Phosphorylation Of Transcription Factor EB Research Articles

Role of TFEB-autophagy lysosomal pathway in palmitic acid induced renal tubular epithelial cell injury

Lysosomal dysfunction and impaired autophagic flux are involved in the pathogenesis of lipotoxicity in the kidney. Here, we investigated the role of transcription factor EB (TFEB), a master regulator of autophagy-lysosomal pathway, in palmitic acid induced renal tubular epithelial cells injury. We examined lipid accumulation, autophagic flux, expression of Ps211-TFEB, and nuclear translocation of TFEB in HK-2 cells overloaded with palmitic acid (PA). By utilizing immunohistochemistry, we detected TFEB expression in renal biopsy tissues from patients with diabetic nephropathy and normal renal tissue adjacent to surgically removed renal carcinoma (controls), as well as kidney tissues from rat fed with high-fat diet (HFD) and low-fat diet (LFD). We found significant lipid accumulation, increased apoptosis, accompanied with elevated Ps211-TFEB, decreased nuclear TFEB, reduced lysosome biogenesis and insufficient autophagy in HK-2 cells treated with PA. Kidney tissues from patients with diabetic nephropathy had lower nuclear and total levels of TFEB than that in control kidney tissues. Level of renal nuclear TFEB in HFD rats was also lower than that in LFD rats. Exogenous overexpression of TFEB increased the nuclear TFEB level in HK-2 cells treated with PA, promoted lysosomal biogenesis, improved autophagic flux, reduced lipid accumulation and apoptosis. Our results collectively indicate that PA is a strong inducer for TFEB phosphorylation modification at ser211 accompanied with lower nuclear translocation of TFEB. Impairment of TFEB-mediated lysosomal biogenesis and function by palmitic acid may lead to insufficient autophagy and promote HK-2 cells injury.

PTPRC Inhibits Ferroptosis of Osteosarcoma Cells via Blocking TFEB/FTH1 Signaling.

Protein tyrosine phosphatase receptor type C (PTPRC) is reported to function as an oncogenic role in various cancer. However, the studies on the roles of PTPRC in osteosarcoma (OS) are limited. This study aimed to explore the potentials of PTPRC in OS. mRNA levels were detected by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Protein expression was detected by western blot. Lysosome biogenesis was determined using immunofluorescence. The binding sites of transcription factor EB (TFEB) on the promoter of ferritin heavy chain 1 (FTH1) were predicted by the online dataset JASPAR and confirmed by luciferase and chromatin immunoprecipitation (ChIP) assays. Cell death was determined using propidium iodide (PI) and TdT-mediated dUTP nick-end labeling (TUNEL) staining. The results showed that PTPRC was significantly overexpressed in OS tissues and cells. PTPRC knockdown promoted the phosphorylation and nuclear translocation of TFEB. Moreover, PTPRC knockdown markedly promoted lysosome biogenesis and the accumulation of ferrous ion (Fe2+), whereas decreased the release of glutathione (GSH). Besides, PTPRC knockdown significantly promoted autophagy and downregulated mRNA expression of FTH1 and ferritin light chain (FTL). Additionally, TFEB transcriptionally inactivated FTH1. PTPRC knockdown significantly promoted the ferroptosis of OS cells, which was markedly alleviated by TFEB shRNA. Taken together, PTPRC knockdown-mediated TFEB phosphorylation and translocation dramatically promoted lysosome biogenesis, ferritinophagy, as well as the ferroptosis of OS cells via regulating FTH1/FTL signaling. Therefore, PTPRC/TFEB/FTH1 signaling may be a potential target for OS.

Deregulation of mTORC1-TFEB axis in human iPSC model of GBA1-associated Parkinson's disease.

