Institut für Pharmakologie und Toxikologie, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, Drackendorfer Straße 1, D-07747, Jena, Germany.
7TM Antibodies GmbH, Hans-Knöll-Straße 6, D-07745, Jena, Germany.
Commun Biol. 2023 Apr 15;6(1):419. doi: 10.1038/s42003-023-04786-2.
G protein-coupled receptors (GPCRs) are important signal transducers that are phosphorylated upon activation at intracellular serine and threonine residues. Although antibodies that specifically recognize the phosphorylation state of GPCRs have been available for many years, efficient immunolocalization of phosphorylated receptors in their tissues of origin has not been possible. Here, we show that phosphorylation of receptors is highly unstable during routine immunohistochemical procedures, requiring the use of appropriate phosphatase inhibitors particular during tissue perfusion, post-fixation, and cryoprotection but not during immunostaining of tissue sections. We provide proof of concept using phosphorylation state-specific μ-opioid receptor (MOP) and cannabinoid receptor 1 (CB1) antibodies. Indeed, three of four well-characterized phosphosite-specific MOP antibodies, including pS375-MOP, pT376-MOP, and pT379-MOP, showed robust neuronal immunostaining in brain and spinal cord sections of opioid-treated mice only after inclusion of phosphatase inhibitors. We then extended this approach to the CB1 receptor and demonstrated that one of three newly-generated phosphosite-specific CB1 antibodies, namely pS425-CB1, showed striking staining of fibers and varicosities in brain slices from cannabinoid-treated mice. Although subsequent experiments showed that phospho-CB1 immunostaining was less sensitive to phosphatases, we conclude that the use of phosphatase inhibitors should always be considered in the development of immunohistochemical procedures for new phosphosite-specific GPCR antibodies. In summary, we anticipate that this improved protocol will facilitate the widespread use of phosphorylation state-specific antibodies to monitor the activation of endogenous GPCRs under physiological and pharmacological conditions. Our approach may also prove useful to confirm target engagement of GPCR drug candidates in native tissues.
G 蛋白偶联受体（GPCRs）是重要的信号转导分子，在细胞内丝氨酸和苏氨酸残基被磷酸化后被激活。尽管已经有多年来专门识别 GPCR 磷酸化状态的抗体，但在其起源组织中有效免疫定位磷酸化受体一直是不可能的。在这里，我们表明，在常规免疫组织化学过程中，受体的磷酸化状态高度不稳定，需要在组织灌注、固定后和冷冻保护期间使用适当的磷酸酶抑制剂，但在组织切片免疫染色过程中不需要。我们使用磷酸化状态特异性μ-阿片受体（MOP）和大麻素受体 1（CB1）抗体提供了概念验证。事实上，四种经过充分表征的磷酸化特异性 MOP 抗体中的三种，包括 pS375-MOP、pT376-MOP 和 pT379-MOP，仅在包含磷酸酶抑制剂后，才在阿片类药物处理的小鼠的大脑和脊髓切片中显示出强烈的神经元免疫染色。然后，我们将这种方法扩展到 CB1 受体，并证明三种新生成的磷酸化特异性 CB1 抗体中的一种，即 pS425-CB1，在来自大麻素处理的小鼠的脑片中显示出纤维和小泡的显著染色。尽管随后的实验表明，磷酸化 CB1 免疫染色对磷酸酶的敏感性较低，但我们得出结论，在开发用于新磷酸化特异性 GPCR 抗体的免疫组织化学程序时，应始终考虑使用磷酸酶抑制剂。总之，我们预计这种改进的方案将促进广泛使用磷酸化特异性抗体来监测生理和药理学条件下内源性 GPCR 的激活。我们的方法也可能被证明对确认候选 GPCR 药物在天然组织中的靶标结合有用。
