Factor E3 Research Articles

Role of the Hippo-YAP/TAZ Pathway in Epithelioid Hemangioendothelioma and its Potential as a Therapeutic Target.

Epithelioid hemangioendothelioma (EHE) is a rare malignant vascular tumor arising from vascular endothelial cells. This study delves into the molecular mechanisms underlying EHE, with a specific focus on the Hippo-YAP/TAZ pathway. EHE is characterized molecularly by transcriptional co-activator with a PDZ-motif (TAZ)-calmodulin binding transcription activator 1 (CAMTA1) or Yes-associated protein (YAP)-transcription factor E3 (TFE3) fusions. YAP/TAZ, a transcription co-activator, binds to transcription factors and regulates gene expression. The YAP/TAZ and its upstream Hippo pathway are involved in cell proliferation and cell contact inhibition, regulating organ size and carcinogenesis. In addition to oncogenic effects, dysfunction or gene duplication of the Hippo pathway results in a poor prognosis due to epithelial-mesenchymal transformation of epithelial cells, stem cell transformation, and increased drug resistance. Notably, the TAZ-CAMTA1 fusion is specific to EHE, and genetic alterations in the Hippo pathway other than this fusion gene are absent in EHE. The TAZ-CAMTA1 fusion is a promising therapeutic target. This review summarizes recent advances in EHE, focusing on the role of the Hippo-YAP/TAZ pathway in EHE and its potential as a therapeutic target for drug development.

Histopathologic classification and immunohistochemical features of papillary renal neoplasm with potential therapeutic targets.

Papillary renal cell carcinoma (pRCC) is the second most common histological subtype of renal cell carcinoma and is considered a morphologically and molecularly heterogeneous tumor. Accurate classification and assessment of the immunohistochemical features of possible therapeutic targets are needed for precise patient care. We aimed to evaluate immunohistochemical features and possible therapeutic targets of papillary renal neoplasms. We collected 140 papillary renal neoplasms from three different hospitals and conducted immunohistochemical studies on tissue microarray slides. We performed succinate dehydrogenase B, fumarate hydratase, and transcription factor E3 immunohistochemical studies for differential diagnosis and re-classified five cases (3.6%) of papillary renal neoplasms. In addition, we conducted c-MET, p16, c-Myc, Ki-67, p53, and stimulator of interferon genes (STING) immunohistochemical studies to evaluate their pathogenesis and value for therapeutic targets. We found that c-MET expression was more common in pRCC (classic) (p = .021) among papillary renal neoplasms and Ki-67 proliferation index was higher in pRCC (not otherwise specified, NOS) compared to that of pRCC (classic) and papillary neoplasm with reverse polarity (marginal significance, p = .080). Small subsets of cases with p16 block positivity (4.5%) (pRCC [NOS] only) and c-Myc expression (7.1%) (pRCC [classic] only) were found. Also, there were some cases showing STING expression and those cases were associated with increased Ki-67 proliferation index (marginal significance, p = .063). Our findings suggested that there are subsets of pRCC with c-MET, p16, c-MYC, and STING expression and those cases could be potential candidates for targeted therapy.

Blockage of Akt activation suppresses cadmium-induced renal tubular cellular damages through aggrephagy in HK-2 cells

We have reported that an environmental pollutant, cadmium, promotes cell death in the human renal tubular cells (RTCs) through hyperactivation of a serine/threonine kinase Akt. However, the molecular mechanisms downstream of Akt in this process have not been elucidated. Cadmium has a potential to accumulate misfolded proteins, and proteotoxicity is involved in cadmium toxicity. To clear the roles of Akt in cadmium exposure-induced RTCs death, we investigated the possibility that Akt could regulate proteotoxicity through autophagy in cadmium chloride (CdCl2)-exposed HK-2 human renal proximal tubular cells. CdCl2 exposure promoted the accumulation of misfolded or damaged proteins, the formation of aggresomes (pericentriolar cytoplasmic inclusions), and aggrephagy (selective autophagy to degrade aggresome). Pharmacological inhibition of Akt using MK2206 or Akti-1/2 enhanced aggrephagy by promoting dephosphorylation and nuclear translocation of transcription factor EB (TFEB)/transcription factor E3 (TFE3), lysosomal transcription factors. TFEB or TFE3 knockdown by siRNAs attenuated the protective effects of MK2206 against cadmium toxicity. These results suggested that aberrant activation of Akt attenuates aggrephagy via TFEB or TFE3 to facilitate CdCl2-induced cell death. Furthermore, these roles of Akt/TFEB/TFE3 were conserved in CdCl2-exposed primary human RTCs. The present study shows the molecular mechanisms underlying Akt activation that promotes cadmium-induced RTCs death.

