The PML and SP100-containing nuclear bodies (NBs) represent the best-studied example of a defined nuclear substructure the integrity of which is compromised in certain human diseases, including leukemia, neurodegenerative disorders and viral infection.
Nuclear proteins that are localized in discrete domains within the nucleus include the leukemia-associated acute myelogenous leukemia (AML) and promyelocytic leukemia (PML) factors, the SC-35 RNA-processing factors, nucleolar proteins and components of both transcriptional and DNA replication complexes.
Fusion gene products such as PML-RARalpha and BCR-ABL generated by leukemia-specific chromosomal translocations have been identified as target molecules for the treatment of leukemia.
Targeting of PML/RARalpha using a loss of function strategy in acute promyelocytic leukemia (APL) is a direct therapeutic approach for patients and may be the basis of future gene therapy for this leukemia.
In previous studies, we demonstrated that expression of a human PML-RARA complementary DNA in murine granulocyte precursor cells initiated the development of leukemia.
Models to explain the origin of this leukemia propose a block in cell differentiation due to aberrant repression of retinoic acid responsive genes and/or disruption of the function of the PML-containing nuclear bodies.
As models for the PML/RARalpha-positive LSC we used: (i) Sca1+/lin- murine HSC retrovirally transduced with PML/RARalpha; (ii) LSC from mice with PML/RARalpha-positive leukemia; (iii) the side population of the APL cell line NB4.
The great success of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) in treating acute promyelocytic leukemia through modulation of the causative PML-RARalpha oncoprotein represents the first two paradigms of mutant TFs-targeting therapeutic strategies for leukemia.
This study further supports the presence of preferential sites of DNA damage induced by mitoxantrone in PML and RARA genes that may underlie the propensity to develop this subtype of leukemia after exposure to this agent.
Here we show that retinoic acid also triggers growth arrest of leukemia-initiating cells (LICs) ex vivo and their clearance in PML-RARA mouse APL in vivo.
Using hierarchical clustering analysis to compare acute myeloid leukemia genetic subgroups based on their similarity of septin expression changes, we found that MLL-SEPT2 and MLL-SEPT6 neoplasias cluster together apart from the remaining subgroups and that PML-RARA leukemia presents under-expression of most septin family genes.
In addition, DNA methylation profiles segregated patients with CEBPA aberrations from other subtypes of leukemia, defined four epigenetically distinct forms of AML with NPM1 mutations, and showed that established AML1-ETO, CBFb-MYH11, and PML-RARA leukemia entities are associated with specific methylation profiles.
Previous studies indicated that in acute promyelocytic leukemia (APL), a subtype of acute myelogenous leukemia (AML) bearing the leukemia promoting PML/RARα fusion protein, let-7c expression seems to be controlled by the host gene promoter, in which canonical Retinoic Acid Responsive Elements (RAREs) are bound by PML/RARα in an all transretinoic acid (ATRA)-sensitive manner.
Promyelocytic leukemia zinc finger (PLZF) acts as a tumor-suppressor gene in a series of cancers including prostate, melanoma, colon cancer and leukemia.
Importantly, this proliferation signature was absent from the poorly leukemogenic p50/RARA fusion model, implying a critical role for PML in the altered cell-cycle kinetics and ability to initiate leukemia.