Hitting the Sweet Spot: How Glucose Metabolism Is Orchestrated in Space and Time by Phosphofructokinase-1

Glycolysis is the central metabolic pathway across all kingdoms of life. Intensive research efforts have been devoted to understanding the tightly orchestrated processes of converting glucose into energy in health and disease. Our review highlights the advances in knowledge of how metabolic and gene networks are integrated through the precise spatiotemporal compartmentalization of rate-limiting enzymes. We provide an overview of technically innovative approaches that have been applied to study phosphofructokinase-1 (PFK1), which represents the fate-determining step of oxidative glucose metabolism. Specifically, we discuss fast-acting chemical biology and optogenetic tools that have delineated new links between metabolite fluxes and transcriptional reprogramming, which operate together to enact tissue-specific processes. Finally, we discuss how recent paradigm-shifting insights into the fundamental basis of glycolytic regulatory control have shed light on the mechanisms of tumorigenesis and could provide insight into new therapeutic vulnerabilities in cancer.

Role of Glycolytic and Glutamine Metabolism Reprogramming on the Proliferation, Invasion, and Apoptosis Resistance through Modulation of Signaling Pathways in Glioblastoma

Glioma cells exhibit genetic and metabolic alterations that affect the deregulation of several cellular signal transduction pathways, including those related to glucose metabolism. Moreover, oncogenic signaling pathways induce the expression of metabolic genes, increasing the metabolic enzyme activities and thus the critical biosynthetic pathways to generate nucleotides, amino acids, and fatty acids, which provide energy and metabolic intermediates that are essential to accomplish the biosynthetic needs of glioma cells. In this review, we aim to explore how dysregulated metabolic enzymes and their metabolites from primary metabolism pathways in glioblastoma (GBM) such as glycolysis and glutaminolysis modulate anabolic and catabolic metabolic pathways as well as pro-oncogenic signaling and contribute to the formation, survival, growth, and malignancy of glioma cells. Also, we discuss promising therapeutic strategies by targeting the key players in metabolic regulation. Therefore, the knowledge of metabolic reprogramming is necessary to fully understand the biology of malignant gliomas to improve patient survival significantly.

A Five-LLPS Gene Risk Score Prognostic Signature Predicts Survival in Hepatocellular Carcinoma

Background

Primary liver cancer, dominated by hepatocellular carcinoma (HCC), is one of the most common cancer types and the third leading cause of cancer death in 2020. Previous studies have shown that liquid-liquid phase separation (LLPS) plays an important role in the occurrence and development of cancer including HCC, but its influence on the patient prognosis is still unknown. It is necessary to explore the effect of LLPS genes on prognosis to accurately forecast the prognosis of HCC patients and identify relevant targeted therapeutic sites.

Methods

Using The Cancer Genome Atlas dataset and PhaSepDB dataset, we identified LLPS genes linked to the overall survival (OS) of HCC patients. We applied Least Absolute Shrinkage and Selection Operator (LASSO) Cox penalized regression analysis to choose the best genes for the risk score prognostic signature. We then analysed the validation dataset and evaluated the effectiveness of the risk score prognostic signature. Finally, we performed quantitative real-time PCR experiments to validate the genes in the prognostic signature.

Results

We identified 43 differentially expressed LLPS genes that were associated with the OS of HCC patients. Five of these genes (BMX, FYN, KPNA2, PFKFB4, and SPP1) were selected to generate a prognostic risk score signature. Patients in the low-risk group were associated with better OS than those in the high-risk group in both the training dataset and the validation dataset. We found that BMX and FYN had lower expression levels in HCC tumour tissues, whereas KPNA2, PFKFB4, and SPP1 had higher expression levels in HCC tumour tissues. The validation demonstrated that the five-LLPS gene risk score signature has the capability of predicting the OS of HCC patients.

Conclusion

Our study constructed a five-LLPS gene risk score signature that can be applied as an effective and convenient prognostic tool. These five genes might serve as potential targets for therapy and the treatment of HCC.

