Enhanced hexosamine metabolism drives metabolic and signaling networks involving hyaluronan production and O-GlcNAcylation to exacerbate breast cancer

Breast cancer therapy: from the perspective of glucose metabolism and glycosylation

Breast cancer is a leading cause of mortality and the most prevalent form of malignant tumor among women worldwide. Breast cancer cells exhibit an elevated glycolysis and altered glucose metabolism. Moreover, these cells display abnormal glycosylation patterns, influencing invasion, proliferation, metastasis, and drug resistance. Consequently, targeting glycolysis and mitigating abnormal glycosylation represent key therapeutic strategies for breast cancer. This review underscores the importance of protein glycosylation and glucose metabolism alterations in breast cancer. The current research efforts in developing effective interventions targeting glycolysis and glycosylation are further discussed.

Tolerable glycometabolic stress boosts cancer cell resilience through altered N-glycosylation and Notch signaling activation

Chronic metabolic stress paradoxically elicits pro-tumorigenic signals that facilitate cancer stem cell (CSC) development. Therefore, elucidating the metabolic sensing and signaling mechanisms governing cancer cell stemness can provide insights into ameliorating cancer relapse and therapeutic resistance. Here, we provide convincing evidence that chronic metabolic stress triggered by hyaluronan production augments CSC-like traits and chemoresistance by partially impairing nucleotide sugar metabolism, dolichol lipid-linked oligosaccharide (LLO) biosynthesis and N-glycan assembly. Notably, preconditioning with either low-dose tunicamycin or 2-deoxy-D-glucose, which partially interferes with LLO biosynthesis, reproduced the promoting effects of hyaluronan production on CSCs. Multi-omics revealed characteristic changes in N-glycan profiles and Notch signaling activation in cancer cells exposed to mild glycometabolic stress. Restoration of N-glycan assembly with glucosamine and mannose supplementation and Notch signaling blockade attenuated CSC-like properties and further enhanced the therapeutic efficacy of cisplatin. Therefore, our findings uncover a novel mechanism by which tolerable glycometabolic stress boosts cancer cell resilience through altered N-glycosylation and Notch signaling activation.

Endothelial cells metabolically regulate breast cancer invasion toward a microvessel

Breast cancer metastasis is initiated by invasion of tumor cells into the collagen type I-rich stroma to reach adjacent blood vessels. Prior work has identified that metabolic plasticity is a key requirement of tumor cell invasion into collagen. However, it remains largely unclear how blood vessels affect this relationship. Here, we developed a microfluidic platform to analyze how tumor cells invade collagen in the presence and absence of a microvascular channel. We demonstrate that endothelial cells secrete pro-migratory factors that direct tumor cell invasion toward the microvessel. Analysis of tumor cell metabolism using metabolic imaging, metabolomics, and computational flux balance analysis revealed that these changes are accompanied by increased rates of glycolysis and oxygen consumption caused by broad alterations of glucose metabolism. Indeed, restricting glucose availability decreased endothelial cell-induced tumor cell invasion. Our results suggest that endothelial cells promote tumor invasion into the stroma due, in part, to reprogramming tumor cell metabolism.

O-GlcNAcylation at the center of antitumor immunity

The post-translational modification known as O-GlcNAcylation is a highly dysregulated process in tumors, and a key contributor to malignant transformation. In contrast, after three decades since its discovery, very little has been revealed about this process in the immune system. With the prospect of targeting O-GlcNAcylation as tumor therapy, greater understanding of how it regulates immune responses in the context of the tumor microenvironment will be needed. Here, we discuss recent discoveries from which a picture is emerging that O-GlcNAcylation, in either tumors or in immune cells, could negatively impact overall antitumor immune responses. We propose that interference with O-GlcNAcylation thus holds promise for cancer treatment from both perspectives.

Hyaluronic acid: More than a carrier, having an overpowering extracellular and intracellular impact on cancer

Hyaluronic acid (HA), also named hyaluronan, is an omnipresent component of the tissue microenvironment. It is extensively used to formulate targeted drug delivery systems for cancer. Although HA itself has pivotal influences in various cancers, its calibers are somewhat neglected when using it as delivering platform to treat cancer. In the last decade, multiple studies revealed roles of HA in cancer cell proliferation, invasion, apoptosis, and dormancy through pathways like mitogen-activated protein kinase-extracellular signal-regulated kinase (MAPK/ERK), P³⁸, and nuclear factor kappa-light chain-enhancer of activated B cells (NFκB). A more fascinating fact is that the distinct molecular weight (MW) of HA exerts disparate effects on the same type of cancer. Its overwhelming use in cancer therapy and other therapeutic products make collective research on the sundry impact of it on various types of cancer, an essential aspect to be considered in all of these domains. Even the development of new therapies against cancer needed meticulous studies on HA because of its divergence of activity based on MW. This review will provide painstaking insight into the extracellular and intracellular bioactivity of HA, its modified forms, and its MW in cancers, which may improve the management of cancer.

