Fakroun, Ali
(2025)
Glutamine metabolism and DNA repair in breast cancer.
PhD thesis, University of Nottingham.
Abstract
Metabolic reprogramming and genomic instability are two key cancer hallmarks. The link between these two hallmarks in different types of cancer has yet to be fully explored. Cancer cells alter their metabolic pathways to meet their necessary energy and cellular block demands. They also modulate the expression of their DNA repair proteins to encounter the DNA damage caused by exogenous and endogenous factors, such as reactive oxygen species. This thesis investigates the association between glutamine metabolism and the DNA repair pathway in breast cancer, focusing on Solute Carrier Family 7 Member 5 (SLC7A5) and two DNA repair proteins, Flap endonuclease 1 (FEN1) and Exonuclease 1 (EXO1). These genes were selected based on their moderate positive correlation at the mRNA level, as identified through Breast Cancer Gene-Expression Miner v5.1 (bc-GenExMiner v5.1) dataset, and due to their established biological relevance in previous cancer studies. SLC7A5 functions as an amino acid exchanger, mediating the uptake of essential large neutral amino acids, particularly leucine, in exchange for intracellular glutamine. This activity supports glutamine-dependent mammalian target of rapamycin complex 1 (mTORC1) signalling, which fuels cell growth and biosynthesis. Meanwhile, FEN1 and EXO1 are structure-specific nucleases involved in distinct DNA repair pathways, base excision repair and mismatch repair, respectively, both play critical roles in preserving genomic stability under oxidative stress.
The biological and clinical outcome of SLC7A5 co-expression with either FEN1 or EXO1 was assessed in large, annotated cohorts of breast cancer at the mRNA and protein levels. In vitro, functional assay experiments were conducted to find the role of SLC7A5/FEN1 high expression in tumour behaviour, and further proteomic analysis was carried out to find common interacting proteins between the two pathways.
The high expression of SLC7A5 and either FEN1 or EXO1 at the mRNA and protein level was associated with poor prognosis, while the high expression of SLC7A5/FEN1 was linked to adverse outcomes in ER-positive tumours, and the high expression of SLC7A5/EXO1 was associated with poor outcomes in ER-negative tumours. Assay experiments demonstrated that double knockdown of SLC7A5 and FEN1 impaired proliferation, reduced breast cancer cell migration and invasion ability, caused S phase cell cycle arrest, and induced apoptosis. Furthermore, the dual knockdown of SLC7A5 and FEN1 disrupted mitochondrial function, marked by reduced ATP production and respiratory capacity, reinforcing their role in maintaining metabolic fitness. Proteomic analysis identified shared interacting proteins enriched in pathways related to DNA repair, RNA metabolism, and mitochondrial function, supporting a functional link between these biological systems.
Collectively, this thesis explored a novel association between glutamine metabolism and DNA repair pathways in breast cancer. The findings position SLC7A5/FEN1 and SLC7A5/EXO1 high expression as clinically relevant prognostic biomarkers and lay the foundation for therapeutic strategies that co-target metabolic and DNA repair vulnerabilities in breast cancer.
Actions (Archive Staff Only)
 |
Edit View |
Tools
Tools
