Interleukin-6 mediates PSAT1 expression and serine metabolism in TSC2-deficient cells

Loss of Tuberous Sclerosis Complex 2 confers inflammation via dysregulation of Nuclear factor kappa-light-chain-enhancer of activated B cells

Background

Aberrant activation of mTORC1 is clearly defined in TSC, causing uncontrolled cell growth. While mTORC1 inhibitors show efficacy to stabilise tumour growth in TSC, they are not fully curative. Disease facets of TSC that are not restored with mTOR inhibitors might involve NF-κB. The study aimed to characterise NF-κB in the context of TSC.

Results

Enrichment of NF-κB-regulated genes was observed in TSC patient tumours, SEN/SEGAs, cortical tubers and a TSC tumour-derived cell line (621 - 101). Highlighting an inflammatory component of TSC, TSC cell models showed an elevated level of NF-κB and STAT3 activation. Herein, we report a dysregulated inflammatory phenotype of TSC2-deficient cells where NF-κB promotes autocrine signalling involving IL-6. Of importance, mTORC1 inhibition does not block this inflammatory signal to promote STAT3, while NF-κB inhibition was much more effective. Combined mTORC1 and NF-κB inhibition was potent at preventing anchorage-independent growth of TSC2-deficient cells, and unlike mTORC1 inhibition alone was sufficient to prevent colony regrowth after cessation of treatment.

Conclusion

This study reveals autocrine signalling crosstalk between NF-κB and STAT3 in TSC cell models. Furthermore, the data presented indicate that NF-κB pathway inhibitors could be a viable adjunct therapy with the current mTOR inhibitors to treat TSC.

Augmented ERO1α upon mTORC1 activation induces ferroptosis resistance and tumor progression via upregulation of SLC7A11

BACKGROUND

The dysregulated mechanistic target of rapamycin complex 1 (mTORC1) signaling plays a critical role in ferroptosis resistance and tumorigenesis. However, the precise underlying mechanisms still need to be fully understood.

METHODS

Endoplasmic reticulum oxidoreductase 1 alpha (ERO1α) expression in mTORC1-activated mouse embryonic fibroblasts, cancer cells, and laryngeal squamous cell carcinoma (LSCC) clinical samples was examined by quantitative real-time PCR (qRT-PCR), western blotting, immunofluorescence (IF), and immunohistochemistry. Extensive in vitro and in vivo experiments were carried out to determine the role of ERO1α and its downstream target, member 11 of the solute carrier family 7 (SLC7A11), in mTORC1-mediated cell proliferation, angiogenesis, ferroptosis resistance, and tumor growth. The regulatory mechanism of ERO1α on SLC7A11 was investigated via RNA-sequencing, a cytokine array, an enzyme-linked immunosorbent assay, qRT-PCR, western blotting, IF, a luciferase reporter assay, and a chromatin immunoprecipitation assay. The combined therapeutic effect of ERO1α inhibition and the ferroptosis inducer imidazole ketone erastin (IKE) on mTORC1-activated cells was evaluated using cell line-derived xenografts, LSCC organoids, and LSCC patient-derived xenograft models.

RESULTS

ERO1α is a functional downstream target of mTORC1. Elevated ERO1α induced ferroptosis resistance and exerted pro-oncogenic roles in mTORC1-activated cells via upregulation of SLC7A11. Mechanically, ERO1α stimulated the transcription of SLC7A11 by activating the interleukin-6 (IL-6)/signal transducer and activator of transcription 3 (STAT3) pathway. Moreover, ERO1α inhibition combined with treatment using the ferroptosis inducer IKE exhibited synergistic antitumor effects on mTORC1-activated tumors.

CONCLUSIONS

The ERO1α/IL-6/STAT3/SLC7A11 pathway is crucial for mTORC1-mediated ferroptosis resistance and tumor growth, and combining ERO1α inhibition with ferroptosis inducers is a novel and effective treatment for mTORC1-related tumors.

