Streptococcus salivarius Ss-08 Extracellular Vesicles Suppress OSCC Progression via Inhibition of JAG1–NOTCH1 Signaling

Streptococcus salivarius-derived extracellular vesicles (SsEVs) have emerged as important mediators of host–microbe communication, but their role in oral squamous cell carcinoma (OSCC) remains unclear. In this study, SsEVs were isolated and characterized by transmission electron microscopy and nanoparticle tracking analysis, and their uptake by CAL-27 cells was confirmed by fluorescence imaging. Functional assays demonstrated that SsEVs inhibited the proliferation, migration, and invasion of CAL-27 cells in a concentration-dependent manner. RNA sequencing revealed substantial transcriptional reprogramming following SsEV treatment, with enrichment analyses indicating the suppression of pathways associated with cell adhesion, extracellular matrix remodeling, lipid metabolism, and particularly Notch signaling. Gene set enrichment analysis (GSEA) and gene set nariant analysis (GSVA) consistently identified Notch signaling as significantly downregulated. Further validation showed that SsEVs markedly decreased the expression of JAG1, NOTCH1, and HEYL at both the mRNA and protein levels. In a CAL-27 xenograft model, SsEV treatment significantly inhibited tumor growth and reduced JAGGED1, NOTCH1, and HEYL expression in tumor tissues, as confirmed by immunohistochemistry. Collectively, these findings demonstrate that SsEVs suppress OSCC progression both in vitro and in vivo by inhibiting the JAG1–NOTCH1–HEYL signaling axis, suggesting that microbiota-derived extracellular vesicles may represent a promising therapeutic approach for OSCC.