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MTORC1 drives HIF-1? and VEGF-A signalling via multiple mechanisms involving 4E-BP1, S6K1 and STAT3.

ABSTRACT: Recent clinical trials using rapalogues in tuberous sclerosis complex show regression in volume of typically vascularised tumours including angiomyolipomas and subependymal giant cell astrocytomas. By blocking mechanistic/mammalian target of rapamycin complex 1 (mTORC1) signalling, rapalogue efficacy is likely to occur, in part, through suppression of hypoxia-inducible factors (HIFs) and vascular endothelial growth factors (VEGFs). We show that rapamycin reduces HIF-1? protein levels, and to a lesser extent VEGF-A levels, in renal cystadenoma cells in a Tsc2+/- mouse model. We established that mTORC1 drives HIF-1? protein accumulation through enhanced transcription of HIF-1? mRNA, a process that is blocked by either inhibition or knockdown of signal transducer and activation of transcription 3 (STAT3). Furthermore, we demonstrated that STAT3 is directly phosphorylated by mTORC1 on Ser727 during hypoxia, promoting HIF-1? mRNA transcription. mTORC1 also regulates HIF-1? synthesis on a translational level via co-operative regulation of both initiation factor 4E-binding protein 1 (4E-BP1) and ribosomal protein S6 kinase-1 (S6K1), whereas HIF-1? degradation remains unaffected. We therefore proposed that mTORC1 drives HIF-1? synthesis in a multifaceted manner through 4E-BP1/eIF4E, S6K1 and STAT3. Interestingly, we observed a disconnect between HIF-1? protein levels and VEGF-A expression. Although both S6K1 and 4E-BP1 regulate HIF-1? translation, VEGF-A is primarily under the control of 4E-BP1/eIF4E. S6K1 inhibition reduces HIF-1? but not VEGF-A expression, suggesting that mTORC1 mediates VEGF-A expression via both HIF-1?-dependent and -independent mechanisms. Our work has important implications for the treatment of vascularised tumours, where mTORC1 acts as a central mediator of STAT3, HIF-1?, VEGF-A and angiogenesis via multiple signalling mechanisms.

SUBMITTER: Dodd KM

PROVIDER: S-EPMC4172452 | biostudies-literature | 2015 Apr

REPOSITORIES: biostudies-literature

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mTORC1 drives HIF-1α and VEGF-A signalling via multiple mechanisms involving 4E-BP1, S6K1 and STAT3.

Dodd K M KM Yang J J Shen M H MH Sampson J R JR Tee A R AR

Oncogene 20140616 17

Recent clinical trials using rapalogues in tuberous sclerosis complex show regression in volume of typically vascularised tumours including angiomyolipomas and subependymal giant cell astrocytomas. By blocking mechanistic/mammalian target of rapamycin complex 1 (mTORC1) signalling, rapalogue efficacy is likely to occur, in part, through suppression of hypoxia-inducible factors (HIFs) and vascular endothelial growth factors (VEGFs). We show that rapamycin reduces HIF-1α protein levels, and to a l ...[more]

PMID: 24931163

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Project description:BackgroundThe airway epithelium is a major target tissue in respiratory infections, and its antiviral response is mainly orchestrated by the interferon regulatory factor-3 (IRF3), which subsequently induces type I (β) and III (λ) interferon (IFN) signalling. Dual specificity mitogen-activated protein kinase kinase (MEK) pathway contributes to epithelial defence, but its role in the regulation of IFN response in human primary airway epithelial cells (AECs) is not fully understood. Here, we studied the impact of a small-molecule inhibitor (MEKi) on the IFN response following challenge with two major respiratory viruses rhinovirus (RV2) and respiratory syncytial virus (RSVA2) and a TLR3 agonist, poly(I:C).MethodsThe impact of MEKi on viral load and IFN response was evaluated in primary AECs with or without a neutralising antibody against IFN-β. Quantification of viral load was determined by live virus assay and absolute quantification using qRT-PCR. Secretion of cytokines was determined by AlphaLISA/ELISA and expression of interferon-stimulated genes (ISGs) was examined by qRT-PCR and immunoblotting. A poly(I:C) model was also used to further understand the molecular mechanism by which MEK controls IFN response. AlphaLISA, siRNA-interference, immunoblotting, and confocal microscopy was used to investigate the effect of MEKi on IRF3 activation and signalling. The impact of MEKi on ERK and AKT signalling was evaluated by immunoblotting and AlphaLISA.ResultsHere, we report that pharmacological inhibition of MEK pathway augments IRF3-driven type I and III IFN response in primary human AECs. MEKi induced activation of PI3K-AKT pathway, which was associated with phosphorylation/inactivation of the translational repressor 4E-BP1 and activation of the protein synthesis regulator p70 S6 kinase, two critical translational effectors. Elevated IFN-β response due to MEKi was also attributed to decreased STAT3 activation, which consequently dampened expression of the transcriptional repressor of IFNB1 gene, PRDI-BF1. Augmented IFN response translated into inhibition of rhinovirus 2 replication in primary AECs but not respiratory syncytial virus A2.ConclusionsOur findings unveil MEK as a key molecular mechanism by which rhinovirus dampens the epithelial cell's antiviral response. Our study provides a better understanding of the role of signalling pathways in shaping the antiviral response and suggests the use of MEK inhibitors in anti-viral therapy against RV.

Dataset Information

MTORC1 drives HIF-1? and VEGF-A signalling via multiple mechanisms involving 4E-BP1, S6K1 and STAT3.

Publications

mTORC1 drives HIF-1α and VEGF-A signalling via multiple mechanisms involving 4E-BP1, S6K1 and STAT3.

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