Serine metabolism in macrophage polarization

OBJECTIVE

Emerging studies have revealed that macrophages possess different dependences on the uptake, synthesis, and metabolism of serine for their activation and functionalization, necessitating our insight into how serine availability and utilization impact macrophage activation and inflammatory responses.

METHODS

This article summarizes the reports published domestically and internationally about the serine uptake, synthesis, and metabolic flux by the macrophages polarizing with distinct stimuli and under different pathologic conditions, and particularly analyzes how altered serine metabolism rewires the metabolic behaviors of polarizing macrophages and their genetic and epigenetic reprogramming.

RESULTS

Macrophages dynamically change serine metabolism to orchestrate their anabolism, redox balance, mitochondrial function, epigenetics, and post-translation modification, and thus match the distinct needs for both classical and alternative activation.

CONCLUSION

Serine metabolism coordinates multiple metabolic pathways to tailor macrophage polarization and their responses to different pathogenic attacks and thus holds the potential as therapeutic target for types of acute and chronic inflammatory diseases.

Metabolic Enzymes in Viral Infection and Host Innate Immunity

Metabolic enzymes are central players for cell metabolism and cell proliferation. These enzymes perform distinct functions in various cellular processes, such as cell metabolism and immune defense. Because viral infections inevitably trigger host immune activation, viruses have evolved diverse strategies to blunt or exploit the host immune response to enable viral replication. Meanwhile, viruses hijack key cellular metabolic enzymes to reprogram metabolism, which generates the necessary biomolecules for viral replication. An emerging theme arising from the metabolic studies of viral infection is that metabolic enzymes are key players of immune response and, conversely, immune components regulate cellular metabolism, revealing unexpected communication between these two fundamental processes that are otherwise disjointed. This review aims to summarize our present comprehension of the involvement of metabolic enzymes in viral infections and host immunity and to provide insights for potential antiviral therapy targeting metabolic enzymes.

IL-6/JAK2-dependent G6PD phosphorylation promotes nucleotide synthesis and supports tumor growth

OBJECTIVE

Tumor cells hijack inflammatory mechanisms to promote their own growth. IL-6 is one of the major cytokines, and is frequently upregulated in tumors. The pentose phosphate pathway (PPP) generates the indispensable building blocks to produce various nucleotides. Here we aimed to determine whether and how PPP is timely tuned in response to IL-6 to support tumor growth.

METHODS

Protein expression was examined by immunoblot. Protein interaction was examined by immunoprecipitation. Tumor cell proliferation in in vitro culture was examined by BrdU assay and colony formation assay. Tumor cell proliferation in mouse xenograft model was examined by Ki-67 staining.

RESULTS

Here we show that the metabolic flux of PPP and enzymatic activity of glucose-6-phosphate dehydrogenase (G6PD) is rapidly induced under IL-6 treatment, without obvious changes in G6PD expression level. Mechanistically, Janus kinase 2 (JAK2) phosphorylates G6PD Y437 under IL-6 treatment, which accentuates G6PD enzymatic activity by promoting G6PD binding with its substrate G6P. Further, JAK2-dependent G6PD Y437 phosphorylation is required for IL-6-induced nucleotide biosynthesis and tumor cell proliferation, and is associated with the progression of oral squamous cell carcinoma.

CONCLUSIONS

Our findings report a new mechanism implicated in the crosstalk between tumor cells and inflammatory microenvironment, by which JAK2-dependent activation of G6PD governs nucleotide synthesis to support tumor cell proliferation, thereby highlighting its value as a potential anti-tumor target.

Amino Acid Metabolism in Bone Metastatic Disease

PURPOSE OF REVIEW

Breast and prostate tumors frequently metastasize to the bone, but the underlying mechanisms for osteotropism remain elusive. An emerging feature of metastatic progression is metabolic adaptation of cancer cells to new environments. This review will summarize the recent advances on how cancer cells utilize amino acid metabolism during metastasis, from early dissemination to interactions with the bone microenvironment.

