Acts as a coactivator during transcriptional activation of nuclear genes related to mitochondrial biogenesis and cell growth. Involved in the transcription coactivation of CREB and NRF1 target genes. Interacts with CREB1 and NRF1. Colocalizes with NRF1. Strongly expressed in heart and skeletal muscle, moderately in lung, placenta, intestine, liver, kidney, spleen, thymus, colon and brain. Also expressed in several oncocytic thyroid tumors. Up-regulated by serum (at protein level).