Stomatin‑like protein 2 induces metastasis by regulating the expression of a rate‑limiting enzyme of the hexosamine biosynthetic pathway in pancreatic cancer

The GFPT2-O-GlcNAcylation-YBX1 axis promotes IL-18 secretion to regulate the tumor immune microenvironment in pancreatic cancer

The immunosuppressive microenvironment caused by several intrinsic and extrinsic mechanism has brought great challenges to the immunotherapy of pancreatic cancer. We identified GFPT2, the key enzyme in hexosamine biosynthesis pathway (HBP), as an immune-related prognostic gene in pancreatic cancer using transcriptome sequencing and further confirmed that GFPT2 promoted macrophage M2 polarization and malignant phenotype of pancreatic cancer. HBP is a glucose metabolism pathway leading to the generation of uridine diphosphate N-acetylglucosamine (UDP-GlcNAc), which is further utilized for protein O-GlcNAcylation. We confirmed GFPT2-mediated O-GlcNAcylation played an important role in regulating immune microenvironment. Through cellular proteomics, we identified IL-18 as a key downstream of GFPT2 in regulating the immune microenvironment. Through CO-IP and protein mass spectrum, we confirmed that YBX1 was O-GlcNAcylated and nuclear translocated by GFPT2-mediated O-GlcNAcylation. Then, YBX1 functioned as a transcription factor to promote IL-18 transcription. Our study elucidated the relationship between the metabolic pathway of HBP in cancer cells and the immune microenvironment, which might provide some insights into the combination therapy of HBP vulnerability and immunotherapy in pancreatic cancer.

Structure-activity relationships for the G-quadruplex-targeting experimental drug QN-302 and two analogues probed with comparative transcriptome profiling and molecular modeling

The tetrasubstituted naphthalene diimide compound QN-302 binds to G-quadruplex (G4) DNA structures. It shows high potency in pancreatic ductal adenocarcinoma (PDAC) cells and inhibits the transcription of cancer-related genes in these cells and in PDAC animal models. It is currently in Phase 1a clinical evaluation as an anticancer drug. A study of structure-activity relationships of QN-302 and two related analogues (CM03 and SOP1247) is reported here. These have been probed using comparisons of transcriptional profiles from whole-genome RNA-seq analyses, together with molecular modelling and molecular dynamics simulations. Compounds CM03 and SOP1247 differ by the presence of a methoxy substituent in the latter: these two compounds have closely similar transcriptional profiles. Whereas QN-302 (with an additional benzyl-pyrrolidine group), although also showing down-regulatory effects in the same cancer-related pathways, has effects on distinct genes, for example in the hedgehog pathway. This distinctive pattern of genes affected by QN-302 is hypothesized to contribute to its superior potency compared to CM03 and SOP1247. Its enhanced ability to stabilize G4 structures has been attributed to its benzyl-pyrrolidine substituent fitting into and filling most of the space in a G4 groove compared to the hydrogen atom in CM03 or the methoxy group substituent in SOP1247.

Regulation of protein O-GlcNAcylation by circadian, metabolic, and cellular signals

O-linked β-N-acetylglucosamine (O-GlcNAcylation) is a dynamic post-translational modification that regulates thousands of proteins and almost all cellular processes. Aberrant O-GlcNAcylation has been associated with numerous diseases, including cancer, neurodegenerative diseases, cardiovascular diseases, and type 2 diabetes. O-GlcNAcylation is highly nutrient-sensitive since it is dependent on UDP-GlcNAc, the end product of the hexosamine biosynthetic pathway (HBP). We previously observed daily rhythmicity of protein O-GlcNAcylation in a Drosophila model that is sensitive to the timing of food consumption. We showed that the circadian clock is pivotal in regulating daily O-GlcNAcylation rhythms given its control of the feeding-fasting cycle and hence nutrient availability. Interestingly, we reported that the circadian clock also modulates daily O-GlcNAcylation rhythm by regulating molecular mechanisms beyond the regulation of food consumption time. A large body of work now indicates that O-GlcNAcylation is likely a generalized cellular status effector as it responds to various cellular signals and conditions, such as ER stress, apoptosis, and infection. In this review, we summarize the metabolic regulation of protein O-GlcNAcylation through nutrient availability, HBP enzymes, and O-GlcNAc processing enzymes. We discuss the emerging roles of circadian clocks in regulating daily O-GlcNAcylation rhythm. Finally, we provide an overview of other cellular signals or conditions that impact O-GlcNAcylation. Many of these cellular pathways are themselves regulated by the clock and/or metabolism. Our review highlights the importance of maintaining optimal O-GlcNAc rhythm by restricting eating activity to the active period under physiological conditions and provides insights into potential therapeutic targets of O-GlcNAc homeostasis under pathological conditions.

