Work

Notch1 Receptor Regulates AKT Protein Activation Loop (Thr308) Dephosphorylation through Modulation of the PP2A Phosphatase in Phosphatase and Tensin Homolog (PTEN)-null T-cell Acute Lymphoblastic Leukemia Cells

Year: 2013

Type: article

Abstract: Notch1 activating mutations occur in more than 50% of T-cell acute lymphoblastic leukemia (T-ALL) cases and increase expression of Notch1 target genes, some of which activate AKT. HES1 transcriptionally silences phosphatase and tensin homolog ( PTEN ), resulting in AKT activation, which is reversed by Notch1 inhibition with γ-secretase inhibitors (GSIs). Mutational loss of PTEN is frequent in T-ALL and promotes resistance to GSIs due to AKT activation. GSI treatments increased AKT-Thr 308 phosphorylation and signaling in PTEN-deficient, GSI-resistant T-ALL cell lines (Jurkat, CCRF-CEM, and MOLT3), suggesting that Notch1 represses AKT independent of its PTEN transcriptional effects. AKT-Thr 308 phosphorylation and downstream signaling were also increased by knocking down Notch1 in Jurkat (N1KD) cells. This was blocked by treatment with the AKT inhibitor perifosine. The PI3K inhibitor wortmannin and the protein phosphatase type 2A (PP2A) inhibitor okadaic acid both impacted AKT-Thr 308 phosphorylation to a greater extent in nontargeted control than N1KD cells, suggesting decreased dephosphorylation of AKT-Thr 308 by PP2A in the latter. Phosphorylations of AMP-activated protein kinaseα (AMPKα)-Thr 172 and p70S6K-Thr 389 , both PP2A substrates, were also increased in both N1KD and GSI-treated cells and responded to okadaic acid treatment. A transcriptional regulatory mechanism was implied because ectopic expression of dominant-negative mastermind-like protein 1 increased and wild-type HES1 decreased phosphorylation of these PP2A targets. This was independent of changes in PP2A subunit levels or in vitro PP2A activity, but was accompanied by decreased association of PP2A with AKT in N1KD cells. These results suggest that Notch1 can regulate PP2A dephosphorylation of critical cellular regulators including AKT, AMPKα, and p70S6K. Background: PTEN loss promotes resistance to γ-secretase inhibitors by increasing AKT signaling in T-cell acute lymphoblastic leukemia (T-ALL) with mutant activated Notch1. Results: Notch1 inhibition increases AKT phosphorylation and involves the PP2A phosphatase. Conclusion: Notch1 regulates PP2A dephosphorylation of AKT-Thr 308 by impacting association of PP2A with AKT. Significance: Better understanding of regulation of AKT signaling by Notch1 may lead to new therapies for T-ALL.

Source: Journal of Biological Chemistry

DOI: 10.1074/jbc.m113.451625

Authors: Eric C. Hales, Steven M. Orr, Amanda Larson Gedman, Jeffrey W. Taub, Larry H. Matherly

Institutions: Wayne State University, Children's Hospital of Michigan, The Barbara Ann Karmanos Cancer Institute

Language: English

Topic: PI3K/AKT/mTOR signaling in cancer

Subfield: Molecular Biology

Field: Biochemistry, Genetics and Molecular Biology

Domain: Life Sciences

SDG: Good health and well-being

Open Access status: hybrid

Estimated APC paid: $3,430