TFE3/PI3K/Akt/mTOR Axis in Renal Cell Carcinoma Affects Tumor Microenvironment

The role of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway in renal cell carcinoma (RCC) progression, metastasis, and resistance to therapies has not been investigated thoroughly. Transcription factor E3 (TFE3) expression is related to a poorer prognosis and tumor microenvironment in patients with RCC. This study aimed to determine the relationship between TFE3 and the PI3K/Akt pathway. TFE3 down-regulation was achieved by transient transfection of siRNA and shRNA in UOK146 cells. TFE3 overexpression was induced by transient transfection with pcDNA3.1 encoding the constitutively active form of TFE3. The cells were treated with mammalian target of rapamycin (mTOR) and PI3K inhibitors. Western blot was performed to detect TFE3, programmed death-ligand 1, phospho-Akt, and Akt. Phospho-Akt expression increased significantly upon TFE3 down-regulation, and decreased significantly upon up-regulation. When RCC cells were treated with a PI3K inhibitor (LY294002), TFE3 expression increased and phospho-Akt expression decreased. Data from this study indicate that TFE3 plays a role in the PI3K/Akt pathway in RCC. The results of this study suggest that PI3K/Akt inhibitors may aid in the treatment of patients with RCC by affecting the tumor microenvironment.

Abstract 5425: MITF/TFE regulatory programs in neural crest migration are co-opted in melanoma metastasis

Abstract Introduction: Microphthalmia-associated transcription factor (MITF) is a critical regulator of melanocyte differentiation and melanoma oncogenesis. Melanoma expression profiling has revealed a strong trend between low MITF expression levels and invasive behavior. However, it is unclear how low levels of MITF are connected to invasive behavior. Preliminary data from our lab has identified transcription factor E3 (TFE3), a MITF paralog, as a transcriptional regulator in MITF-low melanoma states. We hypothesize that in melanoma cells with low MITF levels, TFE3 promotes invasion. To assess the possibility that the antagonistic regulatory interaction between MITF and a paralog was coopted from the embryo, we examine migratory behavior of neural crest cells in zebrafish embryos that are wild-type, mitfa loss-of-function (LOF) mutants, tfec (TF3 ortholog) LOF mutants, or mitfa/tfec double LOF embryos. Methods: We evaluated TFE3 levels by Western blot in a panel of melanoma cell lines known to express a range of MITF expression levels. We mutated TFE3 exon 4, which encodes the DNA binding domain, using a single guide RNA, and assessed cellular invasive potential using an in vitro transwell invasion assay. CUT&RUN sequencing was used to profile TFE3 genomic binding. Zebrafish embryos were generated in which the mitfa promoter drove expression of RNA encoding green fluorescent protein (GFP), and of the genotypes mentioned above. From transgenic wild-type and mitfa LOF mutant embryos we isolated GFP-expressing cells and conducted single cell-RNA sequencing. We assessed migration of GFP-labeled cells by fluorescent microscopy in 20-48 hour post fertilization zebrafish embryos of all genotypes mentioned above. Results: We found that melanoma cell lines with high levels of MITF (SKMEL3 and SKMEL28) had low levels of TFE3 protein, and those with low levels of MITF (A375 and RPMI 7952) had high levels of TFE3 protein. The TFE3-high cell lines were more invasive in vitro than the TFE3-low cell lines. TFE3-high cell lines depleted of TFE3 were less in invasive in vitro than parental cells. CUT&RUN profiling of TFE3 demonstrates that TFE3 binds mesenchymal-like enhancers in MITF-low cell lines. Single cell RNA sequencing revealed that in a melanocyte precursor cluster present in both wild types and in mitfa mutants, expression of tfec was higher in the latter. Finally, migration of GFP-expressing cells was higher in mitfa LOF mutant embryos than in mitfa/tfec double LOF mutant embryos. Conclusion: These data indicate that reduction of MITF expression up-regulates TFE3 expression in melanoma and tfec in zebrafish melanocytes, although the mechanism of this regulation is unclear. They also show that TFE3 and Tfec promote migration of metastatic melanoma and melanocyte precursors, respectively. Because regulatory mechanisms in cancer are often coopted from embryonic cells, studying the embryo may illuminate cancer pathogenesis. Citation Format: Jeremy Chang, Katelyn Campbell, Rachel Moore, Robert Cornell, Colin Kenny. MITF/TFE regulatory programs in neural crest migration are co-opted in melanoma metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5425.