Differential Effects of Pancreatic Cancer-Derived Extracellular Vesicles Driving a Suppressive Environment

Pancreatic ductal adenocarcinoma (PDAC) cells display extensive crosstalk with their surrounding environment to regulate tumor growth, immune evasion, and metastasis. Recent advances have attributed many of these interactions to intercellular communication mediated by small extracellular vesicles (sEVs), involving cancer-associated fibroblasts (CAF). To explore the impact of sEVs on monocyte lineage transition as well as the expression of checkpoint receptors and activation markers, peripheral blood monocytes from healthy subjects were exposed to PDAC-derived sEVs. Additionally, to analyze the role of sEV-associated HA in immune regulation and tissue-resident fibroblasts, monocytes and pancreatic stellate cells were cultured in the presence of PDAC sEVs with or depleted of HA. Exposure of monocytes to sEVs resulted in unique phenotypic changes in HLA-DR, PD-L1, CD86 and CD64 expression, and cytokine secretion that was HA-independent except for IL-1β and MIP1β. In contrast, monocyte suppression of autologous T cell proliferation was reduced following exposure to HA-low sEVs. In addition, exposure of stellate cells to sEVs upregulated the secretion of various cytokines, including MMP-9, while removal of HA from PDAC-derived sEVs attenuated the secretion of MMP-9, demonstrating the role of sEV-associated HA in regulating expression of this pro-tumorigenic cytokine from stellate cells. This observation lends credence to the findings from the TCGA database that PDAC patients with high levels of enzymes in the HA synthesis pathway had worse survival rates compared with patients having low expression of these enzymes. PDAC-derived sEVs have an immune modulatory role affecting the activation state of monocyte subtypes. However, sEV-associated HA does not affect monocyte phenotype but alters cytokine secretion and suppression of autologous T cell proliferation and induces secretion of pro-tumorigenic factors by pancreatic stellate cells (PSC), as has been seen following the conversion of PSCs to cancer-associated fibroblasts (CAFs). Interruption of the hexosamine biosynthetic pathway, activated in PDAC producing the key substrate (UDP-GlcNAc) for HA synthesis, thus, represents a potential clinical interception strategy for PDAC patients. Findings warrant further investigations of underlying mechanisms involving larger sample cohorts.

Convergent Approaches to Delineate the Metabolic Regulation of Tumor Invasion by Hyaluronic Acid Biosynthesis

Metastasis is the leading cause of breast cancer-related deaths and is often driven by invasion and cancer-stem like cells (CSCs). Both the CSC phenotype and invasion are associated with increased hyaluronic acid (HA) production. How these independent observations are connected, and which role metabolism plays in this process, remains unclear due to the lack of convergent approaches integrating engineered model systems, computational tools, and cancer biology. Using microfluidic invasion models, metabolomics, computational flux balance analysis, and bioinformatic analysis of patient data, the functional links between the stem-like, invasive, and metabolic phenotype of breast cancer cells as a function of HA biosynthesis are investigated. These results suggest that CSCs are more invasive than non-CSCs and that broad metabolic changes caused by overproduction of HA play a role in this process. Accordingly, overexpression of hyaluronic acid synthases (HAS) 2 or 3 induces a metabolic phenotype that promotes cancer cell stemness and invasion in vitro and upregulates a transcriptomic signature predictive of increased invasion and worse patient survival. This study suggests that HA overproduction leads to metabolic adaptations to satisfy the energy demands for 3D invasion of breast CSCs highlighting the importance of engineered model systems and multidisciplinary approaches in cancer research.

Hyperglycemia and O-GlcNAc transferase activity drive a cancer stem cell pathway in triple-negative breast cancer

BACKGROUND

Enhanced glucose metabolism is a feature of most tumors, but downstream functional effects of aberrant glucose flux are difficult to mechanistically determine. Metabolic diseases including obesity and diabetes have a hyperglycemia component and are correlated with elevated pre-menopausal cancer risk for triple-negative breast cancer (TNBC). However, determining pathways for hyperglycemic disease-coupled cancer risk remains a major unmet need. One aspect of cellular sugar utilization is the addition of the glucose-derived protein modification O-GlcNAc (O-linked N-acetylglucosamine) via the single human enzyme that catalyzes this process, O-GlcNAc transferase (OGT). The data in this report implicate roles of OGT and O-GlcNAc within a pathway leading to cancer stem-like cell (CSC) expansion. CSCs are the minor fraction of tumor cells recognized as a source of tumors as well as fueling metastatic recurrence. The objective of this study was to identify a novel pathway for glucose-driven expansion of CSC as a potential molecular link between hyperglycemic conditions and CSC tumor risk factors.

METHODS

We used chemical biology tools to track how a metabolite of glucose, GlcNAc, became linked to the transcriptional regulatory protein tet-methylcytosine dioxygenase 1 (TET1) as an O-GlcNAc post-translational modification in three TNBC cell lines. Using biochemical approaches, genetic models, diet-induced obese animals, and chemical biology labeling, we evaluated the impact of hyperglycemia on CSC pathways driven by OGT in TNBC model systems.

RESULTS

We showed that OGT levels were higher in TNBC cell lines compared to non-tumor breast cells, matching patient data. Our data identified that hyperglycemia drove O-GlcNAcylation of the protein TET1 via OGT-catalyzed activity. Suppression of pathway proteins by inhibition, RNA silencing, and overexpression confirmed a mechanism for glucose-driven CSC expansion via TET1-O-GlcNAc. Furthermore, activation of the pathway led to higher levels of OGT production via feed-forward regulation in hyperglycemic conditions. We showed that diet-induced obesity led to elevated tumor OGT expression and O-GlcNAc levels in mice compared to lean littermates, suggesting relevance of this pathway in an animal model of the hyperglycemic TNBC microenvironment.

