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MTOR kinase inhibition causes feedback-dependent biphasic regulation of AKT signaling.

ABSTRACT: UNLABELLED:mTOR kinase inhibitors block mTORC1 and mTORC2 and thus do not cause the mTORC2 activation of AKT observed with rapamycin. We now show, however, that these drugs have a biphasic effect on AKT. Inhibition of mTORC2 leads to AKT serine 473 (S473) dephosphorylation and a rapid but transient inhibition of AKT T308 phosphorylation and AKT signaling. However, inhibition of mTOR kinase also relieves feedback inhibition of receptor tyrosine kinases (RTK), leading to subsequent phosphoinositide 3-kinase activation and rephosphorylation of AKT T308 sufficient to reactivate AKT activity and signaling. Thus, catalytic inhibition of mTOR kinase leads to a new steady state characterized by profound suppression of mTORC1 and accumulation of activated AKT phosphorylated on T308, but not S473. Combined inhibition of mTOR kinase and the induced RTKs fully abolishes AKT signaling and results in substantial cell death and tumor regression in vivo. These findings reveal the adaptive capabilities of oncogenic signaling networks and the limitations of monotherapy for inhibiting feedback-regulated pathways. SIGNIFICANCE:The results of this study show the adaptive capabilities of oncogenic signaling networks, as AKT signaling becomes reactivated through a feedback-induced AKT species phosphorylated on T308 but lacking S473. The addition of RTK inhibitors can prevent this reactivation of AKT signaling and cause profound cell death and tumor regression in vivo, highlighting the possible need for combinatorial approaches to block feedback-regulated pathways.

SUBMITTER: Rodrik-Outmezguine VS

PROVIDER: S-EPMC3227125 | biostudies-literature | 2011 Aug

REPOSITORIES: biostudies-literature

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mTOR kinase inhibition causes feedback-dependent biphasic regulation of AKT signaling.

Rodrik-Outmezguine Vanessa S VS Rodrik-Outmezguine Vanessa S VS Chandarlapaty Sarat S Pagano Nen C NC Poulikakos Poulikos I PI Scaltriti Maurizio M Moskatel Elizabeth E Baselga José J Guichard Sylvie S Rosen Neal N

Cancer discovery 20110617 3

<h4>Unlabelled</h4>mTOR kinase inhibitors block mTORC1 and mTORC2 and thus do not cause the mTORC2 activation of AKT observed with rapamycin. We now show, however, that these drugs have a biphasic effect on AKT. Inhibition of mTORC2 leads to AKT serine 473 (S473) dephosphorylation and a rapid but transient inhibition of AKT T308 phosphorylation and AKT signaling. However, inhibition of mTOR kinase also relieves feedback inhibition of receptor tyrosine kinases (RTK), leading to subsequent phospho ...[more]

PMID: 22140653

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Project description:BACKGROUND:The intermediate-conductance Ca2+-activated K+ channel KCa3.1 was recently shown to control the phenotype switch of reactive astrogliosis (RA) in Alzheimer's disease (AD). METHODS:KCa3.1 channels expression and cell localization in the brains of AD patients and APP/PS1 mice model were measured by immunoblotting and immunostaining. APP/PS1 mice and KCa3.1-/-/APP/PS1 mice were subjected to Morris water maze test to evaluate the spatial memory deficits. Glia activation and neuron loss was measured by immunostaining. Fluo-4AM was used to measure cytosolic Ca2+ level in ?-amyloid (A?) induced reactive astrocytes in vitro. RESULTS:KCa3.1 expression was markedly associated with endoplasmic reticulum (ER) stress and unfolded protein response (UPR) in both A?-stimulated primary astrocytes and brain lysates of AD patients and APP/PS1 AD mice. The KCa3.1 channel was shown to regulate store-operated Ca2+ entry (SOCE) through an interaction with the Ca2+ channel Orai1 in primary astrocytes. Gene deletion or pharmacological blockade of KCa3.1 protected against SOCE-induced Ca2+ overload and ER stress via the protein kinase B (AKT) signaling pathway in astrocytes. Importantly, gene deletion or blockade of KCa3.1 restored AKT/mechanistic target of rapamycin signaling both in vivo and in vitro. Consistent with these in vitro data, expression levels of the ER stress markers 78-kDa glucose-regulated protein and CCAAT/enhancer-binding protein homologous protein, as well as that of the RA marker glial fibrillary acidic protein were increased in APP/PS1 AD mouse model. Elimination of KCa3.1 in KCa3.1-/-/APP/PS1 mice corrected these abnormal responses. Moreover, glial activation and neuroinflammation were attenuated in the hippocampi of KCa3.1-/-/APP/PS1 mice, as compared with APP/PS1 mice. In addition, memory deficits and neuronal loss in APP/PS1 mice were reversed in KCa3.1-/-/APP/PS1 mice. CONCLUSIONS:Overall, these results suggest that KCa3.1 is involved in the regulation of Ca2+ homeostasis in astrocytes and attenuation of the UPR and ER stress, thus contributing to memory deficits and neuronal loss.

Dataset Information

MTOR kinase inhibition causes feedback-dependent biphasic regulation of AKT signaling.

Publications

mTOR kinase inhibition causes feedback-dependent biphasic regulation of AKT signaling.

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