PALB2 mutations increase oncogenic properties of breast epithelial cells by enhancing JAM3 and PARVB expression
Hanna Tuppurainen1, Marjut Nätynki1, Niina Laurila1
1Laboratory of Cancer Genetics and Tumor Biology, Translational Medicine Research Unit, Biocenter Oulu and Faculty of Medicine, Medical Research Center Oulu, University of Oulu, FI-90220 Oulu, Finland.
Abstract:
High-risk genes, heterozygous pathogenic mutations of which predispose to familial breast cancers, typically encode factors securing a proper DNA damage response. PALB2 is one such major cellular factor that is needed for alleviation of genomic, replicative, and oxidative stresses. Thus, it has a crucial role in maintaining genomic integrity and protecting cells against cancer. While the malfunctions in DNA damage repair of PALB2-mutated cells have extensively been documented, our research continues to explore cells' other pro-tumorigenic characteristics, focusing particularly on the early stages of malignancy development. Recently, we generated biallelically and monoallelically PALB2-mutated cell lines in a non-malignant background and reported that also their migratory capacity had enhanced together with changes in their transcriptomes and formation of three-dimensionally grown spheroids. Here we demonstrate that JAM3 and PARVB are among the top up-regulated genes in PALB2-mutated cells and that knockdown of the genes reduce migration of the cells and morphological abnormalities of PALB2-mutated spheroids. Macropinocytosis that cancer cells utilize to advance their viability, has also enhanced in PALB2-mutated cells in a β-parvin-dependent manner. Knocking down PALB2 or increased DNA damage did not trigger JAM3 and PARVB expression in control cells, suggesting the need for long-term changes in cell fate and/or cellular conditions. However, DNA damage boosted the nuclear accumulation of a macropinosome marker dextran, indicating that PALB2-mutated cells may use the system to replenish nucleotide stocks for DNA repair. Altogether, several mechanisms can increase the oncogenic potential of PALB2-mutated cells and may offer new approaches to treat PALB2-associated cancers.
Insights
Mutations in the PALB2 gene, crucial for DNA repair, enhance cancer cell migration and macropinocytosis. These findings reveal new therapeutic targets for PALB2-associated cancers.
Area of Science:
- Genetics and Molecular Biology
- Cancer Research
- Cell Biology
Background:
- Heterozygous pathogenic mutations in high-risk genes like PALB2 predispose to familial breast cancers by affecting DNA damage response.
- PALB2 is essential for managing genomic, replicative, and oxidative stresses, maintaining genomic integrity, and preventing cancer.
- While DNA repair defects in PALB2-mutated cells are known, other pro-tumorigenic characteristics, especially in early malignancy stages, require further investigation.
Purpose of the Study:
- To investigate non-DNA repair related pro-tumorigenic characteristics of PALB2-mutated cells.
- To identify specific genes and cellular processes contributing to the enhanced oncogenic potential of PALB2-mutated cells.
- To explore potential therapeutic strategies for PALB2-associated cancers.
Main Methods:
- Generation of biallelically and monoallelically PALB2-mutated cell lines in a non-malignant background.
- Transcriptome analysis to identify differentially expressed genes.
- Gene knockdown experiments (JAM3, PARVB, PALB2) to assess functional impact.
- Assessment of cell migration, spheroid formation, and macropinocytosis.
- Investigation of dextran uptake as a marker for macropinocytosis and its relation to DNA damage.
Main Results:
- PALB2-mutated cells exhibit enhanced migratory capacity and altered spheroid formation.
- JAM3 and PARVB are significantly upregulated in PALB2-mutated cells; their knockdown reduces migration and spheroid abnormalities.
- Macropinocytosis is enhanced in PALB2-mutated cells, dependent on β-parvin.
- Upregulation of JAM3 and PARVB is linked to long-term cellular changes, not directly by PALB2 knockdown or DNA damage in control cells.
- DNA damage increases nuclear dextran accumulation in PALB2-mutated cells, suggesting nucleotide replenishment for repair.
Conclusions:
- PALB2 mutations confer enhanced oncogenic potential through multiple mechanisms beyond DNA repair defects, including increased migration and macropinocytosis.
- JAM3 and PARVB are key mediators of migration and morphological changes in PALB2-mutated cells.
- Enhanced macropinocytosis in PALB2-mutated cells may serve to supply nucleotides for DNA repair, linking cellular metabolism to genomic stability.
- These findings offer novel therapeutic targets for PALB2-associated cancers.
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