Molecular mechanism of hypoxia-inducible factor 1alpha -p300 interaction. A leucine-rich interface regulated by a single cysteine.

Hypoxia-inducible factor 1alpha (HIF1alpha) plays a pivotal role in embryogenesis, angiogenesis, and tumorigenesis. HIF1alpha-mediated transcription requires the coactivator p300, at least in part, through interaction with the cysteine- and histidine-rich 1 domain of p300. To understand the molecular basis of this interaction, we have developed a random mutagenesis screen in yeast approach for efficient identification of residues that are functionally critical for protein interactions. As a result, four residues (Leu-795, Cys-800, Leu-818, and Leu-822) in the C-terminal activation domain of HIF1alpha have been identified as crucial for HIF1 transactivation in mammalian systems. Moreover, data from residue substitution experiments indicate the stringent necessity of leucine and hydrophobic cysteine for C-terminal activation domain function. Likewise, Leu-344, Leu-345, Cys-388, and Cys-393 in the cysteine- and histidine-rich 1 domain of p300 have also been shown to be essential for the functional interaction. We propose that hypoxia-induced HIF1alpha-p300 interaction relies upon a leucine-rich hydrophobic interface that is regulated by the hydrophilic and hydrophobic sulfhydryls of HIF1alpha Cys-800.