title: Calcium-regulated changes in mitochondrial phenotype in skeletal muscle cells.
abstract: Cytochrome c expression and mitochondrial biogenesis can be invoked by elevated intracellular Ca(2+) in muscle cells. To characterize the potential role of Ca(2+) as a messenger involved in mitochondrial biogenesis in muscle, we determined the effects of the Ca(2+) ionophore A-23187 on the expression of nuclear- and mitochondrially encoded genes. Treatment of myotubes with 1 microM A-23187 for 48-96 h increased nuclear-encoded beta-subunit F(1)ATPase and malate dehydrogenase (MDH) mRNA levels by 50-100% (P < 0.05) but decreased mRNA levels of glutamate dehydrogenase (GDH) by 19% (P < 0.05). mRNA levels of the cytochrome c oxidase (COX) nuclear-encoded subunits IV, Vb, and VIc were unchanged, whereas the mitochondrially encoded subunits COX II and COX III were decreased by 30 and 70%, respectively (P < 0.05). This was paralleled by a 20% decrease (P < 0.05) in COX activity. These data suggest that cytoplasmic Ca(2+) differentially regulates the mRNA level of nuclear and mitochondrial genes. The decline in COX II and III mRNA may be mediated by Tfam, because A-23187 modestly reduced Tfam levels by 48 h. A-23187 induced time-dependent increases in Egr-1 mRNA, along with the activation of ERK1/2 and AMP-activated protein kinase. MEK inhibition with PD-98059 attenuated the increase in Egr-1 mRNA. A-23187 also increased Egr-1, serum response factor, and Sp1 protein expression, transcription factors implicated in mitochondrial biogenesis. Egr-1 overexpression increased nuclear-encoded cytochrome c transcriptional activation by 1.5-fold (P < 0.05) and reduced GDH mRNA by 37% (P < 0.05) but had no effect on MDH or beta-subunit F(1)ATPase mRNA. These results indicate that changes in intracellular Ca(2+) can modify mitochondrial phenotype, in part via the involvement of Egr-1.
authors.affiliation: Dept. of Biology, York University, Toronto, Ontario, M3J 1P3 Canada.
authors.forename: Damien
authors.initials: D
authors.lastname: Freyssenet
authors.forename: Isabella
authors.initials: I
authors.lastname: Irrcher
authors.forename: Michael K
authors.initials: MK
authors.lastname: Connor
authors.forename: Martino
authors.initials: M
authors.lastname: Di Carlo
authors.forename: David A
authors.initials: DA
authors.lastname: Hood
mesh_terms: D055372:AMP-Activated Protein Kinases; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002460:Cell Line; D002467:Cell Nucleus / Q000502:physiology; D051546:Cyclooxygenase 2; D045304:Cytochromes c / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D051766:Early Growth Response Protein 1; D004789:Enzyme Activation / Q000187:drug effects; D015870:Gene Expression / Q000187:drug effects; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism; D007476:Ionophores / Q000494:pharmacology; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008291:Malate Dehydrogenase / Q000378:metabolism; D008931:Mitochondria, Muscle / Q000502:physiology*; D024101:Mitochondrial Proteins / Q000235:genetics; D009097:Multienzyme Complexes / Q000378:metabolism; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D018482:Muscle, Skeletal / Q000166:cytology / Q000201:enzymology / Q000502:physiology*; D009687:Nuclear Proteins; D010641:Phenotype; D011451:Prostaglandin-Endoperoxide Synthases / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D026362:Serum Response Factor / Q000378:metabolism; D016329:Sp1 Transcription Factor / Q000378:metabolism; D013997:Time Factors; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D029867:Xenopus Proteins
chemical_list: D004268:DNA-Binding Proteins; C486111:EGR1 protein, Xenopus; D051766:Early Growth Response Protein 1; D017874:Immediate-Early Proteins; D007476:Ionophores; D007527:Isoenzymes; D024101:Mitochondrial Proteins; D009097:Multienzyme Complexes; D009687:Nuclear Proteins; D012333:RNA, Messenger; D026362:Serum Response Factor; D016329:Sp1 Transcription Factor; D014157:Transcription Factors; D029867:Xenopus Proteins; C422562:mitochondrial transcription factor A; D000001:Calcimycin; D045304:Cytochromes c; D008291:Malate Dehydrogenase; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; C466421:cyclooxygenase-3; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D002118:Calcium