PTEN and glioblastoma: Further studies have demonstrated that the PTEN-Akt pathway also controls c-FLIP ubiquitination via the ubiquitin-specific protease 8 (USP8) and an E3 ubiquitin ligase atrophin-interacting protein 4 (AIP4), leading to prolonged c-FLIP half-life and increased TRAIL resistance in GBM cells [84,85].