title: Calpain activation by ROS mediates human ether-a-go-go-related gene protein degradation by intermittent hypoxia.
abstract: Human ether-a-go-go-related gene (hERG) channels conduct delayed rectifier K(+) current. However, little information is available on physiological situations affecting hERG channel protein and function. In the present study we examined the effects of intermittent hypoxia (IH), which is a hallmark manifestation of sleep apnea, on hERG channel protein and function. Experiments were performed on SH-SY5Y neuroblastoma cells, which express hERG protein. Cells were exposed to IH consisting of alternating cycles of 30 s of hypoxia (1.5% O2) and 5 min of 20% O2. IH decreased hERG protein expression in a stimulus-dependent manner. A similar reduction in hERG protein was also seen in adrenal medullary chromaffin cells from IH-exposed neonatal rats. The decreased hERG protein was associated with attenuated hERG K(+) current. IH-evoked hERG protein degradation was not due to reduced transcription or increased proteosome/lysomal degradation. Rather it was mediated by calcium-activated calpain proteases. Both COOH- and NH2-terminal sequences of the hERG protein were the targets of calpain-dependent degradation. IH increased reactive oxygen species (ROS) levels, intracellular Ca(2+) concentration ([Ca(2+)]i), calpain enzyme activity, and hERG protein degradation, and all these effects were prevented by manganese-(111)-tetrakis-(1-methyl-4-pyridyl)-porphyrin pentachloride, a membrane-permeable ROS scavenger. These results demonstrate that activation of calpains by ROS-dependent elevation of [Ca(2+)]i mediates hERG protein degradation by IH.
authors.affiliation: Institute for Integrative Physiology, Biological Sciences Division, University of Chicago, Chicago, Illinois.
authors.forename: N
authors.initials: N
authors.lastname: Wang
authors.affiliation: Institute for Integrative Physiology, Biological Sciences Division, University of Chicago, Chicago, Illinois.
authors.forename: H S
authors.initials: HS
authors.lastname: Kang
authors.affiliation: Institute for Integrative Physiology, Biological Sciences Division, University of Chicago, Chicago, Illinois.
authors.forename: G
authors.initials: G
authors.lastname: Ahmmed
authors.affiliation: Institute for Integrative Physiology, Biological Sciences Division, University of Chicago, Chicago, Illinois.
authors.forename: S A
authors.initials: SA
authors.lastname: Khan
authors.affiliation: Institute for Integrative Physiology, Biological Sciences Division, University of Chicago, Chicago, Illinois.
authors.forename: V V
authors.initials: VV
authors.lastname: Makarenko
authors.affiliation: Institute for Integrative Physiology, Biological Sciences Division, University of Chicago, Chicago, Illinois.
authors.forename: N R
authors.identifier: http://orcid.org/0000-0003-4570-1380
authors.initials: NR
authors.lastname: Prabhakar
authors.affiliation: Institute for Integrative Physiology, Biological Sciences Division, University of Chicago, Chicago, Illinois jnanduri@uchicago.edu.
authors.forename: J
authors.initials: J
authors.lastname: Nanduri
mesh_terms: D000313:Adrenal Medulla / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D002154:Calpain / Q000378:metabolism*; D015687:Cell Hypoxia; D002478:Cells, Cultured; D000072237:ERG1 Potassium Channel; D004789:Enzyme Activation; D051638:Ether-A-Go-Go Potassium Channels / Q000235:genetics*; D005260:Female; D006801:Humans; D008297:Male; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D059748:Proteolysis; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism*
chemical_list: D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; D017382:Reactive Oxygen Species; D002154:Calpain
keywords: adrenal medullary chromaffin cells; apnea of prematurity; arrhythmia; oxidative stress; sleep apnea