The Expression and Function of Wilms' Tumor 1 in Malignant Glioma

• Main Author: Clark, Aaron J.
• Format: Others
• Published: VCU Scholars Compass 2006
• Subjects: apoptosis; gene therapy; p53; ionizing radiation; tumorigenicity; brain tumor; glioblastoma; Anatomy; Medicine and Health Sciences; Nervous System
• Online Access: http://scholarscompass.vcu.edu/etd/1006; http://scholarscompass.vcu.edu/cgi/viewcontent.cgi?article=2005&context=etd

The Wilms' tumor 1 gene is overexpressed in many types of cancer and is associated with poor prognosis and resistance to anti-cancer therapies. In vitro studies in non-glioma cells types have demonstrated that WTl plays a role in increased proliferation, resistance to apoptosis, and increased cellular invasion. We aimed to thoroughly characterize the expression pattern of Wilms' tumor 1 in human malignant glioma and discern its function in this complex disease process. We screened a large sample of established human malignant glioma cell lines and glioma tissue specimens of all grades for WT1 expression. The majority of cell lines and 80% of all glioma tissue expressed WTI mRNA, all of which expressed WTl(+KTS) isoforms. Further screening of the glioblastoma specimens for p53 mutation followed by logistic regression analysis demonstrated a positive correlation between WTl expression and wild-type p53 (p = 0.04). To determine if WTl and p53 functionally interacted, we generated LN-229 glioblastoma cells that stably expressed WTl. As LN-229 cells harbor a p53 mutation, transient transfection with wild-type p53 induced apoptosis. However, stable WTI expression did not protect cells from p53-mediated cell death. We then generated U87MG cells (p53 wild-type) that stably expressed WT1 to model an endogenous p53 response. It is well known that after treatment with ionizing radiation, U87MG cells readily undergo p53-mediated apoptosis. Again, WTI expression did not protect against ionizing radiation induced p53-mediated cell death. We next examined the effect of transient WTI silencing on ionizing radiation induced cell death in T98G and LN-18 cells which express endogenous WTl. Combination treatment with ionizing radiation and silencing of WTI using short interfering RNA caused a decrease in viability and clonogenic survival relative to radiation alone in both cell lines. Lastly, we studied the effect of stable WTl silencing using short hairpin RNA on glioblastoma cell tumorigenicity. Stable transduction of U25 1MG and LN-18 cells with WTI short hairpin RNA resulted in a marked decrease in proliferation. WTI silencing in U251MG cells also caused a decrease in in vitro invasion. WTl silencing in U251MG cells caused an increase in tumor latency and a decrease in tumor growth rate when cells were used to subcutaneously inoculate nude mice. Not only do these studies support an oncogenic role for WTI in glioma biology, they provide encouraging evidence that WTl may be a therapeutic target for molecular treatment of glioblastoma.