RECENT FINDINGS

Recent studies have suggested that certain metabolic preferences for amino acids may be associated with bone metastasis. Once in the bone microenvironment, cancer cells encounter a favorable microenvironment, where a changing nutrient composition of the tumor-bone microenvironment may alter metabolic interactions with bone-resident cells to further drive metastatic outgrowth. Enhanced amino acid metabolic programs are associated with bone metastatic disease and may be further augmented by the bone microenvironment. Additional studies are necessary to fully elucidate the role of amino acid metabolism on bone metastasis.

Glutaredoxin-1 promotes lymphangioleiomyomatosis progression through inhibiting Bim-mediated apoptosis via COX2/PGE2/ERK pathway

BACKGROUND

Lymphangioleiomyomatosis (LAM) is a female-predominant interstitial lung disease, characterized by progressive cyst formation and respiratory failure. Clinical treatment with the mTORC1 inhibitor rapamycin could relieve partially the respiratory symptoms, but not curative. It is urgent to illustrate the fundamental mechanisms of TSC2 deficiency to the development of LAM, especially mTORC1-independent mechanisms. Glutaredoxin-1 (Glrx), an essential glutathione (GSH)-dependent thiol-oxidoreductase, maintains redox homeostasis and participates in various processes via controlling protein GSH adducts. Redox signalling through protein GSH adducts in LAM remains largely elusive. Here, we demonstrate the underlying mechanism of Glrx in the pathogenesis of LAM.

METHODS

1. Abnormal Glrx expression in various kinds of human malignancies was identified by the GEPIA tumour database, and the expression of Glrx in LAM-derived cells was detected by real-time quantitative reverse transcription (RT-qPCR) and immunoblot. 2. Stable Glrx knockdown cell line was established to evaluate cellular impact. 3. Cell viability was determined by CCK8 assay. 4. Apoptotic cell number and intracellular reactive oxygen species (ROS) level were quantified by flow cytometry. 5. Cox2 expression and PGE2 production were detected to clarify the mechanism of Bim expression modulated by Glrx. 6. S-glutathionylated p65 was enriched and detected by immunoprecipitation and the direct regulation of Glrx on p65 was determined. 7. The xenograft animal model was established and photon flux was analyzed using IVIS Spectrum.

RESULTS

In LAM, TSC2 negatively regulated abnormal Glrx expression and activation in a mTORC1-independent manner. Knockdown of Glrx increased the expression of Bim and the accumulation of ROS, together with elevated S-glutathionylated proteins, contributing to the induction of apoptotic cell death and inhibited cell proliferation. Knockdown of Glrx in TSC2-deficient LAM cells increased GSH adducts on nuclear factor-kappa B p65, which contributed to a decrease in the expression of Cox2 and the biosynthesis of PGE2. Inhibition of PGE2 metabolism attenuated phosphorylation of ERK, which led to the accumulation of Bim, due to the imbalance of its phosphorylation and proteasome degradation. In xenograft tumour models, knockdown of Glrx in TSC2-deficient LAM cells inhibited tumour growth and increased tumour cell apoptosis.

CONCLUSIONS

Collectively, we provide a novel redox-dependent mechanism in the pathogenesis of LAM and propose that Glrx may be a beneficial strategy for the treatment of LAM or other TSC-related diseases.