CONCLUSIONS

Taken together, our data revealed a mechanism whereby hyperglycemic conditions activated a CSC pathway in TNBC models. This pathway can be potentially targeted to reduce hyperglycemia-driven breast cancer risk, for instance in metabolic diseases. Because pre-menopausal TNBC risk and mortality are correlated with metabolic diseases, our results could lead to new directions including OGT inhibition for mitigating hyperglycemia as a risk factor for TNBC tumorigenesis and progression.

GNPNAT1 is a potential biomarker correlated with immune infiltration and immunotherapy outcome in breast cancer

Background

Glucosamine 6-phosphate N-acetyltransferase (GNPNAT1) is a crucial enzyme involving hexosamine biosynthesis pathway and is upregulated in breast cancer (BRCA). However, its biological function and mechanism on patients in BRCA have not been investigated.

Methods

In this study, the differential expression of GNPNAT1 was analyzed between BRCA tissues and normal breast tissues using the Cancer Genome Atlas (TCGA) database and Gene Expression Omnibus (GEO) database, which was validated by quantitative real-time polymerase chain reaction, Western blot and immunohistochemistry. Then, the potential clinical value of GNPNAT1 in BRCA was investigated based on TCGA database. Functional enrichment analyses, including Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, Gene Set Variation Analysis, were performed to explore the potential signaling pathways and biological functions involved in GNPNAT1 in BRCA. Tumor immune infiltration was analyzed using ESTIMATE, CIBERSORT and TISIDB database; and immune therapy response scores were assessed using TIDE. Finally, Western blot, Cell counting kit-8 and Transwell assay were used to determine the proliferation and invasion abilities of breast cancer cells with GNPNAT1 knockdown.

Results

GNPNAT1 was up-regulated in BRCA tissues compared with normal tissues which was subsequently verified in different cell lines and clinical tissue samples. Based on TCGA and GEO, the overexpression of GNPNAT1 in BRCA contributed to a significant decline in overall survive and disease specific survive. Functional enrichment analyses indicated that the enriched pathways in high GNPNAT1 expression group included citrate cycle, N-glycan biosynthesis, DNA repair, and basal transcription factors. Moreover, the overexpression of GNPNAT1 was negatively correlated with immunotherapy response and the levels of immune cell infiltration of CD8+ T cells, B cells, natural killer cells, dendritic cells and macrophages. Knockdown of GNPNAT1 impairs the proliferation and invasion abilities of breast cancer cells.

Conclusion

GNPNAT1 is a potential diagnostic, prognostic biomarker and novel target for intervention in BRCA.

A functional gene module identification algorithm in gene expression data based on genetic algorithm and gene ontology

Since genes do not function individually, the gene module is considered an important tool for interpreting gene expression profiles. In order to consider both functional similarity and expression similarity in module identification, GMIGAGO, a functional Gene Module Identification algorithm based on Genetic Algorithm and Gene Ontology, was proposed in this work. GMIGAGO is an overlapping gene module identification algorithm, which mainly includes two stages: In the first stage (initial identification of gene modules), Improved Partitioning Around Medoids Based on Genetic Algorithm (PAM-GA) is used for the initial clustering on gene expression profiling, and traditional gene co-expression modules can be obtained. Only similarity of expression levels is considered at this stage. In the second stage (optimization of functional similarity within gene modules), Genetic Algorithm for Functional Similarity Optimization (FSO-GA) is used to optimize gene modules based on gene ontology, and functional similarity within gene modules can be improved. Without loss of generality, we compared GMIGAGO with state-of-the-art gene module identification methods on six gene expression datasets, and GMIGAGO identified the gene modules with the highest functional similarity (much higher than state-of-the-art algorithms). GMIGAGO was applied in BRCA, THCA, HNSC, COVID-19, Stem, and Radiation datasets, and it identified some interesting modules which performed important biological functions. The hub genes in these modules could be used as potential targets for diseases or radiation protection. In summary, GMIGAGO has excellent performance in mining molecular mechanisms, and it can also identify potential biomarkers for individual precision therapy.

Dysregulation of hexosamine biosynthetic pathway wiring metabolic signaling circuits in cancer

Metabolite sensing, a fundamental biological process, plays a key role in metabolic signaling circuit rewiring. Hexosamine biosynthetic pathway (HBP) is a glucose metabolic pathway essential for the synthesis of uridine diphosphate N-acetylglucosamine (UDP-GlcNAc), which senses key nutrients and integrally maintains cellular homeostasis. UDP-GlcNAc dynamically regulates protein N-glycosylation and O-linked-N-acetylglucosamine modification (O-GlcNAcylation). Dysregulated HBP flux leads to abnormal protein glycosylation, and contributes to cancer development and progression by affecting protein function and cellular signaling. Furthermore, O-GlcNAcylation regulates cellular signaling pathways, and its alteration is linked to various cancer characteristics. Additionally, recent findings have suggested a close association between HBP stimulation and cancer stemness; an elevated HBP flux promotes cancer cell conversion to cancer stem cells and enhances chemotherapy resistance via downstream signal activation. In this review, we highlight the prominent roles of HBP in metabolic signaling and summarize the recent advances in HBP and its downstream signaling, relevant to cancer.

