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Nucleosome-releasing factor: a new role for factor VII-activating protease (FSAP)

Sacha Zeerleder^*,1, Bas Zwart^*, Henk te Velthuis, Femke Stephan^*, Rishi Manoe^*, Irma Rensink^* and Lucien A. Aarden^*

^* Department of Immunopathology, Sanquin Research at CLB and Landsteiner Laboratory, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands; and

Business Unit Reagents, Sanquin, Amsterdam, The Netherlands

¹Correspondence: Department of Immunopathology, Sanquin Research at CLB, Plesmanlaan 125, 1066 CX Amsterdam, The Netherlands. E-mail: s.zeerleder{at}sanquin.nl

Plasma proteins such as early complement components and IgM are involved in the removal of late apoptotic or secondary necrotic (sn) cells. We have recently described how a plasma protease that could be inhibited by the protease inhibitor aprotinin was essential to remove nucleosomes from sn cells. An obvious candidate, plasmin, did indeed have nucleosome-releasing factor (NRF) activity. However, recalcified plasma (r-plasma) retained its NRF activity after plasminogen depletion, which suggests the existence of another protease responsible for NRF activity in plasma. In this study we have used size-exclusion and anion-exchange chromatography to purify the protease responsible for NRF activity in plasma. SDS-PAGE analysis of chromatography fractions containing NRF activity revealed a protein band corresponding with NRF activity. Sequence analysis showed this band to be factor VII-activating protease (FSAP). We developed monoclonal antibodies to FSAP and were able to completely inhibit NRF activity in plasma with monoclonal antibodies to FSAP. Using affinity chromatography we were able to purify single-chain (sc) FSAP from r-plasma. Purified scFSAP efficiently removes nucleosomes from sn cells. We report that factor VII-activating protease may function in cellular homeostasis by catalyzing the release of nucleosomes from secondary necrotic cells.—Zeerleder, S., Zwart, B., te Velthuis, H., Stephan, F., Manoe, R., Rensink, I., Aarden, L. A. Nucleosome-releasing factor: a new role for factor VII-activating protease (FSAP).

Key Words: apoptosis • hyaluronan binding protein • SLE • plasmin • monoclonal • single chain