title: Chronic nicotine induces hypoxia inducible factor-2α in perinatal rat adrenal chromaffin cells: role in transcriptional upregulation of KATP channel subunit Kir6.2.
abstract: Fetal nicotine exposure causes impaired adrenal catecholamine secretion and increased neonatal mortality during acute hypoxic challenges. Both effects are attributable to upregulation of ATP-sensitive K(+) channels (K(ATP) channels) and can be rescued by pretreatment with the blocker, glibenclamide. Although use of in vitro models of primary and immortalized, fetal-derived rat adrenomedullary chromaffin cells (i.e., MAH cells) demonstrated the involvement of α7 nicotinic ACh receptor (nAChR) stimulation and the transcription factor, HIF-2α, the latter's role was unclear. Using Western blots, we show that chronic nicotine causes a progressive, time-dependent induction of HIF-2α in MAH cells that parallels the upregulation of K(ATP) channel subunit, Kir6.2. Moreover, a common HIF target, VEGF mRNA, was also upregulated after chronic nicotine. All the above effects were prevented during co-incubation with α-bungarotoxin (100 nM), a specific α7 nAChR blocker, and were absent in HIF-2α-deficient MAH cells. Chromatin immunoprecipitation (ChIP) assays demonstrated binding of HIF-2α to a putative hypoxia response element in Kir6.2 gene promoter. Specificity of this signaling pathway was validated in adrenal glands from pups born to dams exposed to nicotine throughout gestation; the upregulation of both HIF-2α and Kir6.2 was confined to medullary, but not cortical, tissue. This study has uncovered a signaling pathway whereby a nonhypoxic stimulus (nicotine) promotes HIF-2α-mediated transcriptional upregulation of a novel target, Kir6.2 subunit. The data suggest that the HIF pathway may be involved in K(ATP) channel-mediated neuroprotection during brain ischemia, and in the effects of chronic nicotine on ubiquitous brain α7 nAChR.
authors.affiliation: Department of Biology, McMaster University, 1280 Main St. West, Hamilton, Ontario, Canada L8S 4K1. salmas@univmail.cis.mcmaster.ca
authors.forename: Shaima
authors.initials: S
authors.lastname: Salman
authors.forename: Stephen T
authors.initials: ST
authors.lastname: Brown
authors.forename: Colin A
authors.initials: CA
authors.lastname: Nurse
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D051792:Basic Helix-Loop-Helix Proteins / Q000096:biosynthesis* / Q000502:physiology; D002461:Cell Line, Transformed; D019439:Chromaffin Cells / Q000378:metabolism*; D005260:Female; D054086:KATP Channels / Q000096:biosynthesis*; D018811:Maternal Exposure / Q000009:adverse effects; D009538:Nicotine / Q000008:administration & dosage*; D024661:Potassium Channels, Inwardly Rectifying / Q000096:biosynthesis*; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects / Q000378:metabolism*; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar; D015203:Reproducibility of Results; D014158:Transcription, Genetic / Q000502:physiology; D015854:Up-Regulation / Q000502:physiology*; D000099162:Endothelial PAS Domain-Containing Protein 1; D000099161:Kcnj11 Channel
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D054086:KATP Channels; D009538:Nicotine; D024661:Potassium Channels, Inwardly Rectifying; D000099162:Endothelial PAS Domain-Containing Protein 1; D000099161:Kcnj11 Channel