Mechanism of PKC-mediated desensitization of the morphine-activated mu opioid receptor in neurones

阿片类镇痛药物如吗啡的重复给药导致耐受性的发展，从而为了获得相同水平的反应，必须增加药物的给药剂量。吗啡通过激活位于大脑和脊髓神经细胞外膜上的特定蛋白质（受体）产生深刻的行为效应（镇痛、呼吸抑制和欣快）。这些受体的长期激活导致它们被关闭（脱敏），这种脱敏可能是耐受性的主要组成部分。我们最近提供的证据表明，当被吗啡激活时，受体脱敏的机制涉及一种称为蛋白激酶C的蛋白质，它通过一种称为磷酸化的过程关闭吗啡信号。然而，我们目前还不了解蛋白激酶C的磷酸化是如何在吗啡作用下触发这种关闭的。在这个应用中，我们建议确定蛋白激酶C磷酸化如何关闭神经细胞中的吗啡信号。特别是，我们将确定在神经细胞中是否是蛋白激酶C介导的受体本身的磷酸化或介导脱敏的另一种蛋白质。为了做到这一点，我们将在神经细胞中表达吗啡受体，这些神经细胞已经被改变以去除受体上被蛋白激酶C磷酸化的潜在位点。鉴于蛋白激酶C磷酸化似乎是吗啡和相关药物耐受性的关键组成部分，我们现在确定所涉及的确切机制是非常重要的。在这个项目中，我们的目标是实现这一目标，以便在未来可以开发新的方法来克服与吗啡使用和滥用有关的问题。

Repeated administration of opioid analgesic drugs such as morphine results in the development of tolerance whereby to obtain the same level of response increasing doses of the drug must be administered. Morphine produces it profound behavioural effects (analgesia, respiratory depression and euphoria) by activating specific proteins (receptors) located on the outer membrane of nerve cells in the brain and spinal cord. Prolonged activation of these receptors results in them being switched off (desensitized) and this desensitization may be a major component of tolerance. We have recently provided evidence that when activated by morphine, the mechanism of receptor desensitization involves a protein called protein kinase C, which switches off morphine signalling by a process called phosphorylation. However, we do not at present understand how phosphorylation by protein kinase C triggers this switching off in response to morphine. In this application, we propose to determine exactly how protein kinase C phosphorylation switches off morphine signalling in nerve cells. In particular, we will determine in the nerve cells whether or not it is protein kinase C-mediated phosphorylation of the receptor itself or another protein which mediates the desensitization. To do this we will express morphine receptors in nerve cells that have been altered to remove potential sites on the receptor that are phosphorylated by protein kinase C. Given that protein kinase C phosphorylation appears to be a crucial component of tolerance to morphine and related drugs, it is very important that we now determine the exact mechanism involved. In this project we aim to achieve this so that in the future new approaches can be developed to overcome the problems associated with morphine use and abuse.