Mutations in the GBA1 gene are the single most frequent genetic risk factor for Parkinson's disease (PD). Neurodegenerative changes in GBA1-associated PD have been linked to the defective lysosomal clearance of autophagic substrates and aggregate-prone proteins. To elucidate novel mechanisms contributing to proteinopathy in PD, we investigated the effect of GBA1 mutations on the transcription factor EB (TFEB), the master regulator of the autophagy-lysosomal pathway (ALP). Using PD patients' induced-pluripotent stem cells (iPSCs), we examined TFEB activity and regulation of the ALP in dopaminergic neuronal cultures generated from iPSC lines harboring heterozygous GBA1 mutations and the CRISPR/Cas9-corrected isogenic controls. Our data showed a significant decrease in TFEB transcriptional activity and attenuated expression of many genes in the CLEAR network in GBA1 mutant neurons, but not in the isogenic gene-corrected cells. In PD neurons, we also detected increased activity of the mammalian target of rapamycin complex1 (mTORC1), the main upstream negative regulator of TFEB. Increased mTORC1 activity resulted in excess TFEB phosphorylation and decreased nuclear translocation. Pharmacological mTOR inhibition restored TFEB activity, decreased ER stress and reduced α-synuclein accumulation, indicating improvement of neuronal protiostasis. Moreover, treatment with the lipid substrate reducing compound Genz-123346, decreased mTORC1 activity and increased TFEB expression in the mutant neurons, suggesting that mTORC1-TFEB alterations are linked to the lipid substrate accumulation. Our study unveils a new mechanism contributing to PD susceptibility by GBA1 mutations in which deregulation of the mTORC1-TFEB axis mediates ALP dysfunction and subsequent proteinopathy. It also indicates that pharmacological restoration of TFEB activity could be a promising therapeutic approach in GBA1-associated neurodegeneration.

TFEB and TFE3 drive kidney cystogenesis andtumorigenesis.

Birt-Hogg-Dubé (BHD) syndrome is an inherited familial cancer syndrome characterized by the development of cutaneous lesions, pulmonary cysts, renal tumors and cysts and caused by loss-of-function pathogenic variants in the gene encoding the tumor-suppressor protein folliculin (FLCN). FLCN acts as a negative regulator of TFEB and TFE3 transcription factors, master controllers of lysosomal biogenesis and autophagy, by enabling their phosphorylation by the mechanistic Target Of Rapamycin Complex 1 (mTORC1). We have previously shown that deletion of Tfeb rescued the renal cystic phenotype of kidney-specific Flcn KO mice. Using Flcn/Tfeb/Tfe3 double and triple KO mice, we now show that both Tfeb and Tfe3 contribute, in a differential and cooperative manner, to kidney cystogenesis. Remarkably, the analysis of BHD patient-derived tumor samples revealed increased activation of TFEB/TFE3-mediated transcriptional program and silencing either of the two genes rescued tumorigenesis in human BHD renal tumor cell line-derived xenografts (CDXs). Our findings demonstrate in disease-relevant models that both TFEB and TFE3 are key drivers of renal tumorigenesis and suggest novel therapeutic strategies based on the inhibition of these transcription factors.

P38 MAPK-dependent phosphorylation of TFEB promotes monocyte-to-macrophage differentiation.

The transcription factor EB (TFEB) regulates energy homeostasis and cellular response to a wide variety of stress conditions, including nutrient deprivation, oxidative stress, organelle damage, and pathogens. Here we identify S401 as a novel phosphorylation site within the TFEB proline-rich domain. Phosphorylation of S401 increases significantly in response to oxidative stress, UVC light, growth factors, and LPS, whereas this increase is prevented by p38 MAPK inhibition or depletion, revealing a new role for p38 MAPK in TFEB regulation. Mutation of S401 in THP1 cells demonstrates that the p38 MAPK/TFEB pathway plays a particularly relevant role during monocyte differentiation into macrophages. TFEB-S401A monocytes fail to upregulate the expression of multiple immune genes in response to PMA-induced differentiation, including critical cytokines, chemokines, and growth factors. Polarization of M0 macrophages into M1 inflammatory macrophages is also aberrant in TFEB-S401A cells. These results indicate that TFEB-S401 phosphorylation links differentiation signals to the transcriptional control of monocyte differentiation.

