HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

J. Biol. Chem., Vol. 283, Issue 8, 5034-5045, February 22, 2008

This Article Full Text Full Text (PDF) Supplemental Data All Versions of this Article: 283/8/5034    most recent M708844200v1 Submit a Letter to Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Birts, C. N. Articles by Wilton, D. C. Search for Related Content PubMed PubMed Citation Articles by Birts, C. N. Articles by Wilton, D. C. Social Bookmarking                      What's this?

A Catalytically Independent Physiological Function for Human Acute Phase Protein Group IIA Phospholipase A₂

CELLULAR UPTAKE FACILITATES CELL DEBRIS REMOVAL^*

From the School of Biological Sciences, University of Southampton, Bassett Crescent East, Southampton, SO16 7PX, United Kingdom

Human group IIA phospholipase A₂ (IIA PLA₂) is an acute phase protein first identified at high concentrations in synovial fluid from patients with rheumatoid arthritis. Its physiological role has since been debated; the enzyme has a very high affinity for anionic phospholipid interfaces but expresses almost zero activity with zwitterionic phospholipid substrates, because of a lack of interfacial binding. We have prepared the cysteine-containing mutant (S74C) to allow the covalent attachment of fluorescent reporter groups. We show that fluorescently labeled IIA was taken up by phorbol 12-myristate 13-acetate-activated THP-1 cells in an energy-dependent process involving cell surface heparan sulfate proteoglycans. Uptake concurrently involved significant cell swelling, characteristic of macropinocytosis and the fluorescent enzyme localized to the nucleus. The endocytic process did not necessitate enzyme catalysis, ruling out membrane phospholipid hydrolysis as an essential requirement. The enzyme produced supramolecular aggregates with anionic phospholipid vesicles as a result of bridging between particles, a property that is unique to this globally cationic IIA PLA₂. Uptake of such aggregates labeled with fluorescent anionic phospholipid was dramatically enhanced by the IIA protein, and uptake involved binding to heparan sulfate proteoglycans on activated THP-1 cells. A physiological role for this protein is proposed that involves the removal of anionic extracellular cell debris, including anionic microparticles generated as a result of trauma, infection, and the inflammatory response, and under such conditions serum levels of IIA PLA₂ can increase 1000-fold. A similar pathway may be significant in the uptake into cells of anionic vector DNA involving cationic lipid transfection protocols.

Received for publication, October 26, 2007 , and in revised form, December 17, 2007.

^* This work was supported by a studentship (to C. N. B.) from the Biotechnology and Biological Sciences Research Council (UK). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. S1-S8.

¹ To whom correspondence should be addressed: School of Biological Sciences, University of Southampton, Bassett Crescent East, Southampton, SO16 7PX, UK. Tel.: 44-2380594308; Fax: 44-2380594459; E-mail: dcw{at}soton.ac.uk.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?