Development of a metabolism-related signature for predicting prognosis, immune infiltration and immunotherapy response in breast cancer

Breast cancer (BRCA) is the most commonly diagnosed cancer and among the top causes of cancer deaths globally. The abnormality of the metabolic process is an important characteristic that distinguishes cancer cells from normal cells. Currently, there are few metabolic molecular models to evaluate the prognosis and treatment response of BRCA patients. By analyzing RNA-seq data of BRCA samples from public databases via bioinformatic approaches, we developed a prognostic signature based on seven metabolic genes (PLA2G2D, GNPNAT1, QPRT, SHMT2, PAICS, NT5E and PLPP2). Low-risk patients showed better overall survival in all five cohorts (TCGA cohort, two external validation cohorts and two internal validation cohorts). There was a higher proportion of tumor-infiltrating CD8⁺ T cells, CD4⁺ memory resting T cells, gamma delta T cells and resting dendritic cells and a lower proportion of M0 and M2 macrophages in the low-risk group. Low-risk patients also showed higher ESTIMATE scores, higher immune function scores, higher Immunophenoscores (IPS) and checkpoint expression, lower stemness scores, lower TIDE (Tumor Immune Dysfunction and Exclusion) scores and IC50 values for several chemotherapeutic agents, suggesting that low-risk patients could respond more favorably to immunotherapy and chemotherapy. Two real-world patient cohorts receiving anti-PD-1 therapy were applied for validating the predictive results. Molecular subtypes identified based on these seven genes also showed different immune characteristics. Immunohistochemical data obtained from the human protein atlas database demonstrated the protein expression of signature genes. This research may contribute to the identification of metabolic targets for BRCA and the optimization of risk stratification and personalized treatment for BRCA patients.

Identification of hexosamine biosynthesis pathway as a novel prognostic signature and its correlation with immune infiltration in bladder cancer

Background: Urinary bladder cancer (UBC) is one of the common urological malignancies, lacking reliable biomarkers to predict clinical outcomes in UBC patients. Thus, it is needed to identify the novel diagnostic/prognostic biomarkers to stratify the high-risk UBC patients. As a shunt pathway of glycolysis, the hexosamine biosynthesis pathway (HBP) has been implicated in carcinogenesis. However, its prognostic value in UBC remains unclear.

Methods: The RNA sequencing and mRNA microarray datasets were downloaded from The Cancer Genome Atlas (TCGA) and the Gene Expression Omnibus databases. The expression levels of five HBP genes were analyzed in normal and UBC samples, and their associations with stage, grade and survival were plotted. The performance of HBP risk group was evaluated by receiver-operating characteristics (ROC) curve. The HBP signature was generated by Gene Set Variation Analysis (GSVA) and its association with clinicopathological parameters and survival were analyzed. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were carried out to examine the potential biological functions of HBP using DAVID online tool. The infiltration estimation fraction of immune cells was performed using CIBERSORT-ABS algorithm. Gene set enrichment analysis (GSEA) was used to explore the potential function of HBP in tumor immunoregulation.

Results: Four HBP genes were upregulated in UBCs compared to normal tissues in TCGA-BLCA dataset. The upregulation of all five HBP genes was significantly associated with tumor grade and stage of UBC in three independent UBC datasets. The expression of HBP genes predicted poor clinical outcomes in UBC patients in both TCGA-BLCA and GSE13507 datasets. The high-risk group based on HBP genes showed a poor prognosis. Furthermore, HBP signature was positively associated with tumor grade and stage in TCGA-BLCA dataset and with tumor grade, stage, distal metastasis and poor survival in GSE13507 dataset. Interestingly, high-HBP signature group exhibited a high infiltration of immune cells, particularly the macrophage population.

Conclusion: We identified that HBP was a promising prognostic biomarker in UBC patients and strongly associated with immune infiltration.

SP and KLF Transcription Factors in Cancer Metabolism

Tumor development and progression depend on reprogramming of signaling pathways that regulate cell metabolism. Alterations to various metabolic pathways such as glycolysis, oxidative phosphorylation, lipid metabolism, and hexosamine biosynthesis pathway are crucial to sustain increased redox, bioenergetic, and biosynthesis demands of a tumor cell. Transcription factors (oncogenes and tumor suppressors) play crucial roles in modulating these alterations, and their functions are tethered to major metabolic pathways under homeostatic conditions and disease initiation and advancement. Specificity proteins (SPs) and Krüppel-like factors (KLFs) are closely related transcription factors characterized by three highly conserved zinc fingers domains that interact with DNA. Studies have demonstrated that SP and KLF transcription factors are expressed in various tissues and regulate diverse processes such as proliferation, differentiation, apoptosis, inflammation, and tumorigenesis. This review highlights the role of SP and KLF transcription factors in the metabolism of various cancers and their impact on tumorigenesis. A better understanding of the role and underlying mechanisms governing the metabolic changes during tumorigenesis could provide new therapeutic opportunities for cancer treatment.

