Nuclear receptor coactivator that directly binds nuclear receptors and stimulates the transcriptional activities in a hormone-dependent fashion. Plays a central role in creating a multisubunit coactivator complex, probably via remodeling of chromatin. Involved in the coactivation of different nuclear receptors, such as for steroids (GR and ER), retinoids (RARs and RXRs), thyroid hormone (TRs), vitamin D3 (VDR) and prostanoids (PPARs). Displays histone acetyltransferase activity. Also involved in the coactivation of the NF-kappa-B pathway via its interaction with the NFKB1 subunit (By similarity). acetyl-CoA + L-lysyl-[protein] = CoA + H(+) + N(6)-acetyl-L-lysyl-[protein] Coactivator activity on nuclear receptors and NF-kappa-B pathways is enhanced by various hormones, and the TNF cytokine, respectively. TNF stimulation probably enhances phosphorylation, which in turn activates coactivator function. In contrast, acetylation by CREBBP apparently suppresses coactivation of target genes by disrupting its association with nuclear receptors (By similarity). Interacts with the histone acetyltransferase protein CREBBP. These two proteins are present in a complex containing NCOA2, IKKA, IKKB and IKBKG. Interacts with PCAF and NR3C1 (By similarity). Interacts with CARM1. Interacts with CASP8AP2. Interacts with ATAD2 and this interaction is enhanced by estradiol (By similarity). Interacts with PSMB9. Binds to CSNK1D (By similarity). Found in a complex containing NCOA3, AR and MAK. Interacts with DDX5. Interacts with NPAS2 (By similarity). Interacts with NR4A3 (via AF-1 domain) (PubMed:12709428). Interacts with ESRRB; mediates the interaction between ESRRB and RNA polymerase II complexes and allows NCOA3 corecruitment to ESRRB, KLF4, NANOG, and SOX2 enhancer regions to trigger ESRRB-dependent gene activation involved in self-renewal and pluripotency (PubMed:23019124). Mainly cytoplasmic and weakly nuclear. Upon TNF activation and subsequent phosphorylation, it translocates from the cytoplasm to the nucleus (By similarity). Not expressed in all steroid sensitive tissues. Highly expressed in the female reproductive system, in both oocyte and smooth muscle cells of the oviduct, but not expressed in the uterine endometrium. Highly expressed in mammary glands. Expressed moderately in smooth muscle cells of both blood vessels and intestines, and weakly expressed in hepatocytes. In brain, highly expressed in neurons of the hippocampus, and in mitral cell and granule layers of the olfactory bulb. Expressed moderately in the internal layer of cerebellum. Not expressed in the spinal chord, cardiac muscle, skeletal muscle, thymus and pancreas. Contains three Leu-Xaa-Xaa-Leu-Leu (LXXLL) motifs. Motifs 1 and 2 are essential for the association with nuclear receptors, and constitute the RID domain (Receptor-interacting domain) (By similarity). Acetylated by CREBBP. Acetylation occurs in the RID domain, and disrupts the interaction with nuclear receptors and regulates its function (By similarity). Methylated by CARM1. Phosphorylated by IKK complex. Regulated its function (By similarity). Defects result in diverse phenotype of postnatal growth retardation, such as dwarfism, delayed puberty, abnormal reproductive function and mammary gland growth retardation. Belongs to the SRC/p160 nuclear receptor coactivator family.