RESUMO
INTRODUCTION: Cancer-associated thrombosis is one of the major causes of worse prognosis among tumor-bearing patients. Extracellular vesicles derived from cancer cells, which can be divided mainly into microvesicles and exosomes, can participate in several tumor progression phenomena. Tumor-derived microvesicles positive for tissue factor (TF) have been associated with thrombotic risk in certain cancer types. Cancer cell-derived exosomes, however, have not. In this study we evaluated the capacity of extracellular vesicles (EVs, containing both microvesicles and exosomes) derived from breast-cancer cell lines in promoting platelet activation, aggregation and plasma coagulation, in experiments that access both TF-dependent and -independent activities. MATERIALS AND METHODS: EVs were isolated from the conditioned media of two human mammary carcinoma cell lines: MDA-MB-231 (highly invasive) and MCF-7 (less invasive). TF-independent EV/platelet interaction, platelet P-selectin exposure and aggregation were evaluated. Western blotting, plasma clotting and platelet aggregation in the presence of plasma were performed for the measurement of TF-dependent activity in EVs. RESULTS: Interaction between MDA-MB-231 EVs and washed platelets led to increased platelet P-selectin exposure and platelet aggregation compared to MCF-7 EVs. MDA-MB-231 EVs had higher TF protein levels and TF-dependent procoagulant activity than MCF-7 EVs. Consequently, TF-dependent platelet aggregation was also induced by MDA-MB-231 EVs, but not by MCF-7 EVs. CONCLUSION: Our results suggest that MDA-MB-231 EVs induce TF-independent platelet activation and aggregation, as well as TF-dependent plasma clotting and platelet aggregation by means of thrombin generation. In this context, aggressive breast cancer-derived EVs may contribute to cancer-associated thrombosis.
Assuntos
Neoplasias da Mama/genética , Vesículas Extracelulares/metabolismo , Tromboplastina/metabolismo , Trombose/etiologia , Neoplasias da Mama/metabolismo , Linhagem Celular Tumoral , Vesículas Extracelulares/patologia , Feminino , Humanos , Ativação Plaquetária , Agregação Plaquetária , Trombose/patologiaRESUMO
Cancer cells display high proliferation rates and survival provided by high glycolysis, chemoresistance and radioresistance, metabolic features that appear to be activated with malignancy, and seemed to have arisen as early in evolution as in unicellular/prokaryotic organisms. Based on these assumptions, we hypothesize that aggressive phenotypes found in malignant cells may be related to acquired unicellular behavior, launched within a tumor when viral and prokaryotic homologs are overexpressed performing likely robust functions. The ensemble of these expressed viral and prokaryotic close homologs in the proteome of a tumor tissue gives them advantage over normal cells. To assess the hypothesis validity, sequences of human proteins involved in apoptosis, energetic metabolism, cell mobility and adhesion, chemo- and radio-resistance were aligned to homologs present in other life forms, excluding all eukaryotes, using PSI-BLAST, with further corroboration from data available in the literature. The analysis revealed that selected sequences of proteins involved in apoptosis and tumor suppression (as p53 and pRB) scored non-significant (E-value>0.001) with prokaryotic homologs; on the other hand, human proteins involved in cellular chemo- and radio-resistance scored highly significant with prokaryotic and viral homologs (as catalase, E-value=zero). We inferred that such upregulated and/or functionally activated proteins in aggressive malignant cells represent a toolbox of modern human homologs evolved from a similar key set that have granted survival of ancient prokaryotes against extremely harsh environments. According to what has been discussed along this analysis, high mutation rates usually hit hotspots in important conserved protein domains, allowing uncontrolled expansion of more resistant, death-evading malignant clones. That is the case of point mutations in key viral proteins affording viruses escape to chemotherapy, and human homologs of such retroviral proteins (as Ras, Akt and EGFR) can elicit the same phenotype. Furthermore, a corollary to this hypothesis presumes that target-directed anti-cancer therapy should target human protein domains of low similarity to prokaryotic homologs for a well-succeeded anti-cancer therapy.