PML NBs (ND10) and Daxx: from nuclear structure to protein function.

Proteins that combine PML NBs (ND10) can be divided into two groups: "transient" (that accumulate at PML NBs upon over-expression, interferon-induced up-regulation, block of proteosomal degradation, environmental stress or viral infection) and "constitutive" that co-localize with PML in the majority of cultured cells. One of the few "constitutive" components of PML NBs is the death domain-associated protein Daxx. While PML NBs are the most obvious depositories of Daxx, there are multiple alternative localization of this protein in the nucleus and cytoplasm, suggesting differential functionality of Daxx at different cellular compartments and stages of the cell cycle. The purpose of this review is to analyze Daxx spatiotemporal behavior within and outside of PML NBs and to discuss functions attributed to these localizations. We suggest that Daxx can participate in numerous cellular functions as a mediator of protein interactions, thus acting as a fine tuning instrument in highly orchestrated cellular processes; we also envision PML NBs accumulation of Daxx as an "out of action" storage depot.