The Hexosamine Biosynthesis Pathway: Regulation and Function

The hexosamine biosynthesis pathway (HBP) produces uridine diphosphate-N-acetyl glucosamine, UDP-GlcNAc, which is a key metabolite that is used for N- or O-linked glycosylation, a co- or post-translational modification, respectively, that modulates protein activity and expression. The production of hexosamines can occur via de novo or salvage mechanisms that are catalyzed by metabolic enzymes. Nutrients including glutamine, glucose, acetyl-CoA, and UTP are utilized by the HBP. Together with availability of these nutrients, signaling molecules that respond to environmental signals, such as mTOR, AMPK, and stress-regulated transcription factors, modulate the HBP. This review discusses the regulation of GFAT, the key enzyme of the de novo HBP, as well as other metabolic enzymes that catalyze the reactions to produce UDP-GlcNAc. We also examine the contribution of the salvage mechanisms in the HBP and how dietary supplementation of the salvage metabolites glucosamine and N-acetylglucosamine could reprogram metabolism and have therapeutic potential. We elaborate on how UDP-GlcNAc is utilized for N-glycosylation of membrane and secretory proteins and how the HBP is reprogrammed during nutrient fluctuations to maintain proteostasis. We also consider how O-GlcNAcylation is coupled to nutrient availability and how this modification modulates cell signaling. We summarize how deregulation of protein N-glycosylation and O-GlcNAcylation can lead to diseases including cancer, diabetes, immunodeficiencies, and congenital disorders of glycosylation. We review the current pharmacological strategies to inhibit GFAT and other enzymes involved in the HBP or glycosylation and how engineered prodrugs could have better therapeutic efficacy for the treatment of diseases related to HBP deregulation.

STOML2 restricts mitophagy and increases chemosensitivity in pancreatic cancer through stabilizing PARL-induced PINK1 degradation

Pancreatic cancer remains one of the most lethal diseases with a relatively low 5-year survival rate, and gemcitabine-based chemoresistance occurs constantly. Mitochondria, as the power factory in cancer cells, are involved in the process of chemoresistance. The dynamic balance of mitochondria is under the control of mitophagy. Stomatin-like protein 2 (STOML2) is located in the mitochondrial inner membrane and is highly expressed in cancer cells. In this study, using a tissue microarray (TMA), we found that high STOML2 expression was correlated with higher survival of patients with pancreatic cancer. Meanwhile, the proliferation and chemoresistance of pancreatic cancer cells could be retarded by STOML2. In addition, we found that STOML2 was positively related to mitochondrial mass and negatively related to mitophagy in pancreatic cancer cells. STOML2 stabilized PARL and further prevented gemcitabine-induced PINK1-dependent mitophagy. We also generated subcutaneous xenografts to verify the enhancement of gemcitabine therapy induced by STOML2. These findings suggested that STOML2 regulated the mitophagy process through the PARL/PINK1 pathway, thereby reducing the chemoresistance of pancreatic cancer. STOML2-overexpression targeted therapy might be helpful for gemcitabine sensitization in the future.

Stomatin-like protein 2 deficiency exacerbates adverse cardiac remodeling

Myocardial fibrosis, oxidative stress, and autophagy both play key roles in the progression of adverse cardiac remodeling. Stomatin-like protein 2 (SLP-2) is closely related to mitochondrial function, but little is known about its role and mechanism in cardiac remodeling. We developed doxorubicin (Dox), angiotensin (Ang) II, and myocardial ischemia-reperfusion (I/R) injury induced cardiac remodeling model and Dox treated H9C2 cell injury model using SLP-2 knockout (SLP-2^-/-) mice and H9C2 cells with low SLP-2 expression. We first examined cardiac functional and structural changes as well as levels of oxidative stress, apoptosis and autophagy. We found that SLP-2 deficiency leads to decreased cardiac function and promotes myocardial fibrosis. After Dox and Ang II treatment, SLP-2 deficiency further aggravated myocardial fibrosis, increased myocardial oxidative stress and apoptosis, and activated autophagy by inhibiting PI3K-Akt-mTOR signaling pathway, ultimately exacerbating adverse cardiac remodeling. Similarly, SLP-2 deficiency further exacerbates adverse cardiac remodeling after myocardial I/R injury. Moreover, we extracted cardiomyocyte mitochondria for proteomic analysis, suggesting that SLP-2 deficiency may be involved in myocardial I/R injury induced adverse cardiac remodeling by influencing ubiquitination of intramitochondrial proteins. In addition, the oxidative stress, apoptosis and autophagy levels of H9C2 cells with low SLP-2 expression were further enhanced, and the PI3K-Akt-mTOR signaling pathway was further inhibited under Dox stimulation. Our results suggest that SLP-2 deficiency promotes myocardial fibrosis, disrupts normal mitochondrial function, overactivates autophagy via PI3K-Akt-mTOR signaling pathway, affects the level of ubiquitination, leads to irreversible myocardial damage, and ultimately exacerbates adverse cardiac remodeling.

