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(Arteriosclerosis, Thrombosis, and Vascular Biology. 2009;29:1587.)
© 2009 American Heart Association, Inc.

Cell Biology/Signaling

Proteasome Inhibitors Enhance Endothelial Thrombomodulin Expression via Induction of Krüppel-Like Transcription Factors

Toyoko Hiroi; Clayton B. Deming; Haige Zhao; Baranda S. Hansen; Elisabeth K. Arkenbout; Thomas J. Myers; Michael A. McDevitt; Jeffrey J. Rade

From the Department of Medicine (T.H., C.B.D., H.Z., B.S.H., E.K.A., M.A.M., J.J.R.), Johns Hopkins University School of Medicine, Baltimore, Md; and Millennium Pharmaceuticals Inc (T.J.M.), Cambridge, Mass.

Correspondence to Jeffrey J. Rade, MD, Division of Cardiology, Johns Hopkins School of Medicine, Ross 1165, 720 Rutland Avenue, Baltimore, MD 21205. E-mail jjrade{at}jhmi.edu

Objective— Impairment of the thrombomodulin–protein C anticoagulant pathway has been implicated in pathological thrombosis associated with malignancy. Patients who receive proteasome inhibitors as part of their chemotherapeutic regimen appear to be at decreased risk for thromboembolic events. We investigated the effects of proteasome inhibitors on endothelial thrombomodulin expression and function.

Methods and Results— Proteasome inhibitors as a class markedly induced the expression of thrombomodulin and enhanced the protein C activating capacity of endothelial cells. Thrombomodulin upregulation was independent of NF-B signaling, a principal target of proteasome inhibitors, but was instead a direct consequence of increased expression of the Krüppel-like transcription factors, KLF2 and KLF4. These effects were confirmed in vivo, where systemic administration of a proteasome inhibitor enhanced thrombomodulin expression that was paralleled by changes in the expression of KLF2 and KLF4.

Conclusions— These findings identify a novel mechanism of action of proteasome inhibitors that may help to explain their clinically observed thromboprotective effects.

Proteasome inhibitors induced thrombomodulin expression in endothelial cells consequent to upregulation of the KLF2 and KLF4 transcription factors. Systemic administration of a proteasome inhibitor enhanced thrombomodulin expression that was paralleled by changes in expression of KLF2 and KLF4.

Key Words: proteasome inhibitor • thrombomodulin • Kruppel-like transcription factor • protein C • thrombosis