Papers In Press, published online ahead of print May 23, 2008
J. Biol. Chem, 10.1074/jbc.M706563200
Submitted on August 8, 2007
Revised on May 19, 2008
Accepted on May 23, 2008
The copper-binding domain of sparc mediates cell survival in vitro via interaction with integrin beta 1 and activation of integrin-linked kinase
Matt S. Weaver, Gail A. Workman, and E. Helene Sage
Hope Heart Program, Benaroya Research Institute at Virginia Mason, Seattle, WA 98101-2795
Corresponding Author: hsage{at}benaroyaresearch.org
Secreted protein acidic and rich in cysteine (SPARC) is important for the normal growth and maintenance of the murine lens. SPARC-null animals develop cataracts associated with a derangement of the lens capsule basement membrane and alterations in lens fiber morphology. Cellular stress and disregulation of apoptotic pathways within lens epithelial cells (LEC) are linked to cataract formation. To identify molecular targets of SPARC that are linked to this disorder, we stressed wild-type (WT) and SPARC-null LEC by serum deprivation or exposure to tunicamycin. SPARC enhanced signaling by integrin-linked kinase (ILK), a serine/threonine-kinase known to enhance cell survival in vitro. In response to stress, an ILK-dependent decrease in apoptosis was observed in WT relative to SPARC-null LEC. Co-immunoprecipitation and cross-linking of cell lysates revealed enhanced levels of a SPARC-integrin
1 complex during stress. Competition with monoclonal antibodies and peptides indicated that the copper-binding domain of SPARC is required for SPARC-mediated response to stress. Inhibiting the binding and/or activity of ILK, integrin
1, or SPARC resulted in increased apoptosis of stressed LEC. We conclude that SPARC protects cells from stress-induced apoptosis in vitro, via an interaction with integrin
1 heterodimers that enhances ILK activation and pro-survival activity.