Multifunctional protein that is involved in the regulation of many processes including tumor suppression, apoptosis, cell cycle progression or transcription. Promotes apoptosis by favouring the activation of caspase-9/CASP9 and allowing apoptosome formation. In addition, plays a role in the modulation of histone acetylation and transcription as part of the INHAT (inhibitor of histone acetyltransferases complex. Inhibits the histone-acetyltranferase activity of EP300/CREBBP (CREB-binding protein and EP300/CREBBP-associated factor by histone masking. Preferentially binds to unmodified histone H3 and sterically inhibiting its acetylation and phosphorylation leading to cell growth inhibition. Participates in other biochemical processes such as regulation of mRNA nuclear-to-cytoplasmic translocation and stability by its association with ELAVL1 (Hu-antigen R. Plays a role in E4F1-mediated transcriptional repression as well as inhibition of protein phosphatase 2A.