Characterization of ARD1 variants in mammalian cells

Mouse ARD1 (mARD1) has been reported to negatively regulate the hypoxia-inducible factor 1α (HIF-1α) protein by acetylating a lysine residue and enhancing HIF-1α ubiquitination and degradation. However, it was recently reported that human ARD1 (hARD1) does not affect HIF-1α stability. To further explore the activities of the two orthologs, three mouse (mARD1198, mARD1225, mARD1235) and two human (hARD1131, hARD1235) variants were identified and characterized. Among these, mARD1225 was previously reported as a novel negative regulator of HIF-1α. Amino acid sequence analysis showed that the C-terminal region (aa 158–225) of mARD1225 completely differs from those of mouse and human ARD1235, although all three proteins share a well-conserved N-acetyltransferase domain (aa 45–130). The effects of ARD1 variants were evaluated with respect to HIF-1α stability and acetylation activity. Interestingly, mARD1225 strongly decreased the level of HIF-1α and increased the extent of acetylation, whereas mARD1235 and hARD1235 variants had a much weaker effect on HIF-1α stability and acetylation. These results suggest that ARD1 variants might have different effects on HIF-1α stability and acetylation, which may reflect diverse biological functions that remain to be determined.