Xinghua Liu

Fusobacterium nucleatum promotes CRC progression in vivo without directly affecting CRC cell proliferation in vitro.

High MANCR expression is associated with increased PD-L1+ macrophage infiltration and shorter overall survival in patients with CRC.

Fusobacterium nucleatum is a key microbial driver of colorectal cancer progression. In this study, we identified an intercellular signaling axis through which F. nucleatum remodels the immune microenvironment. Analysis of 54 clinical colorectal cancer specimens revealed that high intratumoral F. nucleatum load correlated significantly with PD-L1 upregulation in tumor-associated macrophages, diminished CD8+ T-cell cytotoxicity, and poor patient prognosis. Mechanistically, F. nucleatum infection activated NF-κB signaling in colorectal cancer cells to induce the transcription of the long noncoding RNA mitotically associated long noncoding RNA (MANCR), which was selectively packaged into exosomes via the ESCRT-III/ALIX complex and transferred to macrophages. In recipient macrophages, exosomal MANCR interacted with HNRNP U to increase PD-L1 mRNA stability, leading to sustained PD-L1 surface expression. In humanized mouse models, F. nucleatum exposure inhibited CD8+ T-cell infiltration and suppressed granzyme B activity, thereby compromising antitumor immunity and facilitating tumor proliferation and metastasis. These findings demonstrate that F. nucleatum exploits a tumor-derived exosomal long noncoding RNA network to remotely manipulate macrophage plasticity. Therefore, targeting the F. nucleatum/MANCR/PD-L1 axis may represent a viable strategy to overcome immune resistance in the colorectal cancer microenvironment. Significance:Fusobacterium nucleatum exploits tumor-derived exosomal MANCR to stabilize PD-L1 in macrophages, providing a mechanism of bacterial-driven immune evasion and a potential therapeutic target to restore antitumor immunity in colorectal cancer.

Baseline characteristics of the study participants.

Primers used for qRT-PCR in this study.

Identification of HNRNP U as a MANCR-binding protein by LC-MS/MS.

Quantification of PD-L1 immunofluorescence intensity in macrophages and single-cell RNA-sequencing analysis of the association between MANCR and macrophage PD-L1 expression.

Elevated Fusobacterium nucleatum abundance is associated with poor prognosis and an immunosuppressive tumor microenvironment in colorectal cancer.

Representative immunofluorescence images of PD-L1 expression in macrophages under coculture- and exosome-mediated conditions.

HNRNP U mediates MANCR-dependent regulation of PD-L1 expression and mRNA stability in macrophages.