Genomic sequence, structural organization and evolutionary conservation of the 13.2-kDa subunit of rat NADH:ubiquinone oxidoreductase

Glucocorticoid and thyroid hormone receptors in mitochondria of animal cells

This article concerns the localization of glucocorticoid and thyroid hormone receptors in mitochondria of animal cells. The receptors are discussed in terms of their potential role in the regulation of mitochondrial transcription and energy production by the oxidative phosphorylation pathway, realized both by nuclear-encoded and mitochondrially encoded enzymes. A brief survey of the role of glucocorticoid and thyroid hormones on energy metabolism is presented, followed by a description of the molecular mode of action of these hormones and of the central role of the receptors in regulation of transcription. Subsequently, the structure and characteristics of glucocorticoid and thyroid hormone receptors are described, followed by a section on the effects of glucocorticoid and thyroid hormones on the transcription of mitochondrial and nuclear genes encoding subunits of OXPHOS and by an introduction to the mitochondrial genome and its transcription. A comprehensive description of the data demonstrates the localization of glucocorticoid and thyroid hormone receptors in mitochondria as well as the detection of potential hormone response elements that bind to these receptors. This leads to the conclusion that the receptors potentially play a role in the regulation of transcription of mitochondrial genes. The in organello mitochondrial system, which is capable of sustaining transcription in the absence of nuclear participation, is presented, responding to T3 with increased transcription rates, and the central role of a thyroid receptor isoform in the transcription effect is emphasized. Lastly, possible ways of coordinating nuclear and mitochondrial gene transcription in response to glucocorticoid and thyroid hormones are discussed, the hormones acting directly on the genes of the two compartments by way of common hormone response elements and indirectly on mitochondrial genes by stimulation of nuclear-encoded transcription factors.

Adaptations of skeletal muscle to exercise: rapid increase in the transcriptional coactivator PGC-1

Endurance exercise induces increases in mitochondria and the GLUT4 isoform of the glucose transporter in muscle. Although little is known about the mechanisms underlying these adaptations, new information has accumulated regarding how mitochondrial biogenesis and GLUT4 expression are regulated. This includes the findings that the transcriptional coactivator PGC-1 promotes mitochondrial biogenesis and that NRF-1 and NRF-2 act as transcriptional activators of genes encoding mitochondrial enzymes. We tested the hypothesis that increases in PGC-1, NRF-1, and NRF-2 are involved in the initial adaptive response of muscle to exercise. Five daily bouts of swimming induced increases in mitochondrial enzymes and GLUT4 in skeletal muscle in rats. One exercise bout resulted in approximately twofold increases in full-length muscle PGC-1 mRNA and PGC-1 protein, which were evident 18 h after exercise. A smaller form of PGC-1 increased after exercise. The exercise induced increases in muscle NRF-1 and NRF-2 that were evident 12 to 18 h after one exercise bout. These findings suggest that increases in PGC-1, NRF-1, and NRF-2 represent key regulatory components of the stimulation of mitochondrial biogenesis by exercise and that PGC-1 mediates the coordinated increases in GLUT4 and mitochondria.

Autonomous regulation in mammalian mitochondrial DNA transcription

The regulation of the oxidative phosphorylation system (OXPHOS) biogenesis in eukaryotic cells is unique since it involves the expression of two genomes, the mitochondrial DNA (mtDNA) and the nuclear DNA (nDNA). The considerable effort done in collecting information on the factors that influence the expression of the genes encoded in mtDNA and nDNA has revealed that a multiplicity of regulatory options are available in mammalian cells to perform this task. Thus, at least three archetypal situations can be distinguished: mitochondrial proliferation, mitochondrial differentiation, and mitochondrial local tuning (MLT). Each of them seems to be predominantly under the control of specific strategies of regulation, although the description of the detailed molecular mechanisms involved is still in its beginnings. In the present review, we focus on the evidence supporting the existence of mechanisms for autonomous regulation of mtDNA transcription and its role in the integrated regulation of the OXPHOS system biogenesis.

A human cDNA encoding the homologue of NADH: ubiquinone oxidoreductase subunit B13

A cDNA encoding the human homologue of bovine NADH:ubiquinone oxidoreductase (complex I of mitochondrial respiratory chain) subunit B13 has been isolated. The clone contains an open reading frame of 348 bp, 23 bp of 5'-untranslated sequence (UTR) and a long 3'UTR of 1088 bp. The deduced amino-acid sequence is 87% identical to bovine B13. Human B13 mRNA expression was observed in all tissues examined with highest levels in heart, skeletal muscle and brain. Southern analysis of human genomic DNA revealed the presence of multigene family.