Published online before print May 3, 2007

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Copyright © 2007 American Society for Investigative Pathology
American Journal of Pathology, doi:10.2353/ajpath.2007.060831

Accepted for publication March 28, 2007.

Article

Myeloperoxidase Interacts with Endothelial Cell-Surface Cytokeratin 1 and Modulates Bradykinin Production by the Plasma Kallikrein-Kinin System

Joshua M. Astern^*@, William F. Pendergraft III^*, Ronald J. Falk^*, J. Charles Jennette^*, Alvin H. Schmaier, Fakhri Mahdi^¶, and Gloria A. Preston^*

From the University of North Carolina Kidney Center,* the Division of Nephrology and Hypertension, and the Department of Pathology and Laboratory Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; Case Western Reserve University, Cleveland, Ohio; and the University of Michigan,^¶ Ann Arbor, Michigan

^@ To whom correspondence should be addressed. E-mail: jastern{at}med.unc.edu.

	Abstract

During an inflammatory state, functional myeloperoxidase (MPO) is released into the vessel as a result of intravascular neutrophil degradation. One mechanism of resulting cellular injury involves endothelial internalization of MPO, which causes oxidative damage and impairs endothelial signaling. We report the discovery of a protein that facilitates MPO internalization, cytokeratin 1 (CK1), identified using affinity chromatography and mass spectrometry. CK1 interacts with MPO in vitro, even in the presence of 100% human plasma, thus substantiating biological relevance. Immunofluorescent microscopy confirmed that MPO added to endothelial cells can co-localize with endogenously expressed CK1. CK1 acts as a scaffolding protein for the assembly of the vasoregulatory plasma kallikrein-kinin system; thus we explored whether MPO and high molecular weight kininogen (HK) reside on CK1 together or whether they compete for binding. The data support cooperative binding of MPO and HK on cells such that MPO masked the plasma kallikrein cleavage site on HK, and MPO-generated oxidants caused inactivation of both HK and kallikrein. Collectively, interactions between MPO and the components of the plasma kallikrein-kinin system resulted in decreased bradykinin production. This study identifies CK1 as a facilitator of MPO-mediated vascular responses and thus provides a new paradigm by which MPO affects vasoregulatory systems.