Inactivation of the Fusobacterium nucleatum Rnf complex reduces FadA-mediated amyloid formation and tumor development

Area of Science:

• Microbiology and Cancer Biology
• Molecular Genetics and Pathogenesis

Background:

• Fusobacterium nucleatum is an oral bacterium linked to colorectal cancer (CRC) progression.
• The FadA adhesin, an amyloid-forming protein, is crucial for CRC tumorigenesis.
• The Rnf complex, a conserved respiratory enzyme, is implicated in F. nucleatum virulence.

Purpose of the Study:

• To investigate the role of the Rnf complex in regulating FadA-mediated CRC tumor formation.
• To elucidate the molecular mechanisms by which the Rnf complex influences FadA processing and assembly.

Main Methods:

• Molecular genetic studies involving rnfC deletion mutants.
• Analysis of fadA transcript levels, precursor FadA (pFadA) production, and FadA assembly.
• Investigation of Rnf complex regulation of response regulators (CarR, ArlR, S1) and signal peptidase LepB.
• Assessment of bacterial adhesion, invasion of CRC cells, and in vitro spheroid tumor formation.

Main Results:

• Rnf complex disruption significantly reduced fadA transcript levels and pFadA production.
• Rnf complex regulates FadA processing via response regulators and the signal peptidase LepB.
• Rnf deficiency diminished F. nucleatum invasion of CRC cells and in vitro tumor spheroid formation, without affecting initial adhesion.

Conclusions:

• The Rnf complex modulates FadA adhesin expression and CRC tumorigenesis through a regulatory network involving response regulators and LepB.
• This pathway is critical for FadA post-translational processing and surface amyloid assembly, impacting bacterial virulence.
• Targeting the Rnf-LepB-FadA axis could offer novel strategies against F. nucleatum-driven CRC.