COL1A1-Mediated Bmp1/Tgf-β Signaling Augments EMT and M2 Macrophage Polarization in Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) is a lethal malignancy characterized by frequent metastasis. Utilizing a 4-NQO-induced murine model and single-cell RNA sequencing, we identified a distinct Collagen Type I Alpha 1 Chain (Col1a1+) epithelial subpopulation that is significantly expanded in OSCC, exhibits the highest epithelial-mesenchymal transition (EMT) signature, and correlates with poor patient survival. Functional studies demonstrated that Col1a1 knockdown in OSCC cell lines (HSC3, SCC25) attenuated TGF-β-induced EMT, impaired migration and invasion in vitro, and reduced tumor burden in a conditional knockout mouse model. Transcriptomic profiling following Col1a1 silencing revealed the suppression of TGF-β signaling and ECM-receptor interaction pathways. We further identified BMP1 as a key downstream effector, demonstrating a direct physical interaction between COL1A1 and BMP1, and showed that COL1A1 potentiates BMP1's proteolytic activity. Rescue experiments confirmed that BMP1 is essential for COL1A1-driven tumor growth, metastasis, and TGF-β pathway activation in vivo. Furthermore, we uncovered an immunomodulatory role for the COL1A1-BMP1 axis, whereby it promotes M2 macrophage polarization via TGF-β secretion to foster an immunosuppressive tumor microenvironment. This effect was reversible using either BMP1 knockdown or TGF-β neutralization. In conclusion, our study establishes a novel COL1A1-BMP1-TGF-β signaling cascade that drives OSCC progression by autonomously enhancing tumor cell malignancy and non-autonomously reprogramming the immune landscape, nominating this axis as a promising therapeutic target. Implications: These findings identify a novel COL1A1-BMP1 axis driving both OSCC malignancy and immunosuppression, offering potential diagnostic markers and therapeutic targets for the clinic.