Transcriptional coactivator for CREB1 which activates transcription through both consensus and variant cAMP response element (CRE) sites.Acts as a coactivator, in the SIK/TORC signaling pathway,being active when dephosphorylated and acts independently of CREB1 'Ser-133' phosphorylation.Enhances the interaction of CREB1 with TAF4.Regulates the expression of specific CREB-activated genes such as the steroidogenic gene,StAR.Potent coactivator of PGC1alpha and inducer of mitochondrial biogenesis in muscle cells.Also coactivator for TAX activation of the human T-cell leukemia virus type 1 (HTLV-1) long terminal repeats (LTR).In the hippocampus, involved in late-phase long-term potentiation (L-LTP) maintenance at the Schaffer collateral-CA1 synapses.May be required for dendritic growth of developing cortical neurons.