POMGNT1 and glioblastoma: In this light, POMGNT1 clearly exerts a pro-oncogenic role in glioblastoma, likely by inhibiting the intrinsic phosphatase activity of receptor-type protein tyrosine phosphatase β/ζ (RPTPβ/ζ) through its O-mannosyl glycosylation possibly mediated by both POMGNT1 and GnT-Vb, the latter being highly expressed in the brain [114, 155–157] and also through downregulation of RPTPβ/ζ protein expression mediated by POMGNT1 [114].