Fagopyrum dibotrys extract alleviates hepatic steatosis and insulin resistance, and alters autophagy and gut microbiota diversity in mouse models of high-fat diet-induced non-alcoholic fatty liver disease.

Non-alcoholic fatty liver disease (NAFLD) is a major global health concern with increasing prevalence, with a lack of currently available effective treatment options; thus, the investigation of novel therapeutic approaches is necessary. The study aimed to investigate the outcomes and mechanisms of action of Fagopyrum dibotrys extract (FDE) in a high-fat diet (HFD)-induced mouse model of obesity. The findings showed that FDE supplementation attenuated glucose tolerance, insulin resistance (IR), hepatic steatosis, and abnormal lipid metabolism. In addition, FDE also promoted autophagic activity and inhibited the phosphorylation of transcription factor EB in HFD-fed mice. Furthermore, gut microbiota characterization via 16S rRNA sequencing revealed that the supplementation of FDE increased Bacteroidetes and Verrucomicrobia populations while decreased Firmicutes, thus modifying the gut microbiome. FDE also increased the relative abundance of Akkermansia. Our findings suggest that FDE may protect against HFD-induced NAFLD by activating autophagy and alleviating dysbiosis in the gut microbiome. FDE may be beneficial as a nutraceutical treatment for NAFLD.

Mesenchymal stem cells exosomal let-7a-5p improve autophagic flux and alleviate liver injury in acute-on-chronic liver failure by promoting nuclear expression of TFEB

Acute-on-chronic liver failure is a distinct clinical syndrome characterized by a dysregulated immune response and extensive hepatocyte death without satisfactory therapies. As a cytoplasmic degradative and quality-control process, autophagy was implicated in maintaining intracellular homeostasis, and decreased hepatic autophagy was found in many liver diseases and contributes to disease pathogenesis. Previously, we identified the therapeutic potential of mesenchymal stem cells (MSCs) in ACLF patients; however, the intrinsic mechanisms are incompletely understood. Herein, we showed that MSCs restored the impaired autophagic flux and alleviated liver injuries in ACLF mice, but these effects were abolished when autophago-lysosomal maturation was inhibited by leupeptin (leu), suggesting that MSCs exerted their hepatoprotective function in a pro-autophagic dependent manner. Moreover, we described a connection between transcription factor EB (TFEB) and autophagic activity in this context, as evidenced by increased nuclei translocation of TFEB elicited by MSCs were capable of promoting liver autophagy. Mechanistically, we confirmed that let-7a-5p enriched in MSCs derived exosomes (MSC-Exo) could activate autophagy by targeting MAP4K3 to reduce TFEB phosphorylation, and MAP4K3 knockdown partially attenuates the effect of anti-let-7a-5p oligonucleotide via decreasing the inflammatory response, in addition, inducing autophagy. Altogether, these findings revealed that the hepatoprotective effect of MSCs may partially profit from its exosomal let-7a-5p mediating autophagy repairment, which may provide new insights for the therapeutic target of ACLF treatment.

Covalent JNK Inhibitor, JNK-IN-8, Suppresses Tumor Growth in Triple-Negative Breast Cancer by Activating TFEB- and TFE3-Mediated Lysosome Biogenesis and Autophagy

