Glycogen synthase kinase 3β (GSK3β) phosphorylates and thereby regulates a wide range of protein substrates involved in diverse cellular functions. Some GSK3β substrates, such as c-Myc and Snail, are nuclear transcription factors, suggesting the possibility that GSK3β function is controlled through its nuclear localization. Here, using ARPE-19 and MDA-MB-231 human cell lines, we found that inhibition of mTOR complex 1 (mTORC1) leads to partial redistribution of GSK3β from the cytosol to the nucleus and to a GSK3β-dependent reduction of the levels of both c-Myc and Snail. mTORC1 is known to be controlled by metabolic cues, such as by AMP-activated protein kinase (AMPK) or amino acid abundance, and we observed here that AMPK activation or amino acid deprivation promotes GSK3β nuclear localization in an mTORC1-dependent manner. GSK3β was detected on several distinct endomembrane compartments, including lysosomes. Consistently, disruption of late endosomes/lysosomes through a perturbation of RAS oncogene family member 7 (Rab7) resulted in loss of GSK3β from lysosomes and in enhanced GSK3β nuclear localization as well as GSK3β-dependent reduction of c-Myc levels. These findings indicate that the nuclear localization and function of GSK3β is suppressed by mTORC1 and suggest a link between metabolic conditions sensed by mTORC1 and GSK3β-dependent regulation of transcriptional networks controlling cellular biomass production.

Glycogen synthase kinase 3β (GSK3β) phosphorylates and regulates a wide range of substrates involved in diverse cellular functions. Some GSK3β substrates, such as c-myc and snail, are nuclear-resident transcription factors, suggesting possible control of GSK3β function by regulation of its nuclear localization. Inhibition of mechanistic target of rapamycin (mTORC1) led to partial redistribution of GSK3β from the cytosol to the nucleus, and GSK3β-dependent reduction of the expression of c-myc and snail. mTORC1 is controlled by metabolic cues, such as by AMP-activated protein kinase (AMPK) or amino acid abundance. Indeed AMPK activation or amino acid deprivation promoted GSK3β nuclear localization in an mTORC1-dependent manner. GSK3β was detected in several distinct endomembrane compartments, including lysosomes. Consistently, disruption of late endosomes/lysosomes through perturbation of Rab7 resulted in loss of GSK3β from lysosomes, and enhanced GSK3β nuclear localization as well as GSK3β-dependent reduction of c-myc levels. This indicates that GSK3β nuclear localization and function is suppressed by mTORC1, and suggests a new link between metabolic conditions sensed by mTORC1 and GSK3β-dependent regulation of transcriptional networks controlling biomass production.Summary statement (15-30 words)GSK3β nuclear localization and function is negatively regulated by the metabolic and mitogenic sensor mTORC1. mTORC1 control of GSK3β localization requires Rab7 and lysosomal membrane traffic.

The Epidermal Growth Factor (EGF) Receptor (EGFR) is a receptor tyrosine kinase that when deregulated can drive tumor growth and can also contribute to drug resistance. Upon binding its ligand EGF, EGFR triggers the activation of many signaling pathways including phosphatidylinpositol‐3‐kinase (PI3K)/Akt, Ras‐Erk, signal transducer and activator of transcription (STAT), and phospholipase C γ1 (PLCγ1). EGFR may also control DNA repair mechanisms, although this phenomenon this remains poorly understood. Control of DNA repair by EGFR may be particularly relevant in the context of action of and resistance to anti‐cancer drugs that cause DNA damage (e.g. cisplatin). We examined how acute activation (10–30 min) of EGFR by ligand stimulation regulates DNA damage and repair responses induced by chronic (16 h) cisplatin treatment. To do so, we examined various markers of DNA damage and repair such as γH2AX and 53BP1. We observed that as little as 10 min of EGF stimulation is sufficient to elicit remodelling of DNA damage and repair markers such as γH2AX in chronic cisplatin‐treated cells. This indicates that acute EGFR activation triggers signaling pathway(s) that control the DNA damage response and/or DNA repair. Using these methods, we dissected the contribution of various EGFR signaling pathways and membrane traffic phenomena to this EGFR‐dependent control of DNA repair. This work may reveal new ways to enhance the efficacy of existing chemotherapies such as cisplatin for cancer treatment.Support or Funding InformationThis work was supported by a Project Grant and a New Investigator Salary Award from the Canadian Institutes of Health Research (CIHR) to C.N.AThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The EGFR is an oncogene that when dysregulated, can cause tumour progression. Upon binding ligand, EGFR triggers activation of many signalling pathways including PI3K/Akt, RasErk, STAT, and PLCγ1. EGFR may also control DNA repair mechanism, although this remains poorly understood. Control of DNA repair by EGFR may be particularly relevant in the context of action and resistance of cancer drugs that cause DNA damage (eg. Cisplatin). I have examined how acute activation (10-30 minutes) of EGFR regulates DNA repair induced by cisplatin treatments and by examination of repair-markers such as γH2AX. I observed that as little as 10 minutes of EGF stimulation is sufficient to elicit remodelling of γH2AX in chronic cisplatin-treated cells. Using these methods, I dissected the EGFR signals and membrane traffic phenomena required for EGFR-dependent control of DNA repair. This work may reveal new ways to enhance the efficacy of existing chemotherapies, such as cisplatin, for cancer treatment.

