title: A novel PTEN-dependent link to ubiquitination controls FLIPS stability and TRAIL sensitivity in glioblastoma multiforme.
abstract: Phosphatase and tensin homologue (PTEN) loss and activation of the Akt-mammalian target of rapamycin (mTOR) pathway increases mRNA translation, increases levels of the antiapoptotic protein FLIP(S), and confers resistance to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in glioblastoma multiforme (GBM). In PTEN-deficient GBM cells, however, the FLIP(S) protein also exhibited a longer half-life than in PTEN mutant GBM cells, and this longer half-life correlated with decreased FLIP(S) polyubiquitination. FLIP(S) half-life in PTEN mutant GBM cells was reduced by exposure to an Akt inhibitor, but not to rapamycin, suggesting the existence of a previously undescribed, mTOR-independent linkage between PTEN and the ubiquitin-dependent control of protein stability. Total levels of the candidate FLIP(S) E3 ubiquitin ligase atrophin-interacting protein 4 (AIP4) were comparable in PTEN wild-type (WT) and PTEN mutant GBM cells, although in PTEN-deficient cells, AIP4 was maintained in a stable polyubiquitinated state that was less able to associate with FLIP(S) or with the FLIP(S)-containing death inducing signal complex. Small interfering RNA-mediated suppression of AIP4 levels in PTEN WT cells decreased FLIP(S) ubiquitination, prolonged FLIP(S) half-life, and increased TRAIL resistance. Similarly, the Akt activation that was previously shown to increase TRAIL resistance did not alter AIP4 levels, but increased AIP4 ubiquitination, increased FLIP(S) steady-state levels, and suppressed FLIP(S) ubiquitination. These results define the PTEN-Akt-AIP4 pathway as a key regulator of FLIP(S) ubiquitination, FLIP(S) stability, and TRAIL sensitivity and also define a novel link between PTEN and the ubiquitin-mediated control of protein stability.
authors.affiliation: Brain Tumor Research Center, Department of Neurological Surgery and University of California San Francisco Comprehensive Cancer Center, University of California San Francisco, San Francisco, California 94158-9001, USA.
authors.forename: Amith
authors.initials: A
authors.lastname: Panner
authors.forename: Courtney A
authors.initials: CA
authors.lastname: Crane
authors.forename: Changjiang
authors.initials: C
authors.lastname: Weng
authors.forename: Alberto
authors.initials: A
authors.lastname: Feletti
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Parsa
authors.forename: Russell O
authors.initials: RO
authors.lastname: Pieper
mesh_terms: D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000737:chemistry* / Q000378:metabolism*; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D005909:Glioblastoma / Q000378:metabolism* / Q000473:pathology; D006207:Half-Life; D006801:Humans; D047468:Immunoprecipitation; D051379:Mice; D018345:Mice, Knockout; D051059:PTEN Phosphohydrolase / Q000502:physiology*; D011494:Protein Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000494:pharmacology; D012097:Repressor Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination; D023041:Xenograft Model Antitumor Assays
chemical_list: D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D053221:TNF-Related Apoptosis-Inducing Ligand; D025801:Ubiquitin; C432966:ITCH protein, human; D044767:Ubiquitin-Protein Ligases; D011494:Protein Kinases; C546842:MTOR protein, human; C546843:mTOR protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D051059:PTEN Phosphohydrolase; D020123:Sirolimus