Discovery of Critical Virulence Factors of Fusobacterium nucleatum in Promoting of Oral Squamous Cell Carcinoma

Fusobacterium nucleatum, a known Gram-negative oral commensal in human, has been shown recently to contribute to the initiation and progression of colorectal cancer (CRC) and oral squamous cell carcinoma (OSCC). The existence of F. nucleatum in above-mentioned cancers has led to poor prognosis, and its abundance has shown to increase gradually from stage I to IV. In general, there are roughly 53,000 new oral cancer cases in the US every year and the prevalence among men and women is about 1.7% and 0.7%. However, understanding about the mechanism of F. nucleatum-induced oral cancer has not been well established. In this study, we aim to identify the key regulators of F. nucleatum which play pivotal roles in direct and indirect interactions with OSCC to promote the aggressiveness and invasiveness of the disease.

Experiments will first be demonstrated by using oral squamous cell carcinoma cell line, SCC-15, to observe the interactions with F. nucleatum wild type, ATCC 23726 and ATCC 25586, and cell surface adhesin mutant strains, RadD, Fap2 and galK. As some of the cell surface receptors in F. nucleatum have been proved to participate in the CRC progression, therefore, HCT 116, a colorectal carcinoma cell line will be included as a positive control as well. Meantime, more in-house F. nucleatum mutant strains will be created and involved in this study. Clinical F. nucleatum strains which were previously isolated from OSCC and non-OSCC patients’ saliva in Taiwan will also be included in the analysis.

Our preliminary data reproduced some of the initial critical observation published previously. By treating HCT 116 cells with bacterial supernatant, F. nucleatum wild type strains have promoted both the cell proliferation and migration of HCT 116 while F. nucleatum cell surface adhesin mutant strains lost those abilities. The same approaches with the addition of invasion and adhesion assays will be applied on SCC-15 to observe the outcomes and further analyze the major factors of the effects. SCC-15 will also be challenged by bacterial cell suspension to determine the mechanism of direct bacterial-host interactions. Our F. nucleatum clinical strains have been screened through by using whole cell suspension and previous data has shown that the F. nucleatum isolates which were extracted from OSCC patients displayed increased invasiveness than the non-OSCC group. Detailed investigation on the differences, for example the abundance or variety of cell surface receptors, and secretion proteins between the two groups of bacteria will be conducted in the future. 
By uncovering the detailed mechanism behind F. nucleatum-dependent OSCC progression, we hope to provide important knowledge towards the development of novel OSCC prevention and treatment strategies.