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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. 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. 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.
SPARC Promotes Glioma Migration and Invasion. 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 migration and 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, such as increasing MT1-MMP expression and MMP2 activation. However, we have also found that SPARC decreases VEGF expression and secretion and it decreases glioma proliferation. These latter observations are important, because 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
- Courtney Giordano (Ph.D. candidate in Pharmacology)
- Undergraduate Students
- Ridwan Alam (MedStart Program)
- Swathi Nallapa (MedStart Program)
- Research Coordinators
- Bill Golembieski, B.Sc.
- Chad Schultz, B.Sc.
- Lab Alumni
- Heather McClung, Ph.D. (2011)
Selected Recent Publications
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1. 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.
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2. 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 56:1061-1075, 2008.
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3. Martino M, Mochizuki M, Rothenfluh DA, Rempel SA, Hubbell JA, Barker TH. Controlling integrin specificity and stem cell differentiation in 2-D and 3-D environments through regulation of fibronectin domain stability. Biomaterials 30:1089-97, 2009.
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4. Thomas SL, Alam R, Lemke N, Schultz LR, Gutiérrez JA, Rempel SA. PTEN augments SPARC suppression of proliferation and inhibits SPARC-induced migration by suppressing SHC-RAF-ERK and AKT signaling. Neuro-Oncology 12:941-955, 2010.
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5. Weaver M, Workman G, Schultz CR, Lemke N, Rempel SA, Sage EH. Proteolysis of the matricellular protein hevin by matrix metalloproteinase-3 produces a SPARC-like fragment (SLF) associated with neovasculature in a murine glioma model. J Cell Biochem. 2011 Jun 17. doi: 10.1002/jcb.23235. [Epub ahead of print]
Links
http://www.henryford.com/body.cfm?id=48881
http://www.henryford.com/body.cfm?id=55681
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