The role of TFE3 in mediating skeletal muscle mitochondrial adaptations to exercise training.

Transcription factor E3 (TFE3) is a transcription factor that activates the expression of lysosomal genes involved in the clearance of dysfunctional mitochondria, termed mitophagy. With exercise, TFE3 is presumed to optimize the mitochondrial pool through the removal of organelles via lysosomes. However, the molecular mechanisms of the involved pathways remain unknown. Wild-type (WT) and TFE3 knockout (KO) mice were subjected to 6 wk of voluntary wheel running as an endurance training regimen. This was followed by a 45-min bout of in situ stimulation of the sciatic nerve innervating hindlimb muscles to evaluate muscle fatigue and contractile properties. A subset of animals was treated with colchicine to measure autophagy and mitophagy flux. Fatigability during stimulation was reduced with training in WT animals, as seen by a 13% increase in the percentage of maximum force at 5 min of stimulation, and a 30% increase at 30 minutes. Permeabilized fiber oxygen consumption was also improved with training. Concurrent with improved muscle and mitochondrial function, cytochrome c oxidase (COX) activity and COX I protein expression were increased in trained WT animals compared to untrained animals, signifying an increase in mitochondrial content. These training adaptations were abolished with the loss of TFE3. Surprisingly, the absence of TFE3 did not affect lysosomal content nor did it blunt the induction of mitophagy flux with contractile activity compared to WT mice. Our results suggest that the loss of TFE3 compromises beneficial training adaptations that lead to improved muscle endurance and mitochondrial function.NEW & NOTEWORTHY Our understanding of the role of transcription factor E3 (TFE3) in skeletal muscle is very limited. This research shows that TFE3 plays a direct role in skeletal muscle mitochondrial enhancement with exercise training, thereby introducing a paradigm shift in our perception of the function of TFE3 in mitochondrial maintenance, beyond mitophagy. This research serves to introduce TFE3 as a protein that holds promise as a future therapeutic target for metabolic diseases and skeletal muscle dysfunction.

Cholesteryl Hemiazelate Present in Cardiovascular Disease Patients Causes Lysosome Dysfunction in Murine Fibroblasts.

There is growing evidence supporting the role of fibroblasts in all stages of atherosclerosis, from the initial phase to fibrous cap and plaque formation. In the arterial wall, as with macrophages and vascular smooth muscle cells, fibroblasts are exposed to a myriad of LDL lipids, including the lipid species formed during the oxidation of their polyunsaturated fatty acids of cholesteryl esters (PUFA-CEs). Recently, our group identified the final oxidation products of the PUFA-CEs, cholesteryl hemiesters (ChE), in tissues from cardiovascular disease patients. Cholesteryl hemiazelate (ChA), the most prevalent lipid of this family, is sufficient to impact lysosome function in macrophages and vascular smooth muscle cells, with consequences for their homeostasis. Here, we show that the lysosomal compartment of ChA-treated fibroblasts also becomes dysfunctional. Indeed, fibroblasts exposed to ChA exhibited a perinuclear accumulation of enlarged lysosomes full of neutral lipids. However, this outcome did not trigger de novo lysosome biogenesis, and only the lysosomal transcription factor E3 (TFE3) was slightly transcriptionally upregulated. As a consequence, autophagy was inhibited, probably via mTORC1 activation, culminating in fibroblasts' apoptosis. Our findings suggest that the impairment of lysosome function and autophagy and the induction of apoptosis in fibroblasts may represent an additional mechanism by which ChA can contribute to the progression of atherosclerosis.

