SLC35B4 Stabilizes c-MYC Protein by O-GlcNAcylation in HCC

Human Conjunctival Transcriptome in Acanthamoeba Keratitis: An Exploratory Study

PURPOSE

The purpose of this study was to identify conjunctival transcriptome differences in patients with Acanthamoeba keratitis compared with keratitis with no known associated pathogen.

METHODS

The host conjunctival transcriptome of 9 patients with Acanthamoeba keratitis (AK) is compared with the host conjunctival transcriptome of 13 patients with pathogen-free keratitis. Culture and/or confocal confirmed Acanthamoeba in 8 of 9 participants with AK who underwent metagenomic RNA sequencing as the likely pathogen. Cultures were negative in all 13 cases where metagenomic RNA sequencing did not identify a pathogen.

RESULTS

Transcriptome analysis identified 36 genes differently expressed between patients with AK and patients with presumed sterile, or pathogen-free, keratitis. Gene enrichment analysis revealed that some of these genes participate in several biologic pathways important for cellular signaling, ion transport and homeostasis, glucose transport, and mitochondrial metabolism. Notable relatively differentially expressed genes with potential relevance to Acanthamoeba infection included CPS1, SLC35B4, STEAP2, ATP2B2, NMNAT3, and AKAP12.

CONCLUSIONS

This research suggests that the local transcriptome in Acanthamoeba keratitis may be sufficiently robust to be detected in the conjunctiva and that corneas infected with Acanthamoeba may be distinguished from the inflamed cornea where no pathogen was identified. Given the low sensitivity for corneal cultures, identification of differentially expressed genes may serve as a suggestive transcriptional signature allowing for a complementary diagnostic technique to identify this blinding parasite. Knowledge of differentially expressed genes may also direct investigation of disease pathophysiology and suggest novel pathways for therapeutic targets.

Protein O-GlcNAcylation: The sweet hub in liver metabolic flexibility from a (patho)physiological perspective

O-GlcNAcylation is a dynamic, reversible and atypical O-glycosylation that regulates various cellular physiological processes via conformation, stabilisation, localisation, chaperone interaction or activity of target proteins. The O-GlcNAcylation cycle is precisely controlled by collaboration between O-GlcNAc transferase and O-GlcNAcase. Uridine-diphosphate-N-acetylglucosamine, the sole donor of O-GlcNAcylation produced by the hexosamine biosynthesis pathway, is controlled by the input of glucose, glutamine, acetyl coenzyme A and uridine triphosphate, making it a sensor of the fluctuation of molecules, making O-GlcNAcylation a pivotal nutrient sensor for the metabolism of carbohydrates, amino acids, lipids and nucleotides. O-GlcNAcylation, particularly prevalent in liver, is the core hub for controlling systemic glucose homeostasis due to its nutritional sensitivity and precise spatiotemporal regulation of insulin signal transduction. The pathology of various liver diseases has highlighted hepatic metabolic disorder and dysfunction, and abnormal O-GlcNAcylation also plays a specific pathological role in these processes. Therefore, this review describes the unique features of O-GlcNAcylation and its dynamic homeostasis maintenance. Additionally, it explains the underlying nutritional sensitivity of O-GlcNAcylation and discusses its mechanism of spatiotemporal modulation of insulin signal transduction and liver metabolic homeostasis during the fasting and feeding cycle. This review emphasises the pathophysiological implications of O-GlcNAcylation in nonalcoholic fatty liver disease, nonalcoholic steatohepatitis and hepatic fibrosis, and focuses on the adverse effects of hyper O-GlcNAcylation on liver cancer progression and metabolic reprogramming.

Protein glycosylation alterations in hepatocellular carcinoma: function and clinical implications

Hepatocellular carcinoma (HCC) is the third leading cause of cancer death worldwide. Understanding the cancer mechanisms provides novel diagnostic, prognostic, and therapeutic markers for the management of HCC disease. In addition to genomic and epigenomic regulation, post-translational modification exerts a profound influence on protein functions and plays a critical role in regulating various biological processes. Protein glycosylation is one of the most common and complex post-translational modifications of newly synthesized proteins and acts as an important regulatory mechanism that is implicated in fundamental molecular and cell biology processes. Recent studies in glycobiology suggest that aberrant protein glycosylation in hepatocytes contributes to the malignant transformation to HCC by modulating a wide range of pro-tumorigenic signaling pathways. The dysregulated protein glycosylation regulates cancer growth, metastasis, stemness, immune evasion, and therapy resistance, and is regarded as a hallmark of HCC. Changes in protein glycosylation could serve as potential diagnostic, prognostic, and therapeutic factors in HCC. In this review, we summarize the functional importance, molecular mechanism, and clinical application of protein glycosylation alterations in HCC.

O-GlcNAcylation-induced GSK-3β activation deteriorates pressure overload-induced heart failure via lack of compensatory cardiac hypertrophy in mice

O-GlcNAc transferase (OGT) modulates many functions of proteins via O-GlcNAcylation that adds O-linked β-N-acetylglucosamine (O-GlcNAc) to the serine/threonine residues of proteins. However, the role of O-GlcNAcylation in cardiac remodeling and function is not fully understood. To examine the effect of O-GlcNAcylation on pressure overload-induced cardiac hypertrophy and subsequent heart failure, transverse aortic constriction (TAC) surgery was performed in wild type (WT) and Ogt transgenic (Ogt-Tg) mice. Four weeks after TAC (TAC4W), the heart function of Ogt-Tg mice was significantly lower than that of WT mice (reduced fractional shortening and increased ANP levels). The myocardium of left ventricle (LV) in Ogt-Tg mice became much thinner than that in WT mice. Moreover, compared to the heart tissues of WT mice, O-GlcNAcylation of GSK-3β at Ser9 was increased and phosphorylation of GSK-3β at Ser9 was reduced in the heart tissues of Ogt-Tg mice, resulting in its activation and subsequent inactivation of nuclear factor of activated T cell (NFAT) activity. Finally, the thinned LV wall and reduced cardiac function induced by TAC4W in Ogt-Tg mice was reversed by the treatment of a GSK-3β inhibitor, TDZD-8. These results imply that augmented O-GlcNAcylation exacerbates pressure overload-induced heart failure due to a lack of compensatory cardiac hypertrophy via O-GlcNAcylation of GSK-3β, which deprives the phosphorylation site of GSK-3β to constantly inactivate NFAT activity to prevent cardiac hypertrophy. Our findings may provide a new therapeutic strategy for cardiac hypertrophy and subsequent heart failure.

Metabolite-derived protein modifications modulating oncogenic signaling

Malignant growth is defined by multiple aberrant cellular features, including metabolic rewiring, inactivation of tumor suppressors and the activation of oncogenes. Even though these features have been described as separate hallmarks, many studies have shown an extensive mutual regulatory relationship amongst them. On one hand, the change in expression or activity of tumor suppressors and oncogenes has extensive direct and indirect effects on cellular metabolism, activating metabolic pathways required for malignant growth. On the other hand, the tumor microenvironment and tumor intrinsic metabolic alterations result in changes in intracellular metabolite levels, which directly modulate the protein modification of oncogenes and tumor suppressors at both epigenetic and post-translational levels. In this mini-review, we summarize the crosstalk between tumor suppressors/oncogenes and metabolism-induced protein modifications at both levels and explore the impact of metabolic (micro)environments in shaping these.