PTPRZ1 and glioblastoma: Although the role of mTOR in the PTN/PTPRZ1 signaling axis has not been studied in glioblastoma stem cells, it has been shown that mTOR activation contributes to their malignant biological behaviors [31], making it tempting to speculate that mTOR is activated downstream of PTN binding to PTPRZ1 in these cells as well.