Rare Missense Variants of the Human β4 Subunit Alter Nicotinic α3β4 Receptor Plasma Membrane Localisation

Abstract

α3β4 nicotinic acetylcholine receptors (nARs) are pentameric ligand-gated cation channels that function in peripheral tissue and in the peripheral and central nervous systems, where they are critical mediators of ganglionic synaptic transmission and modulators of reward-related behaviours. In the pentamer, two α3β4 subunit couples provide ligand-binding sites, and the fifth single (accessory) subunit (α3 or β4) regulates receptor trafficking from the endoplasmic reticulum to the cell surface. A number of rare missense variants of the human β4 subunit have recently been linked to nicotine dependence and/or sporadic amyotrophic lateral sclerosis, and altered responses to nicotine have been reported for these variants; however, it is unknown whether the effects of mutations depend on the subunit within the ligand-binding couples and/or on the fifth subunit. Here, by expressing single populations of pentameric receptors with fixed stoichiometry in cultured cells, we investigated the effect of β4 variants in the fifth position on the assembly and surface exposure of α3β4 nAChRs. The results demonstrate that the missense mutations in the accessory subunit alone, despite not affecting the assembly of α3β4 receptors, alter their trafficking and surface localisation. Thus, altered trafficking of an otherwise functional nAChR may underlie the pathogenic effects of these mutations.

The Role of Nicotinic Receptors on Ca2+ Signaling in Bovine Chromaffin Cells

“…Our data indicate that the spatial localization of the molecular elements, along with the stimulation of nicotinic receptors, plays a crucial role in improving the secretory response, supporting the idea that nicotinic receptors promote the co-localization of VDCCs and vesicles to prepare the cell to release a huge volume of catecholamines in case of vital situations, as hypothesized in some works [6,29], and in accordance with the vision of the cytoskeleton as a dynamic structure modulating exocytosis [10,30]. Moreover, it has been reported that mutations in nicotinic receptors could alter their localization and functioning [31], leading, for example, to the dysregulation of the stress response in knockout mice [32].…”