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

Abstract

Background: lynx1 reduces sensitivity of ␣4␤2 nAChRs in vitro and also reduces nicotinic responses in vivo. Results: The GPI protein, lynx1, affects ␣4/␣4 dimer formation in the ER, altering plasma membrane ␣4␤2 stoichiometry. Conclusion: nAChR modulation can occur as early as the ER, by biasing the starting material for receptor assembly. Significance: Acute pharmacology and behavior caused by PM nAChRs may be modified by molecules governing nAChR assembly.

Mechanisms of Inhibition and Potentiation of α4β2 Nicotinic Acetylcholine Receptors by Members of the Ly6 Protein Family

“…Because the magnitude of this effect is so extreme, very few receptors must reside at the cell surface to be antagonized. The majority of the inhibition of ␣4␤2 activity by Lynx2 that we measured also seems unlikely to be caused by changes in receptor stoichiometry, like those attributed to Lynx1, which are thought to reduce receptor affinity for agonist (30,34). While we cannot rule out such a role for Lynx2, inhibition by this protein should be surmountable by increasing the concentration of agonist, whereas the inhibition we measured is not.…”

“…These functions have been attributed to the biophysical properties of Lynx1 and Lynx2, which include acceleration of ␣4␤2 desensitization and an increase in the EC 50 for receptor activation by agonist (33,34,39,47). Evidence also exists for Lynx1 facilitating ␣4␤2 receptor assembly (30).…”

“…Some Ly6 proteins, such as Lynx1 and Lynx2, have been shown to accelerate desensitization and reduce the sensitivity of nAChRs to agonist (33,34). Recently evidence has emerged that the latter effect may in part be caused by Ly6-mediated alterations in subunit oligomerization and thus ␣4␤2 stoichiometry (30). Such changes could affect both receptor sensitivity to acute agonist as well as the percentage of receptors that are susceptible to up-regulation by chronic nicotine.…”

“…For example, it has been proposed that by promoting assembly of ␣4␤2 heteromers, nicotine acts like a chaperone for nAChRs (24, 26 -28). Recent evidence also suggests that nicotine can alter the stoichiometry of nAChRs by shifting assembly from low affinity ␣4 3 ␤2 2 toward high affinity ␣4 2 ␤2 3 receptors (29,30). Finally, it has also been proposed that nicotine exposure imposes on ␣4␤2 receptors a form of hysteresis in which receptors undergo conformational changes that leave them in a more activatable state (25).…”

Lynx1 and Aβ1–42 bind competitively to multiple nicotinic acetylcholine receptor subtypes

“…Our experiments involve addition of soluble Ws-Lynx1 for relatively short time to intact cells, and therefore likely reflect an effect on membrane surface nAChRs. In N2a cells, Lynx1 was recently reported to associate with α4β2 nAChRs in the endoplasmic reticulum, where it affected assembly of these receptors and reduced the sensitivity to acetylcholine (Nichols et al, 2014).…”