Downregulation of PSAT1 inhibits cell proliferation and migration in uterine corpus endometrial carcinoma

Phosphoserine aminotransferase 1 (PSAT1) has been associated with the occurrence and development of various carcinomas; however, its function in uterine corpus endometrial carcinoma (UCEC) is unknown. We aimed to explore the relationship between PSAT1 and UCEC using The Cancer Genome Atlas database and functional experiments. PSAT1 expression levels in UCEC were employed using the paired sample t-test, Wilcoxon rank-sum test, the Clinical Proteomic Tumor Analysis Consortium database, and the Human Protein Atlas database, while survival curves were constructed using the Kaplan-Meier plotter. We performed Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis to explore the possible functions and related pathways of PSAT1. Furthermore, single-sample gene set enrichment analysis was performed to detect the relationship between PSAT1 and tumor immune infiltration. StarBase and quantitative PCR were used to predict and verify the interactions between miRNAs and PSAT1. The Cell Counting Kit-8, EdU assay, clone formation assay, western blotting and flow cytometry were used to evaluate cell proliferation. Finally, Transwell and Wound healing assays were used to assess cell invasion and migration. Our study found that PSAT1 was significantly overexpressed in UCEC, and this high expression was associated with a worse prognosis. A high level of PSAT1 expression was associated with a late clinical stage and, histological type. In addition, the results of GO and KEGG enrichment analysis showed that PSAT1 was mainly involved in the regulation of cell growth, immune system and cell cycle in UCEC. In addition, PSAT1 expression was positively correlated with Th2 cells and negatively correlated with Th17 cells. Furthermore, we also found that miR-195-5P negatively regulated the expression of PSAT1 in UCEC. Finally, the knockdown of PSAT1 resulted in the inhibition of cell proliferation, migration, and invasion in vitro. Overall, PSAT1 was identified as a potential target for the diagnosis and immunotherapy of UCEC.

Targeting tumor exosomal circular RNA cSERPINE2 suppresses breast cancer progression by modulating MALT1-NF-𝜅B-IL-6 axis of tumor-associated macrophages

BACKGROUND

Circular RNAs (circRNAs) have important regulatory functions in cancer, but the role of circRNAs in the tumor microenvironment (TME) remains unclear. Moreover, we also explore the effects of si-circRNAs loaded in nanoparticles as therapeutic agent for anti-tumor in vivo.

METHODS

We conducted bioinformatics analysis, qRT-PCR, EdU assays, Transwell assays, co-culture system and multiple orthotopic xenograft models to investigate the expression and function of circRNAs. Additionally, PLGA-based nanoparticles loaded with si-circRNAs were used to evaluate the potential of nanotherapeutic strategy in anti-tumor response.

RESULTS

We identified oncogene SERPINE2 derived circRNA, named as cSERPINE2, which was notably elevated in breast cancer and was closely related to poor clinical outcome. Functionally, tumor exosomal cSERPINE2 was shuttled to tumor associated macrophages (TAMs) and enhanced the secretion of Interleukin-6 (IL-6), leading to increased proliferation and invasion of breast cancer cells. Furthermore, IL-6 in turn increased the EIF4A3 and CCL2 levels within tumor cells in a positive feedback mechanism, further enhancing tumor cSERPINE2 biogenesis and promoting the recruitment of TAMs. More importantly, we developed a PLGA-based nanoparticle loaded with si-cSERPINE2, which effectively attenuated breast cancer progression in vivo.

CONCLUSIONS

Our study illustrates a novel mechanism that tumor exosomal cSERPINE2 mediates a positive feedback loop between tumor cells and TAMs to promote cancer progression, which may serve as a promising nanotherapeutic strategy for the treatment of breast cancer.

Dysregulated lipid metabolism in lymphangioleiomyomatosis pathogenesis as a paradigm of chronic lung diseases

