Tryptophan 621 and serine 667 residues of Daxx regulate its nuclear export during glucose deprivation.

The cellular target responsible for the nuclear export of Daxx has been identified as chromosomal region maintenance 1 (CRM1), which is a carrier protein for nuclear export and a receptor for the nuclear export signal (NES) of Daxx. Binding of Daxx to CRM1 was increased early during glucose deprivation and then gradually decreased. This interaction was inhibited by leptomycin B, a specific inhibitor of CRM1-dependent nuclear export. Substitution of the serine 667 amino acid residue of Daxx with alanine reduced the interaction with CRM1 during glucose deprivation, suggesting that the phosphorylation of Ser-667 is required for its binding to CRM1 and for its subsequent nuclear export. Data from coupled transcription-translation studies reveal that the NES (amino acids 565-575) of Daxx is a binding site for CRM1. Interestingly, constitutive export of Daxx has occurred by replacement of the tryptophan 621 Daxx residue with alanine. These results suggest that this tryptophan residue plays a key role in masking the NES of Daxx from its receptor, CRM1, in the resting state, whereas phosphorylation of serine 667 would release the NES, which could then be recognized by the CRM1.