To validate the ChIP results, we analysed the co-precipitation of PGC-1 targets and found enrichment of promoter fragments of lamin A, phosphoenolpyruvate carboxykinase 1 and insulin receptor substrate-1 (Fig.?1b). the activity and amount of mitochondria is subject Salermide to regulation by a transcriptional network. A key transcriptional regulator of mitochondrial biogenesis is the peroxisome proliferator-activated receptor gamma co-activator 1 (PGC-1)1. PGC-1 is detectable in tissues with high energy demand such as heart, skeletal muscle, brown adipose tissue (BAT), liver and brain2. Beside mitochondrial biogenesis PGC-1 regulates different metabolic adaptation processes like gluconeogenesis in the liver3, glucose uptake and fatty acid oxidation in the skeletal muscle4, adaptive thermogenesis in BAT5, fatty acid oxidation in heart6 and neuronal energy homeostasis and ROS-detoxification in the brain7, 8. Dysregulation of PGC-1 has been connected to many neurodegenerative and metabolic disorders; Parkinsons, Alzheimers and Huntingtons disease, Amyotrophic Lateral Sclerosis (ALS)9, 10, type 2 diabetes11, obesity12 and heart failure13, 14 are just some examples. PGC-1 itself is subject to intensive regulation on transcriptional and posttranslational level, thus the amount of PGC-1 expression, the subcellular localization and its phosphorylation, acetylation and sumoylation state control its activity. PGC-1 is a master regulator of metabolic adaptation and responds to diverse stressors. The activity of PGC-1 is modulated by fasting or the calorie-restriction mimetic resveratrol15, by altered oxygenation14 or ?-adrenergic stimulation16 to name a few. Knock-out of PGC-1 is viable, but the animals display failures in thermogenesis and energy homeostasis and are lean and hyperactive due to striatal degeneration patterns reminiscent of the neurodegenerative disorder Huntingtons disease17. In fact it has been shown, that mutant huntingtin negatively impacts the expression of PGC-110, 18. Ribosomes are responsible for the synthesis of all cellular proteins. The key step in ribosomal biogenesis is transcription of the rDNA by RNA polymerase I and its specific transcription factors in the nucleolus, where the pre-ribosomes are assembled. Mitochondria possess mito-ribosomes that in humans translate 13 different proteins of the respiratory chain. The majority of mitochondrial structure and biogenesis is dependent on the translation products of the cytosolic ribosomes19, thus mitochondrial biogenesis is at least partially dependent on ribosomal biogenesis. Therefore, we speculated that ribosomal biogenesis and mitochondrial biogenesis might be linked by a common transcriptional regulator like PGC-1. Here, we demonstrate that PGC-1 locates to the nucleolus, associates with the rDNA and controls rDNA transcription in response to multiple stimuli in several tissues and cell types. Moreover, we identify PGC-1 as a tissue specific modulator of rDNA transcription, Salermide a function that is impaired in individuals carrying the Huntingtons disease mutation. Results PGC-1 localizes to the nucleolus and associates with the unmethylated rDNA The transcriptional co-activator PGC-1 shuttles between cytosol and nucleus depending on its activation state20. Asking if the nuclear PGC-1 co-localizes to the site of rDNA transcription, the nucleolus, we performed immunocytochemical staining under ambient O2 concentrations in PGC-1 expressing HEK Rabbit Polyclonal to RAD17 cells. Confocal microscopy revealed a clear enrichment of PGC-1 in nucleoli (Fig.?1a). This nucleolar localization was confirmed in N2A cells (Supplementary Figure?S1). Salermide Quantification of confocal microscopy revealed a significant overlap between mean signal intensities Salermide of PGC-1 and the nucleolar marker nucleolin in both cell lines (Supplementary Figure?S2). To investigate PGC-1 localization under near physiological conditions, we repeated the experiment at 3% O2 and found predominant localization of the transcriptional cofactor in the cytoplasm. When activated by addition of resveratrol, PGC-1 again shuttles to the nucleolus (Supplementary Salermide Figure?S3a). The expression level of PGC-1a does not change between 3% and 21% O2 neither on mRNA nor on protein level (Supplementary Figure?S3b). Open in a separate window Figure 1 Localization of.