Imatinib sensitizes T-cell lymphocytes from chronic myeloid leukemia patients to FasL-induced cell death: a brief communication.

There is now substantial evidence that imatinib may affect immune responses, especially those mediated by T lymphocytes. Fas (CD95/Apo-1), a cell death receptor, is a key regulator of the immune system. We have explored the consequences of treatment on the Fas system in chronic myeloid leukemia patients treated with imatinib. In comparison with healthy controls, we found not only a mild blood lymphopenia but also impairment of phytohemagglutinin activation in CD4Fas and CD8Fas lymphocytes of imatinib-treated patients. Moreover, these lymphocyte populations were more sensitive to FasL-induced cell death in relation to an increase in Fas expression at the cell surface. Taken together, these results reveal the role of Fas receptor in the lymphopenia observed in patients treated with imatinib, with potential deleterious consequences on antileukemic responses against this immunogenic hematological malignancy.

Tristetraprolin inhibits Ras-dependent tumor vascularization by inducing vascular endothelial growth factor mRNA degradation.

Vascular endothelial growth factor (VEGF) is one of the most important regulators of physiological and pathological angiogenesis. Constitutive activation of the extracellular signal-regulated kinase (ERK) pathway and overexpression of VEGF are common denominators of tumors from different origins. We have established a new link between these two fundamental observations converging on VEGF mRNA stability. In this complex phenomenon, tristetraprolin (TTP), an adenylate and uridylate-rich element-associated protein that binds to VEGF mRNA 3'-untranslated region, plays a key role by inducing VEGF mRNA degradation, thus maintaining basal VEGF mRNA amounts in normal cells. ERKs activation results in the accumulation of TTP mRNA. However, ERKs reduce the VEGF mRNA-destabilizing effect of TTP, leading to an increase in VEGF expression that favors the angiogenic switch. Moreover, TTP decreases RasVal12-dependent VEGF expression and development of vascularized tumors in nude mice. As a consequence, TTP might represent a novel antiangiogenic and antitumor agent acting through its destabilizing activity on VEGF mRNA. Determination of TTP and ERKs status would provide useful information for the evaluation of the angiogenic potential in human tumors.