Role of O-GlcNAcylation on cancer stem cells: Connecting nutrient sensing to cell plasticity

Tumor growth and metastasis can be promoted by a small sub-population of cancer cells, termed cancer stem-like cells (CSCs). While CSCs possess capability in self-renewing and differentiating, the hierarchy of CSCs during tumor growth is highly plastic. This plasticity in CSCs fate and function can be regulated by signals from the tumor microenvironment. One emerging pathway in CSCs that connects the alteration in microenvironment and signaling network in cancer cells is the hexosamine biosynthetic pathway (HBP). The final product of HBP, UDP-N-acetylglucosamine (UDP-GlcNAc), is utilized for glycosylating of membrane and secreted proteins, but also nuclear and cytoplasmic proteins by the post-translational modification O-GlcNAcylation. O-GlcNAcylation and its enzyme, O-GlcNAc transferase (OGT), are upregulated in nearly all cancers and been linked to regulate many cancer cell phenotypes. Recent studies have begun to connect OGT and O-GlcNAcylation to regulation of CSCs. In this review, we will discuss the emerging role of OGT and O-GlcNAcylation in regulating fate and plasticity of CSCs, as well as the potential in targeting OGT/O-GlcNAcylation in CSCs.

Extrinsic hyaluronic acid induction differentially modulates intracellular glutamine metabolism in breast cancer stem cells

The effect of low and high molecular weight hyaluronic acid on glutamine metabolism in luminal and basal breast cancer and cancer stem cells is being investigated. In luminal cell lines (MCF-7), HA enhances the intracellular utilization of gln in redox metabolism and decreases its use in TCA. On the contrary, in MDAMB-231 cells, HA induces the uptake of gln to be utilized in anaplerosis rather than ROS maintenance. However, in MCF-7 CSCs, HA induces up-regulation of xCT, further, it uses gln-derived glutamate for the exchange of cystine, thus maintaining ROS levels through xCT. MDA-MB-231 CSCs reduce the secretion of glutamate in response to HA and decrease the gln flux towards reductive carboxylation. Conclusively, our study demonstrated that although the uptake of gln is enhanced by HA, it is differentially utilized intracellularly in breast cancer cells. This study could significantly influence the therapeutics involving HA and Gln in breast cancer.

High Levels of Hyaluronic Acid Synthase-2 Mediate NRF2-Driven Chemoresistance in Breast Cancer Cells

Hyaluronic acid (HA), a ligand of CD44, accumulates in some types of tumors and is responsible for tumor progression. The nuclear factor erythroid 2-like 2 (NRF2) regulates cytoprotective genes and drug transporters, which promotes therapy resistance in tumors. Previously, we showed that high levels of CD44 are associated with NRF2 activation in cancer stem like-cells. Herein, we demonstrate that HA production was increased in doxorubicin-resistant breast cancer MCF7 cells (MCF7-DR) via the upregulation of HA synthase-2 (HAS2). HA incubation increased NRF2, aldo-keto reductase 1C1 (AKR1C1), and multidrug resistance gene 1 (MDR1) levels. Silencing of HAS2 or CD44 suppressed NRF2 signaling in MCF7-DR, which was accompanied by increased doxorubicin sensitivity. The treatment with a HAS2 inhibitor, 4-methylumbelliferone (4-MU), decreased NRF2, AKR1C1, and MDR1 levels in MCF7-DR. Subsequently, 4-MU treatment inhibited sphere formation and doxorubicin resistance in MCF7-DR. The Cancer Genome Atlas (TCGA) data analysis across 32 types of tumors indicates the amplification of HAS2 gene is a common genetic alteration and is negatively correlated with the overall survival rate. In addition, high HAS2 mRNA levels are associated with increased NRF2 signaling and poor clinical outcome in breast cancer patients. Collectively, these indicate that HAS2 elevation contributes to chemoresistance and sphere formation capacity of drug-resistant MCF7 cells by activating CD44/NRF2 signaling, suggesting a potential benefit of HAS2 inhibition.

Mechanisms of coordinating hyaluronan and glycosaminoglycan production by nucleotide sugars

Hyaluronan is a versatile macromolecule capable of an exceptional range of functions from cushioning and hydration to dynamic signaling in development and disease. Because of its critical roles, hyaluronan production is regulated at multiple levels including epigenetic, transcriptional, and post-translational control of the three hyaluronan synthase (HAS) enzymes. Precursor availability can dictate the rate and amount of hyaluronan synthesized and shed by the cells producing it. However, the nucleotide-activated sugar substrates for hyaluronan synthesis by HAS also participate in exquisitely fine tuned cross talking pathways that intersect with central carbohydrate metabolism. Multiple UDP-sugars have alternative metabolic fates and exhibit coordinated and reciprocal allosteric control of enzymes within their biosynthetic pathways to preserve appropriate precursor ratios for accurate partitioning among downstream products, while also sensing and maintaining energy homeostasis. Since the dysregulation of nucleotide sugar and hyaluronan synthesis is associated with multiple pathologies, these pathways offer opportunities for therapeutic intervention. Recent structures of several key rate-limiting enzymes in the UDP-sugar synthesis pathways have offered new insights to the overall regulation of hyaluronan production by precursor fate decisions. The details of UDP-sugar control and the structural basis for underlying mechanisms are discussed in this review.

