JAK-2 V617F mutation increases heparanase procoagulant activity

Area of Science:

• Hematology
• Molecular Biology
• Oncology

Background:

• Patients with polycythaemia vera (PV), essential thrombocythaemia (ET), and primary myelofibrosis (PMF) exhibit an elevated risk of arterial and venous thrombosis.
• A correlation exists between the JAK-2 V617F mutation and thrombotic events in ET patients, though the underlying mechanism remains unclear.
• Heparanase protein enhances blood coagulation by forming a complex with tissue factor (TF), increasing factor Xa production and activating the coagulation cascade.

Purpose of the Study:

• To investigate the procoagulant activity of heparanase in myeloproliferative neoplasms (MPNs).
• To explore the relationship between JAK-2 V617F mutation, erythropoietin receptor signaling, and heparanase activity in MPNs.

Main Methods:

• Immunostaining of bone marrow biopsies from 40 patients (ET, PV, PMF, CML) for heparanase, TF, and TF pathway inhibitor (TFPI).
• In vitro studies using erythropoietin receptor-positive cell lines (U87, MCF-7) transfected with JAK-2 V617F mutation.
• Assessment of heparanase levels and procoagulant activity in response to JAK-2 inhibitors (Ruxolitinib, VZ3) and hydroxyurea.

Main Results:

• Heparanase and TFPI staining were more pronounced in ET, PV, and PMF compared to CML, with the strongest signal in JAK-2 positive ET biopsies.
• Upregulation of heparanase and increased procoagulant activity were observed in cells overexpressing JAK-2 V617F mutation.
• JAK-2 inhibitors and hydroxyurea reversed the increased heparanase activity, while erythropoietin elevated it.

Conclusions:

• JAK-2 signaling, via the erythropoietin receptor, plays a significant role in upregulating heparanase.
• These findings suggest a novel mechanism contributing to thrombosis in JAK-2 positive ET patients.