Targeting the Acute Promyelocytic Leukemia-Associated Fusion Proteins PML/RAR[alpha] and PLZF/RAR[alpha] with Interfering Peptides

In acute promyelocytic leukemia (APL), hematopoietic differentiation is blocked and immature blasts accumulate in the bone marrow and blood. APL is associated with chromosomal aberrations, including t(15;17) and t(11;17). For these two translocations, the retinoic acid receptor alpha (RAR[alpha]) is fused to the promyelocytic leukemia (PML) gene or the promyelocytic zinc finger (PLZF) gene, respectively. Both fusion proteins lead to the formation of a high-molecular-weight complex. High-molecular-weight complexes are caused by the "coiled-coil" domain of PML or the BTB/POZ domain of PLZF. PML/RAR[alpha] without the "coiled-coil" fails to block differentiation and mediates an all-trans retinoic acid-response. Similarly, mutations in the BTB/POZ domain disrupt the high-molecular-weight complex, abolishing the leukemic potential of PLZF/RAR[alpha]. Specific interfering polypeptides were used to target the oligomerization domain of PML/RAR[alpha] or PLZF/RAR[alpha]. PML/RAR[alpha] and PLZF/RAR[alpha] were analyzed for the ability to form high-molecular-weight complexes, the protein stability and the potential to induce a leukemic phenotype in the presence of the interfering peptides. Expression of these interfering peptides resulted in a reduced replating efficiency and overcame the differentiation block induced by PML/RAR[alpha] and PLZF/RAR[alpha] in murine hematopoietic stem cells. This expression also destabilized the PLZF/RAR[alpha]-induced high-molecular-weight complex formation and caused the degradation of the fusion protein. Targeting fusion proteins through interfering peptides is a promising approach to further elucidate the biology of leukemia.