The RAR alpha-PLZF chimera associated with Acute Promyelocytic Leukemia has retained a sequence-specific DNA-binding domain

In most cases, Acute Promyelocytic Leukemia (APL) is associated with t(15;17) translocation which juxtaposes sequences from PML and retinoic acid receptor alpha (RAR alpha) genes. The generated PML-RAR alpha fusion interferes with wild type RAR alpha-mediated transcription and disrupts subnuclear compartments, known as PML bodies. Both defects are corrected by all trans retinoic acid (ATRA) therapy which induces differentiation of leukemic cells and clinical remission. In a rare APL syndrome associated,vith t(11;17), fusion of the RAR alpha gene with the PLZF gene, encoding a Zinc-finger protein produces two reciprocal RAR alpha chimeras, Although PLZF-RAR alpha and PML-RAR alpha are similar in their apparent dominant negative effects, t(11;17)-associated APL is refractory to ATRA therapy. In a yeast two-hybrid genetic screening, we isolated clones encoding the GAL4 transactivation domain fused to various parts of PLZF. Using these autonomously transactivating hybrids, similar in structure to the RAR alpha-PLZF fusion, we mapped the DNA-binding domain of PLZF to the last five Zinc-fingers, a region retained in RAR alpha-PLZF chimera and characterized a specific PLZF target sequence. Our data support the hypothesis that RAR alpha-PLZF chimera is not an inert product of reciprocal translocation and may thus contribute to ATRA unresponsiveness of t(11;17)-associated APL.