Renal cell carcinoma associated with Xp11.2 translocation/transcription factor E3 gene fusion: A case report and literature review

Renal cell carcinoma associated with Xp11.2 translocation/transcription factor E3 gene fusion: A case report and literature review

FGF-18 Protects the Injured Spinal cord in mice by Suppressing Pyroptosis and Promoting Autophagy via the AKT-mTOR-TRPML1 axis.

Spinal cord injury (SCI) is a severe medical condition with lasting effects. The efficacy of numerous clinical treatments is hampered by the intricate pathophysiological mechanism of SCI. Fibroblast growth factor 18 (FGF-18) has been found to exert neuroprotective effects after brain ischaemia, but its effect after SCI has not been well explored. The aim of the present study was to explore the therapeutic effect of FGF-18 on SCI and the related mechanism. In the present study, a mouse model of SCI was used, and the results showed that FGF-18 may significantly affect functional recovery. The present findings demonstrated that FGF-18 directly promoted functional recovery by increasing autophagy and decreasing pyroptosis. In addition, FGF-18 increased autophagy, and the well-known autophagy inhibitor 3-methyladenine (3MA) reversed the therapeutic benefits of FGF-18 after SCI, suggesting that autophagy mediates the therapeutic effects of FGF-18 on SCI. A mechanistic study revealed that after stimulation of the protein kinase B (AKT)-transient receptor potential mucolipin 1 (TRPML1)-calcineurin signalling pathway, the FGF-18-induced increase in autophagy was mediated by the dephosphorylation and nuclear translocation of transcription factor E3 (TFE3). Together, these findings indicated that FGF-18 is a robust autophagy modulator capable of accelerating functional recovery after SCI, suggesting that it may be a promising treatment for SCI in the clinic.

Inhibiting autophagy before it starts

ABSTRACT Autophagy, an important cellular stress response mechanism, is often exploited by a variety of cancer cells to sustain rapid growth under stresses such as nutrient deprivation and hypoxia. Autophagy also plays a key role in tumor resistance to chemotherapy, radiotherapy or targeted therapy. Inhibition of autophagy is therefore a promising tumor treatment strategy. However, there is still a lack of effective autophagy inhibitors suitable for clinical use. Most drug development has focused on enzymes like the VPS34 and ULK1 kinases, or the cysteine protease ATG4B, which plays different roles in autophagy. We discovered a drug molecule Eltrombopag that inhibits the expression of autophagic lysosomal genes at the stage of transcriptional level, where the synthesis of these proteins has not really begun, by directly inhibiting the TFEB (transcription factor EB). This drug can improve the therapeutic effect of Temozolomide on glioblastoma treatment, further confirming the value of inhibiting autophagy in the treatment of cancer. Abbreviation: VPS34: vacuolar protein sorting 34; ULK1: unc-51 like autophagy activating kinase 1; TFEB: transcription factor EB; MITF: microphthalmia-associated transcription factor; TFE3: transcription factor E3; EO: Eltrombopag; ITC: isothermal titration calorimetry; bHLH-LZ: basic helix-loop-helix leucine zipper; LAMP1: lysosomal-associated membrane protein 1; CTSF: cathepsin F; HEXA: hexosaminidase subunit alpha.

Bexarotene improves motor function after spinal cord injury in mice.

