Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125.
J Gen Physiol. 2014 Jan;143(1):51-66. doi: 10.1085/jgp.201311102.
Chronic exposure to nicotine up-regulates high sensitivity nicotinic acetylcholine receptors (nAChRs) in the brain. This up-regulation partially underlies addiction and may also contribute to protection against Parkinson's disease. nAChRs containing the α6 subunit (α6* nAChRs) are expressed in neurons in several brain regions, but comparatively little is known about the effect of chronic nicotine on these nAChRs. We report here that nicotine up-regulates α6* nAChRs in several mouse brain regions (substantia nigra pars compacta, ventral tegmental area, medial habenula, and superior colliculus) and in neuroblastoma 2a cells. We present evidence that a coat protein complex I (COPI)-mediated process mediates this up-regulation of α6* or α4* nAChRs but does not participate in basal trafficking. We show that α6β2β3 nAChR up-regulation is prevented by mutating a putative COPI-binding motif in the β3 subunit or by inhibiting COPI. Similarly, a COPI-dependent process is required for up-regulation of α4β2 nAChRs by chronic nicotine but not for basal trafficking. Mutation of the putative COPI-binding motif or inhibition of COPI also results in reduced normalized Förster resonance energy transfer between α6β2β3 nAChRs and εCOP subunits. The discovery that nicotine exploits a COPI-dependent process to chaperone high sensitivity nAChRs is novel and suggests that this may be a common mechanism in the up-regulation of nAChRs in response to chronic nicotine.
慢性暴露于尼古丁会在上调大脑中的高敏性烟碱型乙酰胆碱受体(nAChRs)。这种上调部分是成瘾的基础,也可能有助于预防帕金森病。含有α6 亚基的 nAChRs(α6* nAChRs)在大脑的几个区域的神经元中表达,但对慢性尼古丁对这些 nAChRs 的影响知之甚少。我们在此报告,尼古丁可上调几个小鼠脑区(黑质致密部、腹侧被盖区、内侧缰核和上丘)和神经母细胞瘤 2a 细胞中的α6* nAChRs。我们提供了证据表明,一种衣壳蛋白复合物 I(COPI)介导的过程调节了α6或α4 nAChRs 的这种上调,但不参与基础转运。我们表明,通过突变β3 亚基中的一个假定的 COPI 结合基序或抑制 COPI,可以防止α6β2β3 nAChR 的上调。同样,COPI 依赖性过程对于慢性尼古丁引起的α4β2 nAChRs 的上调是必需的,但对于基础转运则不是必需的。突变假定的 COPI 结合基序或抑制 COPI 也会导致α6β2β3 nAChRs 和 εCOP 亚基之间的Förster 共振能量转移的归一化减少。发现尼古丁利用 COPI 依赖性过程来伴侣高敏性 nAChRs 是新颖的,这表明这可能是慢性尼古丁引起的 nAChRs 上调的共同机制。