A chronic inflammatory condition characterizes various lung diseases. Interestingly, a great contribution to inflammation is made by altered lipids metabolism, that can be caused by the deregulation of the mammalian target of rapamycin complex-1 (mTORC1) activity. There is evidence that one of mTOR downstream effectors, the sterol regulatory element-binding protein (SREBP), regulates the transcription of enzymes involved in the de novo fatty acid synthesis. Given its central role in cell metabolism, mTOR is involved in several biological processes. Among those, mTOR is a driver of senescence, a process that might contribute to the establishment of chronic lung disease because the characteristic irreversible inhibition of cell proliferation, associated to the acquisition of a pro-inflammatory senescence-associated secretory phenotype (SASP) supports the loss of lung parenchyma. The deregulation of mTORC1 is a hallmark of lymphangioleiomyomatosis (LAM), a rare pulmonary disease predominantly affecting women which causes cystic remodeling of the lung and progressive loss of lung function. LAM cells have senescent features and secrete SASP components, such as growth factors and pro-inflammatory molecules, like cancer cells. Using LAM as a paradigm of chronic and metastatic lung disease, here we review the published data that point out the role of dysregulated lipid metabolism in LAM pathogenesis. We will discuss lipids' role in the development and progression of the disease, to hypothesize novel LAM biomarkers and to propose the pharmacological regulation of lipids metabolism as an innovative approach for the treatment of the disease.

Loss of myeloid Tsc2 predisposes to angiotensin II-induced aortic aneurysm formation in mice

RATIONALE

Genetic studies have proved the involvement of Tuberous sclerosis complex subunit 2 (Tsc2) in aortic aneurysm. However, the exact role of macrophage Tsc2 in the vascular system remains unclear. Here, we examined the potential function of macrophage Tsc2 in the development of aortic remodeling and aortic aneurysms.

METHODS AND RESULTS

Conditional gene knockout strategy combined with histology and whole-transcriptomic analysis showed that Tsc2 deficiency in macrophages aggravated the progression of aortic aneurysms along with an upregulation of proinflammatory cytokines and matrix metallopeptidase-9 in the angiotensin II-induced mouse model. G protein-coupled receptor 68 (Gpr68), a proton-sensing receptor for detecting the extracellular acidic pH, was identified as the most up-regulated gene in Tsc2 deficient macrophages compared with control macrophages. Additionally, Tsc2 deficient macrophages displayed higher glycolysis and glycolytic inhibitor 2-deoxy-D-glucose treatment partially attenuated the level of Gpr68. We further demonstrated an Tsc2-Gpr68-CREB network in macrophages that regulates the inflammatory response, proteolytic degradation and vascular homeostasis. Gpr68 inhibition largely abrogated the progression of aortic aneurysms caused by Tsc2 deficiency in macrophages.

CONCLUSIONS

The findings reveal that Tsc2 deficiency in macrophages contributes to aortic aneurysm formation, at least in part, by upregulating Gpr68 expression, which subsequently drives proinflammatory processes and matrix metallopeptidase activation. The data also provide a novel therapeutic strategy to limit the progression of the aneurysm resulting from Tsc2 mutations.

LAM Cells as Potential Drivers of Senescence in Lymphangioleiomyomatosis Microenvironment

Senescence is a stress-response process characterized by the irreversible inhibition of cell proliferation, associated to the acquisition of a senescence-associated secretory phenotype (SASP), that may drive pathological conditions. Lymphangioleiomyomatosis (LAM) is a rare disease in which LAM cells, featuring the hyperactivation of the mammalian Target of Rapamycin Complex 1 (mTORC1) for the absence of tuberin expression, cause the disruption of the lung parenchyma. Considering that LAM cells secrete SASP factors and that mTOR is also a driver of senescence, we deepened the contribution of senescence in LAM cell phenotype. We firstly demonstrated that human primary tuberin-deficient LAM cells (LAM/TSC cells) have senescent features depending on mTOR hyperactivation, since their high positivity to SA-β galactosidase and to phospho-histone H2A.X are reduced by inducing tuberin expression and by inhibiting mTOR with rapamycin. Then, we demonstrated the capability of LAM/TSC cells to induce senescence. Indeed, primary lung fibroblasts (PLFs) grown in LAM/TSC conditioned medium increased the positivity to SA-β galactosidase and to phospho-histone H2A.X, as well as p21^WAF1/CIP1 expression, and enhanced the mRNA expression and the secretion of the SASP component IL-8. Taken together, these data make senescence a novel field of study to understand LAM development and progression.