Spinal cord injury is a challenge in orthopedics because it causes irreversible damage to the central nervous system. Therefore, early treatment to prevent lesion expansion is crucial for the management of patients with spinal cord injury. Bexarotene, a type of retinoid, exerts therapeutic effects on patients with cutaneous T-cell lymphoma and Parkinson's disease. Bexarotene has been proven to promote autophagy, but it has not been used in the treatment of spinal cord injury. To investigate the effects of bexarotene on spinal cord injury, we established a mouse model of T11-T12 spinal cord contusion and performed daily intraperitoneal injection of bexarotene for 5 consecutive days. We found that bexarotene effectively reduced the deposition of collagen and the number of pathological neurons in the injured spinal cord, increased the number of synapses of nerve cells, reduced oxidative stress, inhibited pyroptosis, promoted the recovery of motor function, and reduced death. Inhibition of autophagy with 3-methyladenine reversed the effects of bexarotene on spinal cord injury. Bexarotene enhanced the nuclear translocation of transcription factor E3, which further activated AMP-activated protein kinase-S-phase kinase-associated protein 2-coactivator-associated arginine methyltransferase 1 and AMP-activated protein kinase-mammalian target of rapamycin signaling pathways. Intravenous injection of transcription factor E3 shRNA or intraperitoneal injection of compound C, an AMP-activated protein kinase blocker, inhibited the effects of bexarotene. These findings suggest that bexarotene regulates nuclear translocation of transcription factor E3 through the AMP-activated protein kinase-S-phase kinase-associated protein 2-coactivator-associated arginine methyltransferase 1 and AMP-activated protein kinase-mammalian target of rapamycin signal pathways, promotes autophagy, decreases reactive oxygen species level, inhibits pyroptosis, and improves motor function after spinal cord injury.

Adult-Onset Renal Cell Carcinoma Associated with Xp11.2 Translocation/TFE3 Gene Fusion: 2 Case Reports and Review of Literature

Renal cell carcinoma (RCC) is the most common type of kidney cancer in adults, it represents 90-95% of neoplasms arising from the kidney. The Xp11.2 RCC translocation is a subtype of RCC that is defined by different translocations involving the Xp11.2 chromosome, all of which result in transcription factor E3 (TFE3) gene fusions. We presented 2 adult cases of Xp11-RCC, one patient had lymph node metastases and the second patient also had liver metastases. Both patients improved with surgical treatment by radical total nephrectomy with lymph node dissection, in addition to neoadjuvant medical treatment.

TFE3-mediated impairment of lysosomal biogenesis and defective autophagy contribute to fluoride-induced hepatotoxicity

Excessive fluoride exposure can cause liver injury, but the specific mechanisms need further investigation. We aimed to explore the role of impaired lysosomal biogenesis and defective autophagy in fluoride-induced hepatotoxicity and its potential mechanisms, focusing on the role of transcription factor E3 (TFE3) in regulating hepatocyte lysosomal biogenesis. To this end, we established a Sprague-Dawley (SD) rat model exposed to sodium fluoride (NaF) and a rat liver cell line (BRL3A) model exposed to NaF. The results showed that NaF exposure diminished liver function and led to apoptosis as well as autophagosome accumulation and impaired autophagic degradation. In addition, NaF exposure caused compromised lysosome biogenesis and decreased lysosomal degradation, and inhibited TFE3 nuclear translocation. Notably, the mTOR inhibitors rapamycin (RAPA) and Ad-TFE3 promoted lysosomal biogenesis and enhanced lysosomal degradation function. Furthermore, RAPA and Ad-TFE3 reduced NaF-induced apoptosis by alleviating impaired autophagic degradation. In conclusion, NaF impairs lysosomal biogenesis by inhibiting TFE3 nuclear translocation, decreasing lysosomal degradation function, resulting in impaired autophagic degradation, and ultimately inducing apoptosis. Therefore, TFE3 may be a promising therapeutic target for fluoride-induced hepatotoxicity.

