Department of Molecular Cell Biology and Immunology, Cancer Center Amsterdam, Amsterdam Infection and Immunity Institute, Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam, Netherlands.
Department of Medical Oncology, Cancer Center Amsterdam, Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam, Netherlands.
Front Immunol. 2021 Apr 22;12:673454. doi: 10.3389/fimmu.2021.673454. eCollection 2021.
Dendritic cells (DCs) are key initiators of the adaptive immunity, and upon recognition of pathogens are able to skew T cell differentiation to elicit appropriate responses. DCs possess this extraordinary capacity to discern external signals using receptors that recognize pathogen-associated molecular patterns. These can be glycan-binding receptors that recognize carbohydrate structures on pathogens or pathogen-associated patterns that additionally bind receptors, such as Toll-like receptors (TLRs). This study explores the early signaling events in DCs upon binding of α2-3 sialic acid (α2-3sia) that are recognized by Immune inhibitory Sialic acid binding immunoglobulin type lectins. α2-3sias are commonly found on bacteria, e.g. Group B , but can also be expressed by tumor cells. We investigated whether α2-3sia conjugated to a dendrimeric core alters DC signaling properties. Through phosphoproteomic analysis, we found differential signaling profiles in DCs after α2-3sia binding alone or in combination with LPS/TLR4 co-stimulation. α2-3sia was able to modulate the TLR4 signaling cascade, resulting in 109 altered phosphoproteins. These phosphoproteins were annotated to seven biological processes, including the regulation of the IL-12 cytokine pathway. Secretion of IL-10, the inhibitory regulator of IL-12 production, by DCs was found upregulated after overnight stimulation with the α2-3sia dendrimer. Analysis of kinase activity revealed altered signatures in the JAK-STAT signaling pathway. PhosphoSTAT3 (Ser727) and phosphoSTAT5A (Ser780), involved in the regulation of the IL-12 pathway, were both downregulated. Flow cytometric quantification indeed revealed de- phosphorylation over time upon stimulation with α2-3sia, but no α2-6sia. Inhibition of both STAT3 and -5A in moDCs resulted in a similar cytokine secretion profile as α-3sia triggered DCs. Conclusively, this study revealed a specific alteration of the JAK-STAT pathway in DCs upon simultaneous α2-3sia and LPS stimulation, altering the IL10:IL-12 cytokine secretion profile associated with reduction of inflammation. Targeted control of the STAT phosphorylation status is therefore an interesting lead for the abrogation of immune escape that bacteria or tumors impose on the host.
树突状细胞 (DCs) 是适应性免疫的关键启动者，在识别病原体后，能够使 T 细胞分化偏向，引发适当的反应。DCs 具有通过识别病原体相关分子模式的受体来区分外部信号的非凡能力。这些受体可以是识别病原体上碳水化合物结构的糖结合受体，也可以是额外结合受体（如 Toll 样受体 (TLR)）的病原体相关模式识别受体。本研究探讨了 DC 结合 α2-3 唾液酸 (α2-3sia) 后早期的信号事件，α2-3sia 被免疫抑制性唾液酸结合免疫球蛋白型凝集素识别。α2-3sias 通常存在于细菌上，例如 B 群，但也可以由肿瘤细胞表达。我们研究了与树突状核心结合的 α2-3sia 是否改变了 DC 的信号转导特性。通过磷酸蛋白质组学分析，我们发现 α2-3sia 结合后，无论是单独结合还是与 LPS/TLR4 共刺激后，DC 的信号转导谱都存在差异。α2-3sia 能够调节 TLR4 信号级联反应，导致 109 个磷酸化蛋白发生改变。这些磷酸化蛋白被注释到七个生物学过程，包括 IL-12 细胞因子途径的调节。 overnight 刺激 α2-3sia 树突状后，发现 DC 分泌的抑制性调节 IL-12 产生的细胞因子 IL-10 上调。激酶活性分析显示 JAK-STAT 信号通路的特征发生改变。参与调节 IL-12 途径的磷酸化 STAT3 (Ser727) 和磷酸化 STAT5A (Ser780) 均下调。流式细胞术定量分析确实显示，刺激 α2-3sia 后随着时间的推移去磷酸化，但没有 α2-6sia。在 moDCs 中抑制 STAT3 和 -5A 会导致与 α-3sia 触发的 DC 相似的细胞因子分泌谱。综上所述，本研究揭示了 DCs 同时受到 α2-3sia 和 LPS 刺激时 JAK-STAT 通路的特异性改变，改变了与炎症减轻相关的 IL10:IL-12 细胞因子分泌谱。因此，靶向控制 STAT 磷酸化状态是细菌或肿瘤对宿主产生免疫逃逸的一个有趣的靶点。
