Enterococcus faecalis Extracellular Vesicles Deliver the Bacterial GTPase Obg to Hijack mTOR Signalling in Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is associated with gut microbiota dysbiosis, yet specific oncogenic mechanisms remain elusive. We identified Enterococcus faecalis (EF) as significantly enriched in human liver tumours, where its abundance correlates with disease severity. Both live EF and its conditioned medium promoted HCC cell proliferation, protein translation and tumourigenesis. Mechanistically, EF-derived extracellular vesicles (EF-EVs) deliver the bacterial GTPase Obg to activate the host mTOR pathway and drive tumour progression. EF-Obg contains a Ras-like G domain homologous to the mTOR regulator Rheb and binds mTOR via a conserved G1 motif. CRISPR interference-mediated knockdown of obg in EF abolished mTOR activation and tumourigenic capacity in vivo. Clinically, high EF-Obg expression in HCC tissues correlates with mTOR hyperactivation and reduced patient survival. The mTOR inhibitor Everolimus effectively suppressed tumour growth in an EF-colonied orthotopic model, highlighting its therapeutic potential for HCC patients with high EF burden. Collectively, this work establishes a causal link between tumour-resident E. faecalis and hepatocarcinogenesis, revealing EF-Obg as a cross-kingdom activator of mTOR and providing a rationale for microbiota-guided personalised therapy in HCC.