Colocalization and heteromerization between the two human oncogene POZ/zinc finger proteins, LAZ3 (BCL6) and PLZF

Most acute promyelocytic leukemia (APL) cases are associated with recurrent translocations between the gene of retinoic receptor alpha and that of PML (t(15;17)) or PLZF (t(11;17)), PML localizes onto discrete intranuclear do mains, the PML-nuclear bodies, and displays anti-oncogenic and pro-apoptoti c properties. PLZF encodes a transcription factor belonging to the (PO) und er barZ/domain and Kruppel zinc finger (POK) family which interacts directl y with PML, PLZF is related to another POK protein, LAZ3(BCL6), which is st ructurally altered, and presumably misexpressed, in many non-Hodgkin lympho ma (NHL) cases. PLZF and LAZ3 share many functional properties: both inhibi t cell growth, concentrate into punctated nuclear subdomains and are sequen ce-specific transcriptional repressors recruiting a histone deacetylase-rep ressing complex. Given these similarities, we tested whether both proteins could be targeted by each other, Here, LAZ3 and PLZF are shown to colocaliz e onto nuclear dots. Moreover, truncated derivatives of one protein, which display a diffuse nuclear localization, are recruited onto nuclear dots by the full-length other. The colocalization and the reciprocal 'rescue' is th e result of a direct interaction between LAZ3 and PLZF, as indicated by yea st two hybrid assays, in vitro immunoprecipitations, and GST pull down expe riments. In contrast to LAZ3 homomerization, LAZ3/PLZF heteromerization in yeast does not solely depend on POZ/POZ contacts but rather also relies on interactions between the two zinc finger regions and 'cross' contacts betwe en the zinc finger region and the POZ domain of each partner, Likewise, LAZ 3 shows some colocalization with the PLZF partner PML upon stable overexpre ssion of both proteins in CHO cells and interacts with PML in yeast. Finall y, endogenous LAZ3 and PLZF are co-induced and partially colocalized in mye loid MDS cells, These data indicate that a physical interaction between LAZ 3 and PLZF underlies their simultaneous recruitment onto multiproteic nucle ar complexes, presumably involved in transcriptional silencing and whose in tegrity (for APL) and/or function (for APL and NHL) may be altered in oncog enesis.