The μ-opioid receptor gene undergoes extensive alternative splicing to generate an array of splice variants. One group of splice variants excludes the first transmembrane (TM) domain and contains six TM domains. These 6TM variants are essential for the action of a novel class of analgesic drugs, including 3-iodobenzoyl-6β-naltrexamide, which is potent against a spectrum of pain models without exhibiting the adverse side effects of traditional opiates. The 6TM variants are also involved in analgesic action through other drug classes, including δ-opioid and κ-opioids and α₂-adrenergic drugs. Of the five 6TM variants in mouse, mouse μ-opioid receptor (mMOR)-1G is abundant and conserved from rodent to human. In the present study, we demonstrate a new function of mMOR-1G in enhancing expression of the full-length 7TM μ-opioid receptor, mMOR-1. When coexpressed with mMOR-1 in a Tet-Off inducible CHO cell line, mMOR-1G has no effect on mMOR-1 mRNA expression but greatly increases mMOR-1 protein expression in a dose-dependent manner determined by opioid receptor binding and [³⁵S] guanosine 5′-3-O-(thio)triphosphate binding. Subcellular fractionation analysis using OptiPrep density gradient centrifugation shows an increase of functional mMOR-1 receptor in plasma membrane–enriched fractions. Using a coimmunoprecipitation approach, we further demonstrate that mMOR-1G physically associates with mMOR-1 starting at the endoplasmic reticulum, suggesting a chaperone-like function. These data provide a molecular mechanism for how mMOR-1G regulates expression and function of the full-length 7TM μ-opioid receptor.

中文翻译：

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截短的六跨膜剪接变体 MOR-1G 通过异二聚化增强全长七跨膜 μ-阿片受体的表达。

所述μ阿片受体基因经过广泛可变剪接的剪接变体，以产生阵列。一组剪接变体不包括第一个跨膜 (TM) 域并包含六个 TM 域。这些 6TM 变体对于一类新型镇痛药物（包括 3-iodobenzoyl-6 β -naltrexamide）的作用至关重要，该药物对一系列疼痛模型有效，而不会表现出传统阿片类药物的不良副作用。的6TM变体也通过其他药物类别涉及镇痛作用，包括δ阿片和κ-阿片类药物和α ₂ -肾上腺素能药物。在小鼠的 5 个 6TM 变体中，小鼠μ-阿片受体 (mMOR)-1G 从啮齿动物到人类都是丰富且保守的。在本研究中，我们证明了 mMOR-1G 在增强全长 7TM μ-阿片受体 mMOR-1表达方面的新功能。当在 Tet-Off 诱导型 CHO 细胞系中与 mMOR-1 共表达时，mMOR-1G 对 mMOR-1 mRNA 表达没有影响，但以剂量依赖性方式大大增加 mMOR-1 蛋白表达，由阿片受体结合决定 [ ^35] S] 鸟苷 5'-3- O-（硫代）三磷酸结合。使用 OptiPrep 密度梯度离心进行的亚细胞分级分析显示，富含质膜的组分中功能性 mMOR-1 受体增加。使用共免疫沉淀方法，我们进一步证明 mMOR-1G 从内质网开始与 mMOR-1 物理结合，表明具有分子伴侣样功能。这些数据为 mMOR-1G 如何调节全长 7TM μ-阿片受体的表达和功能提供了分子机制。