G蛋白偶联受体激酶(GRKs)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(GPCRs)并磷酸化它们的细胞内部分,最终阻断信号传播并经常诱导受体内化。然而,越来越多的证据表明,GRKs还可以控制GPCR调控之外的细胞功能。免疫细胞通常同时表达GRK家族的两到四个成员(GRK2,GRK3,GRK5,GRK6),但是我们对它们在初级免疫细胞中的相互作用的了解非常有限。特别是,我们缺少全面的研究,比较这种GRK相互作用对(a)一种白细胞类型内的多种GPCRs的作用,和(b)几个免疫细胞亚群之间的一个特异性GPCR。为了解决这个问题,我们生成了单个小鼠模型,四种主要免疫细胞类型的组合和完全GRK敲除(中性粒细胞,T细胞,B细胞和树突状细胞),并系统地解决了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,GRKs的组合消耗在白细胞中具有多效性和细胞类型特异性作用,其中许多是无法预测的。缺乏所有四个GRK家族成员的嗜中性粒细胞对广泛的GPCR配体显示出增加的趋化迁移反应。而其他免疫细胞类型的组合GRK消耗导致促进和抗迁移反应。GRK2和GRK6在T细胞和B细胞中的联合消耗显示出不同的功能结果(a)不同细胞类型中的一种GPCR类型,和(b)一种细胞类型中的不同GPCR。这些GPCR型和细胞型特异性效应反映在体外淋巴细胞趋化性改变和体内定位中。最后,我们提供的证据表明,完全GRK缺乏会损害树突状细胞的体内平衡,这出乎意料地是由于体外和体内的树突状细胞分化和成熟缺陷造成的。一起,我们的发现证明了免疫细胞中GRK功能的复杂性,这超出了特定白细胞类型的GPCR脱敏。此外,他们强调需要研究原代免疫细胞中的GRK功能,以解决它们在每个白细胞亚群中的特定作用.
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 in vitro and localization in vivo. Lastly, we provide evidence that complete GRK deficiency impairs dendritic cell homeostasis, which unexpectedly results from defective dendritic cell differentiation and maturation in vitro and in vivo. 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.