The heterogeneity and aggressiveness of triple-negative breast cancer (TNBC) contribute to its early recurrence and metastasis. Despite substantial research to identify effective therapeutic targets, TNBC remains elusive in terms of improving patient outcomes. Here, we report that a covalent JNK inhibitor, JNK-IN-8, suppresses TNBC growth both in vitro and in vivo. JNK-IN-8 reduced colony formation, cell viability, and organoid growth in vitro and slowed patient-derived xenograft and syngeneic tumor growth in vivo. Cells treated with JNK-IN-8 exhibited large, cytoplasmic vacuoles with lysosomal markers. To examine the molecular mechanism of this phenotype, we looked at the master regulators of lysosome biogenesis and autophagy transcription factor EB (TFEB) and TFE3. JNK-IN-8 inhibited TFEB phosphorylation and induced nuclear translocation of unphosphorylated TFEB and TFE3. This was accompanied by an upregulation of TFEB/TFE3 target genes associated with lysosome biogenesis and autophagy. Depletion of both TFEB and TFE3 diminished the JNK-IN-8-driven upregulation of lysosome biogenesis and/or autophagy markers. TFEB and TFE3 are phosphorylated by a number of kinases, including mTOR. JNK-IN-8 reduced phosphorylation of mTOR targets in a concentration-dependent manner. Knockout of JNK1 and/or JNK2 had no impact on TFEB/TFE3 activation or mTOR inhibition by JNK-IN-8 but inhibited colony formation. Similarly, reexpression of either wildtype or drug-nonbinding JNK (C116S) in JNK knockout cells did not reverse JNK-IN-8-induced TFEB dephosphorylation. In summary, JNK-IN-8 induced lysosome biogenesis and autophagy by activating TFEB/TFE3 via mTOR inhibition independently of JNK. Together, these findings demonstrate the efficacy of JNK-IN-8 as a targeted therapy for TNBC and reveal its novel lysosome- and autophagy-mediated mechanism of action.

MEK1/2 inhibition rescues neurodegeneration by TFEB-mediated activation of autophagic lysosomal function in a model of Alzheimer’s Disease

Alzheimer’s Disease (AD) is a progressive neurodegenerative disorder, which is characterized by cognitive deficit due to synaptic loss and neuronal death. Extracellular amyloid β plaques are one of the pathological hallmarks of AD. The autophagic lysosomal pathway is the essential mechanism to maintain cellular homeostasis by driving clearance of protein aggregates and is dysfunctional in AD. Here, we showed that inhibiting MEK/ERK signaling using a clinically available MEK1/2 inhibitor, trametinib (GSK1120212, SNR1611), induces the protection of neurons through autophagic lysosomal activation mediated by transcription factor EB (TFEB) in a model of AD. Orally administered trametinib recovered impaired neural structures, cognitive functions, and hippocampal long-term potentiation (LTP) in 5XFAD mice. Trametinib also reduced Aβ deposition via induction of autophagic lysosomal activation. RNA-sequencing analysis revealed upregulation of autophagic lysosomal genes by trametinib administration. In addition, trametinib inhibited TFEB phosphorylation at Ser142 and promoted its nuclear translocation, which in turn induced autophagic lysosomal related genes, indicating that trametinib activates the autophagic lysosomal process through TFEB activation. From these observations, we concluded that MEK inhibition provides neuronal protection from the Aβ burden by increasing autophagic lysosomal activity. Thus, MEK inhibition may be an effective therapeutic strategy for AD.

GSK-3β inhibition elicits a neuroprotection by restoring lysosomal dysfunction in neurons via facilitation of TFEB nuclear translocation after ischemic stroke

