Bigenomic functional regulation of all 13 cytochrome c oxidase subunit transcripts in rat neurons in vitro and in vivo.
Cytochrome c oxidase is a multisubunit, bigenomically encoded inner mitochondrial membrane protein. Its enzymatic activity and amount in the brain vary with metabolic demands, but the precise regulation of all 13 subunits to form a functional holoenzyme in a 1:1 stoichiometry is not well understood. To determine if all 13 subunit transcripts were coordinately regulated by functional alteration in neurons, cultured primary neurons were depolarized by potassium chloride for 5-24 h, or tetrodotoxin inactivated for 2-6 days. In vivo studies were done on rats monocularly enucleated for 4 days to 2 weeks. Expressions of cytochrome c oxidase subunit mRNAs were measured by real-time quantitative polymerase chain reaction. Results showed that in vitro, all 13 transcripts were significantly up-regulated after 5 h of depolarizing stimulation. With tetrodotoxin blockade, however, the three mitochondrial-encoded transcripts were down-regulated earlier than the 10 nuclear ones (2 days versus 4 days). In vivo, all three mitochondrial-encoded subunit mRNAs were also down-regulated earlier than the nuclear ones in deprived visual cortex (4 days versus 1 week after monocular enucleation). Cytochrome c oxidase activity and protein levels were significantly decreased in parallel after 4 days of deprivation in vitro and 1 week in vivo. Our results are consistent with a coordinated mechanism of up-regulation of all 13 transcripts in response to functional stimulation, but an earlier and more severe down-regulation of the mitochondrial transcripts than the nuclear ones in response to functional deprivation. Thus, the mitochondrial subunits may play a more important role in regulating cytochrome c oxidase protein amount and activity in neurons. Our results also point to the need of all 13 subunits to form a functional holoenzyme.
Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA.
H L
HL
Liang
S
S
Ongwijitwat
M T T
MT
Wong-Riley
D000704:Analysis of Variance; D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D015153:Blotting, Western / Q000379:methods; D002478:Cells, Cultured; D003576:Electron Transport Complex IV / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000502:physiology*; D016678:Genome / Q000502:physiology*; D007150:Immunohistochemistry / Q000379:methods; D066298:In Vitro Techniques; D009474:Neurons / Q000187:drug effects / Q000201:enzymology*; D011189:Potassium Chloride / Q000494:pharmacology; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D012683:Sensory Deprivation / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors; D014785:Vision, Ocular / Q000502:physiology; D014793:Visual Cortex / Q000166:cytology
D000779:Anesthetics, Local; D021122:Protein Subunits; D012333:RNA, Messenger; D013779:Tetrodotoxin; D011189:Potassium Chloride; D003576:Electron Transport Complex IV