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Updated: Dec 31, 2025
Defining Gene Functions in Tumorigenesis by Ex vivo Ablation of Floxed Alleles in Malignant Peripheral Nerve Sheath Tumor Cells
Published on: August 25, 2021
Widespread overexpression of epitope-tagged Mdm4 does not accelerate tumor formation in vivo
Sarah De Clercq1, Agnieszka Gembarska, Geertrui Denecker
1Laboratory for Molecular Cancer Biology, Department of Biomedical Molecular Biology, VIB-UGent, Technologiepark, B-9052 Ghent, Belgium.
Abstract:
Mdm2 and Mdm4 are critical negative regulators of p53. A large body of evidence indicates that elevated expression of either Mdm2 or Mdm4 may favor tumor formation by inhibiting p53 tumor suppression function. To explore this possibility in vivo, we generated conditional Mdm2 and Mdm4 transgenic mice. We show that although both transgenes are designed to be expressed ubiquitously and at comparable levels, only the Mdm4 transgenic protein is produced at high levels in vivo. In contrast, exogenous Mdm2 is constitutively degraded in a proteasome-dependent manner, indicating that cells are equipped with efficient mechanisms that prevent Mdm2 accumulation in vivo. Mice that are homozygous for the Mdm4 transgene die during embryogenesis owing to severe vascular maturation defects. Importantly, this lethality is not rescued on a p53-null background, indicating that high levels of Mdm4 impact on a pathway(s) other than p53 that controls vascular and embryonic development. Mice expressing a single copy of the Mdm4 transgene are viable and, surprisingly, are not prone to spontaneous, radiation-induced or Emicro-myc-induced tumor formation. The findings have clear implications for cancer etiology as well as for cancer therapy.
Insights
High levels of Mdm4 protein, but not Mdm2, accumulate in vivo. Mdm4 overexpression causes embryonic lethality via p53-independent pathways, and does not increase tumor formation in mice.
Area of Science:
- Molecular Biology
- Oncology
- Developmental Biology
Background:
- Mdm2 and Mdm4 are key negative regulators of the p53 tumor suppressor.
- Elevated Mdm2 or Mdm4 expression is implicated in tumor formation by inhibiting p53.
- Understanding their in vivo regulation is crucial for cancer research.
Purpose of the Study:
- To investigate the in vivo expression and function of Mdm2 and Mdm4 using transgenic mouse models.
- To determine the impact of Mdm2 and Mdm4 overexpression on p53 activity and tumor development.
- To explore potential p53-independent roles of Mdm4 in development.
Main Methods:
- Generation of conditional Mdm2 and Mdm4 transgenic mice for ubiquitous expression.
- Analysis of protein levels and degradation pathways (proteasome-dependent).
- Assessment of embryonic lethality, vascular defects, and tumor formation (spontaneous, radiation-, and Emicro-myc-induced).
Main Results:
- Exogenous Mdm2 is rapidly degraded, preventing accumulation, unlike Mdm4.
- Homozygous Mdm4 transgenic mice exhibit embryonic lethality due to vascular defects, independent of p53.
- Mice with one Mdm4 transgene copy are viable and show no increased tumor susceptibility.
Conclusions:
- Mammalian cells possess robust mechanisms to prevent Mdm2 accumulation in vivo.
- Mdm4 plays a critical role in embryonic vascular development through p53-independent pathways.
- Mdm4 overexpression alone does not promote tumorigenesis, challenging its direct role in cancer etiology.
