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Transgenic expression of PML/RARalpha impairs myelopoiesis
E Early1, M A Moore, A Kakizuka
1Department of Medicine, Laboratory of Molecular Medicine, Sloan-Kettering Institute, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
Abstract:
The translocation found in acute promyelocytic leukemia rearranges the promyelocytic leukemia gene (PML) on chromosome 15 with the retinoic acid receptor alpha (RARalpha) on chromosome 17. This yields a fusion transcript, PML/RARalpha, a transcription factor with reported dominant negative functions in the absence of hormone. Clinical remissions induced with all-trans retinoic acid (RA) treatment in acute promyelocytic leukemia are linked to PML/RARalpha expression in leukemic cells. To evaluate the PML/RARalpha role in myelopoiesis, transgenic mice expressing PML/RARalpha were engineered. A full-length PML/RARalpha cDNA driven by the CD11b promoter was expressed in transgenic mice. Expression was confirmed in the bone marrow with a reverse transcription PCR assay. Basal total white blood cell and granulocyte counts did not appreciably differ between PML/RARalpha transgenic and control mice. Cell sorter analysis of CD11b+ bone marrow cells revealed similar CD11b+ populations in transgenic and control mice. However, in vitro clonal growth assays performed on peripheral blood from transgenic versus control mice revealed a marked reduction of myeloid progenitors, especially in those responding to granulocyte/ macrophage colony-stimulating factor. Granulocyte/macrophage colony-stimulating factor and kit ligand cotreatment did not overcome this inhibition. Impaired myelopoiesis in vivo was shown by stressing these mice with sublethal irradiation. Following irradiation, PML/RARalpha transgenic mice, as compared with controls, more rapidly depressed peripheral white blood cell and granulocyte counts. As expected, nearly all control mice (94.4%) survived irradiation, yet this irradiation was lethal to 45.8% of PML/RARalpha transgenic mice. Lethality was associated with more severe leukopenia in transgenic versus control mice. Retinoic acid treatment of irradiated PML/RARalpha mice enhanced granulocyte recovery. These data suggest that abnormal myelopoiesis due to PML/RARalpha expression is an early event in oncogenic transformation.
Insights
The PML/RARalpha fusion protein in acute promyelocytic leukemia impairs myeloid progenitor development and reduces survival after irradiation. Retinoic acid treatment aids granulocyte recovery in these mice.
Area of Science:
- Hematology
- Molecular Biology
- Oncology
Background:
- Acute promyelocytic leukemia (APL) is characterized by the PML/RARalpha fusion transcript.
- This fusion protein plays a role in leukemogenesis and response to all-trans retinoic acid (RA).
Purpose of the Study:
- To investigate the role of PML/RARalpha in myelopoiesis using a transgenic mouse model.
- To assess the impact of PML/RARalpha on myeloid progenitor function and in vivo stress response.
Main Methods:
- Engineered transgenic mice expressing PML/RARalpha under the CD11b promoter.
- Confirmed expression via reverse transcription PCR.
- Assessed bone marrow cell populations and in vitro myeloid progenitor growth.
- Evaluated survival and blood cell counts after sublethal irradiation.
Main Results:
- Transgenic mice showed reduced myeloid progenitor growth in vitro.
- PML/RARalpha mice exhibited impaired recovery and increased lethality following irradiation.
- Retinoic acid treatment improved granulocyte recovery in irradiated transgenic mice.
Conclusions:
- PML/RARalpha expression leads to abnormal myelopoiesis, an early event in oncogenic transformation.
- The fusion protein compromises hematopoietic stem cell function and stress tolerance.