Trigonochinene E promotes lysosomal biogenesis and enhances autophagy via TFEB/TFE3 in human degenerative NP cells against oxidative stress

BackgroundMacroautophagy (henceforth autophagy) is the major form of autophagy, which delivers intracellular cargo to lysosomes for degradation. Considerable research has revealed that the impairment of lysosomal biogenesis and autophagic flux exacerbates the development of autophagy-related diseases. Therefore, reparative medicines restoring lysosomal biogenesis and autophagic flux in cells may have therapeutic potential against the increasing prevalence of these diseases. PurposeThe aim of the present study was thus to explore the effect of trigonochinene E (TE), an aromatic tetranorditerpene isolated from Trigonostemon flavidus, on lysosomal biogenesis and autophagy and to elucidate the potential underlying mechanism. MethodsFour human cell lines, HepG2, nucleus pulposus (NP), HeLa and HEK293 cells were applied in this study. The cytotoxicity of TE was evaluated by MTT assay. Lysosomal biogenesis and autophagic flux induced by 40 μM TE were analyzed using gene transfer techniques, western blotting, real-time PCR and confocal microscopy. Immunofluorescence, immunoblotting and pharmacological inhibitors/activators were applied to determine the changes in the protein expression levels in mTOR, PKC, PERK, and IRE1α signaling pathways. ResultsOur results showed that TE promotes lysosomal biogenesis and autophagic flux by activating the transcription factors of lysosomes, transcription factor EB (TFEB) and transcription factor E3 (TFE3). Mechanistically, TE induces TFEB and TFE3 nuclear translocation through an mTOR/PKC/ROS-independent and endoplasmic reticulum (ER) stress-mediated pathway. The PERK and IRE1α branches of ER stress are crucial for TE-induced autophagy and lysosomal biogenesis. Whereas TE activated PERK, which mediated calcineurin dephosphorylation of TFEB/TFE3, IRE1α was activated and led to inactivation of STAT3, which further enhanced autophagy and lysosomal biogenesis. Functionally, knockdown of TFEB or TFE3 impairs TE-induced lysosomal biogenesis and autophagic flux. Furthermore, TE-induced autophagy protects NP cells from oxidative stress to ameliorate intervertebral disc degeneration (IVDD). ConclusionsHere, our study showed that TE can induce TFEB/TFE3-dependent lysosomal biogenesis and autophagy via the PERK-calcineurin axis and IRE1α-STAT3 axis. Unlike other agents regulating lysosomal biogenesis and autophagy, TE showed limited cytotoxicity, thereby providing a new direction for therapeutic opportunities to use TE to treat diseases with impaired autophagy-lysosomal pathways, including IVDD.

Transcription factor E3 renal cell carcinoma presenting as secondary hypertension.

Microphthalmia-associated transcription factor family (transcription factor E3 or transcription factor EB) translocation renal cell carcinomas (RCCs) are rare neoplasms. These renal neoplasms can be either asymptomatic and incidentally discovered on imaging or symptomatic, with the most common presenting symptoms being hematuria, pain, and abdominal mass, or paraneoplastic event. In conventional RCCs, hypertension is considered a risk factor and a possible paraneoplastic event, whereas, in translocation RCCs, prior exposure to cytotoxic chemotherapy is the only known risk factor, and hypertension as an isolated associated paraneoplastic event has never been reported. Interestingly, hypertension as the only presenting symptom in RCC is extremely rare. We report a case of transcription factor E3 positive RCC in a young adult presenting only with hypertension that normalized after radical nephrectomy. To the best of our knowledge, this is the first reported case of hypertension secondary to microphthalmia-associated transcription translocation RCC.

Clinicopathologic, treatment and prognosis study of 46 Xp11.2 translocation/TFE3 gene fusion renal cell carcinomas