A Novel Approach for the Discovery of Biomarkers of Radiotherapy Response in Breast Cancer

Radiotherapy (RT) is an important treatment modality for the local control of breast cancer (BC). Unfortunately, not all patients that receive RT will obtain a therapeutic benefit, as cancer cells that either possess intrinsic radioresistance or develop resistance during treatment can reduce its efficacy. For RT treatment regimens to become personalised, there is a need to identify biomarkers that can predict and/or monitor a tumour's response to radiation. Here we describe a novel method to identify such biomarkers. Liquid chromatography-mass spectrometry (LC-MS) was used on conditioned media (CM) samples from a radiosensitive oestrogen receptor positive (ER⁺) BC cell line (MCF-7) to identify cancer-secreted biomarkers which reflected a response to radiation. A total of 33 radiation-induced secreted proteins that had higher (up to 12-fold) secretion levels at 24 h post-2 Gy radiation were identified. Secretomic results were combined with whole-transcriptome gene expression experiments, using both radiosensitive and radioresistant cells, to identify a signature related to intrinsic radiosensitivity. Gene expression analysis assessing the levels of the 33 proteins showed that 5 (YBX3, EIF4EBP2, DKK1, GNPNAT1 and TK1) had higher expression levels in the radiosensitive cells compared to their radioresistant derivatives; 3 of these proteins (DKK1, GNPNAT1 and TK1) underwent in-lab and initial clinical validation. Western blot analysis using CM samples from cell lines confirmed a significant increase in the release of each candidate biomarker from radiosensitive cells 24 h after treatment with a 2 Gy dose of radiation; no significant increase in secretion was observed in the radioresistant cells after radiation. Immunohistochemistry showed that higher intracellular protein levels of the biomarkers were associated with greater radiosensitivity. Intracellular levels were further assessed in pre-treatment biopsy tissues from patients diagnosed with ER⁺ BC that were subsequently treated with breast-conserving surgery and RT. High DKK1 and GNPNAT1 intracellular levels were associated with significantly increased recurrence-free survival times, indicating that these two candidate biomarkers have the potential to predict sensitivity to RT. We suggest that the methods highlighted in this study could be utilised for the identification of biomarkers that may have a potential clinical role in personalising and optimising RT dosing regimens, whilst limiting the administration of RT to patients who are unlikely to benefit.

Inhibition of GFAT1 in lung cancer cells destabilizes PD-L1 protein

Immunotherapy using checkpoint blockers (antibodies) has been a major advance in recent years in the management of various types of solid cancers including lung cancer. One target of checkpoint blockers is programmed death ligand 1 (PD-L1) expressed by cancer cells, which engages programmed death 1 (PD-1) on T cells and Natural Killer (NK) cells resulting in suppression of their activation and cancer-killing function, respectively. Apart from antibodies, other clinically relevant agents that can inhibit PD-L1 are limited. PD-L1 protein stability depends on its glycosylation. Here we show that L-glutamine:D-fructose amidotransferase 1 (GFAT1) a rate-limiting enzyme of the hexosamine biosynthesis pathway (HBP) which produces uridine diphosphate-N-acetyl-β-glucosamine (UDP-GlcNAc), a precursor for glycosylation, is required for the stability of PD-L1 protein. Inhibition of GFAT1 activity markedly reduced interferon γ (IFNγ)-induced PD-L1 levels in various lung cancer cell lines. GFAT1 inhibition suppressed glycosylation of PD-L1 and accelerated its proteasomal degradation. Importantly, inhibition of GFAT1 in IFNγ-treated cancer cells enhanced the activation of T cells and the cancer-killing activity of NK cells. These findings support using GFAT1 inhibitors to manipulate PD-L1 protein level that could augment the efficacy of immunotherapy for lung cancer.

The α2δ1 subunit of the voltage-gated calcium channel acts as a potential candidate for breast cancer tumor initial cells biomarker

BACKGROUND

The voltage-gated calcium channel subunit alpha 2 delta 1 (α2δ1) is a functional tumor initial cells (TICs) marker for some solid cancer cells. This study aimed to investigate whether α2δ1 can be used as a potential TIC marker for breast cancer cells.

METHODS

α2δ1+ and α2δ1- cells were identified and sorted from the breast cancer cell lines MDA-MB-231, MDA-MB-435s and ZR-75-1 by Immunofluorescence (IF) and Fluorescent-activated cell sorting (FACS) analyses. Spheroid formation in vitro and tumorigenesis in NOD/SCID mice were assessed to determine the self-renewal and serial transplantation abilities of these cells. Using a lentivirus infection system for α2δ1 in breast cancer cell lines, we determined the mRNA levels of stemnessassociated genes by quality real-time PCR (qRT-PCR). Boyden chamber and wounding assays were further performed to detect the migration of α2δ1 overexpression cells. Bioinformatics explored the relationship of molecular classification of breast cancer and drug resistance.

RESULTS

α2δ1 presents on the cytomembrane of breast cancer cells, with a positive rate of 1.5-3%. The α2δ1+ cells in breast cancer cell lines have a stronger self-renewal ability and tumor initiating properties in vitro and in vivo. Overexpressing α2δ1 successfully enhanced the sphere-forming efficiency, and upregulated the expression of stemness-associated genes, and increased cell migration. However, seldom significant was available between estrogen receptor +/- (ER+/-), progesterone receptor (PR+/-), and Her2+/-.

CONCLUSIONS

Breast cancer cells positive for the α2δ1 charactered tumor initiation, and α2δ1 is a potential TIC marker for breast cancer that further promotes the migration.

