PTBP1 and central nervous system cancer: To further examine the role of SON in PTBP1 and PTBP2 expression, we reduced SON expression in the U87MG glioblastoma cell line and two different lines of patient-derived-glioma stem cells (GSCs), established previously (GSC #83, mesenchymal GSCs; GSC #84, proneural GSCs)48, using validated siRNA or shRNA27.