PI3K/AKT signaling inhibits NOTCH1 lysosome‐mediated degradation

Abstract

The pathways of NOTCH and PI3K/AKT are dysregulated in about 60% and 48% of T-cell acute lymphoblastic leukemia (T-ALL) patients, respectively. In this context, they interact and cooperate in controlling tumor cell biology. Here, we propose a novel mechanism by which the PI3K/AKT pathway regulates NOTCH1 in T-ALL, starting from the evidence that the inhibition of PI3K/AKT signaling induced by treatment with LY294002 or transient transfection with a dominant negative AKT mutant downregulates NOTCH1 protein levels and activity, without affecting NOTCH1 transcription. We showed that the withdrawal of PI3K/AKT signaling was associated to NOTCH1 phosphorylation in tyrosine residues and monoubiquitination of NOTCH1 detected by Ubiquitin capture assay. Co-immunoprecipitation assay and colocalization analysis further showed that the E3 ubiquitin ligase c-Cbl interacts and monoubiquitinates NOTCH1, activating its lysosomal degradation. These results suggest that the degradation of NOTCH1 could represent a mechanism of control by which NOTCH1 receptors are actively removed from the cell surface. This mechanism is finely regulated by the PI3K/AKT pathway in physiological conditions. In pathological conditions characterized by PI3K/AKT hyperactivation, such as T-ALL, the excessive AKT signaling could lead to NOTCH1 signaling dysregulation. Therefore, a therapeutic strategy directed to PI3K/AKT in T-ALL could contemporaneously inhibit the dysregulated NOTCH1 signaling. © 2015 Wiley Periodicals, Inc.

IL-4-dependent Jagged1 expression/processing is associated with survival of chronic lymphocytic leukemia cells but not with Notch activation

“…The above evidence that the IL-4-induced increase in Notch1/2 activation was independent of Jag1 upregulation prompted us to investigate the molecular pathways responsible for this event. It has been shown that in T-ALL cells, a role in promoting deregulated Notch1 activation is played by an excessive PI3K/AKT signaling 53 . Based on these observations and given the hyperactivation of PI3Kδ/AKT signaling in CLL 38 , 49 and our evidence that IL-4 further increased PI3Kδ/AKT activity, we examined whether inhibiting this pathway could contrast the stimulatory effect of IL-4 on Notch1 expression.…”

“…Several of these events regulating Notch activation are in turn regulated by signaling pathways often aberrantly activated in tumor cells. In T-ALL cells, hyperactive PI3K/AKT signaling deregulates Notch1 activation inhibiting its lysosome-mediated degradation 53 . In breast cancer stem cells, high levels of prolyl-isomerase Pin1 sustain Notch signaling protecting Notch1 and Notch4 from proteasomal degradation 66 .…”

Multiple myeloma-derived Jagged ligands increases autocrine and paracrine interleukin-6 expression in bone marrow niche

“…Total cells protein were extracted with RIPA lysis buffer as previously reported [ 69 ]. Protein samples (40 μg) were run on a 4-12% NuPAGE gel (ThermoScientific), transferred onto a nitrocellulose membrane (Biorad), and blocked with 5% non-fat milk in TBS-T (20 mM Tris-Cl, pH 7.5, 150 mM NaCl, 0.05% Tween-20).…”

Cancer Cells Exploit Notch Signaling to Redefine a Supportive Cytokine Milieu

“…Besides this canonical Notch pathway, in oncogenesis and inflammation, it has been described a non-canonical Notch signaling which is γ-secretase independent ( 3 ). Notch signaling is tightly controlled by several mechanisms, including degradation mediated by the proteasome and lysosome machineries ( 4 , 5 ). The cancer-related aberrant activation of Notch pathway affects the biology of the single tumor cell and its interaction with the surrounding microenvironment ( 6 ).…”