Upregulation of GNPNAT1 Predicts Poor Prognosis and Correlates With Immune Infiltration in Lung Adenocarcinoma

BACKGROUND

Glucosamine 6-phosphate N-acetyltransferase (GNPNAT1) is a key enzyme in the hexosamine biosynthetic pathway (HBP), which functions as promoting proliferation in some tumors, yet its potential biological function and mechanism in lung adenocarcinoma (LUAD) have not been explored.

METHODS

The mRNA differential expression of GNPNAT1 in LUAD and normal tissues was analyzed using the Cancer Genome Atlas (TCGA) database and validated by real-time PCR. The clinical value of GNPNAT1 in LUAD was investigated based on the data from the TCGA database. Then, immunohistochemistry (IHC) of GNPNAT1 was applied to verify the expression and clinical significance in LUAD from the protein level. The relationship between GNPNAT1 and epigenetics was explored using the cBioPortal database, and the miRNAs regulating GNPNAT1 were found using the miRNA database. The association between GNPNAT1 expression and tumor-infiltrating immune cells in LUAD was observed through the Tumor IMmune Estimation Resource (TIMER). Finally, Gene set enrichment analysis (GSEA) was used to explore the biological signaling pathways involved in GNPNAT1 in LUAD.

RESULTS

GNPNAT1 was upregulated in LUAD compared with normal tissues, which was verified through qRT-PCR in different cell lines (P < 0.05), and associated with patients' clinical stage, tumor size, and lymphatic metastasis status (all P < 0.01). Kaplan-Meier (KM) analysis suggested that patients with upregulated GNPNAT1 had a relatively poor prognosis (P < 0.0001). Furthermore, multivariate Cox regression analysis indicated that GNPNAT1 was an independent prognostic factor for LUAD (OS, TCGA dataset: HR = 1.028, 95% CI: 1.013-1.044, P < 0.001; OS, validation set: HR = 1.313, 95% CI: 1.130-1.526, P < 0.001). GNPNAT1 overexpression was correlated with DNA copy amplification (P < 0.0001), low DNA methylation (R = -0.52, P < 0.0001), and downregulation of hsa-miR-30d-3p (R = -0.17, P < 0.001). GNPNAT1 expression was linked to B cells (R = -0.304, P < 0.0001), CD4+T cells (R = -0.218, P < 0.0001), and dendritic cells (R = -0.137, P = 0.002). Eventually, GSEA showed that the signaling pathways of the cell cycle, ubiquitin-mediated proteolysis, mismatch repair and p53 were enriched in the GNPNAT1 overexpression group.

CONCLUSION

GNPNAT1 may be a potential prognostic biomarker and novel target for intervention in LUAD.

Signaling Pathways Involved in Nutrient Sensing Control in Cancer Stem Cells: An Overview

Cancer cells characteristically have a high proliferation rate. Because tumor growth depends on energy-consuming anabolic processes, including biosynthesis of protein, lipid, and nucleotides, many tumor-associated conditions, including intermittent oxygen deficiency due to insufficient vascularization, oxidative stress, and nutrient deprivation, results from fast growth. To cope with these environmental stressors, cancer cells, including cancer stem cells, must adapt their metabolism to maintain cellular homeostasis. It is well- known that cancer stem cells (CSC) reprogram their metabolism to adapt to live in hypoxic niches. They usually change from oxidative phosphorylation to increased aerobic glycolysis even in the presence of oxygen. However, as opposed to most differentiated cancer cells relying on glycolysis, CSCs can be highly glycolytic or oxidative phosphorylation-dependent, displaying high metabolic plasticity. Although the influence of the metabolic and nutrient-sensing pathways on the maintenance of stemness has been recognized, the molecular mechanisms that link these pathways to stemness are not well known. Here in this review, we describe the most relevant signaling pathways involved in nutrient sensing and cancer cell survival. Among them, Adenosine monophosphate (AMP)-activated protein kinase (AMPK) pathway, mTOR pathway, and Hexosamine Biosynthetic Pathway (HBP) are critical sensors of cellular energy and nutrient status in cancer cells and interact in complex and dynamic ways.

Cell Energy Metabolism and Hyaluronan Synthesis

Hyaluronan (HA) is a linear glycosaminoglycan (GAG) of extracellular matrix (ECM) synthesized by three hyaluronan synthases (HASes) at the plasma membrane using uridine diphosphate (UDP)-glucuronic acid (UDP-GlcUA) and UDP-N-acetylglucosamine (UDP-GlcNAc) as substrates. The production of HA is mainly regulated by hyaluronan synthase 2 (HAS2), that can be controlled at different levels, from epigenetics to transcriptional and post-translational modifications. HA biosynthesis is an energy-consuming process and, along with HA catabolism, is strongly connected to the maintenance of metabolic homeostasis. The cytoplasmic pool of UDP-sugars is critical for HA synthesis. UDP-GlcNAc is an important nutrient sensor and serves as donor substrate for the O-GlcNAcylation of many cytosolic proteins, including HAS2. This post-translational modification stabilizes HAS2 in the membrane and increases HA production. Conversely, HAS2 can be phosphorylated by AMP activated protein kinase (AMPK), a master metabolic regulator activated by low ATP/AMP ratios, which inhibits HA secretion. Similarly, HAS2 expression and the deposition of HA within the pericellular coat are inhibited by sirtuin 1 (SIRT1), another important energetic sensor, confirming the tight connection between nutrients availability and HA metabolism.