PFKFB4 interacts with FBXO28 to promote HIF-1α signaling in glioblastoma

Glioblastoma is a highly aggressive brain tumor for which there is no cure. The metabolic enzyme 6-Phosphofructo-2-Kinase/Fructose-2,6-Biphosphatase 4 (PFKFB4) is essential for glioblastoma stem-like cell (GSC) survival but its mode of action is unclear. Understanding the role of PFKFB4 in tumor cell survival could allow it to be leveraged in a cancer therapy. Here, we show the importance of PFKFB4 for glioblastoma growth in vivo in an orthotopic patient derived mouse model. In an evaluation of patient tumor samples of different cancer entities, PFKFB4 protein was found to be overexpressed in prostate, lung, colon, mammary and squamous cell carcinoma, with expression level correlating with tumor grade. Gene expression profiling in PFKFB4-silenced GSCs revealed a downregulation of hypoxia related genes and Western blot analysis confirmed a dramatic reduction of HIF (hypoxia inducible factor) protein levels. Through mass spectrometric analysis of immunoprecipitated PFKFB4, we identified the ubiquitin E3 ligase, F-box only protein 28 (FBXO28), as a new interaction partner of PFKFB4. We show that PFKFB4 regulates the ubiquitylation and subsequent proteasomal degradation of HIF-1α, which is mediated by the ubiquitin ligase activity of FBXO28. This newly discovered function of PFKFB4, coupled with its cancer specificity, provides a new strategy for inhibiting HIF-1α in cancer cells.

Effect of PFKFB4 on the Prognosis and Immune Regulation of NSCLC and Its Mechanism

Background

NSCLC (non-small cell lung cancer) has become the malignancy with the highest incidence and mortality rate worldwide. Fructose-6-phosphate 2-kinase/fructose-2,6-bisphosphatase 4 (PFKFB4) is a key regulator of glycolysis with both kinase and phosphatase activities. The Warburg effect, or increased glycolysis in tumors, provides the metabolic basis for cancer cell proliferation and metastasis, and the Warburg pathway enzyme PFKFB4 is a newly identified important kinase. This study aimed to elucidate the poor prognostic relevance of PFKFB4 in non-small cell lung cancer tissues and its relationship with immune cell infiltration, immune cell biomarkers, and immune checkpoints.

Methods

In this study, immunohistochemical methods were used to assess PFKFB4 expression levels in 140 surgical specimens from patients with histologically confirmed non-small cell lung cancer and to investigate the relationship between PFKFB4 expression levels and the patients’ clinicopathological characteristics. The impact of PFKFB4 expression on prognosis was evaluated using Kaplan–Meier survival analysis and Cox regression analysis.

Results

When compared to normal paracrine tissues, PFKFB4 expression was enhanced in lung cancer tissues, and Kaplan–Meier survival analysis revealed that patients with high PFKFB4 expression had a worse prognosis. In NSCLC, PFKFB4 was found to be associated with immune cell infiltration and immunological checkpoints.

Conclusion

PFKFB4 expression may be upregulated as a sign of poor prognosis in NSCLC, and PFKFB4 may be implicated not only in the genesis and progression of NSCLC but also in its immunological control.

Canonical and Non-Canonical Roles of PFKFB3 in Brain Tumors

PFKFB3 is a bifunctional enzyme that modulates and maintains the intracellular concentrations of fructose-2,6-bisphosphate (F2,6-P2), essentially controlling the rate of glycolysis. PFKFB3 is a known activator of glycolytic rewiring in neoplastic cells, including central nervous system (CNS) neoplastic cells. The pathologic regulation of PFKFB3 is invoked via various microenvironmental stimuli and oncogenic signals. Hypoxia is a primary inducer of PFKFB3 transcription via HIF-1alpha. In addition, translational modifications of PFKFB3 are driven by various intracellular signaling pathways that allow PFKFB3 to respond to varying stimuli. PFKFB3 synthesizes F2,6P2 through the phosphorylation of F6P with a donated PO4 group from ATP and has the highest kinase activity of all PFKFB isoenzymes. The intracellular concentration of F2,6P2 in cancers is maintained primarily by PFKFB3 allowing cancer cells to evade glycolytic suppression. PFKFB3 is a primary enzyme responsible for glycolytic tumor metabolic reprogramming. PFKFB3 protein levels are significantly higher in high-grade glioma than in non-pathologic brain tissue or lower grade gliomas, but without relative upregulation of transcript levels. High PFKFB3 expression is linked to poor survival in brain tumors. Solitary or concomitant PFKFB3 inhibition has additionally shown great potential in restoring chemosensitivity and radiosensitivity in treatment-resistant brain tumors. An improved understanding of canonical and non-canonical functions of PFKFB3 could allow for the development of effective combinatorial targeted therapies for brain tumors.