Lysosomal dysfunction is an essential pathogenesis of autophagic neuronal injury after ischemic stroke. As a result of cerebral ischemia, transcription factor EB (TFEB) is greatly phosphorylated by prominently activated glycogen synthase kinase-3β (GSK-3β). This increased TFEB phosphorylation decreases its nuclear translocation and subsequently leads to reduced lysosomal biosynthesis, which ultimately results in lysosomal dysfunction. The present study is to investigate whether the lysosomal dysfunction in neurons can be restored to alleviate post-stroke damage by GSK-3β inhibition.The GSK-3β activity was inhibited by pre-treatment with CHIR-99021 (CHIR) for 3 days before middle cerebral artery occlusion (MCAO) surgery in rats. Besides, the lysosomal capacity was altered by pre-administration with Bafilomycin A1 (Baf-A1) and EN6, respectively. Twenty-four hours after MCAO/reperfusion, the penumbral tissues were obtained to detect the GSK-3β, cytoplasmic and nuclear TFEB, and proteins in autophagic/lysosomal pathway by western blot and immunofluorescence, respectively. Meanwhile, the infarct volume, neurological deficits and neuron survival were assessed to evaluate the neurological outcomes elicited by GSK-3β inhibition. The results demonstrated that the neurological injury could be significantly mitigated by GSK-3β inhibition in MCAO + CHIR group, compared with that in MCAO group. Moreover, CHIR-facilitated TFEB nuclear translocation in neurons was coupled with reinforced lysosomal activities and attenuated autophagic substrates. However, GSK-3β inhibition-induced neuroprotection was greatly counteracted by Baf-A1-weakened lysosomal capacity. Conversely, EN6-reinforced lysosomal activities further ameliorated the autophagic/lysosomal signaling, and synergistically alleviated the neurological damage upon GSK-3β inhibition after MCAO/reperfusion. Our data suggests that GSK-3β inhibition-augmented neuroprotection against ischemic stroke is elicited by restoring the lysosomal dysfunction in neurons.

TSC2 regulates lysosome biogenesis via a non-canonical RAGC and TFEB-dependent mechanism

Tuberous Sclerosis Complex (TSC) is caused by TSC1 or TSC2 mutations, resulting in hyperactivation of the mechanistic target of rapamycin complex 1 (mTORC1). Transcription factor EB (TFEB), a master regulator of lysosome biogenesis, is negatively regulated by mTORC1 through a RAG GTPase-dependent phosphorylation. Here we show that lysosomal biogenesis is increased in TSC-associated renal tumors, pulmonary lymphangioleiomyomatosis, kidneys from Tsc2+/− mice, and TSC1/2-deficient cells via a TFEB-dependent mechanism. Interestingly, in TSC1/2-deficient cells, TFEB is hypo-phosphorylated at mTORC1-dependent sites, indicating that mTORC1 is unable to phosphorylate TFEB in the absence of the TSC1/2 complex. Importantly, overexpression of folliculin (FLCN), a GTPase activating protein for RAGC, increases TFEB phosphorylation at the mTORC1 sites in TSC2-deficient cells. Overexpression of constitutively active RAGC is sufficient to relocalize TFEB to the cytoplasm. These findings establish the TSC proteins as critical regulators of lysosomal biogenesis via TFEB and RAGC and identify TFEB as a driver of the proliferation of TSC2-deficient cells.

C-Abl Inhibition Activates TFEB and Promotes Cellular Clearance in a Lysosomal Disorder.

SummaryThe transcription factor EB (TFEB) has emerged as a master regulator of lysosomal biogenesis, exocytosis, and autophagy, promoting the clearance of substrates stored in cells. c-Abl is a tyrosine kinase that participates in cellular signaling in physiological and pathophysiological conditions. In this study, we explored the connection between c-Abl and TFEB. Here, we show that under pharmacological and genetic c-Abl inhibition, TFEB translocates into the nucleus promoting the expression of its target genes independently of its well-known regulator, mammalian target of rapamycin complex 1. Active c-Abl induces TFEB phosphorylation on tyrosine and the inhibition of this kinase promotes lysosomal biogenesis, autophagy, and exocytosis. c-Abl inhibition in Niemann-Pick type C (NPC) models, a neurodegenerative disease characterized by cholesterol accumulation in lysosomes, promotes a cholesterol-lowering effect in a TFEB-dependent manner. Thus, c-Abl is a TFEB regulator that mediates its tyrosine phosphorylation, and the inhibition of c-Abl activates TFEB promoting cholesterol clearance in NPC models.

