The adenovirus E1A-associated cellular p300 transcriptional co-activator protein functions as a histone acetyltransferase that regulates transcription via chromatin remodeling and is important in the processes of cell proliferation and differentiation. p300 (also known as KAT3B) acetylates all four core histones in nucleosomes, as well as non-histone targets. p300 mediates cAMP-gene regulation by binding specifically to phosphorylated CREB protein. p300 has also been identified as a co-activator of HIF1A (hypoxia-inducible factor 1 alpha), which plays a role in the stimulation of hypoxia-induced genes such as VEGF. Defects in this gene are a cause of Rubinstein-Taybi syndrome and its dysfunction is linked to a number of human diseases including Parkinson"s, Huntington"s, and Alzheimer"s diseases. p300 may also play a role in epithelial cancer.