Purification from human milk of matriptase complexes with secreted serpins: mechanism for inhibition of matriptase other than HAI-1

Authors

I-Chu Tseng, University of Maryland at Baltimore
Feng-Pai Chou, University of Maryland at Baltimore
Sheng-Feng Su, University of Maryland at Baltimore
Michael Oberst, MedImmune, Gaithersburg, Maryland
Nandakumar Madayiputhiya, University of Nebraska - LincolnFollow
Ming-Shyue Lee, College of Medicine National Taiwan University
Jehng-Kang Wang, National Defense Medical Center, Taipei, Taiwan
David E. Sloane, Brigham and Women's Hospital, Boston, Massachusetts
Michael Johnson, Georgetown University
Chen-Yong Lin, University of Maryland at Baltimore

Date of this Version

2008

Citation

Am J Physiol Cell Physiol. 295(2): C423-C431

Comments

Copyright © 2008, American Physiological Society

Abstract

Matriptase, a type 2 transmembrane serine protease, is predominately expressed by epithelial and carcinoma cells in which hepatocyte growth factor activator inhibitor 1 (HAI-1), a membrane-bound, Kunitz-type serine protease inhibitor, is also expressed. HAI-1 plays dual roles in the regulation of matriptase, as a conventional protease inhibitor and as a factor required for zymogen activation of matriptase. As a consequence, activation of matriptase is immediately followed by HAI-1-mediated inhibition, with the activated matriptase being sequestered into HAI-1 complexes. Matriptase is also expressed by peripheral blood leukocytes, such as monocytes and macrophages; however, in contrast to epithelial cells, monocytes and macrophages were reported not to express HAI-1, suggesting that these leukocytes possess alternate, HAI- 1-independent mechanisms regulating the zymogen activation and protease inhibition of matriptase. In the present study, we characterized matriptase complexes of 110 kDa in human milk, which contained no HAI-1 and resisted dissociation in boiling SDS in the absence of reducing agents. These complexes were further purified and dissociated into 80-kDa and 45-kDa fragments by treatment with reducing agents. Proteomic and immunological methods identified the 45-kDa fragment as the noncatalytic domains of matriptase and the 80-kDa fragment as the matriptase serine protease domain covalently linked to one of three different secreted serpin inhibitors: antithrombin III, α1- antitrypsin, and α2-antiplasmin. Identification of matriptaseserpin inhibitor complexes provides evidence for the first time that the proteolytic activity of matriptase, from those cells that express no or low levels of HAI-1, may be controlled by secreted serpins.