Max Planck Institute of Immunobiology and Epigenetics, Freiburg, Germany.
International Max Planck Research School for Immunobiology, Epigenetics and Metabolism (IMPRS-IEM), Freiburg, Germany.
Front Immunol. 2022 Nov 14;13:1039803. doi: 10.3389/fimmu.2022.1039803. eCollection 2022.
G-protein coupled receptor kinases (GRKs) participate in the regulation of chemokine receptors by mediating receptor desensitization. They can be recruited to agonist-activated G-protein coupled receptors (GPCRs) and phosphorylate their intracellular parts, which eventually blocks signal propagation and often induces receptor internalization. However, there is growing evidence that GRKs can also control cellular functions beyond GPCR regulation. Immune cells commonly express two to four members of the GRK family (GRK2, GRK3, GRK5, GRK6) simultaneously, but we have very limited knowledge about their interplay in primary immune cells. In particular, we are missing comprehensive studies comparing the role of this GRK interplay for (a) multiple GPCRs within one leukocyte type, and (b) one specific GPCR between several immune cell subsets. To address this issue, we generated mouse models of single, combinatorial and complete GRK knockouts in four primary immune cell types (neutrophils, T cells, B cells and dendritic cells) and systematically addressed the functional consequences on GPCR-controlled cell migration and tissue localization. Our study shows that combinatorial depletions of GRKs have pleiotropic and cell-type specific effects in leukocytes, many of which could not be predicted. Neutrophils lacking all four GRK family members show increased chemotactic migration responses to a wide range of GPCR ligands, whereas combinatorial GRK depletions in other immune cell types lead to pro- and anti-migratory responses. Combined depletion of GRK2 and GRK6 in T cells and B cells shows distinct functional outcomes for (a) one GPCR type in different cell types, and (b) different GPCRs in one cell type. These GPCR-type and cell-type specific effects reflect in altered lymphocyte chemotaxis and localization Lastly, we provide evidence that complete GRK deficiency impairs dendritic cell homeostasis, which unexpectedly results from defective dendritic cell differentiation and maturation and . Together, our findings demonstrate the complexity of GRK functions in immune cells, which go beyond GPCR desensitization in specific leukocyte types. Furthermore, they highlight the need for studying GRK functions in primary immune cells to address their specific roles in each leukocyte subset.
G 蛋白偶联受体激酶 (GRK) 通过介导受体脱敏参与趋化因子受体的调节。它们可以被募集到激动剂激活的 G 蛋白偶联受体 (GPCR) 并磷酸化其细胞内部分，这最终阻断信号传递，并且经常诱导受体内化。然而，越来越多的证据表明，GRK 还可以控制 GPCR 调节之外的细胞功能。免疫细胞通常同时表达 GRK 家族的两到四个成员 (GRK2、GRK3、GRK5、GRK6)，但我们对它们在原代免疫细胞中的相互作用知之甚少。特别是，我们缺乏比较这种 GRK 相互作用在以下方面的作用的综合研究：(a) 一种白细胞类型内的多种 GPCR，以及 (b) 几种免疫细胞亚群之间的一种特定 GPCR。为了解决这个问题，我们在四种原代免疫细胞 (中性粒细胞、T 细胞、B 细胞和树突状细胞) 中生成了单一、组合和完全 GRK 敲除的小鼠模型，并系统地研究了它们对 GPCR 控制的细胞迁移和组织定位的功能后果。我们的研究表明，GRK 的组合缺失在白细胞中有多种细胞类型特异性的多效作用，其中许多作用是无法预测的。缺乏所有四个 GRK 家族成员的中性粒细胞对广泛的 GPCR 配体表现出增强的趋化迁移反应，而其他免疫细胞类型中的组合 GRK 缺失则导致促迁移和抗迁移反应。T 细胞和 B 细胞中 GRK2 和 GRK6 的联合缺失显示出 (a) 不同细胞类型中一种 GPCR 类型的不同功能结果，以及 (b) 一种细胞类型中的不同 GPCR。这些 GPCR 类型和细胞类型特异性作用反映在淋巴细胞趋化性和定位的改变上。最后，我们提供了证据表明，完整的 GRK 缺乏会损害树突状细胞的动态平衡，这出乎意料地是由于树突状细胞分化和成熟缺陷所致。总的来说，我们的研究结果表明了 GRK 在免疫细胞中的功能的复杂性，这超越了特定白细胞类型中的 GPCR 脱敏作用。此外，它们强调了在原代免疫细胞中研究 GRK 功能的必要性，以解决它们在每个白细胞亚群中的特定作用。
