Limited Cleavage of Extracellular Matrix Protein BM-40 by Matrix Metalloproteinases Increases Its Affinity for Collagens

Abstract

The 33-kDa matrix protein BM-40 (SPARC, osteonectin) consists of an acidic N-terminal domain I, a central cysteine-rich follistatin-like module, and a C-terminal extracellular calcium-binding (EC) module. Previous studies attributed collagen IV and high affinity calcium binding of BM-40 to its EC module, which was shown by x-ray crystallography to consist of an EF-hand pair surrounded by several ␣-helical and loop segments. This module was now shown by surface plasmon resonance assay to bind with similar affinities to collagens I, III, and V. Cleavage of recombinant BM-40 and its EC module by collagenase-3, gelatinases A and B, matrilysin, and stromelysin-1 showed similar fragment patterns, whereas collagenase-1 was inactive. Some differences were, however, observed in cleavage rates and the preference of certain cleavage sites. Edman degradation of fragments demonstrated only three to four major cleavage sites in the central region of domain I and a single uniform cleavage in helix C of the EC module. Cleavage is accompanied by a 7-20-fold increase in binding activity for collagens I, IV, and V but revealed only small effects on calcium-dependent ␣-helical changes in the EC module. The data were interpreted to indicate that helix C cleavage is mainly responsible for enhancing collagen affinity by exposing the underlying helix A of the EC module. A similar activation may also occur in situ as indicated previously for tissue-derived BM-40.The small calcium-binding glycoprotein (33 kDa) referred to as BM-40, SPARC, or osteonectin has been shown to have a widespread occurrence in extracellular matrices of various organs with a particularly high expression found during morphogenesis, tissue remodeling, and repair. The protein exhibits anti-adhesive properties in cell culture and modulates the expression of certain extracellular receptors. Several extracellular ligands have been identified for BM-40 including some collagen types and cytokines (1). This indicated various binding sites on BM-40 in agreement with a previous proposal of a mosaic structure for the protein (2). The most recent interpretation of the domain structure based on recombinant deletion mutants and a crystal structure of a fragment encompassing the C-terminal 150 residues (3, 4) demonstrated an acidic and flexible N-terminal domain I (ϳ50 residues) followed by a follistatin-like (FS) 1 module (ϳ75 residues) and a novel extracellular calcium-binding (EC) module (ϳ150 residues). X-ray crystallography of this EC module demonstrated two opposing calcium-binding EF hands, as found in many intracellular proteins (5), which were in close contact to an extended ␣ helix (4). A combination of adjacent FS and EC modules has been detected in the cDNA sequences of several more extracellular proteins suggesting the existence of a protein family (1, 3, 4). Yet it is not known so far whether they are functionally related to BM-40.The binding of BM-40 to the fibril-forming collagens I, III, and V and basement membrane collagen IV has been demonstrated and depended ...

SPARC is expressed by macroglia and microglia in the developing and mature nervous system

“…Different tenascin-R peptide fragments can either inhibit or promote microglial migration (Liao et al, 2005). SPARC can similarly be cleaved by proteases and MMPs to yield peptides with distinct functions (Lane et al, 1994;Iruela-Arispe et al, 1995;Sasaki et al, 1997), and can also regulate protease expression and activation (Brekken and Sage, 2000;McClung et al, 2007). Since many proteases are up-regulated after injury by microglia and other cells (Yong, 2005;del Zoppo et al, 2007), it is possible that cleavage of SPARC might facilitate the rapid process motility and chemotaxis of activated microglia (Davalos et al, 2005;Nimmerjahn et al, 2005;Kurpius et al, 2006).…”

Characterization of SMOC-1, a Novel Modular Calcium-binding Protein in Basement Membranes

“…BM-40 binds to collagen IV and fibrillar collagens through its EC domain (5,60). This binding interaction is relevant for the localization of BM-40 in vivo as type I collagen-deficient mice do not retain BM-40 in the extracellular matrix (61).…”

Gelatinase-mediated migration and invasion of cancer cells

“…SPARC also induces MMP-1, -3 and -9 expression (Tremble et al, 1993), and the MMPs may be activated by uPA-mediated processes (Mazzieri et al, 1997;Ramos-DeSimone et al, 1999). Furthermore, SPARC can be proteolytically processed by MMPs (Sasaki et al, 1997), and the MMP-cleaved SPARC fragments modulate cell proliferation, migration and angiogenesis .…”

“…Indeed, some substrates show over 200-fold selectivity towards MMP-2 Kridel et al, 2001). (Morodomi et al, 1992;Okada et al, 1990) Native collagen type: I yes no (Aimes and Quigley, 1995) III yes no (Berton et al, 2000) IV yes yes (Morodomi et al, 1992) V yes yes (Morodomi et al, 1992) VII yes (Seltzer et al, 1989) X yes (Cole et al, 1993) XI yes (Smith et al, 1991) XVIII yes (Ferreras et al, 2000) Aggrecan yes yes (Fosang et al, 1992) BM-40/SPARC/ Osteonectin yes yes (Sasaki et al, 1997) Brevican yes no Decorin yes no (Imai et al, 1997) Elastin yes yes Entactin/nidogen no yes (Mayer et al, 1993;Sires et al, 1993) Fibrillin yes yes (Ashworth et al, 1999) Fibrin yes (Lelongt et al, 2001) Fibrinogen yes yes (Bini et al, 1996;Lelongt et al, 2001) Fibronectin yes no (Okada et al, 1990) Laminin yes yes (Giannelli et al, 1997;Morodomi et al, 1992) Link protein yes yes (Nguyen et al, 1993) NG2 proteoglycan yes (Larsen et al, 2003) Neurocan yes (Turk et al, 2001) Tenascin yes no (Siri et al, 1995) Vitronectin yes yes (Imai et al, 1995) α2-macroglobulin yes yes (Arbelaez et al, 1997) αB-crystallin yes (Starckx et al, 2003) Amyloid protein precursor yes (LePage et al, 1995) Big endothelin-1 yes yes (Fernandez-Patron et al, 2002) Calcitonin gene-related peptide (CGRP) yes (Fernandez-Patron et al, 2000) Complement protein C1q yes yes (Ruiz et al, 1999) Connective tissue-activating peptide-III (CTAP-III) yes (Van den Eph B1 tyrosine kinase receptor yes no Epithelial-cell derived neutrophil activating pept...…”