| Summary: | <p>Abstract</p> <p>Background</p> <p>Medulloblastoma is the most common malignant brain tumor of childhood. Children who relapse usually die of their disease, which reflects resistance to radiation and/or chemotherapy. Improvements in outcome require a better understanding of the molecular basis of medulloblastoma growth and treatment response. <it>TP73 </it>is a member of the <it>TP53 </it>tumor suppressor gene family that has been found to be overexpressed in a variety of tumors and mediates apoptotic responses to genotoxic stress. In this study, we assessed expression of <it>TP73 </it>RNA species in patient tumor specimens and in medulloblastoma cell lines, and manipulated expression of full-length TAp73 and amino-terminal truncated ΔNp73 to assess their effects on growth.</p> <p>Methods</p> <p>We analyzed medulloblastoma samples from thirty-four pediatric patients and the established medulloblastoma cell lines, Daoy and D283MED, for expression of <it>TP73 </it>RNA including the full-length transcript and the 5'-terminal variants that encode the ΔNp73 isoform, as well as <it>TP53 </it>RNA using quantitative real time-RTPCR. Protein expression of TAp73 and ΔNp73 was quantitated with immunoblotting methods. Clinical outcome was analyzed based on <it>TP73 </it>RNA and p53 protein expression. To determine effects of overexpression or knock-down of TAp73 and ΔNp73 on cell cycle and apoptosis, we analyzed transiently transfected medulloblastoma cell lines with flow cytometric and TUNEL methods.</p> <p>Results</p> <p>Patient medulloblastoma samples and cell lines expressed full-length and 5'-terminal variant <it>TP73 </it>RNA species in 100-fold excess compared to non-neoplastic brain controls. Western immunoblot analysis confirmed their elevated levels of TAp73 and amino-terminal truncated ΔNp73 proteins. Kaplan-Meier analysis revealed trends toward favorable overall and progression-free survival of patients whose tumors display TAp73 RNA overexpression. Overexpression of TAp73 or ΔNp73 induced apoptosis under basal growth conditions <it>in vitro </it>and sensitized them to cell death in response to chemotherapeutic agents.</p> <p>Conclusion</p> <p>These results indicate that primary medulloblastomas express significant levels of <it>TP73 </it>isoforms, and suggest that they can modulate the survival and genotoxic responsiveness of medulloblastomas cells.</p>
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