Proteomics profiling identifies extracellular vesicles' cargo associated with tumour cell induced platelet aggregation

Cancer patients have an increased risk of developing venous thromboembolism, with up to 30% dying within a month of their development. Some cancer cells are known to induce platelet aggregation, and this interaction is understood to contribute to thrombosis and haematogenous metastasis. Many researchers have reported on extracellular vesicles (EVs) released from platelets. However, less is known about how cancer cells' EVs may affect platelet function. Here EVs released by triple-negative breast cancer (TNBC) cell line variants were extensively investigated in this regard.

TNBC cells induce platelet aggregation. Furthermore, the cell-free EVs induced this undesirable effect. A number of EV cargo proteins were identified that may be relevant as therapeutic targets.

EVs were separated from conditioned media of TNBC Hs578T and Hs578Ts(i)8 cells using filtration and ultracentrifugation and were characterised by nanoparticle tracking analysis, immunoblots, and transmission electron microscopy. Blood samples from consenting donors were procured, and their platelets collected by differential centrifugation. Light transmission aggregometry and optical microscopy evaluated the potential interaction of TNBC cells and their EVs with platelets. Global proteomic analysis was performed on the EVs, by in-solution digestion and mass spectrometry. Data analysis included the use of Perseus, FunRich, and Vesiclepedia. Immunoblotting was used as a secondary method to investigate some key EV cargo proteins identified by the global proteomics approach.

Both TNBC cell variants induced platelet aggregation. Increasing cell numbers significantly reduced the time taken for platelet aggregation to occur. EVs released by the cells also resulted in platelet aggregation. The time to induce platelet aggregation was EV dose-dependent. Proteomics profiling and immunoblotting of the EVs' cargo identified candidate proteins (including uPAR and PDGFRβ) that may be involved during this process. Conclusions: TNBC cells induce platelet aggregation. Furthermore, the cell-free EVs induced this undesirable effect. A number of EV cargo proteins were identified that may be relevant as therapeutic targets.