Modeling genetic errors predisposing to breast cancer: role of PALB2 and MCPH1 mutations in malignant transformation of mammary epithelial cells
Thesis event information
Date and time of the thesis defence
Place of the thesis defence
F202, Aapistie 5
Topic of the dissertation
Modeling genetic errors predisposing to breast cancer: role of PALB2 and MCPH1 mutations in malignant transformation of mammary epithelial cells
Doctoral candidate
Master of Science Hanna Tuppurainen
Faculty and unit
University of Oulu Graduate School, Faculty of Medicine, Research Unit of Translational Medicine
Subject of study
Medicine
Opponent
Professor Klaus Elenius, University of Turku
Custos
Docent Hellevi Peltoketo, University of Oulu
Modeling breast cancer-predisposing PALB2 and MCPH1 gene errors in mammary epithelial cells
The aim of this doctoral thesis project was to reveal how PALB2 and MCPH1 mutations affect the functions of otherwise non-cancerous human mammary epithelial cells and contribute to the early steps of breast cancer tumorigenesis. In order to study this, MCF10A cells were gene-edited to mutate either PALB2 or MCPH1. The results showed comprehensive and previously unreported changes in the gene expression and behavior of mammary epithelial cells upon PALB2 and MCPH1 protein defects.
Breast cancer is the most common cancer in women and up to 10% of the cases are caused by pathogenic germline gene variants. PALB2 is a major high-risk breast cancer susceptibility gene, as PALB2 germline mutations predispose their heterozygous female carriers to the disease with a relative risk above seven. MCPH1 represents a moderate-risk breast cancer susceptibility gene and is also widely downregulated in sporadic cancers. PALB2 and MCPH1 proteins are vital in DNA damage response and cell cycle regulation.
Transcriptome profiling and functional analyses verified that PALB2- and MCPH1-mutated cell lines replicated cell phenotypes typical for PALB2 and MCPH1 dysfunction. These included weakened DNA repair capacity and cell division errors in the former ones and premature chromosome condensation in the latter ones. Other hallmarks of cancer were also enriched in the PALB2- and MCPH1-mutated cells, indicating essential and previously unreported roles for PALB2 and MCPH1 in maintaining cell homeostasis. The cells showed enhanced migration and invasion capacity, and they formed enlarged spheroids in three-dimensional cell culture. PALB2-deficient spheroids were further anomalous, being multilayer, having protrusions and agglomerating together, all of which are characteristics of oncogenic transformation. The functional alterations in the PALB2-mutated cells were partially due to enhanced TGFβ signaling and the overexpression of its target gene KRT14. Cell adhesion-related genes JAM3 and PARVB were also upregulated in the PALB2-mutated cells and contributed to the malignant features of the cells. In addition, PARVB overexpression enhanced macropinocytosis, a form of endocytosis common in cancer, in the PALB2-deficient cells. In conclusion, the results demonstrated novel mechanisms for how PALB2- or MCPH1 mutations may predispose their carriers to cancer.
Breast cancer is the most common cancer in women and up to 10% of the cases are caused by pathogenic germline gene variants. PALB2 is a major high-risk breast cancer susceptibility gene, as PALB2 germline mutations predispose their heterozygous female carriers to the disease with a relative risk above seven. MCPH1 represents a moderate-risk breast cancer susceptibility gene and is also widely downregulated in sporadic cancers. PALB2 and MCPH1 proteins are vital in DNA damage response and cell cycle regulation.
Transcriptome profiling and functional analyses verified that PALB2- and MCPH1-mutated cell lines replicated cell phenotypes typical for PALB2 and MCPH1 dysfunction. These included weakened DNA repair capacity and cell division errors in the former ones and premature chromosome condensation in the latter ones. Other hallmarks of cancer were also enriched in the PALB2- and MCPH1-mutated cells, indicating essential and previously unreported roles for PALB2 and MCPH1 in maintaining cell homeostasis. The cells showed enhanced migration and invasion capacity, and they formed enlarged spheroids in three-dimensional cell culture. PALB2-deficient spheroids were further anomalous, being multilayer, having protrusions and agglomerating together, all of which are characteristics of oncogenic transformation. The functional alterations in the PALB2-mutated cells were partially due to enhanced TGFβ signaling and the overexpression of its target gene KRT14. Cell adhesion-related genes JAM3 and PARVB were also upregulated in the PALB2-mutated cells and contributed to the malignant features of the cells. In addition, PARVB overexpression enhanced macropinocytosis, a form of endocytosis common in cancer, in the PALB2-deficient cells. In conclusion, the results demonstrated novel mechanisms for how PALB2- or MCPH1 mutations may predispose their carriers to cancer.
Last updated: 8.5.2025