Abstract
We report the first observation that endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) can decrease when a central nervous system drug acts as an intracellular pharmacological chaperone for its classic receptor. Transient expression of α4β2 nicotinic receptors (nAChRs) in Neuro-2a cells induced the nuclear translocation of activating transcription factor 6 (ATF6), which is part of the UPR. Cells were exposed for 48 h to the full agonist nicotine, the partial agonist cytisine, or the competitive antagonist dihydro-β-erythroidine; we also tested mutant nAChRs that readily exit the ER. Each of these four manipulations increased Sec24D-enhanced green fluorescent protein fluorescence of condensed ER exit sites and attenuated translocation of ATF6-enhanced green fluorescent protein to the nucleus. However, we found no correlation among the manipulations regarding other tested parameters [i.e., changes in nAChR stoichiometry (α42β23 versus α43β22), changes in ER and trans-Golgi structures, or the degree of nAChR up-regulation at the plasma membrane]. The four manipulations activated 0 to 0.4% of nAChRs, which shows that activation of the nAChR channel did not underlie the reduced ER stress. Nicotine also attenuated endogenously expressed ATF6 translocation and phosphorylation of eukaryotic initiation factor 2α in mouse cortical neurons transfected with α4β2 nAChRs. We conclude that, when nicotine accelerates ER export of α4β2 nAChRs, this suppresses ER stress and the UPR. Suppression of a sustained UPR may explain the apparent neuroprotective effect that causes the inverse correlation between a person's history of tobacco use and susceptibility to developing Parkinson's disease. This suggests a novel mechanism for neuroprotection by nicotine.
Footnotes
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The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.This work was supported by the National Institutes of Health National Institute of Neurological Disorders and Stroke [Grant NS11756]; the National Institutes of Health National Institute on Aging [Grant AG033954]; National Institutes of Health National Institute on Drug Abuse Kirschstein National Research Service Award [Grant DA030877] (to C.I.R.); Targacept; Louis and Janet Fletcher; the Michael J. Fox Foundation; a California Tobacco-Related Disease Research Program postdoctoral fellowship [Grant 18FT-0066] (to R.S.); a Beckman Institute fellowship (to C.I.R.); and a California Tobacco-Related Disease Research Program New Investigator Award [Grant 19KT-0032] (to J.M.M.).
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
ABBREVIATIONS:
- ATF6
- activating transcription factor 6
- BT
- bleedthrough
- CHOP
- C/EBP homologous protein
- DHβE
- dihydro-β-erythroidine
- eCFP
- enhanced cyan fluorescent protein
- eGFP
- enhanced green fluorescent protein
- eIF2α
- eukaryotic initiation factor 2α
- peIF2α
- phosphorylated eukaryotic initiation factor 2α
- ER
- endoplasmic reticulum
- ERES
- endoplasmic reticulum exit site(s)
- Whigh
- fractional area of high-normalized Förster resonance energy transfer component
- FRET
- Förster resonance energy transfer
- nAChR
- nicotinic acetylcholine receptor
- NFRET
- normalized Förster resonance energy transfer
- PERK
- protein kinase RNA-like endoplasmic reticulum kinase
- PM
- plasma membrane
- ROI
- region of interest
- SePhaChARNS
- selective pharmacological chaperoning of acetylcholine receptor number and stoichiometry
- TG
- trans-Golgi
- TGN
- trans-Golgi network
- TIRFM
- total internal reflection fluorescence microscopy
- UPR
- unfolded protein response
- wt
- wild-type
- GalT
- galactosyltransferase
- FBS
- fetal bovine serum
- DMEM
- Dulbecco's modified Eagle's medium
- TBS
- Tris-buffered saline.
- Received January 13, 2012.
- Accepted February 28, 2012.
- Copyright © 2012 The American Society for Pharmacology and Experimental Therapeutics
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