RIP1 activates PI3K-Akt via a dual mechanism involving NF-kappaB-mediated inhibition of the mTOR-S6K-IRS1 negative feedback loop and down-regulation of PTEN.
Therapeutic inhibition of mammalian target of rapamycin (mTOR) in cancer is complicated by the existence of a negative feedback loop linking mTOR to the phosphatidylinositol 3-kinase (PI3K)-Akt pathway. Thus, mTOR inhibition by rapamycin or TSC1/2 results in increased PI3K-Akt activation. The death domain kinase receptor interacting protein 1 (RIP1) plays a key role in nuclear factor-kappaB (NF-kappaB) activation and also activates the PI3K-Akt pathway through unknown mechanisms. RIP1 has recently been found to be overexpressed in glioblastoma multiforme, the most common adult primary malignant brain tumor, but not in grade II to III glioma. Our data suggest that RIP1 activates PI3K-Akt using dual mechanisms by removing the two major brakes on PI3K-Akt activity. First, increased expression of RIP1 activates PI3K-Akt by interrupting the mTOR negative feedback loop. However, unlike other signals that regulate mTOR activity without affecting its level, RIP1 negatively regulates mTOR transcription via a NF-kappaB-dependent mechanism. The second mechanism used by RIP1 to activate PI3K-Akt is down-regulation of cellular PTEN levels, which appears to be independent of NF-kappaB activation. The clinical relevance of these findings is highlighted by the demonstration that RIP1 levels correlate with activation of Akt in glioblastoma multiforme. Thus, our study shows that RIP1 regulates key components of the PTEN-PI3K-Akt-mTOR pathway and elucidates a novel negative regulation of mTOR signaling at the transcriptional level by the NF-kappaB pathway. Our data suggest that the RIP1-NF-kappaB status of tumors may influence response to treatments targeting the PTEN-PI3K-mTOR signaling axis.
Department of Neurology, University of Texas Southwestern Medical Center, Dallas, TX 75390-8813, USA.
Seongmi
S
Park
Dawen
D
Zhao
Kimmo J
KJ
Hatanpaa
Bruce E
BE
Mickey
Debabrata
D
Saha
David A
DA
Boothman
Michael D
MD
Story
Eric T
ET
Wong
Sandeep
S
Burma
Maria-Magdalena
MM
Georgescu
Vivek M
VM
Rangnekar
Sandili S
SS
Chauncey
Amyn A
AA
Habib
D001932:Brain Neoplasms / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D005909:Glioblastoma / Q000235:genetics*; D006801:Humans; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D028861:Nuclear Pore Complex Proteins / Q000235:genetics* / Q000378:metabolism*; D051059:PTEN Phosphohydrolase / Q000235:genetics* / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D011494:Protein Kinases; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases
D016328:NF-kappa B; D028861:Nuclear Pore Complex Proteins; D051059:PTEN Phosphohydrolase; D019869:Phosphatidylinositol 3-Kinases; D011494:Protein Kinases; D051057:Proto-Oncogene Proteins c-akt; D016601:RNA-Binding Proteins; D058570:TOR Serine-Threonine Kinases; C119724:AGFG1 protein, human; C546842:MTOR protein, human; C494929:PTEN protein, human