The role of metabolic reprogramming in pancreatic cancer chemoresistance

Pancreatic cancer is characterized by hidden onset, high malignancy, and early metastasis. Although a few cases meet the surgical indications, chemotherapy remains the primary treatment, and the resulting chemoresistance has become an urgent clinical problem that needs to be solved. In recent years, the importance of metabolic reprogramming as one of the hallmarks of cancers in tumorigenesis has been validated. Metabolic reprogramming involves glucose, lipid, and amino acid metabolism and interacts with oncogenes to affect the expression of key enzymes and signaling pathways, modifying the tumor microenvironment and contributing to the occurrence of drug tolerance. Meanwhile, the mitochondria are hubs of the three major nutrients and energy metabolisms, which are also involved in the development of drug resistance. In this review, we summarized the characteristic changes in metabolism during the progression of pancreatic cancer and their impact on chemoresistance, outlined the role of the mitochondria, and summarized current studies on metabolic inhibitors.

Targeting SLP2-mediated lipid metabolism reprograming restricts proliferation and metastasis of hepatocellular carcinoma and promotes sensitivity to Lenvatinib

SLP2, a protein located on mitochondrial, has been shown to be associated with mitochondrial biosynthesis. Here we explored the potential mechanisms by which SLP2 regulates the development of hepatocellular carcinoma. SLP2 could bind to the c-terminal of JNK2 to affect the ubiquitinated proteasomal degradation pathway of JNK2 and maintain the protein stability of JNK2. The increase of JNK2 markedly increases SREBP1 activity, promoting SREBP1 translocation into the nucleus to promote de novo lipogenesis. Alteration of the JNK2 C-terminal disables SLP2 from mediating SLP2-enhanced de novo lipogenesis. YTHDF1 interacts with SLP2 mRNA in a METTL3/m⁶A-dependent manner. In a spontaneous HCC animal model, SLP2/c-Myc/sgP53 increases the incidence rate of spontaneous HCC, tumor volume, and tumor number. Importantly, statistical analyses show that levels of SLP2 correlate with tumor sizes, tumor metastasis, overall survival, and disease-free survival of the patients. Targeting the SLP2/SREBP1 pathway effectively inhibits proliferation and metastasis of HCC tumors with high SLP2 expression in vivo combined with lenvatinib. These results illustrate a direct lipogenesis-promoting role of the pro-oncogenic SLP2, providing a mechanistic link between de novo lipogenesis and HCC.

Glutamine-fructose-6-phosphate transaminase 2 (GFPT2) is upregulated in breast epithelial-mesenchymal transition and responds to oxidative stress

Breast cancer cells that have undergone partial epithelial–mesenchymal transition (EMT) are believed to be more invasive than cells that have completed EMT. To study metabolic reprogramming in different mesenchymal states, we analyzed protein expression following EMT in the breast epithelial cell model D492 with single-shot LFQ supported by a SILAC proteomics approach. The D492 EMT cell model contains three cell lines: the epithelial D492 cells, the mesenchymal D492M cells, and a partial mesenchymal, tumorigenic variant of D492 that overexpresses the oncogene HER2. The analysis classified the D492 and D492M cells as basal-like and D492HER2 as claudin-low. Comparative analysis of D492 and D492M to tumorigenic D492HER2 differentiated metabolic markers of migration from those of invasion. Glutamine-fructose-6-phosphate transaminase 2 (GFPT2) was one of the top dysregulated enzymes in D492HER2. Gene expression analysis of the cancer genome atlas showed that GFPT2 expression was a characteristic of claudin-low breast cancer. siRNA-mediated knockdown of GFPT2 influenced the EMT marker vimentin and both cell growth and invasion in vitro and was accompanied by lowered metabolic flux through the hexosamine biosynthesis pathway (HBP). Knockdown of GFPT2 decreased cystathionine and sulfide:quinone oxidoreductase (SQOR) in the transsulfuration pathway that regulates H₂S production and mitochondrial homeostasis. Moreover, GFPT2 was within the regulation network of insulin and EGF, and its expression was regulated by reduced glutathione (GSH) and suppressed by the oxidative stress regulator GSK3-β. Our results demonstrate that GFPT2 controls growth and invasion in the D492 EMT model, is a marker for oxidative stress, and associated with poor prognosis in claudin-low breast cancer.

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GFPT2 is upregulated following EMT.

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GFPT2 is a marker for claudin-low breast cancer.

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GFPT2 affects vimentin, cell proliferation, and cell invasion.

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GFPT2 responds to oxidative stress.

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GFPT2 is regulated by insulin and EGF.