Adhesion and invasion dynamics of fusobacterium nucleatum in colorectal cancer

Neo, Onalenna (2024). Adhesion and invasion dynamics of fusobacterium nucleatum in colorectal cancer. University of Birmingham. Ph.D.

Neo2025PhD.pdf
Text - Accepted Version
Restricted to Repository staff only until 1 August 2026.
Available under License Creative Commons Attribution Non-commercial No Derivatives.
Download (6MB) | Request a copy

Abstract

ABSTRACT

The role of microbial dysbiosis in colorectal cancer (CRC), which ranks amongst the top five deadliest cancers, has gained a lot of research interest recently. This study focused on the bacterium Fusobacterium nucleatum, which is often enriched in CRC patients compared to healthy controls. The overarching aim of the study was to investigate the adhesion and invasion dynamics of three F. nucleatum subspecies, namely subspecies (ssp.) nucleatum (FNN23), ssp. polymorphum (FNP) and ssp. animalis (FNA), to improve understanding of the mechanism of action of F. nucleatum in CRC. Adhesion and invasion assays were performed using a monolayer model of a CRC cell line, Caco-2. Subspecies-specific differences in the levels of adhesion to CRC cells were observed, with FNP having higher adhesion levels than the other two subspecies. The adhesins, FadA and Fap2 are important F. nucleatum virulence factors in CRC. Therefore, their contribution to adherence and invasion, in FNN23 was investigated using deletion mutants of the adhesins. The mutations resulted in decreased adherence and invasion of Caco-2 cells by FNN23. The decrease was greater with the Fap2 mutant than the FadA mutant strain. Additionally, this study determined the impact on adhesion and invasion of Tspan6, a protein belonging to the tetraspanin family of proteins which have been implicated in various aspects of cancer. While Tspan6 expression improved the adherence of FNN23 to Caco-2 cells, it decreased that of FNA and made no difference to FNP adherence. Interestingly, the invasion of FNN23 to Tspan6 expressing cells was decreased, but no significant impact on FNA and FNP invasion was observed. Furthermore, the impact of the bacterial growth phase on adhesion dynamics was also investigated. FNN23 and FNA samples experienced over 2-fold increases in their levels of adherence at the exponential compared to the stationary phase, while FNP adherence remained unaffected. Then, bacterial RNA sequencing was performed to establish whether there were differences in the expression of adhesins and other virulence factors resulting in the observed differences in adherence and invasion of the subspecies. Global gene expression differences between stationary and exponential-phase bacteria were observed. In addition, differences in the expression of adhesion genes at the exponential and stationary phases were discovered. This study also demonstrated differential induction of cytokine and chemokines by the F. nucleatum subspecies compared to controls using the Olink target 48 cytokine and chemokine assay service. Lastly, paired metagenomics and transcriptomics analyses were performed on 57 CRC samples and their controls to determine the impact of the metagenomic profile on gene expression. Metagenomic differences led to differences in immune cell composition and the expression of Hallmark pathways. Understanding the adherence and invasion dynamics of F. nucleatum subspecies is key to uncovering key mechanisms important in F. nucleatum virulence CRC, which can help inform diagnostics and therapeutic interventions.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):