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MDM4 actively restrains cytoplasmic mTORC1 by sensing nutrient availability.
Francesca Mancini1,2, Emanuela Teveroni3, Giusy Di Conza4,5
1Institute of Cell Biology and Neurobiology, National Research Council of Italy (CNR), 00143, Rome, Italy. chicca.mancini@tiscali.it.
Molecular Cancer
|March 9, 2017
Summary
MDM4 acts as a nutrient sensor, inhibiting mTORC1 activity independently of p53. This finding reveals a novel metabolism-related tumor-suppressing function for MDM4 in cancer.
Area of Science:
- Oncology
- Molecular Biology
- Cellular Metabolism
Background:
- Tumor-related factors significantly influence metabolic pathways, leading to cancer-specific metabolic alterations.
- MDM4, a p53-inhibitor, exhibits context-dependent oncogenic or anti-survival roles.
- Understanding MDM4's regulation of cellular metabolism is crucial for cancer research.
Purpose of the Study:
- To investigate the regulatory relationship between MDM4 and mTORC1.
- To elucidate the role of MDM4 in cellular metabolism and its implications in cancer.
- To determine if MDM4's function is dependent on p53.
Main Methods:
- Overexpression and silencing of MDM4 in cell culture.
- In vitro kinase assays with purified proteins.
- In vivo studies using a transgenic mouse model overexpressing MDM4.
- Analysis of The Cancer Genome Atlas (TCGA) database (N=356) for MDM4 and mTOR correlations.
- 3D cell cultures to assess p53-independent MDM4 activity.
Main Results:
- MDM4 inhibits mTORC1 activity upon nutrient deprivation by binding to mTOR, independent of p53.
- MDM4 reduces the phosphorylation of p70S6K1, a downstream target of mTORC1, in vitro and in vivo.
- MDM4 diminishes cell size and proliferation, and inhibits mTORC1-mediated mammosphere formation.
- MDM4 transcript levels are inversely correlated with mTOR levels in breast tumors from TCGA.
Conclusions:
- MDM4 functions as a nutrient sensor that inhibits mTORC1.
- MDM4 exhibits a metabolism-related tumor-suppressing function.
- The p53-independent inhibition of mTORC1 by MDM4 offers new insights into cancer metabolism regulation.
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