PurposeTo report the clinicopathological features and mid- to long-term oncologic results of Xp11.2 translocation/transcription factor E3 (TFE3) gene fusion renal cell carcinomas (Xp11.2 translocation RCCs) in a single large-volume centrecentre.MethodsClinical and follow-up data of 46 patients who were diagnosed with Xp11.2 translocation RCC and underwentunderwent surgical intervention were retrospectively reviewed.ResultForty-six Xp11.2 translocation RCC patients were identified from 4218 renal tumour patients who were underwentunderwent surgery in our centrecentre from Jan. 2014 to Apr. 2020. The incidence of Xp11.2 translocation RCCs in our centre was 1.09%. During a median follow-up period of 30.5 months, 4 patients died of the disease. The total median overall survival and cancer specific survival were 30.0 months and 24.0 months, respectively. The 1-year, 3-year and 5-year OS rates were 97.4%, 88.8%, and 88.8%, respectively. In multivariable analysis, displaying symptoms when diagnosed (p = 0.019), lymph node metastasis (p = 0.002) and distal metastasis (p = 0.020) were identified as risk factors for poor prognosis.ConclusionXp11.2 translocation RCC is a type of renal cell carcinoma with a relatively low incidence and various prognoses. Early-stage Xp11.2 translocation RCCs have a similar prognosis to most typical RCCs, but late-stage Xp11.2 translocation RCCs can lead to poor oncological outcomes.

Splitting Hairs: Folliculin Parts the Good From the Bad in mTORC1 Control Over Lipid Metabolism

Gosis BS, Wada S, Thorsheim C, et al. Inhibition of nonalcoholic fatty liver disease in mice by selective inhibition of mTORC1. Science 2022;376(6590):eabf8271. The mechanistic target of rapamycin complex 1 (mTORC1) is a signaling kinase complex that mediates several fundamental processes, including de novo lipogenesis. Therefore, mTORC1 is an attractive target to treat nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH). However, a barrier to effectively target mTORC1 is an incomplete understanding of how mTORC1 regulates liver fat metabolism. To illustrate this point, both hyperactivating and inactivating mTORC1 signaling attenuates de novo lipogenesis and hepatic fat accumulation in mice. What is known is that mTORC1 activates de novo lipogenesis by phosphorylating 2 primary downstream effectors—p70 S6 kinase (P70S6K) and transcription factor E3 (TFE3)—which both promote de novo lipogenesis. At the same time, these de novo lipogenesis–promoting actions of mTORC1 are counterbalanced by an important negative feedback loop; mTORC1-P70S6K signaling inhibits the insulin receptor complex to attenuate further anabolic insulin signaling. Therefore, selective targeting of mTORC1 through TFE3, which prevents de novo lipogenesis but does not break the P70S6K anabolic insulin signaling feedback loop, could be an ideal target for NAFLD. Gosis and colleagues provided exciting new data to unify prior disparate observations and identify a potential therapeutic target for NAFLD. They identified the GTPase-activating protein folliculin (FLCN) as a factor that confers mTORC1 substrate specificity for TFE3, but not p70S6K. Using a variety of diet-induced models for NAFLD/NASH, they showed that liver-specific FLCN deletion blocked mTORC1-mediated TFE3 phosphorylation, thereby promoting lipid catabolic gene transcription. However, FLCN deletion preserved the insulin-mediated P70S6K-negative feedback loop, thereby reducing further anabolic insulin signaling. In these diet-induced NAFLD/NASH models, FLCN deletion promoted fat oxidation and prevented fat accumulation and fibrosis in the liver. Furthermore, in established diet-induced NASH, inhibiting FLCN reversed fat accumulation and fibrosis marker gene expression, but not fibrosis scores. The numerous strengths of this study include the detailed mechanistic in vivo genetic models used to demonstrate the cell biology, physiology, and translational significance of this pathway. Equally exciting, the clinical and translational impact is that these data nominate FLCN as a novel and tractable target to precisely inhibit mTORC1 signaling to treat NAFLD, NASH, and their complications, albeit a specific mechanism to target FLCN in patients will need to be developed. Although both of these studies (Science 2022;376(6590):eabf8271; Ann Intern Med 2022;175:74–83) offered insights into promising therapeutic options for NAFLD, the challenge of preventing the ensuing liver fibrosis remains, and additional studies are needed to determine whether either of these options will “crack that nut.” Further Insights Into the Impact of Bariatric Surgery on the Progression of Nonalcoholic Fatty Liver DiseaseGastroenterologyVol. 163Issue 2PreviewSeeberg KA, Borgeraas H, Hofsø H, et al. Gastric bypass versus sleeve gastrectomy in type 2 diabetes: effects on hepatic steatosis and fibrosis: a randomized controlled trial. Ann Intern Med 2022;175:74–83. Full-Text PDF

