The copper binding domain of SPARC mediates cell survival in vitro via interaction with integrin beta1 and activation of integrin-linked kinase.
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 SPARCg-null LEC. Co-immunoprecipitation and cross-linking of cell lysates revealed enhanced levels of a SPARC-integrin beta1 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 beta1, 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 beta1 heterodimers that enhances ILK activation and pro-survival activity.
Weaver
Matt S
MS
Hope Heart Program, Benaroya Research Institute at Virginia Mason, Seattle, Washington 98101-2795, USA.
Workman
Gail
G
Sage
E Helene
EH
D000818:Animals; D017209:Apoptosis; D001665:Binding Sites; D002386:Cataract / Q000235:genetics; D002470:Cell Survival / Q000502:physiology*; D003300:Copper / Q000378:metabolism*; D004847:Epithelial Cells / Q000166:cytology / Q000502:physiology; D019012:Integrin beta1 / Q000378:metabolism*; D007908:Lens, Crystalline / Q000254:growth & development / Q000473:pathology / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D015676:Osteonectin / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D000099200:Scaffold Protein ILK
D003300:Copper; D019012:Integrin beta1; D015676:Osteonectin; D017346:Protein Serine-Threonine Kinases; D017382:Reactive Oxygen Species; D000099200:Scaffold Protein ILK