1. ¹Department of Surgery, Duke University Medical Center, Durham, NC, USA
2. ²Department of Pathology, Duke University Medical Center, Durham, NC, USA
3. ³Department of Medicine, Duke University Medical Center, Durham, NC, USA
4. ⁴Department of Neurobiology, Duke University Medical Center, Durham, NC, USA
5. ⁵Preston Robert Tisch Brain Tumor Center, Duke University Medical Center, Durham, NC, USA

Correspondence: Dr JN Rich, Preston Robert Tisch Brain Tumor Center, Duke University Medical Center, PO Box 2900, Durham, NC 27710, USA. E-mail: rich0001@mc.duke.edu

Received 21 July 2006; Revised 26 October 2006; Accepted 27 October 2006; Published online 8 January 2007.

Abstract

Secreted protein acidic and rich in cysteine (SPARC) is an extracellular glycoprotein expressed in several solid cancers, including malignant gliomas, upon adoption of metastatic or invasive behaviors. SPARC expression in glioma cells promotes invasion and survival under stress, the latter process dependent on SPARC activation of AKT. Here we demonstrate that downregulation of SPARC expression with short interfering RNA (siRNA) in glioma cells decreased tumor cell survival and invasion. SPARC siRNA reduced the activating phosphorylation of AKT and two cytoplasmic kinases, focal adhesion kinase (FAK) and integrin-linked kinase (ILK). We determined the contributions of FAK and ILK to SPARC effects using SPARC protein and cell lines engineered to overexpress SPARC. SPARC activated FAK and ILK in glioma cells previously characterized as responsive to SPARC. Downregulation of either FAK or ILK expression inhibited SPARC-mediated AKT phosphorylation, and targeting both FAK and ILK attenuated AKT activation more potently than targeting either FAK or ILK alone. Decreased SPARC-mediated AKT activation correlated with a reduction in SPARC-dependent invasion and survival upon the downregulation of FAK and/or ILK expression. These data further demonstrate the role of SPARC in glioma tumor progression through the activation of intracellular kinases that may provide novel therapeutic targets for advanced cancers.