Expression of Alternative Splice Variants of 6-Phosphofructo-2-kinase/Fructose-2,6-bisphosphatase-4 in Normoxic and Hypoxic Melanoma Cells

Cancer-specific isoenzyme of phosphofructokinase II (PFKFB4), as our previous research has shown, may be one of the most important enzymes contributing to the intensification of glycolysis in hypoxic malignant melanoma cells. Although the PFKFB4 gene seems to play a crucial role in the progression of melanoma, so far there are no complete data on the expression of PFKFB4 at the isoform level and the influence of hypoxia on alternative splicing. Using RT-qPCR and semi-quantitative RT-PCR, we presented the PFKFB4 gene expression profile at the level of six isoforms described in the OMIM NCBI database in normoxic and hypoxic melanoma cells. Additionally, using VMD software, we analyzed the structure of isoforms at the protein level, concluding about the catalytic activity of individual isoforms. Our research has shown that five isoforms of PFKFB4 are expressed in melanoma cells, of which the D and F isoforms are highly constitutive, while the canonical B isoform seems to be the main isoform induced in hypoxia. Our results also indicate that the expression profile at the level of the PFKFB4 gene does not reflect the expression at the level of individual isoforms. Our work clearly indicates that the PFKFB4 gene expression profile should be definitely analyzed at the level of individual isoforms. Moreover, the analysis at the protein level allowed the selection of those isoforms whose functional validation should be performed to fully understand the importance of PFKFB4 expression in the metabolic adaptation of malignant melanoma cells.

E2F2 drives glioma progression via PI3K/AKT in a PFKFB4-dependent manner

AIMS

The effects of PFKFB4 on glycolysis during the cancer progression has been investigated, while its role in glioma remains unclear. The present study evaluated the molecular mechanism of PFKFB4 in glycolysis of glioma progression.

MATERIALS AND METHODS

The pan-cancer platform SangerBox was inquired to investigate the E2F2 expression in tumors. The E2F2 expression was studied by qRT-PCR and immunohistochemistry in collected glioma and normal brain tissues and by qRT-PCR and western blot in glioma cells. The relationship between the E2F2 expression in glioma tissues and patients' prognosis was analyzed. The cell malignant phenotype, glycolysis, growth and metastasis were examined by CCK-8, EdU, colony formation, flow cytometry, wound healing, Transwell assays, ELISA kits, and tumorigenesis and metastasis assays. Downstream targets of E2F2 were searched in hTFtarget, followed by pathway enrichment analysis. The expression of these targets and their correlation with E2F2 expression in gliomas were investigated through the GEPIA website. After ChIP and luciferase assays, the effect of the target on glioma was investigated.

KEY FINDINGS

E2F2 was overexpressed in glioma patients and predicted poor prognoses. E2F2 promoted cell proliferation, colony formation, DNA synthesis, migration, invasion and glycolysis, and inhibited apoptosis. Meanwhile, inhibition of E2F2 suppressed the growth and metastasis of gliomas. E2F2 elevated the PFKFB4 expression transcriptionally by binding to its promoter and activated PI3K/AKT pathway. The promotion of glioma metastasis and glycolysis by E2F2 was mitigated by PFKFB4 knockdown.

SIGNIFICANCE

E2F2-mediated transcriptional enhancement of PFKFB4 expression regulated the phosphorylation of PI3K/AKT to promote glioma malignancy progression.