Submitted October 23, 2007
Accepted February 29, 2008
Synergistic interactions between interferon-
and TRAIL modulate c-FLIP in endothelial cells, mediating their lineage-specific sensitivity to thrombotic thrombocytopenic purpura plasma-associated apoptosis
Radu Stefanescu, Dustin Bassett, Rozbeh Modarresi, Francisco Santiago, Mohamad Fakruddin, and Jeffrey Laurence*
Dept. of Medicine, Division of Hematology-Oncology, Weill Medical College-Cornell, New York, NY, United States
Global TB Vaccine Foundation, AERAS, Rockville, MD, United States
* Corresponding author; email: jlaurenc{at}med.cornell.edu.
Microvascular endothelial cell (MVEC) injury coupled to progression of platelet microthrombi facilitated by ADAMTS13 deficiency is characteristic of idiopathic and human immunodeficiency virus (HIV)-linked thrombotic thrombocytopenic purpura (TTP). Cytokines capable of inducing MVEC apoptosis in vitro are upregulated in both TTP and HIV infection. However, the concentrations of these cytokines required to elicit EC apoptosis in vitro are 2-3 log-fold greater than present in patient plasmas. We report that clinically relevant levels of tumor necrosis factor-related apoptosis inducing ligand (TRAIL) and interferon (IFN)-
act in synergy to induce apoptosis in dermal MVEC, but have no effect on large vessel EC or pulmonary MVEC. This reflects the tissue distribution of TTP lesions in vivo. Sensitivity to TTP plasma or TRAIL + IFN- is paralleled by enhanced ubiquitination of the caspase 8 regulator c-FLIP, targeting it for proteasome degradation. c-FLIP silencing with anti-FLIP siRNA in pulmonary MVEC rendered them susceptible to TTP plasma and cytokine-mediated apoptosis, while upregulation of c-FLIP by gene transfer partially protected dermal MVEC from such injury. TTP plasma-mediated apoptosis appears to involve cytokine-induced acceleration of c-FLIP degradation, sensitizing cells to TRAIL-mediated caspase 8 activation and cell death. Suppression of TRAIL or modulation of immunoproteasome activity may have therapeutic relevance in TTP.
