The poor prognosis of glioma patients is largely due to the highly invasive nature of these tumors. Secreted protein acidic and rich in cysteine (SPARC) is highly expressed in gliomas. We have demonstrated that SPARC has disparate effects in vitro and in vivo, promoting glioma invasion while slowing glioma proliferation. The ability to alter these phenotypes makes it a prime therapeutic target for the treatment of gliornas. However, it is not known whether these two mechanisms can be targeted independently, thereby allowing the inhibition of its role in invasion but permitting its growth-suppressive effect. In addition the invasive phenotype is complex, requiring both changes in tumor cell motility as well as degradation of the extracellular matrix (ECM) to provide space for infiltrating cells. SPARC's role in both of these functions may also need to be targeted separately. Furthermore, it is not known if SPARC functions within the cell, or what contribution, if any, brain endogenous SPARC may contribute to the process. We propose that SPARC modulates ECM degradation, tumor cell motility, and tumor cell proliferation via separate mechanisms. The following Specific Aims are directed at characterizing these independent pathways.
In Specific Aim 1, we will characterize the extracellular mechanisms by which SPARC modulates invasion in vitro.
This aim will focus on SPARC's ability to promote invasion by increasing the degradation of the adjacent ECM. In particular, we will examine its interactions with the ECM protein vitronectin, with the SPARC-upregulated enzymes that modulate ECM degradation (MMP-2, MT1-MMP, PAl-1), and the alpha v integrins.
In Specific Aim 2, we will characterize the extracellular mechanisms by which SPARC modulates invasion in vivo. We will perform parallel experiments in vivo to determine whether endogenous SPARC plays a role in SPARC-induced invasion and whether the induced invasion can be inhibited by interfering with integrin and/or MMP activity.
In Specific Aim 3, we will determine whether the loss of SPARC in tumor cells is sufficient to inhibit tumor invasion and increase tumor growth and proliferation in vivo. We will use a novel tumor model consisting of p53-/- / Sparc +/+ versus p53-/- / Sparc -/-transformed astrocytes to determine whether the loss of SPARC converts the highly invasive p53-/- / Sparc +/+ tumors into noninvasive, highly proliferative tumors.
In Specific Aim 4, we will determine whether SPARC mediates motility, but not proliferation, via beta1 integrin-dependent or -independent intracellular signaling. We will also determine whether SPARC's regulation of the phenotypes results from differences in cellular versus extracellular localization.
Showing the most recent 10 out of 14 publications
