Crosstalk between BCR-ABL and protease-activated receptor 1 (PAR1) suggests a novel target in chronic myeloid leukemia.

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by the presence of the Philadelphia chromosome, which generates the oncogene BCR-ABL1. Protease-activated receptor 1 (PAR1) is involved in tumor progression and angiogenesis. We have previously reported that PAR1 expression is elevated in human leukemias that display a more aggressive clinical behavior, including the blast crisis of CML. In this study, we analyzed the crosstalk between the oncoprotein BCR-ABL and PAR1 in CML. Leukemic cell lines transfected with the BCR-ABL1 oncogene showed significantly higher expression levels of PAR1 compared with that of wild-type counterparts. This phenomenon was reversed by treatment with tyrosine kinase inhibitors (TKIs). Conversely, treatment with the PAR1 antagonist SCH79797 inhibited BCR-ABL expression. The PAR1 antagonist induced apoptosis in a dose- and time-dependent manner. Higher vascular endothelial growth factor (VEGF) levels were observed in cells transfected with BCR-ABL1 than in their wild-type counterparts. VEGF expression was strongly inhibited after treatment with either TKIs or the PAR1 antagonist. Finally, we evaluated PAR1 expression in CML patients who were either in the blast or chronic phases and had either received TKI treatment or no treatment. A significant decrease in PAR1 expression was observed in treatment-responsive patients, as opposed to a significant increase in PAR1 expression levels in treatment-resistant patients. Patients classified as high risk according to the Sokal index showed higher PAR1 expression levels. Our results demonstrate the crosstalk between BCR-ABL and PAR1. These data may offer important insight into the development of new therapeutic strategies for CML.

TR47, a PAR1-based peptide, inhibits melanoma cell migration in vitro and metastasis in vivo.

Activated Protein C (APC) is a serine-protease that displays antithrombotic and anti-inflammatory properties. In addition, cleavage of protease-activated receptor 1 (PAR1) by APC exerts endothelial cytoprotective actions. The effects of APC on endothelial cells may be reproduced by TR47, a PAR1-based peptide that mimics the novel N-terminus of PAR1 generated upon cleavage at Arg-46 by APC. In this study we demonstrate that wild-type APC and its signaling-proficient mutant, APC-2Cys (which has dramatically reduced anticoagulant activity), display similar inhibitory effects towards the transendothelial migration of A375 human melanoma cells. Consistent with this observation, APC and APC-2Cys significantly reduced the in vivo metastatic potential of the B16F10 murine melanoma cells. TR47 recapitulated the in vitro and in vivo protective profiles of APC and APC-2Cys. Treatment of EA.hy926 endothelial cells with TR47 (20 µM) significantly decreased the A375 cell migration. In addition, treatment of C57/BL6 mice with a single TR47 dose (125 µg/animal) strongly reduced the metastatic burden of B16F10 cells. Together, our results suggest that protection of the endothelial barrier by APC/TR47-mediated signaling pathways might be a valuable therapeutic approach to prevent metastasis.

Breast-cancer extracellular vesicles induce platelet activation and aggregation by tissue factor-independent and -dependent mechanisms.

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.