Expression level and differential JAK2-V617F-binding of the adaptor protein Lnk regulates JAK2-mediated signals in myeloproliferative neoplasms.

Activating mutations in signaling molecules, such as JAK2-V617F, have been associated with myeloproliferative neoplasms (MPNs). Mice lacking the inhibitory adaptor protein Lnk display deregulation of thrombopoietin/thrombopoietin receptor signaling pathways and exhibit similar myeloproliferative characteristics to those found in MPN patients, suggesting a role for Lnk in the molecular pathogenesis of these diseases. Here, we showed that LNK levels are up-regulated and correlate with an increase in the JAK2-V617F mutant allele burden in MPN patients. Using megakaryocytic cells, we demonstrated that Lnk expression is regulated by the TPO-signaling pathway, thus indicating an important negative control loop in these cells. Analysis of platelets derived from MPN patients and megakaryocytic cell lines showed that Lnk can interact with JAK2-WT and V617F through its SH2 domain, but also through an unrevealed JAK2-binding site within its N-terminal region. In addition, the presence of the V617F mutation causes a tighter association with Lnk. Finally, we found that the expression level of the Lnk protein can modulate JAK2-V617F-dependent cell proliferation and that its different domains contribute to the inhibition of multilineage and megakaryocytic progenitor cell growth in vitro. Together, our results indicate that changes in Lnk expression and JAK2-V617F-binding regulate JAK2-mediated signals in MPNs.

Interaction between paracetamol and warfarin in patients: a double-blind, placebo-controlled, randomized study.

BACKGROUND AND OBJECTIVES: Paracetamol (acetaminophen) has occasionally been reported to interact with warfarin. The primary end-point of this study was to investigate whether paracetamol initiation potentiates the anticoagulant effect of warfarin and the mechanism of the interaction. DESIGN AND METHODS: In a double-blind placebo-controlled, randomized, cross-over study, 20 patients on stable oral anticoagulant therapy with warfarin for at least 1 month were randomized to receive placebo or paracetamol 1g four times daily for 14 days. International Normalized Ratio (INR) and clotting factors activities were measured before the first administration and then on days 2, 4, 7, 9, 11,14. RESULTS: Mean INR rose rapidly after the start of paracetamol and was significantly increased within one week of paracetamol intake compared to placebo, p=0.0002. The INR values reached a mean maximum of 3.45+/-0.78 with paracetamol versus 2.66+/-0.73 with placebo (p=0.03), corresponding to a maximum increase from baseline of 1.20+/-0.62 with paracetamol versus 0.37+/-0.48 with placebo (p<0.001). Together with the rise in INR on paracetamol treatment there were significant reductions in the vitamin K-dependent clotting factors II, VII, IX and X. INTERPRETATION AND CONCLUSIONS: The most plausible hypothesis to explain the in vivo interaction is that paracetamol (or its metabolites) interfere with enzymes involved in vitamin K-dependent coagulation factor synthesis. Paracetamol at 4 g daily (a dose higher than that used in clinical practice) potentiates the anticoagulant response produced by warfarin. Clinicians should be aware of this clinically significant and underestimated interaction.

Prevalence of insulin resistance syndrome in southwestern France and its relationship with inflammatory and hemostatic markers.

OBJECTIVE: To assess the prevalence and relationships of insulin resistance syndrome (IRS) with inflammatory and hemostatic markers in a representative sample of the population of Southwestern France aged 35-64 years. RESEARCH DESIGN AND METHODS: In this cross-sectional study, data were collected from 597 men and 556 women and were assessed regarding BMI, blood pressure, total and HDL cholesterol levels, triglyceride level, glucose level, plasma insulin level, white blood cell count, fibrinogen level, factor VII level, von Willebrand factor, C-reactive protein level, soluble intercellular adhesion molecule, soluble vascular cell adhesion molecule-1, and soluble CD(14). Insulin resistance was defined by homeostasis model assessment > or =3.8. RESULTS: Prevalence of IRS was higher in men than in women (23 vs. 12%, respectively; P < 0.001) and increased with age in both sexes (9, 24, and 34% for age groups 35-44, 45-54, and 55-64 years, respectively, for men and 4, 10, and 21% for women). After adjusting for age, alcohol consumption, tobacco smoking, and also for menopause in women, subjects (men and women) with IRS had significantly higher white blood cell count, factor VII levels, coagulating factor VII levels, and C-reactive protein levels than the other subjects. In men, further increases in soluble intercellular adhesion molecule and soluble vascular cell adhesion molecule-1 were noted, whereas in women, the differences were borderline significant. Conversely, no differences were found in fibrinogen, von Willebrand factor, and soluble CD(14) in both sexes. CONCLUSIONS: IRS is relatively common in residents of Southwestern France and is related to a deleterious increase in hemostatic and inflammatory parameters.