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Sandra A. Rempel, Ph.D.
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RESEARCH INTERESTS:
Glioma Invasion:
Glioblastomas are the most malignant and heterogeneous brain tumors. Study of the genetic changes in glioblastomas confirms that there are distinct disease subtypes (Fig. 1). Approximately 90% of glioblastomas develop rapidly without evidence of lower grade precursor tumors. These are designated as primary or “de novo” tumors. The remaining 10% develop through progressive changes from low-grade diffuse astrocytoma and/or anaplastic astrocytoma. Expression profiles show significant differences in gene expression between the subsets. For example, the subsets are distinguished by major differences in losses or mutations of the tumor suppressor genes PTEN and TP53. However it is clear that there is not one marker presented in Figure 1 that can be used independently to decisively distinguish the subtype. Therefore, the overall tumor genetic profile needs to be assessed. Additional markers are also required to further distinguish minor subsets within these major subsets. Of clinical importance, these differences in genotype amongst the glioblastomas may significantly impact the development of novel, targeted therapies and underscores the need for individual tumor assessment.
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Fig. 1. Genetic pathways to primary (de novo) and secondary glioblastomas. Adapted from Ohgaki H. and Kleihues P. Am J Pathol 170:1445:1453, 2007. |
SPARC as a Therapeutic Target for Glioma. Glioblastoma heterogeneity also occurs at the phenotypic level where different regions within the tumor may be undergoing different biological processes such as necrosis, proliferation, angiogenesis, apoptosis, and tumor cell migration and invasion into the adjacent brain. Since the poor prognosis of patients with astrocytomas, and especially glioblastomas, is largely due to their highly infiltrative nature, innovative approaches to inhibit invasion are essential. We have therefore looked for genes that are involved in regulating the infiltrative/invasive phenotype. Such genes could theoretically be therapeutic targets to treat all grades of gliomas. To this end, we first created astrocytoma and glioblastoma cDNA libraries. Subtractive hybridization between these cDNA libraries identified several candidate genes expressed in all grades of glioma, including Secreted Protein Acidic and Rich in Cysteine (SPARC), also known as osteonectin and BM-40. SPARC overexpression in all grades was confirmed in primary human tumors. To determine whether SPARC promotes invasion of these tumors, the non-invasive U87MG glioma cell line, which has low endogenous SPARC, was transfected with control or SPARC expression vectors. Using these cells, we demonstrated that SPARC expression promotes glioma invasion in vitro and in vivo, suggesting that it is a potential therapeutic target to inhibit glioma invasion. We have since found that SPARC regulates several mechanisms that promote invasion. It decreases glioma proliferation, decreases VEGF expression and secretion, increases MT1-MMP expression and MMP2 activation, and increases glioma invasion in vivo. Thus, a major consequence to targeting SPARC to inhibit invasion may result in the unwanted increase in tumor proliferation and angiogenesis. Therefore, it becomes important to characterize the downstream signaling cascades regulated by SPARC, allowing the targeting of SPARC-induced invasion, while permitting retention of SPARC-induced inhibition of proliferation and angiogenesis. We have found that the heat shock protein HSP27 mediates SPARC-induced glioma invasion.
HSP27 as a Therapeutic Target for Glioma Invasion. HSP27 is a member of the large chaperone family of heat shock proteins (HSPs) that responds to stress, such as heat, hypoxia, radiation, and serum deprivation. Overexpression of the HSPs allows cells to survive under normally lethal conditions. Of interest for our research, HSP27 also regulates its function in actin remodeling, contractility, and cell migration. We are currently investigating the signaling mechanisms through which HSP27 regulates glioma migration, as well as evaluating its role as a glioma therapeutic target.
Effects of Genetic Background on SPARC and HSP27 Functions. We do not know whether the other genetic mutations/deletions that occur in the primary versus the secondary tumors have an effect on SPARC or HSP27 function. Therefore, additional research projects are focused on the impact of PTEN and p53 tumor suppressor gene loss on SPARC- and HSP27-invasion.
The research utilizes standard in vitro molecular and cellular approaches including gene transduction and cloning, 1D and 2D western blot analyses, immunoprecipitation, manipulation/ inhibition of gene expression using siRNA, shRNA, and kinase inhibitors, and imaging with standard and confocal microscopy. In vivo assessments of gene expression effects are assessed by immunohistochemistry of xenograft tumors of transfected cells, human glioma cells, and human tumor stem cell-like neurospheres in rat brains, or assessment of gene expression in human tumors specimens (individual specimens or tissue arrays).
Current Lab Personnel
- Graduate Students
- Heather McClung (Ph.D. candidate in Pharmacology)
- Postdoctoral Fellow
- Stacey Thomas, Ph.D.
- Research Coordinators
- Bill Golembieski, B.Sc.
- Chad Schultz, B.Sc.
Selected Recent Publications
1. Barker TH, Baneyx G, Cardó-Vila M, Workman GA, Weaver M, Menon PM, Dedhar S, Rempel SA, Arap W, Pasqualini R, Vogel V, Sage EH. SPARC Regulates Extracellular Matrix Organization Through its Modulation of Integrin-Linked Kinase Activity. JBC 280:36483-36493, 2005.
2. Rempel SA, Hawley RC, Gutiérrez, JA, Mouzon E, Bobbitt KR, Lemke N, Schultz C, Schultz LR, Golembieski W, Koblinski J, VanOsdol S, Miller CG. Splenic and Immune Alterations of the Sparc-Null Mouse Accompany a Lack of Immune Response. Genes and Immunity 8:262-74, 2007.
3. McClung H, Thomas SL, Osenkowski P, Toth M, Menon P, Raz A, Fridman R, Rempel SA. SPARC Upregulates MT1-MMP Expression, MMP2 Activation, and the Secretion and Cleavage of Galectin-3 in U87MG Glioma Cells. Neuroscience Letters 419:172-177, 2007.
4, Yunker CK, Golembieski W, Lemke N, Cazacu S, Schultz CR, Brodie C, Rempel SA. SPARC-induced increase in glioma matrix and decrease in vascularity are associated with reduced VEGF expression and secretion. Int J Cancer 122:2735-2743, 2008.
5. Golembieski W, Thomas SL, Schultz CR, Yunker CK, McClung H, Cazacu S, Barker T, Sage EH, Brodie C, Rempel SA. HSP27 Mediates SPARC-Induced Changes in Glioma Morphology, Migration and Invasion. Glia (On-line, 2008).
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