GSK-3β inhibition by curcumin mitigates amyloidogenesis via TFEB activation and anti-oxidative activity in human neuroblastoma cells

The translocation of transcription factor EB (TFEB) to the nucleus plays a pivotal role in the regulation of basic cellular processes, such as lysosome biogenesis and autophagy. Autophagy is an intracellular degradation system that delivers cytoplasmic constituents to the lysosome, which is important in maintaining cellular homeostasis during environmental stress. Furthermore, oxidative stress is a critical cause for the progression of neurodegenerative diseases. Curcumin has anti-oxidative and anti-inflammatory activities, and is expected to have potential therapeutic effects in various diseases. In this study, we demonstrated that curcumin regulated TFEB export signalling via inhibition of glycogen synthase kinase-3β (GSK-3β); GSK-3β was inactivated by curcumin, leading to reduced phosphorylation of TFEB. We further showed that H2O2-induced oxidative stress was reduced by curcumin via the Nrf2/HO-1 pathway in human neuroblastoma cells. In addition, we showed that curcumin induced the degradation of amyloidogenic proteins, including amyloid-β precursor protein and α-synuclein, through the TFEB-autophagy/lysosomal pathway. In conclusion, curcumin regulates autophagy by controlling TFEB through the inhibition of GSK-3β, and increases antioxidant gene expression in human neuroblastoma cells. These results contribute to the development of novel cellular therapies for neurodegenerative diseases.

C-Abl Inhibition Activates TFEB: A Novel Way To Promote Cellular Clearance in Lysosomal Disorders

Lysosomes fulfill multiple functions involved in cellular homeostasis and their dysfunction leads to substrates accumulation causing neurodegenerative diseases. The transcription factor EB (TFEB) has emerged as a master regulator of lysosomal biogenesis, exocytosis and autophagy, promoting the clearance of substrates stored in cells. c-Abl is a tyrosine kinase that participates in cellular signaling in physiological and pathophysiological conditions. In this study, we explored the connection between c-Abl and TFEB. Here we show that under pharmacological and genetic c-Abl inhibition, TFEB translocates into the nucleus promoting the expression of its target genes independently of its well-known regulator, mTORC1. Active c-Abl induces TFEB phosphorylation on tyrosine and the inhibition of this kinase promotes lysosomal biogenesis, autophagy and exocytosis. c-Abl inhibition in pharmacological Niemann Pick type-C (NPC) models, a neurodegenerative disease characterized by cholesterol accumulation in lysosomes, promotes a cholesterol-lowering effect in a TFEB dependent manner. In genetic NPC models, c-Abl inhibition promotes cellular clearance through TFEB activation. We propose the modulation of this novel c-Abl/TFEB axis, using the FDA-approved drugs Imatinib or Nilotinib, as a therapeutic strategy to treat different neurodegenerative storage disorders.

MTOR hyperactivity mediates lysosomal dysfunction in Gaucher's disease iPSC-neuronal cells.

ABSTRACTBi-allelic GBA1 mutations cause Gaucher's disease (GD), the most common lysosomal storage disorder. Neuronopathic manifestations in GD include neurodegeneration, which can be severe and rapidly progressive. GBA1 mutations are also the most frequent genetic risk factors for Parkinson's disease. Dysfunction of the autophagy-lysosomal pathway represents a key pathogenic event in GBA1-associated neurodegeneration. Using an induced pluripotent stem cell (iPSC) model of GD, we previously demonstrated that lysosomal alterations in GD neurons are linked to dysfunction of the transcription factor EB (TFEB). TFEB controls the coordinated expression of autophagy and lysosomal genes and is negatively regulated by the mammalian target of rapamycin complex 1 (mTORC1). To further investigate the mechanism of autophagy-lysosomal pathway dysfunction in neuronopathic GD, we examined mTORC1 kinase activity in GD iPSC neuronal progenitors and differentiated neurons. We found that mTORC1 is hyperactive in GD cells as evidenced by increased phosphorylation of its downstream protein substrates. We also found that pharmacological inhibition of glucosylceramide synthase enzyme reversed mTORC1 hyperactivation, suggesting that increased mTORC1 activity is mediated by the abnormal accumulation of glycosphingolipids in the mutant cells. Treatment with the mTOR inhibitor Torin1 upregulated lysosomal biogenesis and enhanced autophagic clearance in GD neurons, confirming that lysosomal dysfunction is mediated by mTOR hyperactivation. Further analysis demonstrated that increased TFEB phosphorylation by mTORC1 results in decreased TFEB stability in GD cells. Our study uncovers a new mechanism contributing to autophagy-lysosomal pathway dysfunction in GD, and identifies the mTOR complex as a potential therapeutic target for treatment of GBA1-associated neurodegeneration.