NUPR1 promotes the proliferation and metastasis of oral squamous cell carcinoma cells by activating TFE3-dependent autophagy

Oral squamous cell carcinoma (OSCC) is the most common type of oral malignancy, and metastasis accounts for the poor prognosis of OSCC. Autophagy is considered to facilitate OSCC development by mitigating various cellular stresses; nevertheless, the mechanisms of autophagy in OSCC cell proliferation and metastasis remain unknown. In our study, high-sensitivity label-free quantitative proteomics analysis revealed nuclear protein 1 (NUPR1) as the most significantly upregulated protein in formalin-fixed paraffin-embedded tumour samples derived from OSCC patients with or without lymphatic metastasis. Moreover, NUPR1 is aberrantly expressed in the OSCC tissues and predicts low overall survival rates for OSCC patients. Notably, based on tandem mass tag-based quantitative proteomic analysis between stable NUPR1 knockdown OSCC cells and scrambled control OSCC cells, we confirmed that NUPR1 maintained autophagic flux and lysosomal functions by directly increasing transcription factor E3 (TFE3) activity, which promoted OSCC cell proliferation and metastasis in vitro and in vivo. Collectively, our data revealed that the NUPR1–TFE3 axis is a critical regulator of the autophagic machinery in OSCC progression, and this study may provide a potential therapeutic target for the treatment of OSCC.

Inhibition of nonalcoholic fatty liver disease in mice by selective inhibition of mTORC1.

Nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) remain without effective therapies. The mechanistic target of rapamycin complex 1 (mTORC1) pathway is a potential therapeutic target, but conflicting interpretations have been proposed for how mTORC1 controls lipid homeostasis. We show that selective inhibition of mTORC1 signaling in mice, through deletion of the RagC/D guanosine triphosphatase-activating protein folliculin (FLCN), promotes activation of transcription factor E3 (TFE3) in the liver without affecting other mTORC1 targets and protects against NAFLD and NASH. Disease protection is mediated by TFE3, which both induces lipid consumption and suppresses anabolic lipogenesis. TFE3 inhibits lipogenesis by suppressing proteolytic processing and activation of sterol regulatory element-binding protein-1c (SREBP-1c) and by interacting with SREBP-1c on chromatin. Our data reconcile previously conflicting studies and identify selective inhibition of mTORC1 as a potential approach to treat NASH and NAFLD.

Inositol triphosphate–triggered calcium release from the endoplasmic reticulum induces lysosome biogenesis via TFEB/TFE3

Lysosomes serve as dynamic regulators of cell and organismal physiology by integrating the degradation of macromolecules with receptor and nutrient signaling. Previous studies have established that activation of the transcription factor EB (TFEB) and transcription factor E3 (TFE3) induces the expression of lysosomal genes and proteins in signaling-inactive starved cells, that is, under conditions when activity of the master regulator of nutrient-sensing signaling mechanistic target of rapamycin complex 1 is repressed. How lysosome biogenesis is triggered in signaling-active cells is incompletely understood. Here, we identify a role for calcium release from the lumen of the endoplasmic reticulum in the control of lysosome biogenesis that is independent of mechanistic target of rapamycin complex 1. We show using functional imaging that calcium efflux from endoplasmic reticulum stores induced by inositol triphosphate accumulation upon depletion of inositol polyphosphate-5-phosphatase A, an inositol 5-phosphatase downregulated in cancer and defective in spinocerebellar ataxia, or receptor-mediated phospholipase C activation leads to the induction of lysosome biogenesis. This mechanism involves calcineurin and the nuclear translocation and elevated transcriptional activity of TFEB/TFE3. Our findings reveal a crucial function for inositol polyphosphate-5-phosphatase A–mediated triphosphate hydrolysis in the control of lysosome biogenesis via TFEB/TFE3, thereby contributing to our understanding how cells are able to maintain their lysosome content under conditions of active receptor and nutrient signaling.