PTEN posttranslational inactivation and hyperactivation of the PI3K/Akt pathway sustain primary T cell leukemia viability
Ana Silva, … , Angelo A. Cardoso, Joao T. Barata
Ana Silva, … , Angelo A. Cardoso, Joao T. Barata
Published October 1, 2008
Citation Information: J Clin Invest. 2008;118(11):3762-3774. https://doi.org/10.1172/JCI34616.
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Research Article Hematology

PTEN posttranslational inactivation and hyperactivation of the PI3K/Akt pathway sustain primary T cell leukemia viability

Abstract

Mutations in the phosphatase and tensin homolog (PTEN) gene leading to PTEN protein deletion and subsequent activation of the PI3K/Akt signaling pathway are common in cancer. Here we show that PTEN inactivation in human T cell acute lymphoblastic leukemia (T-ALL) cells is not always synonymous with PTEN gene lesions and diminished protein expression. Samples taken from patients with T-ALL at the time of diagnosis very frequently showed constitutive hyperactivation of the PI3K/Akt pathway. In contrast to immortalized cell lines, most primary T-ALL cells did not harbor PTEN gene alterations, displayed normal PTEN mRNA levels, and expressed higher PTEN protein levels than normal T cell precursors. However, PTEN overexpression was associated with decreased PTEN lipid phosphatase activity, resulting from casein kinase 2 (CK2) overexpression and hyperactivation. In addition, T-ALL cells had constitutively high levels of ROS, which can also downmodulate PTEN activity. Accordingly, both CK2 inhibitors and ROS scavengers restored PTEN activity and impaired PI3K/Akt signaling in T-ALL cells. Strikingly, inhibition of PI3K and/or CK2 promoted T-ALL cell death without affecting normal T cell precursors. Overall, our data indicate that T-ALL cells inactivate PTEN mostly in a nondeletional, posttranslational manner. Pharmacological manipulation of these mechanisms may open new avenues for T-ALL treatment.

Authors

Ana Silva, J. Andrés Yunes, Bruno A. Cardoso, Leila R. Martins, Patrícia Y. Jotta, Miguel Abecasis, Alexandre E. Nowill, Nick R. Leslie, Angelo A. Cardoso, Joao T. Barata

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Figure 5

Inhibition of PI3K induces selective cell death of T-ALL cells displaying hyperactivation of the PI3K/Akt pathway and does not affect normal T cell precursors.

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Inhibition of PI3K induces selective cell death of T-ALL cells displayin...
(A) Normal thymocytes (n = 10) and primary leukemia cells (n = 15) were treated with 10 or 25 μM LY294002 for 48 h. Viability index to control untreated samples is shown. (B) Annexin V–FITC versus propidium iodide (PI) dot plots of representative cases. Percent viable cells are shown. (C) PTEN-negative (T-ALL patient 01) and PTEN-positive (T-ALL patient 05) patient samples were analyzed for viability by forward scatter–side scatter distribution. Numbers within plots indicate percent viable cells. FSC, forward scatter; SSC, side scatter. (D and E) T-ALL patients were reevaluated for PI3K/Akt pathway activation by Western blot analysis of phosphorylated Akt, GSK-3β, and PTEN. (F) T-ALL patient 19, with basal PI3K/Akt hyperactivation, and T-ALL patient 08, without such activation, were cultured with 2 different doses of LY294002 and analyzed for viability after 24 h. Also shown is 1 thymocyte sample as a control for unresponsiveness to LY294002 treatment. Numbers within plots indicate percent viable cells for each condition. (G) Responsiveness to LY294002 treatment at 24 h of culture of T-ALL samples without PI3K/Akt constitutive activation (negative) and with hyperactivation of the pathway (positive). Results are representative of 2 independent experiments. (H) Primary leukemia cells were cultured for 48 h in the presence of TBB (n = 12) or DRB (n = 9). TBB and DRB showed no significant effect on viability of normal thymocytes (n = 7). Data in A, G, and H are mean ± SEM. “Medium” denotes culture medium with DMSO vehicle control.