Abstract 2619: DNA damage agents promote TFEB function and induce pro-survival autophagy signals

Abstract The transcription factor EB (TFEB) was identified as a master regulator of autophagy and lysosomal biogenesis. We recently demonstrated that TFEB is aberrantly regulated in pancreatic cancer (PDAC) cells. Interference with TFEB impairs PDAC cell growth supporting an important role for TFEB in maintaining PDAC cell phenotype. Given the limited impact of chemotherapeutic drugs in the context of PDAC, we aimed at testing whether the aberrantly regulated TFEB in PDAC cells could confer resistance to DNA damage agents, commonly used in PDAC therapeutic regimens. Methods: Experiments were performed in PDAC cells (MIA PaCa2, PANC1). The DNA damage agents gemcitabine, 5-FU, cisplatin and doxorubicin were used. Autophagic flux was measured upon 4-hours treatment with bafilomycin A1. Results: Treatment with DNA damage agents 1) increased the autophagic flux in PDAC cells. This autophagic signal was associated with 2) the dephosphorylation and nuclear accumulation of TFEB. The mTORC1 pathway is well-known to regulate TFEB phosphorylation and nuclear localization of TFEB. 3) However, the impact of the DNA damage agents on TFEB appeared independent of the mTORC1 pathway since no modulation in the phosphorylation of the mTORC1 target S6K1 was observed. To delineate whether TFEB influenced the response to DNA damage agents, we generated stable populations of PDAC cells expressing a non-targeting or shRNA targeting TFEB. Interfering with TFEB function 4) prevented the autophagic response upon treatment with DNA damage agents. This correlated with 5) increased accumulation of DNA damage and 6) increased sensitivity to the DNA damage agents. Conclusion: Our results suggest that DNA damage agents can induce a pro-survival autophagic response involving TFEB. Interfering with TFEB function limits the autophagic response and leads to increased sensitivity to DNA damage agents. Altogether, our results suggest that the aberrantly expressed TFEB in PDAC cells could confer resistance to DNA damage agents by, among others, promoting autophagy and limiting DNA damage accumulation. Citation Format: Benoit Marchand, Marie-Josée Boucher. DNA damage agents promote TFEB function and induce pro-survival autophagy signals [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2619.

A TFEB nuclear export signal integrates amino acid supply and glucose availability

How cells coordinate the response to fluctuating carbon and nitrogen availability required to maintain effective homeostasis is a key issue. Amino acid limitation that inactivates mTORC1 promotes de-phosphorylation and nuclear translocation of Transcription Factor EB (TFEB), a key transcriptional regulator of lysosome biogenesis and autophagy that is deregulated in cancer and neurodegeneration. Beyond its cytoplasmic sequestration, how TFEB phosphorylation regulates its nuclear-cytoplasmic shuttling, and whether TFEB can coordinate amino acid supply with glucose availability is poorly understood. Here we show that TFEB phosphorylation on S142 primes for GSK3β phosphorylation on S138, and that phosphorylation of both sites but not either alone activates a previously unrecognized nuclear export signal (NES). Importantly, GSK3β is inactivated by AKT in response to mTORC2 signaling triggered by glucose limitation. Remarkably therefore, the TFEB NES integrates carbon (glucose) and nitrogen (amino acid) availability by controlling TFEB flux through a nuclear import-export cycle.

