PML SUPPRESSES ONCOGENIC TRANSFORMATION OF NIH 3T3 CELLS BY ACTIVATEDNEU/

The chromosomal translocation t(15;17)(q22;q12) is a consistent featur e of acute promyelocytic leukemia (APL) that results in the disruption of genes for the zinc finger transcription factor PML and the retinoi c acid receptor alpha (RAR alpha). We have previously shown that PML i s a growth suppressor and is able to suppress transformation of NIH/3T 3 by activated neu oncogene. In the study presented here, the full-len gth PML cDNA was transfected into B104-1-1 cells (NIH/3T3 cells transf ormed by the activated neu oncogene) by retrovirally mediated gene tra nsfer. We found that expression of PML could reverse phenotypes of B10 4-1-1 including morphology, contact-limiting properties, and growth ra te in both transient-expression and stable transfectants. We also demo nstrated that PML is able to suppress clonogenicity of B104-1-1 in sof t agar assay and tumorigenicity in nude mice. These results strongly s upport our previous finding that PML is a transformation or growth sup pressor. Our results further demonstrate that expression of PML in B10 4-1-1 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 leukemogenesis.