Phosphorylated PPARGC1A (PGC-1alpha) does not bind DNA directly but instead interacts with other transcription factors, notably NRF1 and NRF2 (via HCF1). NRF1 and NRF2 together with PPARGC1A activate the transcription of nuclear-encoded, mitochondrially targeted proteins such as TFB2M, TFB1M, and TFAM. PGC-1beta and PPRC appear to act similarly to PGC-1alpha but have not been as well studied. Transcription of PPARGC1A itself is upregulated by CREB1 (in response to calcium), MEF2C/D, ATF2, and PPARGC1A. Transcription of PPARGC1A is repressed by NR1D1 (REV-ERBA).