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 3

PTEN expression and activity are regulated by CK2 in PTEN-positive T-ALL.

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PTEN expression and activity are regulated by CK2 in PTEN-positive T-ALL...
(A) PTEN in vitro lipid phosphatase activity was determined after immunoprecipitation of endogenous PTEN from normal thymocytes (n = 5) and PTEN-positive primary leukemia cells (n = 4). PTEN activity was normalized to the levels of immunoprecipitated PTEN in each sample. (B) PTEN phosphorylation at S380 was determined by immunoblotting. Results shown are from 2 independent analyses representative of a total of 8 thymocyte samples and 14 PTEN-positive T-ALL specimens. T-ALL patient 14 showed no PI3K/Akt basal hyperactivation (see Table 1). (C) Immunoblot analysis of CK2α and CK2β expression. (D and E) CK2 levels in normal thymocytes (n = 3) and T-ALL primary cells (n = 4) were quantified by densitometry analysis regarding CK2α (D) and CK2β (E). See Table 1 for expression of CK2 in 12 total cases analyzed. (F) CK2 kinase activity in thymocyte (n = 6) and T-ALL (n = 5) sample lysates was measured in vitro. (G) TAIL7, HPB-ALL, or primary T-ALL cells were treated for 2.5 h with DMSO vehicle control or 25 μM TBB, and levels of expression and phosphorylation of indicated proteins were analyzed by immunoblotting. p-PTEN (sev) indicates PTEN phosphorylation at the cluster S380/T382/T383/S385. (H) TAIL7 cells treated for 2.5 h with DMSO vehicle control (untreated) or 25 μM TBB were lysed, and in vitro lipid phosphatase activity of immunoprecipitated PTEN was assessed in triplicate. Values in A, D–F, and H are mean ± SEM.