title: SPARC/osteonectin induces matrix metalloproteinase 2 activation in human breast cancer cell lines.
abstract: Activation of the matrix metalloproteinase 2 (MMP-2) has been shown to play a major role in the proteolysis of extracellular matrix (ECM) associated with tumor invasion. Although the precise mechanism of this activation remains elusive, levels of the membrane type 1-MMP (MT1-MMP) at the cell surface and of the tissue inhibitor of MMP-2 (TIMP-2) appear to be two important determinants. Induction of MMP-2 activation in cells cultivated on collagen type I gels indicated that the ECM is important in the regulation of this process. In this study, we show that SPARC/osteonectin, a small ECM-associated matricellular glycoprotein, can induce MMP-2 activation in two invasive breast cancer cell lines (MDA-MB-231 and BT549) but not in a noninvasive counterpart (MCF-7), which lacks MT1-MMP. Using a set of peptides from different regions of SPARC, we found that peptide 1.1 (corresponding to the NH2-terminal region of the protein) contained the activity that induced MMP-2 activation. Despite the requirement for MT1-MMP, seen in MCF-7 cells transfected with MT1-MMP, the activation of MMP-2 by SPARC peptide 1.1 was not associated with increased steady-state levels of MT1-MMP mRNA or protein in either MT1-MMP-transfected MCF-7 cells or constitutively expressing MDA-MB-231 and BT549 cells. We did, however, detect decreased levels of TIMP-2 protein in the media of cells incubated with peptide 1.1 or recombinant SPARC; thus, the induction of MMP-2 activation by SPARC might be due in part to a diminution of TIMP-2 protein. We conclude that SPARC, and specifically its NH2-terminal domain, regulates the activation of MMP-2 at the cell surface and is therefore likely to contribute to the proteolytic pathways associated with tumor invasion.
authors.affiliation: Lombardi Cancer Center and Department of Cell Biology, Georgetown University Medical Center, Washington, DC 20007, USA.
authors.forename: C
authors.initials: C
authors.lastname: Gilles
authors.forename: J A
authors.initials: JA
authors.lastname: Bassuk
authors.forename: H
authors.initials: H
authors.lastname: Pulyaeva
authors.forename: E H
authors.initials: EH
authors.lastname: Sage
authors.forename: J M
authors.initials: JM
authors.lastname: Foidart
authors.forename: E W
authors.initials: EW
authors.lastname: Thompson
mesh_terms: D000595:Amino Acid Sequence; D000906:Antibodies / Q000494:pharmacology; D001665:Binding Sites; D001943:Breast Neoplasms / Q000201:enzymology*; D003094:Collagen / Q000494:pharmacology; D004789:Enzyme Activation; D018093:Gelatinases / Q000378:metabolism*; D006801:Humans; D016023:Integrins / Q000276:immunology; D020778:Matrix Metalloproteinase 2; D008666:Metalloendopeptidases / Q000378:metabolism*; D008969:Molecular Sequence Data; D009361:Neoplasm Invasiveness; D015676:Osteonectin / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D010446:Peptide Fragments / Q000494:pharmacology; D019716:Tissue Inhibitor of Metalloproteinase-2 / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D000906:Antibodies; D016023:Integrins; D015676:Osteonectin; D010446:Peptide Fragments; D019716:Tissue Inhibitor of Metalloproteinase-2; D003094:Collagen; D018093:Gelatinases; D008666:Metalloendopeptidases; D020778:Matrix Metalloproteinase 2