mTORC1-USP30-LEF1 Cascade Regulates Cancer Stemness and Malignant Progression Through Mitonuclear Crosstalk

Area of Science:

• Cell Biology
• Molecular Oncology
• Biochemistry

Background:

• USP30 is a deubiquitinase primarily known for mitochondrial functions in mitophagy.
• Its role in the nucleus and cancer biology remains unexplored.

Purpose of the Study:

• To investigate the nuclear functions of USP30 in cancer.
• To elucidate the mechanisms by which USP30 affects cancer stemness and chemoresistance in triple-negative breast cancer (TNBC).

Main Methods:

• Immunofluorescence and cell fractionation to determine USP30 localization.
• Western blotting and site-directed mutagenesis to study phosphorylation and nuclear translocation.
• Co-immunoprecipitation and in vitro deubiquitination assays to analyze protein interactions and enzymatic activity.
• Reporter assays to assess WNT signaling.
• In vivo metastasis models in mice.

Main Results:

• USP30 localizes to both mitochondria and the nucleus.
• Nutrient deprivation induces USP30 nuclear translocation by suppressing mTORC1-mediated phosphorylation at serine 104.
• Nuclear USP30 inhibits cancer stemness and chemoresistance in TNBC by deubiquitinating TCF/LEF1, disrupting β-catenin/LEF1 complex formation with co-activators.
• USP30 downregulation in TNBC tissues correlates with reduced nuclear levels and increased metastasis.
• Overexpression of nuclear USP30 reduces lung metastasis in TNBC mouse models.

Conclusions:

• USP30 possesses a novel nuclear function as a tumor suppressor in TNBC.
• USP30 nuclear translocation is a regulated process crucial for inhibiting WNT signaling and cancer stemness.
• Targeting USP30 nuclear localization presents a potential therapeutic strategy against breast cancer metastasis.