This Article Full Text Full Text (PDF) All Versions of this Article: 0008-5472.CAN-09-1287v1 69/20/7911    most recent Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Panner, A. Articles by Pieper, R. O. PubMed PubMed Citation Articles by Panner, A. Articles by Pieper, R. O.

A Novel PTEN-Dependent Link to Ubiquitination Controls FLIP_S Stability and TRAIL Sensitivity in Glioblastoma Multiforme

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

Requests for reprints: Russell O. Pieper, Helen Diller Family Comprehensive Cancer Center, Room 287, Box 0520, University of California San Francisco, 1450 3rd Street, San Francisco, CA 94158-9001. Phone: 415-502-7132; Fax: 415-502-6779; E-mail: rpieper{at}cc.ucsf.edu or Andrew T. Parsa, Helen Diller Family Comprehensive Cancer Center, Room 286, Box 0520, University of California San Francisco, 1450 S. 3rd Street, San Francisco, CA 94158-9001. Phone: 415-353-2629; Fax: 415-353-2889; E-mail: parsaa{at}neurosurg.ucsf.edu.

Key Words: AIP4 • TRAIL • ubiquitination

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. [Cancer Res 2009;69(20):7911–6]