Intracellular Fragmentation of Bone Resorption Products by Reactive Oxygen Species Generated by Osteoclastic Tartrate-resistant Acid Phosphatase

doi:10.1074/jbc.274.33.22907

Intracellular Fragmentation of Bone Resorption Products by Reactive Oxygen Species Generated by Osteoclastic Tartrate-resistant Acid Phosphatase*

From the ^‡Institute of Biomedicine, Department of Anatomy, University of Turku, FIN-20520 Turku, Finland,^§Department of Orthopaedics and Traumatology, Helsinki University Central Hospital, FIN-00260 Helsinki, Finland,^¶Department of Medicine and Hematology, University of Texas Health Science Center, San Antonio, Texas 78284-7880, ^‖Bone and Mineral Centre, The Rayne Institute, London WC1E 6JJ, United Kingdom,^**Biocenter Oulu and World Health Organization Collaborating Centre for Research on Reproductive Health, University of Oulu, FIN-90220 Oulu, Finland, and ^§§Department of Biosciences, University of Helsinki, FIN-00014 Helsinki, Finland

Abstract

Tartrate-resistant acid phosphatase (TRAP) is highly expressed in bone-resorbing osteoclasts and activated macrophages. It has been suggested that a redox-active iron in the binuclear iron center of TRAP could have the capacity to react with hydrogen peroxide to produce highly destructive reactive oxygen species (ROS). Here we show that TRAP can generate ROS in vitro and that cells over-expressing TRAP produce higher amounts of intracellular ROS than their parent cells. We further demonstrate that these ROS can be targeted to destroy collagen and other proteins. In resorbing osteoclasts, TRAP was found in transcytotic vesicles transporting matrix degradation products through the cell, suggesting that TRAP-facilitated fragmentation of endocytosed material takes place in a specific cellular compartment. These results suggest that bone matrix degradation occurs not only extracellularly in the resorption lacunae but also intracellularly in the transcytotic vesicles. We propose that proteins containing redox-active iron could represent a novel mechanism of physiological fragmentation of organic molecules. This mechanism could be important in tissue remodeling and as a defense mechanism of phagocytosing cells.

Footnotes

↵* This work was supported by grants from the Academy of Finland, State Technology Development Center of Finland (TEKES), and the Sigrid Juselius Foundation. World Health Organization Collaborating Center for Research on Reproductive Health is supported by the Ministry of Education, Social Affairs and Health and the Ministry of Foreign Affairs, Finland.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵§§ To whom correspondence should be addressed. Tel.: 358-2-333 7232; Fax: 358-2-333 7352; E-mail: kalervo.vaananen@utu.fi.
Abbreviations:

RB

ruffled border

FSD

functional secretory domain

ROS

reactive oxygen species

TRAP

tartrate-resistant acid phosphatase

MDA

malondialdehyde acetal

CA II

carbonic anhydrase II

MMP-9

matrix metalloproteinase 9

DCFH-DA

2′,7′-dichlorofluorescin diacetate
- Received January 12, 1999.
- Revision received April 27, 1999.
The American Society for Biochemistry and Molecular Biology, Inc.