Nicotine exploits a COPI-mediated process for chaperone-mediated up-regulation of its receptors

Abstract

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.

Nicotine Dependence Reveals Distinct Responses from Neurons and Their Resident Nicotinic Receptors in Medial Habenula

“…5). These data are consistent with recent findings indicating that MHb a6 subunits, which are concentrated in MHbVI (Shih et al, 2014), upregulate following chronic nicotine treatment (Henderson et al, 2014). Conversely, we did not find nAChR activity to be functionally enhanced in MHbVL after chronic nicotine treatment (Fig.…”

“…These findings are in line with our previous study using mouse strains expressing green fluorescent protein-tagged a6 subunits, where a6 subunit immunoreactivity was demonstrated in MHbVI cells (Shih et al, 2014). Our findings are similarly consistent with those of Henderson et al (2014), who also demonstrated a6 subunits in a subregion of MHb consistent with MHbVI.…”

“…Our previous studies strongly suggest that functional a6* nAChRs are expressed in MHbVI (Henderson et al, 2014;Shih et al, 2014). We conducted further pharmacological experiments to test this hypothesis.…”

Lynx1 Shifts α4β2 Nicotinic Receptor Subunit Stoichiometry by Affecting Assembly in the Endoplasmic Reticulum

“…SEP is fluorescent at pH 7.4 but is quenched at pH Ͻ 7.0 (22). Previously, when linked to the extracellular portion of Cys loop receptors and other membrane proteins, SEP has provided evidence that a portion of the tagged protein is present in intracellular compartments, as well as on the PM (15,(23)(24)(25). For the present study, once the SEP construct was verified electrophysiologically (see Figs.…”

Mechanisms of Action and Persistent Neuroplasticity by Drugs of Abuse

“…Proposed mechanisms have included decreased turnover of receptors (Peng et al, 1994), desensitization of surface receptors (Fenster et al, 1999), enhancement of receptor maturation (Sallette et al, 2005), and slow stabilization of receptors in a high-affinity state that is more easily activated (Vallejo et al, 2005). However, recent consensus of opinion, at least for upregulation of a4b2* nAChRs, has converged on the notion that nicotine acts as a pharmacological chaperone (Kuryatov et al, 2005;Henderson et al, 2014;Srinivasan et al, 2011Srinivasan et al, , 2012. Pharmacological chaperoning of intracellular nAChRs is proposed to facilitate subunit assembly in the ER and enhance export of assembled receptors from the ER and their transport and insertion into the membrane.…”