Background: The level of c-Myc is closely associated with high pathological grade and the poor prognosis of gliomas. Vascular endothelial growth factor (VEGF) is the most important angiogenic factor that potently stimulates the proliferation and migration of vascular endothelial cells. This study aimed to address the biological importance of c-Myc in the development of gliomas, we downregulated the expression of c-Myc in the human glioblastoma cell line IN500 and studied the in vitro effect on cellular growth, proliferation, and apoptosis and the expression of VEGF and the in vivo effect on tumor formation in a xenograft mouse model.
Methods: IN500Δ cells were stably transfected with shRNA-expressing plasmids for either c-Myc (pCMYC-shRNA) or as a control (pCtrl-shRNA). Following establishment of stable cells, the mRNA expressions of c-Myc and VEGF were examined by reverse transcription (RT)-PCR, and c-Myc and VEGF proteins by Western blotting and immunohistochemistry. Cell-cycle progression and apoptosis were determined by flow cytometry. The in vivo effect of targeting c-Myc was determined by subcutaneous injection of stable cells into immunodeficient nude mice.
Results: The stable transfection of pCMYC-shRNA successfully knocked down the steady-state mRNA and protein levels of c-Myc in IN500, which positively correlated with the downregulation of VEGF. Downregulating c-Myc in vitro also led to G1-S arrest and enhanced apoptosis. In vivo, targeting c-Myc reduced xenograft tumor formation and resulted in significantly smaller tumors.
Conclusions: c-Myc has multiple functions in glioblastoma development that include regulating cell-cycle, apoptosis, and VEGF expression. Targeting c-Myc expression may be a promising therapy for malignant glioma.