依赖性作用，并且PDE4D可能起着主要作用。
