Role of platelet-derived microparticles in angiogenesis and tumor progression.

Platelets are key players in hemostasis, but are also involved in fundamental processes of vascular biology such as angiogenesis, tissue regeneration, and tumor metastasis. Microparticles (MP) are small plasma membrane vesicles shed from cells upon their activation or apoptosis. Platelet-derived microparticles (PMP) constitute the majority of the pool of MP circulating in the blood. In this review we will summarize some possible roles of PMP other than participation in blood coagulation. PMP can express and transfer functional receptors from platelet membranes, increase expression of adhesion molecules on cells, stimulate the release of cytokines, activate intracellular signaling pathways, alter vascular reactivity, induce angiogenesis, and are involved in cancer metastasis. The role of PMP in cancer development is unknown but a high PMP level is highly correlated with aggressive tumors and a poor clinical outcome. It has been reported that PMP can stimulate proliferation and adhesion of cancer cells. Given their documented association with pathological conditions, PMP may serve as biomarkers for disease status or as a possible new target for anti-platelet drugs to treat cancer or inflammation. On the other hand, local PMP application may be found useful for developing novel therapeutic strategies targeting angiogenesis-related conditions.