Characterization of ARD1 variants in mammalian cells

Mouse ARD1 (mARD1) has been reported to negatively regulate the hypoxia-inducible factor 1 alpha (IIIF-1 alpha) protein by acetylating a lysine residue and enhancing HIF-1 alpha ubiquitination and degradation. However. it was recently reported that human ARD1 (hARD1) does not affect HIF-1 alpha stability. To further explore the activities of the two orthologs, three mouse (mARDl(198), mARDl(225), mARDl(235)) and two human (hARDl(131), hARDl(235)) variants were identified and characterized. Among these, mARDl(225) was previously reported as a novel negative regulator of HIF-1 alpha. Amino acid sequence analysis showed that the C-terminal region (aa 158 225) of mARDl(225), completely differs from those of mouse and human ARDl(235), although all three proteins share a well-conserved N-acetyltransferase domain (aa 45 130). The effects of ARDl variants were evaluated with respect to HIF-1 alpha stability and acetylation activity. Interestingly, mARDl(225) strongly decreased the level of HIF-1 alpha and increased the extent of acetylation, whereas mARDl(235) and hARDl(235) variants had a much weaker effect on HIF-1 alpha stability and acetylation. These results suggest that ARD1 variants might have different effects on HIF-1 alpha stability and acetylation, which may reflect diverse biological functions that remain to be determined. (c) 2005 Elsevier Inc. All rights reserved.