Regulatory Effects of Mammalian Target of Rapamycin-mediated Signals in the Generation of Arsenic Trioxide Responses

• Published in: The Journal of biological chemistry 2008-01, Vol.283 (4), p.1992-2001
• Main Authors: Altman, Jessica K., Yoon, Patrick, Katsoulidis, Efstratios, Kroczynska, Barbara, Sassano, Antonella, Redig, Amanda J., Glaser, Heather, Jordan, Alison, Tallman, Martin S., Hay, Nissim, Platanias, Leonidas C.
• Format: Article
• Language: English
• Subjects: Antineoplastic Agents - pharmacology; Antineoplastic Agents - therapeutic use; Apoptosis - drug effects; Apoptosis - genetics; Arsenic Trioxide; Arsenicals - pharmacology; Arsenicals - therapeutic use; Eukaryotic Initiation Factors - genetics; Eukaryotic Initiation Factors - metabolism; Gene Deletion; Humans; K562 Cells; Leukemia, Myeloid, Acute - drug therapy; Leukemia, Myeloid, Acute - genetics; Leukemia, Myeloid, Acute - metabolism; Neoplastic Stem Cells - metabolism; Oxides - pharmacology; Oxides - therapeutic use; Protein Kinases - genetics; Protein Kinases - metabolism; Proto-Oncogene Proteins c-akt - genetics; Proto-Oncogene Proteins c-akt - metabolism; Ribosomal Protein S6 Kinases - genetics; Ribosomal Protein S6 Kinases - metabolism; RNA, Small Interfering - genetics; Signal Transduction - drug effects; Signal Transduction - genetics; TOR Serine-Threonine Kinases; Tuberous Sclerosis Complex 2 Protein; Tumor Suppressor Proteins - genetics; Tumor Suppressor Proteins - metabolism; U937 Cells
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M705227200

Arsenic trioxide (As2O3) is a potent inducer of apoptosis of leukemic cells in vitro and in vivo, but the mechanisms that mediate such effects are not well understood. We provide evidence that the Akt kinase is phosphorylated/activated during treatment of leukemia cells with As2O3, to regulate downstream engagement of mammalian target of rapamycin (mTOR) and its effectors. Using cells with targeted disruption of both the Akt1 and Akt2 genes, we found that induction of arsenic trioxide-dependent apoptosis is strongly enhanced in the absence of these kinases, suggesting that Akt1/Akt2 are activated in a negative feedback regulatory manner, to control generation of As2O3 responses. Consistent with this, As2O3-dependent pro-apoptotic effects are enhanced in double knock-out cells for both isoforms of the p70 S6 kinase (S6k1/S6k2), a downstream effector of Akt and mTOR. On the other hand, As2O3-dependent induction of apoptosis is diminished in cells with targeted disruption of TSC2, a negative upstream effector of mTOR. In studies using primary hematopoietic progenitors from patients with acute myeloid leukemia, we found that pharmacological inhibition of mTOR enhances the suppressive effects of arsenic trioxide on leukemic progenitor colony formation. Moreover, short interfering RNA-mediated inhibition of expression of the negative downstream effector, translational repressor 4E-BP1, partially reverses the effects of As2O3. Altogether, these data provide evidence for a key regulatory role of the Akt/mTOR pathway in the generation of the effects of As2O3, and suggest that targeting this signaling cascade may provide a novel therapeutic approach to enhance the anti-leukemic properties of As2O3.