THE ACUTE PROMYELOCYTIC LEUKEMIA SPECIFIC PML AND PLZF PROTEINS LOCALIZE TO ADJACENT AND FUNCTIONALLY DISTINCT NUCLEAR-BODIES

Acute promyelocytic leukaemia is characterized by translocations that involve the retinoic acid receptor a (RAR alpha) locus on chromosome 1 7 and the PML locus on 15 or the PLZF locus on 11. The resulting abnor mal translocation products encode for PML/ RAR alpha or PLZF/RAR alpha fusion proteins. There is increasing experimental evidence that the A PL-specific fusion proteins have similar biologic activities on differ entiation and survival and that both components of the fusion proteins (PML or PLZF and RAR alpha) are indispensable for these biological ac tivities. The physiologic function of PML or PLZF or whether PML and P LZF; contribute common structural or functional features to the corres ponding fusion proteins is not known. We report here immunofluorescenc e studies on the cellular localization of PLZF and PLZF/RAR alpha and compare it with the localization of PML and PML/RAR alpha. PLZF locali zes to nuclear domains of 0.3-0.5 microns, approximately 14 per cell i n the KG1 myeloid cell line. These PLZF-bodies are morphologically sim ilar to the domains reported for PML (PML-NBs). There is tight spatial relationship between about 30% of PLZ-NBs and PML-NBs: they partially overlap. However, PML and PLZF do not form soluble complexes in vivo. PLZF- and PML-NBs are functionally distinct. Adenovirus E4-ORF3 prote in expression alters the structure of the PML-NBs and-interferon incre ases the number of PML-NBs and neither has any effect on PLZF NBs. The localization of PLZF/RAR alpha is different to that of PLZF and RAR a lpha. The nuclear distribution pattern of PLZF/RAR alpha is one of hun dreds of small dots (microspeckles) less than 0.1 micron. Expression o f PLZF/RAR alpha did not provoke disruption of the PML-NBs. Go-express ion of PML/RAR alpha and PLZF/RAR alpha in U937 cells revealed apparen t colocalization. Overall the results suggest that the PML-and PLZF-NB s are distinct functional nuclear domains, but that they may share com mon regulatory pathways and/or targeting sequences, as revealed by the common localization of their corresponding fusion proteins.