Peter Hemmerich

PML nuclear bodies (PML NBs) are present in almost every human cell type. Under normal growth conditions, mammalian cell nuclei contain 5 to 30 spherical PML NBs ranging in size between 0.2 and 1 µm. PML NBs locally accumulate a dynamic range of specific proteins, many of which are key regulators of various nuclear processes: apoptosis, proteolysis, senescence, gene regulation, tumor suppression, DNA damage response and antiviral response. The promyelocytic leukemia (PML) protein constitutes the scaffold component of PML NBs; in the absence of PML expression, the NB does not form and all proteins normally targeted to these domains adopt a diffuse localization or concentrate into random microspeckles. Thus the integrity of these structures may be critically important for normal cell functioning. Although or because so many cellular pathways have been linked to PML NBs and its component parts the precise role of these macromolecular assemblies is not known. The current model suggests that PML NBs serve as recruitment sites for specific nuclear protein modification, sequesteration and/or complex assembly.