Angiostatic cues from the matrix: Endothelial cell autophagy meets hyaluronan biology

The extracellular matrix encompasses a reservoir of bioactive macromolecules that modulates a cornucopia of biological functions. A prominent body of work posits matrix constituents as master regulators of autophagy and angiogenesis and provides molecular insight into how these two processes are coordinated. Here, we review current understanding of the molecular mechanisms underlying hyaluronan and HAS2 regulation and the role of soluble proteoglycan in affecting autophagy and angiogenesis. Specifically, we assess the role of proteoglycan-evoked autophagy in regulating angiogenesis via the HAS2-hyaluronan axis and ATG9A, a novel HAS2 binding partner. We discuss extracellular hyaluronan biology and the post-transcriptional and post-translational modifications that regulate its main synthesizer, HAS2. We highlight the emerging group of proteoglycans that utilize outside-in signaling to modulate autophagy and angiogenesis in cancer microenvironments and thoroughly review the most up-to-date understanding of endorepellin signaling in vascular endothelia, providing insight into the temporal complexities involved.

Hyaluronan: Metabolism and Function

As a major polysaccharide component of the extracellular matrix, hyaluronan plays essential roles in the organization of tissue architecture and the regulation of cellular functions, such as cell proliferation and migration, through interactions with cell-surface receptors and binding molecules. Metabolic pathways for biosynthesis and degradation tightly control the turnover rate, concentration, and molecular size of hyaluronan in tissues. Despite the relatively simple chemical composition of this polysaccharide, its wide range of molecular weights mediate diverse functions that depend on molecular size and tissue concentration. Genetic engineering and pharmacological approaches have demonstrated close associations between hyaluronan metabolism and functions in many physiological and pathological events, including morphogenesis, wound healing, and inflammation. Moreover, emerging evidence has suggested that the accumulation of hyaluronan extracellular matrix and fragments due to the altered expression of hyaluronan synthases and hyaluronidases potentiates cancer development and progression by remodeling the tumor microenvironment. In addition to the well-known functions exerted by extracellular hyaluronan, recent metabolomic approaches have also revealed that its synthesis can regulate cellular functions via the reprogramming of cellular metabolism. This review highlights the current advances in knowledge on the biosynthesis and catabolism of hyaluronan and describes the diverse functions associated with hyaluronan metabolism.

Roles of Proteoglycans and Glycosaminoglycans in Cancer Development and Progression

The extracellular matrix (ECM) spatiotemporally controls cell fate; however, dysregulation of ECM remodeling can lead to tumorigenesis and cancer development by providing favorable conditions for tumor cells. Proteoglycans (PGs) and glycosaminoglycans (GAGs) are the major macromolecules composing ECM. They influence both cell behavior and matrix properties through direct and indirect interactions with various cytokines, growth factors, cell surface receptors, adhesion molecules, enzymes, and glycoproteins within the ECM. The classical features of PGs/GAGs play well-known roles in cancer angiogenesis, proliferation, invasion, and metastasis. Several lines of evidence suggest that PGs/GAGs critically affect broader aspects in cancer initiation and the progression process, including regulation of cell metabolism, serving as a sensor of ECM's mechanical properties, affecting immune supervision, and participating in therapeutic resistance to various forms of treatment. These functions may be implemented through the characteristics of PGs/GAGs as molecular bridges linking ECM and cells in cell-specific and context-specific manners within the tumor microenvironment (TME). In this review, we intend to present a comprehensive illustration of the ways in which PGs/GAGs participate in and regulate several aspects of tumorigenesis; we put forward a perspective regarding their effects as biomarkers or targets for diagnoses and therapeutic interventions.

Inhibition of HAS2 and hyaluronic acid production by 1,25-Dihydroxyvitamin D3 in breast cancer

1,25-Dihydroxyvitamin D₃ (1,25D3) induces growth arrest and apoptosis in breast cancer cells in vivo and in vitro, however the exact mechanisms are unclear. Although the vitamin D receptor (VDR), a ligand dependent transcription factor, is required for growth regulation by vitamin D, the specific target genes that trigger these effects are unknown. Genomic profiling of murine mammary tumor cells with differential VDR expression identified 35 transcripts that were altered by the 1,25D3-VDR complex including Hyaluronan Synthase-2 (Has2). Here we confirmed that 1,25D3 reduces both HAS2 gene expression and hyaluronic acid (HA) synthesis in multiple models of breast cancer. Furthermore, we show that the growth inhibitory effects of 1,25D3 are partially reversed in the presence of high molecular weight HA. HAS2 expression and HA production are elevated in immortalized human mammary epithelial cells induced to undergo epithelial-mesenchymal transition (EMT) through stable expression of TGFβ, SNAIL or TWIST and in those expressing oncogenic H-RAS^V12, indicating that deregulation of HA production may be an early and frequent event in breast tumorigenesis. 1,25D3 also reduces HA secretion and acts additively with an HA synthesis inhibitor to slow growth of cells expressing TGFβ, SNAIL and TWIST. Analysis of mammary gland and tumors from Vdr knockout mice suggest that loss of VDR is associated with enhanced HAS2 expression and HA production in vivo. These data define a novel role for 1,25D3 and the VDR in control of HA synthesis in epithelial tissues that likely contributes to its anti-cancer actions.