Osteosarcoma (OS) represents the predominant primary malignant bone tumor among children and young adults and continues to present major therapeutic obstacles. This investigation explored the involvement of exosomes, which serve as critical mediators of cell-to-cell signaling, in driving OS advancement and pinpointed promising therapeutic candidates. Experiments performed in both in vitro cellular systems and in vivo animal models revealed that exosomes secreted by OS cells substantially accelerated tumor cell proliferation, motility, and invasive capacity. Proteomic profiling through data-independent acquisition mass spectrometry demonstrated prominent enrichment of the proto-oncogene tyrosine-protein kinase YES1 within OS-derived exosomes. Comprehensive bioinformatics evaluation combined with clinical data analysis established that YES1 exhibits elevated expression in various malignancies and is linked to unfavorable patient outcomes. In OS, increased YES1 levels were specifically associated with diminished overall survival and more adverse prognostic features. Quantitative PCR, Western blot, and immunohistochemistry (IHC) analyses of patient-derived samples confirmed markedly higher YES1 abundance in OS tissues than in corresponding normal tissues. Functional mechanistic experiments utilizing YES1 silencing (shYES1) and forced expression (OE YES1) constructs, alongside exosome treatment and pharmacological pathway modulators, identified ERK phosphorylation as a key mediator of YES1-induced oncogenic properties. shYES1 cells exhibited pronounced suppression of proliferation, migration, and invasion, which was partly restored upon exosome addition and further diminished by MAPK pathway inhibition. Conversely, OE YES1 cells displayed strongly augmented malignant traits that were intensified by exosomes and additionally enhanced through MAPK pathway stimulation. Supporting Western blot data showed lowered phosphorylation of MEK and ERK, accompanied by elevated phosphorylation of p38 and JNK in YES1-depleted cells, with inverse patterns in the overexpression setting. These shifts in phosphorylation status were counteracted or lessened by EGF/IL-1β stimulation or U0126/SB-203580 application, respectively, while total levels of MEK, JNK, p38, and ERK proteins remained stable. Multiplex IHC further substantiated bioinformatics predictions by revealing a strong association between YES1 expression and immune-associated pathways within OS specimens. Overall, the results emphasize the central contribution of exosomal YES1 to OS development and its interplay with tumor immunology, underscoring its potential value as both a prognostic biomarker and a viable therapeutic target. This research elucidates the mechanisms through which YES1 influences malignant behavior and immune regulation, thereby contributing fresh perspectives toward enhancing clinical management and outcomes for OS patients.