MAP4K3 mediates amino acid-dependent regulation of autophagy via phosphorylation of TFEB

Autophagy is the major cellular pathway by which macromolecules are degraded, and amino acid depletion powerfully activates autophagy. MAP4K3, or germinal-center kinase-like kinase, is required for robust cell growth in response to amino acids, but the basis for MAP4K3 regulation of cellular metabolic disposition remains unknown. Here we identify MAP4K3 as an amino acid-dependent regulator of autophagy through its phosphorylation of transcription factor EB (TFEB), a transcriptional activator of autophagy, and through amino acid starvation-dependent lysosomal localization of MAP4K3. We document that MAP4K3 physically interacts with TFEB and MAP4K3 inhibition is sufficient for TFEB nuclear localization, target gene transactivation, and autophagy, even when mTORC1 is activated. Moreover, MAP4K3 serine 3 phosphorylation of TFEB is required for TFEB interaction with mTORC1-Rag GTPase-Ragulator complex and TFEB cytosolic sequestration. Our results uncover a role for MAP4K3 in the control of autophagy and reveal MAP4K3 as a central node in nutrient-sensing regulation.

Oxidative Stress Induces Neuronal Apoptosis Through Suppressing Transcription Factor EB Phosphorylation at Ser467

Background/Aims: This study determined the role and mechanism of action of transcription factor EB (TFEB) in H₂O₂-induced neuronal apoptosis. Methods: SH-SY5Y cells were treated with Akt inhibitor/activator and different concentrations of H₂O₂. Cell apoptosis was detected by flow cytometric analysis. Akt and TFEB phosphorylation and PARP cleavage were determined by Western blotting. HEK293T cells were transfected with different truncated TFEB mutants and HA-Akt-WT; SH-SY5Y cells were transfected with Flag-vector, Flag-TFEB, Flag-TFEB-S467A or Flag-TFEB-S467D; and TFEB interaction with Akt was determined by co-immunoprecipitation and GST pull-down assays. Results: A low concentration of H₂O₂ induces TFEB phosphorylation at Ser467 and nuclear translocation, facilitating neuronal survival, whereas a high concentration of H₂O₂ promotes SH-SY5Y cell apoptosis via suppressing TFEB Ser467 phosphorylation and nuclear translocation. The TFEB-S467D mutant is more easily translocated into the nucleus than the non-phosphorylated TFEB-S467A mutant. Further, Akt physically binds to TFEB via its C-terminal tail interaction with the HLH domain of TFEB and phosphorylates TFEB at Ser467. Mutation of TFEB-Ser467 can prevent the phosphorylation of TFEB by Akt, preventing inhibition of oxidative stress-induced apoptosis. Conclusions: Oxidative stress induces neuronal apoptosis through suppressing TFEB phosphorylation at Ser467 by Akt, providing a novel therapeutic strategy for neurodegenerative diseases.

An Evolutionarily Conserved PLC-PKD-TFEB Pathway for Host Defense.

The mechanisms that tightly control the transcriptionof host defense genes have not been fully elucidated. We previously identified TFEB as a transcription factor important for host defense, but the mechanisms that regulate TFEB during infection remained unknown. Here, we used C.elegans to discover a pathway that activates TFEB during infection. Gene dkf-1, which encodes a homolog of protein kinase D (PKD), was required for TFEB activation in nematodes infected with Staphylococcus aureus. Conversely, pharmacological activation of PKD wassufficient to activate TFEB. Furthermore, phospholipase C (PLC) gene plc-1 was also required for TFEB activation, downstream of Gαq homolog egl-30 and upstream of dkf-1. Using reverse and chemical genetics, we discovered a similar PLC-PKD-TFEB axis in Salmonella-infected mouse macrophages. In addition, PKCα was required in macrophages. These observations reveal a previously unknown host defense signaling pathway, which has been conserved across one billion years of evolution.