Investigating the disease-promoting abilities of gut bacteria in colorectal tumour cells

Robson, James

Abstract

Colorectal cancer (CRC) is the third most common malignancy worldwide and the second leading cause of cancer-related death. The global burden of CRC is rising, particularly in younger populations. This increase has been attributed to lifestyle factors, chiefly diet, and their effects on the colonic microbiome. Several species of bacteria have been identified in high abundance from the gastrointestinal tract of CRC patients, and have been shown to exert direct and indirect pro-tumorigenic effects both in vivo and in vitro. However, what is unclear is whether these bacteria promote CRC development and progression across the entire adenoma-carcinoma sequence, or whether the interactions of bacteria with benign tumours differ from those with malignant ones.
Three CRC-associated species of bacteria, Bacteroides fragilis, Enterococcus faecalis and Fusobacterium nucleatum, in addition to the probiotic species Escherichia coli Nissle 1917, were investigated using the gentamicin protection assay to determine how they interact with the benign colorectal adenoma tumour cell line RG/C2, and the malignant adenocarcinoma line HCT116. All bacterial species were found to attach to and invade both cell lines. However, attachment was found to be higher in RG/C2 cells, in contrast to invasion which was higher in HCT116 cells. All species could also persist within tumour cells, and this bacterial infection promoted significant increases in cell yield whilst reducing apoptosis. There was evidence that B. fragilis and F. nucleatum may promote a Warburg-like metabolic effect in HCT116 cells, by upregulating glycolysis. In both wound healing and transwell filter migration assays, E. coli Nissle and F. nucleatum were able to promote both individual and collective cell migration in HCT116 cells; however, no bacterial species influenced migration in benign RG/C2 cells. Furthermore, F. nucleatum also promoted HCT116 invasion, suggesting that this species may be a driver of late-stage disease.
This thesis demonstrates that in a 2D model, there are differential bacterial interactions with colorectal tumour cells representing different CRC stages. It highlights that specific species are able to promote migration and invasion in malignant cells in vitro, but cannot confer this phenotype to benign cells. Despite this, all species investigated may promote tumour progression by increasing cell yield through the inhibition of apoptosis, possibly facilitating the accumulation of further genetic damage. In conclusion, this research demonstrates that colonisation of tumours by these species may contribute to poorer patient prognosis by accelerating CRC progression, and that these effects should be investigated in a more complex model of CRC. This thesis highlights the need to incorporate our knowledge of microbial contribution to CRC development and progression into future treatment and diagnostic strategies.

Citation

Robson, J. Investigating the disease-promoting abilities of gut bacteria in colorectal tumour cells. (Thesis). University of the West of England. Retrieved from https://uwe-repository.worktribe.com/output/7434617

• Thesis Type: Thesis
• Deposit Date: May 31, 2021
• Publicly Available Date: Oct 21, 2021
• Keywords: colorectal cancer, microbiome, microbiota
• Public URL: https://uwe-repository.worktribe.com/output/7434617
• Award Date: Oct 21, 2021