ATP5b and Bioenergetic Plasticity in Breast Cancer Metastasis and Tumour Microenvironment Interactions

Breast cancer is the most diagnosed form of cancer in New Zealand, with the majority of breast cancer associated deaths attributed to metastasis. During the metastatic cascade, tumour cells have been shown to alter the contributions of glycolysis and oxidative phosphorylation to overall ATP generation, indicating a need for tumour cell bioenergetic plasticity during metastasis. These changes in tumour cell bioenergetics are also influenced by interactions with other cell populations in the tumour microenvironment.

This project assessed the ability of 4T1 ATP5b lo cells to form lung metastases in BALB/c mice. As ATP5b encodes a sub-unit of ATP synthase, these cells had a reduced ability to produce ATP via oxidative phosphorylation, thereby reducing their bioenergetic plasticity compared to WT cells. 4T1 ATP5b lo and WT cells were first transfected with the fluorescent protein tdTomato to allow tumour cell visualisation. Both cell lines were characterised by assessing growth rate and oxygen consumption profiles.

Intravenous injection of 1 x 106 ATP5b lo tdTomato cells into the lateral tail vein resulted in the formation of experimental lung metastases with no significant difference in metastatic burden observed with respect to WT tdTomato injected mice. This indicated these cells with slightly reduced ATP5b expression possessed sufficient bioenergetic plasticity to lodge in the lungs and proliferate when administered directly into the bloodstream. Further research is required to validate these results in a more extreme model of reduced bioenergetic plasticity and assess whether bioenergetically compromised cells can undergo the complete metastatic cascade beyond intravenous seeding within the lung.

As tumour cell bioenergetics is linked with the presence and function of other cells within the tumour microenvironment, neutrophil and macrophage abundance/localisation was also assessed via immunofluorescent staining. No significant differences in neutrophil and macrophage abundance/localisation were observed between both treatment groups. Further investigation is required to elucidate whether the function of tumour microenvironment cell populations is altered in response to a reduction in tumour cell bioenergetic plasticity.