The EGFR is an oncogene that when dysregulated, can cause tumour progression. Upon binding ligand, EGFR triggers activation of many signalling pathways including PI3K/Akt, RasErk, STAT, and PLCγ1. EGFR may also control DNA repair mechanism, although this remains poorly understood. Control of DNA repair by EGFR may be particularly relevant in the context of action and resistance of cancer drugs that cause DNA damage (eg. Cisplatin). I have examined how acute activation (10-30 minutes) of EGFR regulates DNA repair induced by cisplatin treatments and by examination of repair-markers such as γH2AX. I observed that as little as 10 minutes of EGF stimulation is sufficient to elicit remodelling of γH2AX in chronic cisplatin-treated cells. Using these methods, I dissected the EGFR signals and membrane traffic phenomena required for EGFR-dependent control of DNA repair. This work may reveal new ways to enhance the efficacy of existing chemotherapies, such as cisplatin, for cancer treatment.

Glycogen synthase kinase 3β (GSK3β) is a serine/threonine kinase that regulates numerous cellular processes such as apoptosis, self‐renewal, growth, and metabolism. GSK3β phosphorylates over 100 substrates ranging from cytosolic to nuclear substrate targets, including c‐myc, a key ongogenic transcription factor, leading to control of c‐myc stability. GSK3β is itself regulated by phosphorylation on S9 by signals such as Akt (activated within the phosphatidylinositol‐3kinase, PI3K, signaling pathway), resulting in reduced GSK3β kinase activity. Given the wide range of substrates and the incomplete regulation of GSK3β by S9 phosphorylation, it is likely that other mechanisms gate GSK3β function.GSK3β may be localized within different cellular compartments such early endosomes, the nucleus, and in multivesicular bodies. However, how GSK3β localization is regulated, and how this may control GSK3β function is poorly understood, which we have examined here. Specifically, we examined how mTORC1, a key cellular sensor of mitogenic and metabolic signals, controls GSK3β localization and function. Using pharmacological inhibitors of mTORC1 and GSK3β, as well as siRNA gene silencing approaches, we uncovered that GSK3β‐mediated c‐myc degradation is negatively regulated by mTORC1. Using fluorescence microscopy approaches, we find that inhibition of PI3K‐Akt‐mTOR signaling axis, and metabolic insufficiency (e.g. amino acid deficiency), elicit GSK3β nuclear translocation from the cytosol, suggesting that mTORC1 mediates GSK3β nucleocytoplasmic shuttling. Consistent with regulation of GSK3β by mTORC1, we also uncovered that GSK3β localizes to LAMP1 positive late endosome/lysosomes, and perturbations of late endosome/lysosome membrane traffic impacted nuclear localization of GSK3β. This suggests that late endosomes/lysosomal compartments serve as organizing platforms, integrating mitogenic and metabolic signals via mTORC1 to elicit GSK3β cytosolic retention, thus impacting access of GSK3β to nuclear targets and controlling c‐myc degradation. Understanding how mTORC1 dependent signals regulate GSK3b subcellular localization to control GSK3β function may give useful insight to the development of drugs and therapies targeting GSK3β for the treatment of cancer cell growth and survival.Support or Funding InformationThis work is supported by a Discovery Grant from the Natural Science and Engineering Research Council (of Canada), an Early Researcher Award from the Ontario Ministry of Research, Innovation and Science, and a New Investigator Award from the Canadian Institutes of Health Research to C.N.A.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.