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PML suppresses oncogenic transformation of NIH/3T3 cells by activated neu
1Division of Laboratory Medicine, University of Texas M.D. Anderson Cancer Center, Houston 77030, USA.
Abstract:
The chromosomal translocation t(15;17)(q22;q12) is a consistent feature of acute promyelocytic leukemia (APL) that results in the disruption of genes for the zinc finger transcription factor PML and the retinoic acid receptor alpha (RAR alpha). We have previously shown that PML is a growth suppressor and is able to suppress transformation of NIH/3T3 by activated neu oncogene. In the study presented here, the full-length PML cDNA was transfected into B104-1-1 cells (NIH/3T3 cells transformed by the activated neu oncogene) by retrovirally mediated gene transfer. We found that expression of PML could reverse phenotypes of B104-1-1 including morphology, contact-limiting properties, and growth rate in both transient-expression and stable transfectants. We also demonstrated that PML is able to suppress clonogenicity of B104-1-1 in soft agar assay and tumorigenicity in nude mice. These results strongly support our previous finding that PML is a transformation or growth suppressor. Our results further demonstrate that expression of PML in B104-1-1 cells has little effect on cell cycle distribution. Western blot analysis demonstrated that suppression of neu expression in B104-1-1 by PML was insignificant in the transient transfection experiment but significant in the PML stable transfectants. This study suggests that PML may suppress neu expression and block signaling events associated with activated neu. This study supports our hypothesis that disruption of the normal function of PML, a growth or transformation suppressor, is a critical event in APL leukomogenesis.
Insights
The promyelocytic leukemia (PML) protein acts as a growth suppressor, reversing cancer cell phenotypes and inhibiting tumor formation. Its disruption is critical in acute promyelocytic leukemia (APL) development.
Area of Science:
- Molecular Biology
- Oncology
- Cell Biology
Background:
- Acute promyelocytic leukemia (APL) is linked to the t(15;17) chromosomal translocation.
- This translocation disrupts the PML and retinoic acid receptor alpha (RAR alpha) genes.
- Previous research indicated PML functions as a growth and transformation suppressor.
Purpose of the Study:
- To investigate the tumor-suppressive capabilities of the PML protein.
- To determine if PML can reverse oncogenic phenotypes in transformed cells.
- To explore the mechanism by which PML suppresses transformation.
Main Methods:
- Retrovirally mediated gene transfer of full-length PML cDNA into neu-oncogene-transformed NIH/3T3 cells (B104-1-1).
- Assessment of phenotypic changes including morphology, cell growth, and soft agar colony formation.
- Evaluation of tumorigenicity in nude mice models.
- Western blot analysis to assess neu expression levels.
Main Results:
- PML expression reversed malignant phenotypes in B104-1-1 cells, including morphology and growth rate.
- PML suppressed clonogenicity in soft agar and reduced tumor formation in vivo.
- PML significantly suppressed neu expression in stable transfectants, suggesting a role in blocking neu-associated signaling.
Conclusions:
- PML functions as a potent growth and transformation suppressor.
- PML may exert its suppressive effects by downregulating neu expression and its downstream signaling pathways.
- Disruption of PML's function is a key event in the leukemogenesis of APL.